Lecture 09 Limnology study of inland waters Ecology

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 bacteria 2. Filtering and gathering collector: feed on bacteria found in FPOM 3. Grazers: feed on algae on surfaces 4. 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 (freeswimming 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 loticadapted 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_wetl ands. html – http: //biology. kenyon. edu/fennessy/AMN%20 Wetland %20 Webpage/Comps%20 Webpage/thebroadperspec tive. htm