Water column

About: Water column is a research topic. Over the lifetime, 13706 publications have been published within this topic receiving 496626 citations.

Geochemistry of recent TOC-rich sediments from the Gulf of California and the Black Sea

Abstract: Major and minor elements (incl. Ag, As, Ba, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sr, V, Zn) have been determined in recent sediments from the Gulf of California upwelling area and Black Sea sapropels in order to reinterpret their chemical composition in view of reliable seawater and plankton data. The chemistry of the Gulf of California sediments reflects regeneration processes which occur in the water column; i.e. only a small fraction (<10%) of elements like Cd, which in seawater are coupled to the »labile« nutrients (C, N, P), is buried in the sedimentary column. In contrast, elements like the more resistant nutrients (Si) undergo a deeper regeneration cycle (Ba). Several trace metals which are present in comparatively higher concentrations in seawater (As, Mo, U, V) and at the same time are reactive under reducing conditions and/or are able to form stable Sulfides, are fixed in the sediments during early diagenesis. The early diagenetic behavior of Ba is closely related to bacterial sulfate reduction. The formation of barite concretions is discussed. Anoxic conditions in the water column act as ideal traps for a number of redox sensitive and/or stable sulfide forming elements. A simple trace metal balance calculation shows that the chemical composition of Black Sea sapropels is controlled by fluvial and Mediterranean seawater element input and the accumulation rate of terrigenous detrital material.

Relationships between benthic community condition, water quality, sediment quality, nutrient loads, and land use patterns in Chesapeake Bay

Abstract: Associations between macrobenthic communities, measures of water column and sediment exposure, and measures of anthropogenic activities throughout the watershed were examined for the Chesapeake Bay, U.S. The condition of the macrobenthic communities was indicated by a multimetric benthic index of biotic integrity (B-IBI) that compares deviation of community metrics from values at reference sites assumed to be minimally altered by anthropogenic sources of stress. Correlation analysis was used to examine associations between sites with poor benthic condition and measures of pollution exposure in the water column and sediment. Low dissolved oxygen events were spatially extensive and strongly correlated with benthic community condition, explaining 42% of the variation in the B-IBI. Sediment contamination was spatially limited to a few specific locations including Baltimore Harbor and the Southern Branch of the Elizabeth River and explained about 10% of the variation in the B-IBI. After removing the effects of low dissolved oxygen events, the residual variation in benthic community condition was weakly correlated with surrogates for eutrophication—water column concentrations of total nitrogen, total phosphorus, and chlorophylla. Associations between benthic conditions and anthropogenic inputs and activities in the watershed were also studied by correlation analysis. Benthic condition was negatively correlated with measures of urbanization (i.e., population density, point source loadings, and total nitrogen loadings) and positively correlated with watershed forestation. Significant correlations were observed with population density and nitrogen loading below the fall line, but not above it, suggesting that near-field activities have a greater effect on benthic condition than activities in the upper watershed. At the tributary level, the frequency of low dissolved oxygen events and levels of sediment contaminants were positively correlated with population density and percent of urban land use. Sediment contaminants were also positively correlated with point source nutrient loadings. Water column total nitrogen concentrations were positively correlated with nonpoint nutrient loadings and agricultural land use while total phosphorus concentrations were not correlated with land use or nutrient loadings. Chlorophylla concentrations were positively correlated with nitrogen and phosphorus concentrations in the water column and with agricultural land use but were not correlated with nutrient loads.

Trace Elements In Water, Fish and Sediment from Tuskegee Lake, Southeastern Usa

Abstract: The concentrations of trace elements in water, sediment and fish samples from Tuskegee Lake located in Southeastern United States were investigated in this study The Lake is utilized both as a source for municipal drinking water, and for recreational fishing The water quality characteristics over two sampling periods, the speciation of metals in the Lake sediments, the risk to water column contamination and levels of heavy metals in largemouth bass (Micropterus salmoides) samples from the Lake were evaluated The Lake water quality characteristics were mostly below the recommended drinking water standards by the United StatesEnvironmental Protection Agency (US EPA) and the European Union (EU) except for aluminum, iron, manganese and thallium In addition, the average values of Cr, As, Mn, Zn and Cl- in the water samples analyzed were higher than the respective reference values for fresh water To study the speciation of metals in the Lake sediments, ten elements (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V, and Zn) in four grain sizes (< 710 μm – 250 μm, < 250 μm – 75 μm, < 75 μm – 53μm, and < 53 μm) were subjected to sequential extractions Irrespective of grain size, the elements analyzed were distributed in both the non-residual and residual phases except Ni that was found only in the residual fraction The potential risk to Lake water contamination was highest downstream (Sites 1 and 2) based on the calculated global contamination factors From the calculated individual contamination factors, Mn and Pb followed by Zn, Cu, Cr, Co and V posed the highest risk to water contamination Based on this study, the human health risks for heavy metals in fish caught from Tuskegee Lake are low for now, and irrespective of the source of fish, concentrations of metals in muscle tissues were all below the recommended Food and Agriculture Organization (FAO) maximum limits for Pb (05 mg Kg-1), Cd (05 mg Kg-1), Cu (30 mg Kg-1), and Zn (30 mg Kg-1) in fish

The Late Pleistocene - Holocene palaeolimnology of Lake Victoria East Africa, based upon elemental and isotopic analyses of sedimentary organic matter

Abstract: Three piston cores from Lake Victoria (East Africa) have been analysed for organic carbon (TOC) and nitrogen (TN) content, stable isotopes (δ13C and δ15N), and Hydrogen Index (HI). These data are combined with published biogenic silica and water content analyses to produce a detailed palaeolimnological history of the lake over the past ca. 17.5 ka. Late Pleistocene desiccation produced a lake-wide discontinuity marked by a vertisol. Sediments below the discontinuity are characterised by relatively low TOC and HI values, and high C/N, δ13C and δ15N, reflecting the combined influence of abundant terrestrial plant material and generally unfavourable conditions for organic matter preservation. A thin muddy interval with lower δ13C and higher HI and water content indicates that dry conditions were interrupted by a humid period of a few hundred years duration when the lake was at least 35 m deep. The climate changed to significantly more humid conditions around 15.2 ka when the dry lake floor was rapidly flooded. Abundant macrophytic plant debris and high TOC and δ13C values at the upper vertisol surface probably reflect a marginal swamp. δ13C values decrease abruptly and HI begins to increase around 15 ka BP, marking a shift to deeper-water conditions and algal-dominated lake production. C/N values are relatively low during this period, suggesting a generally adequate supply of nitrogen, but increasing δ15N values reflect intense utilisation of the lake's DIN reservoir, probably due to a dramatic rise in productivity as nutrients were released to the lake from the flooded land surface. An abrupt drop in δ13C and δ15N values around 13.8-13.6 ka reflects a period of deep mixing. Productivity increased due to more efficient nutrient recycling, and δ13C values fell as 12C-rich CO2 released by bacterial decomposition of the organic material was brought into the epilimnion. A weak drop in HI values suggests greater oxygen supply to the hypolimnion at this time. Better mixing was probably due to increased wind intensity and may mark the onset of the Younger Dryas in the region. After the period of deep mixing, the water column became more stable. TOC, C/N, δ13C and HI values were at a maximum during the period between 10 and 4 ka, when the lake probably had a stratified water column with anoxic bottom waters. A gradual decrease in values over the last 4000 yrs suggest a change to a more seasonal climate, with periodic mixing of the water column. Rising sediment accumulation rates and a trend to more uniform surface water conditions over the last 2000 yrs are probably a result of increased anthropogenic impact on the lake and its catchment. Following a maximum at the time of the rapid lake-level rise during the terminal Pleistocene, δ15N has remained relatively low and displays a gradual but consistent trend to lower values from the end of the Pleistocene to the present. TN values have risen during the same period. The lack of correlation between δ13C and δ15N, and the absence of any evidence for isotopic reservoir effects despite the rise in TN, suggests that the atmosphere, rather than the lake's dissolved nitrogen pool has been the principal source of nitrogen throughout the Holocene. The importance of atmospheric N fixation to Lake Victoria's nitrogen cycle thus predates by a very considerable margin any possible anthropogenic eutrophication of the lake.