Spatial-temporal variation of dissolved N2 and denitrification in an agricultural river network, southeast China

Modeling increased riverine nitrogen export: Source tracking and integrated watershed-coast management

“…Long water residence time may facilitate N removal capacity through denitrification while denitrification effectiveness may decline in hyper-N rich rivers (Chen et al, 2014;Mulholland et al, 2008;Seitzinger et al, 2006;Seitzinger et al, 2002). Direct measurement of excess dissolved N 2 (ΔN 2 , denitrification product) and estimation of area-weighted N 2 emission flux in the Jiulong River network during 2010-2011 suggest that gaseous N removal accounts for 25% (North River) and 21% (West River) of riverine N export (Chen et al, 2014). However, considering the short water residence time and shallow water depth compared to larger rivers, we set L N to 0.25 in the North River and 0.…”

“…Although sewage and industrial wastewater have been partly treated in Longyan and Zhangzhou since the early 2000s, mainly for reduction of chemical oxygen demand (COD), the amount of nutrient discharged to waterbodies has continued to increase (Chen et al, 2013). In addition to sewage treatment plants, dense residential housing is usually built along the river, resulting in the direct discharge of a large quantity of wastes and an increase in ammonium concentration (Chen et al, 2014).…”

“…Deep water, lower oxygen and sediment together cause more anaerobic sediment and hence denitrification in dam reservoirs (Seitzinger et al, 2006;Trimmer et al, 2012). The North River has more artificial reservoirs with a larger storage capacity compared with the West River, contributing to a higher gaseous N removal through denitrification (Chen et al, 2014). Given the minor capacity of reservoirs relative to total river discharge, the retention fractions by reservoirs (D N ) in both rivers are relatively small (b 0.01).…”

Riverine N2O production, emissions and export from a region dominated by agriculture in Southeast Asia (Jiulong River)

“…The Jiulong River consists of two major tributaries (North River and West River) and the total discharge is 12.4 Â 10 9 m 3 y À1 , of which the North River accounts for approximately two-thirds. Riverine N is mainly from agricultural sources, but differs between the West River and North River (Chen et al, , 2014b. Livestock are widespread in the upper North River (Longyan city and suburban area), producing a large amount of animal wastes and extreme nutrient pollution.…”

“…Although this study focused on N 2 O, we stressed the advantage of measuring N 2 along with N 2 O to explore the relative importance of nitrification and denitrification to N 2 O production. The objectives of the present study were: (1) to explore spatial variations in riverine N 2 O concentration and emission fluxes across the river network and key factors controlling the spatial pattern; (2) to assess river N 2 O yield relative to N 2 (data extracted from an accompanying study reported elsewhere (Chen et al, 2014b)) to understand how much of this undesired greenhouse gas has been emitted during N removal from the aquatic system; and (3) to roughly estimate the time series of riverine N 2 O export to estuary through a model established in relation to DIN concentration, based on the direct measurements from this study and long-term monitoring of DIN. Together with a comparison of worldwide reported data for various aquatic ecosystems (river, reservoir and estuary), this study provides a systematic assessment of how riverine N 2 O production, emission and export from an agricultural watershed that has responded to increased human perturbation during rapid economic development in China.…”