Abstract
The Caddo Lake watershed is located in northeastern Texas and encompasses much of Cass, Harrison, and Marion counties. The watershed is drained by major streams and tributaries flowing in an easterly direction over Eocene-aged rocks and sediments of the Wilcox and Claiborne groups, and empty into the western arm of Caddo Lake. Since 1995, Caddo Lake and some of its tributaries have been included on the State of Texas Clean Water Act 303(d) list by the Texas Commission on Environmental Quality (TCEQ) for impairment due to mercury content in edible tissue, depressed dissolved oxygen, base metal concentrations, and low pH values. The purpose of this multi-year study was to characterize base metal concentrations in stream water and sediments in the Caddo Lake watershed, and document the potential watershed transport and contribution to the impairment of Caddo Lake. Recent water (n = 58) and sediment (n = 116) sampling at 29 sites revealed copper, lead, and zinc concentrations within normal limits and below EPA actionable standards. Mercury concentrations were elevated at 21 of the 29 sampling sites, which could lead to methylation and bioavailability to organisms at all trophic level.
Highlights
Caddo Lake is a 25,400-acre (10,300 ha) lake and associated wetland on the border between Texas and Louisiana
In order to determine the geochemical characteristics of stream water and sediments in the Caddo Lake watershed, 116 sediment and 58 water samples were collected from 29 sampling locations in Big Cypress, Black Cypress, and Little Cypress bayous from October 2016 to July 2019 (Figure 5)
Big Cypress Bayou downstream of Lake O’ the Pines was listed for low pH, depressed dissolved oxygen, and elevated mercury concentrations in edible tissue
Summary
Caddo Lake is a 25,400-acre (10,300 ha) lake and associated wetland on the border between Texas and Louisiana. Caddo Lake drains an area of approximately 4247 km and has a storage capacity of 0.216 km, with major tributaries including Big Cypress, Little Cypress, and Black Cypress bayous (Winemiller et al, 2005) accounting for approximately 70% of the total drainage area of the watershed (Figure 1). In 1971, 8000 acres of Caddo Lake and the watershed were designated as a Wetlands of International Importance by the Ramsar Convention; currently Caddo Lake is one of only 29 sites in the United States serving as an internationally protected wetland and includes one of the largest flooded cypress forests in the United States (Figure 2)
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