Publication Summary

Sediment cores were collected from Walupt Lake, Loon Lake, and Wannacut Lake as part of a long-term study evaluating mercury trends through sediment cores across Washington State.

Mercury concentrations at Walupt Lake are low, and recent levels represent a decline over previous measurements. Mercury analyses throughout the cores indicated peak flux rates at Loon Lake occurred during the early 1990s and have since declined. Peak fluxes at Wannacut Lake took place in the early 1930s concurrent with hard-rock mining in the drainage basin. Flux rates declined after mining stopped, and current levels are similar to Loon Lake.

In 2005 the Washington State Legislature provided funding to the Washington State Department of Ecology (Ecology) to develop a long-term monitoring program for mercury in freshwater systems. Mercury is the first pollutant to be studied under the state′s Persistent, Bioaccumulative, Toxic Chemicals (PBT) Reduction Strategy.

This report presents results of the second year of using of age-dated sediment cores to evaluate mercury deposition. During August 2007, Ecology collected sediment cores and surface sediments from three lakes: Walupt (Lewis County), Loon (Stevens County), and Wannacut (Okanogan County).

Sediment cores were analyzed for 210lead, total lead, and mercury; dates were applied to the sediment core using the constant rate of supply (CRS) model. Surface grab samples were analyzed only for mercury.

The Walupt Lake sediment core displayed an overall decreasing trend in mercury dry concentrations; however, dates were not applied to the core due to a poor 210lead signal.

Loon Lake sediments have received little mercury contamination over the past 50 years. Mercury flux rates peaked in the mid-1990s at 22 ug/m2/yr and are currently at 15 ug/m2/yr. The flux rate decline detected at Loon Lake is attributed to reduced sedimentation, not reduced atmospheric loading.

Wannacut Lake sediments were severely contaminated with lead and mercury from mining activity in the lake′s catchment from the late 1800s to 1940. A peak mercury flux of 361 ug/m2/yr was measured in 1932. Contamination stopped abruptly after mining activity ceased within the lake′s drainage, and mercury levels dropped accordingly. Flux rates at Wannacut Lake are currently 10 ug/m2/yr.

Mercury concentrations and flux rates are low for all three lakes. The low flux rates can be attributed to the distance of the lakes from human-caused point sources, rural catchments, and low sedimentation.

Link to EIM data for User Study ID cfur0002