Use of Historical Water Quality and Weather Data to Assess the Chemical Impact of Changing Weather Patterns on Lake Winona, Arkansas

摘要

Lake Winona, located west of Little Rock, Arkansas in the foothills of the Ouachita Mountains, provides 40 percent of the average daily system wide water demand for a population of 400,000 consumers in the greater Central Arkansas area. The lake is fed by streams originating in and flowing through a highly protected, predominantly forested watershed composed of land owned by the United States Forest Service and Central Arkansas Water. Land use restrictions and recreational water use regulations provide for minimal anthropogenic interference. As a result, Lake Winona enjoys exceptional water quality due to the minimal human impact within the watershed and lake itself. Despite the protected nature of the Lake Winona watershed, historical monitoring data illustrates a decline in water quality as seen through an increase in Total Organic Carbon (TOC) levels from 1996 through 2011. Parallel comparisons of measured daily rainfall data with TOC data illustrate a relationship between observed rainfall patterns and measured TOC values. Historical daily weather data recorded at the Lake Winona dam shows changing rainfall patterns in which the occurrence of heavy rain events greater than or equal to 2 inches per day has increased in frequency between 2004 and 2011while less variable rainfall amounts typical of the period 1996 to 2003 appear to have deteriorated. Analysis of historical data from 1996 through 2011 confirmed the supposition of changing observed rainfall and temperature patterns; likewise, data analysis showed a strong association between observed rainfall and measured TOC values. Although water utility personnel certainly cannot control the weather, gaining a better understanding of the relation between observed weather parameters and measured water quality indicators helps to prepare utility operations staff to more rapidly and effectively respond to weather related impacts to raw water sources.