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Nutrient and Sediment Loss from Agricultural Fields by Channel Bypassing of riparian Buffers
Hopkins, Isaac
Hopkins, Isaac
Abstract
Riparian buffer zones are a Best Management Practice (BMP) for controlling the nutrients and sediment that escape agricultural fields during rain events. However, runoff is often concentrated within the field so that a large percentage of the water exits through a small percentage of buffe r, in some cases enough to cause incision and channel formation. We studied channel bypassing of a riparian buffer zone outside Richmond, Virginia, during two natural storm events in 2010. The channel under investigation drained 39% of the field, with a corncropped drainage area of 15.2 hectares. For each storm, we measured rainfall and channel flow depth, and took water samples that we analyzed for a number of constituents, most importantly phosphorus (P), nitrate-N, potassium, and suspended sediment. We calculated instantaneous fluxes (kg/s) and storm fluxes (kg/storm) for these components using a range of extrapolated rating curves. We calculated total phosphorus loss during the September storm to be 0.37 kg/ha, nitrate to be 6.1 kg/ha, potassium to be 14 kg/ha, and total suspended sediment to be 87 kg/ha. These values, especially the potassium and nitrate levels, are very high, which likely stems from fertilizer use, the no-till nature of the field, and dry conditions preceding the storms. During the September storm, ~ 11,500 m3 of water exited the field at this one point in the buffer ( ~40% of the total rainwater that fell), carrying with it significant quantities of nutrients and sediment that are damaging to water ecosystems. Assuming that the drainage of this field is not anomalous, channel bypassing of riparian buffer zones is a significant weakness of that BMP, one which must be addressed by farmers, government, and clean water advocates.
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2011-01-01
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Geology