Ecosystem Health Assessment In Aquatic-terrestrial Ecotone Of Lijiang River

Quantitative assessment of ecosystem health in the water-land ecotone is the foundation for understanding the ecosystem change mechanism of the fragile zone,formulating scientific protection and sustainable use countermeasures of the ecosystems,and maintaining regional sustainable development.We conducted this study in the water-land ecotone along the Lijiang River.First,we established the indicator system for the ecosystem health assessment of the fragile ecotone.And then we employed statistical analysis such as wavelet analysis and cluster analysis to evaluate the water resource carrying capacity,soil quality,climate change,and forest health based on the field survey data.Finally,the ecosystem health of water-land ecotone was assessed and revealed comprehensively.The results are as follows:(1)The forest health status in the water-land ecotone of Lijiang River was good.A total of 37 tree species and 46 shrub species were investigated in the water-land ecotone of the Lijiang River.The main dominant tree species were Pterocarya stenoptera,Celtis sinensis,Sapium sebiferum,Cinnamomum camphora,while the dominant shrub species were Bambusa multiplex,Vitex negundo,Nerium indicum,Morus alba,and Urena lobata.The frequency distribution of tree height,breast diameter,and sectional area showed an inverted J-shaped distribution in both tree and shrub layers.The plant diversity in the study area was relatively rich,and the diversity index,evenness index and richness index of shrub layer were higher than that of arbor layer.Among the 48 plots of the forest health survey,there are 4 excellent ones,27 good ones,15 medium ones,and only 2 bad ones.(2)The content of soil organic matter was positively correlated with soil nitrogen content,soil phosphorus content,soil potassium content and soil water content,but negatively correlated with soil bulk density at the significance level of 0.01.Total nitrogen content,total potassium content and soil water content were positively correlated with the diversity of arbor forests.By contrast,soil bulk density was negatively correlated with the arbor diversity of the forest.The overall soil quality of the water-land ecotone along the Lijiang River was evaluated based on the survey of 48 plots.Five plots were rated as excellent,14 plots as good,26 plots as medium and 3 plots as bad.(3)The average daily temperature of the Li River basin showed a significant increasing trend from 1976 to 2015.The average annual precipitation fluctuated and the average annual potential evapotranspiration showed a decreasing trend.The obvious "evaporation paradox" may be caused by the decreasing trend of meteorological factors,such as atmospheric pressure,relative humidity,average wind speed,and sunshine hours.The main evolution period of climate factors in the study area is 22 years and 32 years,and the main evolution cycle of the hydrological process is 30 years.(4)The carrying capacity of water resources near the water-land ecotone of the Lijiang River was larger than the ecological footprint.But the ecological footprint of per 10,000 yuan GDP water resources was high.It indicated that the utilization efficiency of water resources in the water-land ecotone of Lijiang River was below the average level in China.Though the water resources situation is improving,there will still be pressures on water resources in the future.We suggest that the administrative department adopt the preferential policies and increase funding investment in the direction of environmental protection and water resources protection.(5)The ecosystem health of the water-land ecotone of Lijiang River belongs to the second grade(health).The percentage of ecosystems that belonged to the very healthy,healthy,sub-healthy,abnormal and ill state were 21.79%,22.28%,43.05%,8.61%and 4.21%,respectively.The main factor restricting the ecosystem health of the water-land ecotone of Lijiang River included the level of social and economic development,chemical fertilizer use intensity,pesticide use intensity,enrichment of leisure and recreational facilities,environmental protection investment and so on.For the water-land ecotone of the Lijiang River,the health status of the forest,soil,water resources,and the whole ecosystem is relatively good.In order to maintain the sustainability of regional development,the management departments continue their efforts in eco-protection and reduce the use intensity of chemical fertilizers and pesticides in agricultural production.