The effects of whole-lake nutrient enrichment on mercury contamination in age-1 yellow perch

We evaluated the effect of whole-lake nutrient enrichment on Hg concentration in age-age-1 yellow perch Perca flavescens and assessed whether reduced Hg concentration in fish from enriched lakes could be attributed solely to enhanced fish growth (i.e., growth dilution). A survey of yellow perch in eighteight reference lakes and twotwo experimentally enriched lakes (P input 5 2–6 mg · m22 · d21; N : P . 25 : 1 by atoms) indicated that yellow perch Hg concentration was highly correlated with lake pH and nutrient enrichment (R2 5 0.87). Age-1 yellow perch were four to five times larger and had 50% lower Hg concentrations in enriched lakes than in reference lakes of an equivalent pH (reference lakes 5 0.24 mg Hg/g wet mass; enriched lakes 5 0.11 mg Hg/g). A mass balance model of Hg dynamics indicated that growth dilution could only account for 30–40% of the reduction in yellow perch Hg concentration, suggesting that lake enrichment produced effects on fish Hg concentration that were not explained by differences in growth rate. A change in yellow perch diet likely explains the remainder of the difference in yellow perch Hg concentration between reference and enriched lakes.