Assessment of long-term water quality variation affected by high-intensity land-based inputs and land reclamation in Jiaozhou Bay, China
Abstract With the interactive and accumulative effects of multiple pressures, the dissolved inorganic nitrogen concentration (C DIN ) is increasing considerably and is regarded as the dominant chemical pollutant in Jiaozhou Bay (JZB). To efficiently prevent water quality (WQ) deterioration, the relationships among the C DIN in JZB with anthropogenic pressure indicators (APIs) and coastal carrying indicators (CCIs) were identified using long-term series data (1962–2012). First, the control indicators (CIs) were obtained by the application of a conceptual model analysis, and potential sources were identified by a factor analysis. Second, the key CIs were identified by a regression analysis. Finally, the effects of the key CIs on WQ were quantitatively assessed by numerical model experiments. The results showed that the CIs for the C DIN variation contained both APIs, including terrigenous total nitrogen flux (F TN ) discharged into JZB, river runoff, sea area of reclamation, and the CCIs, including the water area of JZB (S JZB ), chlorophyll-a, dissolved oxygen, pH, salinity and seawater temperature. The APIs on WQ variation were greater than the CCIs. The F TN and S JZB were identified as the key CIs responsible for the variation in the C DIN . The WQ simulation results showed that the increasing trend of the C DIN was caused by the increase in the F TN and the decrease in the S JZB , and the combined effects induced by the two key CIs on the C DIN variation was as high as 79%, higher their separate effects, indicating a synergistic interaction of the two key CIs on the WQ of JZB during the last 50 years. These results illustrated that both terrigenous nitrogen pollutant load control systems and a scientific plan for coastline utilization should be implemented to effectively improve the WQ of JZB. Highlights Long-term variations of water quality (WQ) of Jiaozhou Bay (JZB) were analyzed. Key control indicators (KCIs) of WQ of JZB were identified by multiple approaches. Land-based pollution inputs and land reclamation were the two KCIs of WQ of JZB. Land-based pollution inputs and land reclamation have a joint effect on WQ of JZB. Graphical abstract During the past 50 years, the high-intensity land-based pollutant discharge and land reclamation have been identified as the key control indicators and have a joint contribution on the significant variation of water quality of Jiaozhou Bay, showing synergistic effect on water quality.Note: The C DIN represents dissolved inorganic nitrogen concentration; S JZB is the water area of Jiaozhou Bay (JZB); F TN is the terrestrial total nitrogen flux. [DISPLAY OMISSION]
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