Effects Of Forest Litter Around Reservoir On The Water Quality In Tangpu Reservoir

In recent years, many cities in our country have faced water resources crisis. Reliable and excellent water source is vital for citizens’drinking water safety and sustainable development. As drinking water source in Shaoxing, Tangpu Reservoir serves about3million people and has made huge contributions to economic and social development of Shaoxing, Shangyu and Cixi. Tangpu Reservoir water quality is good, but total nitrogen and total phosphorus are out of limits. In2010, there were blue-green algae, and that brought some hidden troubles to domestic water in the cities, like Shaoxing.At present, many people have studied eutrophic Tangpu Reservoir water quality. Some scholars thought that was because abundant litter was accumulated in the forest land around Tangpu Reservoir and nutrient produced by decomposing of the litter washed up to the reservoir during the rainfall process by surface runoff. Therefore, some people suggested dry branches and fallen leaves in excess around the reservoir should be removed. The main aim of this study is to study the influenced of accumulation of litter around the reservoir (Grade I protected area) on loss of water and soil as well as nutrient and is to figure out advantages and disadvantages of accumulation of litter around the reservoir on water quality, thus providing experimental bases for treatment of reservoirs eutrophication. The experiment set runoff plots by different coverage of litter in Grade I protected area and made contrastive research on loss of water and soil as well as nutrient; the experiment also set monitoring experiment of decomposition of litter and analyzed accumulation of litter around the reservoir on water quality.The construction of experiment plot started from March,2013. The trial of it was in July and monitoring was in August. Monitoring result of runoff plot of different litter coverage showed that average of total nitrogen (TN) concentration in runoff plot without treatment of litter coverage (0treatment) was1.81mg/L and average of total phosphorus (TP) concentration was0.232mg/L; under natural conditions, average of TN of30%of litter coverage treatment in experiment runoff plot was1.52mg/L and average of TP concentration was0.186mg/L; under natural conditions, average of TN concentration of60%of litter coverage treatment in experiment runoff plot was1.41mg/L and average of TP concentration was0.181mg/L; average of TN concentration of100%of litter coverage treatment in experiment runoff plot was0.87mg/L and average of TP concentration was0.127mg/L; under natural conditions, average of TN concentration of150%of litter coverage treatment in experiment runoff plot was0.78gm/L and average of TP concentration was0.123mg/L. The experiment result showed that different litter coverage treatment had great influence on concentration of TN and TP in water quality of forest land surface runoff, namely more litter, lower nutrient concentration. Coverage of litter can better conserve water and soil. Our experiment did not discover that nutrient concentration increased with increasing litter coverage.Soil erosion monitoring in experiment plots with different litter coverage showed that soil erosion amount in the experiment plot without litter coverage treatment (0treatment) from August2013to May2014was115.48g; under natural conditions, soil erosion amount of30%of litter coverage treatment in experiment plot was135.31g; under natural conditions, soil erosion amount of100%of litter coverage treatment in experiment plot was37.3g; under natural conditions, soil erosion amount of150%of litter coverage treatment in experiment plot was50.4g; total nutrient loss caused by soil erosion based on litter coverage was respectively: total loss of TN was48.33mg,40.55mg,26.67,18.12mg, and14.59mg; total loss of TP was36.91mg,33.01mg,31.53mg,8.37mg andll.08mg. The experiment result preliminarily showed that litter coverage can prevent effectively soil erosion and loss of soil nutrient caused by rainfall.With monitoring decomposition of litter in the forest land around the reservoir, from August2013to May2014, litter was19.4g at first and then it was decomposed into16.97g, and decomposition rate was12.5%. According to amount of litter in each experiment plot, litter nutrient decomposition can be calculated. Total nitrogen (TN) decomposed from litter without treatment was Omg, and total phosphorus (TP) decomposed was Omg; under natural conditions, TN decomposed from30%of litter coverage treatment in experiment plot was375.9mg and TP decomposed was44.1mg; under natural conditions, TN decomposed from60%of litter coverage treatment in experiment plot was751.8mg and TP decomposed was88.1mg; TN decomposed from100%of litter coverage treatment in experiment plot was1252.9mg and TP decomposed was146.7mg; under natural conditions, TN decomposed from150%of litter coverage treatment in experiment plot was1879.4mg and TP decomposed was220.1mg; total nutrient loss caused by surface runoff and soil erosion in experiment plot with increasing litter coverage respectively was:total loss of TN was1758.9mg,1352.2mg,1111.6mg,591.1mg and478.6mg. Total loss of TP was respectively:256.2mg,193.5mg,170.8mg,91.9mg and84.3mg. In total, with increasing coverage of litter, total of N and P decomposed by litter increased; however, total of N and P from by loss of surface runoff by rainfall significantly decreased. Therefore, our experiment preliminarily showed increasing coverage of litter significantly reduced loss of soil and water as well as nutrient, instead of bringing more N and P to surface runoff.