Abstract:

Land Use and Cover Change (LUCC) have become the focus of global environmental changes research in 21st century. LUCC caused variations of geographical processes and surface landscape structures, greatly impacting on nutrient biogeochemical cycles and material transport, and produced a series of water environmental and ecological problems. Surface water and soil issues caused by LUCC in intensified agricultural area have attracted the attention of researchers from home and abroad. Agricultural land changes refer to changes of agricultural land use patterns, intensity and types, such as returning cropland to forest/grassland or lakes, abandoned cultivation, changing cultivated land to construction land, farming intensities variation, etc. Taihu region of Jiangsu Province is an important commodity grain base and one of the most intensified land use area in China. During the past 60 years, great changes have taken place in farming systems in the Taihu region under human pressure. Surface water and soil environment in this region deteriorated simultaneously. Based on the method of historical documents investigation, the authors analyzed the characteristics of farming systems and explored the impacts of farming systems changes on surface soil and water environment in Taihu region of Jiangsu Province over past 60 years. It shows that planting area of food crops, such as rice, wheat and corn, decreased annually, while that of economic crops changed relatively stably. Crops depleting soil fertility, such as vegetables, increased, while those improving soil fertility, such as green manure crops, decreased significantly. This led to excessive dependence on chemical fertilizer application. After a long period of screening, crop varieties experienced continuous selections and renewal. Fertilizer types and fertilization intensity changed a lot over past 60 years. The traditional method of manure collection and application was taken place by the application of chemical fertilizer gradually. The ratio of N, P and K in chemical fertilizer was imbalanced for a long time, and it gradually tended to be balanced in recent years. Excessive chemical fertilizer application increased the risks of soil N loss to surface water environment. While since 2000, the decrease of chemical N fertilizer application did not alleviate N pollution in rivers and Lake Tai at the Taihu region, which indicated that impacting factors of surface water environment has changed. Besides agricultural N loss, there are many other sources, such as urban and rural domestic wastewater discharge, rural human and animal waste, industrial wastewater discharge and feed input in aquaculture industry. To reveal quantitatively the contributions of different pollutant sources in lakes, great efforts must be done to monitoring and modeling different pollutant sources comprehensively