Riverine and submarine groundwater nutrients fuel high primary production in a tropical bay.

River discharge has long been recognized as a major source of nutrients supporting high primary production (PP) in Bandon Bay, while submarine groundwater discharge (SGD) and atmospheric deposition have largely been overlooked. In this study, we evaluated contributions of nutrients via river, SGD and atmospheric deposition, and their roles on PP in the bay. Contribution of nutrients from the three sources during different time of the year was estimated. Nutrients supply from Tapi-Phumduang River accounted for two-fold the amount from SGD while very little supply was from atmospheric deposition. Significant seasonal difference in silicate and dissolved inorganic nitrogen were observed in river water. Dissolved phosphorous in river water was mainly (80 % to 90 %) of DOP in both seasons. For the bay water, DIP in wet season was two-fold higher than in dry season while dissolved organic phosphorus (DOP) was only one half of those measured in dry season. In SGD, dissolved nitrogen was mostly inorganic (with 99 % as NH4+), while dissolved phosphorous was predominantly (DOP). In general, Tapi River is the most important source of nitrogen (NO3-, NO2-, and DON), contributing >70 % of all considered sources, especially in wet season, while SGD is a major source for DSi, NH4+ and phosphorus, contributing 50 % to 90 % of all considered sources. To this end, Tapi River and SGD deliver a large quantity of nutrients and support high PP in the bay (337 to 553 mg-C m-2 day-1).

Abundance, composition, and fate of microplastics in water, sediment, and shellfish in the Tapi-Phumduang River system and Bandon Bay, Thailand.

Microplastic contamination in the environment is a global problem, as evidenced by the increasing amount of research worldwide. To our knowledge, this study is the first to investigate the microplastic distribution in Bandon Bay, one of the most important maricultural areas of Thailand. Water and sediment samples from the Tapi-Phumduang River system (n = 10) and Bandon Bay (n = 5) were collected. Water sampling at the river mouth was carried out during a complete tidal cycle to estimate the microplastic flux to the bay during the wet season. Moreover, two commercial bivalve species grown in the bay, the green mussel (Perna viridis) and lyrate Asiatic hard clam (Meretrix lyrata), were analyzed. More items of microplastics were found in the river system than in the bay. During the tide cycle, one-third of the microplastics entering the bay were washed back upstream during high tide. This backflow consisted mainly of larger microplastics. The average daily load of microplastics to the bay was 22.4 × 109 items day-1. The load during low tide was approximately 4-5 times higher than that during high tide. The overall accumulation of microplastics in the bottom sediments of the river and in the bay was similar (p < 0.05). Green mussels showed significantly higher contamination with microplastics than clams. Notably, the small-sized shellfish contained more particles (items/g) than the large ones (p < 0.05). Fibers were detected in virtually all samples: water (98%), sediment (94%), mussels (100%), and clams (95%). Among these, microfibers (<1 mm) were detected in water (71%), sediment (63%), green mussels (63%), and clams (52%). Blue and white particles were the two most frequently observed colors, while the most dominant polymers were rayon, followed by polypropylene (PP) or polyethylene (PE), polyethylene terephthalate (PET), and nylon. To this end, we posit that river discharge was a significant source of microplastics in Bandon Bay, with minor additional contributions from fishing and mariculture activities within the bay. Ultimately, these microplastics may end up in the sediments and living organisms.

Tracing underground sources of pollution to coastal waters off Map Ta Phut, Rayong, Thailand.

We explored the possibility that an underground pathway, "submarine groundwater discharge" (SGD), may contribute to the observed coastal contamination from a large industrial complex on the Gulf of Thailand. Three surveys were performed to map the area for the natural groundwater tracers radon, thoron and salinity. The results from all three surveys were internally consistent showing a point source adjacent to a large pier that serves the complex. It may be that a piling, driven into the ground to support the pier, intercepted a shallow aquifer and this resulted in an underground pathway between land and sea. Some low-density sediments are enriched in radium, we suspect from fly ash from a nearby power plant. Water quality parameters showed that total petroleum hydrocarbons (TPHs) correlated strongly to nitrite, dissolved inorganic phosphate and silica, indicating a common source. Data analysis shows that diffuse seepage accounts for more discharge than the point source.