Sediment depth profiles of total mercury (THg) and monomethylmercury (MMHg)
were collected at 15 sites in an anthropogenically contaminated estuarine
system (Lavaca Bay, TX). THg in the solid phase increased with depth to a m
aximum located at 10-30 cm, which corresponds to historic industrial discha
rges to the bay. MMHg in the solid phase was highest in the upper 0-3 cm of
the cores, decreasing rapidly with depth. The MMHg content of the surface
sediment was a narrowly constrained fraction of the total (0.65 +/- 0.34%)
over a range of sediment types, while making up only 0.01-0.05% of THg at d
epth. Porewater concentrations exhibited trends similar to but more exagger
ated than in the solid phase. The distribution coefficients (log K-d) for i
norganic Hg (IHg = THg - MMHg) were similar in most samples, averaging 4.89
+/- 0.43. The log K-d for MMHg averaged 2.70 +/- 0.78 over all sites and d
epths but exhibited a subsurface minimum of 2.29 +/- 0.67 at the point of m
aximum dissolved Fe. A time series showed a maximum in both solid phase and
porewater MMHg during the early spring, followed by a decrease throughout
the remainder of the year.