Construction Technology Of Vegetation Buffer Zones For Urban Lake:a Case Study Of Moshui Lake

Lake eutrophication which is caused by non-point source pollution is a prominent water issue in China, and the trend is becoming more and more severe. Vegetation buffer zone is considered as the last line of defense to control non-point source pollutants into the water, and it gradually has being taken seriously. To solve the issue of low integrity, poor protective effect of vegetation buffer zone surrounding the urban lake in Wuhan, in this paper, taking Moshui lake as a case and introducing location-weighted landscape index (LWLI), judging the likelihood levels of non-point source pollution of the lake surrounding catchments to determine the locations of the lake vegetation buffer zones. Determining the required width of the buffer zone by LWLI, taking the typical lakes’ nature-approximating plant communities in Wuhan City as the reference system, we propose optimization models of lake buffer zone plant communities. The research results are as follows:(1) Moshui Lake basin is divided into eight catchments by Arcgis analysis of Moshui lake. Total catchment area are9.4824km2, the largest catchment1.9026km2, the smallest catchment0.6084km2and the average area of catchments1.1853km2.there are several larger catchments in the north of Moshui lake (Watershed upstream)than the ones in the south of Moshui lake (Watershed downstream).(2) Land use type of Moshui Lake basin can be classified into six types, farmland, forestland, grassland, built-up land, water and bare land, built-up lands in the Moshui Lake catchment region take up the largest area, being up to74.37%; farm land area is in the second place, only9.38%; forest land, water and bare land almost have the same area; grassland’s area is the smallest, only1.78%.Most of built-up land lies in the north shore; there is a lot of farm land in the south shore; it has a better natural environment in the northeast, retaining much forest land and water; there is large tracts of bare land in the northwest.The results by analysis of LWLI indicate that, the catchment having the most probable risk of non-point source pollution, LWLI of which is up to0.93; while the smallest probable one’s is up to0.63, LWLIs of all catchments are bigger than the standard value of0.5. It indicates that it is more likely to have a risk of non-point source pollution for each catchment.(3) The main buffer zone of catchment1is set by the model of "forestland (90m)+wetland (90m)". Now, the LWLI is still larger than the value, so the width of the buffer zone should be added.150m forest buffer zones and90m wetland buffer zones should be set on the shore nearby the construction land and on the outlet respectively. After planning, the LWLI will be0.49, meeting the standard value’s requirement. The risk of non-point source pollution occurring will be reduced obviously. The buffer zones of catchment2,3and4are set by the model of taking "forestland+wet land" as main body,"wetland" as vice body partly. The main bodies are "forestland (30m)+wetland (120m)","forestland (30m)+wetland (120m)","forestland (30m)+wetland (240m)" respectively. According to the state of the environment and needs of each catchment, additional wetland buffer zones should be set nearby the outlets, the width are90m,30m and30m. After planning, the LWLls will be0.48、0.50and0.49, basically meeting the standard value’s requirement. The risks of non-point source pollution occurring will be reduced obviously inside the regions.The main buffer zones of catchment5,6,7and8are set by the model of "forestland+wetland", the main bodies are "forestland (90m)+wetland (30m)","forestland (90m)+wetland (90m)","forestland (120m)+wetland (60m)""forestland (90m)+wetland (90m)" respectively. In this situation, the LWLIs of catchment5,6,7and8will be0.50,0.45,0.47,0.49, basically meeting the standard value’s requirement. LWL1of catchment5is slightly higher than the standard value. Considering the tension of land space, we reduce the risk of non-point source pollution occurring by improving plants configuration instead of increasing the width.(4) Taking account of environmental differences and specific needs of surrounding land around the riparian; the buffer zones are divided into two kinds, including ecological protection and ecological recreation. Buffer zone of ecological protection is for the catchment surrounded by non-construction land (e.g. farmland, bare ground), in which Plants configuration mainly plays a vital role in non-point source pollution prevention, catchment6and7are the representative catchments. Buffer zone of ecological recreation is for the catchment surrounded by construction land, in which Plants configuration plays a vital role not only in basic ecological function, but also in functions of landscape and recreation, catchment1,2,3,4,5and8are the representative catchments.Buffer zones of ecological protection are divided into two kinds, forestland and wetland. Forestland buffer zones of ecological protection includes:Salix matsudana-Zelkova serrata+Pyracantha fortuneana+Ophiopogon japonicus-Dichondra repens、Pinus thunbergii-Broussonetia papyrifera-Morus alba+Common Camellia+Ophiopogon japonicus-Cynodon dactylon、Sapium sebiferum-Quercus acutissima+Broussonetia papyrifera-Ternstroemia gymnanthera+Reineckia carnea.Wetland buffer zones of ecological protection includes:Triarrherca sacchariflora Phragmites australis+Alternanthera philoxeroides-Trapa bispinosa+Myriophyllum spicatum-Vallisneria natans、Zizania latifolia-Triarrherca sacchariflora+Nymphoides peltatum+Potamogeton crispus、Typha orientalis+Lemna minor-Eichhornia crassipes+Myriophyllum spicatum-Ceratophyllum demersum、Phragmites australis+Roegneria kamoji+Potamogeton maackiamusBuffer zones of ecological recreation are also divided into two kinds, forestland and wetland. Forestland buffer zones of ecological recreation includes: Sapiumsebiferum+Ligustrum quihoui+Ophiopogon japonicus、Pterocarya stenoptera-Liquidambar formosana-Osmanthus fragrans+Ophiopogon japonicus-Oxalis corymbosa、 Magnolia grandiflora-Salix babylonica+Pittosporum tobira-Aucuba chinensis+Medicago minima、Cinnamomum camphora-Ligustrum lucidum+Hibiscus syriacus+Hemerocallis fulva、Salix babylonica-Morus alba+Canna indica-Dichondra repens.Wetland buffer zones of ecological recreation includes:Canna indica-Softstem bulrush+Nymphaea alba+Myriophyllum spicatum-Ceratophyllum demersum、Typha orientalis-Nymphaea alba+Alternanthera philoxeroides-Trapa bispinosa+Ceratophyllum demersum、Typha orientalis-Phragmites australis+Alternanthera philoxeroides-Trapa bispinosa+Myriophyllum spicatum-Vallisneria natans.