Ecological factors regulating mercury contamination of fish from Caddo Lake, Texas, USA

Abstract

Most studies examining the influence of ecological characteristics of fish on Hg concentration in fish tissues have focused on a few variables and been conducted in northern ecosystems. We examined how total length (TL), age, food-web position (estimated using delta13C and delta15N), and habitat were related to total Hg concentrations in 10 species of fish from Caddo Lake, a subtropical reservoir located on the border of Texas and Louisiana, USA. We observed biomagnification in the Caddo Lake fish assemblage, and the enrichment factors (the slope of the relationship between lamda15N and total Hg concentration) in the two habitats were 0.19 and 0.24, similar to those found in other studies. Although trophic position was the best predictor of total Hg concentration between species, age and TL were the best predictors of total Hg concentration within species. Unlike studies conducted in deep lakes, lamda13C values of fish tissue, a measure of the extent to which fish feed in food webs based on pelagic or littoral primary production, was not a good predictor of total Hg concentration in Caddo Lake fish. Total Hg concentrations in fish were elevated in forested-wetland habitats relative to open-water habitats. Data collected in the present study indicate that more Hg likely was available for incorporation into the base of the food web in the forested-wetland habitat than in the open-water habitat. Our results help to clarify the relationship between ecological characteristics of fish and Hg concentration in fish tissue and can be used by researchers as well as public and environmental health officials when designing Hg monitoring studies.

Regional variation in mercury and stable isotopes of red snapper (Lutjanus campechanus) in the northern gulf of Mexico, USA

“…Examination of d 15 N, d 13 C, and d 34 S allowed for the evaluation of whether variation in Hg concentrations could be caused by diet and trophic position differences of red snapper among regions. In the present study, a positive linear relationship existed between Hg concentrations and trophic position (d 15 N) with TL, suggesting the potential for bioaccumulation of Hg with increase in size and trophic position [40][41][42], as has been found in previous studies [6,10]. The average d 15 N values of phytoplankton, the dominant basal resource for red snapper (S.T.…”

Mercury speciation and biomagnification in the food web of Caddo Lake, Texas and Louisiana, USA, a subtropical freshwater ecosystem

“…The limnology of the lake has been described elsewhere [24,37]. Briefly, the western portion of the lake is shallow (many areas <1 m) and characterized by wetland habitat dominated by bald cypress (Taxodium distichum), water elm (Planera aquatica), and other aquatic vegetation, including fanwort (Cabomba caroliniana), common waterweed (Elodea sp.…”

“…Because MeHg biomagnifies, the number of trophic levels in a food web is one of the most important factors determining the concentration of MeHg in the tissues of consumers [23,24]. Stable isotope analysis, especially nitrogen isotopes, has become a powerful tool for studying contaminant biomagnification in wild animal populations, because it allows researchers to assign time-integrated, noninteger estimates of trophic position [25].…”

“…1). Most previous biomagnification studies have focused only on fish and invertebrate communities [24,31,32], and those studies that have included other vertebrate taxa have been conducted only in estuarine or marine ecosystems [30,33,34]. Therefore, data on biomagnification in food webs that include vertebrates other than fish, especially from freshwater ecosystems, are needed.…”

Mercury bioaccumulation and biomagnification in Ozark stream ecosystems

“…Spring waters also contain higher concentrations of CO 2 , dissolved organic carbon (DOC), and hardness ions, and have lower pH and dissolved oxygen concentrations than receiving streams, which they strongly influence (Vinyard and Feder, 1982;Imes et al, 2007;Mugel et al, 2009). Surface waters are hard, alkaline, and low in DOC, conditions not usually associated with Hg methylation or elevated MeHg concentrations in fish (e.g., Brumbaugh et al, 2001;Kamman et al, 2005;Brigham et al, 2009;Chumchall and Hambright, 2009). Nevertheless, concentrations of total mercury (HgT) in fillets of legal-size ( 4305 mm total length) smallmouth bass (Micropterus dolomieu; smallmouth) from Ozark streams typically exceed 0.3 mg/g ww and are included in the statewide consumption advisory (MDHSS, 2010).…”