Control of the Hydraulic Load on Nitrous Oxide Emissions from Cascade Reservoirs

Abstract

Nitrous oxide (N 2 O) emissions show large variability among dam reservoirs, which makes it difficult to estimate N 2 O contributions to global greenhouse gases (GHGs). Because river damming alters hydraulic residence time and water depth, the hydraulic load (i.e., the ratio of the mean water depth to the residence time) was hypothesized to control N 2 O emissions from dam reservoirs. To test this hypothesis, we investigated N 2 O fluxes and related parameters in the cascade reservoirs along the Wujiang River in Southwest China. The N 2 O fluxes showed obvious temporal and spatial variations, ranging from −7.86 to 337.22 μmol m −2 d −1 , with an average of 12.76 μmol m −2 d −1 . Nitrification was the main pathway of N 2 O production in these reservoirs, and seasonal dissolved oxygen (DO) stratification played an important role in regulating the N 2 O production. The reservoir N 2 O flux had a significant negative logarithmic relationship with the hydraulic load, suggesting its control of the N 2 O emission. This was because the hydraulic load was a prerequisite for regulating the nitrification−denitrification and the DO stratification in the dam reservoirs. This empirical relationship will help to estimate the contribution of reservoir N 2 O emissions to global GHGs.

Co-occurrence of planktonic bacteria and archaea affects their biogeographic patterns in China’s coastal wetlands

“…The inlet and outlet waters are lotic, while the wetland waters have a higher hydraulic retention time. This can result in their different microbial communities because hydrologic conditions have been reported to control nutrient biogeochemical cycling [ 44 ] and shape microbial composition [ 45 ]. In addition, wetland vegetation maintain ecosystem structure and function by recycling nutrients, attenuating flow velocities, releasing oxygen and organic carbon, and stabilizing the sediment [ 46 , 47 ].…”

Spatial Variations of N2O Fluxes Across the Water‐Air Interface of Mariculture Ponds in a Subtropical Estuary in Southeast China

“…Nitrification and denitrification are the most important microbial processes influencing N 2 O production in aquatic systems (Beaulieu et al, 2011; D. Q. Wang, Tan, et al, 2015; Wenk et al, 2016) and are governed by various biotic and abiotic factors. Nitrogen (N) substrate and oxygen supply are some key factors controlling the N 2 O production processes (Dalsgaard et al, 2014; Liang et al, 2019; Massara et al, 2018; Yu et al, 2013). In general, a high nitrite (N‐NO 2 − ) concentration can stimulate nitrifier denitrification, which is largely responsible for N 2 O production in sediments (Murray et al, 2015), while a high N‐NH 4 + concentration can promote N 2 O production through hydroxylamine oxidation either in the sediment or the water column (Barnes & Upstill‐Goddard, 2011; J. N. Wang, Chen, et al, 2015).…”

“…In addition, aeration activities can increase the DO level, which in turn can govern the N 2 O production rates by stimulating microbial nitrification (Y. S. Liu et al, 2011; Rosamond et al, 2012). Previous studies have reported that the N‐NH 4 + can be oxidized to N‐NO 3 − via nitrifier nitrification, with N 2 O being a byproduct, under a high DO level (Beaulieu et al, 2015; Liang et al, 2019; Maavara et al, 2019; Rosamond et al, 2011). As a result, the high concentrations of N‐NH 4 + and DO are considered to be favorable for N 2 O production associated with nitrification in aerobic aquatic systems (Cheng et al, 2019; Rosamond et al, 2012; Sturm et al, 2014; Whitfield et al, 2011).…”

“…Similar results have been found in aquaculture ponds, with an enhanced N 2 O production under low DO conditions (Z. Hu et al, 2012, 2013; Liu et al, 2016). Even in a fully oxic water column, oxygen can be rapidly depleted in benthic sediments (Yu et al, 2013), leading to the dominance of anaerobic conditions and thus denitrification process in the subsurface sediment layers (Hinshaw & Dahlgren, 2013; Liang et al, 2019; Xia et al, 2018). Meanwhile, nitrification could cooccur at the oxic‐anoxic interface of pond surface sediments.…”

New insights into mechanisms of sunlight-mediated high-temperature accelerated diurnal production-degradation of fluorescent DOM in lake waters

“…Conversely, autochthonous aquatic DOM includes extracellular polymeric substances (EPS), autochthonous humic-like substances (AHLS), protein-like substances (PLS), aromatic amino acids of various nature, etc (Shammi et al 2017a(Shammi et al , 2017b(Shammi et al , 2017cGuidi et al, 2016;Zhang et al, 2009;Mostofa et al 2013;Yamashita and Tanoue, 2003). These substances occur as major fractions, even if very diluted, in surface waters of lakes, estuaries and oceans 7 , thus they control many important biogeochemical functions and processes in aquatic systems, including cycling of C (Zark and Dittmar, 2018;Guidi et al, 2016;Amon and Benner, 1994), N (Yue et al, 2018;Liang et al 2019), P (Guidi et al, 2016;Carpenter et al, 1998;Parsons et al, 2017) and trace elements (Wan et al, 2019;Helms et al, 2013), as well as nutrient changes associated with diurnal sunlight-induced planktonic photosynthesis (Gao et al, 2010;Jung et al, 2013;Segschneider and Bendtsen., 2013).…”