Seasonal and spatial variation in suspended matter,organic carbon,nitrogen, and nutrient concentrations of the Senegal River in West Africa

The Senegal River is of intermediate size accommodating at present about 3.5 million inhabitants in its catchment. Its upstream tributaries flow through different climatic zones from the wet tropics in the source area in Guinea to the dry Sahel region at the border between Senegal and Mauritania. Total suspended matter, particulate and dissolved organic carbon and nitrogen as well as nutrient concentrations were determined during the dry and wet seasons at 19 locations from the up- to downstream river basin. The aims of the study were to evaluate the degree of human interference, to determine the dissolved and particulate river discharges into the coastal sea and to supply data to validate model results. Statistical analyses showed that samples from the wet and dry season are significantly different in composition and that the upstream tributaries differ mainly in their silicate and suspended matter contents. Nutrient concentrations are relatively low in the river basin, indicating low human impact. Increasing nitrate concentrations, however, show the growing agriculture in the irrigated downstream areas. Particulate organic matter is dominated by C4 plants during the wet season and by aquatic plankton during the dry season. The total suspended matter (TSM) discharge at the main gauging station Bakel was about 1.93 Tg yr⁻¹ which is in the range of the only available literature data from the 1980s. The calculated annual discharges of particulate organic carbon (POC), dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) are 55.8 Gg yr⁻¹, 54.1 Gg yr⁻¹, and 5.3 Gg yr⁻¹, respectively. These first estimates from the Senegal River need to be verified by further studies.     

Characteristics and role of groundwater dissolved organic matter on arsenic mobilization and poisoning in Bangladesh

The fluorescence and molecular weight characteristics of dissolved organic matter (DOM) in groundwater of Bangladesh were investigated to evaluate its multiple roles on arsenic (As) mobilization and poisoning. Fluorescence properties of DOM were measured in groundwater samples collected from two As contaminated areas of Bangladesh (Faridpur at the Ganges floodplain and Sonargaon at the Meghna floodplain) from different locations and depths. The three dimensional excitation–emission matrix (3DEEM) fluorescence spectra of groundwater samples showed two characteristic peaks around Ex/Em = 335–365 nm/435–480 nm for fulvic-like peaks and peak at around Ex/Em = 275–290 nm/310–335 nm for the protein-like materials. The similarity of fluorescence spectra of groundwater and surface water of both the study areas with high intensity of fluorescence and its strong correlation with DOC reflect the in situ generation of fluorescent DOM from sedimentary organic matter (SOM) and recent recharge of terrestrial labile organic carbon into shallow aquifer. High performance size-exclusion chromatography (HPSEC) analysis of DOM shows positive correlations between fluorescence intensities (FI) of small molecular fractions (0.65 kDa) and As concentrations, with the signatures of protein-like peaks of DOM in groundwater. This result provides new evidence that small molecular weight fraction of DOM in groundwater of Bangladesh can play an important role on As mobilization and toxicity. In addition, high concentration of fluorescence materials in DOM of As contaminated groundwater of Bangladesh may pose a threat to public health.     

Occurrence of polycyclic aromatic hydrocarbons (PAHs) in seawater from the Western Taiwan Strait,China

Seawater samples (including surface water and bottom water) were collected from the Western Taiwan Strait (WTS) during June 24–25, 2009; polycyclic aromatic hydrocarbons (PAHs) in dissolved phase and particulate phase were analyzed, respectively. The results showed that the total concentrations of PAHs in the dissolved phase and particulate phase were ranged from 12.3 to 58.0 ng L⁻¹, and 10.3–45.5 ng L⁻¹, which showed a low-middle contamination level in the China Seas. The spatial variability of PAHs may be related to the complicated currents of WTS, especially the Min-Zhe coastal current. PAHs diagnostic ratios suggested that PAHs mainly originated from the inputs of pyrolytic (combustion) sources, which might be contributed to land-based atmospheric deposition. The particle-water partition coefficients of individual PAH showed that partitions were not correlated with suspended particulate matter content, dissolved organic carbon or salinity, similar to the Yangtze coastal area.     

Influence of tuna penning activities on soft bottom macrobenthic assemblages

The influence of tuna penning on soft bottom habitat present in the vicinity of tuna pens and at distances 200 m and 1.5 km away, was assessed by comparing attributes of macroinvertebrate assemblages and sediment quality before (November 2000, March 2001) and after (November 2001, April 2002) initiation of the activity. Results from November 2001 indicated a significant increase in sediment organic carbon and organic nitrogen, and a non-significant increase in the abundance of Capitellidae in the vicinity of the cages. Similar results were obtained 200 m from the cages but not 1.5 km away, where the only change was a significant increase in organic nitrogen in sediment. Results from April 2002 indicated no significant change in sediment organic carbon and organic nitrogen, however, mean sediment grain size decreased significantly in the immediate vicinity of the cages. Changes in attributes of the benthic assemblages and sediment resulted from accumulation of uneaten feed-fish on the seabed.     

Effects of oil dispersants on settling of marine sediment particles and particle-facilitated distribution and transport of oil components

This work investigated effects of three model oil dispersants (Corexit EC9527A, Corexit EC9500A and SPC1000) on settling of fine sediment particles and particle-facilitated distribution and transport of oil components in sediment-seawater systems. All three dispersants enhanced settling of sediment particles. The nonionic surfactants (Tween 80 and Tween 85) play key roles in promoting particle aggregation. Yet, the effects varied with environmental factors (pH, salinity, DOM, and temperature). Strongest dispersant effect was observed at neutral or alkaline pH and in salinity range of 0–3.5 wt%. The presence of water accommodated oil and dispersed oil accelerated settling of the particles. Total petroleum hydrocarbons in the sediment phase were increased from 6.9% to 90.1% in the presence of Corexit EC9527A, and from 11.4% to 86.7% for PAHs. The information is useful for understanding roles of oil dispersants in formation of oil-sediment aggregates and in sediment-facilitated transport of oil and PAHs in marine eco-systems.     

Optical signatures of dissolved organic matter in the watershed of a globally large river (Yangtze River,China)

Parallel factor analysis of fluorescence excitation emission matrices of surface water samples of a globally large river (Yangtze River, China) watershed identified three classes of fluorescent dissolved organic matter (FDOM) that had ex/em = 280/330 nm, 305/385 nm and 350/450 nm respectively, resembling “peak T”, “peak M” and “peak C” commonly identified in natural water, respectively. Peak T (a tyrosine/tryptophan-like FDOM) did not show correlations to peak M or C which were humic-like substances, while a positive correlation (r = 0.935, p < 0.001) was present between the natural log-transformed maximum fluorescence intensity (F_max) of peaks T and M indicating a tight link during their production and processing. F_max values (in Raman unit nm^?1) normalized to dissolved organic carbon (DOC) concentration were low, varying in ranges 15.93–85.95, 29.83–83.54 and 19.73–51.05 × 10^?5 nm^?1 (μmol/L)^?1 for peaks T, M and C, respectively, in line with the history of strong photobleaching of the water samples as indicated by fairly high absorption spectral slope ratios (0.75–1.53 with a mean 1.03). Intermediate fluorescence index (FI) (1.46–1.83 with a mean 1.61) and small specific absorption at 254 nm (0.64–1.93 with a mean 1.15 m^?1 mg^?1 L) of the water samples, indicated the presence of both aquatic microbial DOM (e.g. peak T) and soil DOM (e.g. peak C). Peak C could be substantially removed by UV-A (320–400 nm) irradiation, while peak M was slightly increased when a microbe-containing water was exposed to the same UV-A irradiation. Taken together, peak C was attributed to diffuse soil source while peak M was likely attributed to joint effects of microbial activities and solar irradiation on the chromophores in the sample.     

Determination of dissolved organic matter in streamwater using visible spectrophotometry

Absorbance at 360 nm was measured on 44 filtered streamwater samples of different dissolved organic matter (DOM) contents. A regression equation of DOM on absorbance predicted DOM with a standard error of estimate of 1.26 mgl^?1, Use of a published equation relating dissolved organic carbon (DOC) to absorbance gave DOC values for the samples which were consistent with measured DOM. The method offers considerable potential for rapid quantification of dissolved organic matter concentrations in streamwater.     

Natural radioactivity assessment of surface sediments in the Yangtze Estuary

The activities of the natural radionuclides (²³⁸U, ²³²Th, ²²⁶Ra and ⁴⁰K) of the surface sediments in the Yangtze Estuary were determined and used to evaluate radiation hazards in the study area. The of activities of ²³⁸U, ²³²Th, ²²⁶Ra and ⁴⁰K ranges from 14.1 to 62.3, 26.1 to 71.9, 13.7 to 52.3, and 392 to 898 Bq kg^? 1, respectively, which were comparable to values of other regions in China. The activities of ²³²Th, ⁴⁰K and ²²⁶Ra were clearly different from the global recommended values. The radium equivalent activity was less than the recommended limit of 370 Bq kg^? 1; therefore, the sediment in this area can be safely used for reclamation. The external hazard index values were less than one. The average absorbed gamma dose rate and annual effective dose equivalent values were slightly greater than the world average value. ²²⁶Ra/²³⁸U and ²³²Th/²³⁸U ratios could potentially be applied for tracing sediment source.     

Distributions of polychlorinated biphenyls in the Daliao River estuary of Liaodong Bay,Bohai Sea (China)

The distributions of 41 polychlorinated biphenyls (PCBs) were determined in the aqueous phase, suspended particulate matter (SPM), and sediment of the Daliao River estuary in Liaodong Bay, Bohai Sea (China). The total PCB concentrations ranged from 5.51 to 40.28 ng L⁻¹ in the surface water, from 6.78 to 66.55 ng L⁻¹ dry weight in the SPM, and from 0.83 to 7.29 ng g⁻¹ dry weight in the sediment. The PCB concentrations in water, SPM, and sediment were moderate relative to those reported for other estuary and marine systems around the world. Sedimentary PCB concentrations decreased offshore due to the active deposition of laterally transported river-borne particles. The predominance of the highly chlorinated congeners for the water, SPM, and sediment samples are an indication of either a lack of degradation or the presence of nearby or recent releases into the environment.     

Organic diagenesis in sediment and its impact on the adsorption of bisphenol A and nonylphenol onto marine sediment

Hydrophobic organic contaminants in marine water are mostly adsorbed onto (partitioned into) sediment organic matter (SOM). To study the impact of SOM diagenesis on sediment adsorption properties, artificial sediment with rich SOM content was incubated for more than 120 days. The sediment was sampled every week, and batch sediment adsorption tests were conducted with bisphenol A (BPA) and nonylphenol (NP) as the model pollutants. The results show that the amount of organic matter loaded in the sediment decreased by nearly 80% during incubation. For the incubated sediment, the BPA partition coefficient, K_d, decreased whereas the organic normalized partition coefficient, K_oc, more than doubled. The experiments with NP show an even greater increase in K_oc. Organic matter diagenesis shows a profound effect on the adsorption behavior of sediment, as the SOM residue has an increasing affinity and partition capacity for organic contaminants.     

Baseline survey of sediments and marine organisms in Liaohe Estuary: Heavy metals,polychlorinated biphenyls and organochlorine pesticides

A geographically extensive investigation was carried out to analyze the concentrations of heavy metals, PCBs and OCPs in the sediments and marine organisms collected from the Liaohe Estuary. In order to determine the spatial distribution and potential ecological risk of heavy metals, the surface sediments were collected from 44 sites in the Liaohe Estuary. The results showed that the heavy metal contents in the sediments were observed in the following order: Cr (11.2–84.8 mg/kg) > Cu (1.7–47.9 mg/kg) > Pb (4.3–28.3 mg/kg) > As (1.61–12.77 mg/kg) > Cd (0.06–0.47 mg/kg) > Hg (0.005–0.113 mg/kg). In comparison with the concentrations of heavy metals and POPs in other regions, the concentrations of As, Pb and DDTs in the Liaohe Estuary were generally low, and other pollutant concentrations were inconsistent with those reported in other regions. The contamination factor (CF), the pollution load index (PLI), the geoaccumulation index and the potential ecological risk index were used to analyze the pollution situation, which showed that the heavy metal pollution in Liaohe Estuary is mainly dominated by Cd and Hg. The concentrations of the four heavy metals varied significantly in the three kinds of tested organisms (fish, mollusk and crustacean), indicating the different accumulative abilities of the species. The results obtained in this study provide useful information background information for further ecology investigation and management in this region.     

Interactive influence of water level,sediment heterogeneity,and plant density on the growth performance and root characteristics of Carex brevicuspis

Water level, sediment heterogeneity, and plant density are important factors that determine plant growth, distribution, and community structure. In the present study, we investigated the effects of these factors on the growth and root characteristics of Carex brevicuspis. We conducted an outdoor experiment to monitor biomass accumulation and allocation, relative root distribution mass ratio, longest root length, and total N and P contents of C. brevicuspis plants. We used a factorial design with two water levels (0 cm and −15 cm relative to the soil surface, named high and low water level treatments, respectively), three sediment types (sand/clay sediment with 0–15 cm of sand and 15–30 cm of clay; mixed sediment with 0–30 cm mixture of sand and clay with 1:1 volumw ratio; and clay/sand sediment with 0–15 cm of clay and 15–30 cm of sand), and three plant densities (88 plants per m², 354 plants per m², and 708 plants per m²). Biomass accumulation decreased with increasing plant density and was significantly higher in the low water level and the clay/sand sediment than in the high water level and the other two sediment types. The shoot:root ratio was markedly higher in the high water level than in the low water level and decreased with increasing plant density; further, in the high water level, it was significantly lower in the sand/clay sediment than in the other two sediment types. The relative root distribution mass ratio was markedly higher in the high water level treatments than in the low water level treatments. Further, in the high water level treatments, the relative root distribution mass ratio increased with increasing plant density in the clay/sand sediment and was lower in the sand/clay sediment than in the other two sediment types. The longest root length was significantly lower in the high water level than in the low water level and increased with increasing plant density in the sand/clay sediment in the high water level. Total N content in the plants was influenced only by sediment type; on the other hand, total P content was markedly higher in the high water level than in the low water level. Our data indicate that growth of C. brevicuspis was limited by higher water level, higher density and sand/clay sediment. Plants can increase shoot:root ratio and develop shallow root system to acclimate to high water level and thus could adjust shoot:root ratio and root characteristics, e.g. decrease their shoot:root ratio and allocating more root and increasing root length to the nutrient rich layer to acclimate to conditions of higher density and sediment heterogeneity.     

Sediment–seawater solute flux in a polluted New Zealand estuary

We investigated the sediment–seawater solute flux at five sites in the polluted Avon–Heathcote Estuary, New Zealand, to provide a point of comparison for future studies of the effects of the closure of a major wastewater outfall into the estuary. Sediments collected in winters 2007 and 2008, and summer 2008, ranked consistently in organic matter content. Microelectrode profiling and sediment-core incubations revealed (1) a dominant role of microphytes in regulating solute flux causing significant differences in the dark and light sediment O₂ consumption (R_d, R_l), total sediment O₂ utilisation (TOU_d, TOU_l), and inorganic nutrient flux, (2) consistent ranking of sites in solute flux, and (3) a clear solute-flux signature of the wastewater effluent. Sediment near the wastewater outfall exhibited the highest absolute R and TOU_, the lowest ratio R_l/R_d, the highest dark efflux of dissolved reactive phosphorus and ammonium, and the highest dark and light uptake of nitrate + nitrite.     

云南阳宗海表层沉积物有机质组成结构对磷赋存形态特征的影响

利用连续提取分级的方法定量分析阳宗海表层沉积物磷赋存形态,阐明了沉积物C、N、H和O组成及溶解有机质(DOM)紫外-可见光谱特征,探讨沉积物元素组成及DOM组成结构对不同形态磷含量的影响.结果表明:(1)沉积物潜在可移动磷含量在68.67~124.70 mg/kg之间变化,平均占总磷含量的9.81%,表现为BD-PNa OH-nr PNH_4Cl-P;沉积物稳定磷含量在496.73~908.28 mg/kg之间变化,平均占总磷含量的60.86%.(2)沉积物C、N含量和疏水性DOM光谱参数A_(240-400)表现出北部高、南部低的变化趋势,但H/C、O/C和(N+O)/C摩尔比和亲水性DOM光谱参数A_(240-400)变化趋势则与之恰好相反.(3)沉积物NH4Cl-P含量与C、N和H含量之间呈显著正相关,但与H/C、O/C、(N+O)/C摩尔比和亲水性DOM光谱参数E_2/E_3值之间呈显著负相关;NaOH-rP和BD-P+NaOH-rP含量均与O含量及O/H摩尔比呈显著负相关;NaOH-rP、BD-P+NaOH-rP和HCl-P均与疏水性DOM光谱参数A_(240-400)值之间呈显著正相关.因此,天然有机质元素组成及官能团结构是影响沉积物磷赋存形态的重要因素.     

Application of generalized contaminant retardation factor to a multi‐phase system

In this study, a generalized contaminant retardation factor applicable to a multiphase system where various types of colloids exist simultaneously with contaminants is derived and incorporated into an equilibrium model which is successfully applied to experimental data for which phenanthrene was used as hydrophobic organic contaminants and dissolved organic matter (DOM) or bacteria as mobile carriers. Based on the parameter values for the experimental data regarding the association of phenanthrene with solid matrix, DOM and various bacterial isolates, numerical experiments are performed to examine the transport behaviour of hydrophobic organic contaminants in various types of the multiphase system. Numerical experiments demonstrate that the extent of contaminant transport enhancement depends on the adsorption affinity of the colloid, its concentration and its mobility, and that the importance of a third phase to contaminant transport needs to be evaluated carefully with respect to the relevance of experimental conditions applied to realistic environmental conditions. Copyright © 2003 John Wiley & Sons, Ltd.     

Comparison of sediment transport computations using hydrodynamic versus hydrologic models in the Simiyu River in Tanzania

This paper presents the results of a study that compares the sediment routing of the Simiyu River using the hydrologic model, Soil and Water Assessment Tool (SWAT) and the 1D hydrodynamic simulation software for Rivers and Estuaries (SOBEK-RE) model. Routing in SWAT is completed using the simplified Bagnold’s equation and in the SOBEK-RE model is undertaken using the Saint Venant equation. The upstream boundary conditions for the routing modules were derived from the subcatchments sediment yields that were estimated by SWAT using the Modified Universal Soil Loss Equation (MUSLE). The sediment loads extrapolated or interpolated from the sediment rating curve for the catchment outlet were used for calibration and validation purposes. The SWAT model predicted an erosion rate of 2.09 Mt/yr. The total sediment load transported to the main outlet of the catchment simulated by the SWAT and SOBEK-RE models was equal to 2.94 and 2.72 Mt/yr, respectively. Thus the models computed a net erosion in the channels of 0.84 Mt/yr (SWAT) and 0.63 Mt/yr (SOBEK-RE). When comparing the results of the models for the different reaches of the main channel and main tributaries, the models showed different results both in magnitude and in sign (erosion/deposition). However, in a situation where data is scarce (such as grain size, channel geometry), the more complex hydrodynamic model does not necessarily lead to more reliable results.     

Sediment dynamics in the mudbank of the Yangtze River Estuary under regime shift of source and sink

The southeastern portion of the Yangtze River Estuary (or Yangtze Estuary) was considered to be the deposition center and the mudbank of the Yangtze River Delta.As the fluvial sediment supply began to decline in the 1980s and the reduction accelerated after the completion of the Three Gorge Dam in 2003,more fluvial sediment was trapped decreasing the suspended sediment concentration (SSC) environment in the river mouth area.Moreover,the accretion rate of the mudbank has slowed down in recent dec...     

Land–ocean distribution of allochthonous organic matter in surface sediments of the Chiloé and Aysén interior seas (Chilean Northern Patagonia)

We investigated the relative distribution of allochthonous (i.e., terrigenous) organic matter in the complex, continuous, river–fjord–sound–channel–gulf system of Chile’s North Patagonia (41.5–46.5°S) in order to establish whether this organic matter can reach the open ocean or whether it is largely retained near its fluvial sources. Grain size distribution, total organic carbon and total nitrogen contents, and carbon stable isotope contents (δ¹³C) were quantified in 53 surface sediment samples collected during the CIMAR Fiordos cruises 1, 4, 8, and 10, as were salinity and silicic acid concentrations in the surface waters. A principal component analysis segregated the Chiloé and Aysén interior seas into two zones: (i) the continental fjords, with sediment enriched in allochthonous organic matter, having higher C:N molar ratios (10–14) and lower δ¹³C composition (?23‰ to ?27‰); and (ii) the channels and gulfs, with a prevalent autochthonous marine source, having lower C:N values (6–10) and higher δ¹³C composition (?20‰ to ?23‰). Estuarine waters with low salinity (2–30) and high silicic acid (10–90 μM) were associated with high C:N ratios and low δ¹³C in surface sediments, meaning that terrestrial organic matter was transported up to the mouth of the continental fjords. A two-source mixing model confirmed that allochthonous (terrestrial) organic matter contents (50–90%) associated with local river discharges were present within the continental fjords. On the contrary, autochthonous (marine) organic matter was prevalent (50–90%) at the sites in the marine influenced channels, sounds, and gulfs.     

Environmental behavior of organotin compounds in the coastal environment of Xiamen,China

In 2006, organotins pollution were investigated in the coastal environment of Xiamen, China. Six species of organotin compounds including tributyltin, triphenyltin and their degradation compounds were quantified in the dissolved and particulate phases of the water, and in the sediment using GC-FPD. The concentrations of organotin compounds ranged from 2.2 to 160 ng (Sn) L⁻¹ dissolved in the water, 0.14–6.7 ng (Sn) L⁻¹ in suspended particulate matter and nd ∼ 26 ng (Sn) g⁻¹ (dry weight) in the sediment. The highest concentration of total organotin or tributyltin in water was found in a shipyard and at a station near the inlet of the harbor, indicating fresh inputs of antifouling paints to Xiamen’s coastal environment. Organotin speciation was performed on sediment cores to investigate contamination trends over the past ten years in the harbor. The results of ²¹⁰Pb dating indicated that Xiamen western harbor suffered contamination during 2000. The environmental behavior of organotins such as the enhancement of the microlayer, partitioning between water/suspended particulate matter and between water/sediment are also discussed in this paper.     

Adsorption behaviour of dibutyl phthalate on marine sediments

Laboratory experiments were carried out to investigate the adsorption behaviour of dibutyl phthalate (DBP) on marine sediments collected from five different sites in Victoria Harbour, Hong Kong. DBP adsorption can be well described by the Langmuir isotherm. The maximum DBP adsorption capacity (Q_max) of the marine sediments ranges from 53 to 79 mg g⁻¹, which has a positive correlation with their organic content. Around 90% of the organic can be removed from the sediments with treatment by H₂O₂ oxidation, and the Q_max then decreases to a range between 13 and 22 mg g⁻¹. The black carbon content of the sediments has a much greater DBP adsorption capacity than does the natural organic matter of the sediments. The amount of DBP adsorbed on the sediments increases as the salinity of the marine water increases.