A cross-system analysis of sedimentary organic carbon in the mangrove ecosystems of Xuan Thuy National Park, Vietnam

A cross-system analysis of bulk sediment composition, total organic carbon (TOC), atomic C/N ratio, and carbon isotope composition (δ¹³C) in 82 surface sediment samples from natural and planted mangrove forests, bank and bottom of tidal creeks, tidal flat, and the subtidal habitat was conducted to examine the roles of mangroves in sedimentation and organic carbon (OC) accumulation processes, and to characterize sources of sedimentary OC of the mangrove ecosystem of Xuan Thuy National Park, Vietnam. Sediment grain sizes varied widely from 5.4 to 170.2 μm (mean 71.5 μm), with the fine sediment grain size fraction (< 63 μm) ranging from 11 to 99.3% (mean 72.5%). Bulk sediment composition suggested that mangroves play an important role in trapping fine sediments from river outflows and tidal water by the mechanisms of tidal current attenuation by vegetation and the ability of fine roots to bind sediments. The TOC content ranged from 0.08 to 2.18% (mean 0.78%), and was higher within mangrove forests compared to those of banks and bottoms of tidal creeks, tidal flat, and subtidal sediments. The sedimentary δ¹³C ranged from − 27.7 to − 20.4‰ (mean − 24.1‰), and mirrored the trend observed in TOC variation. The TOC and δ¹³C relationship showed that the factors of microbial remineralization and OC sources controlled the TOC pool of mangrove sediments. The comparison of δ¹³C and C/N ratio of sedimentary OC with those of mangrove and marine phytoplankton sources indicated that the sedimentary OC within mangrove forests and the subtidal habitat was mainly composed of mangrove and marine phytoplankton sources, respectively. The application of a simple mixing model showed that the mangrove contribution to sedimentary OC decreased as follows: natural mangrove forest > planted mangrove forest > tidal flat > creek bank > creek bottom > subtidal habitat.     

Dissolved inorganic carbon dynamics in the waters surrounding forested mangroves of the Ca Mau Province (Vietnam)

Dissolved inorganic carbon (DIC) and ancillary data were obtained during the dry and rainy seasons in the waters surrounding two 10-year-old forested mangrove sites (Tam Giang and Kiên Vàng) located in the Ca Mau Province (South-West Vietnam). During both seasons, the spatial variations of partial pressure of CO₂ (pCO₂) were marked, with values ranging from 704 ppm to 11481 ppm during the dry season, and from 1209 ppm to 8136 ppm during the rainy season. During both seasons, DIC, pCO₂, total alkalinity (TAlk) and oxygen saturation levels (%O₂) were correlated with salinity in the mangrove creeks suggesting that a combination of lower water volume and longer residence time (leading to an increase in salinity due to evaporation) enhanced the enrichment in DIC, pCO₂ and TAlk, and an impoverishment in O₂. The low O₂ and high DIC and pCO₂ values suggest that heterotrophic processes in the water column and sediments controlled these variables. The latter processes were meaningful since the high DIC and TAlk values in the creek waters were related to some extent to the influx of pore waters, consistent with previous observations. This was confirmed by the stochiometric relationship between TAlk and DIC that shows that anaerobic processes control these variables, although this approach did not allow identifying unambiguously the dominant diagenetic carbon degradation pathway. During the rainy season, dilution led to significant decreases of salinity, TAlk and DIC in both mangrove creeks and adjacent main channels. In the Kiên Vàng mangrove creeks a distinct increase of pCO₂ and decrease of %O₂ were observed. The increase of TSM suggested enhanced inputs of organic matter probably from land surrounding the mangrove creeks, that could have led to higher benthic and water column heterotrophy. However, the flushing of water enriched in dissolved CO₂ originating from soil respiration and impoverished in O₂ could also have explained to some extent the patterns observed during the rainy season. Seasonal variations of pCO₂ were more pronounced in the Kiên Vàng mangrove creeks than in the Tam Giang mangrove creeks. The air–water CO₂ fluxes were 5 times higher during the rainy season than during the dry season in the Kiên Vàng mangrove creeks. In the Tam Giang mangrove creeks, the air–water CO₂ fluxes were similar during both seasons. The air–water CO₂ fluxes ranged from 27.1 mmol C m⁻² d⁻¹ to 141.5 mmol C m⁻² d⁻¹ during the dry season, and from 81.3 mmol m⁻² d⁻¹ to 154.7 mmol m⁻² d⁻¹ during the rainy season. These values are within the range of values previously reported in other mangrove creeks and confirm that the emission of CO₂ from waters surrounding mangrove forests are meaningful for the carbon budgets of mangrove forests.     

Distribution and sources of organochlorine pesticides in water and sediments from Daliao River estuary of Liaodong Bay,Bohai Sea (China)

The levels of 19 kinds of organochlorine pesticides (OCPs) in the aqueous phase, suspended particulate matter (SPM), pore water and sediments from Daliao River estuary of Liaodong Bay (Bohai Sea) in northeast China were investigated to evaluate their potential pollution risks. The total OCPs concentrations in the aqueous phase, SPM, pore water and sediments were 3.7–30.1 ng l⁻¹, 4.6–52.6 ng l⁻¹, 157–830 ng l⁻¹ and 2.1–21.3 ng g⁻¹ dry weight, respectively. The concentrations of OCPs, in the Daliao River estuary, are in the mid-range, as compared to those reported in other estuaries worldwide. The distribution of HCHs and DDTs were different indicating different contamination sources. Lindane is the main type of HCH and continuing use in northeast China of ‘pure’ HCH (lindane) rather than technical HCH accounts for the source. The ratios of (DDE + DDD)/DDT in the samples indicate no recent inputs of these chemicals to the estuary.     

Bioaccessibility and mobilisation of copper and zinc in estuarine sediment contaminated by antifouling paint particles

Clean estuarine sediment amended with antifouling paint particles has been digested in biologically relevant reagents in order to evaluate the bioaccessibilities of Cu and Zn to deposit feeders in coastal environments where boat maintenance is important. Concentrations of Cu and Zn in the estuarine sediment of about 20 and 70 μg g⁻¹, respectively, increased to about 930 and 330 μg g⁻¹, respectively, on addition of 1.3% of a composite of fractionated paint particles collected from a boat repair facility. Seawater containing the vertebrate bile salt, sodium taurocholate, representative of surfactants in the digestive environment of deposit feeders, mobilised significantly greater quantities of metal (up to about 2 μg g⁻¹ of both Cu and Zn) than seawater alone, presumably through complexation and exchange reactions. Seawater solutions of the protein, bovine serum albumin (BSA), a surrogate for proteinaceous material and amino acids encountered in the digestive tract, mobilised even greater quantities of metal (up to about 80 and 40 μg g⁻¹ of Cu and Zn, respectively) via strong complexation, although addition of taurocholate reduced this capacity through interactions between the two reagents. Overall, and through feeding, burrowing and bioirrigation, infaunal invertebrates are predicted to greatly accelerate the rate of mobilisation and local dispersal of metals in sediment contaminated by antifouling paint particles.     

The influence of natural and anthropogenic factors on mangrove dynamics over 60 years: The Somone Estuary, Senegal

Although such ecosystems are fragile, this study shows that the anthropogenic damages inflicted on the mangrove forests of West Africa can be reversed over a relatively short time period if environmental conditions are favorable. The mangrove ecosystem of the microtidal Somone Estuary, Senegal, has undergone extreme changes during the last century. The area occupied by mangrove forest was estimated with a diachronic study by GIS for the period 1946-2006. Between 1946 and 1978, 85% of the area was progressively replaced by unvegetated mudflats in the intertidal zones and by barren area in the supratidal zones. Until 1990, this was mainly a result of traditional wood harvesting. The impact was exacerbated by the closing off of the estuary to the sea (1967-1969 and 1987) and by an extended drought (1970 onwards), which resulted in a lack of renewal of water, hypersalinization and acidification. The main factors controlling mangrove evolution in the Somone ecosystem, however, are anthropogenic. Until 1990, traditional wood cutting (for wood and oyster harvesting) was practiced by the local population. Between 1978 and 1989, a small area occupied by the mangroves was stabilized. Since 1992, a modification of mangrove logging and a new reforestation policy resulted in an exponential increase of mangrove area progressively replacing intertidal mudflats. Such success in the restoration of the ecosystem reforestation is supported by favorable environmental conditions: tidal flooding, groundwater influence, rainfall during the wet season, low net accretion rate of about 0.2-0.3 cm year⁻¹, and a ban on the cutting of mangrove wood. The rate of mangrove loss from 1946 to 1978 was 44,000 m² year⁻¹, but this has been offset by restoration efforts resulting in an increase in mangrove area from 1992 to 2006 of 63,000 m² year⁻¹.     

Trophic transfer of methylmercury and trace elements by tropical estuarine seston and plankton

Methylmercury (MeHg) and trace elements (TE), mercury, selenium, cadmium, lead and copper, were determined in a microbial loop composed by three size classes of autotrophic and heterotrophic microorganism samples, 1.2–70 μm (seston, SPM), 70–290 μm (microplankton) and ≥290 μm (mesoplankton) from five sampling stations within a polluted eutrophic estuary in the Brazilian Southeast coast and one external point under the influence of the bay. TE concentrations were within the range reported for marine microorganisms from uncontaminated locations. Microplankton was primarily composed of proto-zooplankton and diatoms (>90%) while approximately 50% of mesoplankton was composed mainly of copepods. MeHg and TE in samples did not differ among the five sampling stations within the bay. Cd, Pb and Cu in seston were higher in the stations sampled inside Guanabara Bay (0.67 μg Cd g⁻¹, 9.26 μg Pb g⁻¹, 8.03 μg Cu g⁻¹) than in the external one (0.17 μg Cd g⁻¹, 3.98 μg Pb g⁻¹ and 2.09 μg Cu g⁻¹). Hg, MeHg and Se did not differ among the five points within the more eutrophic waters of the estuary and the external sampling station. The trophic transfer of MeHg and Se was observed between trophic levels from prey (seston and microplankton) to predator (mesoplankton). The successive amplification of the ratios of MeHg to Hg with increasing trophic levels from seston (43%), to microplankton (59%) and mesoplankton (77%) indicate that biomagnification may be occurring along the microbial food web. Selenium, that is efficiently accumulated by organisms through trophic transference, was biomagnified along the microbial food web, while Hg, Cd, Pb, Cu did not present the same behavior. Concentrations differed between the three size classes, indicating that MeHg and TE accumulation were size-dependent. MeHg and TE concentrations were not related to the taxonomic groups' composition of the planktonic microorganisms. Results suggest the importance of the role of the trophic level and microorganism size in regulating element transfers. Eutrophication dilution may provide a process-oriented explanation for lower MeHg and TE accumulation by the three size classes of microorganisms collected at the five sampling stations within the bay.     

The cycling and oxidation pathways of organic carbon in a shallow estuary along the Texas Gulf Coast

The cycling and oxidation pathways of organic carbon were investigated at a single shallow water estuarine site in Trinity Bay, Texas, the uppermost lobe of Galveston Bay, during November 2000. Radio-isotopes were used to estimate sediment mixing and accumulation rates, and benthic chamber and pore water measurements were used to determine sediment-water exchange fluxes of oxygen, nutrients and metals, and infer carbon oxidation rates. Using ⁷Be and ²³⁴Th_XS, the sediment-mixing coefficient (D_b) was 4.3 ± 1.8 cm² y⁻¹, a value that lies at the lower limit for marine environments, indicating that mixing was not important in these sediments at this time. Sediment accumulation rates (S_a), estimated using ¹³⁷Cs and ²¹⁰Pb_XS, were 0.16 ± 0.02 g cm⁻² y⁻¹. The supply rate of organic carbon to the sediment-water interface was 30 ± 3.9 mmol C m⁻² d⁻¹, of which ∼10% or 2.9 ± 0.44 mmol C m⁻² d⁻¹was lost from the system through burial below the 1-cm thick surface mixed layer. Measured fluxes of O₂ were 26 ± 3.8 mmol m⁻² d⁻¹ and equated to a carbon oxidation rate of 20 ± 3.3 mmol C m⁻² d⁻¹, which is an upper limit due to the potential for oxidation of additional reduced species. Using organic carbon gradients in the surface mixed layer, carbon oxidation was estimated at 2.6 ± 1.1 mmol C m⁻² d⁻¹. Independent estimates made using pore water concentration gradients of ammonium and C:N stoichiometry, equaled 2.8 ± 0.46 mmol C m⁻² d⁻¹. The flux of DOC out of the sediments (DOC_efflux) was 5.6 ± 1.3 mmol C m⁻² d⁻¹. In general, while mass balance was achieved indicating the sediments were at steady state during this time, changes in environmental conditions within the bay and the surrounding area, mean this conclusion might not always hold. These results show that the majority of carbon oxidation occurred at the sediment-water interface, via O₂ reduction. This likely results from the high frequency of sediment resuspension events combined with the shallow sediment mixing zone, leaving anaerobic oxidants responsible for only ∼10–15% of the carbon oxidized in these sediments.     

Diurnal variation of nitric oxide emission flux from a mangrove wetland in Zhangjiang River Estuary,China

The diurnal variation of nitric oxide (NO) emission fluxes from a Kandelia obovata and Avicennia marina mangrove wetland were studied in the Zhangjiang River Estuary Mangrove National Nature Reserve using a dynamic chamber-based technique and a chemiluminescent analyzer. Results from field experiments show that NO emission from K. obovata and A. marina sampling sites reached maximal values of 1.07 ng N m⁻² s⁻¹ and 1.23 ng N m⁻² s⁻¹, respectively after the night tide. Meanwhile NO emission maintained at a steady lower level in daytime for both wetland sites. In laboratory experiments, NO emission from the mangrove wetland soil samples treated with simulated tides in the darkness exhibited higher values than those in the light, therefore it seems that tides and darkness could increase NO emission from mangrove wetlands, while intensive light, high temperature, and dryness in the daytime decreased NO emission. Compared with K. obovata soil samples, the diurnal average NO emission rate of the A. marina site was significantly higher, which was closely related to relatively higher diurnal average CO₂ emission rate, soil available nitrogen content and soil net nitrification rate of the A. marina site. Moreover, soil samples of the A. marina site were more responsive to simulated tides and the addition of nitrogen than those of the K. obovata site.     

Heavy metals in sinking particles and bottom sediments from the eastern Turkish coast of the Black Sea

Concentrations of Cd, Cu, Cr, Co, Ni, Zn, Fe, Mn, Pb, As, and Sb were determined in sediment trap and bottom sediment samples collected seasonally from a station on the eastern Turkish coast of the Black Sea. Cd, Pb and Mn concentrations were highest in the sediment trap samples except during the summer period, whereas Co, Ni, Zn and Fe levels were much lower than corresponding levels found in the surface sediments. Cu, Cr, As and Sb levels showed no definite trend with sediment type. In general, with the exception of Cr, relatively lower metal concentrations in the sediment trap material were determined in the summer period. The highest mass flux, 56.5 g m⁻² day⁻¹, was measured during autumn. The highest flux of heavy metals also occurred during autumn and was strongly dependent on particle mass flux. Based on these results, we suggest that the downward vertical transport of particulate heavy metals in this region is related to the high degree of land erosion and the resultant particulate flux dynamics, which occur here. It was noteworthy that the highest concentrations of Cd, Cu, Co, Zn, Fe and Sb in particles were measured during winter a finding which suggests that enhanced fossil fuel combustion, which occurs during this period in adjacent urban and industrial areas plays an important role in the metal composition of sinking particles in nearshore waters.     

Sedimentary iron inputs stimulate seagrass (Posidonia oceanica) population growth in carbonate sediments

The relationship between sedimentary Fe inputs and net seagrass population growth across a range of Posidonia oceanica meadows growing in carbonate Mediterranean sediments (Balearic Islands, Spain; SE Iberian Peninsula, Spain; Limassol, Cyprus; Sounion, Greece) was examined using comparative analysis. Sedimentary Fe inputs were measured using benthic sediment traps and the net population growth of P. oceanica meadows was assessed using direct census of tagged plants. The meadows examined ranged from meadows undergoing a severe decline to expanding meadows (specific net population growth, from −0.14 yr⁻¹ to 0.05 yr⁻¹). Similarly, Fe inputs to the meadows ranged almost an order of magnitude across meadows (8.6–69.1 mg Fe m⁻² d⁻¹). There was a significant, positive relationship between sedimentary iron inputs and seagrass net population growth, accounting for 36% of the variability in population growth across meadows. The relationship obtained suggested that seagrass meadows receiving Fe inputs below 43 mg Fe m⁻² d⁻¹ are vulnerable and in risk of decline, confirming the pivotal role of Fe in the control of growth and the stability of seagrass meadows in carbonate sediments.     

Petroleum pollution in surface sediments of Daya Bay,South China,revealed by chemical fingerprinting of aliphatic and alicyclic hydrocarbons

Nine surface sediments collected from Daya Bay have been Soxhlet-extracted with 2:1 (v/v) dichloromethane-methanol. The non-aromatic hydrocarbon (NAH) fraction of solvent extractable organic matter (EOM) and some bulk geochemical parameters have been analyzed to determine petroleum pollution of the bay. The NAH content varies from 32 to 276 μg g⁻¹ (average 104 μg g⁻¹) dry sediment and accounts for 5.8–64.1% (average 41.6%) of the EOM. n-Alkanes with carbon number ranging from 15 to 35 are identified to be derived from both biogenic and petrogenic sources in varying proportions. The contribution of marine authigenic input to the sedimentary n-alkanes is lower than the allochthonous input based on the average n-C₃₁/n-C₁₉ alkane ratio. 25.6–46.5% of the n-alkanes, with a mean of 35.6%, are contributed by vascular plant wax. Results of unresolved complex mixture, isoprenoid hydrocarbons, hopanes and steranes also suggest possible petroleum contamination. There is strong evidence of a common petroleum contamination source in the bay.     

The role of two sediment-dwelling invertebrates on the mercury transfer from sediments to the estuarine trophic web

The annual total and organic mercury bioaccumulation pattern of Scrobicularia plana and Hediste diversicolor was assessed to evaluate the potential mercury transfer from contaminated sediments to estuarine food webs. S. plana was found to accumulate more total and organic mercury than H. diversicolor, up to 0.79 mg kg⁻¹ and 0.15 mg kg⁻¹ (wet weight) respectively, with a maximum annual uptake of 0.21 mg kg⁻¹ y⁻¹, while for methylmercury the annual accumulation was similar between species and never exceeded 0.045 mg kg⁻¹ y⁻¹. The higher organic mercury fraction in H. diversicolor is related to the omnivorous diet of this species. Both species increase methylmercury exposure by burrowing activities and uptake in anoxic, methylmercury rich sediment layers. Integration with the annual biological production of each species revealed mercury incorporation rates that reached 28 μg m⁻² y⁻¹, and to extract as much as 11.5 g Hg y⁻¹ (of which 95% associated with S. plana) in the 0.4 km² of the most contaminated area, that can be transferred to higher trophic levels. S. plana is therefore an essential vector in the mercury biomagnification processes, through uptake from contaminated sediments and, by predation, to transfer it to economically important and exploited estuarine species.     

Nitrification in Kochi backwaters

Nitrification rates, as oxidation of ¹⁵N-labelled ammonium and loss of nitrite from N-Serve treated samples, were measured in Kochi backwaters during three seasons. Nitrification rates ranged from undetectable to 166 nmol N L⁻¹ h⁻¹ in the water column and up to 17 nmol N (g wet wt)⁻¹ h⁻¹ in sediments. Nitrification rates were higher in intermediate salinities than in either freshwater or seawater end. Within this salinity range, nitrification rates could be related to ammonium concentrations. As shown by the relation between ammonification and nitrification rates, it is also likely that nitrification is more regulated by renewal rates, rather than by in situ concentrations, of substrate. Among other environmental parameters, temperature and pH may have an influence on nitrification. Potential nitrification rates calculated from loss of nitrite from N-Serve treated, nitrite-enriched samples were about 800 nmol N L⁻¹ h⁻¹ in the water column and 40 nmol N (g wet wt)⁻¹ h⁻¹ in sediments. While these rates are in balance with those of biological ammonium production they may be inadequate to mitigate ammonium pollution in this estuary.     

Litterfall dynamics and nutrient decomposition of arid mangroves in the Gulf of California: Their role sustaining ecosystem heterotrophy

This study shows results on litterfall dynamics and decay in mangrove stands of Avicennia germinans distributed along a latitudinal gradient (three forest sites) in the Gulf of California, in order to assess whether internal sources could support the observed mangrove ecosystem organic deficit in this arid tropic. Total mean annual litterfall production increased southward (712.6 ± 53.3, 1501.3 ± 145.1 and 1506.2 ± 280.5 g DW m⁻² y⁻¹, in the Yaqui, Mayo and Fuerte areas respectively), leaves being the main component of litter in all locations during the entire year, followed by fruits. The wet season (June–September) showed the highest litterfall rates through fruits. The temporal trend of litterfall production was significantly explained through mean air temperature (R² = 68%) whilst total annual litter production in the entire region showed a statistically significant relationship with total soil phosphorus, salinity, total nitrogen, organic matter and tree height (R² = 0.67). Throughout 117 days of the decomposition experiment, the litter lost 50% of its original dry weight in 5.8 days (average decay rate of 0.032 ± 0.04 g DW d⁻¹) and there were not significant differences in the remaining mass after 6 days. The percentage of both C and P released from the litter correlated significantly with the ratio of tidal inundated days to total experiment days (R² = 0.62, p = 0.03 and R² = 0.67, p = 0.02, respectively); however, the frequency of tidal inundation only showed a significant increase in C release from Avicennia litter after 6 and above 48 days of decomposition. Whereas the total C content of litter bags decreased linearly over the decomposition to (% Total C = 5.52 − 0.46 days, R² = 0.81, p = 0.0005), N content displayed an irregular pattern with a significant increase of decay between 48 and 76 days from the beginning of the experiment. The pattern for relative P content of litter revealed reductions of up to 99% of the original (%tot-P = −9.77 to 1.004 days, R² = 0.72, p = 0.01) although most of the P reduction occurred between 17 and 34 days after the experiment started. Soil N and P contents, which exhibited significant differences in the course of the decomposition experiment, appeared to show significant differences between sampling sites, although they were not related to tidal influence, nor by leaf and nutrient leaching. In a global basis, C/N litter ratios decreased linearly (C/N = 32.86 − 0.1006 days, R² = 0.62, p = 0.02), showing a strong and significant correlation with meteorological variables (R² = 0.99, p = 0.01). C/P ratios of litter increased through an exponential function (C/P = 119.35e^0.04day, R² = 0.89, p < 0.001). Changes in the remaining percentage of litter mass during the experiment were significantly correlated with soil C/N ratio (R² = 0.56, p = 0.03) as well as with the soil C/P ratio (R² = 0.98, p < 0.001). Our results of litter decomposition dynamics in this mangrove support the fact of null net primary productivity of the arid mangrove wetlands: fast litter decomposition compensates the ecosystem organic deficit in order to sustain the mangrove productivity. Litter decomposition plays a key role in the ecosystem metabolism in mangroves of arid tropics.     

Mass balance of lead through a small macrotidal estuary: The Morlaix River estuary (Brittany,France)

Dissolved and particulate lead were measured over an annual cycle (12 surveys between February 1998 and January 1999) in the Morlaix River estuary (Brittany, France). The concentrations were investigated in both the water column and the sediment of the river bottom in relation to hydrological conditions. In the water column, dissolved and particulate lead concentrations ranged from 0.1 to 4.4 nM and from 0.04 to 1.9 μmol g^− 1, respectively. Lead concentrations in surface sediment varied from 0.04 to 0.19 μmol g^− 1 and concentrations in the sediment pore water of the estuary were below the detection limit. Compared with the ranges known for pristine estuaries, concentrations of Pb in the water column of the Morlaix River estuary were found to be much higher. Concentrations of Pb also exceeded the lower range of those known for industrialized estuaries. Extensive agricultural activities in the drainage basin may be responsible for Pb levels above pristine conditions. Furthermore, the sediment appeared not to be contaminated. A mass balance was constructed quantifying all known sources and sinks for the Pb in the estuary. Riverine input accounts for most of the total annual metal flux. Burial in sediments was the major sink within the estuary, which acts as a trap especially for the particulate lead. The mass balance shows that the metal accumulation ranged between 414.6 and 446.0 kg year^− 1.     

Sediment accumulation rates in subpolar fjords – Impact of post-Little Ice Age glaciers retreat,Billefjorden, Svalbard

The Little Ice Age (∼1600–1900 AD) and 20th century sediment accumulation rates in Billefjorden, a subpolar fjord on Svalbard, were reconstructed by applying ²¹⁰Pb, ¹³⁷Cs and AMS ¹⁴C datings. The modern sediment accumulation rate decreases from more than 0.39 cm y⁻¹ at the fjord head to 0.08 cm y⁻¹ close to the fjord mouth. However, during the Little Ice Age the sediments accumulated at a much lower rate of 0.02 cm y⁻¹ in the central fjord basin. This difference is most likely related to the rapid retreat of glaciers during the 20th century, when most of them withdrew up to 2 km. The post-Little Ice Age increases in temperature and a negative glacier mass balance resulted in a larger meltwater discharge transferring substantial amounts of sediments released from the glaciers, as well as those eroded from previously stored unconsolidated glacial sediments. A comparison of data from the subpolar fjords of Svalbard suggests that the increase in the sediment accumulation rate is a common trend, and further increases might be expected if climate warming continues. The properties of the fjord sediments (grain size, IRD, coarse-fraction composition, clay mineralogy) from the Little Ice Age and the 20th century showed no distinct differences. The change in the accumulation rate may be the most evident sedimentary record of this climatic change.     

Spatial and temporal distribution of cadmium and copper in water and zooplankton in the Bahía Blanca estuary,Argentina

Cadmium and copper in the dissolved and particulate phase and in zooplankton were determined in the Bahía Blanca estuary during six surveys from March to December 2005. Temperature, pH, salinity, dissolved oxygen, suspended particulate matter, particulate organic matter and chlorophyll-a were also considered. Dissolved Cd was below the detection limit (0.2 μg L⁻¹) for almost the entire study period whereas Cu concentrations (0.5–2.4 μg L⁻¹) indicated a continuous dissolved Cu input. Particulate Cd concentrations ranged from below the detection limit (<0.01) to 28.6 μg g⁻¹ d.w. while particulate Cu ranged from below the detection limit (<0.04) to 53.5 μg g⁻¹ d.w. Cd in mesozooplankton ranged from below the detection limit (<0.01) to 37.4 μg g⁻¹ d.w. Some of the Cd levels were higher than those reported for other aquatic ecosystems. Cu in the mesozooplankton ranged from 1.3 to 89.3 μg g⁻¹ d.w., values which were within the reported values or higher than other studies. The log of the partition coefficients (log (K_d)) of Cd was 0.04, while log (K_d) for Cu ranged from −0.39 to 2.79. These values were lower than both those calculated for other estuaries and the typical coefficients for marine environments. The log of the bioconcentration factor (log BCF) of Cd was 1.78, indicating that Cd concentration was higher in the zooplankton than in the dissolved phase. Log BCF of Cu ranged from 1.15 to 3. The logs of the biomagnification factors (log BMF) of Cd were low, with a range between −3.45 and 2.21 and those for Cu ranged from −0.1 to 3.35. Positive values indicate biomagnification while negative values indicate biodiminution. In general, no significant dissolved Cd concentration appeared to be present in the Bahía Blanca estuary and Cu values did not indicate a critical environmental status. The particulate phase seemed to be the major carrier for Cd and Cu and TPCu values were within the normal values for an anthropogenically stressed estuary but not for a strongly polluted system. This fraction was the most important metal source for the mesozooplankton. Moreover, the highest metal concentrations were in the mesozooplankton since most of the bioconcentration and biomagnification factors were positive, especially for Cu.     

Carbon sources supporting a diverse fish community in a tropical coastal ecosystem (Gazi Bay,Kenya)

Interlinked mangrove–seagrass ecosystems are characteristic features of many tropical coastal areas, where they act as feeding and nursery grounds for a variety of fishes and invertebrates. The autotrophic carbon sources supporting fisheries in Gazi bay (Kenya) were studied in three sites, two located in the tidal creeks flowing through extensive mangrove forests, another site located in the subtidal seagrass meadows, approximately 2.5 km away from the forest. Carbon and nitrogen stable isotope composition of 42 fish species, 2 crustacean species and a range of potential primary food sources (e.g., mangroves, seagrasses and epiphytes, macroalgae) were analysed. There was considerable overlap in the δ¹³C signatures between fish (−16.1 ± 2.1‰), seagrasses (−15.1 ± 3.0‰), seagrass epiphytes (−13.6 ± 3.3‰), and macroalgae (−20.4 ± 3.1‰). Nevertheless, the signatures for most primary producers were sufficiently distinct to indicate that the dominant carbon sources for fish were mainly derived from the seagrass and their associated epiphytic community, and possibly macroalgae. Mangrove-derived organic matter contributes only marginally to the overall fish food web. Carbon supporting these fish communities was derived directly through grazing by herbivorous and some omnivorous fishes, or indirectly through the benthic food web. Fishes from the mangrove creeks had distinctly lower δ¹³C signatures (−16.8 ± 2.0‰) compared to those collected in the adjacent seagrass beds (−14.7 ± 1.7‰). This indicated that these habitats were used as distinct sheltering and feeding zones for the fishes collected, with minimal degree of exchange within the fish communities despite their regular movement pattern.     

The reduction effects of mangrove forest on a tsunami based on field surveys at Pakarang Cape,Thailand and numerical analysis

Using an integrated approach including satellite imagery analysis, field measurements, and numerical modeling, we investigated the damage to mangroves caused by the 2004 Indian Ocean tsunami at Pakarang Cape in Pang Nga Province, Thailand. Comparing pre- and post-tsunami satellite imagery of the study area, we found that approximately 70% of the mangrove forest was destroyed by the tsunami. Based on field observations, we found that the survival rate of mangroves increased with increasing stem diameter. Specifically, we found that 72% of Rhizophora trees with a 25–30 cm stem diameter survived the tsunami impact, whereas only 19% with a 15–20 cm stem diameter survived. We simulated the 2004 Indian Ocean tsunami using the nonlinear shallow-water wave theory to reproduce the tsunami inundation flow and investigated the bending moment acting on the mangrove trees. Results of the numerical model showed that the tsunami inundated areas along the mangrove creeks, and its current velocity reached 5.0 m s⁻¹. Based on the field measurements and numerical results, we proposed a fragility function for mangroves, which is the relationship between the probability of damage and the bending stress caused by the maximum bending moment. We refined the numerical model to include the damage probability of mangrove forests using the obtained fragility function to investigate the tsunami reduction effect of mangrove forest. Under simple numerical conditions related to the mangrove forest, ground level, and incident wave, the model showed that a mangrove forest of Rhizophora sp. with a density of 0.2 trees m⁻² and a stem diameter of 15 cm in a 400 m wide area can reduce the tsunami inundation depth by 30% when the incident wave is assumed to have a 3.0 m inundation depth and a wave period of 30 min at the shoreline. However, 50% of the mangrove forest is destroyed by a 4.5 m tsunami inundation depth, and most of the mangrove forest is destroyed by a tsunami inundation depth greater than 6 m. The reduction effect of tsunami inundation depth decreased when the tsunami inundation depth exceeded 3 m, and was mostly lost when the tsunami inundation depth exceeded 6 m.     

Geotechnical characterization and strain analyses of sediment in the Mauritania Slide Complex,NW-Africa

Mass wasting processes are a common phenomenon along the continental margin of NW-Africa. Located on the high-upwelling regime off the Mauritanian coastline, the Mauritania Slide Complex (MSC) is one of the largest events known on the Atlantic margin with an affected area of ∼30?000 km². Understanding previous failure events as well as its current hazard potential are crucial for risk assessment with respect to offshore installations and tsunamis. We present the results of geotechnical measurements and strain analyses on sediment cores taken from both the stable and the failed part of the MSC and compare them to previously published geophysical and sedimentological data. The material originates from water depths of 1500–3000 m and consists of detached slide deposits separated by undisturbed hemipelagic sediments. While the hemipelagites are characterized by normal consolidation with a downward increase in bulk density and shear strength (from 1.68 to 1.8 g/cm³, 2–10 kPa), the slid deposits of the uppermost debris flow event preserve constant bulk density values (1.75 and 1.8 g/cm³) with incisions marking different flow events. These slid sediments comprise three different matrix types, with normal consolidation at the base (OCR = 1.04), strong overconsolidation (OCR = 3.96) in the middle and normal consolidation to slight overconsolidation at the top (OCR = 0.91–1.28). However, the hemipelagic sediments underlying the debris flow units, which have been ¹⁴C dated at <24 ka BP, show strong to slight underconsolidation (OCR = 0.65–0.79) with low friction coefficients of μ = 0.18. Fabric analyses show deformation intensities R ≥ 4 (ratio σ₁/σ₃) in several of the remobilized sediments. Such high deformation is also attested by observed disintegrated clasts from the underlying unit in the youngest debrites (¹⁴C-age of 10.5–10.9 ka BP). These clasts show strong consolidation and intense deformation, implying a pre-slide origin and amalgamation into the mass transport deposits. While previous studies propose an emplacement by retrogressive failure for thick slide deposits separated by undisturbed units, our new data on geotechnical properties, strain and age infer at least two different source areas with a sequential failure mechanism as the origin for the different mass wasting events.