Trace Metals In Suspended Matter Research Articles

Sediments as a Source of Iron, Manganese, Cobalt and Nickel to Continental Shelf Waters (Louisiana, Gulf of Mexico)

Continental shelf sediments are a key source of trace metals to the ocean. In this study, we investigate the impact of sedimentary processes on water column concentrations of iron (Fe), manganese (Mn), cobalt (Co), and nickel (Ni) at five stations on the Louisiana continental shelf and slope, Gulf of Mexico. The highest trace metal concentrations were observed close to the seafloor at the most nearshore shelf station (water depth of 16 m), with most of the metals present in particulate form. This enrichment in the bottom water is likely the combined effect of input of trace metals in suspended matter from the Mississippi/Atchafalaya Rivers and, for Mn, Co, and Ni, benthic release from the shelf sediments. While particulate matter was the dominant carrier of Fe and Mn in bottom waters in the shelf and slope regions, Co and Ni were nearly exclusively present in dissolved form. Hence, lateral transport of Co and Ni in shelf waters is decoupled from that of Fe and Mn. Concentrations of particulate and dissolved trace metals in the water column generally decreased from the shelf to the slope, while those in the sediment increased. This suggests an increased retention of metals deposited on the sediment with distance from the coast, linked to the decrease in organic matter input and associated reductive sediment processes. The offshore decline in sediment trace metal mobilization is likely typical for river-dominated continental margins where most organic matter is deposited close to the coast.

Temporal and spatial variability of trace metals in suspended matter of the Mandovi estuary, central west coast of India

Studies on the suspended particulate matter (SPM) in the Mandovi estuary, western India indicate that during the monsoon and pre-monsoon, the SPM increases, and the major and trace metals decrease from stations in the upstream to downstream of the estuary. SPM is consistently low at all stations during the post-monsoon. Trace metals (Cu, Ni, Zn, Cr, Pb) show strong inter-relationships. They correlate well with Fe and Mn only during the monsoon. The concentrations of Cr, Cu and Pb are high during the post-monsoon. Enrichment factors and Igeo values of metals indicate that Mn shows significant to strong pollution in all seasons, while Cr, Ni and Zn during monsoon and Cr during the post-monsoon show moderate pollution. SPM is controlled by the turbidity maximum, while major and trace metals are governed seasonally by a combination of river discharge, resuspension, spillage of Fe- Mn particulates, and anthropogenic contamination. Incursion of saline waters deep into the river channel during the dry season facilitates aggregation and settling of particulate-borne pollutants close to the discharge area, thereby keeping the estuarine waters free from major contamination.

Geochemistry of major elements and trace metals in suspended matter of the Scheldt estuary, southwest Netherlands

Abstract The geochemistry of suspended matter from the Scheldt estuary has been studied in eight surveys in 1987–1988. Samples were analyzed for major elements (Al, Ca, Fe, K, Mg, Na, Si, Ti, POC, N, P, S) and trace metals (Ag, Ba, Be, Cd, Co, Cr, Cu, Li, Mn, Ni, Pb, Sn, Sr, V, Zn). Physical mixing of fluvial and marine particulates leads to a continuous decrease in the trace metal content of the suspended matter with increasing salinity. Principal component analysis shows that the effect of desorption processes (e.g., of Cd, Cu, and Zn) on the suspended matter composition is relatively minor as compared to that of particle mixing. A particulate S maximum is present in the upper estuary, reflecting resuspension of reduced sediments. Pore water infusion into the (suboxic) upper estuary is a major source of Fe and Mn to the suspended matter. Due to differences in oxidation kinetics, precipitation of dissolved Mn occurs later (in the lower estuary) than that of Fe (in the upper estuary). Coprecipitation with Mn (hydr)oxides is observed for Ni and Co, but not for the other metals studied. Phytoplankton activity leads to a seasonal shift in the suspended matter composition in the lower estuary. During the spring bloom, the contents of trace metals and lithogenic elements are decreased, in favour of biogenic elements (POC, N, P). This observation is attributed to dilution of mineral particles by phytoplankton which, apparently, has lower trace metal levels. However, the Ba content of the suspended matter is increased during the bloom, which is ascribed to biological formation of barite. Another effect of the spring bloom is depletion of dissolved Cd and Zn (but not of Cu), leading to an increase in their distribution coefficients in the lower estuary. Phytoplankton may both directly (through biological uptake) and indirectly (by increasing the pH) be involved in the seasonal shift of Cd and Zn from the dissolved to the particulate phase. Comparison of recent data on suspended matter composition with historical data shows that the trace metal burden of the Scheldt river has decreased considerably between 1980 and 1995. The decrease in trace metal levels of the fluvial suspended matter amounts to 88% for Cd, 85% for Hg, 74% for As, 59% for Cu, and 50–54% for Cr, Ni, Pb and Zn over the time span considered. However, the Mn content of the fluvial suspended matter has doubled from the early 1970s until the mid 1990s, reflecting the gradual increase in the dissolved oxygen concentration of the river water over the last 20 years.

Partitioning of trace metals in suspended matter from the elbe estuary fractioned by a sedimentation method

The particulate matter in water samples from the freshwater region of the Elbe estuary was fractioned by its setting characteristics. The sedimenting and the permanently suspended fractions of the particulate matter were analyzed separately for trace metals (cd, Pb, Cu, Cr, Co, Ni) and organic composition. The two fractions differed significantly in organic and metal content and 13C in organic matter. Permanently suspended particles rich in riverine biogenic material contained amounts of trace metals enhanced by a factor of about three in comparison to the sedimented fraction. Also, 80% of the total particulate trace metals was transported downstream by this fraction. Along the profile of the Elbe from km 630 to km 670 a decrease in suspended particulate trace metals occurred in both fractions, which amounted to a reduction of approximately 50% between March and June. The largest decrease was detected just below Hamburg harbour and was explained by mixing of highly polluted riverine SPM with less polluted sedimenting SPM from downstream regions. The specific loading of the particulates with trace metals was linked to the particulate organic matter content which was in part degraded during the transport downstream. The adsorption characteristics of the organic matter remained quite constant both over the freshwater profile and at different times of the year and accumulation [C/Metal (g·mg −1)] varied mostly between 0.5 and 1 for Cu, Pb, Cr and Ni and 15 to 30 for Cd. The results indicate that even small changes in the perticulate matter composition might produce great differences in the total particulate tarce-metal content.

Distribution of trace metals in suspended matter of the Scheldt estuary

The distribution of trace metals (Ni, Co, Cr, Zn, Cu, Cd, Pb, Mn) in suspended matter and sediments collected in the Scheldt estuary is investigated as a function of grain size, Al and particulate organic carbon (POC) content. Normalized trace-metal content with respect to Al allows characterization of the origin of the solids and evaluation of their degree of contamination. The suspended matter exhibits strong changes in chemical composition in the tidal zone, indicating mixing of heavily contaminated particles of continental origin with less contaminated marine particles. Flood events strongly influence the trace-metal content of the suspended matter by inducing resuspension processes and intensive transfer of solid material from the river system to the sea. The evolution of the composition of the particles in the mixing zone of the estuary indicates that the trace elements do not behave conservatively and that they are also affected by the changing physico-chemical conditions (salinity, pH, redox) observed in the Scheldt. In order to gain a better understanding of the origin and behaviour of the particulate trace elements in the estuary, a mixing model of suspended matter based on the conservative property of Al is proposed, which enables quantification of the proportion of marine vs. continental solids and to detect non-conservative behaviour of trace elements.

Trace metals in suspended matter from the Rhine/Meuse estuary

The contents of trace metals in suspended matter of the river Rhine have decreased during the last few decades but still exceed background contents. Contamination factors for suspended matter in the river Rhine at Lobith are found to be: Cd (7), Cu (5), Zn (9), Pb (3.5), Ni (2.5) and Cr (3). In the Rhine/Meuse estuary geochemical trace-metal behaviour is influenced by industrial discharges. Budget calculations show that the additional enrichment due to industry is a few percent (0 to 3%) for Cr, Cu, Hg, Ni, Pb and Zn, but is much higher for As (11.5%) and Cd (48.6%). Suspended-matter samples collected in the estuary along a salinity gradient were analysed for major elements and trace metals. The results show a decrease in the suspended-matter contents of Cd, Co, Cu, Cr, Ni, Pb and Zn as a function of salinity. The Sr content shows an increase with salinity. By using Cr as a conservative tracer, the differences in trace-metal contents between freshwater and seawater can be attributed to the physical mixing of relatively contaminated Rhine/Meuse suspended matter with relatively uncontaminated North Sea suspended matter. The results show an enrichment in Mn, Co, Ni and Pb in the samples collected in May 1988 in comparison to the samples collected in March 1989. This may be due to the enhanced oxidation of reduced Mn at higher temperatures. As a result of the formation of Mn-oxyhydroxides the trace metals Ni, Co and Pb are scavenged from the solution.

The fate of trace metals in suspended matter in a mangrove creek during a tidal cycle

The variation of heavy metal content in suspended matter (SM) during tidal cycles in a mangrove creek is described. The stable isotope of carbon was used as a tracer for sources of SM to the system. During tidal cycles three patterns of metal variability were found. The first, represented by Fe, showed an irregular and small variability throughout the cycle; a second, represented by Mn, exhibited a sharp increase in concentration during the rising tide, coincident with the greatest variation of pH and E h. The third pattern, including Cu, Cd, Pb, Ni, Cr and Zn, showed maximum concentration at the peak of the high tide, coincident with a shift in SM source. The stable isotope of carbon indicated that, during low tides, most of the organic carbon exported originated from mangrove plant detritus, while during the high tides organic carbon imported by the system was almost totally of marine origin. This shift of SM source is the principal parameter controlling metal fluxes through the system. Changes in water pH and E h, and manganese precipitation, can also serve as a secondary control. Although the results strongly suggest that the metallic load of marine SM is being immobilized by the mangrove environment, mass balance studies are necessary to show whether a net accumulation of metals is actually occurring.