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1.
In this study, two sediment cores (~70 cm) were collected from separate mangrove forests straddling the Ba Lat Estuary, Red River of northern Vietnam, to examine the origins of sedimentary organic carbon (SOC) and reconstruct the paleoenvironment. In addition, mangrove leaves and particulate organic matter were collected and measured for δ13C to trace the origins of SOC. The cores were analyzed by high-resolution sections for δ13C, TOC, C/N ratios, sediment grain size, water content, and porosity, with values of δ13C, TOC, and C/N ratios ranging from −28.19 to −22.5‰, 2.14–30.94 mg/g, and 10.29–18.32, respectively. The δ13C and TOC relationship indicated that there were some small residual effects of diagenetic processes on TOC and δ13C values in mangrove sediments. However, the shifts of δ13C and C/N ratios from the bottom to the surface sediment of the cores explained the change in organic matter sources, with values of C/N > 12 and δ13C < −25‰, and C/N < 12 and δ13C > −25‰ indicated terrestrial (e.g., mangrove litter) and marine phytoplankton sources, respectively. The covarying δ13C, C/N ratios, and sediment grain sizes during the past 100 years in sediment cores showed that the paleoenvironment may be reconstructed into three environments (subtidal, tidal flat, and intertidal mangrove). General trends in δ13C and C/N followed a gradual increase in the C/N ratio and a concomitant decrease in δ13C from the subtidal, through to tidal flat, and to the intertidal mangrove. δ13C and C/N ratios are therefore effective in measuring the continuum of environmental change in mangrove ecosystem.  相似文献   

2.
With the aim of evaluating temporal changes in sedimentation and organic carbon (Corg) supplied over the last ~100 years, a sediment core was collected at Soledad Lagoon, a costal ecosystem surrounded by mangroves, located in the Cispatá Estuary (Caribbean coast of Colombia). The core sediments were characterized by low concentrations of calcium carbonate (0.2–2.9%), organic matter (3–8%), total nitrogen (0.11–0.38%), and total phosphorus (0.19–0.65 mg g−1). Fe and Al concentrations ranged from 4% to 5%, and Mn from 356 to 1,047 μg g−1. The 210Pb-derived sediment and mass accumulation rates were 1.54 ± 0.18 mm year−1 and 0.08 ± 0.01 g cm−2 year−1, respectively. The sediment core did not provide evidence of human impact, such as enhancement of primary production or nutrient enrichment, which may result from recent land uses changes or climate change. The Corg fluxes estimated for Soledad Lagoon core lay in the higher side of carbon fluxes to coastal ecosystems (314–409 g m−2 year−1) and the relatively high Corg preservation observed (~45%) indicate that these lagoon sediments has been a net and efficient sink of Corg during the last century, which corroborate the importance of mangrove areas as important sites for carbon burial and therefore, long-term sequestration of Corg.  相似文献   

3.
We reconstruct past accretion rates of a salt marsh on the island of Sylt, Germany, using measurements of the radioisotopes 210Pb and 137Cs, as well as historical aerial photographs. Results from three cores indicate accretion rates varying between 1 and 16 mm year−1. Comparisons with tide gauge data show that high accretion rates during the 1980s and 1990s coincide with periods of increased storm activity. We identify a critical inundation height of 18 cm below which the strength of a storm seems to positively influence salt marsh accretion rates and above which the frequency of storms becomes the major factor. In addition to sea level rise, we conclude that in low marsh zones subject to higher inundation levels, mean storm strength is the major factor affecting marsh accretion, whereas in high marsh zones with lower inundation levels, it is storm frequency that impacts marsh accretion.  相似文献   

4.
Karst depressions comprise geomorphologically important sources and sinks for sediments and associated pollutants; yet the sedimentology of many depressions is not well understood in the world. In this paper, the 137Cs technique was employed to estimate recent sedimentation rates in a Chinese polygonal karst depression. The results indicate that the sediment deposition rates ranged from 0.91 to 1.97 mm year−1 from 1963 to 2007, and the average sediment deposition rate and specific deposit yield were estimated to be 1.47 mm year−1 and 20 t km−2 year−1, respectively. These results are consistent with the local monitoring data of runoff fields, which confirms the validity of the overall approach. This shows that the soil loss rate is very low in some karst areas of Southwest China. Above all, the approach appears to offer valuable potential to study surface erosion by estimating sediment deposition rates of karst depressions, rather than the assessment of complicated soil erosion in stony soils of carbonate rock slopes. In addition, the space distribution of surface soil and 137Cs inventories are affected remarkably by the inhomogeneous dissolution of limestone under the soil. It may be an important phenomenon, which exists widely in karst areas, and it is significantly different from other places.  相似文献   

5.
《Sedimentology》2018,65(4):1170-1212
Barrier‐island system evolution is controlled by internal and external forcing mechanisms, and temporal changes in these mechanisms may be recorded in the sedimentary architecture. However, the precise role of individual forcing mechanisms is rarely well understood due to limited chronological control. This study investigates the relative role of forcing conditions, such as antecedent topography, sea‐level rise, sediment supply, storms and climate changes, on the evolution of a Holocene wave‐dominated barrier‐island system. This article presents temporal reconstruction of the depositional history of the barrier‐island system of Rømø in the Wadden Sea in unprecedented detail, based on ground‐penetrating radar profiles, sediment cores, high‐resolution dating and palynological investigations, and shows that ca 8000 years ago the barrier island formed on a Pleistocene topographic high. During the initial phase of barrier evolution, the long‐term sea‐level rise was relatively rapid (ca 9 mm year−1) and the barrier was narrow and frequently overwashed. Sediment supply kept pace with sea‐level rise, and the barrier‐island system mainly aggraded through the deposition of a ca 7 m thick stack of overwash fans. Aggradation continued for ca 1700 years until sea‐level rise had decreased to <2 mm year−1. In the last ca 6000 years, the barrier prograded 4 to 5 km through deposition of a 10 to 15 m thick beach and shoreface unit, despite a long‐term sea‐level rise of 1 to 2 mm year−1. The long‐term progradation was, however, interrupted by a transgression between 4000 years and 1700 years ago. These results demonstrate that the large‐scale morphology of the Danish Wadden Sea shoreline influences the longshore sediment transport flux and the millennial‐scale dispersal of sediment along the shoreline. On decadal to centennial timescales, major storms induced intense beach and shoreface erosion followed by rapid recovery and progradation which resulted in a highly punctuated beach and shoreface record. Major storms contributed towards a positive sediment budget, and the sustained surplus of sediment was, and still is, instrumental in maintaining the aggradational–progradational state of the barrier island.  相似文献   

6.
The distribution of mangrove biomass and forest structure along Shark River estuary in the Florida Coastal Everglades (FCE) has been correlated with elevated total phosphorus concentration in soils thought to be associated with storm events. The passage of Hurricane Wilma across Shark River estuary in 2005 allowed us to quantify sediment deposition and nutrient inputs in FCE mangrove forests associated with this storm event and to evaluate whether these pulsing events are sufficient to regulate nutrient biogeochemistry in mangrove forests of south Florida. We sampled the spatial pattern of sediment deposits and their chemical properties in mangrove forests along FCE sites in December 2005 and October 2006. The thickness (0.5 to 4.5 cm) of hurricane sediment deposits decreased with distance inland at each site. Bulk density, organic matter content, total nitrogen (N) and phosphorus (P) concentrations, and inorganic and organic P pools of hurricane sediment deposits differed from surface (0–10 cm) mangrove soils at each site. Vertical accretion resulting from this hurricane event was eight to 17 times greater than the annual accretion rate (0.30 ± 0.03 cm year−1) averaged over the last 50 years. Total P inputs from storm-derived sediments were equivalent to twice the average surface soil nutrient P density (0.19 mg cm−3). In contrast, total N inputs contributed 0.8 times the average soil nutrient N density (2.8 mg cm−3). Allochthonous mineral inputs from Hurricane Wilma represent a significant source of sediment to soil vertical accretion rates and nutrient resources in mangroves of southwestern Everglades. The gradient in total P deposition to mangrove soils from west to east direction across the FCE associated with this storm event is particularly significant to forest development due to the P-limited condition of this carbonate ecosystem. This source of P may be an important adaptation of mangrove forests in the Caribbean region to projected impacts of sea-level rise.  相似文献   

7.
A sediment core from Guanabara Bay (Brazil) was analyzed for 210Pb dating, grain size, total organic carbon (TOC) and total nitrogen, carbon stable isotope ratio (δ13C), nitrogen stable isotope ratio (δ15N) and the metals Fe, Mn, Ni, Co, Cu, Pb, V and Zn, to assess the influence of land use changes on the aquatic system in a region for which large industrial and urban development is expected in the next few decades. To obtain baseline data for improving the monitoring of the expected increase in anthropogenic impacts from surrounding drainage basins, a multivariate analysis of data from different sediment layers was carried out to evaluate the dated sediment record. The geochemical data suggested three different sedimentary phases along the last 200 years. Before the 1880s, the highest clay and TOC contents were observed, where the C/N ratios and the δ13C values suggested a mixture of algal and terrestrial organic matter and the lowest concentrations of Co, Cu, Pb, V and Zn, for which background levels were estimated (4.6, 2.7, 14.9, 24.3 and 70.2 mg kg−1, respectively). From the 1880s to the 1950s, the metal concentrations and sand particles increased, but no change in organic matter quality was observed, reflecting a period of land use change, still without significant sewage input. After the 1950s, the sedimentation rate increased from 0.42 to 0.77 cm year−1 and increasing urban sewage input was evidenced by lower C/N ratios, higher δ15N, decrease of Fe and Mn concentrations and increased fluxes of metals and TOC, which showed a good relationship with population growth data.  相似文献   

8.
The long term recharge in Gobi Desert from Hexi Corridor to Inner Mongolia Plateau was estimated to be 1 mm year−1 by using the chloride mass balance method from one unsaturated zone profile, which shows that no effective modern recharge is taking place. A good rainfall database from Zhangye provides definition of the stable isotopic composition of modern rainfall. The signature of groundwater from the late Pleistocene differs markedly from that of the Holocene, shown clearly by the compositions of −10.5‰ δ18O as compared with values of −7‰ at the present day. It is apparent that the groundwaters in the Minqin Basin, Ejina Basin and feeding the lake system of the Badain Jaran are part of a regional flow network related to a wetter past climate as source of recharge. The recharge source in the past and to a limited extent in the more arid conditions of the present day included the foothills of the mountains of the Tibetan Plateau. The tritium age determinations accurate to the year are impossible and of no meaning to groundwater studies. A tritium value in the groundwater means multiple recharge ages in this region.  相似文献   

9.
We used a combined field and modeling approach to estimate the potential for submergence for one rapidly deteriorating (Bayou Chitigue Marsh) and one apparently stable (Old Oyster Bayou Marsh) saltmarsh wetland in coastal Louisiana, given two eustatic sea level rise scenarios: the current rate (0.15 cm year−1); and the central value predicted by the Intergovernmental Panel on Climate Change (48 cm by the year 2100). We also used the model to determine what processes were most critical for maintaining and influencing salt marsh elevation including, mineral matter deposition, organic matter production, shallow subsidence (organic matter decomposition + primary sediment compaction), deep subsidence, and sediment pulsing events (e.g., hurricanes). Eight years of field measurements from feldspar marker horizons and surface elevation tables revealed that the rates of vertical accretion at the Bayou Chitigue Marsh were high (2.26 (0.09) cm yr−1 (mean ± SE)) because the marsh exists at the lower end of the tidal range. The rate of shallow subsidence was also high (2.04 (0.1) cm yr−1), resulting in little net elevation gain (0.22 (0.06) cm yr−1). In contrast, vertical accretion at the Old Oyster Bayou Marsh, which is 10 cm higher in elevation, was 0.48 (0.09) cm yr−1. However, there was a net elevation gain of 0.36 (0.08) cm yr−1 because there was no significant shallow subsidence. When these rates of elevation gain were compared to rates of relative sea level rise (deep subsidence plus eustatic sea level rise), both sites showed a net elevation deficit although the Bayou Chitigue site was subsiding at approximately twice the rate of the Old Oyster Bayou site (1.1 cm yr−1 versus 0.49 cm yr−1 respectively). These field data were used to modify, initialize, and calibrate a previously published wetland soil development model that simulates primary production and mineral matter deposition as, feedback functions of elevation. Sensitivity analyses revealed that wetland elevation was most sensitive to changes in the rates of deep subsidence, a model forcing function that is difficult to measure in the field and for which estimates in the literature vary widely. The model also revealed that, given both the current rate of sea level rise and the central value estimate, surface elevation at both sites would fall below mean sea level over the next 100 years. Although these results were in agreement with the field study, they contradicted long term observations that the Old Oyster Bayou site has been in equilibrium with sea level for at least the past 50 years. Further simulations showed that the elevation at the Old Oyster Bayou site could keep pace with current rates of sea level rise if either a lower rate for deep subsidence was used as a forcing function, or if a periodic sediment pulsing function (e.g., from hurricanes) was programmed into the model.  相似文献   

10.
The strata-bound Cu−Pb−Zn polymetallic sulfide deposits occur in metamorphic rocks of greenschist phase of the middle-upper Proterozoic Langshan Group in central Inner Mongolia. δ34S values for sulfides range from −3.1‰ to +37.3‰, and an apparent difference is noticed between vein sulfides and those in bedded rocks. For example, δ34S values for bedded pyrite range from +10.6‰ to +20.0‰, while those for vein pyrite vary from −3.1‰ to +14.1‰. δ34S of bedded pyrrhotite is in the range +7.9‰–+23.5‰ in comparison with +6.5‰–+17.1‰ for vein pyrrhotite. The wide scatter of δ34S and the enrichment of heavier sulfur indicate that sulfur may have been derived from H2S as a result of bacterial reduction of sulfates in the sea water. Sulfur isotopic composition also differs from deposit to deposit in this area because of the difference in environment in which they were formed. The mobilization of bedded sulfides in response to regional metamorphism and magmatic intrusion led to the formation of vein sulfides. δ18O and δ13C of ore-bearing rocks and wall rocks are within the range typical of ordinary marine facies, with the exception of lower values for ore-bearing marble at Huogeqi probably due to diopsidization and tremalitization of carbonate rocks. Pb isotopic composition is relatively stable and characterized by lower radio-genetic lead. The age of basement rocks was calculated to be about 23.9 Ma and ore-forming age 7.8 Ma.207Pb/204Pb−206Pb/204Pb and208Pb/204Pb−206Pb/204Pb plots indicate that Pb may probably be derived from the lower crust or upper mantle. It is believed that the deposits in this region are related to submarine volcanic exhalation superimposed by later regional metamorphism and magmatic intrusion.  相似文献   

11.
The qanat water supply technology, which gravity drains mountain aquifers into valleys, is considered as a culturally appropriate and ecological sustainable design to meet northern Cyprus’ drinking water development needs. This research estimates the boundary and water budget for the proposed qanat recharge area of 370 km2, which is in the upper elevations of the limestone dominated Five Finger Mountain Range. The mountain drainage was analyzed using global elevation data from the Shuttle Ranging Topography Mission (SRTM). Efforts to use Tropical Rainfall Measuring Mission (TRMM) annual precipitation for water budget inputs failed due to extreme error when tested against 10–30 years of meteorological station data; TRMM under-estimated depths on the narrow mountain peaks. Gage records, while few in number, were area averaged to set average annual precipitation inputs at 530 mm year−1. Evaporation was estimated using a complementary relationship areal evapotranspiration (CRAE) model, setting average atmospheric outputs at 221 mm year−1. Recharge to the qanat aquifer was set by subtracting evaporation from precipitation, and then allocating 50% of the remaining water to environmental services. At 25% development, the qanat system supplies 14 mm3 year−1 of water, meeting the drinking water deficit of 13 mm3.  相似文献   

12.
We measured fluxes of NH4+ and NO3− and δ15N of NH4+, sediment, and porewater NH4+ from incubated sediment cores along a nitrate gradient and in different seasons from Childs River, MA. NH4+ flux was low at the downstream site with the lowest concentration of organic matter (high salinity) but otherwise did not differ along the estuary. The δ15N of regenerated NH4+ ranged from +6.1‰ to +15.3‰ but did not vary significantly with season or salinity; the mean for the entire estuary was +10.4 ± 0.5‰. Based on differences between the δ15N of regenerated NH4+ and sediment, and expected isotopic fractionation due to remineralization, we concluded that nitrification occurred after remineralization of NH4+. Differences between the δ15N of regenerated NH4+ and the δ15N of porewater NH4+ provided further evidence of nitrification. We estimated that 11% to 48% of remineralized NH4+ underwent coupled nitrification–denitrification before release into the water column. In spite of losses to denitrification, NH4+ flux released 1.4 mol N m−2 year−1 to the water column and could provide 42% of phytoplankton nitrogen requirements.  相似文献   

13.
Vertical profiles of trace metal (Cd, Pb, Zn, Cu, Ni) concentrations, organic matter content, carbonate content and granulometric composition were determined in two sediment cores from the submarine pit Dragon Ear (Middle Adriatic). Concentrations of the analyzed metals (Cd: 0.06–0.12 mg kg−1, Pb: 28.5–67.3 mg kg−1, Zn: 17.0-65.4 mg kg−1, Cu: 21.1–51.9 mg kg−1, Ni: 27.8–40.2 mg kg−1) were in usual range for Adriatic carbonate marine sediments. Nevertheless, concentrations of Cu, Zn, and especially Pb in the upper layer of sediments (top 12 cm) were higher than in bottom layer, while Cd and Ni concentration profiles were uniform. Regression analysis and principal component analysis were used to interpret distribution of trace metals, organic matter and carbonate content in sediment cores. Results of both analysis showed that concentrations of all trace metals in the core below the entrance to the pit were significantly positively correlated with organic matter and negatively correlated with carbonate, while in the core more distant from the entrance only Pb showed significant positive correlation with organic matter. Obtained results indicated that, except for lead which was enriched in surface sediment, in the time of sampling (before the building of the nautical marina) investigated area belonged to unpolluted areas.  相似文献   

14.
The biogeochemistry of organic matter (OM) in a macrotidal estuary, the Yalujiang River, was studied during two cruises: the flood season in August 1994 and the dry season in April 1996. Surface sediments were collected in the riverine zone (RZ), the turbidity maximum zone (TMZ), and the marine zone (MZ). The molecular distribution of the n-alkanes and fatty acid series and bulk sediment characteristics, such as C:N and δ13C, were used to assess differences in OM source and transport from the river upstream to the marine end member. Higher C:N values typical for terrestrial sources were observed at the upper reach for both seasons. The δ13C of OM in surface sediments varied from −27.3‰ to −21.6‰ in the flood season and from −26.8‰ to −31‰ in the dry season. The concentrations of n-alkanes varied between 0.3–21.4 μg g−1 and the variation of fatty acids was 4.8–32.9 μg g−1. The data showed mixing of terrestrial and autochthonous OM in the middle and lower reaches. The distribution of lipids (n-alkanes and Carbon Preference Index) encountered in this study confirmed the importance of terrestrial OM in the sediment samples from degraded soil material. The distribution of fatty acids suggested important phytoplankton, zooplankton, and microbial signals (short-chain and unsaturated acids; ≤C20). Branched fatty acids, such as the iso- and anteiso-C15 and C17 compounds, relfect bacterial contributions. All samples were characterized by a high proportion of mixture inputs in both seasons. A slight decreasing trend was observed with increasing salinity except for the highest percentage of mixed fatty acids in the TMZ of the flood season. Terrestrial fatty acids were approximately 20% in the flood season and 27–46% in the dry season. Differences in hydrological conditions and primary production between the TMZ, RZ, and MZ resulted in different OM distributions, which are reflected in the sources and degree of diagenesis of the sedimentary OM. Seasonal variation may be strongly influenced by hydrological characteristics rather than primary productivity and anthropogenic activities in the Yalujiang region.  相似文献   

15.
Many small estuaries are influenced by flow restrictions resulting from transportation rights-of-way and other causes. The biogeochemical functioning and history of such systems can be evaluated through study of their sediments. Ten long and six short cores were collected from the length of Jordan Cove, Connecticut, a Long Island Sound subestuary, and analyzed for stratigraphy, radionuclides (14C, 210Pb, 226Ra, 137Cs, and 60Co), and metals (Ag, Cd, Cu, Pb, Zn, Fe, and Al). For at least 3,800 yr, rising sea level has gradually inundated Jordan Cove, filling it with mud similar to that currently being deposited there. Long-term sediment accumulation in the cove averaged close to 0.1 cm yr−1 over the last three millennia. Recent sediment accumulation rates decrease inland from 0.84 cm yr−1 to 0.40 cm yr−1, and are slightly faster than relative sea-level rise at this site (0.3 cm yr−1). Similarity of depth distributions of trace metals was used to confirm relative sediment accumulation rates. 60Co and Ag are derived from sources outside the cove and its watershed, presumably the Millstone nuclear power plant and regional contaminated sediments, respectively. The combined data suggest that Long Island Sound is an important source of sediment to the cove; a minor part of total sediment is supplied from the local watershed. Trace metal levels are strongly correlated with Fe but not with either organic matter or Al. Sediment quality has declined in the cove over the past 60 yr, but only slightly. Cu, Pb, and Zn data correlate strongly with Fe but not with either organic matter or aluminum. Ratios of Ag to Fe and to trace metals suggest that Ag in the cove is derived almost entirely from Long Island Sound. This result supports the notion that Fenormalized Ag can serve as a better tracer of some kinds of contamination than more common and abundant metals, like Cu, Pb, and Zn. *** DIRECT SUPPORT *** A01BY085 00008  相似文献   

16.
Gediz Basin is one of the regions where intense agricultural activities take place in Western Turkey. Erosion and soil degradation have long been causing serious problems to cultivated fields in the basin. This work describes the application of two different 137Cs models for estimating soil erosion rates in cultivated sites of the region. Soil samples were collected from five distinct cultivated regions subject to soil erosion. The variations of 137Cs concentrations with depth in soil profiles were investigated. Soil loss rates were calculated from 137Cs inventories of the samples using both proportional model (PM) and simplified mass balance model (SMBM). When PM was used, erosion and deposition rates varied from −15 to −28 t ha−1 year−1 and from +5 to +41 t ha−1 year−1, respectively; they varied from −16 to −33 t ha−1 year−1 and from +5 to +55 t ha−1 year−1 with SMBM. A good agreement was observed between the results of two models up to 30 t ha−1 year−1 soil loss and gain in the study area. Ulukent, a small representative agricultural field, was selected to compare the present data of 137Cs techniques with the results obtained by universal soil loss equation (USLE) applied in the area before.  相似文献   

17.
Nitrogen addition to soil can play a vital role in influencing the losses of soil carbon by respiration in N-deficient terrestrial ecosystems. The aim of this study was to clarify the effects of different levels of nitrogen fertilization (HN, 200 kg N ha−1 year−1; MN, 100 kg N ha−1 year−1; LN, 50 kg N ha−1 year−1) on soil respiration compared with non-fertilization (CK, 0 kg N ha−1 year−1), from July 2007 to September 2008, in temperate grassland in Inner Mongolia, China. Results showed that N fertilization did not change the seasonal patterns of soil respiration, which were mainly controlled by soil heat-water conditions. However, N fertilization could change the relationships between soil respiration and soil temperature, and water regimes. Soil respiration dependence on soil moisture was increased by N fertilization, and the soil temperature sensitivity was similar in the treatments of HN, LN, and CK treatments (Q 10 varied within 1.70–1.74) but was slightly reduced in MN treatment (Q 10 = 1.63). N fertilization increased soil CO2 emission in the order MN > HN > LN compared with the CK treatment. The positive effects reached a significant level for HN and MN (P < 0.05) and reached a marginally significant level for LN (P = 0.059 < 0.1) based on the cumulative soil respiration during the 2007 growing season after fertilization (July–September 2007). Furthermore, the differences between the three fertilization treatments and CK reached the very significant level of 0.01 on the basis of the data during the first entire year after fertilization (July 2007–June 2008). The annual total soil respiration was 53, 57, and 24% higher than in the CK plots (465 g m−2 year−1). However, the positive effects did not reach the significant level for any treatment in the 2008 growing season after the second year fertilization (July–September 2008, P > 0.05). The pairwise differences between the three N-level treatments were not significant in either year (P > 0.05).  相似文献   

18.
Two boreholes and ten piezometers in the Ganges flood plain were drilled and installed for collecting As-rich sediments and groundwater. Groundwater samples from the Ganges flood plain were collected for the analysis of cations (Ca2+, Mg2+, K+, Na+), anions (Cl−, NO3 −, SO4 2−), total organic carbon (TOC), and trace elements (As, Mn, Fe, Sr, Se, Ni, Co, Cu, Mo, Sb, Pb). X-ray powder diffraction was performed to characterize the major mineral contents of aquifer sediments and X-ray fluorescence (XRF) to analyze the major chemical composition of alluvial sediments. Results of XRF analysis clearly show that fine-grained sediments contain higher amounts of trace element because of their high surface area for adsorption. Relative fluorescence index (15–38 QSU) of humic substance in groundwater was measured using spectrofluorometer, the results revealed that groundwater in the Ganges flood plain contains less organic matter (OM). Arsenic concentration in water ranges from 2.8 to 170 μg/L (mean 50 μg/L) in the Ganges flood plain. Arsenic content in sediments ranges from 2.1 to 14 mg/kg (mean 4.58 mg/kg) in the flood plains. TOC ranges from 0.49 to 3.53 g/kg (mean 1.64 g/kg) in the Ganges flood plain. Arsenic is positively correlated with TOC (R 2 = 0.55) in sediments of this plain. Humic substances were extracted from the sediments from the Ganges flood plain. Fourier transform infrared analysis of the sediments revealed that the plain contains less humic substances. The source of organic carbon was assigned from δ13C values obtained using elemental analysis-isotope ratio mass spectrometry (EA-IRMS); the values (−10 to −29.44‰) strongly support the hypothesis that the OM of the Ganges flood plain is of terrestrial origin.  相似文献   

19.
The mangrove or mud crab, Scylla serrata, is an important component of mangrove fisheries throughout the Indo-Pacific. Understanding crab diets and habitat use should assist in managing these fisheries and could provide additional justification for conservation of the mangrove ecosystem itself. We used multiple chemical tracers to test whether crab movements were restricted to local mangrove forests, or extended to include adjacent seagrass beds and reef flats. We sampled three mangrove forests on the island of Kosrae in the Federated States of Micronesia at Lelu Harbor, Okat River, and Utwe tidal channel. Samples of S. serrata and likely food sources were analyzed for stable carbon (δ13C), nitrogen (δ15N), and sulfur (δ34S) isotopes. Scylla serrata tissues also were analyzed for phosphorus (P), cations (K, Ca, Mg, Na), and trace elements (Mn, Fe, Cu, Zn, and B). Discriminant analysis indicated that at least 87% of the crabs remain in each site as distinct populations. Crab stable isotope values indicated potential differences in habitat use within estuaries. Values for δ13C and δ34S in crabs from Okat and Utwe were low and similar to values expected from animals feeding within mangrove forests, e.g., feeding on infauna that had average δ13C values near −26.5‰. In contrast, crabs from Lelu had higher δ13C and δ34S values, with average values of −21.8 and 7.8‰, respectively. These higher isotope values are consistent with increased crab foraging on reef flats and seagrasses. Given that S. serrata have been observed feeding on adjacent reef and seagrass environments on Kosrae, it is likely that they move in and out of the mangroves for feeding. Isotope mixing model results support these conclusions, with the greatest mangrove ecosystem contribution to S. serrata diet occurring in the largest mangrove forests. Conserving larger island mangrove forests (> 1 km deep) appears to support crab foraging activities.  相似文献   

20.
210Pb geochronologies of Cd, Cu, Hg, and Pb fluxes were obtained from the intertidal mudflat sediments of the coastal lagoons Chiricahueto, Estero de Urías, and Ohuira in the Mexican Pacific. The Cu and Hg sediment concentrations at the three lagoons fell within the ranges of 6–76 μg g−1 and 0.1 to 592 ng g−1, respectively; Chiricahueto and Estero de Urías sediments had comparable Cd and Pb concentrations within the ranges of 0.2–2.1 μg g−1 and 10–67 μg g−1, respectively; whereas in Ohuira lagoon, Cd concentrations were lower (0.1–0.5 μg g−1) and Pb concentrations were higher (115–180 μg g−1) than in the other lagoons. The metal fluxes (μg cm−2 y−1) for the three lagoons fell within the ranges of 0.02–0.15 for Cd, 0.7–6.0 for Cu, 0.001–0.045 for Hg, and 0.7–20 for Pb. The Hg pollution in Estero de Urías was attributed to the exhausts of the thermoelectric plant of Mazatlan and the metal enrichment in Chiricahueto and Ohuira was related to the agrochemical wastes from the croplands surrounding these lagoons.  相似文献   

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