Water environmental planning and management at the watershed scale:A case study of Lake Qilu,China

Water environmental planning and management has become essential for guiding the water pollution control activities.Past water pollution control activities have been site specific,with little thought on water quality standard reaching at the watershed scale.Based on the watershed approach,a seven-step methodological framework for water environmental planning and management was developed.The framework was applied to water environmental planning and management of the Lake Qilu watershed in Yunnan Province,China.Results show that the reduction amount of total nitrogen(TN)under the plan is 1,205 tons per year so that the target of environmental capacity can be reached in 2020.Compared with traditional methods,the framework has its prevalence and could be generalized to analogous watersheds.

Spatial and Temporal Patterns of Soil Nitrogen Distribution under Different Land Uses in a Watershed in the Hilly Area of Purple Soil,China

Quantification of soil spatial and temporal variability at watershed scale is important in ecological modeling, precision agriculture, and natural resources management. The spatio-temporal variations of soil nitrogen under different land uses in a small watershed （12.10 km^2） in the hilly area of purple soil at the upper reaches of the Yangtze River in southwestern China were investigated by using conventional statistics, geostatistics, and a geographical information system in order to provide information for land management and control of environmental issues. A total of 552 soil samples （o to 15 cm） from 276 sites within the watershed were collected in April and August of 2o11, and analyzed for soil total nitrogen （STN） and nitrate nitrogen （NO3-N）. We compared spatial variations of STN and NO3-N under different land uses as well as the temporal variations in April （dry season） and August （rainy season）. Results showed that STN contents were deeply affected by land-use types; median STN values ranged from 0.94to 1.27g.kg-I, and STN contents decreased in the following order： paddy field 〉 foresfland 〉 sloping cropland. No significant difference was found for STN contents between April and August under the same land use. However, NO3- N contents were 23.26, 10.58, and 26.19 mg·kg^-1 in April, and 1.34, 8.51, and 3.00 mg·kg^-1 in August for the paddy field, sloping cropland and forestland, respectively. Nugget ratios for STN indicatedmoderate spatial dependence in the paddy field and sloping cropland, and a strong spatial dependence in forestland. The processes of nitrogen movement, transformation, absorption of plant were deeply influenced by land use types; as a result, great changes of soil nitrogen levels at spatial and temporal scales were demonstrated in the studied watershed.

CRITICAL PROCESSES AND MAJOR FACTORS THAT DRIVE NITROGEN TRANSPORT FROM FARMLAND TO SURFACE WATER BODIES

Agricultural non-point source pollution is increasingly an important issue affecting surface water quality.Currently,the majority of the studies on nitrogen loss have focused on the agricultural field scale,however,the response of surface water quality at the watershed scale into the nitrogen loss at the field scale is poorly understood.The present study systematically reviewed the critical processes and major factors that nitrogen transport from farm fields to surface water bodies.The critical processes of farmland nitrogen entering surface water bodies involve the processes of nitrogen transport from farmland to ditches and the transformation processes of nitrogen during migration in ditches/rivers.Nitrogen transport from farmland to ditches is one of the prerequisites and critical processes for farmland nitrogen transport to surface water bodies.The transformation of nitrogen forms in ditches/rivers is an intermediate process in the migration of nitrogen from farmland to surface water bodies.Nitrogen loss from farmland is related to soil storage and exogenous inputs.Therefore,nitrogen input management should not only consider the current input,but also the contribution of soil storage due to the historical surpluses.Ditches/rivers have a strong retention capacity for nitrogen,which will significantly affect the process of farmland nitrogen entering surface water bodies.The factors affecting nitrogen transformation in river/ditches can be placed in four categories:(1)factors affecting hydraulic retention time,(2)factors affecting contact area,(3)factors affecting biological activity,and(4)forms and amount of nitrogen loading to river/ditches.Ditch systems are more biologically(including plants and microbes)active than rivers with biological factors having a greater influence on nitrogen transformation.When developing pollution prevention and control strategies,ecological ditches can be constructed to increase biological activity and reduce the amount of surplus nitrogen entering the water body.The present research should be valuable for the evaluation of environment impacts of nitrogen loss and the non-point source pollution control.

A Model of Debris Flow Forecast Based on the Water-Soil Coupling Mechanism

Debris flow forecast is an important means of disaster mitigation. However, the accuracy of the statistics-based debris flow forecast is unsatisfied while the mechanism-based forecast is unavailable at the watershed scale because most of existing researches on the initiation mechanism of debris flow took a single slope as the main object. In order to solve this problem, this paper developed a model of debris flow forecast based on the water-soil coupling mechanism at the watershed scale. In this model, the runoff and the instable soil caused by the rainfall in a watershed is estimated by the distrib- uted hydrological model （GBHM） and an instable identification model of the unsaturated soil. Because the debris flow is a special fluid composed of soil and water and has a bigger density, the density esti- mated by the runoff and instable soil mass in a watershed under the action of a rainfall is employed as a key factor to identify the formation probability of debris flow in the forecast model. The Jiangjia Gulley, a typical debris flow valley with a several debris flow events each year, is selected as a case study watershed to test this forecast model of debris flow. According the observation data of Dongchuan Debris Flow Observation and Research Station, CAS located in Jiangjia Gulley, there were 4 debris flow events in 2006. The test results show that the accuracy of the model is satisfied.