Spatiotemporal assessment of marine environmental monitoring programme based on DIN concentration in the Yangtze River estuary and its adjacent sea.

The marine environment is rigorously protected in the Yangtze River Estuary (YRE) and its adjacent sea, and routine monitoring is constantly upgraded. Therefore, scientific and efficient monitoring programmes are needed. Nitrogen is one of the most serious pollutants in the YRE. Obtaining the precise pollution areas of water quality grades (WQGs) are a scientific and management issue that requires optimization of monitoring programmes and interpolation methods. Based on spatiotemporal regression point means of surface with non-homogeneity (STR-PMSN), dissolved inorganic nitrogen (DIN) concentrations were estimated in a stratified heterogeneous estuary. The annual average areas of DIN Grades I and II were classified by interpolating the concentrations; the values were 3145 km2, 1626 km2, 2320 km2 and 3758 km2 for February, May, August and November, respectively. This means that November had the best water condition, and May had the worst. Meanwhile, DIN area changes showed that the water condition changed due to removal of data much more in August and May than in February and November. The descending order of importance was August, May, February and November. Every month represented different runoff periods. Monitoring frequency should not be reduced. Removal of sampling data for the third stratum had a significant effect on the area. When the sampling data for outer boundary meshes of the third stratum were removed, the water condition became worse. However, when the sampling data for inner boundary meshes were removed, the water condition improved. New sites should be added to the outer boundary region to avoid interpolation instability and reduce the sensitivity of the existing sites. This study assesses the spatiotemporal effect of the marine environmental monitoring programmes on pollutant distribution by STR-PMSN, and it offers guidance for more precise data acquisition and processing methods in the YRE and its adjacent sea.

Assessment of heavy metals in water, sediment and shellfish organisms in typical areas of the Yangtze River Estuary, China.

Identifying the transformations of heavy metal in different media is a scientific issue, and geographical detector is applied to evaluate the spatiotemporal stratified heterogeneity mechanisms for heavy metals in the Yangtze River Estuary. Heavy metal concentrations in water and sediment were consistent with lognormal distributions. Their concentrations were organized into four classes. Class 1 included concentrations that were less than or equal to 25%, Class 2 included those between 25%-50%, Class 3 concentrations were between 50%-75% and Class 4 were >75%, which were based on their lognormal distributions. In water and sediment, the mean heavy metal concentrations yearly decreased from 2012 to 2016. The Chongming area was significantly lower than those found in the other areas, which is the least affected area by anthropogenic activities. The explanatory power of sediment to spatiotemporal stratified heterogeneity of heavy metals in shellfish organisms was much greater than that of water.

Spatial distribution, risk assessment and source identification of heavy metals in sediments of the Yangtze River Estuary, China.

The aim of this study was to determine the spatial distribution, potential risks and sources of seven heavy metals in sediments of the Yangtze River Estuary. Analyses of 55 sediment samples revealed that the distributions of metals within the YRE were determined by the combined effects of their sources, hydrodynamic conditions, pH and Eh. According to the geoaccumulation index (Igeo) and sediment quality guidelines, Pb, Cd and Cr were present at low levels of pollution, with Cd posing the largest ecological risk. Positive Factor Matrix (PMF) results indicated that Hg, Zn, As, Pb and Cr mainly originated from natural geological background sources, while Cu originated from anthropogenic activities and atmospheric deposition was the source of Cd. These three sources contributed to 53.0%, 32.8% and 14.2%, respectively of total heavy metal concentrations. These results suggest that reducing the emission of Cd would promote a reduction of potential risks in sediments of the YRE.