Dept of Biology, Lewis and Clark College		Dr Kenneth Clifton
	Biology 141 Lecture Outline

Freshwater ecosystems and wetlands

What is stream order?

Streams are numbered from their source; the lower the number, the closer a stream is to the source (melting snow, a glacier, etc.). Streams of different orders have different characteristics.

Rivers and streams have been highly altered by human activity... how?

How water gets into rivers/streams... remember the hydrological cycle

rainwater percolates to groundwater layer, fills streambed where they are in contact.

subsurface flow in some places.

sheet flow over ground surface if soil infiltration capacity is reached OR if ground surface becomes impermeable as a result of human activity.

all of the land area whose water drains into a particular stream system is that stream's watershed.

Thus land use in the watershed affects the stream's water quality.

Assays of water quality in streams

Discharge (patterns of flow):

the product of current velocity and cross-sectional area of stream.

velocity slowest at bottom and sides because of friction.

reasons for measuring stream discharge.

a steam's "flashiness" refers to temporal variation in stream discharge; highly altered by paving, houses, lawns.

Dissolved oxygen.

oxygen is less concentrated in water than in air; its concentration in water can limit biological activity.

how oxygen gets into water:

diffusion from air, amount depends on temperature and turbulence.

oxygen solubility decreases with water temperature... the warmer the water, the lower the oxygen concentration.

roiling, more turbulent water has more opportunities for mixing and diffusion.

photosynthesis by aquatic producers (thus oxygen levels can have a diurnal cycle, more in the daytime).

how oxygen escapes from water:

diffusion across water surface back into air.

use during respiration by consumers, producers, decomposers (also occurs in groundwater).

production and use are in balance unless humans put organic waste in rivers, which is then broken down by oxygen-requiring decomposers.

The tendency for water to stratify can lead to gradients of oxygen concentration from surface to bottom... mixing of layers disrupts this.

Nutrients (esp. nitrate and phosphate).

how they get into water.

in rainfall and runoff.

through decomposition of organic material in water.

addition of fertilizer or sewage.

additions can lead to eutrophication. (contrast with "oligotrophic", or nutrient poor, systems)

Suspended sediment/turbidity

sources

bottom sediments become entrained by turbulence

suspended organic particles can cloud water

erosion from land and banks

consequences: reduces light for photosynthesis and visually-hunting predators.

Pesticides and other pollutants

Biological components of moving water systems

Primary producers: 3 categories

macrophytes (vascular plants, mosses, green algae): large enough to be seen with naked eye.

phytoplankton (diatoms, green algae, cyanobacteria): microscopic, free-floating.

periphyton: same as above but live attached to substrates, look like light colored "fuzz".

Consumers/decomposers

because much of the organic material in streams is dead matter that falls in, the food chain is not based exclusively on primary production; detritus very important.

variety of taxonomic groups (benthic invertebrates)

larval stages of insects (mayflies, stoneflies, caddis flies, true flies, beetles)

other aquatic inverts: worms, snails, clams and other bivalves

Also, don't forget the potential ecolgical importance of aquatic fungi

adaptations to life in flowing water: bottom-dwelling, flattened bodies

some functional groups (guilds) in freshwater ecosystems

grazers: true primary consumers, feed on periphyton
filterers: fussier about particle size than about whether food is living or dead
shredders: eat larger organic material and macrophytes
microbes and microbial loops
secondary consumers, e.g. salmon

Abundance and diversity of macroinvertebrates an important indicator of stream condition.

Lakes and ponds

Are they closed or open systems?

Seasonal turnover

Oligotrophic and Eutrophic conditions when water movement is constrained

 

Wetlands are also important ecological communities.

Coping with submersion.... Oxygen availability is the biggest issue.

Chemical reduction (the loss of Oxygen molecules) and oxidation occur as soils are submerged and exposed.

Decomposition is dramatically slowed, so organic material can build up.

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