Distribution and burial of organic carbon in sediments from the Indian Ocean upwelling region off Java and Sumatra,Indonesia

Sediments were sampled and oxygen profiles of the water column were determined in the Indian Ocean off west and south Indonesia in order to obtain information on the production, transformation, and accumulation of organic matter (OM). The stable carbon isotope composition (δ¹³C_org) in combination with C/N ratios depicts the almost exclusively marine origin of sedimentary organic matter in the entire study area. Maximum concentrations of organic carbon (C_org) and nitrogen (N) of 3.0% and 0.31%, respectively, were observed in the northern Mentawai Basin and in the Savu and Lombok basins. Minimum δ¹⁵N values of 3.7‰ were measured in the northern Mentawai Basin, whereas they varied around 5.4‰ at stations outside this region. Minimum bottom water oxygen concentrations of 1.1 mL L^?1, corresponding to an oxygen saturation of 16.1%, indicate reduced ventilation of bottom water in the northern Mentawai Basin. This low bottom water oxygen reduces organic matter decomposition, which is demonstrated by the almost unaltered isotopic composition of nitrogen during early diagenesis. Maximum C_org accumulation rates (CARs) were measured in the Lombok (10.4 g C m^?2 yr^?1) and northern Mentawai basins (5.2 g C m^?2 yr^?1). Upwelling-induced high productivity is responsible for the high CAR off East Java, Lombok, and Savu Basins, while a better OM preservation caused by reduced ventilation contributes to the high CAR observed in the northern Mentawai Basin. The interplay between primary production, remineralisation, and organic carbon burial determines the regional heterogeneity. CAR in the Indian Ocean upwelling region off Indonesia is lower than in the Peru and Chile upwellings, but in the same order of magnitude as in the Arabian Sea, the Benguela, and Gulf of California upwellings, and corresponds to 0.1–7.1% of the global ocean carbon burial. This demonstrates the relevance of the Indian Ocean margin off Indonesia for the global OM burial.     

Anthropogenic organic contaminants in water, sediments and benthic organisms of the mangrove-fringed Segara Anakan Lagoon, Java, Indonesia

Segara Anakan, a mangrove-fringed coastal lagoon in Indonesia, has a high diversity of macrobenthic invertebrates and is increasingly affected by human activities. We found >50 organic contaminants in water, sediment and macrobenthic invertebrates from the lagoon most of which were polycyclic aromatic compounds (PACs). Composition of PACs pointed to petrogenic contamination in the eastern lagoon. PACs mainly consisted of alkylated PAHs, which are more abundant in crude oil than parent PAHs. Highest total PAC concentration in sediment was above reported toxicity thresholds for aquatic invertebrates. Other identified compounds derived from municipal sewage and also included novel contaminants like triphenylphosphine oxide. Numbers of stored contaminants varied between species which is probably related to differences in microhabitat and feeding mode. Most contaminants were detected in Telescopium telescopium and Polymesoda erosa. Our findings suggest that more attention should be paid to the risk potential of alkylated PAHs, which has hardly been addressed previously.     

Typhoon-induced precipitation impact on nutrient and suspended matter dynamics of a tropical estuary affected by human activities in Hainan,China

Typhoons regularly hit the coasts along the northern South China Sea during summer monsoon. However, little is known on the effects of typhoon-related heavy precipitation on estuarine dynamics and coastal ecosystems. We analyzed physico-chemical characteristics, and concentrations and composition of dissolved and suspended matter in the Wenchang/Wenjiao Estuary (WWE) on the tropical island of Hainan, China, prior to and after typhoon Kammuri in August 2008. Before the typhoon, the estuary displayed vertical and horizontal gradients. High nutrient inputs from agriculture and widespread aquaculture were to a large extent converted into biomass inside the estuarine lagoon resulting in low export of nutrients to coastal waters and a mainly autochthonous origin of total suspended matter (TSM). Heavy typhoon-associated precipitation increased river runoff, which moved the location of the estuarine salinity gradient seaward. It resulted in an export of dissolved and particulate matter to coastal waters one day after the typhoon. Dissolved nutrients increased by up to an order of magnitude and TSM increased approximately twofold compared to pre-typhoon values. Lower δ¹³C_org and δ¹⁵N and elevated C/N ratios of TSM together with lower chlorophyll a (chl a) concentrations indicated an increased contribution of terrestrial material originating from typhoon-induced soil erosion. Local uptake of excess nutrients inside the lagoon was inhibited because of reduced water transparency and the lack of phytoplankton, which had been washed out by the initial freshwater pulse. Two weeks after the typhoon, TSM concentration and composition had almost returned to pre-typhoon conditions. However, physico-chemical properties and nutrients were still different from pre-typhoon conditions indicating that the estuarine system had not fully recovered. Unusually high chl a concentrations in the coastal zone indicated a phytoplankton bloom resulting from the typhoon-induced nutrient export. The typhoon-induced flushing of the WWE resulted in hyposalinity, reduced water transparency, siltation, as well as temporary eutrophication of coastal waters. These are physiological stressors, which are known to impair the performance of adjacent seagrass meadows and coral reefs. The predicted increase in typhoon frequency and intensity will lead to a frequently recurring exposure of coastal ecosystems to these threats, particularly in the South China Sea region where aquaculture is widespread and tropical cyclone frequency is at a maximum.     

Impact of pond aquaculture effluents on seagrass performance in NE Hainan,tropical China

The impact of pond aquaculture effluents on the distribution and performance of seagrasses was examined in NE Hainan, tropical China. Samples were taken along transects in three back-reef areas with different extent of aquaculture production in their hinterland. High δ¹⁵N in seagrass leaves and epiphytes (6–9‰) similar to values in pond effluents documented aquaculture as dominant nitrogen source in the back-reefs with decreasing impact with distance from shore. Seagrass species abundance, shoot density and biomass were lower and concentrations of nutrients, chlorophyll and suspended matter were higher at nearshore sites with high and moderate pond abundance than at the control site. High epiphyte loads and low δ³⁴S in seagrass leaves suggest temporal shading and sulphide poisoning of the nearshore seagrasses. Observed gradients in environmental parameters and seagrass performance indicate that the distance from the pond outlets and size of the adjacent pond agglomeration are major determinants of seagrass degradation.     

Food preferences of mangrove crabs related to leaf nitrogen compounds in the Segara Anakan Lagoon,Java, Indonesia

The large amounts of leaf litter produced by tropical mangrove forests serve as a major food source for the benthic fauna. The reasons for the preferential consumption of mangrove leaves by crabs are unclear as yet. We investigated the diet, food preferences and consumption rates of 8 dominant grapsoid crab species (Perisesarma spp., Episesarma spp., Metopograpsus latifrons, and Metaplax elegans) in mangroves of Segara Anakan, Java, Indonesia, by means of stomach-content analysis and feeding experiments. Leaves from the five most abundant mangrove tree species (Aegiceras corniculatum, Avicennia alba, Ceriops decandra, Rhizophora apiculata, and Sonneratia caseolaris) were analyzed for organic carbon, total nitrogen, δ¹³C, δ¹⁵N and amino acids and hexosamines. This study is the first that investigated crab food preferences related to the nitrogen compound composition of leaves.Our results show that Episesarma spp. and Perisesarma spp. are omnivorous crabs which mainly feed on detritus, mangrove litter and bark, and on a small amount of roots, algae and animal matter whereas M. elegans is a detritus feeder. In feeding experiments with green, yellow and brown leaves Perisesarma spp. and E. singaporense had the highest consumption rates for brown leaves of R. apiculata and S. caseolaris, and for green leaves of A. alba. Preferred leaves were characterized by a high amount and/or freshness of nitrogenous compounds and their biochemical composition was significantly different from that of disliked leaves (all leaves of A. corniculatum and C. decandra, green and yellow leaves of R. apiculata and S. caseolaris). The presence of the hexosamine galactosamine found only in brown leaves indicates that bacteria contribute to the amount of bioavailable nitrogen compounds. We infer that the nitrogen compound composition rather than the C/N ratio alone is a determinant for bioavailability of mangrove leaves and hence may partly explain the crabs' food preferences.     

溶解作用对南海北部沉积物捕获器碳、氮通量估算的影响

由于化学溶出、物理溶解以及胞外酶等作用,沉积物捕获器中颗粒物在锚系布放期间会发生一定程度的溶解,从而引起沉积物捕获器中碳、氮颗粒物通量的低估。本文对于1987—1988年南海北部中深层沉积物捕获器中碳、氮颗粒物的溶解作用进行了研究。溶解作用对于碳、氮通量估算的影响大致随着深度的增加而减小。总体而言,颗粒有机碳通量低估约3.8%~40.3%,平均值为26.6%。颗粒氮通量低估约4.2%~76.4%,平均值为43.7%。碳、氮颗粒物的溶出量与颗粒物通量大小关系不明显,但是样品储存时间对于碳、氮颗粒物溶解作用的影响较显著,储存时间较长的样品中颗粒物溶出量更大。     

Temporal variability of amino acid, hexosamine, and carbohydrate fluxes on the eastern Brazilian continental margin related to discharge of the São Francisco River, Brazil

Settling particles collected at 1550 m water depth off the São Francisco River, Brazil, between January and May 1995 showed peak fluxes of amino acids, hexosamines, and carbohydrates, which formed the onset of a three-week period of high organic matter (OM) flux, coinciding with the high discharge period of the river. Two phases of OM deposition exist: (1) the fluvial input of nutrients triggering a bloom of non biomineralizing plankton, and (2) suspended sediment mainly derived from shelf erosion increasing the fluxes of refractory OM. This indicates the importance of seasonally varying hydrodynamic conditions and nutrient input from the continent for the production and sedimentation of OM to the continental margin of eastern Brazil.     

Biogeochemical characteristics of coastal waters adjacent to small river–mangrove systems, East Brazil

This study addresses the composition of biogenic matter and the metabolic activity of coastal waters of the eastern Brazilian shelf, bordered by small river–mangrove systems. Oceanic Brazil Current waters induce oligotrophic and near to homogeneous conditions of chemical constituents along the inner shelf. The impact of small river–mangrove systems upon coastal waters is minor and of local nature. Bottom topography, coral reef habitats, and local upwelling also induce minor local spatial variability of dissolved inorganic and organic nutrients and O₂ and CO₂ saturation levels in the coastal waters. Metabolic activity during the daylight period, inferred from O₂ and CO₂ saturation levels, varied from slightly autotrophic to heterotrophic.     

Urbanization Impact on Regional Climate and Extreme Weather: Current Understanding,Uncertainties, and Future Research Directions

Urban environments lie at the confluence of social,cultural,and economic activities and have unique biophysical characteristics due to continued infrastructure development that generally replaces natural landscapes with built-up structures.The vast majority of studies on urban perturbation of local weather and climate have been centered on the urban heat island(UHI)effect,referring to the higher temperature in cities compared to their natural surroundings.Besides the UHI effect and heat waves,urbanization also impacts atmospheric moisture,wind,boundary layer structure,cloud formation,dispersion of air pollutants,precipitation,and storms.In this review article,we first introduce the datasets and methods used in studying urban areas and their impacts through both observation and modeling and then summarize the scientific insights on the impact of urbanization on various aspects of regional climate and extreme weather based on more than 500 studies.We also highlight the major research gaps and challenges in our understanding of the impacts of urbanization and provide our perspective and recommendations for future research priorities and directions.