Study On Influence Of Urban Forest Communities On Precipitation And Soil Erosion In Pearl River Delta

In this research, based on the technique of contrasting analyses and the measurement of integrated experiment, measurements on precipitation, interception, surface runoff, total runoff ,acid rains, hydrolochemical content, water and soil erosion were conducted for the evergreen coniferous-broad leaved mixed forests (I-secondary coniferous-broad leaved mixed forests and II-lower building coniferous-broad leaved mixed forests) in Shun de of Pearl river delta. The mechanisms of redistribution of rainfall, chemical influence of canopy, reducing acid deposition, hydrolochemical content and dynamic characters, purifying water quality, decreasing surface runoff and reducing soil erosion were studied by the numbers, the regression equations of throughfall, stemflow, interception and precipitation were established respectively. The grey forecast model of soil erosion was set up according as the surface runoff magnitude. The results as follow:1. 24.1% of annual rainfall 1619.4mm was intercepted by the evergreen coniferous-broad leaved mixed forests canopy, and only 20.6% of annual rainfall was intercepted by the lower rebuilding evergreen coniferous-broad leaved mixed forests canopy. The crown interception changed the way which rainfall came into forests, and reduced the energy of rainfall. When the precipitation was 77.87mm, the crown interception was 10.02mm and the intercepting rate of the canopy was 12.9%. When the precipitation was 169.33mm, the crown interception was 19.54mm, and the intercepting rate of the canopy was 11.5%. Ina word, the ratio of the canopy interception would reduce when the crown interception was saturation. The relations between throughfall and precipitation in the evergreen coniferous-broad leaved mixed forests were linearity correlation, and the coefficients of correlation were significance; The relations between the stemflow and precipitation were linearity correlation; The relations between the crown interception and precipitation were power function models, and the effect of the modes were distinct at 0.01 level. The hydrological effect rule of the urban forest canopy was opened out.2.Based on acidity observation in forest area, industrial park and residential area in Daliang town of Shunde, it was showed that the order of the pH value of rainfall in forest, industrial park and residential area was pHforest area pHresidential area pHindustrial area.., and the order of the acid rain's frequency was Findustrial area Findustrial area Fforest area The average of pH value of rainfall was 5.81 in Daliang town and Longjiang town. The pH of the water through evergreen coniferous-broad leaved mixed forests and evergreen coniferous-broad leaved mixed rebuilding forests were separately improved 0.67,0.35.So the forests can reduce precipitation's acidity and acid rain's rat;.3.The content of nutrition elements of evergreen coniferous-broad leaved mixed secondary forests and evergreen coniferous-broad leaved mixed rebuilding forests were analyzed, and the content of the both were equally well. The order of nutrition elements' content of precipitation in evergreen coniferous-broad leaved mixed secondary forests at Daliang town was N>Ca>K>Na>Mg>P, and the order of nutrition elements' content of precipitation in evergreen coniferous-broad leaved mixed rebuilding forests at Longjiang town was Ca > N>K>Na>Mg>P. The content of K Ca Na Mg, N and P in throughtful and stemflow was higher than that in precipitation, and the content of S0 S N0 P Cd was higher than that in precipitation. Content of heavy metal elements in total runoff was less than that in precipitation in evergreen coniferous-broad leaved mixed forests at Daliang town, and except for Cu, content of other heavy metal in total runoff wasless than that in precipitation in evergreen coniferous-broad leaved mixed rebuilding forests at Longjiang town. So the forests can purify water quality and the coniferousTbroad leaved mixed forests were better than the coniferous-broad leaved mixed rebuilding forests on purifying water quality.4 The fores...