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1.
The Casamance estuary, on the coast of Senegal, is an inverse hypersaline estuary: salinity increases landward, and dry season salinity values are up to 172 psu due to the evaporation of seawater. Dissolved inorganic carbon (DIC) concentrations decreased landward as a negative linear function of salinity. Thermodynamic modelling and the absence of CaCO3 in the sediments indicate that this loss of DIC was not due to calcite precipitation in the main water body. The innermost, almost landlocked, waters contained high phytoplankton biomass (50–300 μg chl I?1) and high concentrations of allochthonous dissolved organic carbon. Photosynthetic uptake of DIC and subsequent particulate organic carbon sedimentation is proposed as hypothetical explanation of the relationship between DIC and salinity; localized overheating in shallow waters might also be involved.  相似文献   

2.
Sediments from the Mackenzie Valley — two suspended and one river bottom — were analyzed for major and minor elements, mineralogy, particle size, and ability to release trace metals when subjected to mild leaching. Copper and zinc in suspended sediments and cadmium in bottom sediment occurred largely (70 to 84 percent for Cu, 72 to 98 percent for Zn, 75 to 81 percent for Cd) in a form that could not easily be separated from the sediments by 0.1M HC1 and EDTA solutions. Cadmium was present in suspended sediments in low concentrations, and was present totally in sorbed leachable form. Iron, manganese, cobalt and chromium were separable from the particulate phase by mild leaching. It was found that approximately 70 hours were required for an apparent steady state concentration to be attained in such leachings. Reaction of these sediments with Beaufort Sea water (salinity 22.3 parts per thousand) indicated that both iron and manganese were released from sediments to sea water to a very small degree. Copper, lead, and zinc, however, were absorbed by sediments from sea water.  相似文献   

3.
Trace element distributions, partitioning, and speciation were examined at 15 sites in the Patuxent River watershed from May 1995 through October 1997 to determine possible sources of trace elements to the river and estuary, to examine the relationship of the trace element discharges to freshwater discharges as well as to land use and geographic region, to validate previous estimates of loadings to the river, and to provide baseline data for trace elements in the Patuxent River watershed and estuary. Six freshwater sites were examined, representing different basins and geographic provinces, and nine sites along the estuarine salinity gradient. Subregions within the watershed varied considerably in concentrations and areal yields for some elements. Concentrations of As, Cd, Ni, Pb, and Zn were elevated in the Coastal Plain sites compared to the Piedmont sites, while Cu and Hg were more evenly distributed. Cadmium, Cu, Hg, Ni, Pb, and Zn showed overall positive correlations with river flow while As and methylHg (meHg) showed negative correlations with river flow. Concentrations of trace elements in the estuarine portion of the river were generally low, and consistent with mixing between Patuxent River water with elevated concentrations and the lower concentrations of the Chesapeake Bay. Interesting features included a local Cd maximum in the low salinity region of the estuary, probably caused by desorption from suspended sediments, and a significant input of water containing high As concentrations from the Chesapeake Bay and from As being released from bottom sediments in summer. Comparisons between the estimated annual flux of trace elements and the estimates of suspected source terms (atmospheric deposition, urban runoff, and known point sources) suggest that, except for Hg, direct atmospheric deposition is small compared to fluvial loads. Current estimates of trace element inputs from point sources or from urban runoff are inadequate for comparison with other sources, because of inappropriate techniques and/or unacceptably high detection limits. A complete examination of trace element dynamics in the Patuxent River (and in other coastal systems) will require better data for these potential sources.  相似文献   

4.
The differences and similarities between near-pristine estuaries of different latitudinal regions were examined by selecting three tropical systems from North Queensland, Australia (Jardine, Annan, Daintree) and three temperate systems from Scotland, United Kingdom (Inverness, Cromarty, Dornoch Firths) for comparison. Although estuaries from the different regions have a number of unifying features, such as salinity gradients, tidal variations and terrestrial inputs they also have a number of important differences. The most distinct of these is the timing and variability of the major physical forcings on the estuary (e.g., river flow, insolation). The three tropical estuaries were much more episodic than their temperate counterparts, with a much more dynamic salinity structure and more variable riverwater concentrations, so that delivery of material to the estuary is dominated by short-lived flood events. In contrast, seawater concentrations were more stable in the tropical estuaries due to a more constant input of insolation, resulting in year round biological activity. There was biological removal of dissolved inorganic phosphorus in the low salinity region of the tropical Jardine and Daintree estuaries and a low salinity input of nitrate in the tropical Annan estuary most likely due to nitrification in the bottom sediments, and the biological reaction zone in the tropical Annan Estuary was flushed out of the estuarine basin to the edge of the offshore plume during a flood. Similar effects were not seen in the temperate Inverness, Cromarty, and Dornoch Firths. Similarities between estuaries include mid-estuary inputs of ammonium which were seen in both the temperate and tropical estuaries, although they occur under vastly contrasting conditions of low river discharge and periods of flood, respectively. Five of the estuaries show a general increase in dissolved inorganic phosphorus concentrations towards the sea during low flows, reflecting their pristine condition, and all six estuaries had low salinity silicate maxima probably sourced from the dissolution of freshwater biogenic silicate that has been carried seaward, except in the tropical estuaries during the dry season when a benthic source is proposed.  相似文献   

5.

The adjacent Huon and Derwent estuaries in Tasmania have similar climatic and physical characteristics, and provide a good comparison between relatively uncontaminated and industrially polluted estuaries, respectively. Representative samples were collected from both estuaries and analysed for grainsize and trace‐element content (using X‐ray fluorescence and neutron activation analyses). The Huon estuary drains a predominantly forested and agricultural catchment and contains low (baseline) concentrations of trace elements, including lead, zinc and copper. In contrast, the Derwent estuary has a geologically similar yet larger catchment and it passes through an industrialised area in the midestuarine reach. A zinc refinery has, in the past, been a major source of trace‐element contamination. These contaminants are distributed downstream from the refinery by combined fluvial and tidal activity, while the latter also causes upstream movement of contaminants during non‐flood periods. Significant upstream contamination is limited by fluvial bottom flows remobilising contaminated fine sediment during flood periods. Maximum contamination occurs in the region around the refinery with values in the surface sediments ranging from 40 to 565 times baseline levels and from 2 to 55 times the Australian Interim Sediment Quality Guidelines high‐levels for aquatic sediments (maximum 22593 ppm Zn, 3866 ppm Pb and 1182 ppm Cu). In the lower Derwent estuary, contaminant distribution is inversely related to tidal‐flow velocities and is most prominent in the lower energy muddy substrates. Trace‐metal levels in the more recent surficial aquatic sediments are slightly lower than those recorded in a previous study from the area, possibly reflecting the stricter environmental controls now operating.  相似文献   

6.
Factors that govern heavy metal concentration in sediments were examined by a combined analytical, geochemical, and geological approach. The constrains encountered in the determination of the anthropogenic influence are exposed. The region examined was the Krka River estuary located in the typical karst region of the eastern Adriatic, Yugoslavia.Sedimentological research revealed that: the Krka River (main water supplier) is almost free of suspended terrigenous material; the main supplier of suspended terrigenous matter of flysch origin is a small torrent-type Gudua Creek, and that this fine grained terrigenous material is sedimented mostly in the central enlarged part of the estuary, the Prokljan Lake.Three different groups of heavy metals were identified in recent sediments. Increased concentrations of nickel and zinc were found in estuarine sediments due to strongnatural enrichment in source rocks. Manganese and chromium were found to benaturally enriched and depleted in surface layer respectively, due to the different postdepositional geochemical behavior. Lead and copper concentrations were found to be increased in surface sediments in the central part of the estuary, apparently from anthropogenic source.  相似文献   

7.
Spatial distribution and temporal trends studies were carried out at Katedan Industrial Development Area (KIDA) near Hyderabad, capital of Andhra Pradesh state, India under Indo-Norwegian Institutional Cooperation Program, to find out the extent of contamination in streams and lake sediments from the discharge of industrial effluents. Stream and lake sediment samples were collected from the five lakes in the study area and connecting water streams. The samples were analyzed by XRF spectrometer for toxic elements. The studies reveal that the stream sediments with in the KIDA and the impounded Noor Mohammed Lake down stream have high concentration of some of the toxic elements like chromium, nickel, lead, arsenic, zinc etc. The geology of the area indicates that the study area consists of residual soil of acidic rocks, which are predominantly of Archaean gneisses and granites having low to medium concentrations of chromium and nickel. The source of these high concentration of elements like lead 2,300 mg/kg, copper 1,500 mg/kg, arsenic 500 mg/kg, chromium 500 mg/kg etc. cannot be derived from the surrounding acidic rocks and may be attributed to the industrial effluents released in the ditches and random dumping of hazardous solid waste. It was observed that the metal concentrations increased in the streams during the dry season (pre-monsoon period). After the monsoon rains, the metal concentrations in the streams were reduced by half which may be due to dilution. The eroded sediments are deposited in the lake where very high concentrations were encountered. Overflowing of the lake will spread the contamination further downstream. The lake sediments will remain as a major source of contamination by desorption to the water phase regardless of what happens to the effluent discharge in the KIDA. However, some samples showed enrichment of lead, arsenic and nickel during post-monsoon, which were collected near the dumpsite due to the leaching of toxic elements from the dump site to the lakes. Some of the toxic elements like nickel and copper have not shown any dilution but have increased after the rains, which could be due to the leaching of arsenic from the dumpsite to the lake along with rainwater. Geochemical maps showing the distribution of heavy/trace elements in streams and lakes are prepared and presented in this paper. Effect of toxic elements on the health of the residents in the surrounding residential areas is also discussed.  相似文献   

8.
Concentrations of copper, zinc, chromium, lead, cadmium, and phosphorus were obtained from 81 samples of unconsolidated estuarine sediment from Great Bay, New Hampshire. Dispersal of aqueous chromium from localized industrial effluent is believed responsible for an increase in sediment chromium throughout the entire estuary. High phosphorus concentrations exist in sediment near the outfalls from several waste-water treatment plants. There is no evidence for any increase of copper, zinc, lead, or cadmium in this estuary, except for localized high concentrations close to industrial outfalls. Fine-grained sediments and organic carbon correlate highly with all the elements studied, except for chromium. This suggests that conventional agents of sedimentary adsorption are not adequate to explain the incorporation of chromium into sediment under the conditions of heavy industrial discharge which exist in this estuary. Sediment phosphorus correlates highly with minor elements, suggesting that it is an adsorption agent, similar to more typical sedimentary parameters such as organic matter and clay minerals. In such a capacity phosphorus may enhance the sedimentary uptake of other aqueous species, and account for higher chromium sediment concentrations. Comparative data from other sedimentary environments emphasize the environmental significance of these elements in Great Bay.  相似文献   

9.
Since 1991, Mississippi River water has been diverted at Caernarvon, Louisiana, into Breton Sound estuary. Breton Sound estuary encompasses 1100 km2 of fresh and brackish, rapidly subsiding wetlands. Nitrite + nitrate, total Kjeldahl nitrogen, ammonium, total phosphorus, total suspended sediments, and salinity concentrations were monitored at seven locations in Breton Sound from 1988 to 1994. Statistical analysis of the data indicated decreased total Kjeldahl nitrogen with associated decrease in total nitrogen, and decreased salinity concentrations in the estuary due to the diversion. Spring and summer water quality transects indicated rapid reduction of nitrite + nitrate and total suspended sediment concentration as diverted Mississippi River water entered the estuary, suggesting near complete assimilation of these constituents by the ecosystem. Loading rates of nitrite + nitrate (5.6–13.4 g m−2 yr−1), total nitrogen (8.9–23.4 g m−2 yr−1), and total phosphorus (0.9–2.0 g m−2 yr−1) were calculated along with removal efficiencies for these constituents (nitrite + nitrate 88–97%; total nitrogen 32–57%; total phosphorus 0–46%). The low impact of the diversion on water quality in the Breton Sound estuary, along with assimilation of TSS over a very short distance, suggests that more water may be introduced into the estuary without detrimental affects. This would be necessary if freshwater diversions are to be used to distribute nitrients and sediments into the lower reaches of the estuary, in an effort to compensate for relative sea-level rise, and reverse the current trend of rapid loss of wetlands in coastal Louisiana.  相似文献   

10.
The exchange of dissolved nutrients between marshes and the inundating water column was measured using throughflow marsh flumes built, in two microtidal Louisiana estuaries: the Barataria Basin estuary and Fourleague Bay. The flumes were sampled between September 1986 and April 1988, coincident with an extended period of low sea level on the Louisiana coast. The Barataria Basin estuary is in the later, deteriorating stage of the deltaic cycle, characterized by low freshwater inputs and subsiding marshes. Both brackish and saline marshes supplied dissolved organic nitrogen (DON), inorganic nitrogen (ammonium + nitrate + nitrite = DIN), dissolved organic carbon (DOC), and total nitrogen (as total Kjeldahl nitrogen = TKN) to the water column. The export of DIN is probably related to the N accumulated in earlier stages of deltaic development and released as these marshes deteriorate. Coastal brackish marshes of Fourleague, Bay, part of an accreting marsh system in an early, developmental stage of the deltaic cycle, exported TKN to the open water estuary in all samplings. This marsh apparently acted as a short-term buffer of DIN by taking up NH4 + in spring, when baywide concentrations were high, and supplying DIN to the estuary in summer and fall, when concentrations, in the bay were lower. Differences in phosphorus (P), DOC, and DON fluxes between these two estuaries were also observed. The Fourleague Bay site exported soluble reactive phosphorus (SRP) and total phosphorus (TP) and imported DOC. This P export may be related to remobilization of sediment-bound riverine P by the reducing, soils of the marshes. Fluxes of SRP at the Barataria Basin sites were variable and low while DOC was imported. Most imports of dissolved nutrients were correlated with higher upstream [source] concentrations, and flux rates were fairly consistent throughout the tide. Dissolved nutrient exports, did not correlate with upstream concentrations, though, and in many cases the flux was dominated by early, flood tide nutrient release. This pulsed behavior may be caused by rapid diffusion from the sediments early in the tidal cycle, when the sediment-water concentration gradient is largest. Interestuary differences were also seen in particulate organic matter fluxes, as the Fourleague Bay marsh exported POC and PON during all samplings while Barataria Basin imported these nutrients. In general, the magnitude and direction of nutrient exchanges in Louisiana marshes, seem to reflect the deltaic successional stage of the estuary.  相似文献   

11.
《Geochimica et cosmochimica acta》1999,63(19-20):3467-3475
Dissolved and particulate phosphorus, ammonia, and nitrate concentrations were measured in the Dead Sea water column (330 m depth, salinity ca. 340 g/L), in the Lower Jordan River and in springs along its western coast. Dissolved phosphate in the water column is fairly homogeneous, at about 35 μg P/L. Particulate P shows larger variability, 30–50 μg/L. The main inputs of dissolved phosphate into the lake are diffusion from bottom sediments (58%) and the Jordan River inflow (41%). Input from springs is negligible (1%). Biological uptake is a minor removal pathway because in the present Dead Sea, primary production takes place only when major floods occur and dilute the upper layer, about once in 10 years. When this happens, only about 200 ton P, out of a whole-lake reservoir of ca. 5000 ton P, are removed from the biologically active upper layer of about 7 m. Chemical removal pathways, not yet investigated, such as coprecipitation with authigenic aragonite, could be of importance. The average ammonia concentration in the water column has gradually increased from 5.9 mg/L in 1960 to 8.9 mg/L, in 1991. Diffusion from the bottom sediments is a major source of ammonia to the Dead Sea. The annual input from freshwater inflows has been of lesser importance in the 1960s and 1970s. A pollution-derived increase in the ammonia concentration of the Jordan River in the 1980s may partially explain the concomitant rise in the ammonia load of the lake. It is also suggested that following the 1979 overturn, and the yearly turnovers of the 1980s, ammonia might have been produced within the oxygenated water column by mineralization. Nitrate concentration was very low, 20 μg N/L, in the 1960s and increased to 0.2 to 0.5 mg/L in 1981. This increase is shown to be due to human pollution of the Jordan River. We conclude that nutrient concentration in the Dead Sea water column is controlled by physical and chemical factors, whereas biological effects are minimal.  相似文献   

12.
Cadmium (Cd) variations were investigated over an annual cycle (12 surveys between February 1998–January 1999) in the Morlaix estuary (Brittany, France) in both the water column and the benthic compartment in relation to hydrological conditions. The drainage basin of the Morlaix River estuary is predominantly agricultural in character. Dissolved Cd concentrations in the water column varied from 0.04 to 0.48 nM. Particulate Cd concentrations ranged from 1 to 64 nmol g−1. These concentrations reach levels commonly observed in estuaries affected by heavy industrial activities. Extensive agricultural activities in the drainage basin may be responsible for Cd levels above pristine conditions. Metal concentrations varied significantly over the seasonal cycle and the dissolved fraction exhibited high values in summer months. Particulate concentrations were always lowest during this season. In the benthic compartment, Cd concentrations in surface sediment varied from 0.4 to 5.0 nmol g−1 and from 0.2 to 5.0 nM in porewaters. Concentrations in sediment were slightly affected by Cd contamination and temporal changes were important over the seasonal cycle. The variations seem to be controlled by the succession of sedimentation and erosion processes, which are tightly linked to seasonal changes in river discharge. A box model was constructed based on known Cd sources and sinks in the estuary. Cd is chiefly brought into the estuary by the Morlaix River and accumulates within the estuary. The accumulation within the estuary represents from 6.3 to 7.2 kg yr−1.  相似文献   

13.
Submarine groundwater discharge (SGD) is an important source of dissolved elements to the ocean, yet little is known regarding the chemical reactions that control their flux from sandy coastal aquifers. The net flux of elements from SGD to the coastal ocean is dependent on biogeochemical reactions in the groundwater-seawater mixing zone, recently termed the “subterranean estuary.” This paper is the second in a two part series on the biogeochemistry of the Waquoit Bay coastal aquifer/subterranean estuary. The first paper addressed the biogeochemistry of Fe, Mn, P, Ba, U, and Th from the perspective of the sediment composition of cores Charette et al. [Charette, M.A., Sholkovitz, E.R., Hansell, C.M., 2005. Trace element cycling in a subterranean estuary: Part 1. Geochemistry of the permeable sediments. Geochim. Cosmochim. Acta, 69, 2095-2109]. This paper uses pore water data from the subterranean estuary, along with Bay surface water data, to establish a more detailed view into the estuarine chemistry and the chemical diagenesis of Fe, Mn, U, Ba and Sr in coastal aquifers. Nine high-resolution pore water (groundwater) profiles were collected from the head of the Bay during July 2002. There were non-conservative additions of both Ba and Sr in the salinity transition zone of the subterranean estuary. However, the extent of Sr release was significantly less than that of its alkaline earth neighbor Ba. Pore water Ba concentrations approached 3000 nM compared with 25-50 nM in the surface waters of the Bay; the pore water Sr-salinity distribution suggests a 26% elevation in the amount of Sr added to the subterranean estuary. The release of dissolved Ba to the mixing zone of surface estuaries is frequently attributed to an ion-exchange process whereby seawater cations react with Ba from river suspended clay mineral particles at low to intermediate salinity. Results presented here suggest that reductive dissolution of Mn oxides, in conjunction with changes in salinity, may also be an important process in maintaining high concentrations of Ba in the pore water of subterranean estuaries. In contrast, pore water U was significantly depleted in the subterranean estuary, a result of SGD-driven circulation of seawater through reducing permeable sediments. This finding is supported by surface water concentrations of U in the Bay, which were significantly depleted in U compared with adjacent coastal waters. Using a global estimate of SGD, we calculate U removal in subterranean estuaries at 20 × 106 mol U y−1, which is the same order of magnitude as the other major U sinks for the ocean. Our results suggest a need to revisit and reevaluate the oceanic budgets for elements that are likely influenced by SGD-associated processes.  相似文献   

14.
A combination of mixing plots, one-dimensional salt balance modelling, nutrient loading budgets, and benthic flux measurements were used to assess nutrient cycling pathways in the enriched sub-tropical Brunswick estuary during different freshwater flows. A simple model accounting for freshwater residence times and nutrient availability was found to be a good predictor of phytoplankton biomass along the estuary, and suggested that biomass accumulation may become nutrient-limited during low flows and that recycling within the water column is important during blooms. Dissolved inorganic nitrogen (DIN) cycling budgets were constructed for the estuary during different freshwater flows accounting for all major inputs (catchment, sewage, and urban) to the estuary. Internal cycling due to phytoplankton uptake (based on measured biomass) and sediment-water fluxes (based on measured rates in each estuarine reach) was considered. Four different nutrient cycling states were identified during the study. In high flow, freshwater residence times are less than 1 d, internal cycling processes are bypassed and virtually all dissolved, and most particulate, nutrients are delivered to the continental shelf. During the growth phase of a phytoplankton bloom enhanced recycling occurs as residence times increase sufficiently to allow biomass accumulation. Remineralization of phytoplankton detritus during this phase can supply up to 50% of phytoplankton DIN demands. In post-bloom conditions, DIN uptake by phytoplankton decreases in the autumn wet season when biomass doubling times begin to exceed residence times. OM supply to the sediments diminishes and the benthos becomes nutrient-limited, resulting in DIN uptake by the sediments. As flows decrease further in the dry season, there is tight recycling and phytoplankton blooms, and uptake by the sediments can account for the entire DIN loading to the estuary resulting in complete removal of DIN from the water column. The ocean is a potentially important source of DIN to the estuary at this time. The results of the DIN cycling budgets compared favorably with mixing plots of DIN at each time. The results suggest that a combination of different approaches may be useful in developing a more comprehensive understanding of nutrient cycling behavior and the effects of nutrient enrichment in estuaries.  相似文献   

15.
A “snap shot” survey of the Mississippi estuary was made during a period of low river discharge, when the estuarine mixing zone was within the deltaic channels. Concentrations of H+, Ca2+, inorganic phosphorus and inorganic carbon suggest that the waters of the river and the low salinity (<5‰) portion of the estuary are near saturation with respect to calcite and sedimentary calcium phosphate. An input of oxidized nitrogen species and N2O was observed in the estuary between 0 and 4‰ salinity. The concentrations of dissolved NH4 + and O2, over most of the estuary, appeared to be influenced by decomposition of terrestrial organic matter in bottom sediments. The estuarine bottom also appears to be a source of CH4 which has been suggested to originate from petroleum shipping and refining operations. Estuarine mixing with offshore Gulf waters was the dominant influence on distributions of dissolved species over most of the estuary (i.e., from salinities >5‰). The phytoplankton abundance (measured as chlorophylla) increased as the depth of the mixed layer decreased in a manner consistent with that expected for a light-limited ecosystem. Fluxes of NO3 ?+NO2 ? and soluble inorganic phosphorus to the Gulf of Mexico were estimated to be 3.4±0.2×103 g N s?1 and 1.9±0.2 g P s?1 respectively, at the time of this study.  相似文献   

16.
Four sediment cores representing adjacent mudflat and mangrove sub-environments of middle estuary (Shastri) were analyzed for sand, silt, clay, and organic carbon. Total metal concentration of iron (Fe), manganese (Mn), nickel (Ni), zinc (Zn), chromium (Cr), copper (Cu), cobalt (Co), and lead (Pb) and chemical speciation of Fe, Mn, and Co on selected samples was also carried out on mudflat cores. The sediments in the upper middle estuary were found to be deposited under highly varying hydrodynamic energy conditions; whereas lower middle estuary experienced relatively stable hydrodynamic energy conditions with time. The tributary joining the river near the upper middle estuary is found to be responsible for the addition of enhanced organic carbon and metal concentrations. Speciation study indicated Fe and Co are from natural lithogenic origin while Mn is derived from anthropogenic sources. Higher Mn and Co than apparent effects threshold can pose a high risk of toxicity to organisms associated with these sediments.  相似文献   

17.
We examined the effects of seasonal salinity changes on sediment ammonium (NH4 +) adsorption and exchange across the sediment–water interface in the Parker River Estuary, by means of seasonal field sampling, laboratory adsorption experiments, and modeling. The fraction of dissolved NH4 + relative to adsorbed NH4 + in oligohaline sediments rose significantly with increased pore water salinity over the season. Laboratory experiments demonstrated that small (∼3) increases in salinity from freshwater conditions had the greatest effect on NH4 + adsorption by reducing the exchangeable pool from 69% to 14% of the total NH4 + in the upper estuary sediments that experience large (0–20) seasonal salinity shifts. NH4 + dynamics did not appear to be significantly affected by salinity in sediments of the lower estuary where salinities under 10 were not measured. We further assessed the importance of salinity-mediated desorption by constructing a simple mechanistic numerical model for pore water chloride and NH4 + diffusion for sediments of the upper estuary. The model predicted pore water salinity and NH4 + profiles that fit measured profiles very well and described a seasonal pattern of NH4 + flux from the sediment that was significantly affected by salinity. The model demonstrated that changes in salinity on several timescales (tidally, seasonally, and annually) can significantly alter the magnitude and timing of NH4 + release from the sediments. Salinity-mediated desorption and fluxes of NH4 + from sediments in the upper estuary can be of similar magnitude to rates of organic nitrogen mineralization and may therefore be important in supporting estuarine productivity when watershed inputs of N are low.  相似文献   

18.
This study addresses the distribution of total phosphorus (TP) and its inorganic (IP) and organic (OP) fractions, grain-size and organic matter of surface and recent sediments, coupled to the behavior of total and dissolved inorganic phosphorus (TP and DIP) of the water column, of the semi-pristine Guaratuba Bay estuary, SE Brazil. Surface sediment samples were taken at 43 sites spread along the estuarine gradient and recent sediments from 3 short (35 cm long) cores from the upper, central and lower portions of the estuary, respectively. Highest TP and IP concentrations of surface sediments were detected within the upper sector and the transition zone between the upper and central sectors, all characterized by fine sediments, low salinities and water depths. In contrast, the lower sector and its narrow and deep tidal channel, subject to more intense tidal forcing, exhibited a higher fraction of sandy sediments with lower TP, IP and OP contents. In spite of the spatial variability in sediment grain size, IP corresponded to the major fraction of TP in all estuarine sectors and both TP and IP correlated significantly with the fine sedimentary (silt + clay) grain-size fraction. The fine surface sediments acted as a trap for IP at the fresh water–low salinity interface, which also corresponded to the region of a DIP sink in surface waters. In general, the short sediment cores showed that TP and IP contents increased from 15 cm depths to the top layer. Published sedimentation rates from additional cores taken at the sites of the short cores of this study, implied that depositional alterations of TP and IP increased during the early 1970s, which corresponded to the onset of anthropogenic disturbances from crop plantations in the lowland plains of the river end-member and urbanization at the estuary’s mouth and along the adjacent coast.  相似文献   

19.
The distribution of dissolved and particle-bound phosphorus (P) was investigated in the Elbe estuary during March 1995. The forms of particulate P were studied with a sequential extraction technique. Organic P dominated particle-bound P in the outer reaches of the estuary (52%), decreased to a minimum of 21% in the turbidity zone, and increased to 33% further upstream. Fe-bound P was the second most important P species in the outer reaches (27%) and dominated in the turbidity zone (up to 57%) and upstream of the turbidity zone (up to 48%). The P:Fe ratio increased with decreasing salinity, from 0.11 in the outer reaches to about 0.22 at zero salinity. Dissolved inorganic P release from reverine suspended matter was about two to three times larger than release, from marine suspended matter and was dominated by release of Fe-bound P. Dissolved inorganic P release from marine and from riverine organic matter were of equal importance. Because marine suspended matter dominates in the estuary, this suggests riverine organic matter is remineralized much faster than marine organic matter. This is in line with the refractory nature of marine organic matter (no phytoplankton bloom) and the easily degradable character of the riverine suspended matter (phytoplankton bloom) in the Elbe estuary during March 1995.  相似文献   

20.
Seasonal dynamics of dissolved trace metals (Cd, Co, Cu, Ni and Zn) and its relationship with redox conditions and phytoplankton activity has been studied in the Scheldt estuary, during nine surveys carried out between May 1995 and June 1996. Seasonal profiles of dissolved trace metals and general estuarine water quality variables are compared, to identify the geochemical and biological processes responsible for the observed trace metal distributions. In keeping with previous studies, the behavior of dissolved Cd, Cu, and Zn can be explained by the presence of anoxic headwaters and the restoration of dissolved oxygen within the estuary. In the river water, the concentration of dissolved Cu and Zn is generally low, except during winter when dissolved oxygen is present in the water column, although highly undersaturated. Mobilization of particle-bound Cd, Cu, and Zn occurs as dissolved oxygen increases with increasing salinity, possibly because of oxidation of metal sulfides in the suspended matter. The geochemistry of dissolved Co is also related to the redox conditions but in an opposite way. Dissolved Co is mobilized in the anoxic upper estuary, along with the reduction in Mn (hydro) oxides, and subsequently coprecipitated with Mn (hydro) oxides when dissolved oxygen is restored. Conservative behavior is observed for dissolved Ni within the estuary. In the middle estuary, Cd and Zn are readsorbed during phytoplankton blooms, as suggested by the low concentrations of these metals during the most productive periods in spring and early summer. The removal may be caused by direct biological uptake and/or increased adsorption to suspended matter because of the pH increase associated with algae blooms. In the lower estuary, chemical gradients are much weaker and dilution with seawater is the dominant process.  相似文献   

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