Nutrient budgets and biogeochemistry in an experimental agricultural watershed in Southeastern China

Abstract

Abstract. During a two-year field study, an annual nutrient budget and cycles were developed for a small agricultural watershed. The study emphasized the integrated unit of the watershed in understanding the biogeochemistry. It was found that the total nutrient input was 39.1 x 104 kg nitrogen and 3.91 x 104 kg phosphorus in the year 1995, of which the greatest input of nutrients to the watershed was chemical fertilizer application, reaching 34.7 x 104 kg (676 kg/ha) nitrogen and 3.88 x 104 kg (76 kg/ha) phosphorus. The total nutrient output from the watershed was 13.55 x 104 kg nitrogen and 0.40 x 104 kg phosphorus, while the largest output of nitrogen was denitrification, accounting for 44.1% of N output; the largest output of phosphorus was sale of crops, accounting for 99.4% of P output. The results show that the nutrient input is larger than output, demonstrating that there is nutrient surplus within the watershed, a surplus which may become a potential source of nonpoint pollution to area waters. The research showed that both denitrification and volatilization of nitrogen are key ways of nitrogen loss from the watershed. This suggests that careful management of fertilizer application will be important for the sustainable development of agriculture.The research demonstrated that a multipond system within the watershed had high retention rate for both water and nutrients, benefiting the water, nutrient and sediment recycling in the terrestrial ecosystem and helping to reduce agricultural nonpoint pollution at its source. Therefore, this unique watershed system should be recommended due to its great potential relevance for sustainable agricultural development.

Surface Water Quality Assessment of Wular Lake, A Ramsar Site in Kashmir Himalaya, Using Discriminant Analysis and WQI

“…The sites located close to rural residential area showed higher mean total-N concentration mainly in summer season. It has been reported that N fertilizer applied to farmland is the main source of N pollution in surface water [71,72]. The distribution of ortho-P showed significant variation with average higher values (0.04 ± 0.002) in winter contrary to average lower values (0.02 ± 0.001) in summer season.…”

Nutrient budgets for large Chinese estuaries

“…is nutrients sink and/or source within the system. This is due to the application of inorganic N fertilizer (ammonium bicarbonate) in the drainage basins and wastewater discharge (Cao et al, 2005;Sheldrick et al, 2003;Yan et al, 1999;Millennium Ecosystem Assessment, 2005). Phosphate concentrations in 13 rivers are at the pristine level (0.5 µM) and in 5 rivers are at average level (3 µM) compared to the global river data .…”

Dissolved silicate retention and transport in cascade reservoirs in Karst area, Southwest China

“…However, in the last few decades, human activities have caused enormous changes both in the nature and quantity of nutrient fluxes to oceans , of which the rapid increases of phosphate and nitrate inputs was well documented (Meybeck 1998;Yan et al, 1999;Liu et al, 2003;Yan et al, 2003;Biggs et al, 2004;Gächter et al, 2004;Duan et al, 2007), but the fluvial flux of DSi was found continuously decreasing in rivers worldwide (Justić et al, 1995;Conley et al, 2000;Humborg et al, 2000;Vörösmarty and Sahagian, 2000;Paul, 2003;Vörösmarty et al, 2003;Neal et al, 2005;Humborg et al, 2006;Duan et al, 2007;Li et al, 2007;Koszelnik and Tomaszek 2007;Roubeix et al, 2007).…”