基于核示踪的深圳市农用土壤侵蚀特征及评价

运用137Cs和210Pb_ex联合示踪技术,考察深圳特区内外典型区域137Cs和210Pb_ex面积活度的背景值与变化特征,以及典型区农用土壤侵蚀速率、分布特征和主要影响因素. 结果表明:①在城市化剧烈的人为扰动作用下,深圳市的地表土壤环境已经大部分不具备自然土壤的基本属性. 深圳市137Cs面积活度背景值介于99~653Bq/m2之间,仙湖植物园的137Cs实测面积活度背景值最大〔为(653±81)Bq/m2〕,南澳新大村的137Cs实测面积活度背景值最小〔为(99±47)Bq/m2〕. ②随着海拔升高,210Pb_ex的实测面积活度背景值呈增加趋势,这和低纬度地区亚热带海洋性季风气候的水汽运动有关. ③深圳市南澳新大村和公明水库陡坡农用地种果造成的土壤侵蚀已达到了极剧烈的程度,土壤平均侵蚀速率分别高达6150和40530t/(km2·a). 深圳市农用土壤侵蚀具有分布面积广、人为扰动较剧烈、产流产沙集中、侵蚀强度较大等特征. 人为扰动主导的土地开发与陡坡种果是造成城市水土流失的主要影响因素. ④深圳市近30年来快速城市化活动加速了城市土壤侵蚀的发生和发展,亟待加强开发建设项目水土保持、陡坡还林还草等生态治理工作. 

Characterization and Evaluation of Agricultural Soil Erosion in Shenzhen City Using Environmental Radionuclides

Quantitative research on urban soil and water loss is limited because of the complexity of the process and the lack of data accumulation. Nuclear tracer technology is quantitative and has a high resolution, which provides a unique method for understanding the mechanism of urban soil and water loss. A combination of 137Cs and 210Pb_ex tracing was applied to determine the background inventory of 137Cs and 210Pb_ex value and characteristics, agricultural soil erosion rate, distribution, and main factors that influence soil erosion in Shenzhen City. The results indicated that:1) Disturbances from urbanization has greatly altered the natural properties of the surface soil in Shenzhen City. The background inventory of 137Cs in Shenzhen City ranged from 99to 653Bq/m2, being highest in Shenzhen City Fairy Lake Botanical Garden at (653±81) Bq/m2and lowest in XinDaat (99±47) Bq/m2. 2). The background inventory of 210Pb_ex cumulative sedimentation increased with increasing altitude, which is attributed to the amount of the movement of water vapor in the subtropical marine monsoon climate in low-latitude regions. 3) The steep sloped orchards farmland in NanAo and GongMing reservoir in Shenzhen City were seriously eroded, with average soil erosion rates as high as 6,0and 40,0t/(km2·a), respectively. The agricultural soil erosion in Shenzhen City has a wide distribution area and exacerbated by severe human disturbance, with relatively concentrated runoff and sediment and severe erosion intensity. Land development and steep orchard caused by human disturbance were the main factors that influence urban soil and water loss. 4) After nearly 30years of reform and opening-up policies in Shenzhen City, the rapid urbanization accelerated the urban soil erosion. Therefore, projects for soil and water conservation should be implemented, such as returning steep slopes into forests and grasslands, and other ecological management reforms.