Estimating net anthropogenic nitrogen inputs (NANI) in the Lake Dianchi basin of China

摘要

Net anthropogenic nitrogen inputs (NANI) with components of atmospheric Ndeposition, synthetic N fertilizer, agricultural N fixation and N in net foodand feed imports from 15 catchments in the Lake Dianchi basin were determinedover an 11-year period (2000–2010). The 15 catchments range in size from44 km2 to 316 km2 with an average of 175 km2. To reduceuncertainty from scale change methodology, results from data extraction byarea-weighting and land use-weighting methods were compared. Results showthat the methodology for extrapolating data from the county scale towatersheds has a great influence on NANI computation for catchments in theLake Dianchi basin, and that estimates of NANI between the two methods havean average difference of 30% on a catchment basis, while a smallerdifference (15%) was observed on the whole Lake Dianchi basin basis. Theriverine N export has a stronger linear relationship with NANI computed bythe land use-weighting method, which we believe is more reliable. Overall,nitrogen inputs assessed by the NANI approach for the Lake Dianchi basin are9900 kg N km?2 yr?1, ranging from 6600 to28 000 kg N km?2 yr?1 among the 15 catchments. Synthetic Nfertilizer is the largest component of NANI in most subwatersheds. Onaverage, riverine flux of nitrogen in catchments of the Lake Dianchi basinaverages 83% of NANI, far higher than generally observed in NorthAmerica and Europe. Saturated N sinks and a limited capacity fordenitrification in rivers may be responsible for this high percentage ofriverine N export. Overall, the NANI methodology should be applicable insmall watersheds when sufficiently detailed data are available to estimateits components.