NITRATE AND ALKALINITY DURING THE JULY 2012 DROUGHT: URBAN AND AGRICULTURAL WATERSHED RESPONSE OBSERVED IN BUCK CREEK, OHIO, U.S.A

By mid-August 2012, more than 60% of the U.S. was experiencing drought and record temperatures with devastating consequences for crops. Abnormally dry conditions existed over more than 90% of the Mississippi River basin, with as much as 50% of the basin area experiencing extreme and exceptional drought. Understudied are the consequences for water quality in both agricultural and urban environments. With predicted increases in mid-continental droughts, our understanding of water quality response may become critical to watershed stakeholders. Alkalinity and nitrate studies are of importance because their deliveries to global oceans have already dramatically increased in response to human activities. This work quantifies drought effects on alkalinity and nitrate concentrations and their area-normalized yields in a small carbonate stream. The Buck Creek watershed in west-central Ohio (363 km²), a subwatershed of the Ohio River basin, is comprised of agricultural and urban land uses with two principle subwatersheds, upper Buck Creek, which is regulated for flood control, and Beaver Creek which is not flow regulated. While historical stream flow data are not available for Buck Creek, provisional data from a USGS gage on the Mad River near Springfield (03269500), which is immediately downstream of its confluence with Buck Creek, indicated that mean monthly flow was the third lowest in 38 years, reflecting regionally dry conditions. Stream samples were collected above and below combined sewage overflows (CSOs) below the confluence of upper Buck Creek and Beaver Creek during two baseflow days and one storm event in mid-July 2012. Baseflow alkalinity and nitrate ranged from 26.0-30.0 mg C L^-1 and 0.7-1.2 mg N L^-1 while storm flow ranged from 12.6-25.6 mg C L^-1 and 0.3-1.1 N L^-1. During stormflow lower mean alkalinity occurred below the CSO input with the greatest dilution occurring at peak flow. Hourly baseflow nitrate area-normalized yields from Buck Creek (9.9-15.5 g N km^-2) are slightly higher than the average calculated from the Ohio River Basin (6.3 g N km^-2) during July 1988, the lowest flow recorded in July in the last 47 years. However, hourly storm flow area-normalized yields (8.1-31.4 g N km²) were lower than the average reported for the Ohio River (78.9 g N km^-2) during July 1998, the highest flow recorded in July.