Estuary sediment systems

Ca9ador, I., C. Vale, and E Catarino. 2000. Seasonal variation of Zn, Pb, Cu and Cd concentrations in the root + sediment system of Spartina maritima and Halimione portulacoides from Tagus estuary salt marshes. Mar. Environ. Res. 49 279-290. 

Schemes for the classification and intercomparison of the hydraulic characteristics of different estuaries have been devised (see, for example. Dyer, 1973, Chapter 2) and used extensively. Systematic intercomparisons of estuarine sediment systems have not been made, in part because the requisite data have not been gathered. The task of collecting these data is eased once the critical characteristics needed for intercomparison are established. It is suggested that a scheme for the intercomparison of estuarines can be based on the quantities listed in Tables I and IV.

The subject of advective porewater flux and associated chemical transport is covered in Chapter 11 in the context of aquatic bed-sediment systems, which include surface soil-derived particle layers on the bottom of streams, rivers, lakes, estuaries, and the near-shore marine environment. This soil system is a saturated porous medium and therefore the fundamentals of the transport processes and related parameters within this system are identical to that of surface soils. A brief review of advective transport in the subsurface follows. 

Koehnken, L. (1990). The composition of fine-grained weathering products in a large tropical river system, and the transport of metals in fine-grained sediments in a temperate estuary, Ph.D. thesis, Princeton University, Department of Geological and Geophysical Sciences. 

Atchafalaya and Mississippi Rivers. Florida Bay waters, which overlie U-rich sediments, contain much higher ( Ra/ " Ra) activity ratios than other estuaries. The increased ( Ra/ " Ra) values observed at high salinities in the Mississippi/Atchafalaya systems indicate preferential decay of the shorter-lived ""Ra over Ra during estuarine mixing. 

Lapointe BE, O Coimell JD, Garrett GS (1990) Nntrient conphngs between on-site sewage disposal systems, groundwaters, and nearshore surface waters of the Florida Keys. Biogeochem 10 289-307 Li Y-H, Chan L-H (1979) Desorption of Ba and Ra from river-borne sediments in the Hudson estuary. Earth Planet Sci Lett 43 343-350... 

Somayajulu BEK (1994) Uranium isotopes in the Hooghly Estuary, India. Marine Chem 47 291-296 Spechler RM (1994) Saltwater intrasion and the quality of water in the Floridian Aquifer system, northeastern Florida. US Geol Surv Water Resource Invest Rept 92-4174 Sun Y, Torgersen T (1998) Rapid and precise measurement for adsorbed " Ra on sediments. Marine Chem 61 163-171... 

Atmospheric contaminants from smelting works or combustion processes eventually enter the natural drainage system as fall out, and are carried into the rivers. It is probable that the deposition of sediments and the higher pH of marine water, which leads to precipitation, results in a build-up of the heavy metal pollutants in the river estuary. An assessment of this build-up is essentially an analytical problem. 

The high coefficients of sediment-water partition detected, which varied between 500 and 10 000 L kg-1 in estuaries [27,40] and between 3000 and 13 000 L kg-1 in the marine medium [6,34] showed the great adsorption capacity of LAS onto particulate matter. As in continental systems, it has been detected that the more hydrophobic homologues are preferentially adsorbed onto the sediment [3,27,34,35,40],... 

Although the sediments in these systems accumulate Se over time, the small isotopic contrast suggests that dissimilatory reduction is not the dominant accumulation mechanism. If dissimilatory reduction of Se(VI) and/or Se(IV) to Se(0) by bacteria were the dominant mechanism, one would expect the accumulated Se(0) to be enriched in the lighter isotope. In the San Francisco Estuary case, this assumes that the isotopic fractionations measured by Ellis et al. (2003) can be extrapolated to much lower concentrations. Incorporation of Se into algae and macrophyte tissues, followed by decay of some material and conversion of its Se to Se(0), is more consistent with the observed Se isotope data. Notably, the mean Se isotope composition of the Se(0) in the sediments of the Herbel et al. (2002) study was identical to that of the macrophytes. 

In their studies of metals in Chesapeake Bay, however, Bieri et al. (1982) claim that more than 60 % of both the Pb and Mn input is retained in the bed sediments. In their recent studies of heavy metals in Delaware Bay (USA), Church, Tramontano and Murray (1984 and later personal communication) calculated retention of 92 % of the Mn, 37% of the Cu and 32 % of the Cd input to that estuary. However, losses from the estuary in that analysis were based on calculations of the probable flux out of the mouth of the Bay using a layered flow model. When sediment concentrations and accumulation rates were used, only small amounts of Mn and Cd appeared to be retained in the system (Church, personal communication). At this point we are not aware of any convincing evidence that clearly contradicts the findings regarding the behavior of Pb, Cu,Mn or Cd in Narragansett Bay. Unfortunately, the number of mass balances for these elements is so small that this is not a particularly reassuring claim. 

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