The introduction of embankment seawalls to limit the expansion of the exotic C4 perennial grass Spartina alteniflora Loisel in eastern China’s coastal wetlands has more than doubled in the past decades. Previous research focused on the impact of sea embankment reclamation on the soil organic carbon (C) and nitrogen (N) stocks in salt marshes, whereas no study attempted to assess the impact of sea embankment reclamation on greenhouse gas (GHG) fluxes in such marshes. Here we examined the impact of sea embankment reclamation on GHG stocks and fluxes of an invasive Spartina alterniflora and native Phragmites australis dominated salt marsh in the Dongtai wetlands of China’s Jiangsu province. Sea embankment reclamation significantly decreased soil total organic C by 54.0% and total organic N by 73.2%, decreasing plant biomass, soil moisture, and soil salinity in both plants’ marsh. It increased CO2 emissions by 38.2% and 13.5%, and reduced CH4 emissions by 34.5% and 37.1%, respectively, in the Spartina alterniflora and Phragmites australis marshes. The coastal embankment wall also significantly increased N2O emission by 48.9% in the Phragmites australis salt marsh and reduced emissions by 17.2% in the Spartina alterniflora marsh. The fluxes of methane CH4 and carbon dioxide CO2 were similar in both restored and unrestored sections, whereas the fluxes of nitrous oxide N2O were substantially different owing to increased nitrate as a result of N-loading. Our findings show that sea embankment reclamation significantly alters coastal marsh potential to sequester C and N, particularly in native Phragmites australis salt marshes. As a result, sea embankment reclamation essentially weakens native and invasive saltmarshes’ C and N sinks, potentially depleting C and N sinks in coastal China’s wetlands. Stakeholders and policymakers can utilize this scientific evidence to strike a balance between seawall reclamation and invasive plant expansion in coastal wetlands.
This study explored the spatial distribution of phosphorus fractions in river sediments and analyzed the relationship between different phosphorus fractions and their environmental influence on the sediments within different watersheds in Eastern China. River sediments from two inflow watersheds (Hongze and Tiaoxi) to Hongze and Taihu Lake in Eastern China were analyzed by the sequential extraction procedure. Five fractions of sedimentary phosphorus, including freely sorbed phosphorus (NH4Cl-P), redox-sensitive phosphorus (BD-P), bound phosphorus metal oxide (NaOH-P), bound phosphorus calcium (HCl-P), and residual phosphorus (Res-P) were all analyzed. The orders of rankings for the P fractions of the rivers Anhe and Suihe were HCl-P > NaOH-P > BD-P > NH4Cl-P and HCl-P > BD-P > NaOH-P > NH4Cl-P, respectively. For the rank order of the Hongze watershed, HCl-P was higher while the NH4Cl-P contents were significantly lower. The rank order for the Dongtiaoxi River was NaOH-P > HCl-P > BD-P > NH4Cl-P, and that of Xitiaoxi River was NaOH-P > BD-P > HCl-P > NH4Cl-P. Compared with the phosphorus forms of the Tiaoxi watershed, NaOH-P contents were significantly higher compared to HCl-P, which was significantly higher in the Hongze watershed. In comparison, NH4Cl-P contents were significantly lower in both. Variations may be attributed to differential discharge of the P form in the watershed due to land-use changes and urban river ambient conditions.
Greenhouse gas (GHG) emissions from reservoirs are responsible for at most 2% of the overall warming effects of human activities. This study aimed at incorporating the GHG emissions of a reservoir (with irrigation/sugar production as its primary purpose), into the carbon footprint of sugar produced from irrigated sugarcane. This study adopts a life-cycle assessment (LCA) approach and encompasses the cradle-to-gate aspect of the international organization of standardization ISO 14040 guidelines. Results show that total carbon footprint of refined sugar could be as high as 5.71 kg CO2-eq/kg sugar, over its entire life cycle, depending on the priority of purposes allocated to a reservoir and sugarcane productivity. Findings also reveal that the dammed river contributes the most to GHG emissions 5.04 kg CO2-eq/kg sugar, followed by the agricultural stage 0.430 kg CO2-eq/kg sugar, the sugar factory 0.227 kg CO2-eq/kg sugar, and lastly the transportation stage 0.065 kg CO2-eq/kg sugar. The sensitivity analysis shows that carbon footprint CF of sugar production is largely influenced by the rate of biomass decomposition in the impounded reservoir over time, followed by the reservoir drawdown due to seasonal climatic fluctuations. Significant amounts of GHG emissions are correlated with the impoundment of reservoirs for water resource development projects, which may account for up to 80% of total GHG emissions to the reservoir’s primary purpose. Sugar production expansion, coupled with allocating more functions to a reservoir, significantly influences the CF of sugar per service purpose. This study is an indicator for policymakers to comprehend and make plans for the growing tradeoffs amongst key functions of reservoirs.
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