| Since the late 1970’s, concentrations of dissolved inorganic nitrogen (DIN) has been observed to increase continuously in coastal areasnearby Qingdao, acompanying with the rapid development of Qingdao economy. Contamination of DIN showed an uneven distribution pattern, with most areas exceeded the water quality guideline located in the northern and northeastern parts of Jiaozhou Bay. Since 2011, Oingdao municipal governmenthas started to implement a plan aiming to decrease the discharge of ammonia in its administrative region, in step with the country’s management of total pollutants loading control program. However, the expected improvement of the water quality at adjacent sea areas has not been observed accordingly, especially the Jiaozhou Bay. The low efficienty of the current implementation plans may be due to the fact that all towns in Qingdao are forced to decrease the same percentage of nitrogen discharge, without the consideration of the difference in their contributions to the impairment of sea water. Therefore, the current implementation plan should be refined to improve its efficiency. The percentage reduction of nitrogen for different towns of Qingdao should be estimated depending on their contributions to the contamination of sea areas, other than is set as an identical constant. Total dissolved nitrogen (TN) amounts discharged from each town into the sea are the important data for not only eludating the administrative regions attributing to the contamination of sea area but also optimizing the reduction percentage of each town. TN discharged into the sea from the river mouth can be measured by monitoring method or estimated using watershed model. However, it is not possible to monitor the amount of TN discharged from the town that does not abut against the sea. Theoretically, both "addition method" and "subtraction method" on the basis ofwatershed model can be used to estimate the loading of pollutants from terrestrial areas to the sea. Nevertherless, this method has not been developed for estimating the loading amount of pollutants from terrestrial areas into the sea yet. Although it has been applied in estimating pollutants loading into a lake, there is a lack of estimation on the uncertainty of the method, limiting its application in other studies.The objectives of this study were to calculate the loading amount of TN from the 164 towns of Qingdao into the adjacient aea, and to estimate appropriate reducing percentage of TN discharge for these towns on the purpose of improving sea water quality. The major contents of this study are listed as follows:1. The establishment of SWAT model for nitrogen pollutants.(1) SWAT model in Qingdao. SWAT 2009 was adopted to develop the Qingdao SWAT model, covering the entire Qingdao area, including Dagu river watershed, Jiaozhou Bay watershed, Qingdao-Yellow Sea watershed, and the Jiaolai river watershed. Nash-Suttcliffe coefficient (Ens) and Relative Standard Deviation (RSD) were employed to evaluate the fitness of model with the monitoring data and monitored results. The results showed that the developed SWAT model fitted the monitoring data well and it can be used in estimating the amount of nitrogen loading into the river.2. The development of methods for calculating the loading amount of nitrogen from each town in Qingdao into the surrounding sea by using the "addition method". Loading intensities of TN into the sea from the 164 townsin Qingdao were estimated.3. The effects of differentiation emission reduction on nutrients discharge. (1) The results showed that there are 83 overloading towns,50 medium towns, and 31 residue loading towns in Qingdao. (2) The overall over-loading rate of Dagu river watershed was estimated to be approximately 50%. The reduction targets of the 5 counties in Dagu river watershed should be increased about 24% in Laixi,2.4% in Chengyang and decreased 9% in Pingdu,10% in Jimo,7% in Jiaozhou averagely. Discharge of TN from the watershed into the sea can be decreased approximately 30%,6%,5%,9%, and 45% by reducing the usage of fertilizer, livestock feces, rural residential wastewater and sewage factory wastewater discharge, and all of these measures. If all of these measures were taken, the overall over-loading rate can be descreased about 40%, which is still lower than theoverall Dagu river watershed over-load rate (50%). Therefore, more strict measures should be taken by the Qingdao government in order to reduce more discharge of nitrogen into the sea.The major innovation of this study is the development of the method for calculating the TN pollutant discharged into the sea from terrestrial areas based on the SWAT model. In particular, on the basis of the "addition method", the relationships between the monitoring data and the modeled pollutants discharged into the land, into the river and into the sea were established. In addition, the contributions of the nitrogen discharge of the 53 towns in Dagu river watershed to the nitrogen over-loading were quantified and applied in determing the percent reduction of nitrogen emission in these towns. The results of this study are expected to be helpful for making more effective practices for reducing nitrogen discharge in Qingdao and improving the water quality of Jiaozhou Bay. |
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