Hanna Silvennoinen

CARBON DIOXIDE AND METHANE FLUXES IN DRAINED TROPICAL PEAT BEFORE AND AFTER HYDROLOGICAL RESTORATION

Present tropical peat deposits are the outcome of net carbon removal from the atmosphere and form one of the largest terrestrial organic carbon stores on the Earth. Reclamation of pristine tropical peatland areas in Southeast Asia increased strikingly during the last half of the 20th century. Drainage due to land-use change is one of the main driving factors accelerating carbon loss from the ecosystem. Dams were built in drainage-affected peatland area canals in Central Kalimantan, Indonesia, in order to evaluate major patterns in gaseous carbon dioxide and methane fluxes and in peat hydrology immediately before and after hydrologic restoration. The sites included peat swamp forest and deforested burned area, both affected by drainage for nearly 10 years. Higher annual minimum soil water table levels prevailed on both sites after restoration; the deforested site water table level prevailed considerably longer near the peat surface, and the forest water table level remained for a longer period in the topmost 30 cm peat profile after restoration. Forest soil gas fluxes were clearly higher in comparison to the deforested area. Cumulative forest floor CO2 emissions (7305-7444 g x m(-2) x yr(-1); 166.0-169.2 mol CO2 x m(-2) x yr(-1)) and the deforested site CO2 emissions (2781-2608 g x m(-2) x yr(-1); 63.2-59.3 mol CO2 x m(-2) x yr(-1)) did not markedly reflect the notably differing hydrological conditions the year before and after restoration. The forest floor was a weak CH4 sink (-0.208 to -0.368 g x m(-2) x yr(-1); -13.0 to -22.9 mmol CH4 x m(-2) x yr(-1)) and the deforested site a comparable CH4 source (0.197-0.275 g x m(-2) x yr(-1); 12.3-17.1 mmol CH4 x m(-2) x yr(-1)) in the study period. In general, higher soil water table levels had a relatively small effect on the annual CH4 emission budgets. In the two site types the gas flux response into hydrological conditions in degraded tropical peat can be attributed to differing CO2 and CH4 dynamics, peat physical characteristics, and vegetation.

Heterotrophic respiration in drained tropical peat is greatly affected by temperature—a passive ecosystem cooling experiment

Vast areas of deforested tropical peatlands do not receive noteworthy shading by vegetation, which increases the amount of solar radiation reaching the peat surface. Peat temperature dynamics and heterotrophic carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) fluxes were monitored under four shading conditions, i.e. unshaded, 28%, 51% and 90% shading at experiment sites established on reclaimed fallow agricultural- and degraded sites in Central Kalimantan, Indonesia. Groundwater tables on the sites were at about 50 cm depth, the sites were maintained vegetation free and root ingrowth to gasflux monitoring locations was prevented. Half of the four shading areas received NPK-fertilization 50 kg ha �1 for each of N, P and K during the experiment and the other half was unfertilized. Increases in shading created a lasting decrease in peat temperatures, and decreased diurnal temperature fluctuations, in comparison to less shaded plots. The largest peat temperature difference in the topmost 50 cm peat profile was between the unshaded and 90% shaded surface, where the average temperatures at 5 cm depth differed up to 3.7 °C, and diurnal temperatures at 5 cm depth varied up to 4.2 °C in the unshaded and 0.4 °C in the 90% shaded conditions. Highest impacts on the heterotrophic CO2 fluxes caused by the treatments were on agricultural land, where 90% shading from the full exposure resulted in a 33% lower CO2 emission average on the unfertilized plots and a 66% lower emission average on the fertilized plots. Correlation between peat temperature and CO2 flux suggested an approximately 8% (unfertilized) and 25% (fertilized) emissions change for each 1 °C temperature change at 5 cm depth on the agricultural land. CO2 flux responses to the treatments remained low on degraded peatland. Fertilized conditions negatively correlated with N2O efflux with increases in temperature, suggesting a 12–36% lower efflux for each 1 °C increase in peat temperature (at 5 cm depth) at the sites. Despite the apparently similar landscapes of fallow agricultural land and degraded peatland sites, the differences in greenhouse gas dynamics are expected to be an outcome of the long-term management differences.

Low impact of dry conditions on the CO2 exchange of a Northern-Norwegian blanket bog

Northern peatlands hold large amounts of organic carbon (C) in their soils and are as such important in a climate change context. Blanket bogs, i.e. nutrient-poor peatlands restricted to maritime climates, may be extra vulnerable to global warming since they require a positive water balance to sustain their moss dominated vegetation and C sink functioning. This study presents a 4.5 year record of land-atmosphere carbon dioxide (CO2) exchange from the Andoya blanket bog in northern Norway. Compared with other peatlands, the Andoya peatland exhibited low flux rates, related to the low productivity of the dominating moss and lichen communities and the maritime settings that attenuated seasonal temperature variations. It was observed that under periods of high vapour pressure deficit, net ecosystem exchange was reduced, which was mainly caused by a decrease in gross primary production. However, no persistent effects of dry conditions on the CO2 exchange dynamics were observed, indicating that under present conditions and within the range of observed meteorological conditions the Andoya blanket bog retained its C uptake function. Continued monitoring of these ecosystem types is essential in order to detect possible effects of a changing climate. (Less)

Denitrification in the River Estuaries of the Northern Baltic Sea

Abstract Estuaries have been suggested to have an important role in reducing the nitrogen load transported to the sea. We measured denitrification rates in six estuaries of the northern Baltic Sea. Four of them were river mouths in the Bothnian Bay (northern Gulf of Bothnia), and two were estuary bays, one in the Archipelago Sea (southern Gulf of Bothnia) and the other in the Gulf of Finland. Denitrification rates in the four river mouths varied between 330 and 905 μmol N m−2 d−1. The estuary bays at the Archipelago Sea and the Gulf of Bothnia had denitrification rates from 90 μmol N m−2 d−1 to 910 μmol N m−2 d−1 and from 230 μmol N m−2 d−1 to 320 μmol N m−2 d−1, respectively. Denitrification removed 3.6–9.0% of the total nitrogen loading in the river mouths and in the estuary bay in the Gulf of Finland, where the residence times were short. In the estuary bay with a long residence time, in the Archipelago Sea, up to 4.5% of nitrate loading and 19% of nitrogen loading were removed before entering the sea. According to our results, the sediments of the fast-flowing rivers and the estuary areas with short residence times have a limited capacity to reduce the nitrogen load to the Baltic Sea.