1

A Report of the Workshop entitled “Recent Biogeochemical Changes in the

Biogeochemistry of the Great Lakes System (BOGLS)”

Contributions of the BOGLS Steering Committee along with participants of

the Workshop and Community Forums at IAGLR and Goldschmidt2013.

Edited by:

Mark Baskaran, Department of Geology, Wayne State University, Detroit, MI-48202; and

John Bratton, Great Lakes Environmental Research Laboratory, NOAA, Ann Arbor, MI-48108

Steering Committee:

James Bauer (Ohio State), Ruth Blake (Yale U), Robert Hecky (U. Minnesota-Duluth), Norman

Grannemann (USGS), J. Val Klump (U. Wisconsin-Milwaukee), Lawrence Lemke (Wayne

State), Nathaniel Ostrom (Michigan State) and Thomas Johnson (U. Illinois, Urbana-

Champaign)

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Final Report

Executive Summary:

The pelagic and benthic food webs and associated elemental cycles in the Laurentian

Great Lakes have undergone major perturbation over the past 30 years due to factors such as

nutrient abatement and introduction of invasive species (zebra and quagga mussels). Such

human-induced alterations (directly or indirectly) provide a unique opportunity to document how

this natural system has responded and would respond to other such large-scale alterations in the

ecosystem. Thus, the Great Lakes System (GLS) could serve as a ‘model laboratory’ to quantify

biogeochemical changes caused by humans. The changes in the terrestrial ecosystem and

bordering wetlands influence the fundamental biogeochemical processes that take place in the

lakes where complex interactions between the adjoining terrestrial environments with that in the

aquatic system are integrated. Approximately 37 million people live in the Great Lakes basin

with 26 million people relying on the Great Lakes for their drinking water. The water quality has

direct impact not only on human health but also on jobs in agriculture, fisheries, manufacturing,

shipping, and tourism. In order to assess the scientific needs for process-oriented research in the

changes caused by the directly or indirectly human-induced perturbations, a three-day (March

11-13, 2013) workshop was held at Wayne State University, Detroit, Michigan. Sixty scientists

mostly from across the Great Lakes states representing 17 universities, five federal agencies,

among others, with expertise spanning a spectrum of research areas including nutrients and

carbon cycling, key trace elements and isotopes as biogeochemical tracers, geo- and

radiochemistry, ecology, hydrogeology, physical oceanography, modeling, remote sensing, and

climate change, gathered and discussed the state of the Great Lakes system.

The community identified a number of major changes that have taken place recently in

the Laurentian Great Lakes that are remarkable in their scope and speed. The community

recognized the urgent need for a long-term process-oriented study coupled with modeling to

evaluate ecosystem changes in the Great Lakes system. Food webs in the lower lakes have

undergone drastic changes from the expansion of dreissenid mussels, a process that occurred in <

30 years and accelerated greatly in the last 10-15 years. The reengineered ecosystem caused by

the dreissenid mussels has resulted in a ‘benthification’ of the system at the apparent expense of

pelagic food chains. Drastic decline in the abundance of diatoms, zooplankton, benthic

amphipods, forage fish and top piscivorous population have been reported, including ~95%

population decrease of benthic amphipod Diporiea. Filtration of water by dreissenids had

resulted in water clarity exceeding 20 m secchi depths in Lakes Huron and Michigan, which in

turn has resulted in the triggering of resurgence of the submerged macrophyte, Cladophora, in

the near-shore causing fouling of beaches throughout the lakes by decaying algal mats. The

pelagic primary production in Lake Michigan has decreased by ~70% and other winter and

spring blooms have largely disappeared.

The lakes are highly sensitive to climate change, particularly their hydrology (water

levels), radiation budgets, stratification and atmospheric forcing. Decrease in areal extent,

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thickness and duration of the ice cover, increase in water temperature and the increase in

frequency of extreme weather events (resulting in changes in the riverine loading of key macro-

and micro-nutrients) have been reported. Summertime thermal stratification is predicted to

increase in duration by several weeks, exacerbating issues of hypoxia, benthic metabolism and

diagenesis, thermal habitat changes, and the timing of long standing ecological phenomena.

Climate change is expected to have a significant impact on regional climate such as changes in

‘lake effect’ precipitation. The recent climate change is felt faster in L. Superior than in many

coastal ocean areas.

The concentrations and stoichiometric ratios of key nutrients have been considerably

altered during the past century. For example, there has been a net accumulation of nitrate over

the past hundred years in Lake Superior which is reported to have an imbalance in NO3-/PO4

3-

ratios (as high as ~10,000). The factors and processes that lead to these alterations in

stoichiometric ratios in different lakes of the Great Lakes system are not fully understood. While

the chemical reactions (nitrification, denitrification and anammox) are expected to be slower in

Lake Superior due to cooler waters compared to Lakes Michigan, Huron, Erie, and Ontario, other

factors that control N, C and P cycling, N assimilation, and microbial community structure are

not well studied in all the Great Lakes. The degree to which changes result from increases in

external sources discharged to the lakes (rivers/streams, atmospheric deposition, submarine

groundwater discharge), or active in-lake processes (such as nitrification/denitrification,

anammox) is not understood. Despite active removal of PO43-

, Ca2+

, and key bio-limited

elements in the lower lakes and Lake Michigan by dreissenids, answers to questions such as how

the NO3-/PO4

3- ratios have changed the cycling of organic carbon and other micro-nutrients in

lakes that are severely impacted remains unknown.

The inland freshwater seas are similar to marine systems in several respects and are

unique as well. Many of the dominant physical processes are large scale, such as circulation

(affected by the Earth’s rotation), atmospheric forcing mechanisms, upwelling/downwelling,

seiches and internal motions, etc. Ecologically they are young (~10 kyr) with relatively simple

food webs and low biodiversity. This produces an extreme susceptibility to invasion and

perturbation by non-native species.

Lake-wide simultaneous measurements of primary production (PP) and grazing rates in

most lakes are lacking; thus, gaps in our understanding of the cycling of N, P, and Si and their

link to other key micro-nutrients exist. Lack of data during the cooler periods and deeper waters

fuels the uncertainty in PP and grazing estimates. Estimates of PP and respiration rates due to

scaling factors are less reliable due to limited data (or lack of data) during winter months and

from deeper waters.

The key micronutrients such as Fe play a critical role in nitrate utilization by plankton

and thus, the cycling of Fe, Cu, Zn, Cd, Se, V, Mo, Ni, Co are important. Newly-emerging

modern isotope tools could serve as powerful tools in quantifying the sources, pathways and

transport of these micronutrients. The horizontal and vertical transport of key macro- and micro

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nutrients can be investigated using a set of radioactive tracers. Sinkhole vents in some of the

lakes offer a unique opportunity to probe how novel microbial communities adapt and thrive in

extreme environments.

A concerted and focused research effort will provide new knowledge and improve our

fundamental understanding of the processes and yield answers to several key questions. Much of

the historical understanding of the ecology and biogeochemistry of the lakes, while relevant and

informative, is often no longer operative or has been altered in significant ways. At the same

time, the lakes have been the subject of improved physical modeling and forecasting systems and

expanding observing platforms under U.S. Integrated Ocean Observing System (IOOS). The

breadth of our collective knowledge of these closed systems provides a significant baseline on

which to build improved ecological and biogeochemical process models. Both their similarities

and their differences provide opportunities to study fundamental ecological/biogeochemical

dynamics across time and space scales that are relevant to many aquatic systems, from coastal

bays and gulfs, to semi-enclosed seas and estuaries. New and novel approaches, tools, and

analytical techniques are also now available that are ideal for process-oriented research on these

scales.

This report summarizes number of driving questions, gaps and opportunities for future

inquiry that would substantially improve our understanding and ability to sustainably manage

these and similar aquatic systems.

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1. Introduction to the Great Lakes and their Recent History:

1.1 Introduction to the Great Lakes System:

The largest freshwater seas of the world (244,000 km2), the Laurentian Great Lakes

System, has undergone major biogeochemical changes over the past 3 decades due to

anthropogenic activities such as nutrient abatement, introduction of invasive species and human-

induced climate change. Approximately 37 million (11.8% of US population) people live in the

Great Lakes basin of which about 8% of the United States total population relies on the Great

Lakes for their drinking water. The water quality has direct impact not only on humans but also

the economic activity and vitality of the 8 states that adjoin these lakes.

The Great Lake system is similar to oceans in terms of large scale water mass circulation

pattern, discrete coastal zones, shelf breaks and deep basins, yet this system is bounded

physically with constrainable inputs and outputs in the mass balance of micro- and macro

nutrients, carbon and other radionuclides and tracers. In terms of size, these lakes are

intermediate in scale between common lakes and oceans and are complex integrators of

watershed changes, biology, biogeochemistry and regional environmental and climate change

making these systems unique and attractive for tracking how changes, many anthropogenically

induced, reverberate through the system. Relative to more saline waters or ocean basins, the

forces controlling the mixing of water masses are, in some cases, weak or absent (e.g. tidal

currents), and in some cases stronger (e.g. isothermal mixing). Nutrient concentrations range

from hyper-oligotrophic (the P concentrations in Lake Superior are lower than the central North

Pacific gyre) to hyper-eutrophic and nutrient limitation is both complex and varied (Sterner et al.,

2004; Duhamel et al., 2011). This wide range of conditions is embedded within a system that is

logistically accessible to analysis at the appropriate density, geochemically and geologically

similar, but not uniform. Important internal differences, e.g. in residence times, physical

chemistry, loadings, etc. are known and changes are occurring with a speed which is easily

measurable on a scale of years. Thus, the diversity of water depths, differences in the

hydrological residence times, temperature differences and diversity in biota in these five

freshwater inland seas provide an unparalleled opportunity for focused research on the

responsiveness of biogeochemical cycles to human-induced perturbations in ecosystem

properties in semi-enclosed systems (Table 1).

1.2 Recent Rapid Changes in the

Biogeochemistry of the Great Lakes

System:

Historically, changes in the

biogeochemistry of the Great Lakes have

Figure 1: Long-term trends of major ions for

the Great Lakes (Chapra et al., 2012)

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responded rapidly to external stress. The first

acceleration in biogeochemical changes in the

Great Lakes was observed in changes in the

concentrations of major ions in the early to middle

part of the 20th

century (Beeton, 1965) (Figure 1).

The common stressors among great lakes (and many

small lakes as well) include: i) eutrophication, ii)

fisheries exploitation; iii) exotic species; iv)

contaminants; and v) climate change. The major

milestones in the alterations of major nutrients to the

Great Lakes system included: 1950s to 1970:

increases in P loading to the lakes; 1972 to 1990:

mandated P reductions resulting in water quality

improvements (lower P, Chl and fewer algal blooms); 1988-1997: dreissenid mussels invasion

and colonization of all lakes (except Lake Superior), first zebra mussels in shallow regions and

then quagga mussels in deeper water; and 2000-2010: quagga mussel populations explode in

profundal regions of all lakes, except Lake Superior; 1980-present: a warmer, wetter climate.

Excessive nutrients loading from pulse events (e.g., excessive rains over a short period of

time discharging a large amount of nutrients) from the watershed have resulted in eutrophication

in some of the lakes. The implementation of the Clean Water Act

resulted in significant reduction in loading of nutrients that

generated improvements in water quality in tributaries and open

waters throughout the lower lakes, in particular. Yet,

eutrophication remains an issue with some of the most extensive

algal blooms ever observed in some of the lakes. For example, in

2011, ~10% of the surface area of Lake Erie (~2.5 x 103 km

2) was

covered with bloom concentrations, a historical record. This

occurrence is hypothesized to be the consequence of a complex

interactions among climate, invasive species, and changing land

use practices (Figure 2), and is indicative of how quickly the system can revert to an apparently

“previous state” under entirely new conditions.

The rapid, extensive colonization and reengineering of the lower Great Lakes by

dreissenid mussels in the last 20-30 years fundamentally altered the cycling of biogeochemically

important materials with a speed and magnitude which is remarkable even for the Great Lakes

that has resulted arguably in the largest biogeochemical shift in the lakes in recent history

(Hecky et al., 2004), despite the long history with nearly 200 non-native invaders (Figures 3, 4).

This directly and indirectly human-induced large-scale perturbation is an example of an

opportunity to investigate the response of a large land-margin ecosystem which integrates

complex interactions among terrestrial, atmospheric and aquatic components.

Table 1: Ratio of terrestrial catchment (CA) to lake area (LA), mean depth, hydrologic residence time (WRT) and mean nitrate concentration in major lakes in the world (Bootsma and Hecky, 2003; Weiss, 1991) Lake CA/LA Mean

Depth (m)

WRT (y)

NO3-

(mol/L)

Superior 1.6 148 191 20

Michigan 1.6 84 99 12

Huron 2.1 61 22 20

Ontario 3.4 86 6 16

Erie 2.3 18 2.6 18

Baikal 12.1 730 327 7

Great Bear

5 72 131 10

Victoria 2.8 40 123 < 0.5

Figure 2: The largest algal

bloom ever recorded in Lake

Erie was observed in 2011

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1.3 Contrasts in the Biogeochemistry Between all

Five Lakes:

The highly varying inputs of nutrients

among the five lakes, contrasting regeneration of

macro- and micro nutrients due to highly differing

mean

water

depths, hydrological residence times (Quinn, 1992),

and mean annual surface temperatures make each of these lakes unique resulting in differences in

the biogeochemical cycling of nutrients within these five lakes. Influence of internal recycling in

lakes generally is a function of hydrological residence time both on scale of whole lakes as well as locally

within lakes while influence of external loading is associated with the ratio of catchment area to lake area

(CA/LA). The values of CA/LA ratios are given for all five lakes in Table 1, Fig. 5. The annual

mixing of nutrients from the deep water, which is the primary source of nutrients supporting new

production for the deep waters in the lake, can vary substantially from lake to lake and from year

to year due to differences in the vertical mixing of waters (Dymond et al., 1996; Hecky et al.,

1996). The hydrodynamical regimes of the five lakes are not the same. There are striking

contrasts, in terms of ecological status, between the five lakes in the Great Lakes system. A

large and predictable hypoxic zone in Lake Erie, differences in the trophic states from ultra-

oligotrophic (Superior) to hyper-eutrophic (Sandusky Bay, Lake Erie), eutropic to oligotrophic

conditions in Lake Erie, and marked differences in the response to recent climate change in

different lakes (e.g., such as Lake Superior warming at twice the rate of the atmosphere), are

some of the special features of the Great Lakes system. Due to the size of the lakes, the changes

caused by changing climate will be expressed sooner and can be more easily quantified in the

Great Lakes than in the oceans and they may be harbingers of climate change impacts, but not an

indicator of the direction of those changes in the oceans.

Figure 3: Temporal evolution of aquatic

non-native species in the Great Lakes

over 150 years.

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Pre-mussel:

The input of

Figure 4: Changes in the P loading in lakes that are reengineered by zebra mussels. The differences in the

thickness of the arrows indicate the changes taken from pre-mussel to post-mussel periods (From Hecky

et al., 2004).

Post-mussel:

Figure 5: Depths of Lakes and major rivers in the Great Lakes

system

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anthropogenically induced external loading of nutrients to the lake primarily depends on the

population density in the watershed surrounding the lake. The population density in the

watershed surrounding Lake Superior is the lowest and thus, the input of nutrients from sources

such as sewage and fertilizer are relatively minor. Lake Superior is reported to have a century-

long buildup of NO3- such that nitrate is far in excess of P, with a NO

3/PO4

3- molar ratio in deep-

water of 10,000, more than 600 times the mean requirement ratio for primary producers (Sterner

et al., 2007), but the temporal variations for other lakes are less known. The low rates of primary

production coupled with low watershed inputs of organic C input and low OC burial rates to

sediments limit rates of nitrate removal by denitrification in Lake Superior (Johnson et al., 1982;

2012; Finlay et al., 2007). Rates of N cycling processes in the Great Lakes, however, are nearly

lacking thus while changes in nitrate are apparent, the precise causes remain elusive. The

concentrations of dissolved organic carbon vary widely, from about 100 M in Lake Superior to

about ~400 M in Huron, Michigan, Erie and Ontario (Waples et al., 2008). The primary

productivity is the lowest in Lake Superior (12-25 mmol C m-2

d-1

) and highest in Lake Erie (73-

84 mmol C m-2

d-1

; Kumar et al., 2008; Sterner, 2010).

2. Rapid and Unexpected Recent Changes in the Large Lake System:

The major drivers of ecosystem change are changes in the flow of macro- and micro-

nutrients. The overall loadings of phosphorus to the Great Lakes have decreased due to a

combination of regulations to reduce point source loadings and improved agricultural practices to

reduce nonpoint source loadings (e.g., Bertram, 1993; DePinto et al., 1986). For example,

between 1970 and 1990, the total loading of phosphorus to Lake Michigan from point and non-

point sources (such as streams/rivers/tributaries, atmospheric and point sources) decreased by

50% (Miller et al., 2000) and such reductions in the loading of phosphorus have resulted in the

decrease in the turbidity and algal blooms in the lake’s water column and increases in the clarity,

light penetration, and dissolved oxygen, while the introduction of invasive species in late 1980s

(such as zebra and quagga mussels) have bioengineered this ecosystem. The patterns of turbidity

in Lake Erie during 1980s and early 2000s were reported to have been altered with near-shore

waters often clearer than offshore waters whereas in the western and central basin of the lake

there were increases during this period (Cha et al., 2011). Such an increase in clarity has resulted

in deepening of euphotic zone which allows biota to have better access to the nutrient-rich

deeper water in stratified season (Barbiero and Tuchman, 2004). Earlier studies have

documented large changes in productivity and diatom abundance at two stations in Lake Erie,

although lake-wide data is not available (Saxton et al., 2012).

The spread of invasive mussels has led concomitantly to alterations in nutrient ratios

(e.g., C/N and P/N ratios), increased water clarity, and hardening of formerly soft substrates over

large areas, all with implications for shifts in the biogeochemical cycling of both major and

minor elements (Fig. 1). These changes have resulted in the alterations of pelagic and benthic

food webs and associated elemental cycles. In the near-shore areas of Lakes Huron, Erie, and

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Ontario, significant decreases in the

concentrations of P, phytoplankton,

and chlorophyll and Chl-a/P ratios

coincided with the establishment of

dreissenid zebra mussels and later

quagga mussels (e.g., Fahnenstiel et

al., 1995; Nicholls et al., 2002). For

example, less dissolved P in the

water column, either from the

abatement of P loading to lakes or

removal of particulate P from the

near-shore water column by filter-feeding mussels, led to decreased pelagic productivity,

increased benthic macroalgal productivity in littoral waters, less organic material ultimately

settling to the bottom and thus less available materials and energy for benthic communities

(Eberts and George, 2001; Nalepa et al., 2007). Diatoms, once a dominant component of the

spring bloom during the isothermal mixing period, have been significantly reduced in abundance,

resulting in disappearance of the spring phytoplankton bloom in Lake Michigan and dramatic

decreases in some zooplankton species (Figure 6, Vanderploeg et al., 2010, Kerfoot et al., 2010).

Chlorophyll a, phytoplankton carbon biomass, and water column primary production decreased

66%, 87%, and 70%, respectively, in Lake Michigan during 2007-08 as compared to 1995-98

(Fahnenstiel et al., 2010). These changes have affected the annual biogeochemical cycling of

nutrients and carbon as well (Mida et al., 2010). Prior to this shift, dissolved silica uptake during

the spring bloom lowered silica concentrations to near zero (a few molar). Subsequent diatom

settling, dissolution and silica regeneration resulted in an annual cycle of depletion and

regeneration. Annually about 20% of the silica deposited was ultimately buried, with the

remainder recycled back into the overlying water during isothermal conditions. Today, silica

concentrations drop by less than half of their winter seasonal maximum, i.e. dissolved silica

uptake has been significantly reduced in a shift that has been termed “incidental

oligotrophication” (Evans et al., 2011). Gradual increases in spring silica concentration in all

basins of Lakes Michigan and Huron between 1983 and 2008 have been recently reported

(Barbiero et al., 2006; Evans et al., 2011). This shift has transferred nutrients and energy from

the pelagic system to the benthic system in the form of an expanding population of quagga

mussels throughout the lake. The consequences of these changes on the nutrient and energy flow

for benthic carbon metabolism are unknown, but likely dramatic. Since Si is required by

diatoms, the depletion of Si can be used as a measure of diatom and phytoplankton production.

The silica drawdown in lakes Michigan, Huron and Superior is compared in Figure 9. It has been

reported that after the invasion of quagga mussels, there was much less consumption of silica

Year

75 80 85 90 95

Pri

mar

y P

rodu

ctio

n (m

g/m

2/d)

0

200

400

600

800

1000

1200

Saginaw Bay Primary Producers After Zebra Mussels

Zebra Mussels

Benthic Algae (450 mg/m2/d)

Phytoplankton

Figure 6: Drastic decrease in the primary productivity after the

invasion of zebra mussels in Lake Superior

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during winter-spring. A widespread observed decline of Ca in lake waters and was attributed to

the reduction in the

exchangeable Ca

concentration in

catchment soils (Jeziorski

et al., 2008). Such

reduction is caused by a

number of factors that

include acidic deposition,

reduction in atmospheric

deposition of Ca, Ca loss

from forest biomass

harvesting (Jeziorski et

al., 2008). It has been shown that the dreissenids have caused decreases in Ca and

lower lakes due to calcification in producing shells (Chapra et al., 2012). It is estimated that

alkalinity concentrations in decline in Ca due to mussels would reduce soluble reactive

0

0.2

0.4

0.6

1980 1990 2000 2010

Silic

a u

tiliz

atio

n

(mg

/l)

Figure 7: closed symbols, northern basin; Open symbols: southern basin

(data from EPA_GLNPO).

Figure 8: Total P loading reductions exceeded the target. The standard errors vary from 1.5 to 19% of the total lake

load depending on the lake and the year. Lake Superior typically has larger standard errors (9.1% of the load, on

average), while Lake Erie has some of the smallest estimates (3.5% of the average load).

12

phosphorus (SRP) in the waters by approximately 3 mg/L (Arnott and Vanni, 1996; Chapra et

al., 2012). Thus, it appears that mussel shells are a major sink of P and Ca in the lakes where the

mussel shells have dominated. In Lake Ontario, Ca and alkalinity concentrations have fallen and

summer ‘whitings’ are reduced in frequency and in some cases no longer appear (Barbiero et al.,

2006).

3. Long-Term Nutrient Concentration Variations in the Great Lakes:

The concentrations of some of the nutrients have varied widely. The total P loading has

decreased considerably due to management decisions. The total P loading reductions have

exceeded targets in all the 5 lakes and the loading and its variability is now dominated by non-

point sources, mainly runoff, which responds to precipitation (Figure 7). From a large database

of nitrate concentrations from samples collected spanning over a century for Lake Superior,

Sterner et al. (2007) reported a continuous, century-long increase in nitrate whereas phosphate

remains at very low levels (Fig. 8). The NO3- concentration in Lake Ontario increased by more

than a factor of 2 during the last 40 years (Figure 9a,b,c), similar to Lake Superior. There seems

no historical P or Si data going back to a century. The cycling of carbon, nitrogen, silica, calcium

and other key micro-nutrient trace metals (e.g., Zn, Co, Fe, V) in all five lakes have been

affected (Fig. 10). These micro-nutrients play a significant role on the structure of the freshwater

ecosystems and their biological activity which are key factors in regulating the carbon cycle. It is

not known how the dissolved trace element concentrations have changed over the past 30 years

as reliable data based on ultra-clean trace metal sampling are limited. The changes in

biogeochemical cycling of nutrients have resulted in the changes of benthic fauna diversity and

biomass as well flora (e.g., increased abundance of sea grasses, red macroalgae; Figure 5, Hecky

et al., 2004).

3.1 Stoichiometric challenge:

One of the most important differences between freshwater and salt water is stoichiometric

paradigm in that C:N:P ratios of different components of the oceanic ecosystem exhibit little

temporal and spatial variation (Redfield, 1934; Falkowski, 2000). However, the variations of

SRP in lakes are quite large (e.g., Hecky et al., 1993; Elser et al., 2000). The limited spatial and

temporal data on the primary productivity (PP) and respiration rates (RR) adds a large

uncertainty on the controls of stoichiometric ratios, and data on the seasonal and deep water PP

and RR are generally lacking. For example, the elemental ratios of C:P in seston varies

dramatically on a multi-year time scale (100-150 in 1996-1997 to 300-350 in 2000, Sterner et al.,

2007). Such a change has major consequence on the entire food web, species abundance,

secondary production, autotrophy/heterotrophy relationships, etc. (e.g., Elser et al., 2000).

Furthermore, decreased pelagic productivity and lower amounts of organic carbon in benthic

sediments have been driven by alterations in the sources, pathways and cycling of nutrients in the

littoral regions of the Great Lakes system.

13

Dove, 2009

http://www.on.ec.gc.ca/solec/nearshore-water/paper/part5.html

Long-term trend of increasing nitrate: other Great Lakes

Rising NO3- evident in all of the Great Lakes

But not likely to be for the same reasons

NO

3-m

g/L

Lake Ontario 1970-2008

Lake Ontario 1970-2008

Eutrophic

Mesotrophic

0.02

Oligotrophic

0.01

PO

43

-m

g/L

0.03

0.04

0

0.2

0.3

Lake Erie (central basin)

http://www.on.ec.gc.ca/solec/nearshore-water/paper/part5.html

NO

3-m

g/L

Figure 9b: Nitrate concentration in Lake

Superior

Figure 9c: Concentrations of NO3- in L. Superior Figure

8b: NO3- + NO2

- and total Mo in L. Ontario (Sterner et al.,

2007) & Mo-unpublished data (Twiss, 2013)

Figure 9a: Temporal variations of nitrate and phosphate in Lake Ontario over the past ~40

years and nitrate concentrations in the Great Lakes system

14

T

he

concentrations of nitrate in Lake

Superior have been reported to have

increased steadily over the past

century, from ~5 to ~30 mol L-1

(Sterner et al., 2007). While the

phosphate concentrations in Lake

Superior have decreased over the past

4 decades, the atmospheric deposition

of nitrate has remained constant. This has resulted in the present-day severe stoichiometric

imbalance in Lake Superior, with the (NO3-/PO

3-4) ratio of ~10,000 (molar ratio) in the deeper

waters of Lake Superior (Sterner et al., 2007). Continuous gradual increase of spring silica

concentration in some of the lakes (e.g., Lakes Michigan and Huron) from 1983 to 2008 has

altered the N:P:Si stoichiometric ratios. These changes in the cycling of key macro-nutrient

elements in the Great Lakes system have likely altered key micro-nutrient stoichiometry as well

which needs further investigation.

4. Fluxes and Processes of Key Major and Minor Nutrient Elements in the Great Lakes

System:

4.1. Atmospheric deposition of key macro- and micronutrients:

Long-term records of atmospheric deposition of N or P or Si emissions in the airshed of

the Great Lakes are very limited. The relative percentages of the reduction of the nutrients are

different for different nutrients. For example, phosphorus concentrations in precipitation have

decreased from an average of 57 mg as P L-1

in 1976 to an average of 6.4 mg as P L-1

for 1994-

1995 while the volume-weighted mean concentration of NO3- in Lake Michigan did not change

between 1983 (2.0-2.5 mg as NO3-) and 1994-1995 (1.9 mg as NO3

-) (Voldner and Alvo, 1989;

Miller et al., 2000), thus altering the PO43-

/NO3- stoichiometric ratio of the atmospheric input to

Lake Michigan (Miller et al., 2000). The atmospheric emissions of nitrate from U.S. and Canada

over a period of 20 yrs (1980-2000) have been reported to be constant, although temporal

increases were reported between 1940 and 1980 (EPA, 2000; Chen et al., 2000). Simultaneous

year-long measurements of major nutrient elements along with their isotopic ratios are needed in

different air sheds in the Great Lakes system.

4.2 Inputs of micro- and macro nutrients through groundwater discharge studies

Figure 10: Variations in the concentrations of Ca

and alkalinity in all five lakes.

15

Over the past 250 years, the geochemistry of the Great Lakes groundwater and surface

water systems has been altered by regional land use changes including deforestation, wetland

drainage, agriculture, industrialization, and urbanization. Further changes stemming from the

“green revolution” in agricultural practices and accelerating climate change beginning in the

latter half of the twentieth century are anticipated, but not well constrained. The volume,

location, and quality of direct groundwater discharge to the Great Lakes are poorly understood.

Coastal areas, where groundwater discharge is expected to be greatest, are largely ungaged.

Therefore, the amount and chemistry of groundwater discharging to the Great Lakes are not well

known.

Some of the groundwater flow systems in an aquifer system provide base flow to the

streams in response to recharge from the precipitation events. Submarine groundwater discharge

could be one of the significant sources of nutrients and key trace elements to the lakes. The

groundwater component of stream flow (for 195 selected streams in the US part of the Great

Lakes Basin) ranges from 25 to 97%, with an average value of ~67%. Although there is no

estimate on the total amount of direct groundwater discharge to Lake Huron, Superior, Erie and

Ontario, there is an estimate for Lake Michigan. The total groundwater discharge to Lake

Michigan was estimated to be ~2.7 x 103 ft

3 s

-1 (~76.5 m

3/yr; Grannemann and Weaver, 1998).

Highest rates of groundwater discharge were calculated for the northeastern shore of Lake

Michigan. Numerical groundwater flow and transport models are therefore needed, in

conjunction with field measurement (seepage meter covering several locations around the lakes)

and tracer studies (e.g., 234

U/238

U, 223,224,226,228

Ra, 222

Rn, 87

Sr/86

Sr in aquifers and lakes), to

investigate processes controlling nutrient and solute flux across an appropriate range of spatial

and temporal scales. Groundwater flow paths vary from local to regional with travel times

ranging from days to decades to centuries. Regional flow paths through carbonate, siliciclastic,

and crystalline bedrock will likely have different equilibrium chemistries and spatial variability

in both the volume and chemistry of submarine discharge to the Great Lakes is expected.

Consequently, models will enhance our ability to predict: i) flow paths and discharge regions; ii)

estimate geochemical signals; iii) quantify nutrient and solute fluxes; and iv) detect and confirm

anomalous regions. Hence, they will contribute to a greater understanding of the role of

groundwater and surface water hydrology in the biogeochemical cycling of phosphorous,

nitrogen, and micronutrient cycling within Great Lakes ecosystems.

In about 37% of the monitor-well samples in the Lake Erie and Lake St. Clair drainages,

the nitrate concentrations indicated evidences of human influence such as fertilizer, manure or

septic systems and thus, the contribution of nitrate to base-flow in riverine systems is expected to

be significant. Phosphate concentrations in groundwater depend on the bedrock, with siliciclastic

bedrock groundwater exhibiting lower concentrations (0.017-0.020 mg/L) compared to carbonate

rocks (< 0.1 mg/L). Many of the shallow groundwater aquifers is hydraulically connected to the

land surface, based on the presence of tritium in ~83% of the waters from monitor wells which

were recharged after 1953 and 53% of the wells contained a pesticide or elevated nitrate

16

concentration (Myers et al., 2000). However, there is no estimate on the fluxes of N, P, Si or C or

any of the micro-nutrients to the Great Lakes through groundwater discharge.

Recently, three sinkhole vents were discovered in cyanobacterial mats that are similar to

extreme and exotic ecosystems. These cynaobacterial mats thrive in low-O2, conduct both

oxygenic and anoxygenic photosynthesis and these organisms could serve as sentinels of

environmental change (Voorhies et al., 2012). The waters that are discharged in these vents are

anoxic, with high concentrations of sulfate and chloride and low concentrations of nitrate and

oxygen. It remains unknown if there are more sinkhole vents in other areas of Lake Huron and

other lakes in the Great Lakes system, at large. Stable (18

O and H) and radioactive isotope

studies (226

Ra, 228

Ra) in water samples collected near the sediment-water interface at few

kilometers from the sinkhole vents indicate that there several effusive fluxes where highly anoxic

waters are leaking (Baskaran et al., 2014 – in review). These sinkhole vents can serve as analogs

for life in extreme environments.

4.3. Inputs of macro- and micro nutrients from sediments:

The sediment accumulation rates in lacustrine systems are generally higher than the shelf

and deep oceans and the degree of bioturbation that causes the loss of temporal resolution of

sedimentary record is low and hence usually lacustrine sedimentary records are better candidates

for paleo reconstruction studies. There are some sporadic attempts to quantify the transport and

burial rates of organic carbon. Quantitative assessment and numerical models of sediment

dynamics have been conducted in a limited area (e.g., Edgington and Robbins, 1990). The nature

of the bathymetry in the coastal areas in the Great Lakes makes the storm-generated episodic

resuspension and horizontal advection of nutrients, carbon, sediments and other

biogeochemically key material to be significant, although the trapping of the nutrients,

particulate matter containing key elements and isotopes, attenuation and sequestration of key

material fluxes are not investigated. Sediment burial of C seems to be more important in the

shallower lakes, although the data is very limited in the Great Lakes system. Earlier studies on 14

C in POC indicate presence of resuspended material to be the major source of particulate

matter. Data on well-constrained benthic flux estimates of C, N and P are also needed for a

better understanding of the biogeochemical cycling of key macro-nutrients in the lacustrine

system.

4.4. Internal Cycling and regeneration studies:

The internal cycles of macro- and micro nutrients (both dissolved, particulate and

colloidal forms) in the inland sea waters are influenced by a complex set of removal, transport

and transformation processes that include removal by invasive species, atmospheric deposition

from the industrial belt in the Midwestern states, agricultural industry, etc. The hydraulic

residence times of these waters (Table 1) are much lower than the global ocean circulation times

of ~2000 yrs and hence the uniform mixing of the water takes place much quickly compared to

the oceans (Fee et al., 1996). Some of the trace metals (e.g., Fe) has been found to serve both as

17

a limiting factor in the growth of phytoplankton in high-nutrient low chlorophyll regions and for

its regulation of nitrogen fixation.

It has been estimated that the external loading of nutrients is sufficient to meet the algal

demand on a daily basis, while internal cycling meets the overall needs. The influence of internal

cycling/recycling on lakes generally is a function of water residence time, both at the scale of

whole lakes as well as factors and processes that operate locally within lakes while the influence

external loading is associated with the terrestrial catchment to lake area (Table 1). The vertical

distribution of a micro- or macro nutrient results from a combination of processes such as

physical transport, chemical control, and biological activity. The external loading of nutrients

can be relatively easily characterized and quantified, while the internal loading and cycling is

difficult, as it involves quantification of several biogeochemical processes that are not well

understood in the Great Lakes system. Internal loading estimate would require an estimate of

benthic fluxes, rates of particle-recycling of N, P and C, and extent of remineralization of POC,

PON and POP. There are very little data on the benthic fluxes of macro- and micro nutrients for

the Great Lakes system. Furthermore, data on the remineralization term for POC, PON and POP

in the water column from sinking particulate matter are very limited and is confined to a limited

area.

To investigate the cycling and transport of N, P, Si, and OC, some of the U-Th series

radionuclides (e.g., 234

Th, 210

Pb, 210

Po, 210

Bi), cosmogenic radionuclides (e.g., 7Be) and

anthropogenic radionuclides (e.g., 90

Y/90

Sr) have been utilized (e.g., Coale and Bruland, 1985;

Murray et al., 1989; Buesseler et al., 1992; Baskaran et al., 2003; Moran et al., 2003; Cochran

and Masque, 2003; Murray et al., 2005; Waples et al., 2006; Rutgers van der Loeff and Geibert,

2008). Variations in the nature of particulate matter (biogenic versus lithogenic) due to the

presence of dreissenids can be investigated using tracers that trace biogenic particulate matter

(e.g., 210

Po) and terrigenous particulate matter (e.g., 210

Pb). They also can be used to constrain

rates of scavenging and biological uptake by particles and to quantify processes that regulate the

internal cycling and eventual removal of key nutrient elements. Radium isotopes can be used as a

tracer of other alkaline elements such as Ca, Ba, Sr, etc. The abundances of Ca and Ba are

considerably altered in the many of the lakes due to dreissenids and it is likely that Ra is also

altered from the water column. Quantification of sediment resuspension rates using particle-

reactive radionuclides (210

Pb and 7Be) in freshwater system has been conducted (e.g., Jweda et

al., 2008), and amount of release of organic C, N and P from sediments can be quantified from

the sediment resuspension rates.

4.5. Impacts on nutrient cycling due to climate changes:

The major impact of global climate change (or regional climate change) caused by human

perturbation will affect the hydrological cycle the most having the most immediate impact on

future human welfare of those who twelve in the Great Lakes region. The global climate change

has resulted in increasing annual surface air temperature as well changes in the amount and

frequency of precipitation in the Great Lakes region. The climate change will affect the

18

hydrologic balance, biological productivity, and ecosystem structure and water quality.

Continued rise of atmospheric CO2, both from measurements and predicted GCMs will have

significant impacts on the ecosystem of the Great Lake system. Model-predicted global warming

is expected to affect the length of the stratified period in the Great Lakes (by as much as 90 days;

Weiss and Sousounis, 1999). Such elongated period of stratification will result in extended

isolation of warmer hypolimnion from the atmosphere and could result in lower dissolved

oxygen (DO) levels and such lower DO potentially will have enormous impacts on nearly all

segments of the lake ecosystem, including nutrient cycling, benthic metabolism and fisheries

(SOFIS Report, 2003). Changes in the frequency and amount of precipitation could result in the

water level fluctuations, changes in river runoff and lake water evaporation. Changes in the

hydrological cycle expected to accompany global warming will likely have an impact on the

delivery of lithogenic and nutrient elements to the Great Lakes through several processes that

include increased watershed erosion and runoff in several areas. Changes in the wind field

resulting from regional climate change, as a result of global climate change, can alter the water

and nutrient exchange between semi-enclosed bays and the open lake water. For example,

changes in the wind field over the Great lakes basin since 1980 has resulted in a reduced amount

of water exchange between Green Bay and Lake Michigan which has led to the formation of

intensified bottom water hypoxia, increased benthic metabolism within the bay, and warmer

bottom water temperature (Waples and Klump, 2002). Over the last 30 years, the surface water

temperatures in Lake Superior have risen twice as fast as air temperatures (Austin and Coleman

2007). In Lakes Michigan and Huron evaporation has increased significantly, equivalent to a

nearly 4 meter drop in lake level, but this has been offset by increases in precipitation and runoff

(Hanrahan et al. 2010). Decreases in the water levels in Great Lakes and their connecting

channels are of major concern not only for recreation industry but also for other sectors including

transportation industry.

5. Tools for Biogeochemical Cycling Studies:

5.1 Particle-reactive and stable isotopes:

19

A major understanding of the biogeochemical cycles of many elements in aqueous system is

linked to the understanding of the cycling of particle-reactive radionuclides. Several key

biogeochemical processes in the water column including formation, aggregation/disaggregation,

dissolution, and scavenging of biogenic particulate matter, exchange of particle-reactive species

between particles and solution, and export of particulate organic carbon, nitrogen and other

particle-reactive organic matter (e.g., PCBs, PAHs) relies heavily on the natural radioactive

clocks provided by the U-Th series radionuclides along with a set of cosmogenic and

anthropogenic radionuclides

(Ivanovich and Harmon, 1992;

Bourdon et al.,2003;

Krishnaswami and Cochran,

2008; Hong et al., 2011; Kaste

and Baskaran, 2011). While a

large body of data exist utilizing

U-Th series radionuclides as

POC, PON export tracers

(234

Th/238

U and 210

Po/210

Pb) in

the marine systems (Buesseler,

1998; Moran et al., 2003; Waples

et al., 2006), virtually no data

exist in the freshwater system.

Although the 238

U concentration

in freshwater system is very low (~5% of open ocean value) in the Great Lakes (limiting 234

Th/238

U pair for export studies), the 210

Pb concentrations in surface waters are expected to be

significantly higher than that of most other deep ocean basins (210

Po/210

Pb pair can be utilized

export studies) due to differences in the sources of air masses. The half-lives of these nuclides

are short (e.g., 234

Th: 24.1 d; 210

Po: 138.4 d; 210

Bi: 5.1 d) to make these nuclides sensitive to

short-term changes that occur (e.g., POC flux integrated over a week to a few months) in upper

water column. The deficiencies of these nuclides are created by the scavenging of these onto

20

biogenic particulate matter and the sinking of such particulate matter out of the euphotic zone. It

has been documented that 210

Po traces much more efficiently the biogenic organic matter than Th

and hence Po is likely a better tracer for POC and PON export studies (Figure 11,12; Friedrich

and Rutgers van der Loeff, 2002; Verdeny et al., 2007). The lone study in Lake Superior (Chai

and Urban, 2004) that reported similar residence time for 210

Po and 210

Pb is in contrast with

much longer time of 210

Po compared to 210

Pb in the upper 150 m, due to remineralization of

particulate 210

Po in marine system (e.g., Sarin et al., 1999). No other data exists from any of the

other lakes in the Great Lake system to compare with. Using 210

Po-234

Th and 210

Po-210

Pb as

coupled tracers, Friedrich and Rutgers van der Loeff

(2012) estimated the sinking velocities of biogenic Si

and POC. Particle formation and dynamics can be

investigated using the disequilibrium between 210

Po-210

Bi-210

Pb pair, similar to aerosol removal in the

atmosphere. There are limited attempts to quantify

the lateral export suspended particulate matter using radioactive tracers (234

Th, 137

Cs, 7Be) in the

Great Lakes system. For example, the Keweenaw Interdisciplinary Transport Experiment in

Lake Superior (KITES) focused on a region dominated by a strong coastal jet, and the sister

project in Lake Michigan, Episodic Events—Great Lakes Experiment (EEGLE), concentrated on

the biogeochemical effects of a major plume of resuspended sediment that occurs annually in the

southern portion of the lake (Eadie et al. 2008; see JGR special issue, 2004:

http://www.agu.org/journals/ss/EEGLE1/). These studies were limited to one area and had

limited scope in terms of using key micro and macro-nutrients study.

The understanding of nitrogen cycle in the Great Lakes system is very limited, although

the N/P stoichiometry ratios in many of the lakes have drastically changed, mainly due to

increase in N rather than

drastic decrease in P values.

We have currently a better

understanding of N cycle in a

small lake in Switzerland

compared to the Great Lakes.

Although historical data on

the nitrification-

denitrification at the

sediment-water interface and

sediment cores are limited, it

has been shown that the

vertical distribution of 15

N

and 13

C of a dated core from

Figure 11: Parallels between N and Po cycles.

Total production = New production + recycled

production. Magnitude of POC export is

estimated based on mass balances in the

euphotic zone. New production is the supply of

‘new’ nutrients via upwelling and this is

balanced by the export of POC

Figure 12: The nutrient loadings (nitrogen) are easiest to measure in

outflow, and most difficult in internal loading. On a daily basis, most

algal demand is met by recycling. Concentrations are expected to be

in balance of internal and external loading.

21

Lake Ontario varied by ~2‰ over the past 140 years while 15

N values change by ~5-6‰ and it

was attributed to active denitrification at the sediment-water interface (Hodell and Schelske,

1998). The classical view that nitrogen cycle is dominated by nitrification and denitrification is

changing, and ANaerobic AMMonium OXidation (Anammox: NO3- + NH4

+ → N2) and

Dissimilartory Nitrate Reduction to Ammonium (DNRA: NO3- → NH4

+) are increasingly being

recognized as important processes that regulate the nitrogen cycling (Figure 13).

Very limited data is available on denitrification and on DNRA in the Great Lake systems and no

nitrification rate data seem to be available from Lake Huron and Ontario.

5.2 New and Newly Emerging Tools:

Key major nutrients (P, N and

Si) and some of the essential micro-

nutrient trace elements (e.g., Fe, Zn, Co,

V, Mo, and Cu) play important roles in

the biochemical activity in organisms

(e.g., Morel et al., 2003; Morel and

Price, 2003). High precision

measurements of the isotopes of these

micronutrients are available only in the last ~15 years

and there is limited data on their distributions in the Great Lakes system. For example, there are

vertical profiles of Si isotopes (29

Si) for Lake Tanganyika (Figure 14). The d29

Si isotopic ratio

could be useful in studying environmental changes and particularly recent changes in the diatom

utilization (Alleman et al. 2005). Lack of such information prevents the scientific community to

get a good handle on the sources, transport and cycling of these essential elements across the

lakes.

A large number of isotopes are utilized as a set of powerful tools to map the food webs in

terms of the major carbon flows and trophic relationships (Hecky and Hesslein, 1995). For

example, the distribution of phosphate and Cd are similar in marine system (Elderfield and

Rickaby, 2000) and thus, isotopes of Cd can be used to trace the pathways of P because both

species are likely removed from the freshwater sea by biological activity. Zinc which is an

an essential micronutrient

could serve as a tracer for

another macro-nutrient, Si, in

aqueous system (Ellwood and

Hunter, 2000; GEOTRACES

Science Plan, 2006). There is

very limited data on the

Figure 13: Schematic diagram of nitrogen cycling in

an aqueous system (Francis et al., 2007)

Figure 14: Dissolved Si concentration (dashed line) and δ29Si

(bold line) profiles at station TKI (northern basin), TK5 and

TK8 (southern basin) collected in July 2002.

22

isotopic fractionation of nutrient elements as well as micro-nutrient elements and thus, some of

the isotopic tools could serve as powerful tools in assessing nutrient utilization. Isotopes of

nitrogen and oxygen in nitrate are used to quantify the sources and dynamics of nitrate, both

15

N (15

N-NO3) and 18

O (18

O-NO3). It has been shown that the 15

N values of NO3- sources

often overlap and thus combined use of N and O isotopes are powerful (Kendall, 1998; Burns

and Kendall, 2002; Hastings et al., 2003). The 18

O-NO3 from nitrification is largely determined

by the 18

O in water in the ecosystems while 18

O-NO3 values in precipitation is the result of

isotopic fractionation taking place during interactions between oxides of nitrogen and O3 in the

atmosphere (Hastings et al., 2003; Michalski et al., 2011). Oxygen isotopes in phosphate are

used to trace the pathways of phosphate (Jaisi et al., 2011; Paytan and McLaughlin, 2011).

6. Missing Gaps in Knowledge and Key Questions:

A mass balance of C, N, P and Si in the lakes require good estimates on the primary

production, grazing, DOC inputs/outputs from rivers/streams and carbon burial rates. Attempts

for OC budget have been attempted for L. Superior (Urban et al., 2005). Lake-wide studies on

the production and grazing in most lakes are lacking and thus, there are gaps in our

understanding of the N, P, and Si cycling and its link to other key macro- and micro nutrients.

Earlier PP studies are primarily from certain seasons of the year and lack of data during the

colder periods and deeper waters fuels the uncertainty in the C estimate. The uncertainty in the

primary production rate for Lake Superior is mainly due to the scaling-up factors used on the

vertical temperature and chlorophyll data at measured at depths. The chemical reactions

(nitrification, denitrification and anammox) are expected to be slower in Lake Superior due to

cooler waters compared to other lakes (Michigan, Huron, Erie, and Ontario); other factors that

control the N, C and P cycling and N assimilation and microbial community structure are not

studied in all the Great Lakes, whether it is due to increase in external sources discharged to the

lakes (rivers/streams, atmospheric deposition, submarine groundwater discharge), or active in-

lake processes (such as nitrification/denitrification, anammox).

The first step in the transfer of nutrients and C to food chains is the grazing. In eutrophic

environments, the transfer by grazing is less efficient that that observed in oligotrophic waters

and hence the settling of nutrients to deeper waters is primarily controlled by grazing. Thus, the

relative importance of grazing compared to the export of particulate C, N, and P. During vertical

transport of POC, PON, POP, particles undergo remineralization contributing to the dissolved C,

N, and P in the water column. Thus, grazing data using some commonly used protocol (e.g.,

dilution gradient method, Landry and Hassett, 1982) is needed. The small consumers such as

picoplankton (<10 um) could play an important role as dominant consumers relative to the whole

food web. Lake-wide primary production rates from time-series, vertical profiles, and day/night

studies are needed to limit the range of variations on the primary production estimate, using

widely accepted method(s), such as 14

C methodology. Similarly, an estimate on the grazing on

planktons for the whole lake needs to be assessed. It is also essential to measure vertical profiles

of production and establish an empirical relation between production, light and temperature.

23

Establishing such a relationship at different seasons (summer, winter and spring) will help to

constrain the estimate on production. Lake-wide efforts on the simultaneous measurements of

primary productivity and respiration rate with special emphasis on seasonality, year-around

measurements and surface and deep-water measurements of these parameters are important

(including under-ice measurements of production and respiration to quantify autotrophic-

heterotrophic balance). Sporadic and sparse measurements of primary production and respiration

rates most likely have missed the important spatial and temporal variations of the biological

activity and thus, it is urgently needed to quantify these rates.

Recent studies in Lake Erie showed that Fe is required for the stimulation of NO3- draw

down and required for NO3- assimilation (Twiss et al., 2005; Havens et al., 2012). Several other

trace elements such as Co, Zn, Ni, Mn, Cu, also serve as essential micronutrients, and their

distribution, sources, pathways and eventual sinks remain unknown. The biogeochemical cycling

of Fe in the Great Lakes system remains poorly characterized. A potential relationship between

micro-nutrients and macro-nutrients (e.g., PO4-Cd; Si-Zn) could help in identifying and

quantifying processes in the freshwater systems. The trace metal enrichment is likely to play a

significant role on the nutrient assimilation in picoplanktons (Twiss et al., 2005). Low

availability of Fe and other micronutrients could also constrain the primary productivity in the

Great Lakes system. The concentrations of the micronutrients in the lacustrine system are

expected to be very low and large-volume of samples may be required.

With the present understanding of the Great Lakes system, there are several knowledge gaps.

A systematic process-oriented study is expected to answer the questions listed below:

i) How does the onshore-offshore coupling along with the presence of invasive species

affect the coastal trapping, attenuation and sequestration of nutrients, suspended

particulate matter, POC and other key micro-nutrients?

ii) How does the vertical and horizontal transport of nutrients due to episodic events

affect the lacustrine productivity on different temporal and spatial scales?

iii) How does the cycling and internal of loading of nutrients have impacted the

concurrent coastal eutrophication and pelagic oligotrophication in some of the lakes

in the Great Lakes system?

iv) In what time scales the stoichiometric ratios vary in different lakes in the Great Lakes

system? How does this ratio vary in seston in different Great Lakes system? How do

the stoichiometry ratios of nutrients from atmospheric loading compare with that of

terrestrial runoff year around in all the lakes?

v) How did the NO3-/PO4

3- ratios vary over the past 30 years in areas that are severely

impacted by invasive species (zebra and quagga mussels), due to active removal of

PO43-

, Ca, and key bio-limited elements and their isotopes in the lower lakes?

24

vi) How does the seasonal variations of the rates of primary productivity and respiration

and at deeper waters compare with the other decay of organic matter such as CO2

production from heterotrophic processes in different spatial and temporal scales?

vii) How we can quantify the horizontal and vertical transport of key macro- and micro

nutrients using a suite of newly emerging isotopes of Fe, Cu, Zn, Cd, Se,V, Mo, Ni,

Co in conjunction with a suite of particle-reactive radionuclide tracers.

viii) How do the sink terms of P, N, Si, and C vary across the five lakes as a result of

varying extent of denitrification due to varying supply terms of labile organic carbon

to the lake bottom resulting in nitrate build up.

ix) What factors and processes limit the nutrient utilization in the Great Lakes system?

Does it vary from lake to lake? If most lakes are limited by N and P, are there any key

micronutrients, such as Fe, that is limiting the nutrient utilization?

x) How have the quantity and quality of groundwater and surface water discharged to

the Great Lakes been influenced by deforestation, wetland drainage, farming,

industrialization, and urbanization in the Great Lakes watershed? How have these

changes contributed to alteration of biogeochemical cycling of nitrogen, phosphorous,

and other micronutrients in the Great Lakes?

xi) What is the impact of sinkhole vents in the biogeochemical cycling of nutrients in

Lake Huron and other lakes, if they also have sinkhole vents?

xii) How does the filtering activity of dreissenids affect the inorganic nutrient forms of N

and P and the organic forms versus particulate forms of C, N and P.

xiii) How do the anthropogenic alterations on nutrients affect the ecological and

evolutionary trajectories? How the dreissenid mussel invasion has altered the CO2

emissions from freshwater system? and

xiv) How does the trace metal speciation and bioavailability of trace metals in freshwater

seas vary in different lakes

7. Field Sampling, Remote Sensing and Synergies Among Other Federal Agencies:

In field expeditions, it is essential to collect data of standard hydrographic parameters (e.g.,

temperature, oxygen, salinity) in all stations and the data quality is should to be comparable to

that of WOCE and GEOTRACES. Major nutrients (nitrate, phosphate, silicic acid) should also

be measured, again similar to the WOCE and GEOTRACES quality. The field sampling should

focus on areas of prominent sources (river/stream discharges), submarine sinkhole vents, etc.

From a review of the existing data and monitoring stations, sections should be selected to include

major biogeographic regions and gradients of biological productivity. The field sampling should

be coordinated with other federal agencies that have interest in the Great Lakes (EPA, NOAA

Vessels – NASA remote sensing data) and researchers in Canada.

25

From the Great Lakes Workshop 2010 conducted by NASA GRC, it was recognized that

there are significant opportunities for NASA to improve the understanding of the hydrology and

physical limnology of the Great Lakes (e.g., ice, temperature, precipitation, wind velocity,

currents, etc.). NASA current interest includes water cycle (quantity, quality, and availability and

future changes), limnology, climate, ecology and human effect modeling, and remote sensing.

Coastal processes in the Great Lakes are important for Great Lakes, yet often not considered

in national scope. The current interests of NASA include reflectance, surface radiometry, benthic

optical characterization and other atmosphere and water column correction factors relevant to

remote sensing. NOAA has conducted long-term sediment trap studies to investigate sediment

transport along cross and along-shore, benthic nepheloid layers and resuspension. GLNPO/EPA

monitors 11-18 stations in offshore regions in lakes Michigan, Huron and Superior collecting a

suite of limnological parameters.

The satellite remote sensing provides a synoptic view for the whole Great Lakes region of

several parameters of interest that include surface temperature, color, chlorophyll concentration,

colored dissolved organic matter, atmospheric aerosol loading, wind speed and direction.

Moorings with current meters in several sites have been deployed in Lake Superior from ~2007

to present. Current profilers (ADCPs) and thermisters at a range of depths also have been

deployed. The Muskegon Lake Observatory buoy is investigating the metabolism in Lake

Michigan and is being compared to the estimate obtained from bottles (McNair et al., 2013).

Remote sensing using satellites of optically-sensitive compounds (e.g., colored dissolved organic

matter, CDOM) provide valuable information on their sources, fate and transport in lacustrine

systems.

8. Link to the Major Ongoing Oceanographic Research:

The biogeochemical changes that have recently taken place in the estuarine and marine

coastal environments are useful in informing the key biogeochemical changes that have taken

place in inland seas, and vice versa. The distribution of these key macro and micronutrients are

being measured as a part of the GEOTRACES project in major ocean basins (North Atlantic:

2010 and 2011; East Pacific: October-December, 2013). During the first phase of the

GEOTRACES project two cruises (Atlantic inter-calibration cruise: 2008 and Pacific inter-

calibration cruise: 2009) were dedicated to establish the best practices of sampling (particulate

and dissolved), storage and analytical protocols for the contamination-prone elements and

radionuclides (http://www.obs-vlfr.fr/GEOTRACES/science/intercalibration/222-sampling-and-

sample-handling-protocols-for-geotraces-cruises) and thus the best practices of sampling,

storage, and analyses are established for the work in the Great Lakes.

9. Broader Impacts:

The water quality has direct impact on human health of about 8% of the US population.

These set of lakes in the Great Lakes system have different temperatures, water depths,

hydrological residence times, and varying amounts of anthropogenic impacts of macro- and

26

micro nutrients in the watershed and investigations on the sources, fate and transport of micro-

and macro nutrients will yield a dramatically improved knowledge of the nutrient cycles in the

world’s largest lake system. The biogeochemical processes as modified by human impact in the

Great Lakes system vary considerably due to the differences in the land use between their

watersheds. The major human induced perturbations of the nitrogen cycle in the Great Lakes and

their present and continuously growing impacts on the aquatic system, such as eutrophication,

hypoxia in lakes and streams can provide the changes that are taking place. Investigations in the

Great Lakes system provide tools to validate some of the existing models of nutrient transport

and cycling. Similar future perturbations in other large lakes worldwide (e.g., East African rift

lakes, Lake Baikal, Lake Tanganyika, and the Canadian interior great lakes (Great Bear, Great

Slave, Winnipeg, and Athabasca) are likely to happen and hence this study has broader

implications for lacustrine systems around the world. Since the extent of inter-watershed human

perturbations on the watershed varies, documenting the impact of such changes on these lakes

would provide baseline data which can be compared to the future studies, as continued

alterations by humans take place.

Acknowledgments: This Report is a product of the Workshop which was financially supported

by NSF (OCE-1253310), NOAA, NASA, Wayne State University, CILER, Michigan State

University, University of Illinois-Urbana Champaign, University of Minnesota-Duluth, Ohio

State University, University of Wisconsin-Milwaukee, Yale University, Sea-Grant-Wisconsin

and Sea-Grant-New York. Inputs from participants at the International Association of Great

Lakes Research Annual Meeting at West Lafayette, IN, Geochemical Society Meeting at

Florence, Italy, and American Geophysical Union Fall-2013 meeting are deeply appreciated.

Enclosed Appendix: A) BOGLS Workshop (11-13 March 2013) Agenda; B: List of Participants

at the BOGLS Workshop; C: List of participants at the IAGLR Annual Meeting (June 2013),

Geochemical Society Meeting (August 2013) and Fall AGU Meeting (December 2013).

27

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34

Recent Changes in the Biogeochemistry of

the Great Lakes System Workshop

McGregor Conference Center

March 11-13, 2013

Agenda

Monday March 11, 2013

07:30 – all day Lobby Registration

07:30 – 08:30 B/C Continental Breakfast

08:30 - 09:15 F/G/H Technical Session 1

Chair, Mark Baskaran

Welcome, Introductions, Workshop Overview

09:15 – 10:30 F/G/H Plenary Session: Disrupted Biogeochemical Cycles in the

Great Lakes: Challenges and Opportunities for Aquatic Science.

R.E. Hecky, University of Minnesota-Duluth

Presentation: Micronutrient Dynamics in Lakes and Their

Investigation Using New Isotopic Tools. T.M. Johnson, University

of Illinois at Urbana-Champaign

10:30 – 10:45 B/C Refreshment Break

10:45 - 12:30 F/G/H Technical Session 2

Chair, Val Klump

Presentation: Recent Advances in Understanding the Roles and

Reactions of P in Aquatic Systems. R.E. Blake, Yale University

Presentation: The Enigmatic Great Lakes Nitrogen Cycle: Review

and Insights from Isotopic Records. N.E. Ostrom, Michigan State

University

Presentation: Tracing the Biogeochemical Cycling of Key Micro-

and Macro- Nutrients in the Great Lakes System Using a Suite of

35

Particle-Reactive Radionuclides. M. Baskaran, Wayne State

University and V. Klump, University of Wisconsin-Milwaukee

12:00 – 12:30 F/G/H Questions and Discussion: Technical Sessions 1 and 2

Moderated by V. Klump

12:30 – 01:45 B/C Lunch (boxed lunch provided)

01:45 – 03:00 F/G/H Technical Session 3

Chair, Tom Johnson

Plenary Session: Recent Changes in Primary Productivity and

Phytoplankton Dynamics in the Great Lakes.

G. Fahnenstiel, Michigan Technological University

Presentation: Spatio-temporal Variability and Potential Long-Term

Trends in Great Lakes Carbon Cycling. G.A. McKinley, University

of Wisconsin-Madison

Presentation: Carbon Cycling in the Laurentian Great Lakes:

What’s Known? Unknown? Changing? E. Austin-Minor,

University of Minnesota-Duluth

03:00 – 03:30 F/G/H Questions and Discussion: Technical Session 3

Moderated by T. Johnson

03:30 – 03:45 B/C Refreshment Break

03:45 – 05:00 F/G/H Technical Session 4

Chair, Norm Grannemann

Presentation: Gaps in Understanding of the Role of Groundwater in

Great Lakes Biogeochemical Processes. J. Bratton, GLERL-

NOAA, N. Grannemann, USGS, L. Lemke, Wayne State

Presentation: Inertial Oscillations as a Primary Ecosystem Driver.

J. Austin, University of Minnesota-Duluth

05:00 – 05:30 F/G/H Questions and Discussion: Technical Sessions 1-4

Moderated by N. Grannemann

05:30 – 06:00 Lobby Social Break

05:30 – 06:00 A Steering Committee Meeting: Formative Workshop Assessment

06:00 – 07:30 B/C Catered Dinner

36

Recent Changes in the Biogeochemistry of

the Great Lakes System Workshop

McGregor Conference Center

March 11-13, 2013

Agenda

Tuesday March 12, 2013

07:30 – all day Lobby Registration

07:30 – 08:30 B/C Continental Breakfast

08:30 – 08:40 F/G/H Technical Session 5

Chair, Larry Lemke

Goals and objectives for today’s sessions

M. Baskaran, Wayne State University

J. Bratton, GLERL-NOAA

Guidelines for advocacy presentations

L. Lemke, Wayne State University

08:40- 10:30 F/G/H 15-Minute Introductory Talks

Dreissenid Mussels Have Reengineered the Biogeochemistry of the

Great Lakes

H.A. Vanderploeg, GLERL-NOAA

Sediment Trap Studies in the Great Lakes

N. Hawley, NOAA Federal GLERL

5-Minute Advocacy Talks

Important Negative Impacts on the Nitrogen Cycle are Ignored in

the Debate About Managing Eutrophication. D. Bade, Kent State

University

37

Microbiogeochemical Ecophysiological Time Series Analysis in

Lake Michigan: Key to Distinguishing Between Episodic and

Progressive Perturbations. R. L. Cuhel, University of Wisconsin-

Milwaukee

A modeling Approach to identify Factors Driving Increased

Dissolve Reactive Phosphorous Loss from Agricultural Fields in the

Maumee Basin. S. Y. Gerbremariam, Ohio State University

The Effect of Bain Scale Meteorological Events and the Persistence

of Major Invasive Species on Biogeochemical Cycling and

Ecosystem Function in Lake Michigan. C. Aguilar, University of

Wisconsin-Milwaukee

Potential Impacts of Changes in Major Ion Composition on Trace

Metal Interactions with Phytoplankton: the Lake Ontario Example.

M. Twiss, Clarkston University

The Importance of Iron and Sulfur Cycling in the Great Lakes

System. L. Kinsman-Costello, University of Michigan

Great Lakes Traces: A program to Study the Biogeochemical

Cycling of Trace Elements and Their Isotopes in the Great Lakes.

A. Chappez, Central Michigan University

Measuring Particle Flux in the Nearshore: What Are Short-Lived

Radiotracers Telling Us? J.T. Waples, University of Wisconsin-

Milwaukee

10:30-10:50 B/C Refreshment Break

10:50 – 12:30 F/G/H Technical Session 6

Chair, Ruth Blake

5-Minute Advocacy Talks

Carbon Dynamics in Response to Environmental Change?. L. Guo,

University of Wisconsin-Milwaukee

Using Observations to track Lake Metabolism and Their Role in the

Global Carbon Cycle. L. Gereaux, Grand Valley State University

Sediment Biogeochemistry of Great Lakes Sediment. G. Matisoff,

Case Western Reserve University

Unique Cyanobacterial Mats in Lake Huron Sinkholes: Sentinels of

Environmental Change? G. J. Dick, University of Michigan

38

Is Climate Change Tuning the Invisible Engine of the Great Lakes?

V. Denef, University of Michigan

Direct Measurements of Heat, Moisture and Carbon Fluxes on the

Great Lakes. J. Lenters, Limno Tech

Variability of Satellite-Derived Chlorophyll Concentrations and

Colored Dissolved Organic Matter in Lake Superior. C. Mouw,

Michigan Tech University

The Importance of Biogeochemical Water Quality Monitoring.

M.D. Rowe, NOAA/GLERL

Climate Change Impact on Reservoir Thermal Structure and

Turbidity Transport and Some Aspects of Ice Cover Modeling in

New York City Drinking Water Reservoir. N. R. Samal, New York

City Government

` Simulating the 1998 Spring Bloom in Lake Michigan using

FVCOM-Ecosystem Model. J. Wang, University of Michigan

CILER

Pollutant Loads Generated from Lake St. Clair Metroparks during

Dynamic Stormwater Runoff Events. S.P. McElmurry, Wayne

State University

Ballast Water Verification and Early Detection of Invasive Species

J.L. Ram, Wayne State University

A Landscape Ecology Vision for the Great Lakes. M.A. Evans, U.S.

Geological Survey, Great Lakes Science Center

12:30-01:30 B/C Buffet Lunch

01:30 – 02:30 F/G/H Technical Session 7

Chair, Mark Baskaran

Funding Agency Perspectives

NSF- Tele Conference with Don Rice

Larry Liou, NASA

Norm Grannemann, USGS

John Bratton, NOAA

39

Goals and Expectations for Breakout Sessions

M. Baskaran, Wayne State University

02:30 -04:00 J Breakout Session 1A – Micro- and macro-nutrient and carbon

cycling and tracer studies – field studies

I Breakout Session 1B – Modeling, environmental/climate change

and physical oceanography and how these affect the carbon and

nutrient cycling

E Breakout Session 1C – Exchange of water and nutrients between

reservoirs; field and modeling studies; tracer studies

04:00 – 04:15 B/C Refreshment Break

04:15 -05:30 Technical Session 8

Chair, Nathanial Ostrom

J Breakout Session 2A – Nearshore, shallow water dynamics and

processes

I Breakout Session 2B – Offshore, deep water and cross margin

processes

E Breakout Session 2C – Land margin interface and terrestrial

aquatic coupling, atmospheric interactions

0:530 – 0:600 A Steering Committee Meeting: Formative Workshop Assessment

05:30 – 06:30 Lobby Posters

In Situ Approaches to Assess Sediment Contamination. Allen

Burton, Anna Harrison, et al., University of Michigan

40

The importance of winter plankton assemblages in Lake Erie.

Hunter Carrick, Central Michigan University

Surface ground Water Exchange. Lynn Katrib, Wayne State

University

The Dynamics of Hypoxia in Green Bay, Lake Michigan. Val

Klump, University of Wisconsin-Milwaukee

Comparative Effects of Climate on Green Bay Stratification. Shelby

LaBuhn, University of Wisconsin-Milwaukee

Sediment Loading Budgets in the Great Lakes Watershed. Carol

Miller, Wayne State University

Ecosystem Metabolism and Microbial Sources of N2O in Muskegon

Lake, a Eutrophic Area of Concern. Kateri Salk, Michigan State

University

Relative Contribution of Hypoxia and Natural Gas Drilling to

Atmospheric Methane Emissions From Lake Erie. Amy Townsend

Small, University of Cincinnati

Radiocarbon Distributions in Lake Superior, the World’s Largest

Freshwater Lake. Paul Zigah, University of Minnesota-Duluth

41

Appendix-A

Recent Changes in the Biogeochemistry of

the Great Lakes System Workshop

McGregor Conference Center

March 11-13, 2013

Agenda

Wednesday March 13, 2013

07:30 – 08:30 B/C Continental Breakfast

08:30 – 10:30 F/G/H Technical Session 9

Chairs, Jim Bauer/Mark Baskaran

Presentation of Breakout Group Session Summaries

Discussion of Breakout Group Sessions

10:30-10:50 B/C Refreshment Break

10:50-12:00 F/G/H Technical Session 10

Chair, John Bratton

Sensors and Monitoring Networks

Logistics for Field Sampling

Ship Capabilities and Ongoing Efforts. Russell Kreis, USEPA

Blue Heron

University of Minnesota – Duluth

Final Session and Summary of the Workshops

12:00 B/C Boxed lunch

BOGLS Workshop Ends

12:00 A Steering Committee Meeting: Summative Workshop Assessment