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Field spikes were prepared at 207 stream and river sites as part of the U.S. Geological Survey (USGS) National Water Quality Assessment (NAWQA) project between December, 2012, and September, 2015. At the field site, a depth-and width-integrated environmental sample was collected, and one subsample of the environmental sample was spiked with a known amount of a spike mixture. Both the spiked subsample ("spike sample") and another subsample ("environmental sample") of the original water sample were analyzed for pesticides at the USGS National Water Quality Laboratory (NWQL) by direct injection liquid chromatography with tandem mass spectrometry (LC-MS/MS), and were used to calculate the spike recovery of each analyte....
To investigate the effects of imidacloprid on natural stream communities under controlled conditions, experimental streams were dosed with imidacloprid at concentrations ranging from 0.061 to 220 micrograms per liter (µg/L) for a period of 10 days. Natural stream macroinvertebrate communities were obtained from the Cache La Poudre River (Larimer County, CO) by colonizing trays full of large gravel for 75 days. The trays were added to laboratory experimental streams (mesocosms) at the USGS Fort Collins Science Center in Fort Collins, CO. At the end of 10 days, invertebrate abundance metrics were analyzed in relation to measured imidacloprid concentrations in water from the experimental streams. Declines in total...
Dissolved pesticides were measured in weekly water samples from 100 wadeable freshwater streams across eleven states in the Midwestern U.S. during May-August, 2013, as part of the Midwest Stream Quality Assessment study conducted by the U.S. Geological Survey's (USGS) National Water Quality Assessment (NAWQA) Project. Of the 100 stream sites, 12 were urban indicator sites and the remaining 88 sites were located along an agricultural gradient of watershed land use. Twelve depth- and width-integrated water samples were collected at each site within the 14-week study period. Water samples were filtered (0.7 micrometers) and analyzed for 227 pesticide compounds by direct-injection liquid chromatography with tandem mass-spectrometry,...
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