Are There Longitudinal Effects of Forest Harvesting on Carbon Quality and Flow and Methylmercury Bioaccumulation in Primary Consumers of Temperate Stream Networks?

Abstract

Forest harvesting affects dissolved organic matter (DOM) and aqueous mercury inputs as well as the food web structure in small-headwater streams, but how these upstream changes manifest downstream is unclear. To address this uncertainty, we examined DOM quality, autochthony in the caddisfly Hydropsychidae (using δ 2 H), and methylmercury (MeHg) concentrations in stream water and the caddisfly along a longitudinal gradient (first-to fourth-order streams, subcatchments of 50-1900 ha) in paired partially harvested and reference catchments in central Ontario, Canada. Although measures of DOM quality (specific ultraviolet absorbance at 254 nm 2.20-11.62) and autochthony in caddisflies (4.9%-34.0%) varied among sites, no upstream-to-downstream differences in these measures were observed between the paired harvested and reference catchments. In contrast, MeHg levels in stream water (0.06-0.35 ng/L) and caddisflies (29.7-192 µg/kg dry wt) were significantly higher in the upstream sites but not the farthest downstream sites in the harvested catchments compared to the reference catchments. This suggests that while current mitigation measures used by forestry companies did not prevent elevated MeHg in water and invertebrates at smaller spatial scales (subcatchments of 50-400 ha), these upstream impacts did not manifest at larger spatial scales (subcatchments of 800-1900 ha). The present study advances our understanding of spatially cumulative impacts within harvested catchments, which is critical to help forest managers maintain healthy forest streams and their provisioning of aquatic ecosystem services.

Levels of contaminant metals in three species of holothurians from Portugal: Seasonal, sex and tissues variations

“…Most marine animals can accumulate these metals in their bodies mainly due to the environmental conditions in which they are thriving and their trophic level (Rejomon et al, 2010;Worakhunpiset, 2018;Jakimska et al, 2011). This bioaccumulation depends on several endogenous factors, namely the physiological status, geographical region, habitat, fat content, adaptability and characteristics of the biotope (Charbonneau et al, 2022;Driscoll et al, 1994;. In addition to representing a risk to human health due to their toxicity and bioaccumulation characteristics, Cd, Pb and Hg can also cause disturbances in the marine environment, reducing the diversity and abundance of species (Hosono, et al, 2010;2011).…”