Nutrients distribution in the coastal water of East Asia relative to the Kuroshio

Nutrient and heavy metal dynamics in the coastal waters of St. Martin's island in the Bay of Bengal

Seasonal variation observations were conducted in the coastal waters of St. Martin's Island in the Bay of Bengal to examine the influence of physical processes and the distribution pattern of nutrients in the ocean water. Pollution evaluation indices, health index and statistical techniques were incorporated to assess the heavy metal contamination. Two seasons, cool dry winter and pre-monsoon hot, were considered for sampling from 12 stations around the island. The Cool dry winter season has higher nutrient concentrations than the Pre-monsoon Hot season. The concentration of nutrients appeared as follows: Silicate > Nitrate > Ammonia > Phosphate > Nitrite. PCA and Pearson's Correlation showed that fresh water from nearby rivers, deep water upwelling, and, in some situations, modest anthropogenic sources are crucial. Hence, low DO and phosphate levels during the pre-monsoon hot season indicate there is a planktonic process like photosynthesis prevailing. The island's north-western and south-eastern regions have higher nutrient concentrations, which may be seasonal and due to wind action. Pb, Cu, As, Cr, Cd, and Zn were also considered to comprehend the island's geo-chemical perspectives and ecological and human health risks. The Pre-monsoon Heavy Metal Pollution Index (HPI) and Heavy Metal Evaluation Index (HEI) demonstrated that some places are much higher than the threshold limit, even though no significantly higher value was detected in the cool winter season. The Nemerow Index, the Total Ecological Risk Index (TERI), indicated that heavy metal contamination was severe to moderate and low to moderate. Finally, Pearson's correlation showed the association between physical and chemical characteristics, similar to PCA and Pearson's correlation for nutrients and heavy metals. Thus, this research may help shed light on the state of the seas around St. Martin's Island. This study may also provide explicit insights for the authority to take the necessary measures to preserve marine ecology and the associated terrestrial ecosystem.

Seasonal and spatial variations in nutrients under the influence of natural and anthropogenic factors in coastal waters of the northern Yellow Sea, China

Analysis of the common and most influential natural and anthropogenic activities on the spatiotemporal variation in nutrients at a multiannual scale is important. Eleven cruises from 2015 to 2017 were carried out to better elucidate the seasonal and spatial variations in nutrients, as well as the impact factors on dissolved inorganic nitrogen (DIN), phosphorus (DIP) and silicate (DSi). Both nutrient concentrations and forms showed similar and significant seasonal variations over the 3 years, and were closely related to the biomass and species of phytoplankton. Terrestrial inputs had significant effects on the spatial distribution of nutrients throughout the year, especially in the surface water, which showed DIN > DIP>DSi. In summer, shellfish aquaculture and hypoxia jointly affected the spatial distribution of nutrients. The bottom water nutrient concentrations in the aquaculture area were 1.1-2.3 times higher than those outside of the aquaculture area. Seasonal hypoxia can increase the release of DSi and NH₄⁺ from the sediment to the water. In summary, anthropogenic activities and physical conditions jointly influenced the nutrient distributions.

Long-term variation of nitrate in the East Sea, Korea

Long-term variation of nitrate in the East Sea was monitored in order to investigate impact of Three Gorges Dam (TGD) in the Changjiang River's upstream, China and Nakdong River's estuary dam, Korea. Tracing source of nitrate was another objective in this study. For this study, nutrient data were collected for 20 years from 1999 to 2018 in the East Sea, and divided into 4 sections, and evaluated whether a significant difference exists among the averages of nitrate concentrations. The concentrations of nitrate were affected by the major rivers (the Nakdong and the Taehwa Rivers) and Tsushima Warm Current (TWC) which diverged from the Kuroshio Current passing through East China Sea (ECS). Our results also indicated that long-term nitrate concentrations decreased and its reasons. First, the construction of TGD in the upstream of the Changjiang River may have resulted in the decrease of the nitrate supply in the river and ECS which is carried by TWC, toward the East Sea. Second, decrease in the nitrate flux of the Nakdong River's estuary due to the construction of the estuary dam and sewer treatment plant could also be a factor for the nitrate decrease in the East Sea. Therefore, anthropogenic activities from the Nakdong River and Changjiang River had a long-term effect on the East Sea's nitrate concentrations. The amount of nitrate runoff reduced by the anthropogenic activities influenced the nitrate levels over a long period by the flow of currents in the East Sea.

Biogeochemistry of dissolved inorganic nutrients in an oligotrophic coastal mariculture region of the northern Shandong Peninsula, north Yellow Sea

Fourteen field cruises were carried out in a mariculture region of the northern Shandong Peninsula, North Yellow Sea, China from 2016 to 2017 for a better understanding of the biogeochemical behaviors, sources and export of dissolved inorganic nutrients. The spatial variations of nutrients were not obvious due to the influence of complex hydrological and biochemical conditions. Potential nutritional level was characterized in oligotrophy, and trophic status was rated at medium level. A preliminary estimation of nutrient budgets demonstrated that the dissolved inorganic nitrogen (DIN) load was mainly from atmospheric deposition and scallop excretion, accounting for 56.9% and 35.6% of its total influx. Scallop excretion and sediment release were the major source of phosphate (DIP), contributing to 25.2% and 44.3%, while dissolved silicon (DSi) was mainly from sediment release, accounting for 94.2%. In addition, about 136.7 × 10³, 7.3 × 10³ and 485.5 × 10³ mol km^-2 yr^-1 of DIN, DIP and DSi could be converted into other forms, e.g. organic and particulate matter and gas species.