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. / Thesis / Master of Biological Science (MBioSci) / Forest harvesting is an essential and large part of Canada’s economy, and it is important to ensure that its impacts on freshwater systems are minimal. Forest management can increase the amount of the toxic metal mercury entering streams and this can have harmful effects in top predators, like fish, since mercury concentrates through food webs. The knowledge lacking is how different harvesting practices change the amount of mercury in these food webs and whether impacts increase as streams get larger. Of the three basins I studied, the one with harvesting but little assisted regeneration (moderately impacted) had the highest mercury levels in water, leaves, and algae. From upstream to downstream the leaves and biofilm from the moderately impacted basin accumulated less mercury compared to the least harvested basin. Additionally, mercury concentrated less through the food web of this basin. The changes in the moderately impacted basin may be caused by sediments and other materials that transport mercury into the stream and increase water and food levels, but this high mercury was not being transferred to the other organisms in the food web. In conclusion, forest management had some effects on mercury at the base of food webs at a large scale, but patterns through space were inconsistent.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/26194 |
| Date | January 2021 |
| Creators | Negrazis, Lauren |
| Contributors | Kidd, Karen, Biology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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