[Multiple time-scale analysis of nitrogen retention characteristics and influencing factors in Shanmei Reservoir, Fujian, China.] / å±±ç¾Žæ°´åº“æ°®è¥å »ç›æ»žç•™ç‰¹å¾åŠå ¶å½±å“å› ç´ çš„å¤šæ—¶é—´å°ºåº¦åˆ†æž.

The retention effect of reservoir on nitrogen is an important influence factor on the eutrophication prevention and control. In order to reveal the differences of nitrogen retention characteristics and the influence factors at multiple timescales, an ecological dynamic model was developed in Shanmei Reservoir watershed. Based on the retention flux and retention rate calculation, the nitrogen retention effect was analyzed at three time scales of yearly, monthly and daily, respectively. Furthermore, multiple linear correlation analysis was conducted to analyze the influence of inflow runoff, ratio of inflow to outflow, residence time, velocity and temperature on the retention of nitrogen in the reservoir. The results showed that the process of nitrogen retention always displayed fluctuant characteristic at different time scales. On a yearly scale, the reservoir mainly played a role of nitrogen sink; on a monthly scale, seasonal variation of nitrogen retention and release effect made the reservoir as nitrogen sink in wet period and as nitrogen source in dry period; on a daily scale, the nitrogen retention process fluctuated intensely, with the retention rate ranging from -300% to 100% in dry year. At different time scales, ratio of inflow to outflow and velocity were always the important factors to affect nitrogen retention in the reservoir, with significant correlation coefficients consistently. With the time scale changing from yearly to monthly, daily, the influence degree of inflow runoff and temperature on nitrogen retention was gradually strengthened. The correlations between the residence time and retention rate could be positive or negative at different time scales.

[Multiple time scales analysis of spatial differentiation characteristics of non-point source nitrogen loss within watershed].

Identification of the critical source areas of non-point source pollution is an important means to control the non-point source pollution within the watershed. In order to further reveal the impact of multiple time scales on the spatial differentiation characteristics of non-point source nitrogen loss, a SWAT model of Shanmei Reservoir watershed was developed. Based on the simulation of total nitrogen (TN) loss intensity of all 38 subbasins, spatial distribution characteristics of nitrogen loss and critical source areas were analyzed at three time scales of yearly average, monthly average and rainstorms flood process, respectively. Furthermore, multiple linear correlation analysis was conducted to analyze the contribution of natural environment and anthropogenic disturbance on nitrogen loss. The results showed that there were significant spatial differences of TN loss in Shanmei Reservoir watershed at different time scales, and the spatial differentiation degree of nitrogen loss was in the order of monthly average > yearly average > rainstorms flood process. TN loss load mainly came from upland Taoxi subbasin, which was identified as the critical source area. At different time scales, land use types (such as farmland and forest) were always the dominant factor affecting the spatial distribution of nitrogen loss, while the effect of precipitation and runoff on the nitrogen loss was only taken in no fertilization month and several processes of storm flood at no fertilization date. This was mainly due to the significant spatial variation of land use and fertilization, as well as the low spatial variability of precipitation and runoff.

[Coupling SWAT and CE-QUAL-W2 models to simulate water quantity and quality in Shanmei Reservoir watershed].

A coupled watershed-reservoir modeling approach consisting of a watershed distributed model (SWAT) and a two-dimensional laterally averaged model (CE-QUAL-W2) was adopted for simulating the impact of non-point source pollution from upland watershed on water quality of Shanmei Reservoir. Using the daily serial output from Shanmei Reservoir watershed by SWAT as the input to Shanmei Reservoir by CE-QUAL-W2, the coupled modeling was calibrated for runoff and outputs of sediment and pollutant at watershed scale and for elevation, temperature, nitrate, ammonium and total nitrogen in Shanmei Reservoir. The results indicated that the simulated values agreed fairly well with the observed data, although the calculation precision of downstream model would be affected by the accumulative errors generated from the simulation of upland model. The SWAT and CE-QUAL-W2 coupled modeling could be used to assess the hydrodynamic and water quality process in complex watershed comprised of upland watershed and downstream reservoir, and might further provide scientific basis for positioning key pollution source area and controlling the reservoir eutrophication.