Summary of statistical and trend analyses of selected water-quality data collected near the Big Thicket National Preserve, southeast Texas

Abstract

Statistical and trend analyses of selected water-quality data collected at three streamflow stations in the lower Neches River basin, Texas, are summarized in order to document baseline water-quality conditions in stream segments that flow through the Big Thicket National Preserve in southeast Texas. Dissolved-solids concentrations in the streams are small, less than 132 milligrams per liter in 50 percent of the samples analyzed from each of the sites. Dissolved-oxygen concentrations in the Neches River at Evadale (08041000) generally are large, exceeding 8.0 milligrams per liter in more than 50 percent of the samples analyzed. Total nitrogen and total phosphorus concentrations in samples from this site have not exceeded 1.8 milligrams per liter and 0.20 milligram per liter, respectively. Trend tests for dissolved solids and major ions indicate that small downtrends in total alkalinity, dissolved calcium, and hardness occurred in the Meches River at Evadale (08041000) and Pine Island Bayou near Sour Lake (08041700). Small uptrends in dissolved sulfate were detected at all three stations in the study area. INTRODUCTION The Big Thicket National Preserve is located in the lower Neches River basin in southeastern Texas north and northwest of the city of Beaumont (fig. 1). The preserve, established by Congress in 1974, is comprised of approximately 84,500 acres in 12 units including 8 land tracts and 4 water corridors. Additional land is still being acquired. The preserve was established to protect remnants of a complex and diverse biological community. The temperate climate and average annual rainfall of approximately 55 in. promote lush growth of vegetation. Immense tupelo and cypress trees are common in some areas of the preserve; but where historical waterways deposited hills of sand, rain percolates through the sand so fast that some desert vegetation grows. Swamp bogs exist near arid sandhills that support cactus and yucca plants. There are 85 species of trees, more than 60 species of shrubs, and. nearly 1,000 other flowering plants in the preserve. This abundant vegetation supports a wealth of animal species. In an effort to preserve the wide diversity of flora and fauna in Big Thicket National Preserve, the National Park Service has proposed a monitoring program to document the influences of land use on the quality of water in streams in or near the preserve. The purpose of this report is to summarize the results of statistical and trend analyses of selected water-quality data collected at three U.S. Geological Survey streamflow stations in or adjacent to Big Thicket National Preserve. These stations include Neches River at Evadale, Texas (08041000); Village Creek near Kountze, Texas (08041500); and Pine Island Bayou near Sour Lake, Texas (08041700). The results of these analyses will aid the National Parks Service in establishing a water-quality data base and in establishing water-quality standards for significant segments of streams that flow through the preserve. Methodology Statistical analyses of water-quality and related streamflow data were performed by using the Statistical Analysis System (SAS)i/ developed by the SAS Institute of Gary, North Carolina (SAS Institute, Inc., 1982a,b). This computer system has been interfaced with the Geological Survey's National Water Data Storage and Retrieval System (WATSTORE). The SAS computer programs provide data-management functions such.as sorting, merging, copying, and condensing sets of data. SAS also is one of the most advanced proprietory software packages for developing linear-statistical models. The SAS procedure used for the statistical summary of water-quality data included in this report is the Univariate procedure. This procedure produces simple descriptive statistics of numeric variables and provides detailed information on the distribution of their values. Some of the statistical features obtained with the Univariate procedure and tabulated in this report (table 1) include sample size of the number of observations on which statistical calculations were based and the maximum, minimum, and mean values. Other statistical features obtained for constituents with 5 or more observations include the I/ Use of the trade name in this report is for identification purposes only and (foes not constitute endorsement by the U.S. Geological Survey.