The optical and molecular signatures of DOM under the eutrophication status in a shallow,semi-enclosed coastal bay in southeast China

We applied stable carbon isotopes, ultraviolet-visible absorption(UV-Vis), fluorescence excitation-emission matrices spectroscopy(EEMs), and Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR-MS) to investigate the chemical composition and sources of the dissolved organic matter(DOM) in both the water column and pore water in Xiangshan Bay, a representative semi-enclosed and eutrophic bay in Zhejiang Province, China. One protein-like fluorescent component(C1) and two humic-like fluorescent components(C2 and C3) were identified by PARAFAC modeling. The concentration of dissolved organic carbon(DOC), the relative intensities of C2, C3, and black carbon-like compounds are all negatively correlated with salinity, indicating that there is a dilution effect of terrestrial signals by seawater in Xiangshan Bay. The differences in light penetration ability of Xiangshan Bay cause different degrees of photo-degradation, which may play an important role in the transformation of organic matter in Xiangshan Bay. The weak correlation between the C1 fluorescent component and salinity indicates that autochthonous sources cannot dominate the protein-like FDOM in the Xiangshan Bay drainage area. Multiple sources(such as anthropogenic inputs and release of pore water) also affect the distribution of the protein-like fluorescent component under eutrophication conditions. The relative proportion of the protein-like fluorescent component in Xiangshan Bay is on a medium level in China and anthropogenic inputs may be a significant source of DOM in coastal bays.     

Organic matter and nutrient inputs to the Humber Estuary, England

Estuaries are sinks for organic matter and nutrients entering both from their catchments and also from the adjacent lands and urban areas and in turn they are sources of such materials to the adjacent coast. The present paper quantifies the relative amounts of natural and anthropogenic organic matter and nutrients entering the Humber Estuary, Eastern England, including the allochthonous and autochthonous materials, those from urban and industrial sewage and from the catchment drainage of arable land. These data thus give a budget for the estuary which in turn answers questions fundamental to the management of the estuary. The estimations within the study have been carried out against a background of designating estuaries under the European Union Urban Waste-water Treatment Directive and the EU Nitrates Directive. The assessment has particularly addressed the question, related to the former Directive, of whether the Humber Estuary is eutrophic or likely to become eutrophic unless management measures are taken. Thus the paper indicates the nature and value of control measures such as treatment plant upgrading and the designation of Nitrate Vulnerable Zones. The paper includes the recent national and European discussions on the designation of areas under these Directives. Finally, the study has allowed a quantification of the present organic inputs to the estuary in comparison to those entering prior to large scale land-claim which had removed natural organic-producing wetlands.     

Morphology and modern sedimentary deposits of the macrotidal Marapanim Estuary (Amazon,Brazil)

The northern Brazilian coast, east of the Amazon River is characterized by several macrotidal estuarine systems that harbor large mangrove areas with approximately 7600 km². The Marapanim Estuary is influenced by macrotidal regime with moderate waves influence. Morphologic units were investigated by using remote sensing images (i.e., Landsat-7 ETM+, RADARSAT- 1 Wide and SRTM) integrated with bathymetric data. The modern sedimentary deposits were analyzed from 67 cores collected by Vibracore and Rammkersonde systems. Analysis of morphology and surface sedimentary deposits of the Marapanim River reveal they are strongly influenced by the interaction of tidal, wave and fluvial currents. Based on these processes it was possible to recognize three distinct longitudinal facies zonation that revels the geological filling of a macrotidal estuary. The estuary mouth contain fine to medium marine sands strongly influenced by waves and tides, responsible for macrotidal sandy beaches and estuarine channel development, which are characterized by wave-ripple bedding and longitudinal cross-bedding sands. The estuary funnel is mainly influenced by tides that form wide tidal mudflats, colonized by mangroves, along the estuarine margin, with parallel laminations, lenticular bedding, root fragments and organic matter lenses. The upstream estuary contains coarse sand to gravel of fluvial origin. Massive mud with organic matter lenses, marks and roots fragments occur in the floodplain accumulates during seasonal flooding providing a slowly aggrading in the alluvial plain. This morphologic and depositional pattern show easily a tripartite zonation of a macrotidal estuary, that are in the final stage of filling.     

A trophic model for the Danshuei River Estuary, a hypoxic estuary in northern Taiwan

The estuary of the Danshuei River, a hypoxic subtropical estuary, receives a high rate of untreated sewage effluent. The Ecopath with Ecosim software system was used to construct a mass-balanced trophic model for the estuary, and network analysis was used to characterize the structure and matter flow in the food web. The estuary model was comprised of 16 compartments, and the trophic levels varied from 1.0 for primary producers and detritus to 3.0 for carnivorous and piscivorous fishes. The large organic nutrient loading from the upper reaches has resulted in detritivory being more important than herbivory in the food web. The food-chain length of the estuary was relatively short when compared with other tropical/subtropical coastal systems. The shortness of food-chain length in the estuary could be attributed to the low biomass of the top predators. Consequently, the trophic efficiencies declined sharply for higher trophic levels due to low fractions of flows to the top predators and then high fractions to detritus. The low biomass of the top predators in the estuary was likely subject to over-exploitation and/or hypoxic water. Summation of individual rate measurements for primary production and respiration yielded an estimate of −1791 g WW m⁻² year⁻¹, or −95 g C m⁻² year⁻¹, suggesting a heterotrophic ecosystem, which implies that more organic matter was consumed than was produced in the estuary.     

Distribution and sources of sedimentary organic matter in a tropical estuary,south west coast of India (Cochin estuary): A baseline study

Surface sediments samples were collected from 9 stations of the Cochin estuary during the monsoon, post-monsoon and pre-monsoon seasons and were analyzed for grain size, total organic carbon (OC), total nitrogen (TN) and stable isotopic ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) to identify major sources of organic matter in surface sediments. Sediment grain size is found to be the key factor influencing the organic matter accumulation in surface sediments. The δ¹³C values ranges from ?27.5‰ to ?21.7‰ in surface sediments with a gradual increase from inner part of the estuary to the seaward side that suggest an increasing contribution of marine autogenous organic matter towards the seaward side. The δ¹⁵N value varies between 3.1‰ and 6.7‰ and it exhibits complex spatial and seasonal distributions in the study area. It is found that the dynamic cycling of nitrogen through various biogeochemical and organic matter degradation processes modifies the OC/TN ratios and δ¹⁵N to a considerable degree. The fraction of terrestrial organic matter in the total organic matter pool ranges from 13% to 74% in the surface sediments as estimated by δ¹³C based two end member mixing model.     

Mercury flux to estuarine sediments, derived from Pb-210 and Cs-137 geochronologies (Guaratuba Bay, Brazil)

A sediment core from Guaratuba Bay was used to indicate possible Hg modifications to this coastal environment brought about by growing agricultural activity. Sedimentation rates were estimated to be 6.1 mm/year and 5.2 mm/year through 210Pb and 137Cs geochronologies, respectively. Mercury concentrations and organic matter ratios in the surface layers are greater than in the older sediments, supporting the hypothesis of anthropogenic enrichment. Results show that the Hg flux has raised more than twofold during the second half of the 20th century. These results point to the need for further studies to substantiate the hypothesis of anthropogenic enrichment and to quantify point sources of Hg to this estuary.     

Trace metals, PAHs, and PCBs in sediments from the Jobos Bay area in Puerto Rico

This study provides baseline information on the extent of contamination in sediments of the Jobos Bay estuary and surrounding areas in Puerto Rico. Sediments from Jobos Bay area (n = 14) had higher overall average concentrations than those from La Parguera area (n = 5, used as reference site), in μg/g dw, for As (17 vs 9), Cu (29 vs 14), Pb (11 vs 4), and Zn (64 vs 28); and in %, for Fe (2.6 vs 0.6). Sediments (n = 8) screened for PAHs and PCBs exhibited total concentrations (ng/g dw) that ranged from 40.4 to 1912, and from not detected to 11.21, respectively. The quality of sediments of Jobos Bay could be classified as low to moderate pollution. The proximity to anthropogenic sources of contamination warrants a monitoring program for inorganic and organic pollutants in Jobos Bay area for an effective coastal management program of this tropical ecosystem.     

Fate and tidal transport of butyltin and mercury compounds in the waters of the tropical Bach Dang Estuary (Haiphong, Vietnam)

In this work, two field campaigns were performed in July 2008 (wet season) and March 2009 (dry season) to produce original data on the concentration, partition and distribution of mercury and butyltin compounds along the tropical Bach Dang Estuary located in North Vietnam (Haiphong, Red River Delta). The results demonstrate that mercury and butyltin speciation in the surface waters of this type of tropical estuary is greatly affected by the drastic changes in the seasonal conditions. During high river discharge in the wet season, there was a large estuarine input of total Hg and tributyltin, while the longer residence time of the waters during the dry season promotes increasing MMHg formation and TBT degradation. Although most of the Hg and TBT is transported into the estuary from upstream sources, tidal cycle measurements demonstrate that this estuary is a significant source of TBT and MMHg during the wet (～3kgTBT/day) and dry (～3gMMHg/day) seasons.     

Spatio-temporal variation of suspended and sedimentary organic matter quality in the Bay of Marseilles (NW Mediterranean) assessed by biochemical and isotopic analyses

Isotopic and biochemical features of suspended particulate organic matter (POM) in the water column and of sedimentary organic matter (SOM) were investigated seasonally in the Bay of Marseilles. Biochemical compounds (carbohydrates, lipids and proteins) were consistently more concentrated in POM than in SOM, with SOM mainly composed of insoluble carbohydrates. POM displayed lower δ(13)C and higher δ(15)N values than SOM. Phytoplanktonic production represented the major contributor of POM year-round with spatial and seasonal variations. Climatic parameters and wind-induced currents created differences in POM contributions, with more important inputs of terrestrial OM at one sampling site. Spatial and seasonal variations were lower for SOM. The composition of this pool appeared to be linked with the permanent inputs of phytoplankton and Posidonia oceanica detritus. The combined use of biochemical and isotopic analyses was a useful tool to characterize OM pools and would help understanding the trophic functioning of this coastal environment.     

Development of a benthic index to assess sediment quality in the Tampa Bay Estuary

The identification, remedial treatment, and monitoring of contaminated sediments are among the priorities for managers of the Tampa Bay Estuary. Tampa Bay, as an urbanized estuary, is subject to the input of watershed sources of chemical contaminants, including metals, pesticides, and organic chemicals. Although the use of biological indicators and their incorporation into multi-metric indices is not new, the refinement and applications of such techniques for determining environmental condition still require further development and exploration. We present a single Tampa Bay Benthic Index (TBBI) that was developed specifically for Tampa Bay. Stepwise discriminant analysis was applied to a comprehensive list of potential benthic metrics. Results from the stepwise procedure identified the metrics that best discriminated between "healthy" and "degraded" conditions, as defined by sediment contaminant effect levels and dissolved oxygen. Discriminant analysis was then applied to the resultant three variables to determine the linear combination for the index.     

Organic carbon isotope geochemistry of clayey deposits and their associated porewaters, southern Alberta

The organic carbon cycle of slowly permeable, clayey glacial till deposits in the Western Interior Great Plains, southern Alberta, was investigated by examining the relationship between solid organic matter (SOM) in the till sediments and dissolved organic carbon (DOC) in the till porewaters. Geochemically, the tills can be divided into two distinct zones: an upper oxidized (low SOM) till zone, and a lower unoxidized (high SOM) till zone. Till porewaters in both zones are characterized by high DOC contents. Radiocarbon dating and comparison of SOM and DOC fractions suggest DOC in the deep unoxidized zone originated during deglaciation, and is probably representative of groundwater ages in this till zone. In the oxidized zone, DOC originates from variable mixtures of soluble organic matter emplaced during deglaciation, and Cretaceous age coal fragments in this till zone. SOM in the upper till zone was mainly oxidized to CO₂ gas during lowered water table conditions of the Altithermal climatic period. The subsurface production of fossil CO₂ gas has serious implications for using the conventional dissolved inorganic carbon (DIC) ¹⁴C groundwater dating method in these clayey till porewaters.     

Effects of varying estuarine conditions on the sorption of phenanthrene to sediment particles of Yangtze Estuary

The sorption of phenanthrene on the Yangtze Estuary sediment was studied under varying conditions of particle size, sediment organic contents, salinity, and dissolved organic matter (DOM) concentrations. Small sediment particles showed higher trapping capacity for phenanthrene due to the higher organic contents associated. The organic carbon-based partition coefficient of phenanthrene to the Yangtze Estuary sediment was obtained as 7120 L/kg, lower than the values for other soils or sediments reported in previous studies. The magnitude and direction of the salt effect were complicated by the specific DOM studied. The sediment sorption capacity was greatly increased in saline water in the absence of DOM but decreased in the presence of DOM. Given the conditions in the Yangtze Estuary, the equilibrium sorption of phenanthrene would be decreased with increasing salinity. Overall, the nature and content of both sediment-bound and dissolved organic matter dominate the sorption of hydrophobic organic contaminants in the estuary.     

Evaluation of the Ems Estuary ecosystem model

An ecosystem model is used to calculate and summarize carbon budgets within the Ems Estuary, The Netherlands. The similarity between model calculations and field data is established using a validation procedure. Model results show that the seaward boundary concentration for suspended matter is important in determining whether an estuary is an importer or exporter of carbon. Lowered boundary concentrations of suspended matter enhance pelagic primary production, but reduce sedimentation and hence the carbon flux from pelagic to benthic systems.     

Relocation of the Yellow River as revealed by sedimentary isotopic and elemental signals in the East China Sea

The Yellow River (YR) supplies a large amount of nutrients and fresh water to the northern Chinese marginal seas, and greatly influences the ecosystem and current patterns. The relocation of the YR outlet from the southern Yellow Sea (YS) to the Bohai Sea in 1855 was demonstrated using northern East China Sea (ECS) sediment characteristics. Both isotopic (δ¹³C, δ¹⁵N) signals and C/N ratios in the organic matter (OM) indicate that prior to 1750, the predominant source of OM to the sediments was terrestrial. The terrestrial influences continuously weakened until 1855, when the YR estuary moved; after 1855, the OM was characterized by oceanic sources. Major elements (Al, Ti, Fe, Mn) and trace elements (Ni, Cr, Cu, Pb) had a much closer association with Malan loess prior to 1855, as >90% of the YR sediment was loess-derived. These results reveal that the relocation of the YR induced significant changes in the current patterns of the northern China Seas in the last 250 years; however, more studies are needed to further examine these linkages.     

Organic carbon deliveries and their flow related dynamics in the Fitzroy estuary

The Fitzroy estuary (Queensland, Australia) receives large, but highly episodic, river flows from a catchment (144,000 km(2)) which has undergone major land clearing. Large quantities of suspended sediments, and particulate and dissolved organic carbon are delivered. At peak flows, delta(13)C (-21.7+/-0.8 per thousand) and C/N (14.8+/-1.3) of the suspended solids indicate that the particulate organic material entering the estuary is principally soil organic carbon. At the lower beginning flows the particulate organic matter comes from in-stream producers (delta(13)C=-26 per thousand). The DOC load is about 10 times the POC load. Using the inverse method, budgets for POC and DOC were constructed for high and low flows. Under high flows, only a small portion of the POC and DOC load is lost in the estuary. Under dry season (low flow) conditions the estuary is a sink for DOC, but remains a source of POC to the coastal waters.     

Organic carbon and nitrogen stable isotopes in the intertidal sediments from the Yangtze Estuary, China

The natural isotopic compositions and C/N elemental ratios of sedimentary organic matter were determined in the intertidal flat of the Yangtze Estuary. The results showed that the ratios of carbon and nitrogen stable isotopes were respectively −29.8‰ to − 26.0‰ and 1.6‰–5.5‰ in the flood season (July), while they were −27.3‰ to − 25.6‰ and 1.7‰–7.8‰ in the dry season (February), respectively. The δ¹³C signatures were remarkably higher in July than in February, and gradually increased from the freshwater areas to the brackish areas. In contrast, there were relatively complex seasonal and spatial changes in stable nitrogen isotopes. It was also reflected that δ¹⁵N and C/N compositions had been obviously modified by organic matter diagenesis and biological processing, and could not be used to trace the sources of organic matter at the study area. In addition, it was considered that the mixing inputs of terrigenous and marine materials generally dominated sedimentary organic matter in the intertidal flat. The contribution of terrigenous inputs to sedimentary organic matter was roughly estimated according to the mixing balance model of stable carbon isotopes.     

Elemental and stable isotopic constraints on river influence and patterns of nitrogen cycling and biological productivity in Hudson Bay

Elemental (carbon and nitrogen) ratios and stable carbon and nitrogen isotope ratios (δ¹³C and δ¹⁵N) are examined in sediments and suspended particulate matter from Hudson Bay to study the influence of river inputs and autochthonous production on organic matter distribution. River-derived particulate organic matter (POM) is heterogeneous, nitrogen-poor and isotopically depleted, consistent with expectations for OM derived from terrestrial C3 vascular plant sources, and distinct from marine OM sources. Both δ¹³C and C/N source signatures seem to be transmitted to sediments with little or no modification, therefore making good tracers for terrigenous OM in Hudson Bay. They suggest progressively larger contributions from marine sources with distance from shore and secondarily from south to north, which broadly corresponds to the distribution of river inputs to Hudson Bay. Processes other than mixing of marine and terrigenous OM influence sedimentary δ¹⁵N values, including variability in the δ¹⁵N of phytoplankton in the Bay's surface waters due to differences in relative nitrate utilization, and post-production processes, which bring about an apparently constant ¹⁵N-enrichment between surface waters and underlying sediments. Variability in the δ¹⁵N of phytoplankton in the Bay's surface waters, in contrast, seems to be organized spatially with a pattern that suggests an inshore–offshore difference in surface water nitrogen conditions (open- vs. closed-system) and hence the δ¹⁵N value of phytoplankton. The δ¹⁵N patterns, supported by a simple nitrate box-model budget, suggest that in inshore regions of Hudson Bay, upwelling of deep, nutrient-rich waters replenishes surface nitrate, resulting in ‘open system’ conditions which tend to maintain nitrate δ¹⁵N at low and constant values, and these values are reflected in the sinking detritus. River inflow, which is constrained to inshore regions of Hudson Bay, appears to be a relatively minor source of nitrate compared to upwelling of deep waters. However, river inflow may contribute indirectly to enhanced inshore nutrient supply by supporting large-scale estuarine circulation and consequently entrainment and upwelling of deep water in this area. In contrast to previous proposals that Hudson Bay is oligotrophic because it receives too much fresh water (Dunbar, 1993), our results support most of the primary production being organized around the margin of the Bay, where river flow is constrained.     

Deposition and fate of reactive Fe,Mn, P,and C in suspended particulate matter in the Bay of Biscay

Hydrographic structure of the water column, dissolved nutrient concentrations and the distribution of suspended particulate matter were recorded from CDT measurements and Niskin bottles sampling on the continental slope of the Bay of Biscay and on the axis of Capbreton canyon. Ascorbate extraction was applied here for the first time on marine suspended particles to determine the content of reactive Fe- and Mn-oxides, and P associated with Fe-oxides. Hydrographic structure of the south-eastern part of the Bay of Biscay did not change during the last three decades. Particulate organic carbon (POC) contents dropped strongly with depth, showing that organic matter mineralization was efficient in the water column. Organic matter mineralized in the water column had a Redfield N:P ratio. POC percent of particles collected at depth were higher during a bloom period, suggesting that some new organic matter reached the bottom. Contents of Fe and Mn extracted with the ascorbate leaching solution showed that suspended particles originated from the Gironde estuary, one of the major sources of particles in the Bay of Biscay. Intermediate and deeper nepheloid layers occurred in the Capbreton canyon. Particles of nepheloid layers were enriched in Mn- and Fe-oxides because they originated from resuspension of surface sediment.     

Grain size characteristics of surface sediment and its response to the dynamic sedimentary environment in Qiantang Estuary,China

The composition and grain size characteristics of sediment in estuarine and coastal environments provide important information on the material source, hydrodynamic environment, environmental events,etc. However, few studies have focused on the sediment characteristics of the entire Qiantang Estuary,particularly, on the correlation between hydrodynamics and sediment properties. Through systematic sampling of the surface sediment in a large area of the Qiantang Estuary, the spatial distribution ch...     

Distribution and sources of polynuclear aromatic hydrocarbons in Mangrove surficial sediments of Deep Bay, China

Twelve sediment samples collected from three transects of mangrove swamp of Deep Bay, Shenzhen, China, were determined for polynuclear aromatic hydrocarbons (PAHs). The total PAHs concentrations ranged from 237 to 726 ng g(-1) dry weight, and showed strong correlation with total organic carbon (TOC), clay content and Pb concentrations. The highest PAHs concentrations were found in the samples from mangrove sediments. Overall, PAHs in Deep Bay sediment were lower than those in other developed areas. The biological effect due to PAHs alone in Deep Bay is expected to be low, based on the comparisons of individual and total PAHs concentrations determined in the sediment with those in USEPA sediment quality guidelines. Four and five-ring compounds dominated the PAHs composition pattern profiles. Principal component analysis (PCA) was applied to further investigate the source of PAHs. The PAH sources of Deep Bay mangrove swamp were suggested to be primarily combustion of fossil fuel, especially leaded-gasoline exhaust.