Study On The Change Of Soil Quality And Its Influence On Water Quality In Small Karst Basin

Because of the ecological vulnerability in Karst area in southwest China,the strong agricultural activities have led to forest reduction,vegetation coverage declination,and which have further caused soil quality degeneration and water quality deterioration.As natural soil changed to agricultural soil,the vegetation types and coverage changes,which will lead to the change in chemical,physical and biological properties of soil.As a result,soil erosion will be strengthened.Not only water loss and soil erosion will cause soil fertility degeneration,but also cause agricultural non-point pollution occurring.In this research, we combined vegetation,soil and water to be a united system to study the effects of soil quality change on water quality variation as vegetation changes in small karst basin,and to clarify the main factors in the influence of water quality.This study may be important in water resource protection,ecology and environment recovering,security monitoring in ecology and environment,and the sustainable utilization of natural resources and so on.In this study,we took the small basins in three counties,GuanLing,PuDing and LiBo,which are situated in the upper reaches of Yangzi and ZhuJian River,as the study area;and we selected three typical degeneration forest sample land and three typical agricultural utilization models as the study objects.Through analyzing soil samples,surface runoff water and shallow groundwater,some important results were obtianed.1.There is obviously the increase soil density,the decrease pore size and increase quantity of clay of soil, the decrease the organic matter,decrease the quantity of nitrogen and phosphorus,the CEC of soil,and decrease urease activity and soil quality,when the reduction of forestry community in the CC drainage area,.The correlation and main contents analysis show that urease and phosphatase can be used as the assessment indicators for the soil quality.The change of soil quality is divided into two levels.For the first type,has following character:the soil capacity,organic matter,acid,nitrogen,phosphorus and physical loam was 1.132g.cm^-3,＞100 g.kg^-1,acid＞40 g.kg^-1,＞400 mg.kg^-1,＞6 mg.kg^-1,＜60%,respectively.Soil with well-structured and strong fertility ability has better quality and its corresponding surface vegetation, which belong to forest ecological system.For the second type,the soil capacity,organic matter,acid, nitrogen,phosphorus and physical loam was 1.17～1.275g.cm^-3,50～86 g.kg^-1,16.03～29.65 g.kg^-1, 212.5～371.5 mg.kg^-1,3.7～4.8 mg.kg^-1,＞67%,respectively.Soil with bad structure and low fertility ability has shrub and shrub-grassplot.2.There were three type of agricultural areas in small karst basin,such as low index of planting crops with corn-dominance dry-farming areas,high index of planting crops with corn/rape/tobacco dry-farming areas,and mixture index of planting crops with corn/rape/tobacco/rice/vegetable dry-farming areas.The order of the total nitrogen,available nitrogen,the available phosphorus,the available potassium,and microbial activity of soil was followed by the order of lower, higher,and mixture index of planting crops.These resulted from human activity such as fertilizing and plantin.There exists significant difference between the areas of low index of planting crops,the areas of high index of planting crops and the complex agriculture areas of high index of planting crops.The analysis shows that the soil density,soil respiration,proteinase and phosphatase can be used as the assessment indicators for the fertility quality of lime soil in the agricultural areas in small karst basin.The quality of soil is classifying into three ranks:the first type mainly includes mixture of agricultural areas of high index of planting crops and the soil in dry-farming areas of high index of planting crops,which have high content of nitrogen and phosphorus,strong fertility capability and high organic quality;the second type mainly includes dry-farming areas of high index of planting crops and the soil in dry-farming areas of low index of planting crops,which have high content of nitrogen and phosphorus,better viscosity of soil quality and common organic quality;the third type mainly includes dry-farming areas of low index of planting crops and the soil in dry-farming areas of high index of planting crops,which have low organic content,low content of nitrogen and phosphorus,inferior soil quality that causes big gradient and easy loss of water and soil.3.The chemical composition of shallow groundwater changes with the forests community declination, The contents of NO₃^-,NH₄⁺,PO₄^3-,SO₄^2-and the permanganate index increase followed this order.And the content of PO₄^3-and the permanganate index among shrub-grassplot ecological system,forest ecological system,and shrub ecological system were markedly different or on a significant different. Correlation and Path Analysis reveal that the contents of NO₃^-,PO₄^3-,NH₄⁺ and the permanganate index, to some extent,are influenced by the changes of vegetation and the soil quality.The contents of ammonium, nitrate,P and K are different in the runoff of the three vegetation areas,which was influence with change the growing seasons.Tweleve indexes was shosed to evaluate water quality,the ground runoffs in the forest ecological system and part of shrub ecological system,shrub-grassplot ecological system and part of shrub ecological system was analyzed by Cluster Analysis.With decalination of the forest community,the chemical composition of shallow groundwater change.Related and Path Analysis reveal that the contents of NO₃^-,PO₄^3-,NH₄⁺ and the permanganate index are increased,but the changes of different types of soil are not obvious.Related analysis and Path Analysis reveal that the contents of NO₃^-,PO₄^3-,NH₄⁺ and the permanganate index are influenced by the soil quality.12 indexes(except Cl^-)was chose to evaluate water quality,results from the Cluster Analysis is classified as follows:groundwater in forest ecological system;groundwater in shrub-grassplot ecological system,part of shrub ecological system and forest ecological system;and ground water in shrub-grassplot ecological system and part of shrub ecological system.The water qualities are different among different types,but not obvious.4.The chemical composition of shallow groundwater is obviously different in the three agriculture ecological system.The contents of NO₃^-,NH₄⁺,PO₄^3-,SO₄^2-and the permanganate index significantly increase followed the order of the lower index of planting crops area,the higher index of planting crops area to higher index of complex planting crops area.The contents of Ca²⁺and K⁺ are gradually increased.And the differences are quite obvious among lower index of planting crops area, the higher index of planting crops area and higher index of complex planting crops area.The contents of NO₃^-,NH₄⁺,PO₄^3-and SO₄^2-in the runoff are obviously higher in the arable land than those in the non-arable land.This raises the potential influence on the quality of water environment.The analysis reveals that the contents of NO₃^-,NH₄⁺,PO₄^3-,SO₄^2-and the permanganate index in the arable land are influenced by the organic matter,the contents of N and P of soil,and changes of vegetation.But for the non-arable land,the contents of NO₃^-,NH₄⁺,PO₄^3-,SO₄^2-and the permanganate index in the runoff are complicatedly influenced by soil quality.With the growing seasons change,the contents of N,P and K change obviously and the contents are different in the ground runoffs of the pepper land and the corn land.12 indexes was chose to evaluate water quality,with the reference to the ground water quality standard,the author will adopt the method of the Cluster Analysis to analyze these three kinds of lands and evaluate the water quality as follows:the first type,e.g.dry farming area with lower index of planting,the index reaches I water standard,this is the excellent water quality.The second type is mainly the dry farming area with higher index of complex planting and some complex agriculture area.The content of NH₄⁺,PO₄^3-reach the standard ofâ…¡-â…¢water quality partly.And the permanganate index reaches the standard ofâ… -â…¡water quality,the water is influenced to some extent. The third type is the complex agriculture area with higher index of planting.The contents of NH₄⁺,NO₃^- excess the ground water standard ofâ…¢partly,PO₄^3-reaches the standard ofâ…¡-â…¢partly,the permanganate index reaches the standard ofâ… -â…¡water quality,the quality of runoffs reaches the standard ofâ…¡-â…¢,part of the indexes excess theâ…¢water quality standard.,and the water is influenced by pollution.5,The chemical composition of shallow groundwater is distinctly varied in different farming regions.The order of the increased permanganate index and the content of SO₄^2-,NO₃^-,NH₄⁺,PO₄^3- in shallow groundwater were followed the order of dry faring areas of lower index with planting crops,complex agriculture areas with higher index planting crops.Compared with non-agriculture land,the content of NO₃^-,NH₄⁺,PO₄^3-及SO₄^2-in farmland with shallow groundwater is high,and the content of nitrogen and phosphorus is higher in higher complex index planting crops farming areas.The analysis shows that the content of NO₃^-,NH₄⁺,PO₄^3-and the permanganate index are influenced by the quality of land to some extent.It is found from doing factor analysis(principal factor analysis "PFA") of 13 water chemistry components that the first principal factor is mainly decided by pH,EC,SO₄^2-,NO₃^-,PO₄^3-,Ca²⁺,Mg²⁺and Na⁺,the second principal factor is mainly decided by HCO₃^-,the index of potassium permanganate and NH₄⁺;The third principal factor is chiefly decided by K⁺,only Cl^- hardly has influence on shallow groundwater.Making the above 12 index with obvious change as evaluating indicator(except Cl^-),the shallow groundwater is divided into 3 degrees.Evaluate 3 sample lands by referring to the groundwater quality standard and choosing main factor such as nitrogen and phosphorus,the first type is chiefly composed of lower planting crops dry areas groundwater,the content of NO₃^- partly reaches the standard ofⅡ～Ⅲgroundwater,the potassium permanganate index is partly above the standard ofâ…¡groundwater,NH₄⁺ is partly above the standard ofâ…¡groundwater(and this type of shallow groundwater is influenced);the second type is mainly constituted by groundwater in higher planting crops dry agriculture areas,the content of NO₃^- reaches the standard ofâ…¡-â…¢groundwater,the permanganate index is partly above the stand ard ofâ…¡groundwater,NH₄⁺ is partly above standard ofâ…¡groundwater(and this type of shallow groundwater is influenced);the third type is mainly made up of groundwater in complex agriculture areas,the content of NO₃^- is partly above the standard ofâ…¢groundwater,the permanganate index reaches the standard ofâ…¡-â…¢groundwater,NH₄⁺ is also partly above the standard ofâ…¡groundwater,the quality of this type is obvious polluted.6,The forest declination in Karst areas results in the declination of land quality,which influence the quality of water.After the land is used for agriculture purpose,with some agronomy measures as fertilization directly results in the changes of land quality.The special double hydrographic structures in Karst make the aquatic environment quality are easily influenced by some environmental factors such as land quality,especially the shallow groundwater is more likely prone to be polluted.Therefore,it is necessary to search for effective agricultural management approaches to control the agricultural non-point pollution which the Karst regions had on aquatic environmental quality.