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| Larger order rivers are characterized by wide widths, deep runs, fine substrates, open canopies, and generally reduced water clarity. Large rivers in good condition generally have lots of snags along their banks that provide high quality habitat for fish and invertebrates. Large rivers are probably the most impacted and threatened rivers in the United States. One of the most threatened biological features of large rivers in the United States are their freshwater mussel populations. Freshwater mussels (Mollusca, Unionidae) are severely affected by chemical pollutants and since the mid-1980s the zebra mussel, Dreissena polymorpha, native to the Caspian Sea, has invaded the Great Lakes and many midwest and eastern waterways in large numbers, threatening native species. | ||||
| Impacts | Agricultural practices, industrial point source pollutants, channelization, snag removal | |||
| Hydrology | Discharge regime- Variable depending on river management
objectives and precipitation events such as spring snowmelt and summer
rains.
Temperature regime - variable depending on elevation and latitude, the large volume of water present in large rivers generally resists short-term (daily) temperature changes. |
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| Instream habitat | Fine to medium substrate, sand may constitute more than 90% of the streambed in lowland rivers. Sand substrates are generally unstable. Aquatic plants may either be abundant or absent depending on water clarity and substrate characteristics. | |||
| Aquatic invertebrate sampling equipment | kick nets, Surber nets, and Hess samplers in coarse substrates, Peterson grabs and corers in fine sediment deposits, drift nets to evaluate food densities available to fish | |||
| Dominant functional feeding groups | Filterers and collector-gatherers, predators | |||
| Invertebrate assemblage members | Coleoptera: Dytiscidae, Haliplidae, Hydrophilidae, Gyrinidae
Diptera: Chironomidae, Culicidae, Simuliidae, Stratiomyidae, Tabanidae Ephemeroptera: Caenidae, Baetidae, Ephemeridae, Potamanthidae, Polymitarcyidae, Tricorythidae Hemiptera: Corixidae, Gerridae, Notonectidae Trichoptera: Hydropsychidae, Hydroptilidae, Leptoceridae Plecoptera: Perlodidae Mollusca: Unionidae |
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