Matter Content Of Sediment Research Articles

Distribution and risk assessment of nutrients and heavy metals from sediments in the world-class water transfer projects

South-to-North Water Diversion Project, a globally renowned engineering feat, aims to address water supply issues. The sediments within reservoirs play a pivotal role in natural ecosystems, not only as habitats for diverse biota but also as repositories of heavy metals, organic matter, and other contaminants. These sediments serve as a critical interface between sediment and water bodies. This comprehensive analysis focused on the spatial patterns of nutrients, organic matter, and heavy metals in the surface layer and profiles of reservoirs, exploring their interconnectedness. Leveraging the integrated pollution index, organic pollution index, potential ecological risk index, and geo-accumulation index, an ecological risk assessment was performed. The key findings are as follows: (i) Along the Middle Route of the South-to-North Diversion Project, the nutrient and organic matter contents in sediments tends to rise with distance from the Danjiangkou Reservoir, with the TN and TC contents increasing by 2.35- and 3.05-fold, respectively. (ii) As the sediment depth increases, the carbon, nitrogen, phosphorus, and organic matter contents exhibit varying degrees of decline, with average decreases of 62.38%, 67.47%, 17.56%, and 41.83% for TN, TC, TP, and OM, respectively. (iii) Among the eight heavy metals, only manganese (Mn) and zinc (Zn) in the Yahekou Reservoir showed moderate pollution levels, according to the geo-accumulation index. The Mn content within the surface sediments of the six reservoirs ranges from 550 to 1837 mg/kg (average, 1019.5 ± 548.3 mg/kg), whereas the Zn content ranges from 89 to 360 mg/kg (average, 156.5 ± 101.6 mg/kg). (vi) Total phosphorus (TP) and total nitrogen (TN) emerged as the primary pollutants in surface sediments. Comprehensive nitrogen and phosphorus pollution assessment revealed that the surface sediment of Danjiangkou Reservoir is mildly polluted, while Baiguishan and Jiangang Reservoirs are moderately polluted, and the rest are heavily contaminated. For the Yahekou and Chaohe Reservoirs, the average pollutant content indicates moderate pollution, while the remaining reservoirs show mild pollution levels.Graphical

THE RELATIONSHIP BETWEEN ORGANIC MATERIAL CONTENT IN SEDIMENTS AND THE ABUNDANCE OF EPIPELIC DIATOMS IN THE INTERTIDAL ZONE OF THE WATERS OF DUMAI CITY, RIAU PROVINCE

This research was conducted in March 2023, located in Koneng Beach, Dumai City. The purpose of this study was to determine the organic matter content and abundance of epipelic diatoms vertically and to analyze the relationship between the organic matter content in sediments and the abundance of epipelic diatoms vertically in the intertidal area of Dumai City Waters. The method used is the survey method. The sampling point is determined using a purposive sampling method. Sampling of epipelic diatoms was carried out using a modified corer, which was then brought to the laboratory to identify and calculate the abundance of diatoms and the sediment samples to calculate the content of organic matter and sediment fractions. Water quality measurements accompanied sampling with a brightness value of 0.57 m, temperature of 33 °C, current speed of 0.33 m/s, salinity of 28 ppt, and pH of 8.13. The results of the analysis of organic matter are 2.55 – 13.38%. The results of the sediment fraction analysis show that the research location is dominated by sandy silt. Nineteen genera of epipelic diatoms were found in the waters of Koneng Beach, Dumai City, with abundance values between 5,291–39,983 ind/cm2. The one-way ANOVA test results obtained an average value of 0.000, meaning there is a significant difference in the abundance of epipelic diatoms between the sediment layers. The results of the linear regression test showed that the effect of sediment organic matter on the abundance of epipelic diatoms was 50.85%.

Nutrient dynamics, carbon storage and community composition on artificial and natural reefs in Bali, Indonesia

Artificial reefs are now commonly used as a tool to restore degraded coral reefs and have a proven potential to enhance biodiversity. Despite this, there is currently a limited understanding of ecosystem functioning on artificial reefs, and how this compares to natural reefs. We used water sampling (bottom water sampling and pore water sampling), as well as surface sediment sampling and sediment traps, to examine the storage of total organic matter (as a measure of total organic carbon) and dynamics of dissolved inorganic nitrate, nitrite, phosphate and ammonium. These biogeochemical parameters were used as measures of ecosystem functioning, which were compared between an artificial reef and natural coral reef, as well as a degraded sand flat (as a control habitat), in Bali, Indonesia. We also linked the differences in these parameters to observable changes in the community structure of mobile, cryptobenthic and benthic organisms between habitat types. Our key findings showed: (1) there were no significant differences in inorganic nutrients between habitat types for bottom water samples, (2) pore water phosphate concentrations were significantly higher on the artificial reef than on both other habitats, (3) total organic matter content in sediments was significantly higher on the coral reef than both other habitat types, and (4) total organic matter in sediment traps in sampling periods May and September were higher on coral reefs than other habitats, but no differences were found in November. Overall, in terms of ecosystem functioning (specifically nutrient storage and dynamics), the artificial reef showed differences from the nearby degraded sand flat, and appeared to have some similarities with the coral reef. However, it was shown to not yet be fully functioning as the coral reef, which we hypothesise is due its relatively less complex benthic community and different fish community. We highlight the need for longer term studies on artificial reef functioning, to assess if these habitats can replace the ecological function of coral reefs at a local level.

DRIFT spectroscopic determination of clay and organic matter in sediment by mixed soil-sediment calibration approach.

Bioavailability and movement of pollutants through land and underground flows are strongly related to some of the sediment characteristics, such as clay minerals and organic matter. Therefore, the determination of clay and organic matter content in sediment is of great importance for environmental monitoring. Clay and organic matter in sediment were determined using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy in combination with multivariate analysis methods. Sediment from different depths was used in combination with the soil samples of different texture. Using multivariate methods and DRIFT spectra, sediments from different depths were successfully grouped according to similarity to different texture soils. Also, a quantitative analysis of clay and organic matter content was performed, where a new calibration approach was used in which sediment samples combined with soil samples were used for principal component regression (PCR) calibration. PCR models for the assessment of clay and organic matter were determined for a total of 57 sediment samples and 32 soil samples, and satisfactory determination coefficients were obtained for linear models (0.7136 for clay and 0.7062 for organic matter). The obtained RPD values for both models gave very satisfactory values of 1.9 for clay, i.e., 1.8 for organic matter.

The role of humic substances in sediment phosphorus release in northern lakes

In northern lakes, which are often stained and productive, the impacts of dissolved organic carbon (DOC) on sediment phosphorus (P) release are largely unexplored. Here we elucidated the factors behind experimentally-derived sediment release rates of P by diffusion (DF) in four Finnish lakes with a range of colour. Next, we extended our analysis to a larger set of northern lakes for further insights regarding possible implications of organic substances on sediment P release.The significant correlation between pore-water soluble reactive P and dissolved iron, and a positive effect of iron-bound sedimentary P (Fe-P) on DF supports the classic paradigm of redox-dependent P release in the four Finnish lakes studied. Nevertheless, the P release from Fe-P may be inhibited by humic substances, as we observed lower Fe-P and negative DF in two humic rich lakes (high DOC). The analysis of a larger set of northern lakes supported the negative effect of humic substances on P release rate (RR) determined by in situ P increases. In this dataset, DOC correlated positively with water colour and negatively with RR. Furthermore, multiple stepwise regression analysis selected sediment total P and organic matter content in sediments (LOI) as the best predictors of RR, similar to a previously published model by Nürnberg (1988). While the model predictions (RRpred) were correlated to RR in the present study, they tended to overestimate RR that was determined in closed experimental systems. The inhibiting effects of humic substances on RR may be manifested in both internal P loading and primary production.

Analysis of Organic Matter Content in Water and Sediment in The Coastal Waters of Bengkalis Island, Riau Province

Anthropogenic activities in the coastal waters of Bengkalis Island, Riau Province are thought to have increased due to human activities (settlements, ports, agriculture, households and industry). This caused an increase in organic matter in water and sediment in coastal waters. The content of organic matter in water and sediment can be used as an indicator of the quality of coastal waters. The research aimed to analyze the content of organic matter in water and sediment in the coastal waters of Bengkalis Island. The used purposive sampling. The research was carried out in April – July 2021, consisting of 4 research stations and each station consisted of 3 sampling points. Sampling was carried out in the intertidal zone in the north and south of Bengkalis Island, namely station I (Air Putih Village), Station II (Jangkang Village), station III (Selat Baru Village) and station IV (Liong Estuary). The results of the analysis of organic matter content in seawater ranged from 32.39-34.89 mg/l, the highest was at station I and the lowest was at station II. The results of the analysis of organic matter content in sediment of Bengkalis Island ranged from 0.01-0.31%, the highest was at station I and the lowest was at station II. A simple linear regression test showed that the relationship between the organic matter content of seawater and sediments in the coastal waters of Bengkalis Island was classified as a strong relationship with a correlation coefficient (r) 0.720 and a coefficient of determination (R2) 0.518. The results also show that the coastal waters of Bengkalis Island have a type of sediment fraction which is dominated by sandy mud.

The Sediment Selectivity of Perinereis aibuhitensis Larvae: Active or Passive?

The selectivity of Perinereis aibuhitensis larvae on different sediment types was studied using an experimental behavioral device in the lab. There were six types of sediment with different organic matter content: 2.19, 2.30, 2.86, 3.25, 3.51, and 5.52%. The results indicated significant differences in the six treatments’ organic matter content (p < 0.05). When the P. aibuhitensis larvae initially attached to the sediment, the larvae’s density showed no significant difference among the six treatments. The density of larvae decreased gradually during the experimental period. It increased with the increasing organic matter content in sediment at every sampling time, but there was no significant difference (p > 0.05). The larvae’s specific growth rate in the first month was significantly higher than those in the second and third months (p < 0.05). The mortality showed no significance at different sediments in equal sampling times, but the mortality was lower in high organic matter content sediments. This study showed that the P. aibuhitensis larvae did not make an active selection; random selection happened when initially attached to the sediment with different organic matter contents. Higher organic matter content in the sediment was more conducive to larvae survival, and the organic matter content is the limitation factor on the mortality and the density. The different densities in the natural habitat of P. aibuhitensis might occur due to the passive selection by the environment.

Organic matter degradation characteristics of coastal marine sediments collected from the Seto Inland Sea, Japan

Organic matter in marine sediment is mainly categorized into three fractions depending on degradability: labile, semi labile and refractory. The degradability of coastal marine sediments depends on the properties of the organic matter contained in the sediments. The purpose of this study was to quantify labile and refractory organic matter in coastal marine sediments with different characteristics collected from the Seto Inland Sea, and to discover the factors controlling the degradability of organic matter. Refractory organic matter content in sediments ranged from 4.7–21.4 mg g−1, a percent composition equivalent to 72–97% of TOC. In contrast, labile and semi-labile content were 0.1–1.4 mg g−1 and 0.1–2.3 mg g−1, respectively, a percent composition equivalent to 0.5–12.9% and 1.8–17.1% of TOC, respectively. Approximately 93% of refractory organic matter was categorized into humin. Organic matter originated from marine phytoplankton settled on the surface of sediments and changed to humin or a refractory organic matter. This study contributes to a better understanding of the organic matter degradation characteristics of coastal marine sediments and provides important parameters for estimating carbon budget and carbon cycling in coastal sea systems.

Species Density and Lead (Pb) Pollution in Mangrove Ecosystem, South Kalimantan

Its crucial to get information about lead (Pb) heavy metal pollution from mining and oil palm plantation on species density in mangrove ecosystem, to anticipate its impacts. This study aimed is to compare the types and densities of vegetation in mangrove ecosystems allegedly due to mining in Setarap village, Tanah Bumbu Regency and oil palm plantations in Kuala Tambangan Village, Tanah Laut Regency. We also analysis the condition of waters (TDS, pH and DO) and organic content in sediments to acquire data from the South Kalimantan mangrove ecosystems. The results showed there were four species of true mangroves (Avicennia alba, Acanthus ebracteatus, Nypa fruticans and Rhizophora apiculate) could live well in the environment affected by mining or oil palm plantations. The species density for trees was low (933 ind/ha) for mangroves affected by coal mines, while those affected by oil palm plantations had higher densities (1,067 ind/ha). pH value of waters in affected area by coal mining showed more acidic value (pH 5.76) especially at the back, while those by palm oil plantations are more acidic (pH 6) in the estuary. Organic matter content in sediments affected by coal mines was in the range of 0.61-6.59%, while those affected by oil palm plantations showed higher values (0.12-2.19%). Lead heavy metal content (Pb) in waters affected by coal mines was 0.031-0.056 mg/L, while the area affected by oil palm plantations was of higher value (0.110-0.128 mg/L). Lead (Pb) levels in sediments indicate higher values than waters, which reach 3.512-6.046 mg/Kg (affected by coal mines), and in areas affected by oil palm plantations reaching 6.658-6.66 mg/Kg. The general conclusion is that vegetation densities in areas affected by coal mines are lower than oil palm plantations. The level of lead (Pb) pollution in the sediments is higher than in the waters.

Carbon metabolic rates and GHG emissions in different wetland types of the Ebro Delta.

Deltaic wetlands are highly productive ecosystems, which characteristically can act as C-sinks. However, they are among the most threatened ecosystems, being very vulnerable to global change, and require special attention towards its conservation. Knowing their climate change mitigating potential, conservation measures should also be oriented with a climatic approach, to strengthen their regulatory services. In this work we studied the carbon biogeochemistry and the specific relevance of certain microbial guilds on carbon metabolisms of the three main types of deltaic wetlands located in the Ebro Delta, north-eastern Spain, as well as how they deal with human pressures and climate change effects. We estimated the metabolic rates of the main carbon-related metabolisms (primary production and respiration) and the resulting carbon and global warming potential balances in sites with a different salinity range and trophic status. With the results obtained, we tried to define the influence of possible changes in salinity and trophic level linked to the main impacts currently threatening deltaic wetlands, on the C-metabolisms and GHG emissions, for a better understanding of the mitigating capacity and their possible enhancement when applying specific management actions. Metabolic rates showed a pattern highly influenced by the salinity range and nutrients inputs. Freshwater and brackish wetlands, with higher nutrient inputs from agricultural runoff, showed higher C-capture capacity (around 220-250 g C m-2 y-1), but also higher rates of degradative metabolisms (aerobic respiration and CH4 emissions). Contrastingly, the rates of C-related metabolisms and C-retention of Salicornia-type coastal salt marshes were lower (42 g C m-2 y-1). The study of the microbial metacommunity composition by the16S RNA gene sequencing revealed a significant higher presence of methanogens in the salt marsh, and also higher metabolic potential, where there was significantly more organic matter content in sediment. Salinity inhibition, however, explained the lower respiration rates, both aerobic and anaerobic, and prevented higher rates of methanogenesis despite the major presence of methanogens. Conservation measures for these wetlands would require, overall, maintaining the sediment contributions of the river basin intending to overcome the regression of the Delta and its salt marshes in a climate change scenario. Particularly, for reducing degradative metabolisms, and favour C-retention, nutrient inputs should be controlled in freshwater and brackish wetlands in order to reduce eutrophication. In salt marshes, the reduction of salinity should be avoided to control increases in methanogenesis and CH4 emissions.

Local environmental variation obscures the interpretation of pyrite sulfur isotope records

Theoretically, within the long-term marine sulfur cycle, pyrite sulfur isotopes (δ34Spy) are determined by the degree of pyrite burial that is controlled by the marine redox conditions. Thus, the secular variation of δ34Spy records the history of marine and atmosphere redox evolution. As such, large magnitude change in δ34Spy in the Proterozoic has been attributed to widespread oceanic anoxia related to generally low atmospheric pO2 levels. However, noisy δ34Spy signals in the past 250 million years cannot be explained by the frequent oscillation of seawater redox, because the global ocean was already fully oxidized. Here, by developing a numerical model, we show that δ34Spy of syndepositional pyrite is significantly affected by local factors, such as organic matter content in sediment, sedimentation rate, and seafloor redox. Thus, the noisy δ34Spy records may reflect local environmental variations rather than the oscillation of global ocean redox. Our study also suggests that δ34Spy alone cannot provide a robust constraint on the global or local ocean redox condition. We suggest that, combining with the pyrite content data and δ34Spy can help quantify local/regional biogeochemical cycles.

Application of the Lake Biotic Index (LBI) in the ecological characterization of a North Patagonian lake in Chile

Increased pollution and degradation of water resources and their associated ecosystems has stimulated the development of tools and methodologies to characterize, estimate, predict, and reverse the environmental impact of anthropic effects on water bodies. The Secondary Water Quality Standards (NSCA) adopted in Chile have incorporated the use of bioindicators complementary to physicochemical analyses, in order to determine the ecological condition of lotic and lentic environments. Our research used the "Lake Biotic Index" (LBI) to establish the ecological condition of Lake Rupanco using benthic macroinvertebrates. The results indicated an Oligo-Eubiotic condition for this lake given the high concentration of oxygen and low organic matter content in sediments, in addition to low biogenic potential and good taxa preservation in both the autumn and spring surveys. Features of the ecological condition obtained through the application of the LBI (benthic subsystem) conform to the results of physicochemical and microalgae analyses undertaken previously in Lake Rupanco (pelagic subsystem). Based on these results, we support application of the LBI index as a complementary tool for the integrated management of lentic ecosystems.

Proper Mode of Using Rice Straw Biochar To Treat Cd-Contaminated Irrigation Water in Mining Regions Based on a Multiyear in Situ Experiment

Biochar has been widely used for immobilizing heavy metals in soils due to its favorable sorption capacity. Previous investigations on heavy metal immobilization in waters by biochar are conducted in laboratory. Knowledge about the long-term effects of in situ biochar application on water bodies contaminated by heavy metals remains scarce. In this research, biochar was derived from cadmium (Cd)-accumulated rice straw. A 35-d laboratory simulation and a three-year field enclosure experiment were carried out to assess the impacts of biochar application on Cd behavior in a water–sediment system of a historically Cd-contaminated irrigation pond. Results indicated that the pH of sediment and overlying water increased with biochar addition in both the lab and field experiments. The rice-straw biochar transformed the Cd in sediments from the exchangeable to residual fraction, because biochar addition increased the pH values and organic matter contents in sediment, leading to the sorption, sequestration, and passivation of Cd by sediment. The Cd concentration in overlying water decreased with the increase in biochar addition, and it continuously decreased with repeated annual application. Overall, for long-term effects of biochar addition on soluble Cd concentrations, the repeated annual addition of 2% biochar exhibited better performance than the repeated annual addition of 1% biochar and one-time addition of 6% biochar. This study provided a proper mode of utilizing rice-straw biochar to treat Cd-contaminated irrigation water in mining regions.

Development of a sediment microbial fuel cell-based biosensor for simultaneous online monitoring of dissolved oxygen concentrations along various depths in lake water

A novel multi-cathode, single-anode system integrating a sediment microbial fuel cell -based biosensor was developed for in-situ, continuous, and online monitoring of dissolved oxygen (DO) concentrations along various depths of lake water. The signal feedback mechanism was evaluated based on a relationship between voltage and DO concentration at corresponding depths. With an external resistance of 1000 Ω, a linear relationship was found (regression coefficient, R2 = 0.9576) between voltage and DO in the range of 0–9 mg L−1. The sensor performance was further optimized under various influence factors. The results of indoor experiments indicated that the optimal anode to single cathode area ratio was 11:1. The sensor signal could also be significantly influenced by organic matter content in sediment; thus, the addition of 5% organic matter could obtain a stable anode potential and a high voltage output. Furthermore, the sensor was operated in-situ for 67 days in a lake environment, which also led to a good correlation between the voltage and DO (R2 = 0.8897). Thus, this integrated system has great potential as an early-warning program to help identify environmental risks in aquatic environments.

Trace metal levels and toxicity in the Huelva Estuary (Spain): A case study with comparisons to historical levels from the past decades

Abstract The Huelva Estuary, in the south of Spain, is a highly polluted area subject to heavy anthropogenic pressures such as coastal urbanization, fishing and tourism activities, commercial transports, as well as petrochemical, agrichemical and intense mining industry. Trace metal levels in sediments from the Huelva Estuary have been largely investigated over the last decades, but an evaluation through the years has not been considered yet. This study analyzed the current concentrations for Cr, Cu, Mn, Ni, Pb, Zn, Fe and organic matter content in sediments from two sampling sites (Muelle Capesa and Mazagon) and toxicity on fertilization and embryogenesis of sea urchin (Paracentrotus lividus). Results were compared with data from the past decades. Zn and Cu displayed higher levels and enrichment in sediments from the Muelle Capesa close to the Huelva industrial area. Mazagon sediment, despite moderate levels and enrichment in Zn and Cu, is proved to be affected by anthropogenic impacts, due to continuous inputs from acid mine drainage and alongshore current transport. In our experiments, sea urchin fertilization rates and larval development were significantly affected by exposure to elutriates from Huelva Estuary sediments. Therefore, the Huelva Estuary area shows a declining but chronic contamination in Zn and Cu, originating from point and diffused anthropic activities, which in turn, are likely to cause adverse effects on the coastal ecosystem.

The effects of a stressed inshore urban reef on coral recruitment in Suva Harbour, Fiji.

A relic inshore reef ecosystem adjacent to the Fijian capital of Suva and another remote inshore reef were monitored monthly from July 2014 to July 2015 for coral recruitment, sedimentation rates, coral cover, temperature, and light intensity. Despite a major sewage spill in Suva Harbour in December 2014, the municipal inshore site exposed to constant anthropogenic activity, recorded no significant differences in coral spat abundance (except for the family Poritidae) on artificial substrata compared to the remote inshore site. Total yearly spat abundance was 106 on municipal reef and 132 on remote reef, while average daily sediment trap collection rates (g cm2/day) were significantly higher in the municipal site for the entire duration of monitoring. Total annual particulate organic matter content in sediment was also significantly higher in the municipal site (107.51 g cm2), compared to the remote site (43.37 g cm2). Mean light intensity was significantly lower for the municipal site (69.81 lum/ft2) compared to the remote site (239.26 lum/ft2), with Photosynthetically Active Radiation also lower for the former (800–1,066.66 µmol m−2 s−1) compared to the latter (3,266.66–3,600 µmol m−2 s−1). The lack of significant differences in coral spat recruitment rates suggests that settling larvae may be unable to distinguish between sub‐optimal and optimal sites probably as a consequence of interference with coral settlement cues arising from anthropogenic development.

Tidally driven sulfidic conditions in Peruvian mangrove sediments

The seasonal influence of tidal regimes on sulfidic conditions was studied in intertidal environments from a mangrove estuary in Northern Peru. Along two sampling stations, creek water and sediment cores were collected during the dry and wet seasons at all tidal phases (ebb, low, flow, and high tides). Physical-chemical parameters were measured in the creek water (temperature, salinity, pH, Eh, and DO), whereas pH, redox potential (Eh), and total organic matter contents were obtained from the sediment cores. In addition, total dissolved sulfide content ∑ (H2S, HS−, H2−) was measured from sediment pore water. During the dry and wet seasons, the creek water pH, Eh, and dissolved oxygen were lowest in low tide, whereas oxygenated conditions and higher pH and Eh values prevailed in high tide. The total organic matter content in sediments was higher during the dry season, with the highest contents observed in the seaward station. Higher average ∑H2S (landward station, 243.1 ± 234.9 μM L−1; seaward station, 544.9 ± 174.4 μM L−1) were noted during wet season compared to dry season (landward station, 5.3 ± 4.5 μM L−1; seaward station, 430.2 ± 435.1 μM L−1). These ∑H2S contents increased towards the bottom of the sediment column, reflecting the anaerobic decomposition of the organic matter and sulfate reduction. This study provides insight to the geochemical dynamics of intertidal mangrove sediments that are sensitive to fluctuating reducing and sulfidic conditions, oscillating at time scales of minutes to hours.

HEAVY METAL SPECIATION IN BOTTOM SEDIMENTS OF THE VYSHNEVOLOTSKY RESERVOIR

The study of heavy metal speciation in bottom sediments of the Vyshnevolotsky water reservoir is presented in this paper. Sequential selective procedure was used to determine the heavy metal speciation in bottom sediments and thermodynamic calculation — to determine ones in interstitial water. It has been shown that Mn are mainly presented in exchangeable and carbonate forms; for Fe, Zn, Pb и Co the forms are related to iron and manganese hydroxides is played an important role; and Cu and Ni are mainly associated with organic matter. In interstitial waters the main forms of heavy metal speciation are free ions for Zn, Ni, Co and Cd, carbonate complexes for Pb, fulvate complexes for Cu. Effects of particle size and organic matter content in sediments on distribution of mobile and potentially mobile forms of toxic elements have been revealed.

Assessment of temporal and spatial water quality in international Gomishan Lagoon, Iran, using multivariate analysis.

Coastal lagoon ecosystems are vulnerable to eutrophication, which leads to the accumulation of nutrients from the surrounding watershed over the long term. However, there is a lack of information about methods that could accurate quantify this problem in rapidly developed countries. Therefore, various statistical methods such as cluster analysis (CA), principal component analysis (PCA), partial least square (PLS), principal component regression (PCR), and ordinary least squares regression (OLS) were used in this study to estimate total organic matter content in sediments (TOM) using other parameters such as temperature, dissolved oxygen (DO), pH, electrical conductivity (EC), nitrite (NO2), nitrate (NO3), biological oxygen demand (BOD), phosphate (PO4), total phosphorus (TP), salinity, and water depth along a 3-km transect in the Gomishan Lagoon (Iran). Results indicated that nutrient concentration and the dissolved oxygen gradient were the most significant parameters in the lagoon water quality heterogeneity. Additionally, anoxia at the bottom of the lagoon in sediments and re-suspension of the sediments were the main factors affecting internal nutrient loading. To validate the models, R2, RMSECV, and RPDCV were used. The PLS model was stronger than the other models. Also, classification analysis of the Gomishan Lagoon identified two hydrological zones: (i) a North Zone characterized by higher water exchange, higher dissolved oxygen and lower salinity and nutrients, and (ii) a Central and South Zone with high residence time, higher nutrient concentrations, lower dissolved oxygen, and higher salinity. A recommendation for the management of coastal lagoons, specifically the Gomishan Lagoon, to decrease or eliminate nutrient loadings is discussed and should be transferred to policy makers, the scientific community, and local inhabitants.

Sedimentary dynamics and benthic macrofauna distribution: Insights from the shoreface in southern Portugal

This study examined temporal distributions of macrobenthic communities in relation to bottom depth and specifically addressed whether variation in sedimentary dynamics affects species composition and functional structure. Sampling was carried in 2014 (February, May and September) off Tavira Island (southern Portugal). In each sampling period, three replicates of sediment samples were collected at 7, 12, 17 and 22 m deep for both macrobenthic and sediment characterisation. Distributional patterns of macrofauna communities were a function of the interaction between depth and temporal variability, influenced by a gradient in hydrodynamics and species recruitment. The duration of sediment remobilisation and the organic matter content in sediments were the main features of the shoreface sedimentary dynamics responsible for differences in macrobenthic species composition and feeding habits. At low depths (7 m), under intense hydrodynamic conditions and longer period of sediment remobilisation, sediments were characterised by slightly gravelly sand with low contents of organic matter and calcium carbonate. Macrobenthic communities inhabiting shallow depths displayed low abundance and species richness, being dominated by grazers and suspension feeders. In contrast, at the highest studied depth (22 m), subject to low sediment remobilisation, sediments were composed by gravelly sand with high contents of organic matter and calcium carbonate. This depth (22 m) was characterised by high abundances and species richness, reflecting a more stable macrobenthic community composed mainly by surface deposit feeders. According to the benthic communities, the seaward limit of significant wave effects on the seabed is around 7 m in low-energy periods and over 17 m in high hydrodynamic energy periods.