Coupling Hydrochemistry and Stable Isotopes (δ2H and δ18O) to Identify the Major Factors Affecting Hydrochemical Evolution of Groundwater in the Western Yellow Sea Coast, China

Groundwater, as a precious fresh water resource, has a profound impact on the social and economic development in coastal areas. Western Yellow Sea coast (WYSC), located in the eastern part of China, is one of the most prosperous areas of China’s economic development and has a great demand for water. WYSC is currently under increasing pressure from groundwater pumped for regional development, and sustainable water management throughout the region must be based on an understanding of the hydrochemical processes that determine the quality of groundwater. This study taking WYSC as the study area, 160 groundwater samples were collected in the field and the content of Ca2+, Mg2+, Na+, K+, Cl-, SO42-, HCO3-, F, Br, δ2H and δ18O in groundwater were tested. The groundwater chemical characteristics, sources of groundwater substances, hydrogeochemical processes and the difference between the Shandong part (SDP) and Jiangsu part (JSP) were studied. The result shows that the content sequence of main cations and anions in groundwater of WYSC are Na+ > Ca2+ > Mg2+ > K+ and HCO3- > Cl- > SO42-. The hydrochemical types of WYSC groundwater are mainly Cl-Na, Cl-Ca, HCO3-Na and HCO3-Ca. The main recharge source of groundwater in the WYSC is precipitation, and the seawater and evaporation also affect the recharge process. The main sources of dissolved substances in groundwater in the WYSC are mineral dissolution, evaporation and seawater. The groundwater in SDP is affected by modern seawater intrusion, while that in JSP may be affected by ancient seawater intrusion. The dissolution and precipitation of various minerals in the groundwater in the WYSC are affected not only by regional conditions but also by seawater intrusion.

Temporal variability in zooplankton community in the western Yellow Sea and its possible links to green tides

Large-scale macro-algal blooms ofUlva prolifera(also called green tides) have appeared each summer since 2008 in the western Yellow Sea. In this study, we investigated the temporal variability in zooplankton community in the western Yellow Sea and its possible links to green tides using data from a long-term plankton survey off the coast of Qingdao, China. Environmental conditions observed in the study area during the green tide period (GTP: June–August, 2008–2013) were compared to the non-green tide period (NGTP: June–August, 2005–2007), to support the contention that variations observed in zooplankton community may be attributed to the green tides, as opposed to natural climatic or environmental variations. Zooplankton assemblage structure observed during the GTP was then compared to the NGTP. Significant variations were detected both in zooplankton abundance and assemblage structure between the two defined periods. The abundance of zooplankton, mainly copepods, was significantly decreased during the GTP. Meanwhile, the relative abundance of copepods decreased by approximately 10% and that of gelatinous zooplankton, including appendicularians, chaetognaths, and medusae, almost doubled (ca. increased by 6.4%). The dominant species of meroplankton completely changed, specifically, polychaeta, and echinoderm larvae were more dominant than decapod and bivalve larvae. With regard to zooplankton size structure, the NGTP showed a higher size diversity with more small-sized organisms, while the GTP showed a lower size diversity in the community. According to general linear models, the interannual variation in summer zooplankton abundance was significantly correlated with green tides. These results indicate that the temporal changes in zooplankton community may have a close link to the green tides.