Nutrient dynamics and eutrophication in the Sea of Marmara: Data from recent oceanographic research

Comparison of conventional and machine learning regression models for accurate prediction of selected optical active components - A case study: The Gulf of Izmit

This study hypothesizes that advanced machine learning (ML) models can more accurately predict certain critical water quality parameters in marine environments compared to conventional regression techniques. We specifically evaluated the spatio-temporal distribution of Chlorophyll-a (Chl-a) and Secchi Disk Depth (SDD) in the Gulf of Izmit using in-situ measurements and Sentinel-2 satellite imagery from October 2021 and 2022. Among the models tested, the Support Vector Regression (SVR) model showed better predictive performance, achieving the lowest RMSE for SDD (1.11-1.70 m) and Chl-a (1.16-4.97 mg/m3) and the lowest MAE for SDD (0.86-1.43 m) and Chl-a (1.03-3.17 mg/m3). Additionally, the study observed a shift from hypertrophic to eutrophic Chl-a conditions and from mesotrophic-eutrophic to oligotrophic SDD conditions between 2021 and 2022, aligning with SVR model predictions and in-situ observations. These findings underscore the potential of ML models to enhance the accuracy of water quality monitoring and management in marine ecosystems.

The marine cartilaginous fishes and sturgeons of the Sea of Marmara: an updated and annotated checklist

A revised checklist of sharks, batoids, and sturgeons in the Sea of Marmara, Turkey encompasses 41 species across 18 families. It provides a concise historical context and addresses issues related to problematic reports. Furthermore, the paper delves into the analysis of taxonomic changes in other literature reports, aiming to provide a framework for upcoming ichthyological surveys and ecological studies, while also presenting relevant data on the economic significance of select species.

Salinity effect on an anaerobic methane- and ammonium-oxidising consortium: Shifts in activity, morphology, osmoregulation and syntrophic relationship

Nitrate-dependent anaerobic methane oxidation (AOM) is a microbial process of both ecological significance for global methane mitigation and application potential for wastewater treatment. It is mediated by organisms belonging to the archaeal family 'Candidatus Methanoperedenaceae', which have so far mainly been found in freshwater environments. Their potential distribution in saline environments and their physiological responses to salinity variation were still poorly understood. In this study, the responses of the freshwater 'Candidatus Methanoperedens nitroreducens'-dominated consortium to different salinities were investigated using short- and long-term setups. Short-term exposure to salt stress significantly affected nitrate reduction and methane oxidation activities over the tested concentration range of 15-200‰ NaCl, and 'Ca. M. nitroreducens' showed the higher tolerance to high salinity stress than its partner of anammox bacteria. At high salinity concentration, near marine conditions of 37‰, the target organism 'Ca. M. nitroreducens' showed stabilized nitrate reduction activity of 208.5 µmol day-1 gCDW-1 in long-term bioreactors over 300 days, in comparison to 362.9 and 334.3 µmol day-1 gCDW-1 under low-salinity conditions (1.7‰ NaCl) and control conditions (∼15‰ NaCl). Different partners of 'Ca.  M. nitroreducens' evolved in the consortia with three different salinity conditions, suggesting the different syntrophic mechanisms shaped by changes in salinity. A new syntrophic relationship between 'Ca. M. nitroreducens' and Fimicutes and/or Chloroflexi denitrifying populations was identified under the marine salinity condition. Metaproteomic analysis shows that the salinity changes lead to higher expression of response regulators and selective ion (Na+/H+) channeling proteins that can regulate the osmotic pressure between the cell and its environment. The reverse methanogenesis pathway was, however, not impacted. The finding of this study has important implications for the ecological distribution of the nitrate-dependent AOM process in marine environments and the potential of this biotechnological process for the treatment of high-salinity industrial wastewater.

A new species of the genus Paraphyllina (Scyphozoa: Coronatae): Paraphyllina kubanci sp. nov. from the Sea of Marmara, Turkey

On August 9, 2008, during the MAREM (Marmara Environmental Monitoring) project survey, a single specimen of an unknown Scyphozoa was caught with a deep-water vertical plankton haul, below the thermo-halocline interface, at maximum 1042 m hauling depth, in the Sea of Marmara (40°44'00″N, 08°00'03″E), Turkey. In the following years, 22 specimens, which ranged in diameter from 18 to 26 mm and had the same characteristics, were caught in the same water mass of the Sea of Marmara during MAREM monitoring surveys. The specimens seem to correspond most closely with the medusae described by Maas (1903), Neppi (1915), and Russell (1956). All these specimens were similar in their essential characteristics, but differed in some details. Likewise, Paraphyllina kubanci sp. nov. differs from other species of the genus in terms of some characteristics, especially in the S-shaped gonads and in the distribution of coloration. It is identified as a new species of the genus Paraphyllina and described here.

Impact of mixing on water quality in the Bosphorus - Implications on sustainable management of wastewater marine discharges

The study established the water quality modelling of the Bosphorus system, based on hydrodynamic data as well as the results of the water quality survey carried out in the last five years. The model revealed significant decrease in the magnitude of pollutant loads in the upper layer at the exit into The Marmara Sea providing numerical proof that no pollutant transport would take place from sewage discharges to the upper layer. A similar modelling approach was implemented at the Bosphorus/Marmara interface, a significant hotspot as it included two major deep marine outfalls. The results asserted that the entire sewage flow would enter the lower flow in The Bosphorus through the interface without an appreciable mixing with the upper flow. This way, the study provided a significant scientific support for the sustainable management of marine discharges in this area, since they have no physical interference with The Marmara Sea.

Distinct patterns of sedimentary phosphorus fractionation and mobilization in the seafloor of the Black Sea, Marmara Sea and Mediterranean Sea

Phosphorus (P) is a key element to all life that is used for structural and functional component of all organisms. The cycling of sedimentary P may differ depending on the redox-conditions of the overlying waters affecting the dynamics, and distribution of P-fractions and the elements that are highly coupled to P cycle. Though biogeochemistry of water column in the three interconnected marine basins of Black, Marmara and Mediterranean Seas have been studied extensively, few studies were carried out to understand sedimentary P dynamics in these regions. In this study, therefore, the biogeochemical cycling of sedimentary P and related variables such as porewater nutrients, sedimentary organic carbon, nitrogen and reactive iron were studied in selected sites at the three interconnected marine basins: Black Sea, Marmara and Northeastern (NE) Mediterranean Sea. The pool of "potentially mobile P" was also determined for the studied sites. The study results showed that porewater and sediment biogeochemistry displayed great variability in the studied sites with the maximum concentrations of porewater phosphate, ammonium, reactive silicate, surface sediment organic carbon, nitrogen, phosphorus and total phosphorus (TP) measured in the hypoxic Marmara Sea and suboxic/anoxic Black Sea. The decline in the TP concentrations of all sediment core samples indicated P-mobilization to the overlying water. The pool of "potentially mobile P" varied between 0.023 and 0.148 mol/m² in the studied sites with the maximum values recorded in suboxic and anoxic/sulfidic parts of the Black Sea. This study predicts that the deoxygenation and eutrophication would further lead to the preferential release of P in these three interconnected marine basins, hence changing the remineralization, N/P molar ratios and eventually transform the deep-water nutrient stocks with implications for internal N/P control on marine ecosystems.

Nitrogen and phosphorus spatio-temporal distribution and fluxes intensifying eutrophication in three tropical rivers of Côte d'Ivoire (West Africa)

Nutrient contamination assessments in the three West African tropical Comoé, Bandama, and Bia Rivers (Côte d'Ivoire) were performed from March 2016 to March 2018. Five stations per river were sampled. Nutrients spatio-temporal distributions were mapped and showed nitrogen concentrations (nitrite 0.001 to 0.025 mg/L NO₂^--N, and nitrate 0.26 to 3.60 mg/L NO₃^--N) increased significantly with rainfall contrary to phosphorus (0.01 to 0.12 mg/L P). The Chl-a and TSI_tsr data revealed the hypereutrophic status of rivers. Moreover, N:P mass ratio suggests nitrogen as the main limiting factor of primary production during the low (March) and high flow periods (October-November), while phosphorus is the limiting factor in June, at the high flow beginning. The land uses around watersheds were the main sources of phosphorus and nitrogen enhancing the rivers' eutrophication. Phosphorus and nitrogen fluxes were related to leaching river catchments and were significant sources of nutrients to the Atlantic Ocean.

Mapping and assessment of future changes in the coastal and marine ecosystem services supply in Lithuania

Assessing and mapping ecosystem services (ES) became an integral part of coastal and marine management practices. Hence, quantitative and validated approaches are lacking, especially to address future conditions. The objective of this study is to apply further existing and develop new methodological frameworks to quantitatively assess and map the current and future supply of 3 ES in the coastal zone of Lithuania: coastal flood protection, nutrient regulation, and maintenance of nursery conditions. For coastal flood ES modelling, 2 time periods (1990 and 2018) and 4 scenarios (A0, A1 A2, A3 - based on future socio-economic changes in Lithuania) were analysed. The coastal flood protection ES model was validated (r² = 0.30) using tree cover density. The results showed spatial differences among the analysed periods but no statistical differences. High supply areas are located in the southern coastal area, while the central part displays a low supply. For nutrient regulation and maintenance of nursery conditions, 7 time periods were analysed: a historical period and 6 scenarios based on Representative Concentration Pathway 4.5 and 8.5 and 3 Shared Socioeconomic Pathways. The nutrient regulation ES model was validated (r² = 0.85) using in situ nutrient. Statistical differences were observed for this ES, but a similar spatial distribution of high and low supply areas. A decrease in the supply was observed comparing the historical period and future scenarios. Maintenance of nursery conditions was validated (r² = 0.72) based on the protection status of the coastal zone. Results show no statistical differences and similar spatial patterns among the periods. Rocky and sandbank areas show a high supply for this ES. Limitations of our work are mainly related to the resolution of the utilised indicators. Nevertheless, the information obtained from our models can support spatial planning and decision-making processes.

Pollutant dynamics between The Black Sea and The Marmara Sea: Basis for wastewater management strategy

The study evaluated pollutant dynamics between The Black Sea and The Marmara Sea using data collected during a marine survey of the region around The Bosphorus strait, in the last five years. A hydraulic model was utilized to define two-layered water exchange in The Bosphorus. Analysis of pollutant exchange indicated The Black Sea as major polluter for the marine environment in The Marmara Sea. Four wastewater outfalls are located along The Bosphorus; Mass balances between the two ends of The Bosphorus indicated losses of 44 t/d total N and 138 t/d COD in the lower layer before reaching The Black Sea. This was explained with a simultaneous nitrification-denitrification process sustained in the low oxygen or anoxic zones around the outfalls, implying that a sustainable wastewater strategy should preclude additional treatment for The Bosphorus discharges, since they do not have an appreciable impact on the water quality of the lower flow.

Identification of allelochemicals from pomegranate peel and their effects on Microcystis aeruginosa growth

This paper studied the inhibitory effect of pomegranate peel (PP) extract on the growth of Microcystis aeruginosa, the model of harmful algal blooms in aquatic environment. The allelochemicals were identified by HPLC-MS/MS from PP and tested by batch experiment through measurement of algal density, chlorophyll a (Chl-a) concentration, maximum quantum yield of photosystem II (Fv/Fm), superoxide dismutase (SOD), and malondialdehyde (MDA) contents. Results showed that both PP powder and PP extract had obvious inhibitory effect on M. aeruginosa growth. Quercetin and luteolin were identified as the allelochemicals to M. aeruginosa growth. However, the inhibitory capacity of luteolin was stronger than that of quercetin. The growth inhibition ratio of luteolin can reach up to 98.7 and 99.1% of the control on day 7 at the dosages of 7 and 10 mg/L, respectively. Moreover, the changes of Chl-a, Fv/Fm, SOD, and MDA in M. aeruginosa confirmed jointly that the allelochemicals cause inhibition of photosystem and oxidative damage to M. aeruginosa cells with the antioxidant defense system being activated, which leads to the aggravation of membrane lipid peroxidation. Thus, luteolin could be used as a promising algaecide for emergency handling of M. aeruginosa blooms. This study might provide a new direction in the management of eutrophication in the future.

Assessment of freshwater discharge into a coastal bay through multi-basin ensemble hydrological modelling

Coastal basins of the Brittany peninsula (France) are hydrological hot spots. A high level of nutrient pollution affects many of these basins and causes algal blooms in several coastal bays; nine have been a specific focus of the European Commission since 2007. The flux of each contributing basin flowing into these bays must be examined to assess the conditions and explore mitigation options. However, this task encounters a large lack of data since most of the basins are ungauged. In this context, this study developed a method which facilitates transposition of hydrographs from gauged basins to ungauged neighbouring basins of interest. Inverting a simple geomorphology-based transfer function of the gauged basin which describes travel time through channels enables the net rainfall time-series to be estimated from the discharge time-series of donor basins. To estimate the net rainfall of a given ungauged catchment, several net rainfall time series of gauged catchments are averaged. The resulting net rainfall is then transposed onto the ungauged target basin and convoluted by its own transfer function to estimate the hydrograph. This allows the transposition of as many hydrographs as there are different donor basins. This ensemble prediction enables the proportion of prediction uncertainty that is due to the heterogeneity in hydrological behaviour to be estimated. Moreover, the time-series of the donor basins are combined to estimate the ungauged net rainfall time-series. This provides a discharge prediction which values all available measurements. The method was applied to the highly controversial Saint Brieuc Bay, where it was possible to quantify the contribution of each coastal basin, even those influenced by dams, and ultimately the entire volume of fresh water entering the bay at an hourly time step. This work opens perspectives to additionally refine estimation of the associated nutrient fluxes.

First report of occurrence, distribution, and composition of microplastics in surface waters of the Sea of Marmara, Turkey

Plastic is produced today in large quantities and used for many purposes. At the end of use, a large part of it gets into the environment, often into the sea and there it is fragmented into the smallest fragments, so-called microplastic (MP). MPs pose a serious challenge to the marine environment such as the sources and properties of MP particles, their impact on marine organisms, and the challenges of environmental pollution. This work, carried out in the fourteen sites in the area, is the first reference to the detection of MP distribution at surface waters in the Sea of Marmara, Turkey. As a result of this study, the average level of MP in the surface was determined to be 1.263 item/m². The results were higher compared of the most other adjacent regions and show that the Sea of Marmara started to face that problem.