Analysis of the spatio-temporal variability of seawater quality in the southeastern Arabian Gulf

Notes on the relation between transparency and plankton content of the surface waters of the Southern Ocean : Hart T.J., 1962. Deep-Sea Res., 9 (2): 109–114

Review on sea water quality (SWQ) monitoring using satellite remote sensing techniques (SRST).

Seawater transparency, one of the important parameters to evaluate the marine ecological environment and functions, can be measured using the Secchi disk depth (SDD). In this study, we use multi-source remote sensing data and other fused data from 2011 to 2020 to study the spatial distribution and variation of SDD off southeastern Vietnam. The monthly average of SDD in the study area has obvious seasonal variation characteristics and shows a double peak characteristic. An important observation is a significant decrease in transparency from July to September each year, which is far lower than other nearby seas. To study this low SDD phenomenon, the generalized additive model (GAM) is used to determine the main environmental factors. The response relationship between SDD and environmental factors on different time scales is explained through empirical mode decomposition (EMD) analysis experiments. The results show that the comprehensive explanation rate of the GAM model is 72.1%, and the main environmental factors affecting SDD all have non-linear response relationships with SDD. The contributions are ranked as sea surface salinity (SSS)> offshore current velocity (Cu)> wind direction (WD)> offshore Ekman transport (ETu)> sea surface temperature (SST)> mean direction of wind waves (MDWW). SDD is positively correlated with SSS and SST, and negatively correlated with Cu and ETu. SSS, Cu, ETu, and SST have a significant effect on SDD at interannual scales. Long-term changes in SDD are driven by SSS, Cu, WD, and SST. Generally, SSS has the most comprehensive impact on SDD. WD indirectly has a non-negligible impact on SDD by changing ocean dynamics processes.

To investigate the spatio-temporal and compositional variation of selected water quality parameters and understand the purifying effects of wetland in Fujin National Wetland Park (FNWP), China, the trophic level index (TLI), paired samples t-test and correlation analysis were used for the statistical analysis of a set of 10 water quality parameters. The analyses were based on water samples collected from 22 stations in FNWP between 2014 and 2016. Results initially reveal that total nitrogen (TN) concentrations are above class V levels (2 mg/L), total phosphorus (TP) concentrations are below class III levels (0.2 mg/L), and that all other parameters fall within standard ranges. Highest values for TN, pH, and Chlorophyll-a were recorded in 2016, while the levels of chemical oxygen demand (CODMn) and biochemical oxygen demand (BOD5) were lowest during this year. Similarly, TN values were highest between 2014 and 2016 while dissolved oxygen (DO) concentrations were lowest in the summer and TP concentrations were highest in the autumn. Significant variations were also found in Secchi depth (SD), TN, CODMn (P < 0.01), TP, and DO levels (P < 0.05) between the inlet and outlet of the park. High-to-low levels of TN, TP, and TDS were found in cattails, reeds, and open water (the opposite trend was seen in SD levels). Tested wetland water had a light eutrophication status in most cases and TN and TP removal rates were between 7.54%–84.36% and 37.50%–70.83%, respectively. Data also show no significant annual changes in water quality within this wetland, although obvious affects from surrounding agricultural drainage were nevertheless recorded. Results reveal a high major nutrient removal efficiency (N and P). The upper limits of these phenomena should be addressed in future research alongside a more efficient and scientific agricultural layout for the regions in and around the FNWP.

The tropical/subtropical South China Sea (SCS) is the largest marginal sea in the world. Like other warm bodies of water, its sea surface temperature (SST) is rising, albeit more slowly (0.012 °C/yr between 1998 and 2016) than that of cold-water regions at high latitudes. The chlorophyll concentration increased at 0.0012 μg/L/yr during that period, and the Secchi disk depth (SDD) increased by 0.035 m/yr. The changes of SST, chlorophyll concentration and SDD, the factors governing changes in ocean biogeochemistry, in the SCS exhibit high temporal-spatial variability, and these parameters varied in opposite directions during the periods 1998–2008 and 2008–2016. The first period witnessed declining SST and SDD and increasing chlorophyll concentration, referring to enhancing primary productivity. The second period witnessed increasing SST and SDD but falling chlorophyll concentration, referring to declining primary productivity. These changes and increasing anthropogenic activities on land may be related to changing biogeochemistry such as decreasing dissolved oxygen concentration in coastal regions. In the SCS basin, however, particulate organic carbon and nitrogen seem to be on the rise.

The occurrence of black-odorous water (BOW) in urban waters is a common problem in China that has occasional, seasonal, and perennial rules. The treatment of urban has become an important task for water managers in China. Based on field BOW spectra and 13 types of water quality parameters measured in Shenzhen City, in this study, we processed three types of spectra, including normalized, difference, and ratio spectra, to reveal the correlation between the spectra and the water quality parameters, especially for the spectra and four indicators that are used to distinguish BOW. The four indicators include Secchi depth (SD), dissolved oxygen (DO), oxidation-reduction potential (ORP), and ammonia nitrogen (NH3-N). Furthermore, we analysed the spectral sensitivity of the different water quality parameters to build a quantitative regression model between the water quality parameters and the portrait spectrum. The results showed the following: (1) Of the four indicators, both SD and NH3-N were significantly related to the spectrum of mild and severe BOW, and the ORP was only significantly related to the spectrum of severe BOW. The correlation between DO and BOW was not significant. (2) For mild BOW, the sensitive bands were 404 to 572 nm and 704 to 864 nm for the SD and 705 to 717 nm for NH3-N. For severe BOW, they were 499 to 606 nm and 730 to 900 nm for the SD, 556 to 664 nm for NH3-N, and 642 to 709 nm for the ORP. (3) The SD had the strongest correlation with the BOW spectrum. The correlation between the SD and the BOW spectrum was symmetrically distributed in the range of 404 to 572 nm near 489 nm, whereas 545 nm appeared as the centre in the range of 499 to 606 nm. (4) The best regression relationship between the SD and BOW was R 489/ R 714 (coefficient of determination R 2 = 0.8806) and R 545 (R 2 = 0.4868) for the mild and severe grades, respectively. The best regression relationship was R 489- R 607 (R 2 = 0.7598) between NH3-N and mild BOW. The results of this study provide important guidance significance and application value regarding the selection of bands, model construction, and result verification for urban BOW using remote sensing.

This study aimed to assess the trophic status and water quality characteristics of twenty ponds in Noakhali Sadar Upazila using the Carlson Trophic State Index (CTSI). Key physical-chemical parameters measured included temperature, pH, total dissolved solids (TDS), dissolved oxygen (DO), electrical conductivity (EC), total nitrogen (TN), total phosphorus (TP), chlorophyll-a, and Secchi depth. The observed ranges for these parameters were: temperature (24-32 °C), pH (6.7-8.42), TDS (46-1604 ppm), DO (4.33-7.46 ppm), EC (91-3208 µS cm⁻¹), TN (0.7-5.6 mg L⁻¹), TP (1.6-122 µg L⁻¹), chlorophyll-a (0.545-8.250 µg L⁻¹), and Secchi depth (0.22-1.13 m). CTSI values ranged from 38.31 to 68.38, indicating trophic conditions from oligotrophic to eutrophic, with Pond-8 approaching hypereutrophic status. Strong positive correlations were found between TDS and EC (r=1.00), TDS and Secchi depth (r=0.63), and EC and Secchi depth (r=0.63). Chlorophyll-a exhibited a positive correlation with temperature (r=0.57) and TP (r=0.52), while showing a moderate negative correlation with Secchi depth (r=–0.46). These relationships underscore the complexity of nutrient dynamics and transparency in these aquatic systems. The results highlight significant spatial variation in pond water quality and trophic status, emphasizing the need for continuous monitoring to prevent nutrient over-enrichment and ecological degradation. This study provides essential baseline data for informed water resource management and supports the implementation of sustainable practices to preserve the ecological health of pond ecosystems in the region.

ABSTRACTLake Tana, a UNESCO World Biosphere Reserve Lake. The lake contains 50% of Ethiopia's freshwater and fertile land, which favoured urbanization, agriculture and irrigation, impacting its ecosystem. Understanding the effects of buffer zone degradation on plankton and water quality was vital for sustainable resource utilization. Therefore, data collection was conducted from December 2020 to May 2021 in the buffered zone, two non‐buffered zones, and the pelagic area of the northern and northeastern parts of Lake Tana twice a month. The study highlighted significant spatial variability in water quality and plankton composition, emphasizing the critical role of buffer zones for maintaining Lake Tana's health. Water temperature, dissolved oxygen (DO), Secchi depth, total dissolved solids (TDS) and nutrient concentrations varied significantly across sites, with degraded buffer zones (Seraba and Kirrigna) showing poorer conditions compared to buffered (Debresina) and pelagic areas. Phytoplankton communities were dominated by Chlorophyceae (46.15%), followed by Bacillariophyceae (30.77%), Cyanophyceae (19.23%) and Euglenophyceae (3.85%). Microcystis was the most abundant genus across all sites but was less prevalent in the buffer zone area. Zooplankton composition also varied significantly, with Rotifera dominating over Copepod and Cladocera. Chlorophyll‐a (Chl‐a) concentrations, an indicator of phytoplankton biomass, were highest in buffered and pelagic areas, showing positive correlations with DO and negative correlations with temperature and turbidity. Human activities significantly impacted water quality and plankton diversity, as evidenced by strong correlations with the human disruption assessment (HDA) score. Significant differences were observed between sites for most parameters, except temperature, oxygen content and zooplankton diversity. Mean Chl‐a concentrations were higher in pelagic (2.64 µg/L) and Debresina (5.3 µg/L) compared to Seraba (2.34 µg/L) and Kirrigna (2.48 µg/L). These findings emphasize the urgent need for policymakers and stakeholders to protect and restore Lake Tana's buffer zones.

Water transparency, measured with Secchi disk depth (SDD), is an important parameter for describing the optical properties of a water body. This study evaluates variations of SDD and related impact factors in the Bohai and Yellow Seas (BYS). Based on a new mechanistic model proposed by Lee et al. (2015) applied to MODIS remote sensing reflectance data, climatological SDD variation from 2003 to 2019 was estimated. The annual mean images showed an increasing trend from the coastal zone to the deep ocean. Lower values were found in the Bohai Sea (BHS), while higher values observed in the center of the southern Yellow Sea (SYS). Additionally, the entire sea has shown a decreasing temporal tend, with the variation rate lowest in the BHS at 0.003 m y−1, and highest in the SYS at 0.015 m y−1. However, the weak increasing trend that appeared since 2017 suggests that water quality seems to have improved. Further, it displayed seasonal patterns of low in winter and spring and high in summer and autumn. The empirical orthogonal function (EOF) analysis of SDD variations over the BYS, shows that the first SDD EOF mode is the highest, strongly correlated with total suspended matter. With the high correlation coefficients of chromophoric dissolved organic matter, it illustrates that the SDD variation is mainly dominated by the optical components in the seawater, although correlation with chlorophyll-a is the weakest. The second and third EOF modes show that photosynthetically available radiation, sea surface temperature, sea surface salinity, and wind speed are the main covariates that cause SDD changes. Water transparency evaluation on a long-term scale is essential for water quality monitoring and marine ecosystem protection.

Application of satellite observations to study the changes of hypoxic conditions in near-bottom water in the western part of Peter the Great Bay (the Sea of Japan)

Bacterial populations were investigated in relation to the environmental parameters in Bolgoda Lake for a period of six months from January 2000 to June 2000. Surface water samples were collected from six sampling stations in the Bolgoda Lake at monthly intervals. Total viable bacterial colony forming units (assumed to be equal to the density of bacterial population), total coliforms and faecal coliforms were studied as biological indicators. Physico-chemical environment parameters included, temperature, pH, electrical conductivity, salinity, Secchi disk depth, dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), orthophosphate and nitrate contents. These were measured using standard methods. Correlations among bacterial densities and selected water quality parameters were investigated. High densities of bacterial populations were recorded at several sampling points in the vicinity of outlet drains which bring domestic and industrial effluents. Low densities of bacterial populations were recorded in samples taken at upstream and downstream of the North Lake. Results also revealed that some chemical parameters may have an effect in the density of bacterial populations. Density of bacterial populations showed a significant negative correlation with Biochemical oxygen demand (BOD) and with phosphate concentration. However, the density of bacterial population did not show a significant correlation with the nitrate content of the surface waters of the Lake. Further the DO, BOD values and PO 4 -3 content indicated organic and inorganic nutrient pollution of surface waters of Bolgoda Lake. However, samples collected from downstream had lower values for above parameters indicating that self- purification is taking place to a certain extent in the Lake. However, results revealed that at present Bolgoda Lake is heavily exposed to pollution from industrial and residential effluents. To avoid catastrophe, measures should be taken to reduce pollution by curtailing sewage disposal and treatment of effluents of nearby factories before being discharged into this Lake. Key words: water quality; Bolgoda Lake; evaluation of water quality Vidyodaya Journal of Science Vol.14(2) 113-133

Water quality trend analysis in Eymir Lake, Ankara

In recent years, human activities have significantly altered Foy's Lake, shifting it from a clear, pristine state to a turbid, eutrophic condition. Thus, this study analyzed seasonal variations of physicochemical parameters, chlorophyll-a levels, and the trophic state index (TSI) to assess water quality and trophic state fluctuations in Foy’s Lake, Chittagong. Sampling was conducted in September 2023 (as wet season) and January 2024 (as dry season) to assess the key water quality parameters including transparency, temperature, pH, dissolved oxygen (DO), electrical conductivity (EC), total dissolved solids (TDS), total hardness (TH), total alkalinity (TA), and chlorophyll-a (Chl-a). Secchi depth (SD) and Chl-a concentration were used to determine trophic conditions based on the Carlson Trophic State Index (CTSI). Results showed that in wet season, temperature, pH, DO, EC, TDS, transparency, TA, TH, and Chl-a ranged from 30.25–30.9°C, 5.4–5.5, 7.21–7.55 mg/L, 123.6–136.3 µS/cm, 51.5–78.48 mg/L, 109.06–126.94 cm, 49.6–68.4 mg/L, 36.09–41.75 mg/L, and 0.824–1.072 µg/L, respectively. In dry season, these values ranged from 28.45–29.02°C, 5.11–5.37, 6.36–6.92 mg/L, 143.7–156.3 µS/cm, 43.24–83.12 mg/L, 183.82–218.98 cm, 95.95–130.71 mg/L, 39.03–43.35 mg/L, and 0.885–0.933 µg/L, respectively. The mean TSI values based on SD and Chl-a were 59.58–48.54 and 31.23–28.75, respectively. Overall, most parameters decreased in the dry season except for transparency, EC, total alkalinity, and total hardness. While temperature, EC, DO, TH, TA, and Chl-a remained within standard limits, transparency exceeded the standard for aquaculture in both seasons. TSI values classified the lake as oligotrophic (Chl-a) and eutrophic (SD) in both seasons. Pearson’s correlation analysis showed strong positive relationships among most parameters. To preserve the ecological integrity and aesthetic value of Foy’s Lake, the study recommends the necessity to develop guidelines for the trophic status monitoring of Foy’s Lake since results suggest the deteriorating lake condition.

Integrated culture is widely used in freshwater pearl mussel(Hyriopsis cumingii) farming;however,water chemistry characteristics relating to H.cumingii farming are poorly understood.To assess the effects of co-cultured fish(grass carp,gibel carp,silver carp and bighead carp or silver carp and bighead carp) and formu-lated fish feed supplement(with or without feed supplement) on water chemistry characteristics,a 155-day field experiment was carried out in land-based enclosures.Four treatments including GGSB-F(co-cultured fish grass carp,gibel carp,silver carp and bighead carp were fed formulated feed),GGSB-NF(co-cultured fish grass carp,gibel carp,silver carp and bighead carp were not fed formulated feed),SB-F(co-cultured fish silver carp,and bighead carp were fed formulated feed) and SB-NF(co-cultured fish silver carp and bighead carp were not fed formulated feed) were established.The results indicated that the combination of co-cultured fish species could significantly affect Ca2+,total alkalinity(ALK),total hardness(HT) and total phosphorus(TP),while the feed supplement regime affected Ca2+,ALK,HT,ammonia(TAN),TP and chemical oxygen demand(CODMn).Dis-solved oxygen(DO) and secchi depth(SD) were lower,while Ca2+,HT,total nitrogen(TN),TP,TAN and CODMn were higher in the GGSB-F enclosures.Conversely,DO and SD were higher,but Ca2+,HT,TN,TP,TAN and CODMn were lower,in the SB-NF enclosures.During the experimental period,Ca2+ decreased,while TN,TP,TAN and CODMn increased.DO and SD were positively correlated with each other and negatively to the levels of TAN,TN,TP,Ca2+ and CODMn.Therefore,water quality management programs should include controlling the concen-tration of TAN and CODMn at the levels below the critical values,and maintaining Ca2+ and DO at high and con-stant levels.

Lentic small water bodies (LSWBs) deteriorate owing to anthropogenic activities, such as untreated domestic and agricultural waste disposal. Moreover, different turnover mechanisms occur during different seasons, contributing to nutrient enrichment and consequent degradation of LSWBs. However, understanding their spatial, temporal, and vertical variations during different seasons is understudied. In addition, studies on the variation in water quality under varying rainfall and land-use conditions are limited. Therefore, in this study, three LSWBs located in Northern India were studied during the pre-monsoon and monsoon seasons (December 2022 to October 2023). Total nitrogen (TN), chlorophyll-a (Chl-a), total phosphorus (TP), temperature, pH, dissolved oxygen (DO), total dissolved solids (TDS), chemical oxygen demand (COD),secchi disk depth (SDD), and water level (WL) were measured monthly. Sentinel-2 and CHIRPS pentad data were used for land use, land cover classification, and rainfall analysis. The spatial analysis indicates that the seasonal shift affects the water quality distribution, especially near the inlets and at the edges. The overall concentrations of TN and TP decreased during the monsoon season; however, they increased significantly at the inlets of the LSWBs. On the other hand, the Chl-a concentration shifted towards the edges due to the inflow during the monsoon. Temporal analysis also suggests that the arrival of the monsoon lowers pH, DO, and TDS. However, the concentrations of TN and TP increased because of agricultural runoff. Chl-a and COD show distinct variations due to the individual LSWBs' local conditions. Vertical variability analysis demonstrated pH, temperature, and TN stratification during the pre-monsoon period. However, during the monsoon, stratification is less significant due to intermixing. Redundancy analysis (RDA) showed that land use and rainfall patterns affected the water quality of LSWB 1, 2, and 3 by 53.49%, 81.62%, and 92.64%, respectively. This shows that land use, land cover, and rainfall changes affect the water quality of LSWBs. This study highlights the negative impact of runoff from agricultural land use as the main factor responsible for increased nutrient levels in the LSWBs.