Daily loads of nutrients, sediment, and chloride at Great Lakes Restoration Initiative USGS edge-of-field and tile stations

As part of the Great Lakes Restoration Initiative, the U.S. Department of Agriculture, Natural Resources Conservation Service; U.S. Environmental Protection Agency; and the U.S. Geological Survey (USGS) have partnered to evaluate the impacts of implementing agricultural conservation practices focused on nutrient management. Monitoring methods have been designed to allow for rapid assessment of water-quality changes in response to conservation efforts by focusing on subsurface-tile drainage and direct surface runoff from fields - the major pathways for nonpoint-source pollution to enter streams. Monitoring stations were established at the field edge that measured runoff volume and enabled the collection of samples that were analyzed for nitrate plus nitrite, ammonia, total Kjeldahl nitrogen, orthophosphate, total phosphorus, suspended sediment, and chloride. Samples were collected by use of an autosampler and sampling was triggered to capture most events throughout a USGS water year (October 1 to September 30). Event samples were combined into flow-weighted composite samples as described in Stuntebeck and others, 2008. Baseflow samples were collected either through the autosampler or as a grab sample direct from the flume. Daily loads were computed using the USGS Graphical Constituent Loading Analysis System (GCLAS; Koltun and others, 2006). GCLAS requires a discharge hydrograph and chemograph as data input; the output is a computed daily load for the given constituent. Since the estimated daily load is based on composite concentrations for individual events, they may not reflect the true daily value, and Sciencebase is being used to provide the final load estimates to be able to explicitly link these estimates to relevant reports and external resources describing their derivation. The total of the daily loads over the course of the event, however, likely reflects the total load for the event, and the estimated loads given in the data table provided are identified using corresponding USGS National Water Information System parameter codes. Koltun, G.F., Eberle, M., Gray, J.R., Glysson, G.D., 2006, User's manual for the Graphical Constituent Loading Analysis System (GCLAS), U.S. Geological Survey Techniques and Methods, 4-C1, 51 p. Stuntebeck, T.D., Komiskey, M.J., Owens, D.W., Hall, D.W., 2008, Methods of data collection, sample collection, and data analysis for edge-of-field, streamgaging, subsurface-tile, and meteorological stations at Discovery Farms and Pioneer Farms in Wisconsin, 2001-07: U.S. Geological Survey Open-File Report 2008 - 1015, 51 p.