Carbon and nitrogen composition and stable isotope as potential indicators of source and fate of organic matter in the salt marsh of the Changjiang Estuary, China

Elemental (TOC, TN, C/N) and stable carbon and nitrogen isotopic (delta(13)C, delta(15)N) compositions were measured for surface sediments, three sediment vibrocores, plants, and suspended particulate matter (SPM) collected from salt marsh of the Changjiang Estuary. The purpose of this study is to characterize the sources of organic matter in sediments and to further elucidate the factors influencing the isotope signature in the salt marsh. Our results indicate that organic matter preserved in the sediments is predominantly controlled by the particulate organic matter in the Changjiang Estuary. The in situ contribution of marsh plants carbon to sediment organic matter is clearest in the high marsh, where the low delta(13)C of the plants (-28.1 per thousand) is reflected by a sediment delta(13)C (-24.7 per thousand) lower than values found for the low marsh and bare flat sediments (-23.4 per thousand and -23.0 per thousand, respectively). The effect of grain size on the spatial difference of isotope composition in the marsh sediments is insignificant, based on the observation that similar isotope values are found in different size particles, both for delta(13)C and delta(15)N. Nutrient utilization by plant assimilation, however, shows great impact on the surface sediment delta(15)N composition, due to the isotope fractionation. With extensive plant coverage and the consequent low surface water nitrate concentration, delta(15)N values of the high marsh surface sediments show (15)N enrichment.     

Fate and effects of heavy metals in salt marsh sediments

The fate and effects of selected heavy metals were examined in sediment from a restored salt marsh. Sediment cores densely covered with Spartina patens were collected and kept either un-amended or artificially amended with nickel (Ni) under standardized greenhouse conditions. Ni-amendment had no significant effect on the fate of other metals in sediments, however, it increased root uptake of the metals. Metal translocation into the shoots was small for all metals. Higher Ni concentrations in plants from amended cores were accompanied by seasonal reductions in plant biomass, photosynthetic capacity and transfer efficiency of open photosystem II reaction centers; these effects, however, were no longer significant at the end of the growing season. Root colonization by arbuscular mycorrhizal fungi (AMF) resembled that of natural salt marshes with up to 20% root length colonized. Although Ni-amendment increased AMF colonization, especially during vegetative growth, in general AMF were largely unaffected.     

Effect of overlying water pH, dissolved oxygen, salinity and sediment disturbances on metal release and sequestration from metal contaminated marine sediments

Experiments were undertaken to examine the key variables affecting metal release and sequestration processes in marine sediments with metal concentrations in sediments reaching up to 86, 240, 700, and 3000 mg kg(-1) (dry weight) for Cd, Cu, Pb and Zn, respectively. The metal release and sequestration rates were affected to a much greater extent by changes in overlying water pH (5.5-8.0) and sediment disturbance (by physical mixing) than by changes in dissolved oxygen concentration (3-8 mg l(-1)) or salinity (15-45 practical salinity units). The physical disturbance of sediments was also found to release metals more rapidly than biological disturbance (bioturbation). The rate of oxidative precipitation of released iron and manganese increased as pH decreased and appeared to greatly influence the sequestration rate of released lead and zinc. Released metals were sequestered less rapidly in waters with lower dissolved oxygen concentrations. Sediments bioturbated by the benthic bivalve Tellina deltoidalis caused metal release from the pore waters and higher concentrations of iron and manganese in overlying waters than non-bioturbated sediments. During 21-day sediment exposures, T. deltoidalis accumulated significantly higher tissue concentrations of cadmium, lead and zinc from the metal contaminated sediments compared to controls. This study suggests that despite the fact that lead and zinc were most likely bound as sulfide phases in deeper sediments, the metals maintain their bioavailability because of the continued cycling between pore waters and surface sediments due to physical mixing and bioturbation.     

Total mercury and methylmercury in freshwater and salt marsh soils of the Mississippi river deltaic plain

Mercury entering wetland environments can be microbially methylated to methylmercury. The purpose of this study was to investigate the historical rate of mercury accumulation and distribution of total and methylmercury in soil profile of Louisiana coastal marshes. Two sediment cores each were taken from Louisiana freshwater marsh and salt marsh. Vertical accretion was determined using the 137Cs dating technique. Total and methylmercury were determined with depth in the soil profiles. The fresh marsh soil on a dry weight basis contained more total and methylmercury than the salt marsh. Average vertical accretion rates in freshwater marsh and salt marsh were 0.90 and 0.75 cm year(-1), respectively. Average total and methylmercury content (to a depth of 30 cm) was 140 and 4.19 microg kg(-1) and 80 and 1.34 microg kg(-1) for the fresh and salt marsh, respectively. Due to greater sediment input resulting in a higher bulk density the salt marsh contained more total mercury per m2 (to 30 cm depth) than the fresh water marsh (5340 microg m(-2) as compared to 2929 microg m(-2)). The amount of methylmercury per m2 to depth of 30 cm was approximately the same for each marsh.     

Halophyte vegetation influences in salt marsh retention capacity for heavy metals

We analysed concentrations of Cu, Cd and Pb in above and belowground tissues of the halophyte species Halimione portulacoides and Spartina maritima, as well as in sediments and pore water between the roots in a Tagus estuary salt marsh (Portugal). From these results we calculated the pools of metals in the compartments mentioned above. Relative percentages of accumulation in each pool were also determined. Our aim was to determine how the type of vegetation in the salt marsh affects overall metal retention capacity of the system. It was concluded that areas colonised by H. portulacoides are potential sources of Cu, Cd and Pb to the marsh ecosystem, whereas areas colonised by S. maritima are more effective sinks at least for Cu and Cd. Consequently, S. maritima seems to contribute more effectively to the stabilisation of metals in salt marsh sediments, reducing their availability to the estuarine system.     

Mercury accumulation in surface sediments of salt marshes of the Bay of Fundy

Mercury contamination in Canada's Bay of Fundy is a priority concern because of elevated levels observed in fish, birds and wildlife. Salt marshes constitute an important part of the Bay's coastline and are potential stores of mercury for the region. We measured the amount of mercury accumulated over a 5-yr period from 1997 to 2002 in surface sediments of seven salt marshes along the New Brunswick coast of the Bay. The seven study sites extended from outer to inner Bay, spanning a gradient in tidal range (6-12 m) and sediment characteristics such as %LOI (4-29%) and sediment deposition rate (0.27-1.76 cm yr(-1)). In each study site, mercury was measured in low and high marsh areas. Sediment mercury concentrations ranged from 7 to 79 ng g(-1) and loading rates ranged from 0.1 to 1.1 mg m(-2). Total estimated 5-yr storage of mercury in salt marsh sediments of the Bay is 854+/-465 kg. We also compared sediment mercury loading to atmospheric inputs measured at a deposition monitoring station operating in New Brunswick from 1997 to 2002 and found that direct atmospheric deposition appears to be a minor input of mercury to these sediments. We are unaware of documentation of mercury loading in salt marshes on a bay-wide scale and over a constrained (5-yr) time period elsewhere.     

Influence of Spartina alterniflora on the mobility of heavy metals in salt marsh sediments of the Yangtze River Estuary, China

Using bio-disturbed sulphide to trace the mobility and transformation of Cu, Pb, Ni and Zn in the sediments of the Spartina alterniflora-dominated salt marsh in the Yangtze River Estuary, measurements were made of the seasonal variations of acid-volatile sulphide (AVS) and of the simultaneously extracted metals (SEM) in the rhizosphere sediments. Microcosm incubation experiments recreating flooding conditions were conducted to evaluate the effect of AVS and other metal binding phases upon the dynamics of Cu, Pb, Ni and Zn in the salt marsh sediments. The results demonstrate that the ratio values of SEM/AVS have a significant seasonal variation in the rhizosphere sediments and that the anoxic conditions in the sediments were likely enhanced by S. alterniflora during the summer and autumn compared with the anoxic conditions resulting from the native species Phragmites australis and Scirpus mariqueter. The incubation experiments suggest that Fe(III) and Mn(IV/III) (hydr)oxides provide important binding sites for heavy metals under oxic conditions, and sulphide provides important binding sites for the Cu and Pb under anoxic conditions. Our observations indicate that the mobility of heavy metals in the salt marsh sediments is strongly influenced by biogeochemical redox processes and that the invasive S. alterniflora may increase the seasonal fluctuation in heavy metal bioavailability in the salt marsh ecosystem.     

Fluorescence of sediment humic substance and its effect on the sorption of selected endocrine disruptors

Humic substances (HS) have a critical influence on the sorption of organic contaminants by soils and sediments. This paper describes investigations into the sorption behavior of three representative endocrine disruptors, bisphenol A (BPA), 17beta-estradiol (E2), and 17alpha-ethynylestradiol (EE2), onto sediments and HS extracted sediments using a batch technique. The organic carbon-normalized partition coefficients (K(oc)) for the extracted HS (K(oc)(hs)) were calculated, and the fluorescence spectra of the HS extraced from different sediment samples were gained using excitation/emission matrix (EEM). Particular attention was paid to the correlations between the fluorescence characteristics of HS and the log K(oc)(hs) of selected endocrine disruptors. The results show that the log K(oc)(hs) values range from 3.14 to 4.09 for BPA, from 3.47 to 4.33 for E2, and from 3.65 to 4.32 for EE2. Two characteristic excitation-emission peaks were observed for HS samples extracted from sediments. They are located at Ex/Em=250-260 nm/400-450 nm (peak alpha') and Ex/Em=310-330 nm/390-400 nm (peak alpha) respectively. The alpha' and alpha peak relative intensities I(alpha')/I(alpha) vary from 0.46 to 1.64 for different extracted HS samples. The similarity between fulvic acids (FA) Ex/Em pairs and those observed for HS indicates that FA is the predominant fraction of HS extracted from sediments. Moreover, the log K(oc)(hs) values of BPA, E2, and EE2 have a negative linear correlation to I(alpha')/I(alpha) values. Peak alpha is often attributed to relatively stable and high molecular weight aromatic fulvic-like matter. Therefore, the result presented here reveals that the abundance of aromatic rings in HS molecular structure plays a critical role in the sorption of selected endocrine disruptors.     

Effects of storage method and duration on the toxicity of marine sediments to embryos of Crassostrea gigas oysters

The objective of laboratory sediment bioassays is to estimate in situ toxicity. This goal is difficult to achieve, as one of the main limitations of sediment toxicity tests is disruption of sediment geochemistry during sampling, handling and preservation. The effects of storage on the estimation of marine sediment toxicity to Crassostrea gigas embryos and larvae were investigated. Three storage methods and four storage periods were compared with three different sediment types contaminated by heavy metals, polycyclic aromatic hydrocarbons (PAHs) and both contaminants. Freezing and freeze-drying considerably increased the toxicity of decanted sediments and their elutriates as compared to the toxicity obtained with fresh sediments. Concerning the elutriates, the toxicity found with frozen and freeze-dried sediments was correlated with DOC, ammonia and PAH contents. However, the toxicity of fresh sediments kept at 4 degrees C increased with increasing duration of storage and was also correlated with the amount of ammonia in the elutriates.     

Chemical characteristics of chromophoric dissolved organic matter in rainwater

Proton nuclear magnetic resonance (¹H-NMR), UV absorbance and excitation-emission matrix (EEM) fluorescence spectroscopy were used to define the chemical characteristics of chromophoric dissolved organic matter (CDOM) in whole and C₁₈ extracted rainwater. The average total recovery of fluorescence determined from the sum of extract and filtrate fractions relative to the whole was 86% suggesting that 14% of fluorescent CDOM in rainwater is comprised of very hydrophobic material that cannot be eluted from the column. Half the fluorescence of rainwater was recovered in the filtrate fraction which is important because it suggests that 50% of the chromophoric material present in precipitation is relatively hydrophilic. The average spectral slope coefficient was smaller in extracted samples (16.3 ± 9.0 μm^?1) relative to whole samples (18.9 ± 2.8 μm^?1) suggesting that the extracted material contains larger molecular weight material. Approximately one-third of the total dissolved organic carbon (DOC) in rainwater exists in the extract fraction suggesting that a large percentage of the uncharacterized DOC in rainwater can be accounted for by these hydrophobic macromolecular species. The fluorescence of extracted samples is strongly correlated with total NMR integration and is most sensitive to aromatic protons suggesting that molecules in this region are the most important in controlling the optical properties of rainwater. The lower removal efficiency of CDOM in rainwater relative to surface waters or the water-soluble fraction of aerosols during solid phase extraction (SPE) suggests that rainwater contains significantly more hydrophilic chromophoric compounds which are compositionally different than found in these other aquatic matrices.     

Long-term effects of mercury in a salt marsh: hysteresis in the distribution of vegetation following recovery from contamination

During four decades, the Ria de Aveiro was subjected to the loading of mercury from a chlor-alkali industry, resulting in the deposition of several tons of mercury in the sediments. The present study evaluates the impact of this disturbance and the recovery processes, temporally and spatially, by means of examining the richness of the species of salt marsh plants and mercury concentrations in sediments over the last fifty years. The temporal assessment showed that the mercury loading induced a shift in the species composition of the salt marsh from a non-disturbed salt marsh with higher species richness to an alternative state dominated by Phragmites australis. The horizontal assessment, through a mercury gradient, presents the same trend, indicating that P. australis is the species most tolerant to higher mercury concentrations, comparative to Halimione portulacoides, Arthrocnemum fruticosum, Triglochin maritima, Juncus maritimus and Scirpus maritimus. After the reduction of mercury discharges in 1994, the salt marsh shows a slowly return path recovery response. The hysteresis in the response results in the temporal gap between the reduction in mercury concentrations in the sediment and the salt marsh species richness response, comparatively to the existing diversity in the local reference marsh.     

Fractionation and spectroscopic properties of fulvic acid and its extract

Novel results were obtained when a fulvic acid was isolated from Acros humic acid and fractionated by traditional preparative thin-layer chromatography. Eight colorful bands were directly viewed and analyzed showing very different fluorescence and absorption properties. The fluorescence quantum yield of the bands ranged from 2% to 9.4%, significantly higher than that of natural humic substances. An aqueous fulvic acid solution was also extracted with methylene chloride (CH(2)Cl(2)) by continuous liquid-liquid extraction. The CH(2)Cl(2) extract was further fractionated by thin-layer chromatography. Eleven highly fluorescent colorful bands and six weakly fluorescent bands were observed and examined. UV-vis absorption and fluorescence (including 3D matrix) spectra and fluorescence quantum yields revealed that each band still represented a mixture of compounds. Moreover, substantial differences in optical properties were observed among bands. A single band possessed the highest fluorescence quantum yield (6%) and highest specific fluorescence (fluorescence/mass), and accounted for 21% of the total fluorescence of the extract. The mass of individual bands varied from 1.6% to 14.1% of the total materials recovered. Components of all fractions were grouped into 11 fluorophore families according to their maxima on 3D matrix fluorescence spectra. No component is dominant in the whole fulvic acid or extracted portion in terms of optical properties. Over 40 natural products are proposed for model chromophores.     

Fate and effects of nutrients and heavy metals in experimental salt marsh ecosystems

Fate and effects of the macro nutrients nitrogen and phosphorus, and the heavy metals zinc, copper and cadmium, brought into experimental salt marsh ecosystems via sediment supply, were studied over a three-year period. The supply of sediment from the Marsdiep (at a low and high rate) and from the harbour of Delfzijl (at a high rate) led to an increase of the macro nutrients and heavy metals in the top soil. The growth of the salt marsh plants Aster tripolium, Puccinellia maritima and Spartina anglica and the uptake of the macro nutrients and heavy metals by the plants was only slightly affected by the addition of sediment. A high load of sediment led to an increase in growth or in the concentrations of the macro nutrients or heavy metals in the plants at a number of sampling dates, but only minor differences between treatments were found. From a mass balance constructed over a three-year study period it could be concluded that about 50% of the macro nutrients and heavy metals were retained in the salt marsh sediment. This was equal to the retained amount of organic matter, indicating that retention of the elements was closely related to retention of organic matter. The 50% loss of the macro nutrients and heavy metals probably occurred via ebb tides after resuspension of sediment and organic matter.     

Long-term copper partitioning of metal-spiked sediments used in outdoor mesocosms

Understanding the effects of sediment contaminants is pivotal to reducing their impact in aquatic environments. Outdoor mesocosms enable us to decipher the effects of these contaminants in environmentally realistic scenarios, providing a valuable link between laboratory and field experiments. However, because of their scale, mesocosm experiments are often complex to set up and manage. The creation of environmentally realistic conditions, particularly when using artificially contaminated sediment, is one issue. Here, we describe changes in geochemistry over 1.5 years of a sediment spiked with four different concentrations of copper, within a large freshwater mesocosm facility. The spiking procedure included proportional amendments with garden lime to counteract the decreases in pH caused by the copper additions. The majority of copper within the spiked mesocosm sediments partitioned to the particulate phase with low microgram per liter concentrations measured in the pore waters and overlying waters. The minimum partition coefficient following equilibration between pore waters and sediments was 1.5?×?10⁴ L/kg, which is well within the range observed for field-contaminated sediments (1?×?10⁴ to 1?×?10⁶ L/kg). Recommendations are made for the in situ spiking of sediments with metals in large outdoor mesocosms. These include selecting an appropriate sediment type, adjusting the pH, allowing sufficient equilibration time, and regular mixing and monitoring of metal partitioning throughout the experimental period.     

Alkaline hydrolysis of humic substances--spectroscopic and chromatographic investigations.

To find out more on the structure of humic substances (HS), isolated dissolved organic carbon (DOC) samples from a brown water lake and a wastewater effluent were fractionated and subjected to alkaline hydrolysis. UV/Vis and fluorescence spectroscopy, as well as size-exclusion chromatography with on-line detection of UV absorption, fluorescence and DOC concentration were used to investigate the structural changes caused by the hydrolysis reaction. Following hydrolysis, the fluorescence intensity increased considerably despite a decrease in the UV absorption. The UV absorption and the DOC data from the SEC experiments revealed a strong shift to smaller molecular sizes after hydrolysis. The spectra of the hydrolysed samples, as well as the size-exclusion chromatograms, were compared to spectra of hydroxybenzoic acids and hydroxycinnamic acids. From this comparison, it can be concluded that the hydrolysis products have a structure similar to these organic acids.     

Mercury in contaminated sediments and pore waters enriched in sulphate (Tagus Estuary,Portugal)

Three sediment cores, collected nearby the effluent of a chlor-alkali industry, were sliced in 0.5-cm layers and centrifuged for pore water extraction. Mercury, Fe and Mn were determined in the solids as total concentration, hydroxylamine extractable fraction and HCl extractable fraction. Sulphur was determined in the HCl extraction. Total and reactive mercury, chlorinity, S(2-), SO(4)(2-), total Fe, and total Mn were measured in pore waters. The solids contained 3.0-60 nmol g(-1) of total Hg and pore waters 70-5800 pM of total Hg and 1.8-76 pM of reactive mercury. Pore waters presented 2.3-94 times more sulphate than the overlying estuarine waters due to the input from the industry. In layers where hydroxylamine extractable Fe exhibited a broad maximum (precipitation of Fe-oxides) sulphate was reduced to S(2-). The competition between the high content of SO(4)(2-) and Fe(III) as electron acceptors, in chemical reactions occurring in the upper sediments, may explain the co-existence of S(2-) and Fe-oxides in the same layers. Mercury was detected in the hydroxylamine extracts (20-29 nmolg(-1)) in the layers where Fe-oxides were formed, and reactive dissolved Hg showed minimum concentrations. The excess of sulphate in pore waters favoured the abundant Fe-oxides in the upper solid sediments, which appear to work as a barrier limiting the escape of mercury to the water column.     

The origin of speciation: trace metal kinetics over natural water/sediment interfaces and the consequences for bioaccumulation

The speciation of heavy metals was measured over a variety of natural and undisturbed water/sediment interfaces. Simultaneously, two benthic species (oligochaete Limnodrilus spp. and the midge Chironomus riparius) were exposed to these sediments. Under occurring redox conditions, free ion activities of trace metals Cd, Cu, Ni, Pb, and Zn were measured with a chelating exchange technique, while geochemical conditions (i.e., redox) remained in tact. Free ion activities were compared with total dissolved concentrations in pore waters and surface waters in order to relate speciation to bioaccumulation. Limnodrilus spp. and C. riparius have accumulation patterns that could be linked to time-dependent exposure concentrations, expressed as chemical speciation, in the surface water and the sediment's pore water. Concentrations of free metal ions in the overlying surface water, rather than in sediment pore water, proved to be the best predictor for uptake. For the first time, measurements are obtained from sediments without disturbing physical-chemical conditions and thus bioavailability, a major restriction of other studies so far.     

Toxicity and heavy metal contamination of surficial sediments from the Bay of Thessaloniki (Northwestern Aegean Sea) Greece

Surficial sediments (the fraction < 2000 microm) from the Bay of Thessaloniki, in the Northwestern Aegean Sea, Greece were examined for heavy metal and organic carbon contents, as well as for acute LUMIStox toxicity of pore waters (PWs), wet sediment elutriates (WSEs) and dry sediment elutriates (DSEs) obtained from the solid material remaining after PW extraction. WSEs where not toxic. EC20/50 values could be measured in some DSE and PW samples. In all sediment samples, the DSE toxicity was greater than the corresponding PW toxicity. Sediment concentrations of total and labile Cd, Pb, Cu, Cr, Zn, Mn, Ni and Fe were determined and evaluated in relation to sediment quality guidelines. Pollution levels ranged from low to high for certain metals. A misfit between sediment toxicities calculated from heavy metal concentrations and those biologically measured was observed. Toxicity values were in general poorly correlated with sediment's heavy metal or organic carbon content. As significant correlation was however found between the DSE toxicity with total Ni and labile Fe, as well as for the PW toxicity with total Ni, labile Fe and labile Cr.     

Net methylmercury production as a basis for improved risk assessment of mercury-contaminated sediments

Sediments contaminated by various sources of mercury (Hg) were studied at 8 sites in Sweden covering wide ranges of climate, salinity, and sediment types. At all sites, biota (plankton, sediment living organisms, and fish) showed enhanced concentrations of Hg relative to corresponding organisms at nearby reference sites. The key process determining the risk at these sites is the net transformation of inorganic Hg to the highly toxic and bioavailable methylmercury (MeHg). Accordingly, Hg concentrations in Perca fluviatilis were more strongly correlated to MeHg (p < 0.05) than to inorganic Hg concentrations in the sediments. At all sites, except one, concentrations of inorganic Hg (2-55 microg g(-1)) in sediments were significantly, positively correlated to the concentration of MeHg (4-90 ng g(-1)). The MeHg/Hg ratio (which is assumed to reflect the net production of MeHg normalized to the Hg concentration) varied widely among sites. The highest MeHg/Hg ratios were encountered in loose-fiber sediments situated in southern freshwaters, and the lowest ratios were found in brackish-water sediments and firm, minerogenic sediments at the northernmost freshwater site. This pattern may be explained by an increased MeHg production by methylating bacteria with increasing temperature, availability of energy-rich organic matter (which is correlated with primary production), and availability of neutral Hg sulfides in the sediment pore waters. These factors therefore need to be considered when the risk associated with Hg-contaminated sediments is assessed.     

Remediation potential of caffeine,oxybenzone, and triclosan by the salt marsh plants <Emphasis Type="Italic">Spartina maritima</Emphasis> and <Emphasis Type="Italic">Halimione portulacoides</Emphasis>

Pharmaceuticals and personal care products (PPCPs) have attracted increasing concern during the last decade because of their widespread uses and continuous release to the aquatic environment. This work aimed to study the distribution of caffeine (CAF), oxybenzone (MBPh), and triclosan (TCS) when they arrive in salt marsh areas and to assess their remediation potential by two different species of salt marsh plants: Spartina maritima and Halimione portulacoides. Experiments were carried out in the laboratory either in hydroponics (sediment elutriate) or in sediment soaked in elutriate, for 10 days. Controls without plants were also carried out. CAF, MBPh, and TCS were added to the media. In unvegetated sediment soaked in elutriate, CAF was mainly in the liquid phase (83%), whereas MBPh and TCS were in the solid phase (90% and 56%, respectively); the highest remediation was achieved for TCS (40%) and mainly attributed to bioremediation. The presence of plants in sediment soaked in elutriate-enhanced PPCPs remediation, decreasing CAF and TCS levels between approximately 20-30% and MBPh by 40%.. Plant uptake, adsorption to plant roots/sediments, and bio/rhizoremediation are strong hypothesis to explain the decrease of contaminants either in water or sediment fractions, according to PPCPs characteristics.