Research On Mechanisms Of Nitrogen And Phosphorus Removal In Restoring Wetland Based On Landscape Ecology

Removal of nitrogen and phosphorus in restoring wetland is frontier in water environment recovery and protection. On landscape scape, the mechanisms of nitrogen and phosphorus removal based on interactions between biology and environment should be understood, which is important for eutrophication control and wetland restoration project design. Qi Xinghu wetland, located in Nansi Lake drainage area, was chose as object. The changes of nitrogen and phosphorus removal efficiencies in different spatial and temporal scale were analyzed, and dominate environmental and spatial factors were determined. The effects of vegetation were studied, and the interactions between plant community succession and nitrogen and phosphorus removal were revealed. The processes of nitrogen and phosphorus removal were discussed based on dynamic models and isotherm models, and the effects of landscape elements were also analyzed. The main results are as following:(1) Changes of nitrogen and phosphorus removal efficiencies were analyzed in time scale:1) Under high nutrient stress, average removal efficiencies of nutrients could be over 80%.2) Nutrients removal efficiencies were not significant difference among summer, spring and autumn. The removal efficiencies in winter obviously decreased, while also could reach more than 50%.3) Nutrients removal efficiencies were not significant difference among years.(2) Effects of environmental and spatial elements on removal efficiencies of nitrogen and phosphorus were analyzed.1) In system scale, Thad significantly positive correlation on the removal of nitrogen, TP and PP. DO and HRT had significantly negative correlation with TN removal. HRT also had significantly negative correlation on TDP and PO43--P removal. Four environmental elements were dominant, in which T and HRT had the greatest effect.2) In patch scale, nutrients removal efficiencies increased with the increasing of HRT, Co, C, A, Vol, L and LSI, while decreased with LPI. Especially, the influence of Co and LPI depended on season. Two environmental elements and eight spatial elements were dominant, in which L had the largest effect.(3) Vegetation had effect on the removal efficiencies of nitrogen and phosphorus.1) CA and LSI of vegetation had significantly positive correlation with environmental elements in all seasons, while the correlations of PD, ED and SHDI of vegetation depended on season. Four vegetation indexes were dominant, in which CA and LSI had the largest effect.2) PLAND, LPI and LSI of water had significantly negative correlation in all seasons, while the effect of CA, ED and SHDI depended on season and form. CA, PLAND and LSI of reed+cattail had high positive effect in all seasons, while ED had great effect in spring and autumn. CA and LSI of lotus benefited nitrogen and phosphorus in all seasons, while PD had high negative effect with phosphorus in spring and summer. The dominant plant community indexes included three in water, five in reed+cattail and three in lotus. Among them, LPI of water and LSI of reed+cattail had the largest effect.(4) Plant succession under nutrients stress was characterized.1) As time goes on, vegetation area increased, numbers of patch decreased, leading to vegetation complicated. 2) Area of reed+cattail increased, which implied this kind of community was dominant in the restoring wetland and benefited nutrients removal.3) Lotus community gradually became complex under high nutrients stress, or even be replaced by other plants communities, while kept single under low nutrients stress. It means lotus was not be used in restoring wetland with high nutrients load.(5) Effects of landscape elements on C* and k were investigated.1) Environmental elements mainly influenced C* of nitrogen and k of nitrogen and phosphorus. DO and pH had negative effect, and HSL had significant positive effect on them. Moreover, C* could increase k of nitrogen.2) Among spatial indexes, PD had positive effect on C* of nitrogen in spring, summer and autumn, and ED had positive effect in spring and summer. MPS had great negative effect on C* of nitrogen on summer. PD also had significant positive effect on k of nitrogen and phosphorus in spring, and Vol had significant negative effect on k of phosphorus in winter.3) Among vegetation indexes, PD had negative effect on C* and k, especially in spring and summer.(6) Reaction models for nitrogen and phosphorus removal based on adsorption theory were studied.1) Both Langmuir and Freundlich isotherm models gave good fit in restoring wetland, and Langmuir model agreed better.2) When Co, HRT, CA, Vol and LSI increased, Langmuir model fitted better.3) The removal was fitted well by both pseudo first-order and pseudo second-order kinetic modes, and pseudo second-order mode fitted better.Removal of nitrogen and phosphorus in restoring wetland is a complex process between biology and environment. This research defined the relationships between nitrogen and phosphorus removal efficiencies and landscape elements, revealed the characteristic of plant succession under nitrogen and phosphorus stress, and discussed the processes of nitrogen and phosphorus removal based on adsorption theory. There results could provide theoretical basis and technical support for wetland restoration and integrated utilization.