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SEDIMENT AND NITROGEN TRANSPORT IN GRASS FILTER STRIPS 1

ABSTRACT: An 18‐month field experiment was conducted to evaluate the effectiveness of grass filter strips in removing sediment and various nitrogen species from runoff. Runoff was collected from six 3.7 m wide experimental plots with 24.7 m long runoff source areas. Two plots had 8.5 m filters, two plots had 4.3 m filters, and two plots had no filters. Runoff was analyzed for total suspended solids (TSS), total Kjeldahl nitrogen (TKN),. filtered TKN (FTKN), NH4+‐N, and NO3‐N. The Mann‐Kendall nonparametric test for trend (changes in filter effectiveness over time) indicated that there were no trends in the yields and concentrations of TSS, NO3‐‐N, NH4‐N, TKN, and FTKN for the 8.5 m filter over time. For the shorter 4.3 m filters, there were significant upward trends in TKN yield and downward trends in TSS, NH4‐N, and FTKN concentrations, indicating that trapping efficiency may have started changing with time. The Kruskal‐Wallis test indicated that the 8.5 m filters reduced median yields and concentrations of TSS and all N species, but the 4.3 m filters only reduced the median yields and concentrations of TSS, NH4+‐N, TKN, and the median concentration of FTKN. The 8.5 and 4.3 m filters reduced contaminate yields and concentrations from 42 to 90 percent and from 20 to 83 percent, respectively.