Impacts Of Farmland Drainage Ditch Connectivity On The Output Of Nitrogen And Phosphorus And Appraisal Of Landscape Pattern

The fact that agricultural reclamation activities are increasing in the tidal flat area,caused the huge loss of purification function of wetlands and as well as non-point sources(NPS)pollution from the reclamation area,and contributed to or even resulted in eutrophication and red tide.The study of agricultural ditch drainage pattern is a crucial issue because it is closely related to nutrient transportation process and purification of nitrogen(N)and phosphorus(P),but the researches based on single ditch cannot explain the influences of agricultural ditch drainage network on the N and P's transportation process and NPS pollutant removal completely.Aiming at the problem of NPS pollution and the reality of large-scale tidal flat reclamationand agricultural development,the objective of this project was to analyse the extent to which the spatial configuration and composition,especially the connectivity of an agricultural drainage ditch network could influence the N and P's transportation process and NPS pollutants retention of a given tidal flat reclamation area.We take a typical reclamation area of Yancheng coast as a case study,and several questions are addressed:(1)What is the output coefficient of N and P from each land use type;(2)How much pollutants could be removed by each kind of drainage ditch;(3)How to modeling the drainage ditch connectivity of ditch corridor network and as well as agricultural landscape connectivity which considers the spatial interactive relation between the ditch network and land use patches;(4)what is the relation of drainage ditch connectivity and transportation of N and P in a given agricultural landscape system;(5)what is the relation between agricultural connectivity and NSP pollutants(N&P)removal and(6)how to developing landscape functional indicator coupling transportation process of N&P and NSP pollution control.To solve these questions will help improving the understanding of pattern-process-services relationships of agricultural landscape,and benefit the agricultural land use planning of tidal flat reclamation areas or plain river-net areas,and also can provide a scientific basis for non-point source pollution control of agricultural landscape system.The main results are as follows:(1)The output of N and P has obvious temporal and spatial distribution.Concentration of nitrogen and phosphorus shows the regularity that concentration of N and P in October before rain less than August before rain less than October after rain less than August after rain.In addition,spatial variance reflected in that first branch ditch and second branch's concentration of N and P show upward trend,and then begin to decline which was affected by the effects of land use changes.(2)DCCI model was Proposed and constructed from the perspective of graph theory.It can be used to describe Agricultural ditch landscape promote or hinder degree of spatial diffusion of N and P.The results of Fitting the model and concentration of nitrogen and phosphorus are as follows:1)under branch ditch scale,concentration of N and P is positive correlations with DCCI.2)Under main ditch scale concentration of N and P is inversely related to DCCI.(3)Considering the factors of land use types and their spatial distribution,ALCI model was proposed and constructed.The Results of Fitting the model and concentration of N and P are as follows:1)under branch ditch and main ditch scale,concentration of N is inversely related to ALCI.It indicate that drainage ditches of different level have positive effect on NSP pollutions removal.2)Drainage ditches have better Purification action on N.3)here are different effect on TN interception for drainage ditches at different scales.(4)Combining DCCI and ALCI models,EA model was proposed based on "source"and "sink" principle.The Results of Fitting EA model and concentration of Li shows that:EA model and Li can draw up to match effective.Besides they are directly related.Overall the model can assess the effect of agricultural ditch drainage pattern nutrient transportation process on purification of N and P efficiently.