| Dianchi Lake is the largest plateau freshwater lake in China.Due to the unreasonable early development and utilization of human beings,wetlands along the lakeside of Dianchi Lake were seriously degraded and the pollution of nitrogen and phosphorus was serious.Since 2008,the Yunnan government has constructed large-scale constructed wetlands in the lakeside of Dianchi Lake to restore the function of the lakeside ecosystem of Dianchi Lake.The impact of constructed wetland on the total phosphorus concentration of Dianchi Lake is a long-term process.Do the matrix,vegetation configuration and growth,landscape pattern of constructed wetlands have any effect on the total phosphorus concentration in Dianchi Lake? And how is it? All of these need to be evaluated by long-term continuous monitoring data.Satellite remote sensing technology is characterized by its macroscopic and periodic nature,which provides technical support for evaluating the response relationship between the lakeshore of Dianchi Lake and the total phosphorus concentration of Dianchi Lake by using the long-term series data.In this paper,the Dianchi Lake and its offshore area are taken as research areas,and the effects of the lakeside vegetation and typical wetland landscape pattern on the total phosphorus concentration of Dianchi Lake from 2005 to 2018 are studied,combined with the total phosphorus load of rivers entering the lake.The main contents and conclusions of this article are as follows:(1)Construction of remote sensing estimation model of total phosphorus concentration in Dianchi Lake and analysis of its spatial and temporal patterns.Based on the analysis of sensitive bands and the correlation between total phosphorus concentration and chlorophyll a concentration and transparency,the direct and indirect estimation models of total phosphorus concentration estimation in Dianchi Lake based on TM and OLI sensors was constructed.The accuracy evaluation of the constructed direct and indirect estimation models shows that the direct estimation model has higher accuracy in estimating the total phosphorus concentration in Dianchi Lake.The direct estimation model was applied to TM and OLI images to obtain the temporal and spatial distribution of the total phosphorus concentration in the Dianchi Lake.The results showed that the total phosphorus concentration in the Dianchi Lake decreased gradually from the lake margin to the lake center,and was higher in the north and south.The total phosphorus concentration showed an increasing trend from February to May,and a decreasing trend from November to January of the following year.From 2005 to 2018,the total phosphorus concentration in Dianchi Lake showed a significant decline.(2)The dynamic change of the vegetation in the lakeside of Dianchi Lake and its response to total phosphorus concentration in Dianchi Lake.Based on the NDVI threshold method,the information of herbs and woody vegetation in the lakeside of Dianchi Lake was extracted.It is found that the area of herbs and woody vegetation in the lakeside of Dianchi Lake shows a significant increase,and the most dramatic increase is from 2010 to 2011.The relationship between vegetation in lakeside and total phosphorus concentration in Dianchi Lake is analyzed from three perspectives: spatial distribution,seasonal difference and distance from the lake coastline,and the following conclusions are drawn:(a)From 2011 to 2018,the total phosphorus concentration in Dianchi Lake decreased significantly at the edge of the lake,which is closely related to the interception of lakeside vegetation.(b)The concept of strong influence zone of lakeside on total phosphorus concentration in Dianchi Lake was put forward.In 2005,the area of strong influence is the largest,which is 1,740 meters away from the shore.In 2017,the area of strong influence is the smallest,which is 570 meters away from the shore.Compared with the normal water period and the high water period,the NDVI has the strongest negative correlation with the total phosphorus concentration in the strongly affected area during the dry season.(c)There is a high correlation between total phosphorus concentration and the area of herbs and woody plants within 900 meters from the lake shore.In the distance of more than 900 meters away from the shoreline of the lake,the correlation between total phosphorus concentration and the area of herbaceous vegetation suddenly decreased,while the correlation with the area of woody vegetation remained high.(3)Analysis of the influence of typical lakeside wetlands on total phosphorus concentration in Dianchi Lake.Taking three typical wetland parks(Haidong wetland,Laoyuhe wetland and Dongdahe wetland)as examples,the relationship between the wetland landscape in the Dianchi Lake coastal zone and the total phosphorus concentration in the strongly affected area was studied.The results show that in the Haidong Wetland,the PLAND of the water has a strong negative correlation with the total phosphorus concentration in Dianchi Lake.This is due to the large number of oxidized ponds in the Haidong Wetland,where various submerged,emerging water plants and artificial harvesting are planted.The NDVI of vegetation in its growth period and the indicators of woody plants in Laoyuhe Wetland have a high correlation with the total phosphorus concentration in Dianchi Lake,which is related to its high coverage aquatic forest.The emerging plants,floating leaf plant and water in the Dongdahe Wetland have a strong correlation with the total phosphorus concentration in Dianchi Lake,which is highly related to their wetland diversity.In addition,taking three wetlands as a whole,based on group thinking,using correlation analysis,variance inflation factor test and stepwise regression,the key indicators of wetland landscapes that have a greater significant impact on the total phosphorus concentration in Dianchi Lake were selected,to analyze the relationship between the wetland landscape pattern and the total phosphorus concentration in the strongly affected area of Dianchi Lake.The selected key indicators and the order of influence level of them on total phosphorus in Dianchi Lake is as follows: CONNECT of water,CONNECT of impervious surface,the NDVI in vegetation growth period,the PLAND of emerging plants and LSI of woody.The CONNECT of water has the greatest impact on total phosphorus in Dianchi Lake,with a relative interpretation rate of 29.97%.Therefore,it is suggested that during the construction and reconstruction of the wetland water diversion system,attention should be paid to reducing the connectivity of the water area,reducing the flow velocity of the internal water body of the wetland,and minimizing the effect of reducing the phosphorus retention by the wetland due to the increase in water connectivity. |
PDF Full Text Request