Patterns of Hg Bioaccumulation and Transfer in Aquatic Food Webs Across Multi-lake Studies in the Northeast US

Abstract

The northeastern USA receives some of the highest levels of atmospheric mercury deposition of any region in North America. Moreover, fish from many lakes in this region carry Hg burdens that present health risks to both human and wildlife consumers. The overarching goal of this study was to identify the attributes of lakes in this region that are most likely associated with high Hg burdens in fish. To accomplish this, we compared data collected in four separate multi-lake studies. Correlations among Hg in fish (4 studies) or in zooplankton and fish (2 studies) and numerous chemical, physical, land use, and ecological variables were compared across more than 150 lakes. The analysis produced three general findings. First, the most important predictors of Hg burdens in fish were similar among datasets. As found in past studies, key chemical covariates (e.g., pH, acid neutralizing capacity, and SO4) were negatively correlated with Hg bioaccumulation in the biota. However, negative correlations with several parameters that have not been previously identified (e.g., human land use variables and zooplankton density) were also found to be equally important predictors. Second, certain predictors were unique to individual datasets and differences in lake population characteristics, sampling protocols, and fish species in each study likely explained some of the contrasting results that we found in the analyses. Third, lakes with high rates of Hg bioaccumulation and trophic transfer have low pH and low productivity with relatively undisturbed watersheds suggesting that atmospheric deposition of Hg is the dominant or sole source of input. This study highlights several fundamental complexities when comparing datasets over different environmental conditions but also underscores the utility of such comparisons for revealing key drivers of Hg trophic transfer among different types of lakes.

Bottom‐up nutrient and top‐down fish impacts on insect‐mediated mercury flux from aquatic ecosystems

“…The MeHg concentration of large midges and dragonflies were not affected by nutrient additions, whereas MeHg concentrations in small midges were enhanced by nutrient additions. In several large field surveys, the concentration of MeHg in biota has been inversely correlated with various measures of trophic state and primary production [13,[34][35][36][37] Table S1. When a significant Nutrient  Fish interaction (N  F) was detected, we tested for simple main effects.…”

Mercury deposition in Southern New Hampshire, 2006–2009

“…Two coal combustion power plants are also located in the southern portion of NH and are likely contributors to the local atmospheric load of Hg. Within the waterways of the Northeastern United States, including NH, biological species have been identified as containing elevated Hg levels (Chen et al, 2005;Evers et al, 2007) with atmospheric deposition considered the dominant source in undisturbed watersheds (Chen et al, 2005). Three MDN sites were previously located in NH with sample collection lasting from 7 to 16 months and the most recent sampling terminated in 2005.…”

Stoichiometric controls of mercury dilution by growth

“…Recent studies have found a positive correlation between the relative availability of N and P and fish mercury concentrations from hundreds of lakes (14,15). High availability of P relative to N (i.e., low N:P) results in a low algal N:P ratio (indicative of high algal quality as food), causing rapid growth in zooplankton, particularly Daphnia (4,16).…”