Identification Of Critical Source Areas Of Nitrogen And Phosphorus In Dagu Watershed And The Establishment Of Feasible Environmental Remediation Measures

Anthropogenic discharge of pollutants in Qingdao, e.g., nitrogen and COD, hasbeen dramastically reduced since the implementation of a plan for controlling thedischarge of land-source pollutants in2006. However, the water quality of JiaozhouBay has not been significantly improved yet till now. This is reasonable as onlypoint-source discharge of pollutants was reduced, while no change was made on theagriculture, rural life and the other non-point sources. Dagu watershed accounted for45%of the land areas of Qingdao City and it is the largest source of pollutants forJiaozhou Bay. Qingdao City developed the “Dagu Watershed Protection and SpaceUse Planning” in2011, and introduced “2013-2015Jiaozhou Bay Watershed PollutionRemediation Action Plan" in2013. Both plans take agriculture, rural life and othernon-point sources as the objects of environmental remediation of the Dagu RiverBasin. The composition and distribution of non-point and point sources are verycomplicated. Therefore, it is necessary to put non-point sources and point sources intothe same framework in order to calculating the total discharge of pollutants andindentifying the critical source areas of non-point sources. Distributed non-pointsource model, such as SWAT (Soil and Water Assessment Tool), is a useful tool in thisarea. The major objectives of this thesis is to develop a method for calculating theno-point and point discharge of nitrogen and phosphorus in Dagu watershed, tocalculate the discharge amount of nitrogen and phosphorus and identify the criticalsource areas in Dagu watershed, and to propose several feasible environmentalremediation measures for controlling nitrogen and phosphorus pollution. The maincontents and conclusions are as follows:1. Field observations and statistical analysis of nitrogen and phosphorus dischargeamounts in Dagu watershed.Field monitoring data show that the middle and upper reaches of Dagu River hada larger discharge of nitrogen and phosphorus in terms of both discharge amount and discharge density (Kg/km~2). In addition, observations in the upstream watershed areasindicate that the discharge of nitrogen and phosphorus are closely related to rainfall,rainfall frequency, as well as agricultural production activities. Statistical analysis ofnitrogen and phosphorus emission amount of Dagu watershed shows that industrialsource, life source, service industry source and agricultural source account for5.18%and2.93%,17.12%and12.39%,0.55%and0.66%,77.15%and84.02%of the totaldischarge of nitrogen and phosphorus, respectively. The emission density of eachsource presents a significant spatial pattern.2. Calculation of the discharge amounts of nitrogen and phosphorus in Daguwatershed by SWAT mode（1）The SWAT required database of Dagu watershed and subbasin delineation.The required data include the Digital Elevation Model (DEM), land use/land covertype map, soil type map, meteorological data, pollution source information and someother data. During the development of the SWAT model in Dagu watershed, nitrogenand phosphorus from the industrial source and urban living source are thought to bedirectly discharged into the river.Animal waste, rural livingsources were are treated aschemical fertilizer applied in each subbasin. The Dagu watershed was divided into35subbasins.（2）Model calibration, validation and simulation. The developed SWAT modelin Dagu watershed was calibrated and validated by the historical investigation dataand field monitoring data obtained in this study. The results showed that thedeveloped SWAT model simulated the field monitoring data very well (Ens>0.5andR~2>0.5). The model was then used to calculate the discharge of nitrogen andphosphorus in Dagu watershed. The annually average discharge amounts of organicnitrogen, inorganic nitrogen and total nitrogen from2002to2012were calculated tobe324.2t,2271.t and2595.2t, respectively. The annually average discharge amountsof organic phosphorus, inorganic phosphorus and total phosphorus were calculated tobe20.4t,385.9t and406.3t, separately. In addition, the monthly variation of nitrogenand phosphorus discharge followed an “inverted V” pattern, with a peak appearing inwet season. The discharge of total nitrogen and total phosphorus in wet seasonaccounted for75.6%and84.3%of the annual discharge of nitrogen and phosphorus.3. The distribution of critical source areas in Dagu watershed and their pollutioncharacteristics. （1）Spatial distribution and constitution of sources of nitrogen and phosphorus inthe Dagu watershed. Model simulation results show that the average annual dischargedensities of total nitrogen and total phosphorus in35subbasins have a significantspatial pattern, with the highest value appeared in the upstream areas, e.g., XaioguRiver, Wugu River and Liuhao River subbasins. The average discharge density oftotal nitrogen and total phosphorus in Dagu watershed were1661.8Kg/km~2and74Kg/km~2, respectively. The results also show that human activities were the mainsources of nitrogen and phosphorus in this area (69%(nitrogen) and58%(phosphorus)). Fertilizer loss and animal waste accounted for49.9%and29.6%of thetotal nitrogen from human activities respectively,41.4%and40.3%of totalphosphorus from human activities respectively.（2）Identification of the critical source areas in Dagu watershed. Soil erosiondensity was calculated in each subbasin. This parameter was calculated to be lowerthan500t/(km~2·a)(slight erosion) in around87%of Dagu watershed.13%of Daguarea is under mild erosion, with a erosion density between500and2500t/(km~2·a).According to the total nitrogen erosion classification standard,27.4%of Daguwatershed is the critical source areas, and the total nitrogen discharge amounts fromthese critical source areas accounted for36.1%of the total nitrogen discharge in Daguwatershed. Farmland is the main source of total nitrogen in the critical source areas,and gleysols and luvisols are the main soil type. Moreover, the contributions of eachsubbasin to the discharge of total nitrogen and total phosphorus from Dagu River toJiaozhou Bay were calculated. The results suggested that the Wugu River regioncontributes the largest to overall discharge of both nutrients to Jiaozhou Bay.4. The establishment of feasible Environmental Remediation Measures of nitrogenand phosphorus in Dagu watershedA variety of environmental remediation measures proposed in “Dagu WatershedProtection and space use planning” were tested by using the developed SWAT modelin Dagu watershed. The results show that reducing the use of fertilizer, and animalwaste, and restoring farmland to forest would be the most feasible environmentalremediation measures in Dagu watershed.In this study, we established a method for calculating the non-point source andpoint source discharge amounts of nitrogen and phosporusin Dagu watershed usingSWAT model. On the basis of this method, the critical source areas of Dagu watershed and critical areas affecting the water quality of Jiaozhou Bay were identified. Inaddition, seaveral feasible Environmental Remediation Measures has been made andvalidated by the model to improve the pollution of nitrogen and phosphorus in Daguwatershed.