Assessment of long-term water quality variation affected by high-intensity land-based inputs and land reclamation in Jiaozhou Bay, China

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 Cls 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 FTN and Sin 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 Sin, 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. (C) 2016 Elsevier Ltd. All rights reserved.