Seasonal and diurnal variations in N2O concentrations and fluxes from three eutrophic rivers in Southeast China

Abstract

This study was performed at three eutrophic rivers in Southeast China aiming to determine the magnitude and patterns of dissolved N 2 O concentrations and fluxes over a seasonal (in 2009) and diurnal (24 h) temporal scale. The results showed that N 2 O concentrations varied from 0.28 to 0.38 (mean 0.32±0.04), 0.29 to 0.46 (mean 0.37±0.07), and 2.07 to 3.47 (mean 2.84±0.63) μg N-N 2 O L −1 in the Fengle, Hangbu and Nanfei rivers, respectively, in the diurnal study performed during the summer of 2008. The study found that mean N 2 O concentration and estimated N 2 O flux (67.89 ± 6.71 µg N-N 2 O m −2 h −1 ) measured from the Nanfei River with serious urban wastewater pollution was significantly higher than those from the Fengle and the Hangbu Rivers with agricultural runoff. In addition, the seasonal study during June and December of 2009 also showed that the mean N 2 O concentration (10.59±14.67 μg N-N 2 O L −1 ) and flux (236.87±449.74 µg N-N 2 O m −2 h −1 ) observed from the Nanfei River were significantly higher than those from the other two rivers. Our study demonstrated both N 2 O concentrations and fluxes exhibited seasonal and diurnal fluctuations. Over three consecutive days during the summer of 2008, N 2 O accumulation rates varied within the range of 3.91-7.21, 2.76-15.71, and 3.23-30.03 µg N-N 2 O m −2 h −1 for the Fengle, Hangbu and Nanfei Rivers, respectively, and exponentially decreased with time.

Effect of dissolved oxygen and nitrogen on emission of N 2 O from rivers in China

“…The component of DIN varied in different rivers as described above. In Nanfei River, DIN was primarily comprised of NH þ 4 , whereas for runoff rivers, the opposite pattern in DIN composition was observed (high NO rapidly under hypoxic conditions in urban rivers (Yang et al, 2011;Yu et al, 2013). On the contrary, For runoff rives, NO 3 -is easy leaching with subsurface runoff or groundwater (NH þ 4 oxidized to NO 3 -in groundwater and recharge to river channel), NO À 3 dominant DIN concentrations in runoff rivers as a result (Boyer et al, 2006;Garnier et al, 2006).…”

“…As N inputs to rivers markedly increase, there is the potential for significant increases in N 2 O production in river systems (Seitzinger, 1988;Bouwman, 1996), and riverine N 2 O emission from China has a measurable impact on global N 2 O emission from aquatic systems (Seitzinger and Kroeze, 1998). Thus far, most reports have focused on N 2 O emissions from lakes, reservoirs and estuaries in China (Wang et al, 2007(Wang et al, , 2009Zhang et al, 2010;Liu et al, 2011;Yang et al, 2012), and direct measurement of riverine N 2 O production and emission in Chinese watersheds has been limited (Yan et al, 2004;Yang et al, 2011;Yu et al, 2013).…”

Modeling nitrous oxide emission from rivers: a global assessment

“…Several studies also indicate that N 2 O flux decreases exponentially as a function of stream order (Garnier et al, 2009;Turner et al, 2015). As a result of temporal and spatial variability in stream hydro-biogeochemical characteristics, there are often large fluctuations in riverine N 2 O fluxes, as well as emission factor, across time and space (Cole & Caraco, 2001;Reay et al, 2003;Beaulieu et al, 2008;Baulch et al, 2011;Yang et al, 2011;Harley et al, 2015). Therefore, based on the limited and local nature of N 2 O emissions, it is difficult to generalize the dominant factors regulating N 2 O emissions at regional to global scales leading to large uncertainties in estimating riverine N 2 O emissions at these larger scales (Outram & Hiscock, 2012;Rosamond et al, 2012).…”

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

“…The top and the bottom line indicate the maximum and minimum value. Reported data has been compiled from publications (Barnes and Owens, 1998;Garcia-Ruiz et al, 1999;McMahon and Dennehy, 1999;De Wilde and de Bie, 2000;Cole and Caraco, 2001;Huttunen et al, 2002;Lima et al, 2002;Harrison and Matson, 2003;LaMontagne et al, 2003;Laursen and Seitzinger, 2004;Harrison et al, 2005;Hendzel et al, 2005;Sikar et al, 2005;Stow et al, 2005;Hlavacova et al, 2006;Tallec et al, 2006;Clough et al, 2007;Ferron et al, 2007;Beaulieu et al, 2008;Guerin et al, 2008;Rajkumar et al, 2008;Silvennoinen et al, 2008;Wilcock and Sorrell, 2008;Garnier et al, 2009;Toyoda et al, 2009;Wang et al, 2009a;Beaulieu et al, 2010;Goncalves et al, 2010;Zhang et al, 2010;Barnes and Upstill-Goddard, 2011;Baulch et al, 2011aBaulch et al, ,b, 2012Deemer et al, 2011;Liu et al, 2011;Yang et al, 2011;Bouillon et al, 2012;Diem et al, 2012;Outram and Hiscock, 2012;Rosamond et al, 2012;Yan et al, 2012;…”

“…In addition, riverine N 2 O also influences the biogeochemistry and N budget of the adjacent estuary, particularly for those river-dominated estuaries. A few studies have addressed N 2 O in China water environments (reservoirs, lakes, rivers, estuaries) which have been subject to intense anthropogenic N inputs over recent decades (Xu et al, 2005;Wang et al, 2007Wang et al, , 2009bWang et al, , 2012Chen et al, 2008a;Zhang et al, 2010;Liu et al, 2011;Yang et al, 2011;Yan et al, 2012;Xia et al, 2013). Nevertheless, very few direct observations of the two end-products (N 2 O and N 2 ) of nitrification and denitrification have been made over river networks to explore N 2 O production, emission and export to estuary.…”