Impacts Of Wetland Landscape Pattern Changes On Water Quality Purification Services And Regional Human Well-being In The Three Rivers Basin North Of Erhai Lake

Landscape is the basic spatial unit and the smallest scale for studying humanenvironment interactions and maintaining sustainability.Landscape sustainability has become an important concern for sustainability science and landscape ecology.As a typical social-ecological system,understanding the mechanism of interaction between landscape patterns,service characteristics and human well-being,and the scale effect of their coupling and coordinating is a key issue to achieve sustainable development.The study area of the paper is the Miju river,Luoshi river,and Yong’an river basin(the three rivers basin north of Erhai Lake)in the upper reaches of Erhai Lake,where water quality is of great concern.Using the spatial distribution maps of wetland landscapes in 2017 and 2021 as data sources,and collecting total phosphorus(TP)and total nitrogen(TN)from 57 surface water samples,to analyze the wetland landscape patterns changes and water quality purification service spatial differences at two scales of basins and sub-basins.Compiling socio-economic yearbook data from 63 administrative villages in the basin,and selecting 11 indicators to assess changes in human well-being.Finally,using Spearman correlation analysis and coupled coordination model to analyze the cascade relationship between wetland landscape,water purification services,and human well-being.The results are as follows.Wetland landscape pattern changes.At basin scale,the total area of wetland landscapes decreased from 18,085.02 ha to 16,372.22 ha(-9.47 %),with paddy fields being the most reduced type(-18.23 %),which were not only converted into natural wetlands or other ecological ditches and wastewater treatment sites for water purification purposes,but also 2,204.24 ha were completely transformed into nonwetland landscapes.At the sub-basin scale,the distribution of wetland landscapes is uneven,with 71.90 % in the Miju river basin,13.92 % in the Luoshi river basin and14.16 % in the Yong’an river basin,and the paddy fields in all three basins are decreasing,with the percentage decreasing by 6.63 %,13.79 % and 10.21 %respectively.The patch pattern index of the basin shows that wetlands are better integrated,with larger patches in paddy fields,smaller patches in ponds,and the most complex shapes in rivers;the type pattern index shows a decline in the number and area of patches in paddy fields and a faster increase in the number and area of patches in wastewater treatment sites and ecological ditches;the landscape pattern index shows that the diversity of wetland landscapes is recovering,with an increase in the number of patches and a more concentrated spatial distribution.Wetland landscape water quality purification services.The water quality of the river is improving,with fewer months below Class V,but there is a large spatial and temporal variation,with Luoshi river being the worst and Miju river being the best,and the dry season being better than the rainy season.At basin scale,TP concentrations in surface water ranged from 0.016-0.180 mg/L,with low concentrations and little spatial variation;TN concentrations ranged from 0.356-1.996 mg/L,with large spatial variation.At sub-basin scale,the TP concentration of surface water was 0.012-0.396mg/L and TN concentration was 0.413-4.370 mg/L,both with large spatial variation.The average TP and TN concentrations of wetland types show that natural wetlands are low artificial wetlands are high,and the average TN concentration of paddy fields(1.676 mg/L)is higher than other wetland types.From water purification services: TP removal rate of catchment units at watershed scale sampling sites ranged from 2.19 %to 58.33 %,TN removal rate from 0.09 % to 49.92 %;TP removal rate of wetland patches at sub-basin scale ranged from 25.41 % to 72.59 %,TN removal rate from6.22 %-56.29 %.Regional human well-being.From the time change of each indicator,the arable land area,per capita arable land area,grain sown area,rural economic income and per capita income of farmers increased,while the total grain production,per capita grain production,pig stock,the number of large livestock and the number of good breed and improved dairy cattle decreased.The comprehensive human well-being level decreased from 0.2489(0.0982-0.7202)to 0.2208(0.0746-0.7715),a serious polarization,whereby the human well-being level increased in 24 villages and decreased in 39 villages.The distribution shows a significant spatial heterogeneity in the human wellbeing levels of villages: the arable land area increases more in the villages upstream of the water system and decreases more in the villages downstream;the high value areas of rural economic income and net per capita income of farmers show a tendency to spread outward;and the livestock population decreases significantly throughout the watershed.Wetland landscape pattern changes,water quality purification services,and human well-being relationships.In terms of pattern and service relationships,the water quality purification services of wetland patches are easily influenced by area,shape,and other landscape types around them.At the basin scale,smaller wetland patches can better perform water quality purification services as their number increases.From the coupling coordination degree of the three cascades,the coupling coordination degree of pattern and well-being is 0.18-0.78,the coupling coordination degree of service and well-being is 0.32-0.88,and the coupling coordination degree of the three is 0.27-0.77,which is barely coordinated overall.By coordinating upstream and downstream of the basin,restructuring crop cultivation,and developing a new model of sustainable development of artificial wetlands that "feeds wetness with wetness",the sustainable wetland landscape of the basin can be realized.