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Seasonal Variation in Sediment and Phosphorus Yields in Four Wisconsin Agricultural Watersheds
Author(s) -
Good Laura Ward,
Carvin Rebecca,
Lamba Jasmeet,
Fitzpatrick Faith A.
Publication year - 2019
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2019.03.0134
Subject(s) - surface runoff , environmental science , hydrology (agriculture) , watershed , snowmelt , streams , water quality , precipitation , sediment , streamflow , storm , frost (temperature) , drainage basin , geography , ecology , geology , meteorology , computer network , paleontology , geotechnical engineering , cartography , machine learning , computer science , biology
Agricultural water quality projects in two distinct topographic regions in Wisconsin collected 5 to 10 yr of continuous stream discharge, suspended sediment (SS), total P (TP), and total dissolved P (TDP) in four watersheds (2100–5000 ha) from 2006 to 2016. Previous agricultural nonpoint SS and TP reduction efforts in two of these watersheds documented cold versus warm season differences in water quality response. The goal of this study was to identify seasonal partitioning of SS, TP, and TDP in storm event loads to inform stream water quality protection efforts. We used National Weather Service Coop Observer frost depth reports to identify dates when watershed soils were frozen. By comparing daily mean event discharge for dates relative to frost, we identified a 32‐d post‐frost high‐discharge “thaw” period. Combined, the frozen and thaw periods contributed about half of the annual SS and TP runoff event loads, ranging from 47 to 63% for SS and from 45 to 51% for TP. The proportion of runoff event TDP during this time was even higher, 62 to 79%, with the majority during thaw. Watershed average volumetric runoff coefficients (event flow/precipitation and snowmelt) were two to four times higher during the freeze and the thaw compared with the rest of the year. To reduce total stream loads in regions with similar climates to Wisconsin, this study indicates that using management practices that curb sediment and P delivery to streams in the winter and early spring may be as important as those designed for nonfrozen conditions. Core Ideas About half of stream event suspended sediment and total P loads were during frost and thaw. A majority of annual event total dissolved P loading was during thaw. Watershed average runoff coefficients were higher in frost and thaw.