Terrestrial diet influences mercury bioaccumulation in zooplankton and macroinvertebrates in lakes with differing dissolved organic carbon concentrations

Abstract

Dietary uptake is a key step in conveying both toxic mercury (Hg; particularly as highly bioavailable methylmercury, MeHg) and essential dietary biochemicals, such as polyunsaturated fatty acids (PUFA), across trophic levels within aquatic food webs. Using stable isotopes and fatty acids we evaluated the role of food sources in size-fractioned plankton and littoral macroinvertebrates for the bioaccumulation of total Hg and MeHg in six oligotrophic and one mesotrophic Swedish lakes with differing concentrations of dissolved organic carbon (DOC). We found that the consumption of both algal and terrestrial diets (assessed by PUFA and long-chain saturated fatty acids, respectively) predicted >66% of the Hg concentration variability in meso-(100-500 µm) and macrozooplankton (>500 µm) in oligotrophic lakes. In the mesotrophic lake, total Hg bioaccumulation in higher trophic level biota, carnivorous macroinvertebrates was also significantly related to terrestrial diet sources (R 2 =0.65, p<0.01). However, lake pH and DOC correlated to total Hg bioaccumulation and bioconcentration across all lakes, suggesting the consumption of different diet sources is mediated by the influence of lake characteristics. This field study reveals that using dietary biomarkers (stable isotopes and fatty acids) together with the physico-chemical lake parameters pH and nutrients together improve our ability to predict Hg bioaccumulation in aquatic food webs. Fatty acids used as dietary biomarkers provide correlative evidence of specific diet source retention in consumers and their effect on Hg bioaccumulation, while pH and nutrients are the underlying physico-chemical lake parameters controlling differences in Hg bioaccumulation between lakes.

Mercury methylation in oxic aquatic macro-environments: a review

“…They conclude that this is probably due to the supply of freshwater that increases the bioavailability of Hg for the base of the food web. Wu et al (2019a) reviewed several works from different aquatic ecosystem on the bio-concentration and the bio-magnification of MeHg at the base of the food chain (phyto and zoo-plankton), to determine which process better predicts MeHg concentration in fish. They found that bio-concentration of MeHg in phytoplankton predicts 63% of the variability of MeHg concentrations in fish, while zooplanktivory diet did not appear to have a significant correlation with MeHg in fish.…”

Effects of Non‐native Fish on Lacustrine Food Web Structure and Mercury Biomagnification along a Dissolved Organic Carbon Gradient

“…Indeed, DOC plays a complex role in the bioavailability of Hg in freshwater ecosystems (Ravichandran 2004; Lavoie et al 2019). Several studies have reported positive relationships between aqueous [THg] and/or [MeHg] with [DOC] in freshwaters (Driscoll et al 1995; Scudder 2010; Braaten et al 2014; Lescord et al 2018; Lavoie et al 2019; Wu et al 2019). Dissolved organic matter and/or DOC can influence Hg levels of freshwaters by facilitating the export of inorganic Hg and MeHg from watersheds to waterbodies (Driscoll et al 1995; Hurley et al 1995).…”