The Effect Of Different Land Use Patterns On Epikarst Springs In Karst Mountains Area

Epikarst spring is the karst shallow groundwater system,which is in the epikarst zone.Its wide distribution is the important factor for people in southwest China karst mountainous area to gather and multiply.Becauce of its high location and convenient to use,it has important significance to the water supply for local people and animals.But the changes of surface vegetation-soil system,which influenced by differert land use patterns ,is impacting on the changes of epikarst springs directly,including the changes of water quanlity and water quality.This text is mainly about six epikarst springs under different land use patterns in Nanchuan area.It focuses on the changes of soils quality and its impact on the water quality of epikarst springs under different land use patterns by the way of analyzing typical soil and water samples.We select water samples every from November,2007 to Novermber,2008.Meanwhile,it studies on seasonal and diurnal variation of physic-chemistry of epikarst springs under tilled land and shrub land.The results show the following main conclusion:Firstly,it is the difference of soil physic-chemistry under different land use patterns.As following:Except Xiaowanlongdong peach forest area and Houguo rock desertification area,the soil bulk density of soil profile under other land uses increased with soil depth.The soil bulk density of soil profile had a good negative relation with soil percentage of pore.The organic matter in soil profile decreased with soil depth.And it was negatively related to the pH of soil profile.The total nitrogen and available nitrogen content of soil profile assembled in surface.The soil organic matter,total nitrogen and available nitrogen had good positive relations with each other. The orders of six land use patterns in soil total nitrogen and soil available nitrogen were the same.In summary,the order of soil total nitrogen and soil available nitrogen was that:tilled land>garden plot>forest land.It illustrates that soil nitrogen content was mainly influenced by hunman activity.And the soil nitrogen content was positively related to intensity of human activity.The soil had a high content of phosphorus,which varied unregularly with depth.Except Boshuwan shrub area,the soil phosphorus content of the other 5 land use patterns assembled in surface and decreased with depth.The soil organic matter,total phosphorus and available phosphorus had positive relations with each other.At last,the total potassium content of soil profile varied unregularly,while the available potassium almost decreased with depth.They had a general relation.Secendly,it is the difference of chemistry of epikarst springs under different land use patterns.As following:The type of Boshuwan epikarst spring is HCO₃-Ca type.At the same time,the type of other five epikarst springs is HCO₃·SO₄-Ca type.The water temperature of six epikarst springs had seasonal variation,which was influenced by air temperature.But the seanonal variation extent of epikarst springs was different.Except the pH of Houguo spring in March,the pH variation of other springs was almost the same.The pH of epikarst springs was higher in wet seanons than in dry seasons.In wet seasons,the pH of epikarst springs was between acid and neutral.In dry season,the pH of epikarst springs was between alkali and neutral.The conductivity of every epikarst spring varied unregularly.Every common ion had seasonal variation. HCO₃^- concentration changed littlely with time.Except Lanhuaguoguancezhan spring, HCO₃^- concentration of the other 5 springs decreased in winter. The NO₃^- concentration and SO₄^2- concentration increased with the coming of wet seasons. PO₄^3- concentration increased sharply,and it had two peak zone. One was in January,the other was in August. Cl^- concentration didn't varied obviously. F concentration varied unregularly with time. Six epikarst springs had a high concentration of NO₃^-,The NO₃^- concentration and SO₄^2- concentration of Houguo epikarst spring were high all the time.The order of Cl^- is that: tilled land > garden plot > forest land and paddy field > dry land. F^- concentration of six epikarst springs had little difference between each other.The concentration of Ca²⁺,Mg²⁺,Na⁺,K⁺ in six epikarst springs changed littlely with time.Fangqiu spring had a high concentration of Na⁺ and K⁺ throughoutly.Thirdly,it is the relation between physic-chemistry of soil and epikarst springs under different land use patterns.As following:The concentration of main ions in springs was positively related to soil bulk density, and it was negatively related to percentage of pore.Such as, SO₄^2- concentration had the most significant relations with soil bulk density and percentage pore. NO₃^- concentration and F concentration also had good relations with soil bulk density and percentage of pore.NO₃^- concentration in epikarst springs had a good positive relation with soil nitrogen. SO₄^2- concentration also had a evident positive relation with soil organic carbon. Organic matter,total phospharus and available phospharus all had a good relation with PO₄^3- concentration.Especial the relation between soil pH and PO₄^3- concentration is significant. K⁺ concentration was positively related to soil potassium,especial it was significantly related to soil total potassium.At last,it is the seasonal and diurnal variation of physic-chemistry of epikarst springs under different land use patterns.As following:The pH,water temperature and conductivity of Boshuwan spring and Lanhuaguoguancezhan spring had good seasonal variation.But their variation extent was different in two springs.The pH of Boshuwan spring was higher than Lanhuaguoguancezhan's.In addition,the conductivity of Lanhuaguoguancezhan spring was higher than Boshuwan's.The Ca²⁺ concentration and HCO₃^- concentration of two springs had a good positive correlation with the conductivity of the springs.As a result ,we can find Ca ⁺ concentration and HCO₃^- concentration of two springs almost had the same seasonal variation with the conductivity,and their peak zone laged behind wet seasons'ending.(When wet season ends, Ca²⁺ concentration and HCO₃^- concentration of two springs are still rising.)In a normal day with no rainfall,water temperature was influenced by air temperation.But water temperature's peak zone of Boshuwan spring laged behind air temperature for about 2 hours. The pH and conductivity of Lanhuagouguancezhan spring varied unregularly. Although the pH and water temperature of Boshuwan spring almost had the same variation and they also had a good correlation with each other.The conductivity of it varied unregularly.During flood pulse,there were two effects influencing these two epikarst springs:dilution effect and water-rock-air effect.Lanhuaguoguancezhan spring was mainly influenced by dilution effect,while Boshuwan spring was mainly influenced by water-rock-air effect.