Cumulative Impacts of Forest Management on the Accumulation and Biomagnification of Mercury and its Relationship to Autochthony in Stream Food Webs in New Brunswick, Canada

Abstract

Forests provide a multitude of ecological services and are one of Canada’s most important natural resources that support a profitable industry, especially in New Brunswick. The activities associated with harvesting and forest management have documented ecological impacts such as the increased mobilization of mercury from the land to adjacent streams. Methylated mercury bioaccumulates and biomagnifies (concentrates) through food webs and in headwater streams forestry has been shown to change its accumulation. However, not much is known about the spatial trends of mercury accumulation and biomagnification through stream food webs and how different forest management practices affect these trends. To delineate these patterns, food webs were sampled across a spatial gradient from three basins experiencing different levels of forest management intensity. At a basin scale, methylmercury concentrations were greatest in filtered water, food sources, and one invertebrate taxa in a harvested but less intensively managed basin, likely due to increased inorganic sediments and dissolved organic carbon also observed. Biomagnification was lower in this same basin, possibly from inefficient trophic transfer of methylmercury from food sources. Longitudinally this basin also showed differences in fine particulate organic matter (FPOM) and coarse particulate organic matter (CPOM) mercury compared to the other basins, likely due to similar spatial patterns in organic matter. In conclusion, mercury dynamics in stream food webs were impacted by forestry primarily in water and basal food sources at a basin scale, but spatial patterns were inconsistent.