Wangshou Zhang

Wangshou Zhang

Watershed management, water pollution, non-point source pollution, watershed ecology at the Nanjing Institute of Geography & Limnology, CAS.

Nitrogen Transport and Retention in a Headwater Catchment with Dense Distributions of Lowland Ponds

The existence of lowland ponds potentially alter watershed nitrogen (N) process via combined changes in runoff and N processing potential, which can significantly buffer watershed N transport. Here, we adopted the conceptual framework of the SPAtially Referenced Regressions On Watershed attributes (SPARROW) model to describe N transport and to explore the buffering roles of lowland ponds in a small headwater watershed of Taihu Lake Basin, China. Our model included variables for nutrient sources, riverine length, precipitation and pond density, and explained 95% of the spatio-temporal variability in total N loads. Model results indicated that the northern parts of this watershed were the hotspot regions, which contributed relative large N yields. While their contributions exhibited high temporal variations, they usually depend upon local precipitation rates. The model results also revealed the processes of landscape N retention. On average, approximately 87% of terrestrial N inputs were removed or retained via denitrification, plant uptake, soil storage and other processes during land-to-water delivery, with 12% removed by lowland ponds and the remaining 75% associated with forestland and other landscapes. By contrast, in-stream retention processes only removed 3% of the total terrestrial N inputs. In the future, riverine N pollution may be further exacerbated by intensified human activities, especially as climate change is expected to enhance extreme rainfall conditions. An integrated N management strategy, which appropriately considers the buffering roles of lowland ponds and other landscapes, is required to optimize N management and protect precious headwater resources.

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