Lecture 09

Limnology - study of inland waters Ecology of Freshwater Ecosystems:Rivers, streams, lakes and wetlands

Three basic types of freshwater ecosystems:• Lotic: rapidly-moving water, for example

streams and rivers.• Lentic: slow-moving water, including pools,

ponds, and lakes.• Wetlands: areas where the soil is

saturated or inundated for at least part of the time.

Loctic: Rivers and Streams

• Rivers and streams can be divided along three dimensions:– Length: Pools + runs– Width: Wetted / active channels– Vertical: Water surface, column

• Riparian zone is a transition area between the aquatic and upland terrestrial environments.

• Rivers and Streams• River basin – area of

land drained by river drainage network– Separated by

watersheds

Dimensions of Stream Structure

Flow Rate• Variation a Function of:

– vegetation/nature of surrounding landscape• Forests ‘damp out’ variation in flow

– Seasonal variation in ppt.• Rainy/dry season climate• Seasonal snow melt

• Impact on flooding• Flood pulse concept: health of river

system depends on maintaining natural variations in flow

River Continuum Concept• Organic matter from vegetation adjacent to stream in headwaters

provides nutrient base coarse particulate organic matter• CPOM FPOM: provides nutrient base for food web in low

reaches of river• See: http://www.cotf.edu/ete/modules/waterq/wqcontinuum.html

for more

• 4 Invert Feeding groups:• Feeding on bacteria in organic matter of various sizes:

1. Shredders: breakdown CPOM: consume bacteria2. Filtering and gathering collector: feed on bacteria found in FPOM

3. Grazers: feed on algae on surfaces4. Gougers: burrow into submerged logs/wood debris

Lakes• Low spot – captures and retains water• Formation involves geologic processes + dam building by

humans• Most FW resides in lakes.

– 20% in Great Lakes of North America

Many Types of Lakes - + 11 types• Glacial lakes • Tectonic Lakes• Landslide lakes• Volcanic lakes• Shoreline lakes

• Littoral zone: Shallows – light reaches bottom

• Limnetic zone: open waters – – Habitat of zooplankton

and nekton (free-swimming organisms)

• Benthic: primary place of decomposition

• Light– Lake color depends on light absorption and

biological activity– Light is increasingly attenuated with water depth

• Temperature – Lakes become thermally stratified as they warm.– Temperatures vary seasonally with depth

• Water Movement– Wind-driven and temperature mixing of the water

column is ecologically important.• Oxygen can be limiting

– Eutrophic vs. oligotrophic lakes

Seasonal Temperature Changes

Nutrients and Lakes:• Oligotrophic:

– Low nutrient availability– Low surface area to volume ratio– Low biological production – well oxygenated– May have high species diversity– Generally older lakes

• Eutrophic: – High biological production– High nutrient availability – particularly N and K– High surface area to volume ratio– may be depleted of oxygen – benthos anaerobic

methane production• Dystrophic:

– Acidic, high in organic matter

From Schoenherr A.A. 1992. A Natural History of California. University of California Press..

Lakes - Human Influences

• Human populations have had profound, usually negative effect.– Municipal and

agricultural run-off eutrophication.

– Exotic species - Zebra Mussels alter ecology

Dams• Major dam builders

– Humans– Beaver

• Damming interrupts both nutrient spiraling and the river continuum– Downstream flow is greatly reduced but a constant

inflow is maintained– The resulting lake develops a heavy bloom of

phytoplankton (or floating plants) due to high nutrient levels of decaying material on the newly flooded land

– Disrupts seasonal fluctuations in flow• Lentic-adapted fish (many introduced exotics) replace lotic-

adapted fish• Pulsed releases of water (hydroelectric dams) can wipe out

or dislodge downstream organisms• Generally water released from hypolimnon is cold and low in

O2

Succession• Accumulated sediment wet meadow• Nutrients from outside lake eutrophication

• Freshwater wetlands (25.6) = terrestrial wetlands

• 6% of Earth’s surface – declining• Importance – various reasons• Various types/degree of wetness

– permanently flooded to periodically saturated soil• Hydrophytic plants

– Obligate wetland plants require saturated soils– Facultative wetland plants can grow in either

saturated or upland soil– Occasional wetland plants are usually found out

of wetland environments but can tolerate wetlands

• Wetlands occur in three topographic situations– Basin wetlands develop in shallow basins,

from upland depressions to filled-in lakes and ponds–water flow is vertical

– Riverine wetlands develop along shallow and periodically flooded banks of rivers–water flow is unidirectional

– Fringe wetlands occur along the coasts of large lakes–water flow is in two directions

25.6 Freshwater Wetlands Are a Diverse Group of Ecosystems

Reduced Oxygen Levels and Wetlands as Biological Filters

• decreased breakdown of organic matter• Wetlands = nutrient sinks

– Nutrient sink = environment that traps nutrients

• Nutrient source = net release of nutrients – results as oxygen is introduced

• Biological filter: remove potentially damaging chemicals from waterways

Hydrologic Regulators• Act as hydrologic buffers

– Water amounts entering may vary• Excess water absorbed and retained

– Water amount leaving remains constant• Impact:

– Water may percolate into aquifers– Prevent down stream flooding

• Prevent damage• Reduce leaching of nutrients

• The loss of wetlands has reached a point where both environmental and socioeconomic values are in jeopardy– Waterfowl habitat– Groundwater supply and quality– Floodwater storage– Sediment trapping

Ecological Issues: The Continuing Decline of Wetlands

• Wetland Protection• Endangered Species Act• Clean Water Act of 1972 – section 404• EPA• State Laws

– California Coastal Commission– Other:

http://ceres.ca.gov/wetlands/introduction/defining_wetlands.html

– http://biology.kenyon.edu/fennessy/AMN%20Wetland%20Webpage/Comps%20Webpage/thebroadperspective.htm