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Spatial and Temporal Variations in Greenhouse Gas Emissions from an Agricultural Reservoir
Citation:
Smolenski, R., J. Beaulieu, A. Townsend-Small, AND C. Nietch. Spatial and Temporal Variations in Greenhouse Gas Emissions from an Agricultural Reservoir. Presented at American Geophysical Union Fall Meeting, 2012, San Francisco, CA, December 03 - 07, 2012.
Impact/Purpose:
To inform the public
Description:
Reservoirs are being built at an increasing rate each year to provide humans with resources such as hydroelectric power and drinking water. These man-made systems have provided society with important services, but these have come at the cost of enhanced greenhouse gas (GHG) emissions. Recent estimates suggest reservoirs are a globally significant source of GHG emissions, but these estimates are largely based on studies of oligotrophic boreal and tropical reservoirs. Reservoirs draining agricultural basins are common throughout much of the developed world and are subject to high nutrient loading rates from the watershed. Excess nutrient loading stimulates algae blooms and degrades water quality in these reservoirs, but surprisingly little is known about how nutrients and algal blooms affect GHG dynamics. To assess GHG dynamics in an agricultural reservoir we measured GHG emission rates, dissolved concentrations, and nutrient chemistry in William H. Harsha Lake, an agricultural reservoir located in southwestern Ohio (USA), on a monthly basis since October, 2011. Dissolved N2O was negatively related to nitrate (r2=0.91, p<0.001) in October 2011, suggesting denitrification was an important source of N2O in the reservoir during fall turnover. Relationships between dissolved N2O and nitrate concentrations were inconsistent during the winter and spring, suggesting nitrate was not limited during these seasons. There was no consistent pattern in dissolved gas concentrations across the length of the reservoir, but concentrations were greater in hypolimnetic than eplimnetic waters during warmer months. The highest N2O and CH4 emissions occurred during lake turn over in the fall (CH4 flux= 4.76E+1 mg CH4 hr-1 m-2, N2O flux= 9.24E+1 μg N2O-N hr-1m-2, and CO2 flux = 8.62E+2 mg CO2 hr-1m-2), while the lowest emission rates were observed during the winter. We found no clear spatial pattern in GHG emission rates across the length of the reservoir. On an annual basis, we estimate the reservoir emits 1.52E+6 kg CH4-C/yr, equivalent to ~11,000 head of dairy cattle. On a per unit area basis, the reservoir was a hotspot of N2O emissions compared to the surrounding agricultural land; however, total annual N2O emissions from the reservoir (3.00E+3 kg N2O-N/yr) constitute only 1% of total watershed N2O emissions due to the much greater area of agricultural lands.
