A nice looking lake, right?

Wrong! It’s a reservoir (an ‘artificial lake’). This is Bull Shoals “Lake” aka Reservoir at the Missouri-Arkansas border.

A ‘reservoir’ is not a ‘lake’ – some key and fundamental differences.

Large wood - but where did it come from?

Its part of the forest that was flooded for recreational fishing

Submerged tree

Bull Shoals Dam – Missouri/Arkansas

Bull Shoals Dam built in 1951 dams the “White River” and forms the bottom-most of four artificial lakes.

Dam built primarily for flood control but also used for power generation and recreational activities. From its completion until 2009, it is estimated that the dam has prevented about $225.5 million in flood damages.

Bulls Shoals makes up 182 km²

Home to different types of aquatic fauna

Very popular for recreation, and….

FISHING!

• Focus of a several largemouth bass stocking programs and fishing competitions

Marvin Bushong

State record bass 13 pounds!

Fish Conservation and Management

CONS 486

Reservoir ecosystems

Reservoir ecosystems

• Reservoir background

• Longitudinal gradients

• Reservoirs vs lakes

• Trophic upsurge/depression

Major theme: Linking science to conservation & management

• Harvest regulations

• Managing fisheries & habitats

• Protecting populations & habitats

• Restoring populations & habitats

• Fisheries exploitation data

• Applied life history data

• Human dimensions: socio-economic data

• Physiology

• Behaviour

• Population ecology

• Ecosystem ecology

• Habitat data (limnology, oceanography)

• Life historyBasic science

Applied science

ManagementConservation

Introduction• We’ve talked mostly about stream and lake systems

– But guess what, there’s more!

• Most reservoirs in N.A. < 50-60 years old

– Created primarily for water storage

– E.g., flood control, domestic water supply, irrigation, navigation, hydroelectric power

• Reservoirs used for recreational purposes (e.g. fishing, boating)

– Sport fishes and their prey have been introduced

– Now majority of all US freshwater fishing occurs in reservoirs!

• There are more reservoirs in the US than Canada - Why?- almost all of Canada was glaciated 10000 years ago- glacial retreat created an abundance of lakes

There are more reservoirs in southern and western US – why?

• Northern US was more glaciated therefore has more lakes than southern US

• What about the west?Location of reservoirs and lakes

Thornton et al. 1990

• In the west (mostly), evaporation exceeds rainfall

Re-cap

• There are more reservoirs in the US than Canada

– Greater demand for water and lack of natural lakes in much of the central and southern parts of the US

• The last glaciation created most of the lakes in Canada

– Only extended into the northern US states

• Water demand is high in western US to support agriculture and large cities

– Also, where evaporation exceeds rainfall, which is where so many of the reservoirs are located

Dam it!

• Canada is one of the world’s largest dam builders

– # large dams in Canada (> 15 m height) is 933

333

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16 11 4 00

50

100

150

200

250

300

350

QUE. ONT. B.C. NFLD. ALB. SSK. MAN. N.S. N.B. N.W.T. Y.T. P.E.I.

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Canadian Dam Association's register of dams (2003)

-hydroelectric power generation (596 dams) -multi-purposes (86 dams)-tailings (82 dams)-water supply (57 dams)-irrigation (51 dams)-flood control (19 dams)-recreation (7 dams)-other purposes (35 dams)

• Reservoirs act like a river/lake hybrid• Due to shape and inflow characteristics: elongated,

dendritic• Three zones – riverine, transitional, lacustrine

Longitudinal gradients

Longitudinal gradients: Riverine zone

• Riverine zone: the reservoir is fairly narrow, shallow

– High flow rates

– High suspended solids

– High nutrients

– Low light penetration

• Energy derived from allochthonous

means

– No thermal stratification

Longitudinal gradients: Lacustrine zone

• Lacustrine zone: the reservoir is wide and usually deep

– Low flow rates

– Low suspended solids

– Low nutrients

– High light penetration

– Sometimes has thermal stratification

• Energy derived from autochthonous means

• Oligotrophic reservoirs will have high oxygen in hypolimnion

– Eutrophic reservoirs will not

Longitudinal gradients: Transition Zone

• Transition zone: all characteristics are intermediate relative to riverine and lacustrine

• Constant addition of nutrients,

organic matter and light penetration

• Constant export of production

• Thus highest production of phyto/zooplankton in this zone

– Nutrients & food resources end up here

– Little stratification: so whole zone is involved in this production

Drainage basin characteristics: lake vs reservoirShoreline Irregularity• Reservoirs have high shoreline irregularity, and is dendritic as a

result of river tributaries being flooded

LAKE

RESERVOIR

Drainage Basin size• Reservoirs have large drainage basin sizes relative to reservoir

area and are always situated at outflow of watersheds; most lakes have small drainage basins relative to their size

LAKE

RESERVOIR

Inflows• Reservoirs have inflows from one or two inputs from high order

streams; lakes have inflows from several small low order streams

LAKE

RESERVOIR

Outflows• Reservoir outflows are human controlled and water can be

released from any thermal strata; lakes are seasonally regulated and just from the epilimnion

LAKE

RESERVOIR

Biological aspects• Phyto/Zooplankton - Reservoirs have longitudinal gradient; lakes have depth

gradient• Benthos – Reservoirs have low biomass (especially with drawdowns in littoral

and sedimentation in profundal); lakes have higher biomass• Natural fish community – Reservoirs have low diversity and colonizer (rapid ‘r’)

riverine species which are not usually recreationally desirable; lakes have higher diversity of species

LAKE

RESERVOIR

Trophic upsurge and depression

• Fish production often extremely high early after reservoir operation starts

–But never maintained at this level

• Trophic upsurge is occurring whereby food and space resources are ideal

Why trophic upsurge?• Trophic upsurge occurs because:

• It’s a new environment so competition is minimal

• Newly inundated areas release their surface nutrients which leads to a boom in phyto/zooplankton

• Most reservoirs do not remove vegetation from inundated areas and these provide:

– Benthic structure (refuges, spawning areas) and

– Epiphytic inverts thrive on the vegetation (food for fish)

• Sounds great……

What could possibly go wrong?

• Trophic depression…

• Occurs 5-20 years after startup

• Nutrient input decreases and the vegetation breaks down

• Competition for limited food and space intensifies

• Sedimentation of spawning areas can also occur

• Standard water withdrawals prevent littoral area from developing

– Fish habitat changes from benthic dominated to pelagic dominated; only structure would be rocks

Benthic dominated fish habitat Pelagic dominated fish habitat

Trophic upsurge Trophic depression

Reservoir age

Pro

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nFish

Vegetation

Nutrients

Zooplankton

Coming up next• We’ll dive into–Ocean ecosystems!