Investigations related to action plans for remediation of Gunneklevfjorden. Detailed mapping of mercury and particle size distribution in water, survey no. 1.

Summary

Previous mass balance calculations have shown that resuspension of contaminated sediments may be an important process explaining the concentrations of mercury in the water mass of Gunneklevfjorden. The objective of the work initiated here is primarily to investigate if detailed mapping of mercury and particles in the water can provide further evidence for this assumption. The report shows the results of the first of three surveys planned. Approximately 60 water samples were collected from 24 stations in the less than 1 km2 wide and 10 m deep fjord, and analyzed for total mercury. Selected samples were filtered and reanalyzed to distinguish between dissolved and total concentrations. In addition, in situ profiles of temperature, salinity, turbidity and particle size distribution (PSD) were measured on standard CTD and a LISST100X probe at 15 of the stations sampled for mercury. The results showed two distinct layers separated at about the depth of the sills (~2.5 m) separating the fjord from the outside areas. Linear regressions revealed that the concentration of total mercury increased significantly (p<0.05) with depth, whereas the concentration of dissolved mercury decreased with increasing depth. Principal component analyses of the PSD-data seemed to indicate a difference of the size pattern between the two water layers, but both the use of the instrument and the interpretation of the huge amount of data generated, is for the time being considered to be in a provisional test phase at our institute. We recommend that the proposed program is followed with a second survey in 2017.