Water–Air Interface Greenhouse Gas Emissions (CO2, CH4, and N2O) Emissions Were Amplified by Continuous Dams in an Urban River in Qinghai–Tibet Plateau, China

Abstract

Continuous dams may lead to great variation in greenhouse gas (GHG) emissions from rivers, which contribute more uncertainty to regional carbon balance. This study is among the first to determine water–air interface GHGs (CO2, CH4, and N2O) in a river with continuous dams in plateau city. Combined static-chamber gas and meteorological chromatography were utilized to monitor the GHGs emission flux at the water–air interface within four continuous dams in the Huoshaogou River in the Qinghai–Tibet Plateau, China. A variation coefficient (VC) and amplification coefficient (AC) were designed to detect the influence of continuous dams on GHG emissions. Results indicate that (1) cascade dams presented an amplifying effect on GHGs emissions from the water-air interface. The VCs of three types of GHGs are 3.7–6.7 times higher than those of the undammed area. The ACs of three types of GHGs are 2.7–4.1 times larger than environmental factors; (2) the average GHG emission fluxes in some dams are higher than that of the first dam, indicating that an amplifying effect may have been accumulated by some continuous dams; (3) EC, pH, Twater, Tair and TDS are found to be principle influencing factors of GHG emission and light intensity, Twater, TOC (plant), TN (sediment) and TOC (sediment) are found to be associated with accumulative changes in GHG emission.

Spatiotemporal Variability of the Nitrous Oxide Concentrations and Fluxes From a Cascaded Dammed River

“…Such pattern of N 2 O concentrations was consistent with previous reports in other single or cascaded river-reservoir systems (Liu et al, 2009b;Liu et al, 2011a;Liu et al, 2017;Cheng et al, 2019). For example, Yang et al (2020) found that the N 2 O emissions in the impoundment-affected Huoshaogou River were much higher than the upper rivers as influenced by enrichment of N and OC in sediment after river damming. Liu et al (2017) also found that the N 2 O emission fluxes in released water sections were five times higher than those in reservoir sections in Dongfeng Reservoirs.…”

“…On the other hand, it is well known that hydraulic residence time could govern N processing time and gaseous N emissions in rivers (Hohener and Gachter, 1993;Harrison et al, 2008; Alexander et al, 2009) and that the long hydrological residence time allowed bacteria to settle down and to drive nitrogen mineralization and decomposition (Wang et al, 2018a;Chen et al, 2020;Deng et al, 2020). Thus, the hydraulic residence time and related hydrologic load have been considered as the important factors driving the variations of N 2 O concentrations in cascade reservoirs (Liang et al, 2019;Shi et al, 2020;Yang et al, 2020). In this study, the N 2 O concentrations and fluxes were found to be positively correlated with hydraulic residence time and negative with hydraulic load significantly (Figure 7), implying the regulating and controlling of hydrological conditions on the spatial variations of N 2 O emissions in the Wubu River cascaded reservoirs.…”

“…Cascade damming, leading to a series of successive "river-reservoir-release" systems along river mainstream, can generate refilter and redistribute for the transportation of C, N, and P along the river continuum (Chen et al, 2020). The dynamic processes and spatial patterns of N 2 O emissions in cascade river-reservoirs systems are thus more complex than single reservoir-river system (Jin et al, 2018;Liang et al, 2019;Shi et al, 2020;Wu et al, 2020;Yang et al, 2020). Particularly, Liang et al (2019) found that cascade damming and accompanying fragmentation of hydraulic load significantly dominated exceptionally spatial variability of N 2 O fluxes in the cascade reservoirs along the Wujiang River in Southwest China, implying significant differences between reservoirs and rivers.…”

Biological response to 5 years of operations of cascade rubber dams in a plateau urban river, China

“…From the perspective of space, the peak of biomass appeared in the first barrage. It may be associated with the fact that organic matter tends to deposited behind the first dam (Yang et al, 2020). Zooplankton had the largest growth among the three organisms, while it also presented the largest temporal and spatial fluctuations.…”

“…In China, small rubber dams are often constructed continuously on a river for tens of kilometers, and thus their cumulative effect can be significant, especially for plateau areas where river ecosystems are fragile (Dong, Liu, Liu, Wang, & Wang, 2014; Yang et al, 2020). The current study focuses on the cascaded rubber dams in an urban river of the Qinghai‐Tibet Plateau.…”