Lab 3 Stream assessment - Laboratory 3 Stream Assessment 2...

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Stream Assessment Laboratory 3
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2 L ABORATORY 3: S TREAM A SSESSMENT INTRODUCTION Ecology is the study of how organisms interact with their environments. An ecosystem is a level of ecological study that includes all the organisms in a given area as well as the physical factors with which they interact. Aquatic ecosystems include freshwater streams and lakes, brackish coastal marshes, and salty oceans. The distinction between saltwater and freshwater habitats is fundamental in aquatic ecology. The kinds of organisms that can live in a given water body must be adapted to the water's salinity, or concentration of dissolved salts. Aquatic ecology is also affected by the amount of dissolved oxygen in the water, by the levels of mineral nutrients, and by the penetration of sunlight to various water depths. The creation of food energy by plant photosynthesis is possible only near the water surface, because the amount of sunlight that can penetrate water decreases rapidly with depth. A lack of adequate mineral nutrients is another limiting factor in some aquatic environments, such as cold, swiftly moving streams and high mountain lakes. Temperature is somewhat less important in determining aquatic life zones than is the case in terrestrial ecosystems. Freshwater ecosystems can be divided into three categories: flowing waters (streams and rivers), standing waters (lakes and ponds), and the shallow vegetation-dominated wetlands that are transitional between freshwater and terrestrial ecosystems. Flowing-water ecosystems, represented by rivers and streams, are different from all other aquatic ecosystems, because their waters run as a current from a source to a mouth. Rivers may originate from a variety of sources, including lakes, springs pouring forth from the earth, or meltwater from mountain snows and glaciers. Headwater streams in the upper reaches of a river system are often shallow and swiftly-flowing. Heavily oxygenated and frequently cold, these waters are almost entirely dependent for food energy on detritus, the dead organic material that comes from overhead plants or that is washed into the stream by surface flow after precipitation. Streamlined fish can fight the current, while many other creatures have adaptations such as suckers that enable them to attach themselves to rocks or logs so they are not swept away. Pools, which develop where water backs up behind plant or rock obstructions, usually support more life than do fast-flowing sections of the stream. Downstream, in their lower reaches, rivers and streams tend to become wider, deeper, slower-flowing, and usually warmer. These conditions allow for more photosynthetic organisms, and therefore are less dependent on detritus (dead organic matter) for an energy source. Stream life is generally more abundant in these lower reaches, though it varies from one stream to another, depending on
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L ABORATORY 3: S TREAM A SSESSMENT 3 variations in soil and climate, and on the degree of human interference with the system. As biologically diverse ecosystems, streams offer a wide range of
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Lab 3 Stream assessment - Laboratory 3 Stream Assessment 2...

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