Freshwater wetlands are natural sinks of carbon; yet, wetland conversion for agricultural uses can shift these carbon sinks into large sources of greenhouse gases. We know that the anthropogenic alteration of wetland hydrology and the broad use of N-fertilizers can modify biogeochemical cycling, however, the extent of their combined effect on greenhouse gases exchange still needs further research. Moreover, there has been recent interest in wetlands rehabilitation and preservation by improving natural water flow and by seeking alternative solutions to nutrient inputs. In a microcosm setting, we experimentally exposed soils to three inundation treatments (Inundated, Moist, Drained) and a nutrient treatment by adding high nitrogen load (300 kg ha-1) to simulate physical and chemical disturbances. After, we measured the depth microprofiles of N2O and O2 concentration and CO2 and CH4 emission rates to determine how hydrological alteration and nitrogen input affect carbon and nitrogen cycling processes in inland wetland soils. Compared to the Control soils, N-fertilizer increased CO2 emissions by 40% in Drained conditions and increased CH4 emissions in Inundated soils over 90%. N2O emissions from Moist and Inundated soils enriched with nitrogen increased by 17.4 and 18-fold, respectively. Overall, the combination of physical and chemical disturbances increased the Global Warming Potential (GWP) by 7.5-fold. The first response of hydrological rehabilitation, while typically valuable for CO2 emission reduction, amplified CH4 and N2O emissions when combined with high nitrogen inputs. Therefore, this research highlights the importance of evaluating the potential interactive effects of various disturbances on biogeochemical processes when devising rehabilitation plans to rehabilitate degraded wetlands.

Freshwater wetlands are important carbon sinks with an estimated ~ 450 gigatons of carbon stored in their sediments. However, when disturbed they can become significant sources of carbon emissions. Understanding carbon dynamics in freshwater wetlands is a research priority to maximise carbon drawdown opportunities through effective management. Grazing can have considerable impacts on the health of freshwater wetland functionality. Fencing to exclude livestock from freshwater wetlands is one approach used to reduce grazer impacts; however, this is not always feasible. Managing grazing intensity is one option that is amenable to most farmers and resource managers; however, to date there have been no studies to evaluate its efficacy. The impacts of seasonal grazing intensity (by sheep) on carbon sequestration by rain-filled freshwater wetlands were investigated in south eastern Australia (Wimmera region). Over a 1-year study duration, this research compared: a) the effects of continuous grazing (sheep present across all seasons); b) crash grazing (sheep present within the spring); and c) exclusion plots (controls; no sheep access) on above-ground plant biomass, soil carbon concentration, and fluxes across seasons. Results suggest that above-ground biomass was 6.4% higher within exclusion plots compared to grazed plots in both continuous and crash grazing regimes. Exclusion plots had 30% higher soil carbon concentration compared to grazed plots. Open-continuously grazed plots had higher fluxes (8.69 ± 10.61 g CO2 m−2 day−1) compared with exclusion plots (6.92 ± 15.86 g CO2-e m−2 day−1). This study shows that exclusion plots had higher soil carbon concentration and lower carbon emissions. Further, excluding grazing from wetlands within the Wimmera region would increase above-ground biomass and soil carbon stock by 545,300 tons of carbon while reducing CO2 emissions by 782,412 tons of CO2 year−1.

Globally, freshwater wetlands are significant carbon sinks; however, altering a wetland’s hydrology can reduce its ability to sequester carbon and may lead to the release of previously stored soil carbon. Rehabilitating a wetland’s water table has the potential to restore the natural process of wetland soil carbon sequestration and storage. Further, little is known about the role of microbial communities that mediate carbon cycling during wetland rehabilitation practices. Here, we examined the carbon emissions and microbial community diversity during a wetland rehabilitation process known as “environmental watering” (rewetting) in an Australian, semi-arid freshwater floodplain wetland. By monitoring carbon dioxide (CO2) and methane (CH4) emissions during dry and wet phases of an environmental watering event, we determined that adding water to a degraded semi-arid floodplain wetland reduces carbon emissions by 28–84%. The watering event increased anoxic levels and plant growth in the aquatic zone of the wetland, which may correlate with lower carbon emissions during and after environmental watering due to lower anaerobic microbial decomposition processes and higher CO2 sequestration by vegetation. During the watering event, areas with higher inundation had lower CO2 emissions (5.15 ± 2.50 g CO2 m–2 day–1) compared to fringe areas surrounding the wetland (11.89 ± 4.25 g CO2 m–2 day–1). CH4 flux was inversely correlated with CO2 emissions during inundation periods, showing a 38% (0.013 ± 0.061 g CO2-e m–2 day–1) increase when water was present in the wetland. During the dry phases of environmental watering, there was CH4 uptake within the fringe and aquatic zones (−0.013 ± 0.063 g CO2-e m–2 day–1). A clear succession of soil microbial community was observed during the dry-wet phases of the environmental watering process. This suggests that wetland hydrology plays a large role in the microbial community structure of these wetland ecosystems, and is consequently linked to CO2 and CH4 emissions. Overall, the total carbon emissions (CO2 + CH4) were reduced within the wetland during and after the environmental watering event, due to increasing vegetative growth and subsequent CO2 sequestration. We, therefore, recommend environmental watering practices in this degraded arid wetland ecosystem to improve conditions for wetland carbon sequestration and storage. Further use of this management practice may improve wetland carbon storage across other arid freshwater wetland ecosystems with similar hydrologic regimes.

Oaks (Quercus) are a dominant forest species throughout much of the eastern United States. However, oak regeneration failure due to a myriad of issues (e.g., suppression of natural fire, excess nitrogen deposition, pressure from herbivore activity) is leading to a decline in oak dominance. This change may alter forest hydrology and nutrients through variation in species characteristics. Throughfall (TF) and stemflow (SF) quantity and chemistry were sampled during storm events under oak and non-oak (hickory, Carya) species to quantify differences in canopy-derived water and nutrients from an upland oak-hickory forest in Mississippi. Stemflow partitioning was 86% higher in hickory species compared to oak species (394.50 L m−2; p < 0.001). Across all species, dissolved organic carbon (DOC) was 1.5 times greater in throughfall (p = 0.024) and 8.7 times greater in stemflow (p < 0.001) compared to rainfall. White oak DOC concentrations (TF: 22.8 ± 5.5 mg L−1; SF: 75.1 ± 9.5 mg L−1) were greater compared to hickory species (TF: 21.0 ± 18.3 mg L−1; SF: 34.5 ± 21.0 mg L−1) (p = 0.048). Results show that while smoother-barked hickory species generate more stemflow volume, rougher-barked oak species generate stemflow that is more enriched in nutrients, which is a function of the canopy characteristics of each species. Within a single stand, this study demonstrates how variable water and nutrient fluxes may be and provide insights into species-level variability in oak-hickory forest types that may be undergoing compositional changes.