Pore water mercury concentrations

Branfireun B. A., Bishop K., Roulet N. T., Granberg G., and Nilsson M. (2001) Mercury cycling in boreal ecosystems the long-term effect of acid rain constituents on peatland pore water methylmercury concentrations. Geophys. Res. Lett. 28(7), 1227-1230. 

The distribution of Hg within seepage lakes is a net result of the processes that control Hg transport between the atmosphere, water column, seston, sediments, and groundwater. This discussion focuses on the processes that control the exchange of Hg between the sediments and lake water. We first present data on spatial and temporal concentrations in the water column, sediments, pore water, and groundwater. These data set the context for a subsequent discussion of the chemical and physical processes responsible for the transport of mercury across the sediment-water interface and are necessary for assessing transport rates. 

Figure 4. Mercury concentrations in littoral zone pore waters in Pallette Lake...

Figure 9 Dissolved mercury speciation in sediment pore waters as a function of sulfide concentration. Note that the most bioavailable form, HgS°, is the dominant chemical form at log S <, (—4.7) (source Benoit et al., 1999a).

Sulphate concentrations may also be determined accurately by potentiometric back-titration of excess Ba + with a mercury electrode following the precipitation of BaS04 Mucci, 1991). The seawater sample is freed from most seasalt cations with an ion-exchange-column. Then the eluate is reacted with an excess of barium, and after filtration of precipitated BaS04, the solution is titrated potentiometrically with an EGTA solution (see also Section 11.2) to the endpoint. The method applies over a wide range of salinities and sulphate concentrations in 1 mL or less of seawater and marine pore water samples, however, it is somewhat less precise (c.v. of about 0.6 %) than the simple gravimetric procedure described. 

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