森林生态系统对非点源污染的控制机理与效果及其影响因素

Effects of Forest Ecosystems on Non-point Pollution Control

近年来,因非点源污染造成水体氮磷富营养化的现象日渐增多,而传统的治理方式在非点源污染物的控制上又收效甚微。本文归纳分析了目前国内外关于森林生态系统对非点源污染控制的研究成果,结果发现:森林生态系统主要通过植物体吸收,地被物和土壤层对非点源污染物的吸附等起到净化作用;大量研究表明,森林对N、P等非点源污染物的净化效果明显,削减率多界于60%～90%之间;此外,森林对非点源污染物的削减效果受林带宽度、植被状况、土壤性状、森林经营等因素的影响。

Non-point source pollution,particularly agricultural non-point source pollution,has become a major contributor of water pollution in many countries during recent years.Major lakes and rivers in China have suffered from serious eutrophication problems,e.g.,five lakes（Poyang Lake,Dongting Lake,Taihu Lake,Hongze Lake,and Chaohu Lake）,the Three Gorges Reservoir,Baiyangdian Lake,Nansi Lake,and Yilong Lake.The contribution rate of non-point pollution to eutrophication has been found to be much higher than point source pollution.Although tremendous efforts have been made to control non-point pollution,they seem to be far from effective due to uncertain emissions of the non-point pollutants.As such,people are resorting to purifying natural ecosystems,e.g.,forest riparian buffer has been recommended as one of the Best Management Practices（BMP） for non-point source pollutant control in the United States.The authors comprehensively summarized studies associated with the effects of forest ecosystems on non-point source pollution control.Forest ecosystems have been shown to be of the capacity to adsorb and purify non-point source pollutants mainly through plants,canopy,ground litter,and soil layers.Plant uptake is one of important mechanisms of nutrients control.Part of pollutions carried by rainfall can be intercepted by canopy,while the nutrient content will increase because of eluviations.However,the non-point pollution can be greatly reduced after runoff flow through ground cover and soil layer.Numerous studies show that forests could reduce about 60~90% of the total nitrogen and phosphorus from upper farming areas.Non-point source pollution control is generally affected by many factors.The forest belt width has an impact on the effect of non-point source pollution reduction,and therefore the width needs to be adjusted appropriately.Different tree species show varying absorption capacities of non-point source pollutants;therefore the selection of riparian tree species should be paid much attention.The absorption capacity of forest vegetation for organic matter decreases with maturating trees.The larger the infiltration capacity of riparian buffer soil is and the stronger water improvement and storage capacities are.Denitrification is an important mechanism for N retention,being considered the best way to reduce nitrate.Soil conditions impact the denitrification,including the number and type of denitrification microorganism,active enzymes,soil aeration,nitrate concentration,organic matter,and effective carbon.Forest management practices can also influence non-point pollution control,such as building road,drainage,fertilization,site preparation,and other activities.Disturbance of forests could increase the content of suspended sediment and nutrient in runoff during a certain period.This study can provide reference for the management of non-point source pollution.