| Water is the life source of mankind's survival and development. In China, many rivers and reservoirs have been contaminated due to increasing point-and non-point-source pollution, especially the drinking in the southern area. Therefore, the safety of drinking water is important for the protection of humankind. Reservoir of headwater as a drinking water sources play an important role in the human's normal life. Therefore, it is meaningful not only in theory but also in fact to investigate the mechanism of water resource pollution and its space-time change regularity. An analysis of the change regularity of the water quality in the reservoir is the foundation for water quality protection. Monitoring and assessment are the key approaches for the water protection. They are also the main theoretical basis for creating scientific and reasonable control project. The carriers of pollutants in reservoir water are runoff and sediment. Runoff could carry soluble pollutants; also transport the pollutants which adsorbed by sediments. However these adsorption pollutants were potential pollution source. They can transfer dynamically on the solid-liquid interface when the water environment changed. So the study of adsorption/desorption characteristics of pollutants under different water environment can provide a reference value to reservoir water source protection and regular dredging.Present study used Zhejiang Fushi reservoir watershed as the research region. In order to understand the progress and mechanism of adsorption/desorption and the water condition of this area, done follow working. Firstly,27 water quality monitoring points in this watershed was selected, according to the geologic and hydrological situations. And set eighteen sampling sections in rivers while nine points in the Fushi reservoir. Secondly, the adsorption process and the characteristics of nitrogen and phosphorus was simulated and analyzed in laboratory. And whether there is secondary pollution in river and reservoir were predicted after adsorption simulation experiment. Further more, evaluating and analyzing the water quality of this watershed according monthly measured continuously for two years. The water quality was assessment using the single factor index method, comprehensive index method and fuzzy comprehensive evaluation. Simultaneously, the main pollutants and the composition of pollutant were determined by the weights and composition analysis. The spatial and temporal characteristics of water quality were also studied by the method of Empirical Orthogonal Function. Finally, the environmental capacity were done using step-zero-dimensional and probability water quality model based on the the Gradeâ…¡water. The main results were summarized follows:1. The simulation experiment of phosphorus adsorption indicated that the sediment in river and reservoir had a strong adsorption capacity, and the maximum absorption capacity of different samples was during 150.75 to 238.51 mg/kg and 170.56 to 322.48 mg/kg, and the mean value was 210.96 mg/kg and 237.32 mg/kg, respectively. There were significant correlations between the absorption capacity and clay, phosphorus adsorbed by aluminum, active iron and active aluminum, respectively. The adsorption process could be described by the Langmuir, Freundlich and Temkin equations (R2>0.87). The critical values of second pollution that the adsorption/desorption equilibrium concentration were during 0.05 to 0.15mg/L, and 0.21 to 0.49 mg/L for sediments in river and reservoir. The mean values were 0.097 mg/L and 0.32 mg/L and both of them higher than the TP concentration in river and reservoir. Therefore, secondary phosphorus pollution existed in the river and reservoir, and the sediment in river and reservoir acted as a "phosphorus pollution source".2. The simulation experiment of ammonium nitrogen adsorption indicated that the adsorption progress of ammonium nitrogen by the sediment in river and reservoir could be described using Freundlich equation. The constant of adsorption capacity K was during 21.82 to 100.471/kg and 18.82 to 85.661/kg. The nonlinear constant n was between 1.40 and 1.85, 1.98 and 2.76, respectively. There was a significantly positive relationship between n and total phosphorus, organic matter, cation exchange capacity and so on, while the active aluminum was negative. The critical values of second pollution that the adsorption/desorption equilibrium concentration were during 0.30 to 0.81 mg/L, and 0.19 to 0.83 mg/L, respectively for sediment in river and reservoir. The mean values were 0.47 mg/L and 0.62 mg/L, and both of them higher than the total ammonium concentration in river and reservoir. These results indicated that there was an occurrence of secondary pollution in the river and reservoir, and the sediment acted as an "ammonium pollution source".3. Using the single factor identification index method to assessment the water quality of rivers in Fushi reservoir watershed from July 2009 to June 2011. The results showed that in different region and different time the water quality was quite different. The water quality in tributary was better than the main stream, and the main stream was better than the reservoir. According the water quality change trend, from July 2009 to June 2011 could be divided into two periods. First period was from July 2009 to June 2010. This period the water quality was belonged to the Gradeâ…¡and the Grade III and it was meet the requirement of central surface-drinking water source. The second period was from July 2010 to June 2011. This period the water quality was belonged to Grade V or even worse and unable to meet the requiremenment of central drinking water source.4. The main pollution factors of Fushi reservoir watershed were CODMn and TN according to the fuzzy comprehensive evaluation method. During July 2009 to July 2010, the main pollution was CODMn and the water quality was between Gradeâ… and Gradeâ…¡. From July 2010 to June 2011, the main pollution was TN, and the water quality was Gradeâ…¤. However two-thirds of monitoring time total nitrogen was acted as main pollution factor and the other one-thirds of time CODMn was main pollution factor.5. The component of major pollution factor TN was anal sized. The result showed that there was different nitrogen formation in different periods. During July 2009 to April 2010 inorganic nitrogen was main component in the total nitrogen. Inorganic nitrogen accounted for 6.39% to 92.86% of TN, and was existed as nitrate. During May 2010 to June 2011, inorganic N accounted for 20.97% to 38.48%, and organic nitrogen was the main pollution. These results indicated that existed different nitrogen pollutant sources in different periods.6. Empirical orthogonal functions decomposition indicated that the first eigenvector's variance contribution of all pollution factors in this watershed was during 86.78% to 99.99% and 95.54% to 99.93% respectively for rivers and reservoir. They could reflect the change trends and characteristics of pollution factors in monitored spatial and temporal. All the test factors in all monitoring sites had no obvious change at different spatial except potassium permanganate index increased from the upstream to downstream during July 2009 to June 2011. Dissolved oxygen value in the downstream higher than the upstream. Ammonium nitrogen, total phosphorus and total nitrogen didn't show fixed change in spatial. However total nitrogen increased with the time passed during test time. In the reservoir, only total nitrogen increased during all the monitoring time, others had no obvious change regularity. Both dissolved oxygen and Ammonium nitrogen were in the order of surface>4m>6m, while the potassium permanganate index was 6m>4m>surface. Total phosphorus and total nitrogen in the different monitoring points had no significant change.7. Using zero-dimension water quality model calculated the environmental capacity of potassium permanganate index and total nitrogen based on the Gradeâ…¡water quality. The resulted shown they were exceeded the limited value of Gradeâ…¡. The exceeded amount was wet season period>median water period>dry season. The environmental capacity of ammonium nitrogen and total phosphorus were less than the Gradeâ…¡, and the residual value was also wet season> median water period>dry season. The larger differences of environmental capacity at different periods have some relationship with the river discharge amount and seasonal agricultural production. In detail, in wet season, potassium permanganate index, organic nitrogen and nitrate mainly came from agricultural non-point-source pollution due to runoff, and the junk of river bank. While in median and dry water period, they mainly came from domestic sewage and the junk of poultry farming.8. The water environment capacities of potassium permanganate index and ammonium nitrogen in Fushi reservoir were calculated based on the Gradeâ…¡water quality standard using the water environment capacity model GB3839-83According. The result shown the environment capacity was expressed as the order of wet season>median water period>dry season. And the values were ranged from 3588.33 to 6508.44 kg/d and from 258.33 to 670.19 kg/d. The mean values were 4949.47 kg/d and 454.63 kg/d respectively for potassium permanganate index and ammonium nitrogen. The theoretical water environment capacity of total phosphorus and total nitrogen in Fushi reservoir was calculated according to Vollenweider and Dillonwater environment capacity models. The result shown the environment capacity of them was expressed as the order of wet season>median water period>dry season also. However the factual environmental capacities of them were minus value, which calculated according to the measured value. These results indicated the water environment capacities of total phosphorus and total nitrogen in this reservoir exceeded Gradeâ…¡water quality standard. And the exceeding degree was wet season>median water period >dry season. So, it is clear that this reservoir had been contaminated already and needed water repair, reduce water environment capacity in order to reach the region satisfying water quality goal.The new points of the research as follow:1) This study started with the concepts of watershed systems, and systematic analyzed the sediment of the watershed and water quality. Further more analyzed the spatial and temporal dynamics changes of main pollution factors from its source to transport process. Based on the drinking water Gradeâ…¡standard, the reservoir water quality were assessment and predicted using zero-dimensional water quality model and the probability environmental capacity model. These results provide a reasonable basis for reservoir water quality management and protection.2) The water environmental capacity of different indicators was calculated under the combination between monitoring values of water quality and different hydrographic periods. The environmental capacity were in the order of wet season>median water period>dry season. And this order close related with agricultural production activities. It indicating that agricultural non-point source pollution was the main factors of water pollution in Fushi reservoir.3) Sediment played as source/sink role. However, this role varied depending on the different water environment. Through the simulation of phosphorus and nitrogen adsorption/desorption by the river sediment and reservoir sediment indicated that although the river sediment acted as "pollution sources", however the reservoir bottom sediment have more effect on water quality than river sediment. The reservoir sediment played mainly as a sink in the wet season and as a source in the median water period and dry seasons.Fushi reservoir as our experimental area for two years, and the adsorption of nitrogen and phosphorus, and the water quality and water environmental capacity were simulated by the methods of laboratory simulations and the application of some research models. Although, have some meaningful conclusions, but due to time, experience, research funding and other factors, there are some problems need to be resolved and some studies to be further deepened.
|
PDF Full Text Request