Seston

Glooschenko WA, Strachan WM, Sampson RC. 1976. Distribution of pesticides and polychlorinated biphenyls in water, sediments, and seston of the upper Great Eakes—1974. Pestic Monit J 10 61-67. 

Sabater S, Artigas J, Duran C, Pardos M, Romani AM, Tomes E, Ylla I (2008) Longitudinal variation of sestonic chlorophyll and phytoplankton assemblages in the Ebro River. Sci Total Environ 404 196-206... 

Among arthropods, pyrophosphate granules isolated from barnacles have the capability to bind and effectively detoxify silver and other metals under natural conditions (Pullen and Rainbow 1991). In a Colorado alpine lake, silver concentrations in caddisflies and chironomid larvae usually reflected silver concentrations in sediments seston, however, showed a high correlation with lake water silver concentrations from 20 days earlier (Freeman 1979). 

Amiard-Triquet, C., J.C. Amiard, B. Berthet, and C. Metayer. 1988. Field and experimental study of the bioaccumulation of some trace metals in a coastal food chain seston, oyster (Crassostrea gigas), drill ( Ocenebra erinacea). Water Sci. Technol. 20 13-21. 

These techniques may further enhance the ability of 31P FT-NMR spectroscopy to be used for the identification of hydrosphere DOP. We have demonstrated already that 31P NMR spectroscopy is a viable technique for DOP identification and characterization. 31P NMR spectroscopy may eventually be useful through several of the techniques mentioned in this chapter for studying interactions of DOP with dissolved humic substances, colloids, and seston and particulate adsorption. Hence, 31P FT-NMR spectroscopy... 

Measurements of S cycling in Little Rock Lake, Wisconsin, and Lake Sempach, Switzerland, are used together with literature data to show the major factors regulating S retention and speciation in sediments. Retention of S in sediments is controlled by rates of seston (planktonic S) deposition, sulfate diffusion, and S recycling. Data from 80 lakes suggest that seston deposition is the major source of sedimentary S for approximately 50% of the lakes sulfate diffusion and subsequent reduction dominate in the remainder. Concentrations of sulfate in lake water and carbon deposition rates are important controls on diffusive fluxes. Diffusive fluxes are much lower than rates of sulfate reduction, however. Rates of sulfate reduction in many lakes appear to be limited by rates of sulfide oxidation. Much sulfide oxidation occurs anaerobically, but the pathways and electron acceptors remain unknown. The intrasediment cycle of sulfate reduction and sulfide oxidation is rapid relative to rates of S accumulation in sediments. Concentrations and speciation of sulfur in sediments are shown to be sensitive indicators of paleolimnological conditions of salinity, aeration, and eutrophication. 

Figure 1. Data from the literature indicate that S concentrations in surface lake sediments are poorly correlated with A, lake-water sulfate concentrations (104 lakes) B, sediment carbon content (78 lakes) or C, sediment iron content (22 lakes). Sulfur concentrations in lake sediments typically are lower than concentrations in marine sediments of comparable carbon content (upper line in B). The lower line in B represents the average C S ratio (55) reported in seston (59, 72, 27, 56, 78). Most of the lake sediments reported in the literature have more iron than sulfur. (Data are from references 24-30, 34, 48—51, 55-57, 59-61, 71, 104, 112, 199, 205, 222, and 223.)...

Some fraction of planktonic S is released in the water column as H2S or other volatile S compounds (65, 66), and the remainder settles to the sediments, where it is called seston. King and Klug (73) calculated that particulate matter (seston) collected in sediment traps had lost 60-75% of the protein S present in algae. Although no change in S content or com-... 

Despite the strong relationship between sulfate concentrations and diffusive fluxes, there is no universal relationship between lake sulfate concentrations and concentrations of S in sediments (Figure 1A cf. 24, 26). Concentrations of S in sediments are the net result of inputs from seston, diffusive inputs, recycling to the water, and dilution by other materials. Mathematically this quantity may be expressed as... 

A relationship between the fraction of S in inorganic forms and Fe content exists at depths below 30 cm in sediment cores (Figure 7) but not in surface sediments. The C Stotal (Stotal is the sum of the organic S and inorganic S concentrations) ratios at these depths suggest that the sulfur is derived primarily from seston. The fraction of seston S that is mineralized and retained in these deeper sediments where S inputs are relatively low appears to be determined by the availability of iron. 

Figure 7. Only at the base of sediment cores from 27 lakes is a relationship (r2 = 0.755) observed between the iron content and the fraction of sulfur present as iron sulfides (AVS + CRS). A similar relationship is not observed in surface sediments. As discussed in the text, much of the sulfur at the base of the cores appears to have originated from organic compounds in seston. The relationship may indicate that retention of H2S released during decomposition of seston is determined by the availability of iron. References are...

Primary production (trophic state) affects S retention and speciation in several ways. As primary production increases, inputs of organic S to sediments in seston increase. Hence, as the organic carbon content of sediments increases, S content would be expected to increase proportionally. Such a simple relationship is not observed among nearly 80 lakes for which sediment S and C content are available (Figure IB). However, a line defining the minimum S content does increase linearly with increasing carbon content. The slope of this line corresponds to the mean C S ratio measured in seston... 

Approximately half of the lake sediments in Figure IB have significant sources of S other than seston, but in all lakes seston S in sediments increases with increasing C content. 

Total S content cannot indicate whether increased carbon inputs to sediments cause increased diffusion of sulfate into sediments or restrict reoxidation and release of S from sediments, because the net effect is the same. In a survey of 14 lakes, Rudd et al. (80) did not observe a strong correlation between organic matter content per volume and net diffusive flux of sulfate. However, in English lakes the lowest C S ratios occur in the most productive lakes (24) whether this represents enhanced influx or retarded release is not clear. Among 11 Swiss lakes, ratios of C to S sedimentation rates are relatively constant and substantially below C S ratios in seston net S fluxes... 

Figure 8B. Within individual cores from three of these same lakes, a similarly strong correlation is observed between S and C concentrations. Within each core, C concentrations increase toward the surface because of increasing eutrophication in recent years. The C S ratios indicate that most of the sulfur is not derived from seston (ratio indicated by line labeled algal C S), but from sulfate reduction. Increasing inputs of carbon cause increases in S from both seston and sulfate reduction. Even after eutrophication, C S values remain below the ratio of 2.5 (marine line) typically observed in marine...

If iron limits retention of S in sediments (cf. 50, 30) it would be expected that the fraction of S present as iron sulfides would increase with increasing Fe content of sediments. Although this relationship is observed in deep sediments (Figure 7), fractionation of S between organic and inorganic forms is not determined by iron content in surface sediments. Nor is there any relationship between Fe content and total S content in surface sediments for all lakes reported in the literature (Figure lc). In deep sediments where C S ratios indicate that seston was the major source of sedimentary sulfur... 

Figure 9. A, At the base of sediment cores (30-50 cm) from 48 lakes ratios of C SMat nearly equal the ratio found in seston (indicated by the line labeled mean algal C S). A simplistic explanation is that most of the S is derived from seston, and that C and S are mineralized and lost from sediments at similar rates. B, Within the same cores for which data were available, ratios of C S oni tend to be lower than the ratio in seston (19 of 28 points lie below the line). Together, the figures suggest that much of the mineralized S is retained within the sediments. Figure 7 suggests that such retention is dependent on the avail-ability of iron. References are given in Figure 1.

Figure 9a), a relationship between inorganic S and Fe content may indicate that transformation of seston S to inorganic forms depends on the availability of iron (see also refs. 35-37). Alternatively, it may indicate that in oligotrophic lakes rates of putrefaction are lower than rates of Fe2+ formation (186) as eutrophication proceeds, rates of sulfide production exceed rates of Fe reduction and the relationship between inorganic S and Fe contents is lost. 

Paleolimnological Conditions. Because of the interplay between primary production, oxygen content of bottom waters, and the sulfur content and speciation of sediments, sediment profiles of S probably preserve records of paleolimnological conditions. Several studies (23-25, 205) point to increased S content of sediments as a result of eutrophication. Mechanisms involve both rates of S supply to sediments (seston deposition and diffusive gradients) and rates of S reduction and oxidation. The relative S enrichment... 

Partly because of this concern, the Wisconsin Department of Natural Resources, in cooperation with the Electric Power Research Institute, initiated an extensive study of Hg cycling in seepage lakes of north-central Wisconsin (14). The mercury in temperate lakes (MTL) study used clean sampling and subnanogram analytical techniques for trace metals (10, 17) to quantify Hg in various lake compartments (gaseous phase, dissolved lake water, seston, sediment, and biota) and to estimate major Hg fluxes (atmospheric inputs, volatilization, incorporation into seston, sedimentation, and sediment release) in seven seepage lake systems. 

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. 

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