Agricultural reclamation effects on ecosystem CO2 exchange of a coastal wetland in the Yellow River Delta

Abstract

a b s t r a c tLittle is known about the impacts of agricultural exploitation of coastal wetlands on ecosystem CO 2 exchange, although coastal wetlands have been widely reclaimed for agricultural use across the world. We measured net ecosystem CO 2 exchange (NEE) and its major components, gross primary production (GPP) and ecosystem respiration (R eco ) using an eddy covariance flux technique in a natural coastal wetland (reed) and an adjacent, newly reclaimed farmland (cotton) in the Yellow River Delta, China. The results showed that agricultural reclamation changed the ecosystem CO 2 exchange of the coastal wetland at three distinct levels. Initially, the conversion from the wetland to farmland changed the light response parameters (˛, A max , and R eco, day ) of NEE and temperature sensitivity (Q 10 ) of R eco mainly by changing the dominant vegetation type. Over the growing season, NEE, R eco and GPP were significantly correlated with LAI at both sites and aboveground biomass at the farmland site. Next, the reclamation of wetland modified the diurnal and seasonal dynamics of ecosystem CO 2 exchange. Significant differences in diurnal variations of NEE between the wetland and farmland sites were found during the growing season (with the exception of June and July). Seasonal means of daily GPP and R eco values at the wetland site were higher than those at the farmland. Ultimately, the agricultural reclamation altered the CO 2 sequestration capacity of the coastal wetland. The cumulative NEE in the wetland (−237.4 g C m −2 ) was higher than that in the farmland (−202.0 g C m −2 ). When biomass removal was taken into account, the farmland was a strong source for CO 2 of around 131.9 g C m −2 during the growing season. Overall, land use changes by reclamation altered ecosystem CO 2 exchange at several ecological scales by changing the dominant vegetation type and altering the ecosystem's natural development.

Effects of episodic flooding on the net ecosystem CO2 exchange of a supratidal wetland in the Yellow River Delta

“…Furthermore, faked flux due to warming of IRGA at low temperature was also corrected for half‐hour NEE data [ Yan et al ., ]. Subsequently, quality filtering was applied to eliminate half‐hour flux data resulting from systematic errors according to the following rejection criteria: (1) incomplete half‐hour measurements during system calibration or maintenance [ Jimenez et al ., ]; (2) excessive spikes in the sonic and IRGA data [ Schedlbauer et al ., ]; (3) precipitation, condensation, or bird fouling on the IRGA or sonic anemometer [ Lei and Yang , ; Schedlbauer et al ., ; Jimenez et al ., ]; (4) biologically impossible values of NEE for the reed wetlands (|NEE| > 60 µmol CO 2 m −2 s −1 ) [ Zhou et al ., ; Han et al ., ]; and (5) the flux data under nocturnal low atmospheric turbulence conditions were excluded based on friction velocity ( u *).…”

“…Thus, taking into account the diversity of wetland ecosystems, more studies should be conducted to include different wetland types in different climatic conditions [ Aurela et al ., ]. However, there has been relatively few direct measurement of CO 2 exchange between coastal wetlands and the atmosphere at the ecosystem scale, regardless of their importance in balancing the global carbon budget [ Zhou et al ., ; Moffett et al ., ; Han et al ., ; Xie et al , ].…”

Conversion of coastal wetlands, riparian wetlands, and peatlands increases greenhouse gas emissions: A global meta‐analysis

“…Agricultural management practices (e.g., tillage, fertilization, and irrigation) also had a large impact on GHG emissions in the drained wetlands (DWs). For instance, the application of nitrate fertilizers in CLs increased the ER of CO 2 efflux and N 2 O emissions caused by the high availability of inorganic nitrogen (Snyder, Bruulsema, Jensen, & Fixen, ) while inhibiting CH 4 production (Han et al, ; Jiang, Wang, Hao, & Song, ). Similar to the PASs developed from the natural wetlands, the application of ammonia‐based fertilizers (e.g., dung and urine patches) decreased CH 4 oxidation (Mosier, Schimel, Valentine, Bronson, & Parton, ; Saggar, Hedley, Giltrap, & Lambie, ) and enhanced N 2 O emissions (Pärn et al, ; van Groenigen, Velthof, Bolt, Vos, & Kuikman, ).…”

Environmental Regulation, Technological Innovation and Economic Growth-Taking the Pearl River Delta as an Example

“…In 2014, the Pearl River Delta region produced 5765 billion Yuan of GDP, becoming the important driving force of economy development in Guangdong province [2][3][4] . However, in the rapid process of economic development, industrialization and urbanization, high population densities and aggregation of industries pose significant environmental pollution and ecological unbalance problem.…”