The Study Of Remote Sensing Imagery Water Quality Parameter Algorithms And Spatial And Temporal Patterns Variation Of Water Quality In Lake Liangzi

Lakes are significant parts of inland water.In recent decades,many lakes in the world are experiencing a series problems,such as water quality decline,water eutrophication and destruction of water ecosystems,with the impacts of global climate change and increased human activities.Remote sensing technology has edges of fast,large-scaled and low-cost.And it can be used for long term,large-scaled and dynamic monitoring of lake water quality.Lake Liangzi is the second largest and the first water storage of Hubei Province with high abundant aquatic biodiversity and vegetation coverage rate.As a case study in Lake Liangzi,water quality assessing models are constructed by using Landsat ETM+/OLI multi-spectral images and in situ measured water quality parameters.With the assessed water quality parameters of Lake Liangzi during the period of 2007-2016,we analysed the spatial and temporal patterns of water quality in Lake Liangzi and its main driving forces in the recent decade.The main results are as follows:(1)Construction of water quality parameter assessing algorithms with multi-spectral imagery.The assessing models of Secchi disk transparency(SDT),Total suspended solids(TSS),Chlorophyll a concentration(Chl a),Total nitrogen concentration(TN)and Total phosphorus concentration(TP)in Lake Liangzi were constructed using Landsat multi-spectral imagery.Landsat blue band and near-infrared band are strongly correlated with water SDT and the multivariate linear model of these two bands can estimate water SDT well.The ratio of Landsat green band and blue band is strongly correlated with water TSS and the linear model of this ratio can estimate water TSS well.The ratio of Landsat near-infrared band and red band is strongly correlated with water Chl a and linear model of this ratio can estimate water Chl a well.The Landsat blue band,green band and red band are strongly correlated with water TN and the multivariate linear model of these three bands can estimate water TN well.Landsat near-infrared band,the ratio of near-infrared band and blue band and the ratio of near-infrared band and red band are strongly correlated with water TP and the multivariate linear model of these three variables can estimate water TP well.The accuracy of these algorithms were tested by the in situ water quality parameters in Lake Liangzi.(2)The spatial and temporal patterns of SDT,TSS,Chl a,TN and TP in Lake Liangzi during the period of 2007-2016.The trendency of water quality in Lake Liangzi was declined on the whole.The whole lake water belonged to class II water quality before 2010 and belonged to class III water quality after 2010.The water SDT of Lake Liangzi showed a decreasing trend.The water TSS showed an increasing trend and the variation range was enlarged after 2010.The water Chl a was at low level and the variation range was enlarged after 2010.The water TN showed an increasing trend and the variation range was enlarged after 2010.The water TP showed an increasing trend after 2010.The flood may be the main factor of variation of water quality on long term in Lake Liangzi.The water TSS,Chl a and TN demonstrated a significant seasonal variation in Lake Liangzi.The water TSS was highest in fall and it may because of the tourism and halieutics of Lake Liangzi in fall.The water Chl a was higher in spring and fall and lowest in winter.The water TN was highest in summer.The main factor of Chl a and TN variation may be the precipitation.On spatial patterns,water quality of Lake Niushan was worst and the one of Lake Qianjiang was best in Lake Liangzi.(3)The effects of water brownification and eutrophication on submerged macrophytes.We conducted an experiment to assess effects of water brownification and eutrophication on growth and competition of native and exotic submerged macrophytes.The results show that the biomass of both native and exotic submerged macrophytes exhibited positive responses to water brownification in monoculture.The responses of photosynthetic performance to water brownification were species-specific,and water brownification may decrease the photosynthetic ability of non-native species.Water brownification may decrease the non-native species' ability to compete with native species.In addition,nutrient enrichment in brown water may exacerbate the decrease in competitive ability of the non-native species.Water brownification may decrease invasions of submerged non-native macrophytes and improve the biological resistance.This study enrich the water quality monitoring models by remote sensing,and provide new methods for water remote sensing quality monitoring.In the long time scale,we investigate the spatial and temporal variation pattern and the main factors of the water quality of Lake Liangzi,which provides theoretical evidence of the protection and management for the lake.