Contribution of agricultural liming to riverine bicarbonate export and CO2 sequestration in the Ohio River basin

摘要

[ 1] Chemical weathering of silicates and carbonates is essential in the global cycles of many elements, including carbon. Chemical weathering affects regional and global carbon budgets through the export of bicarbonate, much of which can originate from the atmosphere. Agricultural practices may accelerate chemical weathering from the Mississippi River basin directly or indirectly. Here we investigated one of the direct effects of agricultural practices, liming, on stream bicarbonate export and the carbon budget of agricultural systems. Using geographic information systems (GIS) layers extracted from various sources such as USGS National Land Cover Data set, U. S. Census of Agriculture data, USGS water data, NADP atmospheric acid deposition data, and NASS-USDA crop production data, we estimated the contributions of liming inputs on both the riverine bicarbonate export and atmospheric CO2 sequestration for a subset of agricultural and forested watersheds within the Ohio River basin. Liming rates have slightly decreased from 23.6 to 19.4 g CaCO3 m(-2) cropland yr(-1) from 1954 - 1970 to 1971 - 1987 in six highly agricultural watersheds. The largest decrease was observed in watersheds located in the state of Ohio while a slight increase was observed in watersheds located in the state of Illinois where agricultural practices are the most intense. An average of 21.1 and 22.4 g CaCO3 m(-2) yr(-1) were applied to the two most highly agricultural watersheds (91% agricultural in 1992) located in the state of Illinois during 1954 - 1970 and 1971 - 1987, respectively. Using a calcium mass balance, we estimated that 29% of the total riverine bicarbonate export from the two most agricultural watersheds was by liming and thus liming is important to the cation/anion balance and buffering capacity of streams. The on-site net atmospheric C sequestration by liming from the two most agricultural watersheds was estimated to be 0.95 g C m(-2) yr(-1). However, considering 0.85 g C m(-2) yr(-1) is estimated to be released as CO2 during the production, transport, and spreading of lime, liming as a C sequestration strategy is not attractive.