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Measuring Water Quality–Boat Gunwale Slash

Big Creek Watershed: Boat Gunwale Slash

Monroe County, Arkansas

The goal of the 1972 clean water act was to render the nation’s lakes and streams “fishable and swimmable.” We Americans spent billions to clean up sewage and other dumped materials from rivers in the first years following passage of the act only to learn that water quality standards do not mean actual water quality. We learned that we must understand how the changes we make to our river habitats affect their abilities to be “fishable and swimmable.” Channelization, straightening a stream to to speed runoff, makes rivers muddier. Non-point runoff of nutrients from farm fields fertilizes algae. When the algae dies, the bacteria that decompose the algae use up the oxygen in the water, creating a low-oxygen environment, not healthy for fish or some of the bugs, flies, mussels, and snails–the macroinvertebrates fish feed on. More study of streams large and small was needed to develop accurate measurements of water quality that could be used as a basis for understanding the impact of various land uses on streams.

In 1983 the Arkansas Department of Environmental Quality set out to locate the least-disturbed streams in each watershed in the state in order to study their physical, chemical, and biological characteristics. Within the Big Creek watershed, Boat Gunwale Slash was found to be the Least-Disturbed Ecoregion Reference Stream.

Boat Gunwale Slash rises in poorly drained alluvial deposits. It drains a twenty-three square mile watershed to the White River via Big Creek. Eighty percent of its watershed has been cleared for agriculture.

With a stream gradient of 0.70 feet per mile and a stream velocity of 0.17 feet per second, Boat Gunwale Slash moves slowly and sluggishly in an sinuous channel with low, stable banks, so low that the creek easily spreads out across its floodplain when it floods. Most of its channel and riparian edges are undisturbed. Only its extreme upper reaches have been channelized. Bottomland hardwoods grow on its edges with an understory of shrubs and wetland aquatics. While the stream is fairly clear, the slightest disturbance or increase in stream velocity kicks up the fine, silty clay that lines its bottom, creating turbidity, muddiness

 

Boat Gunwale Slash

Boat Gunwale Slash

 

 

The water quality of any given stream can be determined by which aquatic macroinvertebrates live in it. They dine on bacteria and the decaying plants and animals in a stream. Some thrive on low oxygen conditions because they can swim to the surface and breathe air. Those, that can’t, require high levels of dissolved oxygen in the water and therefore low levels of nutrients, which wash from adjacent fields and fertilize algae. Samples taken in the spring and summer of 1984 found a stable and diverse community of water beetles, various flies and mosquitoes, mayflies, mussels and snails, aquatic worms, leeches, and freshwater shrimp.

A 1983 sampling of fish above and below the highway 146 bridge over Boat Gunwale Slash collected thirty-one different species of fish among them Mosquitofish, Golden Shiner, Pirate Perch; Bowfish, Spotted Sucker Fish; Bluegill; Green, Spotted, and Bantom Sunfish; Minnows and Shiners; and Bluntnose, Slough, and Cypress Darters. The unusually large population of Golden Shiners was probably escapees from nearby fish farms where they were used as feed.

The information gathered from Boat Gunwale Slash and other least-disturbed streams in all regions of Arkansas gave water quality scientists an index against which other streams could be measured for their physical, biological, and chemical health.


            Arkansas Department of Environmental Quality, Water Division, Physical, Chemical, and Biological Characteristics of Least-Disturbed Reference Streams in Arkansas’ Ecoregions,  Volume 1: Data Compilation,June 1987, 1-56; Multi-Agency Wetland Planning Team, Arkansas Wetland Stratagy, 35, http://www.mawpt.org/pdfs/Strategy.pdf.

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