Drought induced pulses of image from a Canadian shield wetland: use of δ34S and δ18O in image to determine sources of sulfur

Following summer drought periods, pulses of elevated image concentrations are frequently observed in streams draining forested catchments that contain wetlands. Delays in the recovery of freshwater streams and lakes in eastern Canada from historically high levels of acidic precipitation have been partially ascribed to these periodic pulses of image. Climate in eastern Canada has also changed within the last 25 a, with a documented increase in summer dryness and duration of droughts. In small forested catchments in the Turkey Lakes Watershed (TLW), image concentrations in streams draining wetlands can be elevated by up to a factor of 7 during post-drought discharge events compared to the annual average. Two neighbouring catchments, one with a series of cascading wetlands and one without any wetlands, were selected for comparison. Stable S and O isotope ratios were analyzed in samples of bulk precipitation, streams, and groundwaters to examine sources of image in post-drought pulses. image in the streams and groundwaters show that image is retained in the wetland via image reduction and stored in the upper peat profile. Nitrate is elevated in soil and groundwaters at TLW due to high rates of nitrification in forest soils and the presence of image can be used to identify piezometers unaffected by image reduction. image shows that higher concentrations of image in deeper groundwater are likely due to oxidation of organic S and not a geologic source of reduced S. Following drought, the low image in streams is consistent with wetland retention by image reduction and much lower than image released by weathering in deep glacial till and bedrock. High image groundwaters and geologic sources do not contribute to the image pulses in streams. Isotopic patterns over 6 a were similar. Pulses of image in the wetland catchments following drought are a result of the oxidation of S previously reduced and stored in the wetland.