Interannual Change Of Suaeda Heteroptera In The Wetland Of Liaohe Estuary And Correlation Study Of Its Influencing Factors

Suaeda heteroptera is an extremely crucial ecological resource in the wetland area,which plays a key role in regulating climate,strengthening flood control and drought resistance,controlling pollution,improving wetland environment,and increasing tourism income.Since1997,there have been two cases that the area of Suaeda heteroptera greatly attenuated in Panjin.The large-scale death of Suaeda heteroptera has a serious impact on the function of wetland and the value of ecotourism in Liaohe estuary.It is of far-reaching significance to carry out study on the interannual changes and influencing factors of Suaeda heteroptera in improving environment of Liao River estuary,and achieving ecological and economic sustainable development.Taken the Liaohe estuary in Panjin as the research area,by using Landsat5,Landsat7 and Landsat8 satellite remote sensing data of long-term sequence and based on the normalized ratio index and the spectral features analysis of typical ground features,decision tree classification model of Liaohe estuary was constructed to classify the targets and extract the information of the Suaeda heteroptera.The spatial-temporal distribution thematic maps of the Suaeda heteroptera from 1997 to 2016 are derived from the geographical information system(GIS)database,and the annual growth area of the Suaeda heteroptera are counted.Meteorological parameters(temperature,precipitation and sunshine hours),hydrological data(runoff volume),environmental data(chemical oxygen demand,ammonia nitrogen,petroleum,etc.)and human activity data are collected.The interannual,seasonal,and monthly changes in climate,hydrology,water quality,and other parameters were analyzed by using linear analysis and anomaly analysis.Statistical correlation coefficient analysis was used to reveal the relationship between meteorology,hydrology,and the environment with the growth area of Suaeda heteroptera.Finally,according to the analysis results,the protection measures and suggestions are provided for the planting and restoration of Suaeda heteroptera.The main conclusions of this paper are as follows:(1)It is found that the single-band threshold method is difficult to distinguish the various types of objects in the study area by analyzing the spectrum of typical objects.The feature classification work of Liaohe estuary wetland can be well completed by the decision tree model based on the difference between normalized spectral features and remote sensing normalized index.(2)From 1997 to 2016,the overall characteristics of the area variation of Suaeda heteroptera in Liaohe estuary wetland are as follows:small-scale volatility phase(1997~2000),extensive death phase(2000~2004),steady increase phase(2005~2014),and sharp decrease phase(2015~2016),the area of Suaeda heteroptera was biggest with 24.15 km~2 in 2014.In 2002,the area of Suaeda heteroptera was smallest with 2.29 km~2.(3)From 1997 to 2016,Panjin's annual average temperature and annual precipitation both showed an upward trend,the climatic tendency rates were 0.141°C/10a and 22.7mm/10a,respectively.The annual sunshine hours showed a downward trend,and the climate trend rate was-190h/10a.The correlation between climate and Suaeda heteroptera area was analyzed by using partial correlation analysis.It was found that climatic factors were not the important factors affecting the growth area of Suaeda heteroptera.(4)There is a certain overlap between the death cycle of Suaeda heteroptera and the dry year of Liaohe River.The vegetation area of Suaeda heteroptera in high flow year is larger than that in dry year.The correlation between runoff from April to June and Suaeda heteroptera area was the highest,the correlation coefficient was 0.899,and the correlation was significant at 0.01level(both sides),it can be seen that the runoff of Liaohe River is one of the main factors affecting the growth area of Suaeda heteroptera.(5)There is a negative correlation between water pollution and the growth area of Suaeda heteroptera.Among the water quality parameters,chemical oxygen demand(COD)had the highest correlation with the vegetation area of Suaeda heteroptera.The correlation coefficient was-0.71,which was significantly correlated at the 0.01 level(both sides).It can be seen that there is a great correlation between the pollution of water body and the growth area of Suaeda heteroptera in wetland area.(6)Human engineering construction and agricultural development are one of the main factors affecting the growth area of Suaeda heteroptera.Water conservancy facilities such as delta plain reservoir,embankments along the sea,and anti-tidal gates cut off the water circulation between land and sea at tidal creeks and changed the hydrodynamic conditions and affected the growth and distribution of vegetation.The development of farmland and aquaculture area directly takes up the growth space of Suaeda heteroptera,resulting in a reduction in the vegetation area of Suaeda heteroptera.