Search

The spatial dynamics of phosphorus and suspended solids were investigated for two years in a 1.8 km agricultural headwater stream, located by Chaohu Lake, southeastern China. The stream form was greatly modified by human activities. The stream could be divided into 4 channelized reaches (1.3 km), a pond reach (0.15 km) and 3 estuary reaches (0.36 km). It was found that the retention of total phosphorus (TP), phosphate and total suspended solids (TSS) predominantly occurred in the pond reach and estuary reaches. TP, phosphate and TSS retained in the pond and estuary reaches accounted for more than 50% of those retained in whole stream. The retention mostly happened in the precipitation-runoff events and it was 10 to 27 times than that in baseflow. The results showed that channelized reaches were the most important source for pollutant release under either runoff or baseflow conditions, and it accounted for more than 90% of whole stream release. There was a high spatial variation of nutrient dynamics in different channelized reaches. The channelized reach directly discharging into the pond did always retain nutrients and TSS under base flow and runoff, whereas the other channelized reaches performed differently in different hydrological conditions. Stream forms, hydrological conditions, and nutrients characteristics controlled the high spatial variation of the nutrients and TSS in the stream, while the human practices would accelerate these spatial patterns.

A field study was conducted to determine the effect of landscape spatial pattern and micro-topography on nutrient transfer via runoff from two catchments into Yuqiao Reservoir in north China. The surface runoff discharge was measured during rainfall events and water samples were analyzed in 2004 and 2005. The mean annual total nitrogen (TN) and total phosphorus (TP) exports per unit area from Caogezhuang catchment (C catchment) were 1.048 and 0.561 kg ha−1 year−1, respectively, while the TN and TP exports from Taohuasi catchment (T catchment) were 0.158 and 0.027 kg ha−1 year−1. In both catchments, village and vineyard shared the highest nutrient export ability due to the accumulated animal waste and heavy application of fertilizer and manure. In T catchment, the distance of village and vineyard was about 1,500 m away from the receiving water and in between were woodland and cropland. In the hydrological pathway, there were sink landscape structures of small stone dams, roadside swale, vegetated filter strip and dry ponds, which could detain water and nutrients. In C catchment, the distance between the village and the receiving water was about 200 m, and the hydrological pathway was compacted roads and ditches with no sink structures. It is suggested that the distance between the pollution source area and the receiving water and the micro-topographical features were the main factors to control the great difference in nutrient export rates. [ABSTRACT FROM AUTHOR]

Spatio-temporal distribution of nitrogen was examined along the gradient from open water to lakeshore in Lake Taihu, China. Two types of undulating littoral zones were selected: natural reed belt and bare lakeshore. The reed belt affected nitrogen transformation and was sink for internal-lake nitrogen, whereas the bare lakeshore showed little effect. During the growing season, NO-N concentration increased by up to 3–5 times from open water to reed belt, while NH-N concentration decreased. It suggested that nitrification was the main nitrogen process in reed belt. Total dissolved nitrogen (TDN) showed little spatial variation, indicating that most of nitrogen released from sediment did not move into open water again. Significant temporal variation of dissolved nitrogen occurred and was similar in both the littoral zone and the open water. Maximum TDN and NH-N concentrations occurred in January, and NO-N in March. Minimum NH-N and NO-N concentrations occurred in July and August, respectively. An increasing total soil nitrogen was found in the surface sediments from reed belt to open water. This further suggested that the reed-covered littoral zone had strong nitrogen transformation potential. [ABSTRACT FROM AUTHOR]