Coastal sediments under the influence of multiple organic enrichment sources: An evaluation using carbon and nitrogen stable isotopes

Source identification of sedimentary organic carbon in coastal wetlands of the western Bohai Sea

Coastal wetlands play a vital role in mitigating climate change, yet the characteristics of buried organic carbon (OC) and carbon cycling are limited due to difficulties in assessing the composition of OC from different sources (allochthonous vs. autochthonous). In this study, we analyzed the total organic carbon (TOC) to total nitrogen (TN) ratio (C/N), stable carbon isotope (δ13C) composition, and n-alkane content to distinguish different sources of OC in the surface sediments of the coastal wetlands on the western coast of the Bohai Sea. The coupling of the C/N ratio with δ13C and n-alkane biomarkers has been proved to be an effective tool for revealing OC sources. The three end-member Bayesian mixing model based on coupling C/N ratios with δ13C showed that the sedimentary OC was dominated by the contribution of terrestrial particulate organic matter (POM), followed by freshwater algae and marine phytoplankton, with relative contributions of 47 ± 21 %, 41 ± 18 % and 12 ± 17 %, respectively. The relative contributions of terrestrial plants, aquatic macrophytes and marine phytoplankton assessed by n-alkanes were 56 ± 8 %, 35 ± 9 % and 9 ± 5 % in the study area, respectively. The relatively high salinity levels and strong hydrodynamic conditions of the Beidagang Reservoir led to higher terrestrial plants source and lower aquatic macrophytes source than these of Qilihai Reservoir based on the assessment of n-alkanes. Both methods showed that sedimentary OC was mainly derived from terrestrial sources (plant-dominated), suggesting that vegetation plays a crucial role in storing carbon in coastal wetlands, thus, the coastal vegetation management needs to be strengthened in the future. Our findings provide insights into the origins and dynamics of OC in coastal wetlands on the western coast of the Bohai Sea and a significant scientific basis for future monitoring of the blue carbon budget balance in coastal wetlands.

Interannual variability in particulate organic matter distribution and its carbon stable isotope signatures from the western Indian shelf waters

Particulate organic carbon and nitrogen (POC, PN, collectively particulate organic matter, POM) and the stable isotopic signature of POC (δ¹³C_POC) are important to delineate its sources and recycling in shelf water. The present study provides insights into the factors responsible for spatial and interannual variability in POM and δ¹³C_POC values along the western Indian shelf waters (8° N -21° N) during the southwest (SW) monsoon (August) 2017 and 2018. The dominance of phytoplankton-derived POM with a negligible terrestrial influence was evident from the positive correlation between POC and TChla contents, ratios of C: N, and δ¹³C_POC signatures. Prominent upwelling signatures [cold nutrient-rich water, higher POM, total Chlorophylla (TChla), and δ¹³C_POC values] were noted in the south (8-12° N), whereas low nutrient warm waters (lower values of POM, TChla, and δ¹³C_POC) were prevalent in the north (13-21° N). Phytoplankton biomass was significantly higher and matured in 2017 due to an early and stronger upwelling in the south. In 2018, delayed and weak upwelling (evident from Ekman offshore transport and pumping velocity) resulted in the late development of phytoplankton bloom and lower POM. Furthermore, considerably lower nutrient supply within the mixed layers in 2018 compared to 2017 was partially attributed to the enhanced spatial expansion of low salinity waters closer to the surface. In the north, in 2018, higher wind speeds enhanced vertical mixing resulting in increased nutrient supply and TChla compared to 2017. We conclude that monsoon wind speed in the northern shelf and strength as well as the timing of the upwelling, including freshwater flux in the south, can be the key factors in modulating the interannual variability in POM distribution and δ¹³C_POC signature in the western Indian Shelf waters.

Assessing spatiotemporal sources of biogenic and anthropogenic sedimentary organic matter from the mainstream Haihe River, China: Using n-alkanes as indicators

Sedimentary organic matter (SOM) plays an important role in the transportation and transformation of various pollutants and the carbon cycle in aquatic and terrestrial ecosystems, especially for seagoing rivers. However, few studies have focused on the sources and factors of SOM in rivers under the significant pressure of high urbanization and industrialization. In this study, we adopted the molecular markers of n-alkanes and their proxies in the mainstream Haihe River to reveal the spatiotemporal distributions and biogenic and anthropogenic sources of SOM. The concentrations of Σ₂₉n-alkanes, Σ_biogenicn-alkanes, and Σ_{anthropogenic}n-alkanes were 4985.6 (127.5-26,296.6), 1872.1 (38.1-9216.9), and 3113.5 (89.4-18,259.7) ng·g^-1 dw (dry weight), respectively. Hybrid sources of n-alkanes were found in this study. The composition distribution and proxies of n-alkanes showed that woody and herbaceous plants are the main sources of biogenic SOM, while incomplete fossil fuel burning and heavy oil emissions served as the main contributors to anthropogenic SOM in the mainstream Haihe River, especially through industrial activities. The average chain length of biogenic n-alkanes (ACL_bio) was verified to quantify the relative contributions of biogenic sources of SOM and proxies; the average chain length of anthropogenic n-alkanes (ACL_anthro), and the ratio of unit short‑carbon to unit long‑carbon anthropogenic n-alkanes (L/H) were verified to quantify the relative contributions of anthropogenic sources of SOM in the river system. Impacts from sedimentary geochemistry (such as total organic carbon (TOC) and grain size of sediments) on n-alkanes were explored, and the correlations of Σ₂₉n-alkanes with TOC and grain size of the river sediment indicated that terrestrial organic matter was the main source of SOM, while emissions from incomplete combustion and intensive manufacturer activities should also not be neglected.

Tracking the impacts of nutrient inputs on estuary ecosystem function

Estuaries are one of the most impacted coastal environments globally, subjected to multiple stressors from urban, industry and coastal development. With increasing anthropogenic activity surrounding estuarine systems, sewage inputs have become a common concern. Stable isotope analysis provides a well-established tool to investigate the incorporation of nitrogen into marine organisms and identify major nutrient sources. Benthic macroinvertebrate communities are often used as bioindicators in ecological studies as they typically display predictable responses to anthropogenic pressures, however have a suite of limitations and costs associated with their use. 16S rDNA amplicon sequencing techniques allow for investigation of the microbial communities inhabiting complex environmental samples, with potential as a tool in the ecological assessment of pollution. These communities have not yet been adequately considered for ecological studies and biomonitoring, with a need to better understand interactions with environmental stressors and implications for ecosystem function. This study used a combination of stable isotope analysis to trace the uptake of anthropogenic nitrogen in biota, traditional assessment of benthic macroinvertebrate communities, and 16S rDNA genotyping of benthic microbial communities. Stable isotope analysis of seagrass and epiphytes identified multiple treated and untreated sewage inputs, ranges of 5.2-7.2‰ and 1.9-4.0‰ for δ¹⁵N respectively, as the dominant nitrogen source at specific locations. The benthic macroinvertebrate community reflected these inputs with shifts in dominant taxa and high abundances of polychaetes at some sites. Microbial communities provided a sensitive indication of impact with a breadth of information not available using traditional techniques. Composition and predicted function reflected sewage inputs, particularly within sediments, with the relative abundance of specific taxa and putative pathogens linked to these inputs. This research supports the growing body of evidence that benthic microbial communities respond rapidly to anthropogenic stressors and have potential as a monitoring tool in urban estuarine systems.

Oyster Biodeposition Alleviates Sediment Nutrient Overload: A Case Study at Shenzhen Bay, China

Oysters are ecological engineers, and previous studies have examined their role as competent facilitators of ecological restoration. However, the decisive role of oysters in the aquatic environment is still debatable because oyster biodeposition (OBD) may also increase the nutrients enriched in sediments. In order to better interpret this problem, we sampled sediment cores from representative oyster culture areas and uncultured areas in Shenzhen Bay. The results have shown that the TOC (total organic carbon) and TN (total nitrogen) decreased significantly (p < 0.05) at the surface sediment layer (0-20-cm deep) and the sediment layer (20-40-cm deep) of the oyster site compared with the reference site. The decreased TOC and TN were also observed at 60- to 100-cm sediment depth in the oyster site. This indicated that the OBD significantly impacted the concentration of TOC and TN in the sediment. To confirm the alleviative role of OBD, we conducted stable isotope (δ¹³C and δ¹⁵N) analyses, which further demonstrated the presence of heavier and less lighter forms of organic carbon and nitrogen sediment. The surface sediment layer (0-20 cm) at the oyster site showed 8% more δ¹³C‰ compared with the control site (p < 0.05), reflecting the reduction in the TOC. In order to reveal the potential microbial mechanisms involved in OBD, we performed a functional analysis using the Geochip5 advanced microarray technology. Regarding carbon metabolism, we observed that genes (encoding pullulanase, glucoamylase, exoglucanase, cellobiase, and xylanase) involved in the degradation of relatively labile C-based molecules (e.g., starch, cellulose, and hemicellulose) were highly represented in an experimental area (p < 0.05). In addition, microbes in the experimental area exhibited a greater capacity for degrading recalcitrant C (e.g., lignin), which involves glyoxal oxidase (glx), manganese peroxidase (mnp), and phenol oxidase. Among the genes controlling nitrogen metabolism, the genes involved in denitrification, assimilation, ammonification, and nitrification were differentially expressed compared with the control area. These results indicated that microbial metabolic roles might have enhanced the C/N-flux speed and reduced the overall nutrient status. We concluded that OBD alleviates sediment nutrient overload under oyster farming from a microbial ecological perspective in a rapidly urbanized coastal area.

δ13C, δ15N and TOC/TN as indicators of the origin of organic matter in sediment samples from the estuary of a tropical river

The present study aimed to determine the total organic carbon (TOC), total nitrogen (TN), the carbon‑nitrogen ratio (TOC/TN), carbon isotope (δ¹³C), and nitrogen isotope (δ¹⁵N) in five sediment cores collected from upstream to downstream of the Rio Serinhaem estuary, State of Bahia, Northeast Brazil, in order to investigate the origin of the deposited organic matter (OM).Significant positive correlation was found between TOC and NT (r_s = 0.75); TOC/TN and TOC (r_s = 0.64); δ¹⁵N and TOC (r_s = 0.72); and δ¹⁵N and TOC/TN (r_s = 0.63). The values of δ¹³C and δ¹⁵N found are characteristic of terrestrial sources. The TOC/TN ratio confirmed the data found for δ¹³C and δ¹⁵N, which recorded the origin of organic matter from terrestrial C3 type plants. Upstream of the estuary, the highest means of TOC/TN were found (T1 = 36.9 and T2 = 24.4), as reflected by the increase in TOC content or reduction in TN. The OM along the estuary is predominantly from plants with a C3 photosynthetic pattern, indicating that the Serinhaem River estuary is considered a relatively well-preserved environment.

Multiple livelihood strategies and high floristic diversity increase the adaptive capacity and resilience of Sri Lankan farming enterprises

Globally farmers are challenged by increasing climate variability and frequency of extreme events. However, traditional farming enterprises demonstrate resilience. To understand the underlying reasons, traditional farming enterprises in Sri Lanka were explored. Eighty-five farming enterprises were sampled across nine locations of the Intermediate agroecological zone using mixed methods. Farming enterprises incorporate On- and Off-farm livelihood components (graphical abstract). On-farm refers to landholdings with land uses including tree-dominant forest gardens (FGs), paddy, cash crops, swidden plots (chenas), plantations and livestock. Off-farm includes employment, trading and grants. We investigated how farming enterprises remained resilient, and which land use had the greatest adaptive capacity and best fulfilled household needs? Farming enterprises were assessed with respect to water availability, farmers' perspectives of climate variability, their socioeconomic characteristics, and land uses in landholdings. Land uses were characterised and compared by floristic diversity, crop: utility benefits, food functions, and those consumed and sold. Results revealed that most respondents were women, had primary school education and engaged full-time in farming. Cultivation was mainly rainfed. Farmers' perceptions of climate variability were supported by meteorological data showing that interannual and seasonal rainfall variability prevailed in the reference and preceding years. Farmers withstood these challenges owing to FGs, which were the oldest and dominant of all land uses, with larger area, highest plant and crop species richness, and crop diversity. Greater numbers of primary and secondary FG crops and products provided multiple household benefits. High floristic diversity, tree-dominance and multifunctionality gave FGs strong adaptive capacity. Nevertheless, farmers adopted multiple land uses with diverse landscape designs and Off-farm livelihood strategies simultaneously because this combination offered greater opportunities, buffered risk and increased resilience in farming enterprises. A clear implication of this study is that policymakers should engage with farmers when planning for a resilient agriculture in a variable climate scenario.

Ecological features of a rocky intertidal community exposed to sewage effluent

Sewage is among the largest components of coastal pollution, showing a variable scale and size when causing an impact. In this study, temporal and spatial sewage-related gradients were identified using univariate and multivariate methods. Phosphates and nitrogen-based nutrients, except nitrate, were associated to sewage. Abundance and species richness decrease with distance from the sewage outfall while evenness increased. Filter-feeder bivalves and grazer crustaceans showed preference for the sewage discharge site. Gastropods were more abundant at an intermediate distance, likely reflecting primary production enhancement by sewage. Beta diversity was lower at the location and time with highest sewage loadings. The turnover component of beta diversity expressed as an absolute or proportional value was also useful to detect temporal and spatial sewage-related gradients. Highly energetic hydrodynamics contributes to ameliorate sewage impacts, yet not enough to veil the effect of pollution in this study.

A Quantitative Assessment of Organic Carbon Content as a Regional Sediment-Condition Indicator

Organic carbon content of sediments, whether directly or indirectly assessed, has often been used as an indicator of marine benthic community condition both in site-specific and regional scale condition assessment studies. The conceptual framework underlying use of this indicator was developed based primarily on site-specific studies. A quantitative analysis of literature data on sediment organic matter impacts in marine systems was conducted to determine whether biotic metrics respond to abiotic indicators of sediment organic content, as predicted by conceptual models, at larger spatial scales. The ability to detect predicted decreases in community metrics (abundance, species richness, species diversity index H', biomass) varied among metrics, with best performance by species richness and H'. There was significant added variation both between and within analytical approaches (loss on ignition, total organic carbon methods), emphasizing the need for careful cross calibration and quality control in studies with multiple laboratory partners. High levels of variability for biotic metrics versus organic carbon metrics appear typical for large scale studies, and organic matter source, site depth, and individual estuarine system differences were important sources of variation. Covariation of organic matter content with percent fine sediments is another known source of variation, but various normalization methods may be inadequate due to inherent sources of variation at estuary level. While likely still useful for point-source studies, multiple major sources of variation appear to limit the usefulness of sediment organic content as a benthic condition indicator at larger spatial scales.

Spatiotemporal variation in environmental features and elemental/isotopic composition of organic matter sources and primary producers in the Yundang Lagoon (Xiamen, China)

Aquatic eutrophication is a major problem globally, leading to significant chemical-compositional changes in the first trophic levels of a food web. These will consequently affect the whole food web dynamics in eutrophic coastal ecosystems. In this study, we analyzed the spatiotemporal variation in water chlorophyll-a, total organic carbon (TOC) and TOC/Chl-a ratio, and in the elemental/isotopic (C_at/N_at, δ¹³C, δ¹⁵N) composition of particulate organic matter (POM), phytoplankton, sedimentary organic matter, benthic microalgae, U. lactuca, and decaying leaves of mangrove plants in the eutrophic, urban lagoon of Yundang (Xiamen, China). Investigations were carried out in four different sectors of the lagoon in March (dominated by Ulva lactuca) and September (dominated by phytoplankton) 2009, and the feasible contribution of potential organic matter (OM) sources to POM was assessed in each period. The results showed significant spatiotemporal variation in δ¹³C and δ¹⁵N of POM, owing to changes in its carbon sources. The POM in the diversion canal (POM_DC) of the lagoon originated mainly from terrestrial OM both in March and September, as evidenced by a C_at/N_at ratio of 12~17 and a TOC/Chl-a ratio exceeding 400, as well as depleted δ¹³C (- 27.3~- 23.7‰) and δ¹⁵N (- 2.8~0.1‰). The POM in the main canal (POM_MC) and the inner (POM_IL) and outer (POM_OL) sectors of the lagoon were largely composed of lagoon-borne phytoplankton in September. This was revealed by TOC/Chl-a values below 100 and enriched δ¹³C values (- 22.7~- 17.9‰) which are close to the values typical for fresh phytoplankton. However, these were strongly regulated by exogenous OM in March. The combined contribution of POM_MC and POM_DC to POM in March reached 64-99% in the inner lagoon and 67-88% in the outer lagoon. Non-living POM, which originates from terrestrial organic detritus, was the main contributor to POM (60.7~85.7%) both in the inner and outer sections of the lagoon. Overall, the present study demonstrates that the temporal changes in the dominance of primary producers were reflected in significant variation in the environmental features and elemental/isotopic composition of OM sources and their contribution to POM in the Yundang Lagoon. To further our understanding of the effects of eutrophication due to different primary producers on the resource partitioning in the Yundang Lagoon, additional studies on the consumers and the whole food web of the lagoon are expected.

Anthropogenic and natural variability in the composition of sedimentary organic matter of the urbanised coastal zone of Montevideo (Río de la Plata)

This study is aimed to identify the different sources of sedimentary organic matter (SOM) within Montevideo coastal zone (MCZ). To this end δ¹³C, δ¹⁵N and C/N ratio were analysed in surface sediments and a sediment core. Sediment core analysis showed that until ~1950CE SOM was mainly marine, observing a shift towards lower δ¹³C in recent sediments, evidencing an estuarine composition. This trend was associated to the climatic variability, which exerted a major influence on the SOM composition, leading to an increased input of terrigenous material and associated anthropogenic contaminants. Surface sediments collected during different El Niño South Oscillation (ENSO) phases did not show inter-annual variability in SOM composition, which was mainly marine in both eastern and western region of MCZ and estuarine in Montevideo Bay. This spatial pattern provides new insights on the dynamics and factors affecting organic matter sources available for primary consumers along the study region.

Geochemical markers of sedimentary organic matter in Todos os Santos Bay, Bahia - Brazil. Indicators of sources and preservation

Natural stable isotopes, such as carbon (C) and nitrogen (N), are modern tools to assess geochemical processes. C and N in organic matter can carry fingerprints of their hydrologic flows and sedimentary processes, including any anthropogenic modification on the natural system. This study focuses on the determination of aliphatic and polycyclic aromatic hydrocarbons and isotopic ratio in the sediment of Todos os Santos Bay (TSB). The isotopic results of the total organic matter indicate varied contribution marine and terrigenous. Typical rates of PAHs mainly indicate a pyrogenic source and mixture between pyrogenic and petrogenic sources. Typical ratios for the n-alkanes indicate the presence of petroleum hydrocarbons. The isotopic composition of n-alkanes suggests a mixture of sources, with the possible contribution of petrogenic.

One-century decline of mollusk diversity as consequence of accumulative anthropogenic disturbance in a tropical estuary (Cuban Archipelago)

In order to infer changes in sediments and mollusk assemblages for the last century, we used biogeochemical data from two ²¹⁰Pb dated cores collected in Sagua La Grande estuary, Cuban Archipelago. We found evidences of cumulative anthropogenic disturbance during the last century, causing considerable depletion of mollusk assemblage diversity and enhancement of the dominance of deposit feeding species. The sequence of impacts assessed was i) eutrophication due to nutrient releases from urban settlements, ii) habitat alteration due to water channeling and damming, and iii) mercury pollution. These successive impacts caused a steady diversity depletion from ca. 70 mollusk species in 1900 to less than five in 2010. Only two species persisted in the estuary: Nuculana acuta and Finella dubia. Hurricanes did not impact the molluscan fauna in the long term. The effects of the anthropogenic impacts suggest that the resilience of this estuarine system is compromised.

Precise and economical dredging model of sediments and its field application: case study of a river heavily polluted by organic matter, nitrogen, and phosphorus

Environmental dredging is an efficient means to counteract the eutrophication of water bodies caused by endogenous release of nitrogen and/or phosphorus from polluted sediments. The huge operational cost and subsequent disposal cost of the dredged polluted sediments, as well as the adverse effect on the benthic environment caused by excessive dredging, make the currently adopted dredging methods unfavorable. Precise dredging, i.e., determining the dredging depth based on the pollution level, not only significantly decreases the costs but also leaves a uniform favorable environment for benthos. However, there is still no feasible process to make this promising method executable. Taking a river heavily polluted by organic compounds as an example, we proposed an executable precise dredging process, including sediment survey, model establishment, data interpolation, and calculation of dredging amount. Compared with the traditional dredging method, the precise one would save 16 to 45% of cost according to different pollutant removal demands. This precise dredging method was adopted by the National Water Project of China to treat the endogenous pollution of Nanfei River in 2010. This research provides a universal scientific and engineering basis for sediment dredging projects.

A geochemical record of environmental changes in sediments from Sishili Bay, northern Yellow Sea, China: anthropogenic influence on organic matter sources and composition over the last 100 years

Total organic carbon (TOC), total nitrogen (TN), δ(13)C and δ(15)N were measured in sediment cores at three sites in Sishili Bay, China, to track the impacts of anthropogenic activities on the coastal environment over the last 100 years. The increased TOC and TN in the upper section of sediment cores indicated a eutrophic process since 1975. In comparison, the TOC and TN in the sediment core near to a scallop aquaculture area displayed a much slower increase, indicating the contribution of scallop aquaculture in mitigating eutrophication. Combined information from δ(13)C, δ(15)N and TOC:TN indicated an increased terrestrial signal, although organic matter sources in Sishili Bay featured a mixture of terrestrial and marine sources, with phytoplankton being dominant. Increased fertilizer use since 1970s contributed to the eutrophic process in Sishili Bay since 1975, and increased sewage discharge from 1990s has added to this process.

The effects of wastewater effluent and river discharge on benthic heterotrophic production, organic biomass and respiration in marine coastal sediments

We examine effects of high river particulate flux and municipal wastewater effluent on heterotrophic organic carbon cycling in coastal subtidal sediments. Heterotrophic production was a predictable (r(2)=0.95) proportion (56%) of oxidized OC flux and strongly correlated with organic/inorganic flux. Consistent growth efficiencies (36%) occurred at all stations. Organic biomass was correlated with total, OC and buried OC fluxes, but not oxidized OC flux. Near the river, production was modest and biomass high, resulting in low P/B. Outfall deposition resulted in depleted biomass and high bacterial production, resulting in the highest P/B. These patterns explain why this region is production "saturated". The δ(15)N in outfall effluent, sediments and dominant taxa provided insight into where, and which types of organisms feed directly on fresh outfall particulates, on older, refractory material buried in sediments, or utilize chemosynthetic symbiotic bacteria. Results are discussed in the context of declining bottom oxygen conditions along the coast.

Trophic level determines levels of brominated flame-retardants in coastal herring gulls

Liver concentrations of eight polybrominated diphenyl ethers (ΣPBDEs: sum of brominated diphenyl ethers [BDE]-28, -47, -99, -100, -153, -154, -183, and -209) ranged from 135 to 985 ngg(-1) lipid weight (lw) in coastal herring gulls (Larus argentatus) from the marine Hvaler Archipelago (The Glomma River Estuary), Norway. Hexabromocyclododecane (HBCD) concentrations ranged from 10 to 698 ngg(-1)lw. High range in δ(13)C indicates that gulls were subject to a diversity of carbon sources, likely reflecting their mixed feeding on terrestrial and marine organisms, or diversity of autochthonous and allochthonous (watershed) energy sources at the bases of their marine/estuarial food chains. Inverse relationships of HBCD, and to somewhat lesser extent of BDE-209, with δ(13)C values suggest higher abundance of these compounds in the land-derived energy-sources of the gulls. Inverse relationships of BDE-99, BDE-183 and BDE-209 with δ(15)N suggest that trophic relationships affect bioaccumulation of these compounds in the herring gulls, with greater bioaccumulation from lower trophic level prey species. This may be because these PBDE congeners are subject of debromination in higher trophic levels prey species of the gulls (e.g., teleost fish). Levels of BDE-209 (up to 95 ng/g lipid) of these herring gulls from 1998 were in the higher range reported in European birds, and not matched by other reports in North Sea seabirds. The present study suggests that the currently used brominated flame-retardants (BFRs), BDE-209 and HBCD relate to changing nutrient allocation in the herring gulls, and represent a risk to seabirds exploiting near-shore and estuary ecosystems.

Carbon and nitrogen stable isotopes in coastal benthic populations under multiple organic enrichment sources

In a dispersive coastal area under multiple organic enrichment sources, stable isotopes were used to trace organic sources of carbon and nitrogen in sediments and benthic macrofauna. The Bivalve Abra alba and the Polychaetes Nephtys sp. and Pectinaria (Lagis) koreni were reliable indicators of the input of terrestrial-derived organic matter into this coastal area, either originated in outfall sewage discharges or estuarine outflow. An isotopic depletion was observed up to 250 m from the outfall branches, much stronger in the biota than in the sediments. An enrichment of 2 ‰ in the sediments, and 2-6 ‰ in the species was noticed in sites located farther than 1500 m from the outfall. Depositivores and carnivores/omnivores gave the best picture of the extension of the sewage dispersion and incorporation into the food web.