ALBERT

Description: Peatlands' vast carbon reserves accumulated under low nitrogen availability. Carbon and nitrogen cycling are inextricably linked, so what are the consequences of increased reactive nitrogen deposition for the sustainability and functioning of peatlands, and does the form of the nitrogen deposition make a difference? We have addressed these questions for an ombrotrophic peatland, Whim bog in SE Scotland, using a globally unique field simulation of reactive N deposition as dry deposited ammonia and wet deposited reduced N, ammonium and oxidised N, nitrate, added as ammonium chloride or sodium nitrate. The effects of 10 yr of reactive N additions, 56 kg N ha−1 yr−1, depended on the N form. Ammonia-N deposition caused the keystone Sphagnum species, together with the main shrub Calluna and the pleurocarpous mosses to disappear, exposing up to 30% of the peat surface. This led to a significant increase in soil water nitrate and nitrous oxide emissions. By contrast wet deposited N, despite significantly reducing the cover of Sphagnum and Pleurozium moss, did not have a detrimental effect on Calluna cover nor did it significantly change soil water N concentrations or nitrous oxide emissions. Importantly 10 yr of wet deposited N did not bare the peat surface nor significantly disrupt the vegetation, enabling the N to be retained within the carbon rich peatland ecosystems. However, given the significant role of Sphagnum in maintaining conditions that retard decomposition this study suggests that all nitrogen forms will eventually compromise carbon sequestration by peatlands through loss of some keystone Sphagnum species.

Description: In this study, we compare annual fluxes of methane (CH4), nitrous oxide (N2O) and soil respiratory carbon dioxide (CO2) measured at nine European peatlands (n = 4) and shrublands (n = 5). The sites range from northern Sweden to Spain, covering a span in mean annual air temperature from 0 to 16 °C, and in annual precipitation from 300 to 1300 mm yr−1. The effects of climate change, including temperature increase and prolonged drought, were tested at five shrubland sites. At one peatland site, the long-term (〉30 yr) effect of drainage was assessed, while increased nitrogen deposition was investigated at three peatland sites. The shrublands were generally sinks for atmospheric CH4 whereas the peatlands were CH4 sources, with fluxes ranging from −519 to +6890 mg CH4-C m−2 yr−1 across the studied ecosystems. At the peatland sites, annual CH4 emission increased with mean annual air temperature, while a negative relationship was found between net CH4 uptake and the soil carbon stock at the shrubland sites. Annual N2O fluxes were generally small ranging from –14 to 42 mg N2O-N m−2 yr−1. Highest N2O emission occurred at the sites that had highest concentration of nitrate (NO3−) in soil water. Furthermore, experimentally increased NO3− deposition led to increased N2O efflux, whereas prolonged drought and long-term drainage reduced the N2O efflux. Soil CO2 emissions in control plots ranged from 310 to 732 g CO2-C m−2 yr−1. Drought and long-term drainage generally reduced the soil CO2 efflux, except at a~hydric shrubland where drought tended to increase soil respiration. When comparing the fractional importance of each greenhouse gas to the total numerical global warming response, the change in CO2 efflux dominated the response in all treatments (ranging 71–96%), except for NO3− addition where 89% was due to change in CH4 emissions. Thus, in European peatlands and shrublands the feedback to global warming induced by the investigated anthropogenic disturbances will be dominated by variations in soil CO2 fluxes.

Description: In this study, we compare annual fluxes of methane (CH4), nitrous oxide (N2O) and soil respiratory carbon dioxide (CO2) measured at nine European peatlands (n = 4) and shrublands (n = 5). The sites range from northern Sweden to Spain, covering a span in mean annual air temperature from 0 to 16 °C, and in annual precipitation from 300 to 1300 mm yr−1. The effects of climate change, including temperature increase and prolonged drought, were tested at five shrubland sites. At one peatland site, the long-term (〉 30 yr) effect of drainage was assessed, while increased nitrogen deposition was investigated at three peatland sites. The shrublands were generally sinks for atmospheric CH4, whereas the peatlands were CH4 sources, with fluxes ranging from −519 to +6890 mg CH4-C m−2 yr−1 across the studied ecosystems. At the peatland sites, annual CH4 emission increased with mean annual air temperature, while a negative relationship was found between net CH4 uptake and the soil carbon stock at the shrubland sites. Annual N2O fluxes were generally small ranging from −14 to 42 mg N2O-N m−2 yr−1. Highest N2O emission occurred at the sites that had highest nitrate (NO3−) concentration in the soil water. Furthermore, experimentally increased NO3− deposition led to increased N2O efflux, whereas prolonged drought and long-term drainage reduced the N2O efflux. Soil CO2 emissions in control plots ranged from 310 to 732 g CO2-C m−2 yr−1. Drought and long-term drainage generally reduced the soil CO2 efflux, except at a hydric shrubland where drought tended to increase soil respiration. In terms of fractional importance of each greenhouse gas to the total numerical global warming response, the change in CO2 efflux dominated the response in all treatments (ranging 71–96%), except for NO3− addition where 89% was due to change in CH4 emissions. Thus, in European peatlands and shrublands the effect on global warming induced by the investigated anthropogenic disturbances will be dominated by variations in soil CO2 fluxes.

Description: Peatlands represent a vast carbon reserve that has accumulated under conditions of low nitrogen availability. Given the strong coupling between the carbon and nitrogen cycles, we need to establish the consequences of the increase in reactive nitrogen deposition for the sustainability of peatlands, and whether the form in which the nitrogen is deposited makes a difference. We have addressed these questions using a globally unique field simulation of reactive N deposition as dry deposited ammonia and wet deposited reduced N, ammonium and oxidised N, nitrate, added as ammonium chloride or sodium nitrate, to an ombrotrophic peatland, Whim bog in SE Scotland. Here we report the fate of 56 kg N ha−1 yr−1 additions over 10 yr and the consequences. The effects of 10 yr of reactive N additions depended on the form in which the N was applied. Ammonia-N deposition caused the keystone Sphagnum species, together with the main shrub Calluna and the pleurocarpous mosses, to disappear, exposing up to 30% of the peat surface. This led to a significant increase in soil water nitrate and nitrous oxide emissions. By contrast wet deposited N, despite significantly reducing the cover of Sphagnum and Pleurozium moss, did not have a detrimental effect on Calluna cover nor did it significantly change soil water N concentrations or nitrous oxide emissions. Importantly 10 yr of wet deposited N did not bare the peat surface nor significantly disrupt the vegetation enabling the N to be retained within the carbon rich peatland ecosystems. However, given the significant role of Sphagnum in maintaining conditions that retard decomposition, this study suggests that all nitrogen forms will eventually compromise carbon sequestration by peatlands through loss of some keystone Sphagnum species.