Methods
Study Location and site selection20 beaver ponds were selected as sample locations based on accessibility, isolation from other beaver ponds, and local interest following consultations (Figure 3). All of the sites are in the Taiga, or the Northern Boreal Plains which are largely dominated by peatlands. Generally, I selected for dams that interrupt water flow from peatlands rather than those situated on rivers as they are more common and characteristic of beaver dams in the area. Each site is within 500 meters from a roadway due to access limitations.
Data collection and analysisWater samples and measurements were taken from the inflow which is upstream, and the outflow of each beaver dam (Figure 4). We sampled the same sites in both June and August to capture seasonal variability in flow through the systems. We collected a grab sample each for total and dissolved mercury and methylmercury concentrations using the clean hands-dirty hands method (St. Louis et al.,1996) to avoid sample contamination. The dissolved mercury and methylmercury samples were filtered within 24 hours of collection through a Nalgene 0.45 µm cellulose nitrate filter tower. All mercury and methylmercury samples were then preserved with trace grade hydrochloric acid until they could be analyzed at the University of Alberta. At the same locations, 3 additional 60ml samples were filtered into acid-washed vials at the time of collection through 0.7 µm Whatman GF/F filters; Samples for dissolved organic carbon concentration were collected in amber bottles and acidified with hydrochloric acid and kept cool until analysis by Ion samples were collected in plastic bottles and frozen until ICP-OES analysis, or colorimetric method analysis (Thermo Fisher, USA). Absorbance was measured from the third, unpreserved sample in a UV-Vis Spectrometer (Shimadzu, China). Water temperature, dissolved oxygen concentration, salinity, pH, electrical conductivity, and redox potential were also measured at each sample location using a YSI ProDSS (xylem, USA). Finally, we collected a sample at each site for Laser Spectroscopic Analysis for stable Oxygen and Hydrogen isotopes (Picarro Water Isotopes Analyzer L2130-I, Picarro, USA) to determine the water isotopic composition. As is common in this field of work, I also kept descriptive field notes of general observations at each site. Table 1. Water chemistry variables measured from each sample location.
|
|