title: Riverine Response of Sulfate to Declining Atmospheric Sulfur Deposition in Agricultural Watersheds.
abstract: Sulfur received extensive study as an input to terrestrial ecosystems from acidic deposition during the 1980s. With declining S deposition inputs across the eastern United States, there have been many studies evaluating ecosystem response, with the exception of agricultural watersheds. We used long-term (22 and 18 yr) sulfate concentration data from two rivers and recent (6 yr) data from a third river to better understand cycling and transport of S in agricultural, tile-drained watersheds. Sulfate concentrations and yields steadily declined in the Embarras (from ∼10 to 6 mg S L) and Kaskaskia rivers (from 7 to 3.5 mg S L) during the sampling period, with an overall -23.1 and -12.8 kg S ha yr balance for the two watersheds. There was evidence of deep groundwater inputs of sulfate in the Salt Fork watershed, with a much smaller input to the Embarras and none to the Kaskaskia. Tiles in the watersheds had low sulfate concentrations (<10 mg S L), similar to the Kaskaskia River, unless the field had received some form of S fertilizer. A multiple regression model of runoff (cm) and S deposition explained much of the variation in Embarras River sulfate ( = 0.86 and 0.80 for concentrations and yields; = 46). Although atmospheric deposition was much less than outputs (grain harvest + stream export of sulfate), riverine transport of sulfate reflected the decline in inputs. Watershed S balances suggest a small annual depletion of soil organic S pools, and S fertilization will likely be needed at some future date to maintain crop yields.
authors.forename: Mark B
authors.initials: MB
authors.lastname: David
authors.forename: Lowell E
authors.initials: LE
authors.lastname: Gentry
authors.forename: Corey A
authors.initials: CA
authors.lastname: Mitchell
mesh_terms: D000383:Agriculture; D004784:Environmental Monitoring; D005308:Fertilizers; D045483:Rivers; D013431:Sulfates / Q000032:analysis*; D013455:Sulfur / Q000032:analysis*; D014872:Water Movements
chemical_list: D005308:Fertilizers; D013431:Sulfates; D013455:Sulfur