Chemical Weathering Rates in the Flyin-W Catchment, Greenwood County, Kansas

Abstract

The cation denudation rate for the Flyin-W catchment, near Eureka, Kansas, was estimated using a mass balance model based on annual cation concentrations and amounts of precipitation and discharge for the catchment. During the period of study, May 1986-April 1987, the cation denudation rate was 2136 + 440 meq-m-2-yr-'. This cation denudation rate is high compared to studies from other areas of the country because the catchment is underlain predominantly by easily weathered limestone and the period of study was one of high precipitation and discharge. The average cation denudation rate for the catchment during years of normal precipitation and discharge is estimated to be 1234 meq-m-2-yr-'. The maximum contribution to the cation denudation rate from anthropogenic acid deposition is estimated to be 5 percent. A mass balance model, modified from Bischoff et al. (1984) was used to estimate the rate of chemical weathering in the Flyin-W catchment, Greenwood County, Kansas. Rates of chemical weathering have been determined for many areas of the eastern and extreme western United States (April et al., 1986; Bischoffet al., 1984; Delthier, 1986; Johnson et al., 1972, 1981; Katz et al, 1985; Miller and Drever, 1977; Velbel, 1985), but there are no studies available for the Great Plains and large portions of the Central Lowlands. The Great Plains and Central Lowlands have not been studied extensively because there is little significant impact of acid precipitation compared to the eastern part of the country. Many of the rock types present in the Great Plains and Central Lowlands are easily weathered and buffer local lakes and streams. This study was designed to provide a basis of comparison for chemical weathering rates in the Great Plains and Central Lowlands and to assess the role of acid precipitation in weathering. In most chemical weathering reactions, hydronium ions in precipitation and soil waters react to remove the more soluble cations, Ca2+, Mg2+, Na+ and K+, from minerals in the soil or on the surface of bedrock. The source for the weathering hydronium ions is primarily from carbonic acid in the This content downloaded from 157.55.39.231 on Thu, 06 Oct 2016 04:20:17 UTC All use subject to http://about.jstor.org/terms 84 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCE soils, but also from organic and other natural soil acids, atmospheric CO2, and anthropogenic sulfuric and nitric acids. Most non-silicate minerals dissolve completely during weathering reactions, whereas silicates are stripped of the more soluble cations, producing clay minerals and iron oxide in situ. Thus, the rate at which cations are removed from a catchment is a measure of the rate of chemical weathering in that catchment.