| With the rapid development of industry and agriculture and the acceleration of urbanization,the water environment effect caused by land use/cover change has become one of the hot issues in this field.Therefore,on the basis of previous studies,I will analyze the changes in land use/cover and analysis of driving forces in the Tian'ezhou-Zhongzhouzi watershed.Based on the experimental results of the sediments of the oxbow lake in Tian'ezhou and Zhongzhouzi,the pollution degree was evaluated.And then the correlation analysis was used to analyze the relationship between land use/cover change of Tian'ezhou-Zhongzhouzi watershed and the potential ecological risk of heavy metal elements and the changes of nitrogen and phosphorus nutrient elements in the sediments.Conclusion as below:(1)From 1987 to 2017,the quantity of land use varied greatly in the area of the Tian'ezhou-Zhongzhouzi watershed.The water area,cultivated land and unutilized land tended to decrease,while the construction land for woodland and urban and rural areas tended to increase.However,the land use type structure of the Tian'ezhou-Zhongzhouzi watershed changed less.The cultivated land and water area were the main types of land use in the Tian'ezhou-Zhongzhouzi watershed.The proportion of forestland and urban construction land increased,but the proportion of the total land use area was still less than 14%,while the proportion of unused land and water area gradually decreased.The most rapid change of land use is woodland,followed by urban and rural construction land and water area,cultivated land and unutilized land vary less frequently.From 1992 to 1999,the comprehensive utilization of land use in the area of Tian'ezhou-Zhongzhouzi watershed has the highest dynamic degree of land use,and the least dynamic integrative land use in 2011-2017.The development of land use in this study area is at a moderate level,but due to natural disasters and other factors,the degree of land use in this study area fluctuates.Land use in 1999 was lower than in1992,and the change in land use level showed a decline,which was related to the increase of water area due to the outbreak of flood in 1999.The implementation of arable land policy and afforestation project will reduce the degree of land use again in2017.From the perspective of land use transfer,the area of cultivated land varies greatly,which mainly changes into urban and rural construction land and forestland,Land for forestry and construction of urban and rural areas are mainly converted into cultivated land,and the water area is mainly converted into water area,while unutilized land is mainly converted into water area and cultivated land.1987-2017 Tian'ezhou-Zhongzhouzi watershed Ecosystem Services Overall Value Increases-Declines.The ecological service value of cultivated land and water area accounts for a higher proportion.During the study period,in addition to the increase of ecological service value of forest land by RMB85 million,other types of land use showed a decrease in different scales.Among them,the decrease of ecological service value of water area is the largest,and the reduction of cultivated land and unutilized land is the least.(2)The drivers of land-use change include natural and humanistic driving forces,The natural driving forces that affect land use/cover change in the Tian'ezhou-Zhongzhouzi watershed are mainly climate change and natural disasters,Humanistic driving force mainly changes in the population,political and economic policies,industrial and agricultural development.The change of water area is closely related to the climate change and natural disasters under the local natural conditions.The change in arable land is driven by changes in the population of the area.The main reason for the change in forest area is the afforestation policies implemented locally.The change of urban and rural construction land and unused land area is closely related to the change of population and the rapid development of industry and agriculture.(3)The potential ecological risk of heavy metals from the bottom to the top of the oxbow lakes in Lake Tian'ezhou and Zhongniuzi Lake belongs to the medium level.However,the risk coefficient of Tian'ezhou Oxbow Lake is slightly higher than that of Zhongzhouzi Oxbow Lake.Oxbow Lake of Zhongzhouzi showed a rising-descending fluctuation trend.In 2012,oxbow Lake of Zhongzhouzi's comprehensive ecological risk of heavy metals has been reduced to a slight degree.The potential ecological risk of heavy metals synthesis in Tian'ezhou oxbow Lake fluctuated greatly,but the overall trend showed a downward trend.The order of the ecological risk of single heavy metals in Tian'ezhou and Zhongzhouzi are Pb>Cu> Ni> Cr> Zn.However the ecological risks of heavy metals Pb and Cu in Zhongzhouzi oxbow lake reached medium,The ecological risks of heavy metals Pb,Cu and Ni in Tian'ezhou Lake are moderate.The evaluation of the pollution degree of nitrogen and phosphorus content in thetwo oxbow lake sediments showed that the TN pollution level of oxbow lake in Tian'ezhou reached moderate and severe pollution.The pollution degree of TN in oxbow Lake of Zhongzhouzi has also reached serious pollution.The TP content of the oxbow lakes of Tian'ezhou and Zhongzhouzi belonged to heavy pollution,but the average TP evaluation index of the oxbow lakes of Tian'ezhou was slightly lower than that of Zhongzhouzi oxbow lakes.(4)After the reform and opening up,the economic and social development in this study area is swift and violent,the process of urbanization is accelerating.Although the rapid growth of urban and rural construction land has caused ecological environment coercion,a number of environmental protection policies implemented by the government effectively protect the local ecological environment,making the change of potential eco-risk level of oxbow Lake negatively correlated with the change of urban and rural construction land area.Plants have a repair effect on heavy metal contaminated soils.With the implementation of various afforestation projects,the area planted around oxbow Lake gradually increased,effectively reducing the heavy metal content entering the yoke lake with surface runoff.Therefore,the potential ecological risk coefficient of oxbow Lake in Zhongzhouzi was negative relationship.The forest land around oxbow Lake in Tian'ezhou is located between the Yangtze River and the lake,which is hard to play a role in the heavy metal pollution from the towns.Therefore,the correlation between the potential ecological risk of heavy metals in oxbow Lake and the change of forest area is weak.The unused land area in the study area showed a downward trend,with the reduced area mainly being converted into watersheds,cultivated lands and woodlands.There is a negative correlation between the potential ecological risk of forestland and heavy metals,so there is an indirect positive correlation between the change of unused land area and the potential ecological risk of heavy metals(5)The rapid growth of urban and rural construction land in the study area.And the waste water from domestic waste generated by activities such as laundry and cooking in the daily life of urban residents contain human waste and domestic waste.Which contains a large number of nitrogen and phosphorus compounds,making the day of Lake Penguin Tian'ezhou and Zhongzhouzi Lake TN,TP content continues to increase.Therefore,the ecological pollution of nutrient elements in the oxbow lake sediments is positively correlated with the change of urban and rural construction landarea in the study area.The unused land around Tian'ezhou and Zhongzhouzi oxbow Lake more into the water to become chickens and goose farms and aquaculture farms.Livestock excrement in the farm contains a lot of nitrogen,phosphorus,ammonia,which polluting water.Therefore,there is an indirect negative correlation between the change of unused land area and the degree of ecological pollution of nutrient element in oxbow Lake. |
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