Sediment Organic Content Research Articles

Environmental heterogeneity of cold seep by biological trait analysis of marine nematodes at Site F cold seep in South China Sea

Cold seeps provide high environmental heterogeneity for marine benthos. Site F is one of the active cold seeps in the South China Sea. In this study, free-living marine nematode communities were investigated at Site F and the adjacent deep-sea area. A total of 67 genera and 32 families were identified. The mean density at cold seep sites ranged from 13.6 to 181.8 ind./10 cm2, and that at the adjacent deep-sea sites ranged from 36.9 to 301.4 ind./10 cm2. At cold seep sites, the most dominant nematode genera were Desmoscolex, Pierrickia, Sabatieria, Halalaimus, and Dorylaimopsis while at deep-sea sites, the most dominant genera were Retrotheristus, Thalassomonhystera, Desmoscolex, Cobbia, and Halalaimus. Deposit feeders of nematodes were dominant at all sites. Results of biological trait analysis showed that there was high environmental heterogeneity for nematodes at Site F. Water depth, sediment organic matter content, and sand proportion had important influences on nematode communities.

DISTRIBUTION AND DIVERSITY OF BIVALVIANS IN THE INTERTIDAL ZONE REGION OF VILLAGE ANAK SETATAH, KEPULAUAN MERANTI REGENCY

This study was conducted from May to June 2022 to know the species, abundance, diversity, and distribution patterns in the tidal areas of Anak Setatah Village. As supporting data in this study, several environmental parameters were also measured, including water quality, sediment type, and sediment organic matter content. The study method was a survey method, where sampling used the quadrat transect method. The results found that there were three species of bivalves. Where the abundance among stations ranged from 0.49 to 0.74 and/m2. The value of the species diversity index ranged from 0.91 to 1.41, which was classified as moderate, and the matter of the distribution pattern ranged from 6.28 to 9.71 with a clumped distribution pattern

Understanding the density patterns of the polychaete Diopatra neapolitana and its relationship with environmental factors in the NW Spain

To understand the density patterns of the tube-forming polychaete Diopatra neapolitana and their relationship with environmental factors, an extensive sampling was conducted in an intertidal, commercially exploited population in the Ría de Vigo (NW Spain). Interpolation of the sampled densities was carried out by Inverse Distance Weighting (IDW). The results showed a heterogeneous, patchy distribution: the average density was 2.56 tubes/0.25 m2, although some areas exhibited a density with more than 30 tubes/0.25 m2 while in others the species was completely absent. Our data also showed that the presence of vegetation (either algae or Zostera) increased the densities of D. neapolitana. To better understand this finding, a second sampling was conducted targeting the three main permanent habitats identified in the study area. This revealed that the spatial location within the intertidal was the most important factor affecting densities. The higher densities observed with increasing latitude and longitude are a consequence of the higher flooding time, that means less water stress and longer submergence time, and involves a reduced likelihood of being caught by shellfish harvesters. The second most important factor explaining D. neapolitana densities was the sediment organic matter content, which is consistent with the observation that the presence of vegetation increases the density of tubes. This work is the first comprehensive approach to understand the spatial structure of densities of D. neapolitana.

Holocene climate and catchment change inferred from the geochemistry of Lashmars Lagoon, Kangaroo Island (Karti/Karta), southern Australia

We present a continuous ∼7000-year sedimentary record from Lashmars Lagoon, Kangaroo Island (Karti/Karta), southern Australia, a region heavily impacted by drought and bushfires in recent decades. Records such as this are vital to contextualise current climatic and environmental shifts, particularly regarding the interplay between hydroclimate and fire-related disturbances in this ecologically sensitive area. We use high-resolution μX-ray fluorescence core scanning, complemented by bulk organic geochemistry and X-ray diffraction mineralogy of catchment soil and lake sediments to reconstruct past climate and catchment processes. Phases of elevated sediment organic matter content (inferred from high Br and total organic carbon) suggest increased lake freshening and productivity, and coincide with increased chemical weathering (inferred from high Al/K and kaolinite/illite and feldspars), likely reflecting the influence of wetter climates. Conversely, periods of high Ca correlate with biogenic carbonate inputs typical of brackish conditions, which we attribute to drier climates or a marine influence. From 7.0 ka, at the mid-Holocene sea level highstand, until 5.7 ka, we suspect Lashmars Lagoon was under virtually continuous influence from the sea. At 5.7 ka, we interpret the abrupt increase in sediment total organic carbon to reflect the severance of the connection to the sea, allowing organic material to accumulate. This, coupled with evidence of high inferred chemical weathering, suggests the climate was relatively wet at the time. After 5.4 ka, our data point to the establishment of drier conditions until the commencement of wetter climates again at 4.5 ka. From 2.5 ka, however, drier climates prevailed again until present. Notably, the climate changes recorded in the sedimentary sequence at Lashmars Lagoon seem to be linked to the strength of the Leeuwin Current, a current that brings warm tropical waters to southern Australia and demonstrates a teleconnection with the El Niño Southern Oscillation, and may well have been an important driver of rainfall on Kangaroo Island (Karti/Karta) over the past ∼7000 years.

Distribution of mudsnail Bullacta caurina along smooth cordgrass Spartina alterniflora invasion stages on a coast of the Yellow Sea, China

On a Chinese coast of the Yellow Sea, a 15-year Spartina alterniflora invasion sequence was classified into five stages: no invasion, initial invasion, immature invasion, mature invasion, and senescing invasion. The effects of invasion on Bullacta caurina distribution were studied. The stem density and vegetation coverage, and sediment organic matter content increased after S. alterniflora invaded, whereas chlorophyll a concentration and porewater salinity decreased. The stem density and vegetation coverage, and porewater salinity were the dominant factors explaining habitat variations. The invasion stages, seasons and their interaction had significant effects on B. caurina density, and the density decreased after initial invasion stage of S. alterniflora. Here, a clumped spatial distribution pattern was detected on B. caurina population. Organic matter content and chlorophyll a concentration were distinguished for predicting B. caurina density. The hydrologic condition, food resources, temperature, and predation risk comprehensively affected B. caurina distribution after S. alterniflora invasion.

Linking environmental monitoring data and the predicted effects of climate change for urban coastal management: A case study of Dublin Bay

Environmental managers of coastal regions must consider the combined effects of climate change and multiple other stressors simultaneously. While routine monitoring programmes exist, this information is usually summarised as a metric or index for ecological status classification and does not integrate the biological and environmental data in a format that is useful for managers. We present a framework using conditional inference tree analyses and Bayesian Network methodology that synthesises monitoring data, identifies links between environmental and biological variables, and predicts the effects of climate change for Dublin Bay, Ireland. The ecological quality status of phytoplankton biomass was usually high but degraded when silica became limiting. Sediment organic content was positively related to benthic invertebrate richness and the abundance of wading birds, although invertebrate communities were most indicative of pristine conditions when sediment organic content was low. Importantly, climate change simulations showed that the ecological status of Dublin Bay will decline in future, which highlights the importance of removing other stressors from the ecosystem.

DISTRIBUTION AND DIVERSITY OF GASTROPODS (MOLLUSCS) IN INTERTIDAL WATERS IN RUPAT SUBDISTRICT, BENGKALIS DISTRICT

This study aims to determine the distribution pattern and diversity of gastropods in the Intertidal Waters of the Rupat Timur District. The research was conducted in February 2022. The research location consisted of 3 stations, each station was placed 3 transects from the highest tide to the lowest tide at different distances. Along the transect lines were placed 3 plots with a size of 3 x 3 m and each plot has a subplot with a size of 1 x 1 m. The method used in this research is the survey method. Parameters measured include gastropod species, distribution patterns, diversity, abundance, relative abundance, and water quality. The results of the study found gastropod species consisting of 9 (nine) families, 12 (twelve) genera, and 13 (thirteen) species. The distribution pattern of gastropods in the research location is clustered with the value of diversity (H') at a moderate level of diversity. Diversity is categorized as moderate. The highest abundance of gastropods was found on the beach of Sukarjo Mesim Village (a station I) with an abundance value of 25,600 ind/ha and the lowest abundance was found on the beach of Teluk Lecah Village (station III) with an abundance value of 11,100 ind/ha, while the highest abundance of gastropods between intertidal subzones was in the upper zone with an abundance value of 20,400 ind/ha and the lowest abundance was in the lower zone with an abundance value of 12,200 ind/ha. The highest relative abundance was Indothais javanica species with a relative abundance value of 18.30%, while the lowest relative abundance was Oliva ornata species with a relative abundance value of 0.85%. Temperature 29-30o C; salinity 28-30 ppt; pH 5-6; DO 5.2-6.4 mg/l. Sediment type in the station I was dominated by mud, station II was dominated by muddy sand and station III was dominated by sand with total sediment organic matter content of 0.46-23.33%.

Effects of Spartina alterniflora invasion on macrobenthic faunal community in different habitats of a mangrove wetland in Zhanjiang, South China

Mangroves are indispensable for maintaining biodiversity and human well-being in local or global, and their structure and functioning highly depend on the macrobenthos Although exotic cordgrass, Spartina alterniflora Loisel, is an increasing threat to the mangrove wetlands (including the associated unvegetated shoals) of China, its effects on the macrobenthic fauna in such wetlands is poorly understood. The macrobenthic faunal communities were compared in (1) an Avicennia marina monoculture vs. an S. alterniflora-invaded A. marina stand (a mixture of A. marina and S. alterniflora) and in (2) an unvegetated shoal vs. an S. alterniflora-invaded shoal that had rapidly become an S. alterniflora monoculture in Zhanjiang, China. The presence of S. alterniflora had little influence on indices of the macrobenthic faunal community in the A. marina monoculture, but significantly decreased the density and biomass of macrobenthic faunal community in the unvegetated shoal. The composition of the macrobenthic faunal community was more similar between the invaded and non-invaded A. marina stand than between the invaded and non-invaded unvegetated shoal. Compared the four habitats, the presence of vegetation significantly decreased the density and biomass of macrobenthic faunal community. Further analysis showed that differences in the macrobenthic faunal community between invaded and non-invaded habitats were associated with increases in the sediment organic matter content and plant density. These results indicate that the effects of S. alterniflora on the macrobenthic faunal community depend on habitat type of mangrove wetland is invaded, whereas additional research is needed to confirm and clarify these findings.

Distribution Characteristics of Carbon, Nitrogen, and Phosphorus and Pollution Load Estimation of Sediments in Danjiangkou Reservoir, China

Danjiangkou Reservoir is a world-famous large artificial freshwater lake that offers water resources for the middle route of the South-to-North Water Diversion Project in China. In this study, the distribution of carbon, nitrogen, and phosphorus in reservoir sediments and their pollution assessments were elucidated at different water periods. The average TN (total nitrogen), TP (total phosphorus), and TOM (total organic matter) contents were 794.8 mg/kg, 807.2 mg/kg, and 8.7% in the nonflood season, respectively. When the time comes to flood season, with the large amount of nitrogen pollution inputted from peripheral nonpoint sources and phosphorus released by the accelerated exchange of water bodies, the average TN concentration increased to 1061.2 mg/kg. In addition, the average TP and TOM contents were reduced to 559.5 mg/kg and 6.3%. Nutrient pollution fluctuated between the safe and lowest level. Reservoir eutrophication risk was low. There was a certain nitrogen enrichment in the Danjiangkou Reservoir, and the flood season was the main period of nitrogen pollution input. Water exchange during flood season might accelerate organic matter degradation. Near the dam, sediment organic matter content increased significantly, reaching severe pollution levels. The results of the simulated sediment nutrient release test showed that the nitrogen and phosphorus in the reservoir would release slowly. Moreover, their annual release flux was calculated as 470.4 t and 87.9 t, respectively. It illustrated that the internal pollution of Danjiangkou Reservoir was light, and the release amount was small, so it was not the main pollution source of the reservoir at present.

CO2 and CH4 fluxes from inundated floodplain ponds: role of diel variability and duration of inundation

Small waterbodies like floodplain ponds are considered to be an important component of the global carbon budget. Although they are found in large numbers worldwide and their numbers are increasing every year due to the creation of new ponds, we do not have sufficient data on direct estimates of emission fluxes from these waterbodies yet. Herein, we present results from a set of 24 ponds located in the Morava River floodplain, Czech Republic. The ponds varied in their origin (man-made vs. natural), size, depth, sediment organic matter content, and macrophyte growth. Water chemistry parameters, concentrations, and exchange of CO2 and CH4 with the atmosphere were directly measured during the day and night from spring to summer 2020. The ponds emitted more CO2 and CH4 during nighttime, and both CO2 and, in particular, CH4 emissions tend to increase with the duration of pond inundation. Total diffusive fluxes of CO2 and CH4 into the atmosphere ranged from −37072.9 to 432683.3 μmol m−2 d−1, and −11485.3 to 95,889.6 μmol m−2 day−1, respectively. Generally, all ponds were found to be a net source of CO2 and CH4 to the atmosphere. In average, ponds emitted 7.64 g CO2-equivalent m−2 d−1. Thus, our results indicate that floodplain ponds are an important source of both CO2 and CH4 to the atmosphere and they should not be omitted in a regional carbon budget.

Statistical approach to identify variables predicting sulphide clay occurrence in southern Finland

Acid sulphate soil and sulphide-bearing sediments cause various challenges in construction projects and land use planning, as well as harmful environmental effects. Fine-grained sulphide sediments were mainly formed in coastal areas during the Litorina Sea water phase at approximately 7000 BP in the capital region of Finland, but not all these sediments contain sulphide clay. In this study, environmental and material property variables related to the depositional conditions of sulphide clay were selected for statistical analyses to find their association with the occurrence of sulphide. The datasets consisted of sulphide investigations by the City of Espoo, the City of Helsinki, and the Geological Survey of Finland. Statistically significant associations were found in the study area between the occurrence of sulphide and enumerative variables (i.e., sediment organic content, total clay depth, topographic class in the Litorina Sea phase, and water depth) in the Litorina Sea phase. Locations where sulphide clay is especially likely to occur consist of organic-rich (≥ 2%) thick clay (≥ 15 m) deposits in a topographically narrow depression with deep Litorina water (≥ 30 m), or where there is a moderate depth clay (3–5 m) in a local depression with shallow Litorina water (10–20 m). The best individual predictor for sulphide clay occurrence in the study area was found to be the sediment organic content, and, together with sediment water content, these variables very accurately predicted the occurrence of sulphide clay. In addition, clay depth is a very good predictor and, together with the topographic class narrow depression and the Litorina water depth or current elevation, can be used to predict sulphide occurrence.

The effects of Cyclina sinensis bioturbation on alkaline phosphatase (APA) and total microbial hydrolytic activities (MBA) in marine clam-shrimp integrated ponds.

This study investigated the influence of Venus clam Cyclina sinensis bioturbation activities on the total benthic microbial and phosphatase activities and selected sediment properties: total phosphorous TP, total organic nitrogen-TON and total organic carbon-TOC. Sediments samples from clam-shrimp integrated-pond and non-clam integrated-pond were sampled for the study in which microbial activity (MBA) and alkaline phosphatase activity (APA), sediment organic contents: TP, TON, TOC, TOM and water quality parameter (dissolved oxygen, temperature, pH and moisture content were analyzed. The p-nitrophenyl phosphate disodium (p-NPP) and Fluorescein diacetate-(FDA) were adopted to measure APA and MBA respectively. Results indicated that microbial activity-MBA and alkaline-phosphatase activity-APA in sediments significantly increased in the pond cultured with clam/shrimp compared to non-clam cultured pond. Phosphate concentration increased significantly and varied among months (p<0.05) implying increased nitrogen concentration in the sediments. The concentrations of total organic nitrogen and total organic carbon didn't differ significantly among months and with the treatments (p>0.05), implying increased TON mineralization. Correlation analyses showed that there was positive correlation with the total microbial activity, alkaline-phosphatase activity, phosphorous concentration and organic matter content within the sediments bioturbated by the Venus clam. The results suggest that, the Venus clam sediment reworking mechanisms in sediment influenced the sediment microbial and APA activities and mineralization thereby affecting the pond alkaline phosphatase enzyme related activities.

Factors Influencing the Distribution of Freshwater Mollusks in the Lakes of the Pyrenees: Implications in a Shifting Climate Scenario

Climate warming is expected to drive an upward altitudinal shift of species distributions in mountain areas. In this study, we consider how environmental variables constrain the distribution of freshwater mollusks across elevations based on an extensive survey of the entire Pyrenean range. Results show that several altitude-related variables are significantly relevant for the distribution of all mollusks (i.e., temperature, sediment organic content). Others respond more precisely to some variables: fine substrate proportion increases the probability of finding Pisidium sensu lato (mostly Euglesa species), and the latter, the macrophyte presence, and Ampullaceana balthica. Despite the low acid-neutralizing capacity in many of the lakes, only the distribution of A. balthica was significantly constrained by this factor, independent from elevation. The results confirm a likely altitudinal expansion of the distributions of all species, particularly toward lakes with a summer surface temperature increasing above 12 °C. The pace of change is expected to differ among species according to different nonlinear thresholds in thermal response, which temperature value increases from Pisidium s.l. to Ampullaceana to Ancylus, and the taxon-specific sensitivity to substrates and chemical conditions.

GASTROPOD COMMUNITY STRUCTURE IN THE INTERTIDAL ZONE OF PASUMPAHAN ISLAND, PADANG CITY, WEST SUMATRA PROVINCE

Pasumpahan Island is one of the islands located in West Sumatra Province which has various activities of daily life, especially in the intertidal zone; it is suspected that it can interfere with the existence of aquatic organisms one of which is gastropods. Studying the structure of gastropod communities in the intertidal zone is an interesting natural laboratory to study. This research was conducted from December 2021 to January 2022 on Pasumpahan Island Padang City West Sumatra Province. The purpose of this study was to determine the structure of the gastropod community which includes species, abundance, diversity, uniformity, dominance, and distribution pattern of gastropods. As supporting data in this study, several environmental parameters were also measured which included water quality, sediment type, and sediment organic matter content. The research method used is a survey method, where sampling using the quadrat transect method is carried out at 3 stations. Based on the results of the study found 13 species of gastropods. The most common species found at all stations was Pythia scarabaeus, where the gastropod abundance values obtained between stations ranged from 2,78 to 5,00 ind/m2. The value of the species diversity index ranged from 1,50 to 2,02, which was moderate, the uniformity index value ranged from 0,77 to 0,88, which was high uniformity, and the dominance index value ranged from 0,16 to 0,29, meaning that there were no species found dominates and the value of the distribution pattern ranges from 1,31 to 2,47 with a clustered distribution pattern

Impact of the Yellow River capture on the paleoenvironmental changes of Hongze Lake, China

The Yellow River (YR) capture of the Huai River had a profound effect on the landscape evolution, ecology, and social development in China, disrupting the evolution of some vital shallow floodplain lakes. Because of the absence of lacustrine sediment provenance analysis, previous studies were inadequate in distinguishing the influence of YR capture on paleoenvironmental changes in these lakes, especially on landscape evolution, redox conditions, lake level changes, and organic productivity. The current study aims to use X-ray fluorescence-core scanning (XRF-CS) and multivariate statistics on a 9.8 m sediment core from Hongze Lake (HZL), China, to analyze the impact of the YR capture on the lake's paleoenvironmental changes and the sediment provenance simultaneously. High-resolution images, magnetic susceptibility, and XRF-based multi-element data were obtained using a GEOTEK Multi-Sensor Core Logger. The calcium (Ca) content indicates the presence of YR sediment in HZL, given the high Ca content in YR sediment and the identification of mainly exogenous sources of Ca in HZL. The high values of Ca indicate that 48.7% of the sediment in the center of HZL is related to the YR's incursion. Periods of higher Ca content coincide with periods of higher oxygenation levels of the lake (as indicated by the ratio of manganese to titanium) and lower organic content in the lake sediment (as indicated by the ratio of incoherent to coherent scatter). These analyses reveal that the YR's capture of HZL significantly increased the lake's oxygen level. Furthermore, the decrease in the organic content of sediment tends to be the result of the accelerated deposition caused by the YR. The decrease in Ca content coincides with an increase in lake levels (as indicated by magnetic susceptibility). Thus, it can be inferred that the embankment on the eastern side of HZL, built to increase lake storage, has reduced the incursion frequency of the YR.

The Effect of Environmental Dredging of Muck on an Assemblage of Benthic Amphipods

To yield environmental benefits, fine sediments with ~10% organic matter, termed muck, were dredged from a tributary to the Indian River Lagoon. Key changes were documented by sampling amphipods, sediments, and the water column near the bottom before dredging, and approximately one month and one year after dredging. Overall, muck yielded the fewest taxa, muck or sediments in creeks that were dredged yielded a moderate number of taxa, and undisturbed sediments in the lagoon yielded the highest number of taxa. Amphipods did not appear in areas with muck until one month and one year after dredging. In contrast, amphipods in sediments that were not muck decreased after dredging. Increases in the occurrence of amphipods paralleled increases in concentrations of dissolved oxygen and decreases in the water, silt/clay, and organic content of sediments. Overall, results indicated that conditions for amphipods were improved by removing muck, and that dredging sandier sediment led to decreased taxonomic richness and numbers of amphipods, which resembled the effects of navigational dredging. Thus, this study suggested that managers should consider the type of sediment to be dredged when permitting projects.

Di-2-ethylhexyl phthalate (DEHP) degradation and microbial community change in mangrove rhizosphere gradients

Di-2-ethylhexyl phthalate (DEHP) is a widespread persistent organic pollutant in the environment. As an ultimate barrier preventing pollutant entry into the ocean, mangrove plays an important role in coastal ecosystem. However, little information is known about DEHP degradation in mangrove rhizosphere. In this study, a rhizobox was used to separate four consecutive rhizosphere compartments with distance of 0–2, 2–4, 4–6, and > 6 mm to the rhizoplane of Kandelia obovata and investigate DEHP gradient degradation behavior in rhizosphere. Sediments closer to the rhizoplane exhibited higher DEHP degradation efficiencies (74.4 % in 0–2 mm layer). More precisely, mangrove rhizosphere promoted the benzoic acid pathway and non-selectively accelerated the production of mono(2-ethylhexyl) phthalate, phthalic acid and benzoic acid. Higher sediment organic matter content, lower pH and less humus in rhizosphere benefited DEHP hydrolysis. In addition, rhizosphere significantly increased microbial biomass and activities comparing to bulk sediments. Some bacterial lineages with potential DEHP degradation capability exhibited a distance-dependent pattern that decreased with the distance to the rhizoplane, including Bacillales, Acidothermaceae, Gammaproteobacteria, and Sphingobacteriales. Our findings suggested that mangrove rhizosphere could accelerate DEHP degradation by altering sediment physicochemical properties and microbial composition, showing positive effects on coastal ecosystem services for eliminating phthalate acid ester contamination.

Effect of past century mining activities on sediment properties and toxicity to freshwater organisms in northern Sweden

The release of toxic metals from local mining activities often represents a severe environmental hazard for nearby lake ecosystems. Previous studies on the impact of mining have primarily focused on single lakes, with less emphasis on spatial and temporal recovery patterns of multiple lakes within the same catchment, but with different hydrological connection and distance to the pollutant source. This knowledge gap prevents us from assessing the real environmental risk of abandoned mines and understanding ecosystem recovery. This study explores the intensity and spatial patterns of sediment contamination and the potential for ecosystem recovery in three lakes in close vicinity of a lead (Pb) and zinc (Zn) mine in Sweden that has been inoperative for >20 years. Dated (210Pb and 137Cs) sediment cores from each lake were used to reconstruct temporal patterns in trace element deposition and relate those with past mining activities. Results show that all lakes were affected by mining, indicated by increasing Pb and Zn concentrations and decreasing organic matter content, at the onset of mining. However, the extent and timing of mining impact differed between lakes, which was partly ascribed to differences in the historical use of tailings and settling ponds. Assessment of toxicity levels in sediments, based on normalized Probable Effect Concentration Quotient (PEC-Q) to organic matter content, provided more consistent results with the historical mining than conventional methods, showing a decreasing impact in lakes once the operations ceased. Still, sediment Pb concentrations were > 10 times higher than pre-mining values, evidencing the urgent need for remediation actions in the study lakes. This study highlights the importance of considering spatial heterogeneity in metal deposition, sediment organic matter content, and hydrological connectivity with tailings when risk assessments are performed in mining-impacted lakes. The use of normalized PEC-Q in toxic assessments is also recommended.

Higher Nighttime Rates of CaCO3 Dissolution in the Nature Reserve Reef, Eilat, Israel in 2015–2016 Compared to 2000–2002

AbstractThe current study (2015–2016) evaluated changes in the net community calcification (NCC) and maximum nighttime CaCO3 dissolution (Dmax) in the Nature Reserve Reef (NRR), northern Gulf of Eilat (GOE), and northern Red Sea, compared to measurements made at the same site during 2000–2002. The NCC and Dmax were calculated as a function of the reef‐water residence time, the difference between the open‐sea total alkalinity (TA) and its reef‐water daily average (for NCC), and its nighttime maximum (for Dmax). The average NCC was 50 ± 13 and 68 ± 22 mmol C m−2 day−1 in 2000–2002 and 2015–2016, respectively. This change is consistent with the live coral cover increase in the NRR during this period, following the final removal of fish cages from the northern GOE in 2008. In contrast, wintertime Dmax values in 2015–2016 were five times higher on average compared to 2000–2002. We hypothesize that these higher rates could be the result of increased boring organism activity and sedimentary organic content, which developed throughout the fish farming period and are maintained by the naturally occurring seasonal eutrophication in the northern GOE. Where, in general, Dmax was higher during the winters, when nighttime reef water aragonite saturation (Ωarag) was lower, while open water chlorophyll a and nitrate were higher, compared to summertime. Thus, it is possible that the combination of seasonal eutrophication and ocean acidification (OA) in the GOE and possibly other coral reef sites around the world, may shift coral reefs to net dissolution even sooner than previously predicted from OA alone.

Bioaccumulation of per- and polyfluoroalkyl substances by freshwater benthic macroinvertebrates: Impact of species and sediment organic carbon content

Per- and polyfluoroalkyl substances (PFAS) in aquatic environments have caused global concern due to their persistence, toxicity, and potential bioaccumulation of some compounds. As an important compartment of the aquatic ecosystem, sediment properties impact PFAS partitioning between aqueous and solid phases, but little is known about the influence of sediment organic carbon content on PFAS bioaccumulation in benthic organisms. In this study, three freshwater benthic macroinvertebrates – worms (Lumbriculus variegatus), mussels (Elliptio complanata) and snails (Physella acuta) – were exposed for 28 days to PFAS spiked synthetic sediment equilibrated with a synthetic surface water. Using microcosms, sediment organic carbon content – 2%, 5% and 8% – was manipulated to assess its impact on PFAS bioaccumulation. Worms were found to have substantially greater PFAS bioaccumulation compared to mussels and snails. The bioaccumulation factors (BAFs) and biota sediment accumulation factors (BSAFs) in worms were both one to two magnitudes higher than in mussels and snails, likely due to different habitat-specific uptake pathways and elimination capacities among species. In these experiments, increasing sediment organic carbon content decreased the bioaccumulation of PFAS to benthic macroinvertebrates. In worms, sediment organic carbon content was hypothesized to impact PFAS bioaccumulation by affecting PFAS partitioning and sediment ingestion rate. Notably, the BSAF values of 8:2 fluorotelomer sulfonic acid (FTS) were the largest among 14 PFAS for all species, suggesting that the benthic macroinvertebrates probably have different metabolic mechanisms for fluorotelomer sulfonic acids compared to fish evaluated in published literature. Understanding the impact of species and sediment organic carbon on PFAS bioaccumulation is key to developing environmental quality guidelines and evaluating potential ecological risks to higher trophic level species.