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.

2.

Shredders: breakdown CPOM: consume bacteria Filtering and gathering collector: feed on bacteria found in FPOM 3.

4.

Grazers: feed on algae on surfaces 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 O 2

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

25.6 Freshwater Wetlands Are a Diverse Group of Ecosystems

• 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

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

Ecological Issues: The Continuing Decline of Wetlands

• 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

• 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_wet lands.html

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