Seawater Quality Research Articles

Integrated water quality and performance assessment of seawater desalination plants along two coasts in Egypt

This study aims to assess feedwater, brine, and drinking water quality related to eight full-scale Egyptian seawater desalination plants. Collected water quality records from plants on the Mediterranean and Red Seas were monthly analyzed to identify different physical, chemical, and biological parameters during 2022. Statistical analysis and water quality indices (WQIs) approaches were applied to evaluate the various water quality states based on the available international and Egyptian guidelines. Analyzed seawater quality properties showed compliance with the most operating permissible limits except for high concentrations of turbidity, fats, oils, and greases, total bacteria in one plant, and iron, manganese, and silica in another plant. The monthly measured Weighted Arithmetic WQI classified 71 % and 100 % of desalination plants as having “Excellent” water rank according to the standard limits of the World Health Organization and the Egyptian Water Quality Standard, respectively. However, 65 % and 52 % of desalination plants were projected into the “good” water quality rank based on the Canadian Council of Ministers of the Environment WQI for the same guidelines. The results indicate that the feed intake type and the location of a desalination plant can optimize its performance efficiency, minimize contamination sources, and mitigate the potential environmental impacts of brine.

Analysis of Sea and River Water Quality Standards Due to Operations and Domestic Activities in the Sanur Port Area, Bali

The development of an area has impacts, both positive and negative impacts. The positive impact is in the form of regional economic growth, employment and development of the surrounding regions. The negative impact is the disruption of the environmental ecosystem and a decrease in environmental quality due to waste generated from development operations, in the form of solid waste (garbage) and liquid waste. The increasing pollution load is also caused by public awareness and business activities in upstream areas that do not manage waste properly, which ultimately leads to all of the waste accumulating in water bodies and causing changes in water quality standards. Sanur Port, which is one of the development centers in its operations, is very vulnerable to environmental pollution impacts. The pollution mechanism originates from activities around Sanur Port and domestic activities which are discharged into rivers and seas in the Sanur area. This research aims to analyze the quality of river water and sea water caused by activities around Sanur Port and community activities based on Decree of the Minister of Environment Number 51 of 2004 and determine the pollution index. Water quality standards use Bali Governor Regulation no. 16 of 2016 concerning Environmental Quality Standards and Quality Standard Criteria for Environmental Damage. This research uses a quantitative approach by collecting primary data from direct observations in the field and secondary data based on previous research reports and government reports. The research results show that TDS in the rainy season tends to be lower than in the dry season, both in the results of testing samples of Abianbase river water, the results of testing samples of sea water in front of the Mak Beng Restaurant and sea water samples in the Sanur Port Pool. In front of Mak Beng, ammonia levels during the rainy season are higher than during the dry season. Ammonia levels in the Abianbase River and sea water in front of Sanur port are lower during the rainy season compared to the dry season. The presence of Coliform bacteria and E. coli shows a tendency to decrease during the rainy season. This decrease is thought to be caused by leaching by rainwater entering marine waters and retailing and changes in ocean currents during the rainy season.

Qualitative Analysis of Seawater Quality on Bulan Island in Batam

In line with the increase in population and socio-economic development activities, various problems arise in marine ecosystems in coastal areas where waste is disposed of or as a result of weathering ships passing by in the waters. This can cause pollution and reduce the quality of seawater physically, chemically, and biologically, and it can damage the balance of the ecosystem. These physicochemical factors include temperature, pH, total solute (TDS), lead (Pb), iron (Fe), magnesium (Mg), sodium (Na), zinc (Zn), nickel (Ni), and copper (Cu). This study aims to help qualitatively improve seawater quality in the Bulan Island region's waters. The research method for the physical parameters of odor, color, and taste used organoleptic methods, while the chemical parameters for pH used a pH meter, TDS used a TDS meter, and contacted metals using a qualitative method. The results of the research are based on the parameters of smell, taste, and color of the Indonesian Ministry of Health standards, while the highest temperature is found in the middle of the sea, namely (31.7 oC). The highest pH parameter was found in the water at Sagulung Port (7.9) and the lowest at seawater (7.5), while the highest TDS value was found in seawater at Sagulung Port (209 ppm) and the lowest at Pulau Bulan Port. (108 ppm), from the results of the pH and TDS tests the three samples still met the standards of the Indonesian Ministry of Health. The metal quality test found that the seawater of Pulau Bulan Port, mid-ocean sea air, and sea air at Sagulung Port identified the presence of Lead (Pb) and Zink (Zn) metals.

Multidimensional information fusion and analysis of ultraviolet absorption spectroscopy: Simultaneous detection method for copper and zinc ion concentrations in seawater

Heavy metal pollution poses a significant threat to marine ecological environments and serves as a crucial indicator for seawater quality assessment. The enrichment of heavy metals severely impacts marine ecosystem health and poses threats to human food safety, underscoring the critical importance of monitoring heavy metal levels in marine waters. In this paper, UV absorption spectroscopy was used to collect the spectra of seawater containing different concentrations of Cu and Zn ions, which overcomes the problems of traditional methods that require extensive pre-treatment and lossy samples. To address the characteristics of the data, the Savitzky-Golay (SG) filtering algorithm is used for preprocessing. The acquired spectra are then subjected to further data analysis using the proposed multidimensional information fusion method called SpectraNet Fusion Algorithm (SFA) for UV absorption spectroscopy. The local feature information extraction module and the whole domain information feature extraction module were respectively used to predict the regression of the data in parallel two-channel, and the output results were integrated to form a new feature map, which was further processed by the feature information fusion module, and finally output the prediction results corresponding to the spectra to realize the accurate detection of Cu and Zn heavy metal ions in seawater. The coefficient of determination (R2) of the model training set established by this method reaches 98.00 %, the root mean square error (RMSE) reaches 0.0389, and the mean absolute error (MAE) reaches 0.0243, combined with the experimental design, the detection range was 5 μg·L−1 to 90 μg·L−1,which realizes simultaneous and high-precision prediction of Cu and Zn heavy metal ions in seawater.

A highly stable electrochemical sensor with antifouling and antibacterial capabilities for mercury ion detection in seawater

The monitoring of heavy metal ions in ocean is crucial for environment protection and assessment of seawater quality. However, the detection of heavy metal ions in seawater with electrochemical sensors, especially for long-term monitoring, always faces challenges due to marine biofouling caused by the nonspecific adsorption of microbial and biomolecules. Herein, an electrochemical aptasensor, integrating both antifouling and antibacterial properties, was developed for the detection of Hg2+ in the ocean. In this electrochemical aptasensor, eco-friendly peptides with superior hydrophilicity served as anti-biofouling materials, preventing nonspecific adsorption on the sensing interface, while silver nanoparticles were employed to eliminate bacteria. Subsequently, a ferrocene-modified aptamer was employed for the specific recognition of Hg2+, leveraging the aptamer's ability to fold into a thymine-Hg2+-thymine (T-Hg2+-T) structure upon interaction, and bringing ferrocene nearer to the sensor surface, significantly amplifying the electrochemical response. The prepared electrochemical aptasensor significantly reduced the nonspecific adsorption in seawater while maintaining sensitive electrochemical response. Furthermore, the biosensor exhibited a linear response range of 0.01–100 nM with a detection limit of 2.30 pM, and realized the accurate monitoring of mercury ions in real marine environment. The research results offer new insights into the preparation of marine antifouling sensing devices, and it is expected that sensors with antifouling and antimicrobial capabilities will find broad applications in the monitoring of marine pollutants.

Sistem Kontrol Kadar Amonia Dan Tinggi Air Pada Kolam Penangkaran Tukik Penyu

Turtles are also one of the animals whose population is decreasing day by daydue to several factors ranging from climate change, disease, environmentaldamage and inadequate processing of conservation techniques and so on. Withthe status of turtles being endangered, special attention is needed for turtles inthe form of cultivating turtles, especially when the turtles are still 0-2 years oldor known as hatchlings. One of the important indicators in hatchling cultivationrequires good seawater quality management. One of the parameters of goodseawater quality is ammonia levels. This ammonia level can be formed naturallyby metabolic wastes and also food waste that decomposes in the water whichresults in the formation of ammonia levels. In turtle hatchling ponds it is alsonecessary to adjust the water level in the pond with a height of 5cm - 10cmbecause newborn hatchlings cannot dive. The importance of regular waterquality control such as ammonia levels and water level in ponds is veryimportant for the success of hatchling cultivation. Therefore, a research onmonitoring and controlling systems for ammonia levels and water levels usingthe TCS3200 color sensor is carried out to read the change in water color afteradministration of an ammonia test solution which will show the value ofammonia levels in water. Previously, water sampling was carried out by DCpumps and ultrasonic sensors to detect water level. Where this system canmonitor and control ammonia levels and height automatically and the resultscan be viewed using a smartphone through the Blynk application

Kajian Kualitas Air Laut dan Sebaran Indeks Pencemaran di Pesisir Utara Kecamatan Palang-Tuban pada Musim Kemarau

The northern coastal area of ​​Palang Sub-District is a densely populated area in the Tuban district with high differentiation of economic activities. The large population and heterogeneous community activities on the northern coastal of Palang Sub-District have the potential to become a source of pollution which results in a decrease in seawater quality. The research aim is to analyze seawater quality on the north coast of Palang Sub-District based on seawater quality parameters and the spatial distribution of the pollution index. It is hoped that this research can help local governments to monitor and control water pollution in the area. Sea water sampling was carried out in the dry season for 2 days at high and low tide conditions. This research analyzes the concentration values ​​of BOD, COD, NO3-, TSS, detergent, oil & grease, pH, temperature, and Total coliform compared to seawater quality standards of PP RI No. 22 of 2021 Appendix VIII on Marine Biota. The spatial distribution of the water quality pollution index is the result of interpolation using the Inverse Distance Weighted (IDW) method from the results of measuring test parameters. The Pearson Correlation statistical test was carried out to determine the level of correlation between the parameters selected in determining water quality. The results of the research show a decline in the quality of the northern coastal waters of Palang-Tuban District with several parameter concentration average values ​​exceeding the quality standards, namely pH = 6.9 (QS = 7.0-8.5); TSS = 29.2 ppm (QS= 20 ppm); Nitrate = 0.4 ppm (QS = 0.06 ppm), BOD5 = 54.8 ppm (QS= 20 ppm), COD = 112.5 ppm (QS= 100 ppm). The water quality status shows that the water conditions are moderately polluted (ST1A), lightly polluted (ST1B-ST5B), and good conditions (ST4C & ST5C). Controlling and reducing the pollution load entering coastal waters needs to be carried out to prevent the quality of coastal waters from decreasing further. One of them is by creating wastewater treatment at every fishing port and fish auction.

Treatment Effect of Long-Term Subsurface-Flow Constructed Wetland on Mariculture Water and Analysis of Wetland Bacterial Community

To improve the quality of natural seawater to meet the needs of aquaculture production, a large-scale subsurface-flow constructed wetland (HSFCW) was constructed and operated stably for 2 years to understand the reasons for its purification effect on natural seawater. The results of the study showed that the system could maintain a high purification effect on natural seawater during aquaculture; the average removal rates of COD, TSS, TN, NH4+-N, and DON (organic nitrogen) were 22.29%, 49.33%, 36.94%, 10.88%, and 44.08%, respectively. Additionally, the HSFCW could effectively remove harmful algae such as Cyanobacteria; the removal rate of dominant algae species in Cyanobacteria was 90.33–97.93%. The pyrosequencing of 16S ribosomal DNA revealed that Proteobacteria, Nitrospirae, and Chloroflexi were the main and key bacterial phyla in the system. Members of these key gates are regarded as playing important roles in resisting water purification. The study results suggest that the subsurface-flow wetland system can effectively improve seawater quality and reduce the density of harmful algae cells.

The physical and biogeochemical parameters along the coastal waters of Saudi Arabia during field surveys in summer, 2021

Abstract. During the last decades, the coastal areas of the Kingdom of Saudi Arabia, on the Red Sea and the Arabian Gulf, have been subjected to intense economic and industrial growth. As a result, it may be expected that the overall environmental status of Saudi Arabian coastal marine waters has been affected by human activities. As a consequence, adequate management of the Saudi Arabian coastal zone requires an assessment of how the various pressures within this zone impact the quality of seawater and sediments. To this end, environmental surveys were conducted over 15 hotspot areas (areas subject to environmental pressures) in the Saudi Arabian coastal zone of the Red Sea and over three hotspot areas in the Saudi Arabian waters of the Arabian Gulf. The survey in the Red Sea, conducted in June/July 2021, acquired measurements from hotspot areas spanning most of the Saudi coastline, extending from near the Saudi–Jordanian border in the north to Al Shuqaiq and Jizan Economic City (close to the Saudi–Yemen border) in the south. The survey in the Arabian Gulf, carried out in September 2021, included the areas of Al Khobar, Dammam and Ras Al Khair. The main objective of both cruises was to record the physical and biogeochemical parameters along the coastal waters of the kingdom, tracing the dispersion of contaminants related to specific pressures. Taken together, these cruises constitute the first multidisciplinary and geographically comprehensive study of contaminants within the Saudi Arabian coastal waters and sediments. The measurements acquired revealed the influence of various anthropogenic pressures on the coastal marine environment of Saudi Arabia and also highlighted a strong influence of hydrographic conditions on the distribution of biochemical properties in the Red Sea and the Arabian Gulf. The data can be accessed at SEANOE https://doi.org/10.17882/96463 (Abualnaja et al., 2023), whereas the details of the sampling stations are available at https://mcep.kaust.edu.sa/cruise-postings (last access: 25 March 2024). The dataset includes the parameters shown in Tables 1a, b and 2a.

Application of ANN for coastal water quality prediction: Quang Binh case study

The coastal areas of Quang Binh province play a crucial role not only in the economic and tourism development of the coastal province but also in the overall development of the Northern Central region. Therefore, monitoring and forecasting seawater quality in this region is vital. However, the water quality condition assessment faces many limitations due to the lack of measured data and the complication of numerical models. Meanwhile, the artificial intelligence model for simulating and predicting water quality has been widely applied due to its timely and reliable calculating abilities. This research has piloted the prediction of some water pollution parameters on the coast of Quang Binh province using an artificial neural network (ANN) model. This presents a novel approach to identifying implicit relationships between variables based on data analysis techniques via ANN. An ANN model was built to analyze the measured environmental time series data at Dong Hoi station, Quang Binh province, from 2002 to 2022. The calculation results of the training (70% of the data set, NSE: 0.81) and testing (the rest 30% of the data set, NSE: 0.5) of the model have satisfied the total coliform parameter, indicating the promise of applying the ANN model for water quality prediction.

Recovery of fishery-stressed seagrass meadows is driven by improvements in wastewater management

As ecosystem engineers, seagrasses provide major benefits to coastal habitats worldwide. Nonetheless, their dynamics remain poorly understood in local areas. Three seagrass (Zostera noltei) meadows located within shellfish beds in Galicia (NW Spain) were selected to assess the intra and inter-annual changes in the habitats by considering the effects of harvesting, temperature and sewage pollution. Seagrass cover increased between April and October, when the sediment temperature ranged from 15 to 20 °C, while in terms of long-term dynamics there was a mean gain of 3 % year−1 between 2004 and 2023. Shellfishing caused mechanical disturbance within the meadows, but the seasonal changes in cover depended on temperature. However, we pointed out the built of new wastewater treatment plants since 1990 that improved water quality as the main driver of the long-term increase in seagrass cover. Environmental policies that enhance seawater quality and limit harvesting pressure are essential to maintain this positive trend.

Physicochemical and ecotoxicological approaches for Moknine Continental Sebkha in Tunisia.

Degradation of water quality is an emerging issue in many developing countries. In this context, industrial and domestic effluents heavily contaminate the coast of Moknine Continental Sebkha in Tunisia. The present study aimed to biomonitor the seawater quality of the Moknine Continental Sebkha coast using physicochemical and ecotoxicological approaches. The ecotoxicological assessment was performed using three species representing different trophic levels, namely Vibrio fischeri, Selenastrum capricornutum, and Lepidium sativum. In the physicochemical analysis such as BOD (biochemical oxygen demand), COD (chemical oxygen demand), TSS (total suspended solids), TOC (total organic carbon), NO3- (nitrate), AOX (adsorbable organic halogen), the recorded levels of pH and total suspended solids did not comply with the Tunisian standard (NT.09.11/1983). The ecotoxicological data confirmed that the tested water samples displayed toxicity to two test indicators L. sativum and S. capricornutum. A targeted chemical screening of the Moknine Continental Sebkha coast previously performed revealed the presence of total mercury, four phthalate acid esters, and one non-phthalate plasticizer, a fact that could explain the observed ecotoxicological effects and therefore might harm the biotic area and the health of the surrounding population.

The impact of the COVID-19 pandemic on the seawater quality of Ha Long Bay, Vietnam

Ha Long Bay is a UNESCO World Heritage Site in Vietnam with unique natural scenery. Development and socio-economic activity impact its water quality. In the context of the Vietnam National Standards, historical follow-up data taken over a five-year period (2016 to 2020), for twenty-eight widely dispersed sampling sites, has been used to carry out a temporal assessment of seawater quality utilizing a Water Quality Index (WQI) method. The analysis shows that the seawater quality is generally acceptable over this period. However, the calculated WQI values for the “pandemic year” of 2020 compared to the data for 2016 to 2019, demonstrate a significantly lesser impact for the bay overall and, more specifically, for seventeen individual sites. Ten sites remain unaffected, and one site shows a significantly higher impact. This study demonstrates how the occurrence of the pandemic in 2020 may be exploited for the interrogation of anthropogenic impacts around the bay.

Growing coastal tourism: Can biomonitoring provide insights into the health of coastal ecosystems?

Coastal tourism's surge raises concerns for Morocco's Agadir marine environment, notably with Taghazout Bay's impact. Our study assesses Taghazout's health, employing a comprehensive approach. Our study evaluates Taghazout's health, adopting a comprehensive approach covering physicochemical, microbiological aspects, macrobenthic fauna, metal pollution, and biomarkers in D. trunculus mollusks. Seawater quality aligns with Moroccan standards, indicating good bathing water. The intertidal zone hosts ten species, dominated by D. trunculus. Biomarker responses in D. trunculus suggest chemical stress. Land-use maps expose significant changes driven by the Taghazout Bay project, impacting approximately 37.99 % of the landscape. Construction activities notably encroached upon the Arganeraie and the coastal zone, creating a stark contrast from 2003. These findings form a crucial database for future studies, contributing significantly to environmental management and sustainable development, aiding informed decision-making and effective coastal ecosystem preservation strategies.

Apparent return of free-living Fucus vesiculosus to the Polish Baltic waters

The underwater meadows of the Puck Bay, once thriving with eelgrass Zostera marina, bladderwrack Fucus vesiculosus and black carrageen Furcellaria lumbricalis, experienced a decline in water quality during the 1960s and 1970s due to untreated sewage pollution. This, together with commercial exploitation, led to the disappearance of bladderwrack in 1977, with unsuccessful attempts at reintroduction in the early 2000s. In December 2023, a SCUBA survey near Rzucewo revealed a numerous bladderwrack in a benthic free-living form after 46 years of absence. The algae were found between 1.7 and 2.7 m depth, loosely positioned on the seabed, often within Z. marina beds, and with blue mussels Mytilus edulis attached. This reappearance suggests a positive trend in seawater quality and overall state of the Puck Bay, especially when combined with recent recovery of other algae species. The apparent return of bladderwrack could enhance ecosystem functionality, benefiting fish recruitment, grazer and algal biomass. Further investigations on bladderwrack's reappearance are needed in order to verify whether this is the only ecotype currently present in the Puck Bay.

Reef fish community structure in the waters of small islands Central Bangka Regency

This study aimed to analyze the community structure of reef fish in the small island waters of Central Bangka. The research was conducted in March 2022 in the waters of Bebuar Island, Ketugar Island, Ketawai Island, and Gusung Asam Central Bangka Regency, Bangka Belitung Islands Province. The coral reef survey method uses purposive sampling and the coral reef fish visual census with data analysis of abundance, diversity index, uniformity, and dominance. In-site water quality measurements included six parameters: temperature, salinity, current, brightness, depth, and pH. The results showed that coral reef cover from 44.60 - 87.00% with the medium to very good category. The abundance of reef fish from 1 to 3 individuals/m2 was dominated by 18 species of the Pomacentridae family. The reef fish diversity index ranged from 2.47 to 2.90, including the medium category. The uniformity index value ranged from 0.79 - 0.94, including the high category, indicating that the species found were evenly distributed across all stations. The dominance index value ranges from 0.07 to 0.15, including low, where no species dominates significantly and the fish are evenly distributed. Temperature, brightness, pH, and salinity are factors that support the growth of coral and reef fish. A water current speed of 0.05 – 0.20 m/s is quite helpful in cleaning coral reefs from mud and can supply oxygen. Water conditions were categorized as good and fulfilled the seawater quality standards.

Study on load allocation of land-based total nitrogen in the Bohai Sea

Total nitrogen (TN) is one of the terrigenous pollutants in the Bohai Sea. A reasonable releasing scheme can effectively improve the seawater quality. Based on the observed TN concentrations and the national pollution control requirements, the TN load ratios of four major rivers around the Bohai Sea are adjusted in multiple levels within the range of 50 %–200 % in the frame of total control. Then, a pollutant transport model is used to evaluate each load allocation scheme by calculating the area of different seawater qualities. The optimum scheme is loads of the Yellow River and Luan River are set to 50 % and 200 % of the levels in 2018, and thus the area of heavily polluted seawater can be decreased by 33.14 %. Additionally, the reasonable TN reduction amounts of four major rivers in 2018–2020 are calculated according to the optimum scheme, which can be provided as a decision-making basis of marine managements.

Use of water quality parameters to assess the ecological health of Atlantic coastal areas in the northwestern Morocco

Coastal waters are confronted with multiple stressors, including chemical contamination/pollution and climate change. Water quality along the Atlantic coast of Morocco was assessed, in this study, at six stations over four seasons, including three heavily industrialized stations (S2, S4, and S6) and three clean stations (S1, S3, and S5), spreading over a distance of ∼300 km from Azemmour to Essaouira cities. The physicochemical characteristics (temperature, salinity, pH, dissolved oxygen, suspended matter, and sulfate), and chlorophyll-a, as well as nutrients (nitrite, nitrate, ammonium, total phosphorus, orthophosphate, and silicate) were analyzed to investigate their spatial and seasonal trends in the study areas. The results revealed significant spatiotemporal variations in the distribution of the hydrological characteristics across the sampling sites. In addition, the observed sulfate and nutrient concentrations showed significant spatial and seasonal differences. The disturbed stations showed the highest concentrations of nutrients, while the clean stations exhibited the highest concentrations of chlorophyll-a, particularly in the spring season. As expected, the compressive pollution index (CPI) and water pollution index (WPi) results supported the pollution status of stations. Accordingly, the surface seawater quality was better in the clean stations compared to the polluted stations. According to the CPI and WPi values, the sampling stations were classified in the following descending order of pollution, from strongly and moderately polluted stations to slightly or unpolluted stations (S4 > S2 > S6 > S1> S3 > S5). The total phosphorus, orthophosphate, sulfate, and chlorophyll-a concentrations were substantially higher than the surface water quality standards of Morocco, especially at the most industrialized stations in the winter.The physicochemical, biological, and nutrient data obtained in this study provide a valuable reference for assessing the ecological quality status of the Atlantic coastal environments in the study areas.

The connection between Submarine Groundwater Discharge and seawater quality: The threat of treated wastewater injected into coastal aquifers

Submarine Groundwater Discharge (SGD) delivers nutrients to the coastal sea triggering phytoplankton blooms, eutrophication, and can also serve as a pathway for contaminants. Wastewater treatment plants (WWTP) including injection wells in coastal areas influence coastal aquifers and might impact the composition and magnitude of SGD fluxes. In tourist areas, wastewater treatment may be less efficient and larger in volume during high seasons, potentially impacting nutrient fluxes from SGD and exacerbating environmental impacts. This study analyzes the nutrient transfer from treated wastewater injection in karstic aquifers to the coastal sea via SGD, considering the impacts of tourism seasonality. This study is conducted in Cala Deià, a small cove in the Balearic Islands, a Mediterranean tourist destination. The findings suggest that the seasonality of tourism, leading to variations in the volume of wastewater treated in the WWTP, influences the dynamics of the coastal aquifer. This leads to increased SGD water and nutrient fluxes to the sea in summer, i.e. the peak tourist season. The measured DIN, DIP, and DSi inventories in the cove are much larger in August than in April (3, 10, and 1.5 times higher, respectively) due to higher input of nutrients in summer due to SGD impacted by the WWTP. These elevated nutrient flows can support algal blooms in the cove, compromising water quality for local swimmers and tourists. Indeed, in August, shoreline stations exhibited eutrophic Chl-a concentrations, with peaks reaching approximately 4 mg Chl-a L−1. These elevated levels suggest the presence of an algal bloom during the survey. The anthropogenic origin of SGD-driven nutrients is traced in seawater and seagrass meadows, as evidenced by high ∂15N signatures indicative of polluted areas. Thus, the high pressure exerted on coastal areas by tourism activities increased the magnitude of SGD nutrient fluxes, thereby threatening coastal ecosystems and the services they provide.

Fuzzy comprehensive evaluation of seawater quality of Larimichthys Crocea mariculture areas in Zhoushan, China

Context Aquaculture is an essential industry and assessing its impact on the environment, particularly water quality, is crucial for sustainable practices. This study aimed to comprehensively evaluate the seawater quality in the Dongji Island yellow croaker (Larimichthys crocea) aquaculture area by using the fuzzy comprehensive evaluation method and field survey. Aims The main objective of this study was to assess the seawater quality in the aquaculture area during 2 consecutive years (2019 and 2020) on the basis of monitoring data. Methods The researchers utilised the fuzzy comprehensive evaluation method to assess seawater quality in the Dongji Island yellow croaker aquaculture area. Seawater monitoring data from 6 months in 2019 and 6 months in 2020 were collected for the evaluation. The method included an annual average evaluation, and membership degrees were calculated for each year and individual months. Qualitative interviews with 30 local fish farmers were conducted to unravel the challenges faced by aquaculture water quality management. Key results The evaluation results indicated that the seawater quality in the aquaculture area was classified as Class I water in both 2019 and 2020 on the basis of the annual average evaluation. However, the membership degrees for 2019 were higher than those for 2020, suggesting that water quality was better in 2019. Furthermore, individual monthly evaluations in 2020 showed varying membership degrees, with May and June having higher membership degrees, indicating better water quality than in other months. August had the lowest membership degree, implying poorer water quality during that month. Conclusions The study demonstrated that the fuzzy comprehensive evaluation method is effective for evaluating seawater quality in aquaculture areas. It also concluded that the water quality in 2019 was superior to that in 2020, raising concerns about potential environmental degradation. Implications The quantitative and qualitative findings of this research have important implications for aquaculture practices in the Zhoushan area. The study highlights the need for continued monitoring and management of water quality to ensure sustainable aquaculture practices and adherence to water-quality policies. Future aquaculture endeavours in the region should consider the potential impact on water quality to maintain a healthy ecosystem.