Construction Technology Of Vegetation Buffer Zones Based On "Source-Sink" Model

There are serious non-point source pollution problems in the Yangtze River upstream caused by special topography, soil and vegetation conditions, irrational land use patterns, the excessive use of pesticides and fertilizers and other factors, while the vegetation buffer zone is the key way to control the non-point source pollution. In this paper, the likelihood levels of non-point source pollution of each catchment of Kaixian county in Chongqing city are judged based on the "source-sink" landscape model and the location-weighted landscape index (LWLI). The locations and widths of the required vegetation buffer zones are determined according to the LWLI. Then, the optimum models of plant communities for vegetation buffer zones in Kaixian are constructed referring to the typical nature-approximating plant communities in the Three Gorges Reservoir. The main results are as follows:(1) The Kaixian county can be divided into five catchments based on the DEM data and the hydro logic analysis module of ArcGIS. The catchment1is the largest one with864.11km2area, and the smallest area of catchment4is683.93km2while the average area of catchments is777.75km2. Based on the ERDAS image analysis software, the land use patterns of Kaixian county are divided into six landscape types, which including grass land, forest land, bare land, farm land, building and water. And the six landscape areas mainly about238.25km2,1835.62km2,37.77km2,1525.23km2,96.24km2and155.62km2respectively. The area of the forest land and farm land make up the largest proportion of Kaixian county. The patch patterns of grass land and bare land mainly distributed in the catchment1.(2) Based on the "source-sink" landscape model, the LWLI of each catchments are calculated from the aspects of the relative distance, relative elevation and slope, respectively. The LWLI of the catchment1, catchment4and catchment5are0.0891,0.4643and0.4936, which are smaller than the threshold of0.5. It indicates that there are unlikely to have a risk of non-point source pollution in the three catchments. The LWLI of the catchment2and catchment3are0.5165and0.5563, which is slightly bigger than the threshold. It indicates that there are more likely to have a risk of non-point source pollution in the two catchments. So the two catchments are needed to set the vegetation buffer zones.(3) In order to set the location of the vegetation buffer zones for catchment2and catchment3, we should take into account of the L WLI, the land use pattern of Kaixian county and the local economic development level. The vegetation buffer zones are mainly set along the shore. Meanwhile the vegetation buffer zones set along the contour of the shore and the structural of the tree+shrub+grass are used as a complementary. When the riparian are occupied by the construction land or residential district, it is better to set the vegetation buffer zones along the contour of the shore which out of range of the construction land or residential district.(4) Based on the width design flow chart of the vegetation buffer zone, judging from the "source-sink" landscape model, when the width of the vegetation buffer zone set to15m along the shore, the LWLI of the catchment2and catchment3are0.4551and0.4211, which is lower than the threshold value of0.5. The results are indicate that the likelihood of non-point source pollution occurring will be reduced obviously in catchment2and catchment3.(5) The plant configuration of fluctuating zone in the catchment2and catchment3is made up of the herbaceous communities and arbor+shrub+herbage communities. Herbaceous communities: Ass. Xanthium sibirium+Cynodon dactylon, Ass. Arthraxon prionodes+Setaria viridis, Ass. Xanthium sibirium+Echinochloa crusgalli, Ass. Arthraxon prionodes+Artemisia lactiflora, Ass. Arthraxon prionodes+Artemisia argyi, Ass. Artemisia apiacea+Imperata cylindrica, Ass. Imperata cylindrica+Artemisia lactiflora, Ass. Hemarthria compressa, Ass. Paspalum paspaloides. Arbor+shrub+grass communities: Lower area (close to water):Salix variegata Franch./Pterocarya stenoptera DC+Alternanthera philoxeroides; Middle area:Cleistocalyx operculatus RoxblTaxodium distichum+Polygonum chinense Linn./Pennisetum sinese Roxb; Upper area (close to bank slope):Taxodium ascendens Brongn./Quercus variabilis Bl.+Cyperus rotundus Linn. (6) The river in catchment2and catchment3is divided into the town river, country river and other river. The vegetation buffer zones in town river has3patterns:Pattern1(Elaeocarpus decipiens Hemsl.+Cornus officinalis Sieb. et Zucc.+Medicago sativa Linn.; Elaeocarpus decipiens Hemsl.+Cercis chinensis Bunge+Medicago sativa Linn.; Elaeocarpus decipiens Hemsl.+Cercis chinensis Bunge+Medicago sativa Linn.); Pattern2(Acer buergerianum Miq.+Ligustrum sinense Lour.+Festuca elata Keng ex E. Alexeev; Cinnamomum camphora (Linn.)Presl.+Lagerstroemia indica Linn.+Festuca elata Keng ex E. Alexeev; Sapium sebiferum (Linn.) Roxb.+Lagerstroemia indica Linn.+Festuca elata Keng ex E. Alexeev); Pattern3(Metasequoia glyptostroboides Hu et Cheng+Salix variegata Franch.+Canna indica Linn.; Ligustrum lucidum Ait.+Hibiscus syriacus Linn.+Cynodon dactylon(Linn.)Pers.; Acerpalmatum Thunb.+Hibiscus syriacus Linn.+Ophiopogon japonicus (Thunb.)Ker Gawl.). The vegetation buffer zones in country river has5patterns:Pattern1(Liquidambar formosana Hance+Lespedeza formosa (Vogel) Koehne+Cynodon dactylon (Linn.) Pers.; Liquidambar formosana Hance+Lespedeza formosa (Vogel) Koehne+Cynodon dactylon (Linn.)Pers.; Ligustrum lucidum Ait.+Nandina domestica Thunb.+Cynodon dactylon (Linn.)Pers.); Pattern2(Salix babylonica Linn.+Rosa bracteata J. C. Wendl.+Cynodon dactylon (Linn.)Pers.; Pinus elliottii Engelm.+Hibiscus syriacus Linn.+Cynodon dactylon (Linn.) Pers.; Pinus elliottii Engelm.+Hibiscus syriacus Linn.+Cynodon dactylon (Linn.) Pers.); Pattern3(Sapium sebiferum (Linn.) Roxb.+Adina rubella Hance+Hemarthria compressa(L. f.)R. Br.; Vernicia fordii(Hemsl.)Airy-Shaw+Cassia corymbosa+Arundinella anomala Steud.; Populus canadensis Moench+Cassia corymbosa+Arundinella anomala Steud.); Pattern4(Salix babylonica Linn.+Saccharum arundinaceum Retz.; Dalbergia hupeana Hance+Pittosporum tobira Ait.+Arundinella anomala Steud.; Metasequoia glyptostroboides Hu et Cheng+Nandina domestica Thunb.+Arundinella anomala Steud.); Pattern5(Hibiscus mutabilis Linn.+Cynodon dactylon (Linn.) Pers.; Hibiscus mutabilis Linn.+Cynodon dactylon (Linn.)Pers.; Liquidambar formosana Hance+Nerium indicum Mill.). The vegetation buffer zones in other river has2patterns:Pattern1(Distylium chinense (Franch. ex Hemsl.) Diels+Arundinella anomala Steud.; Indigofera pseudotinctoria Matsum.-+Arundinella anomala Steud.; Indigofera pseudotinctoria Matsum.+Arundinella anomala Steud.); Pattern2(Cornus officinalis Sieb. et Zucc.+Cynodon dactylon (Linn.) Pers.; Amorpha fruticosa Linn.+Cynodon dactylon (Linn.) Pers.; Amorpha fruticosa Linn.+Cynodon dactylon (Linn.) Pers.)...