R workflow for the analysis of fish tissue mercury concentrations following the invasion of zebra mussels in Minnesota Lakes

Aquatic invasive species can influence mercury methylation and bioaccumulation in lake ecosystems by altering chemical and biological pathways and dynamics. Invasive zebra mussels Dreissena polymorpha, which have invaded lakes and rivers throughout North America, may amplify mercury bioavailability by disrupting food webs and altering biogeochemical processes. This potential amplification has important implications for human health, since fish consumption is the primary human exposure pathway for mercury. Using fish tissue mercury data for 357 lakes collected by the state of Minnesota from 2000 to 2023, we evaluated changes in mercury concentrations in zebra mussel-invaded lakes relative to uninvaded reference lakes for six fish species. We applied a modified Before-After-Control-Impact (BACI) design, comparing fish tissue mercury concentrations before and after zebra mussel invasion to changes over a similar time period in uninvaded reference lakes. The code release contains R code (R Markdown file) for the analysis workflow.