National Water Quality Assessment Program: Eastern Iowa Basins

Relation Between Selected Basin Characteristics, Chlorophyll A, And Nutrients In Eastern Iowa Agricultural Streams

L. R. Roberts

Program abstract of the 110th Session of the Iowa Academy of Science meeting, April 25, 1998, Mason City, Iowa


Nutrient levels and chlorophyll a concentrations in phytoplankton and periphyton were determined in samples from 25 streams in eastern Iowa in August 1997. This study, a part of the U.S. Geological Survey's National Water Quality Assessment Program, was designed to investigate water-quality conditions in small agricultural streams. Sites were categorized according to the width of the wooded riparian buffer strip at and upstream (2-3 miles) of the sampling reach, the dominant soil type in the basin, and the number of livestock confinement facilities in the basin. Concentrations of plankton-chlorophyll a, suspended sediment, dissolved nitrite plus nitrate, dissolved phosphorus, and dissolved orthophosphate were significantly greater at sites dominated by a narrow or absent wooded-riparian buffer upstream of the sampling site than at sites with a more extensive wooded-riparian buffer. Concentrations of dissolved organic carbon were significantly greater, and alkalinity concentrations tended to be higher, at sites in basins dominated by well-drained soils than at sites in basins dominated by poorly-drained soils. Concentrations of chlorophyll a and nutrients were not significantly correlated with the number of livestock confinement facilities in a basin. Concentrations of plankton-chlorophyll a were positively correlated with concentrations of suspended sediment, dissolved nitrite plus nitrate, dissolved phosphorus, dissolved orthophosphate, and suspended organic carbon. In contrast, periphyton-chlorophyll a concentrations were negatively correlated with dissolved ammonia plus organic nitrogen, dissolved nitrite plus nitrate, and suspended organic carbon.


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