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<br />96 <br /> <br />physical environment by trapping heat, redw:ing wind, stabilizing soil, and <br />providing substrates as well as food for animals. All animals are dependent <br />on plant producers either directly or indir.ectly. Those animals using only <br />plant food directly are termed herbivores, and are the primary consumers in <br />the flow of energy through the wtland ecosystem. Som,e animals feed on the <br />herbivores and are, therefore, carnivores, and playa ,secondary consumer <br />role. Higher carnivores that feed on secondary consum.ers are termed <br />tertiary consumers. Some animals, utilize both plants and animals as <br />food and are called oillnivores. A final group, the decomposers, serve to <br />decompose dead organisms and particulate organic mattelr, otherwise known as <br />detritus. <br /> <br />A number of principles have emerged fro., a synthesis of wetland studies <br />that provide a theoretical framework for understanding the structure and <br />function of wetland ecosystems. As fundamental truths, they provide a <br />motivating force upon which additional princIples will be discovered in the <br />future and emerge into scientific Laws. Their primary value at pre:sent is <br />in guiding inquiry by eliminating unnecessary repl1cati'~n and in providing a <br />baseline upon which future studies can be compared" For example, <br /> <br />~~ <br /> <br />1. .A wetland functions typically as pan of a lar;ger ecosystem, <br />interacting with the larger ecosystem's soil, water. and biotic components; <br /> <br />2. Water supply controls the vital fun.:t1,ons of w.etlands; <br /> <br />3. ..The flow of water within wtlands el~ergizes them and provides for <br />essential exchanges of material; <br /> <br />4. Topography (grade levels) in conjunction with water table elevation <br />strongly influences wetland function; <br /> <br />5. Wetland ecosystems function best uncleI' optimum levels of nutrient <br />input and output; - <br /> <br />6. The ability of wtlands to sustain ',pt1mum values depends upon <br />the wetlands' general fitness to support lif.!. <br /> <br />Wetland ecosystems represent either a present or a historical <br />transition between terrestrial and aquatic areas. Thus, ecosystem studies <br />of ."tlands have had to consider input, output and energy flows wi thin a <br />temporal context (Figure 4). Since there arE! many forms of interior or <br />freshwater wetlands, general information on I:heir structure and function in <br />even the best k:lown areas is sparse. The relative importance of specific <br />controlling factors such as precipitation and water fl 0\0 , water quality, <br />nutrient distribution, and seasonal temperature pattern have rarely been <br />treated fully (Livingston and Loucks 1979). <br /> <br />Water movement is the main energy source' that separates still :"ater <br />fro. flowing' water _tlands. The longitudinal (as in riverine or riparian <br />wetlands) and lateral gradients in riverine imd riparian wetlands create a <br />