Distribution and flux assessment of microplastic debris in the middle and lower Chao Phraya River, Thailand.

Microplastic (MP) debris is now a global concern. The Chao Phraya is the largest river in Thailand and transports MPs from terrestrial areas to the ocean. MP debris in its water and sediment were measured in March 2021, September 2021, and March 2022 in five provinces along the watercourse. Hydrological data were also collected to estimate the MP riverine flux between provinces. Size, shape, color, and types of MP polymers were observed, with sedimentation data collected for MP content. Results showed that MPs were found at all sample stations, with average abundance in all province water samples ranging from 0.54 ± 0.05 to 1.07 ± 0.28 pieces/L, while in sediment sample, numbers ranged from 183.84 ± 38.76 to 546.18 ± 86.84 pieces/kg dry weight throughout all seasons. Overall contamination and accumulation were similar between provinces but significantly different between seasons. Sizes of MPs in water varied between seasons with MPs in sediment mostly 330-5,000 µm (Kruskal-Wallis, P < 0.05). Sedimentation of MPs was different between seasons (Kruskal-Wallis, P < 0.05). The highest MP flux values discharged from Samut Prakan Province to the inner Gulf of Thailand were 1.83 × 105 and 1.60 × 105 million items/day in September 2021 and March 2022, respectively.

Influence of size and density on filtration rate modeling and nutrient uptake by green mussel (Perna viridis).

This study investigates green mussel filtration rates based on variation of the mussel size and density, and attempts to correlate these with the amount of Chaetoceros calcitrans consumed by kinetic modeling. The filtration rates were found to be more effective in small mussels and with greater volumes of seawater/mussel which represent low mussel densities in the mussel farms. Under field condition, the first order kinetic model is useful for evaluation of mussel filtration rate. However, the composite exponential kinetic model was determined to better describe filtration rates in a close system. Higher ratios of seawater volume L/g DW mussel tissue, resulted in an increasing filtration rate until a maximum plateau was reached at 10.37 L/h/g DW tissue as determined by first order kinetics. Based on the filtration rate, carbon, nitrogen, and phosphorus uptake by green mussels were found to be 2128.72, 265.41, and 66.67 mg/year/indv, respectively.

Impacts of nutrients and related environmental factors on distribution and size structure of Noctiluca scintillans populations of the eutrophic Tha Chin estuary, Thailand.

This study aimed to analyze the impacts of nutrients and related aquatic factors on changes in the Noctiluca population of the Tha Chin estuary, a nutrient-rich estuary located in the inner Gulf of Thailand. Field surveys were carried out at 30 stations during November 2009 to August 2010. The results indicated high levels of dissolved inorganic nitrogen (DIN; 13.89-46.99 µmol/L) and PO(4)(3-)-P (0.20-3.05 µmol/L) where the Noctiluca red tide occurred, particularly during the high-loading period. Dense populations were usually found in the outer part of the estuary with comparatively high salinity (25-29 psu). The highest Noctiluca density was 72,333 cells L(-1) and the cell diameters ranged between 360 and 460 µm. Proportions of small-sized cells (P(s); less than 300 µm) varied over time. In this study, P(s) showed a positive correlation with levels of PO(4)(3-)-P, while the total population density was significantly affected by levels of NH(4)(+)-N and DIN (p < 0.05). Overall, PO(4)(3-)-P influenced the development of the Noctiluca red tide, with the limitation of PO(4)(3-)-P levels to below 1 µmol/L suggested for controlling Noctiluca red tide outbreaks at their origin. To support environmental conservation and maintain sustainable production in the estuary, the levels of PO(4)(3-)-P should be considered for the further effective development of water quality standards in estuarine zones.

Nutrient loads and their impacts on chlorophyll a in the Mae Klong River and estuarine ecosystem: an approach for nutrient criteria development.

Investigations on the water quality of the Mae Klong River and Estuary were conducted from April 2005 to February 2006 during periods of early-, mid-, and late-loading. Nutrient loads and transfer patterns were studied together with clarification of contaminated sites. The results indicated that NH4+, NO2- + NO3-, Si(OH)4 and PO4(3-) concentrations varied by season and were comparatively high in the mid-loading period. Analysis of DIN:P and Si:P molar ratios indicated that P04(3-) could possibly be a limiting nutrient. Highly contaminated sites were in the middle (Ratchaburi province) and lower (Samut Songkhram province) river zones in which anthropogenic wastewater discharges were significantly (p < 0.05) loaded. Analysis of the DIN and P transfer patterns showed that self-remediation efficiencies were rarely found. The highest DIN and P loads of 23.87 and 4.03 t/day, respectively, were found in Samut Songkhram province. Nutrients were found to contribute to the hypertrophic condition of the lower river and the estuary. The baseline level of chlorophyll a in the upper river was approximately 3.3 microg/L, while levels exceeded 10 microg/L in the estuarine zone. Such chlorophyll a levels were highly significant (p < 0.01) related to DIN and P (with correlation coefficients of 0.44 and 0.37, respectively). In order to maintain river conservation to an acceptable degree, levels of about 20 micromol/L DIN and 1 micromol/L P were suggested as the upper limits. To achieve such levels will require serious consideration with regard to the development of nutrient criteria for water resource conservation management and sustainable utilization purposes.

Integration of aquatic ecology and biological oceanographic knowledge for development of area-based eutrophication assessment criteria leading to water resource remediation and utilization management: a case study in Tha Chin, the most eutrophic river of Thailand.

This research was carried out in Tha Chin Watershed in the central part of Thailand with attempts to apply multidisciplinary knowledge for understanding ecosystem structure and response to anthropogenic pollution and natural impacts leading to a proposal for an appropriate zonation management approach for sustainable utilization of the area. Water quality status of the Tha Chin River and Estuary had been determined by analyzing ecological, hydrological, and coastal oceanographic information from recent field surveys (during March 2006 to November 2007) together with secondary data on irrigation, land utilization, and socio-economic status.Results indicated that the Tha Chin River and Estuary was eutrophic all year round. Almost 100% of the brackish to marine areas reflected strongly hypertrophic water condition during both dry and high-loading periods. High NH(4)(+) and PO(4)(3-) loads from surrounding agricultural land use, agro-industry, and community continuously flew into the aquatic environment. Deteriorated ecosystem was clearly observed by dramatically low DO levels (ca 1 mg/l) in riverine to coastal areas and Noctiluca and Ceratium red tide outbreaks occurred around tidal front closed to the estuary. Accordingly, fishery resources were significantly decreased. Some riverine benthic habitats became dominated by deposit-feeding worms e.g. Lumbriculus, Branchiura, and Tubifex, while estuarine benthic habitats reflected succession of polychaetes and small bivalves. Results on analysis on integrated ecosystem responses indicated that changing functions were significantly influenced by particulates and nutrients dynamics in the system.Based on the overall results, the Tha Chin River and Estuary should be divided into 4 zones (I: Upper freshwater zone; II: Middle freshwater zone; III Lower freshwater zone; and IV: Lowest brackish to marine zone) for further management schemes on water remediation. In this study, the importance of habitat morphology and water flow regimes was recognized. Moreover, nearshore extensive shrimp culture ponds, irrigation canals, and surrounding mangrove habitats belonging to local households seemed to act as effective natural water treatment system that can yet provide food resources in turns. These remediation-production integrated functions should be deserved depth considerations for water quality development of the Tha Chin areas.