Distribution of aquatic macroinvertebrates within peatland pool complexes in the Flow Country, Scotland

Stationary water traps were used to sample the aquatic invertebrates from both shallow, drought-sensitive pools and deeper, more permanent pools on blanket bog in the Flow Country, northern Scotland during 1994–1995, an area important for nature conservation. The differences in numbers of invertebrates trapped, and the differences in species composition and abundance of adult aquatic Coleoptera and Hemiptera (the two most abundant groups caught) between these two pool types, and spatially within the deeper pools, were investigated. Using the same trapping effort, seven times more invertebrates and five times more adult Coleoptera were taken in the deep (A4) pools compared to the shallow (A3) pools, and Hemiptera were almost exclusively trapped in the A4 pools (only 2% of the catch was from A3 pools). DECORANA showed that the Coleoptera species composition of the two pool types was different, although a small overlap existed, presumably because of the proximity of the pool types and of the continuous nature of the variation between them. There was little difference in the numbers taken or species composition of Coleoptera or Hemiptera from the edges or centre of the A4 pools. Smaller Coleoptera species were found in both pool types, although one species was more common in the centre of the larger pools. Larger Coleoptera with a body length of more than 11.6 mm were not found in the A3 pools, only in the deeper A4 type. The A4 pools were found to be more stable seasonally than the shallow pools with respect to invertebrate numbers trapped, and this may be linked to the chance of drying out of the latter in dry periods. The influence of pool stability (through water level) on invertebrate abundance, development and individual species size is discussed, as is the sampling method used, the significance of the peatland fauna and its importance to breeding bird life associated with peatland pool complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Spatial and temporal patterns in the hydrogeochemistry of a poor fen in northern Wisconsin

We studied the factors causing spatial and temporal patterning of interstitial water chemistry in Crystal Bog, a 7 ha northern Wisconsin kettle-hole peatland. Over the course of the snow-free season Crystal Bog exhibited spatial and temporal patterns in chemistry, especially hydrogen-ion, dissolved organic carbon, and specific conductance. The peatland contains a 0.5 ha pond that has water more dilute than the interstitial water of the surrounding peatland. The direction of groundwater flow between the lake and the peatland was seasonally dependent. In the spring and early summer, flow was from the lake into the peatland, especially on the eastern side of the lake. This flow resulted in a plume of relatively dilute surface interstitial water in the peatland. In mid and late summer direction of groundwater flow was from the peatland into the lake and the dilute plume was reduced in areal extent. By fall the direction of water flow was again from the lake to the peatland.The spatial and temporal heterogeneity in water chemistry produced by the seasonal variation in the direction of horizontal water flow was substantial. Minimum and maximum observed concentrations of dissolved organic carbon (DOC) in the interstitial water of the peatland, for example, differed by more than a factor of three, and pH ranged between 3.8 and 5.0. Correlations of DOC with anion deficit and hydrogen ion concentration and experiments of photo-oxidation of water samples showed that organic acids were the primary cause of acidity in the peatland. Specific conductance was highly correlated with DOC, probably because of DOC's correlation with the very conductive hydrogen ion. In Crystal Bog it was possible to use the relatively simple measure of specific conductance to estimate the temporal and spatial distribution of the more difficult to determine DOC.     

Methane emissions from fen,bog and swamp peatlands in Quebec

A static chamber technique was used weekly from spring thaw to winter freezing to measure methane emissions from 10 sites representing subarctic fens and temperate swamps and bogs. Rates of < 200 mg CH₄ m^–2 d^–1 were recorded in subarctic fens: within-site emissions were primarily controlled by the evolution of the peat thermal regime, though significant releases during spring thaw were recorded at some sites. Between subarctic fens, topography and water table elevation were important controls on methane emissions, with the general sequence: pool = horizontal fen> string. Emission rates from the 2 swamp sites were lower (< 20 mg CH₄ m^–2 d^–1 ), except during the spring thaw and when the sites were saturated. The low water table ( < 80 cm depth) in abnormally dry years reduced emission rates; rates were also low from a swamp site which had been drained and cleared of vegetation for horticulture. Methane emission rates were also low (< 5 mg CH₄ m^–2 d^–1) from 2 ombrotrophic bog sites. Laboratory measurements of rates of methane production under anaerobic conditions and methane consumption under aerobic conditions revealed that production rates were generally highest in the surface layers (0 to 2.5 cm depth); production was high in the fens and very low in the bogs. The swamp samples were able to produce methane under anaerobic conditions, but were also able to consume methane under aerobic conditions. Annual methane emission rates are estimated to be 1 to 10 g CH₄ m^–2 from the fens, 1 to 4 g CH4 m^–2 from the swamps and <0.2 g CH₄ m^–2 from the bogs and drained swamp.     

Revegetation of harvested peat surfaces in relation to substrate quality

Abstract. The relationship between substrate quality and pattern of revegetation of harvested peat surfaces was studied by means of a survey and a field experiment examining influences of modest NPK-fertilization on plant colonization of an initially bare peat surface. The harvested peat surfaces varied a great deal in their chemical and physical characteristics and the sites differed in revegetation pattern. Early successional vegetation was dominated by perennial species native to nutrient-poor habitats on all sites. Soluble phosphorus and ash content, mean particle size of surface peat, and thickness of peat layer had the strongest influence in a CCA-ordination of species. The species composition depended on the amount and form of soluble nitrogen in the surface peat. Sites with a high content of phosphorus and ammonium nitrogen, and with a thick peat layer were usually densely revegetated by Eriophorum vaginatum alone, while sites characterized by thin peat layers associated with a high ash content, large particle size and a high content of nitrate nitrogen were mainly dominated by different grass and weed species. Deschampsia cespitosa clearly favoured sites with a high potassium content and small particle sizes of the peat. The importance of nutrient availability for the rate and pattern of colonization was also demonstrated by the field experiment. Application of 20 g/m² of NPK-fertilizer resulted in a significant increase in the number of established plant individuals and marked differences in species composition compared to unfertilized plots.     

CO2 emissions from an undrained tropical peatland: Interacting influences of temperature,shading and water table depth

Emission of CO₂ from tropical peatlands is an important component of the global carbon budget. Over days to months, these fluxes are largely controlled by water table depth. However, the diurnal cycle is less well understood, in part, because most measurements have been collected daily at midday. We used an automated chamber system to make hourly measurements of peat surface CO₂ emissions from chambers root‐cut to 30 cm. We then used these data to disentangle the relationship between temperature, water table and heterotrophic respiration (R_het). We made two central observations. First, we found strong diurnal cycles in CO₂ flux and near‐surface peat temperature (<10 cm depth), both peaking at midday. The magnitude of diurnal oscillations was strongly influenced by shading and water table depth, highlighting the limitations of relying on daytime measurements and/or a single correction factor to remove daytime bias in flux measurements. Second, we found mean daily R_het had a strong linear relationship to the depth of the water table, and under flooded conditions, R_het was small and constant. We used this relationship between R_het and water table depth to estimate carbon export from both R_het and dissolved organic carbon over the course of a year based on water table records. R_het dominates annual carbon export, demonstrating the potential for peatland drainage to increase regional CO₂ emissions. Finally, we discuss an apparent incompatibility between hourly and daily average observations of CO₂ flux, water table and temperature: water table and daily average flux data suggest that CO₂ is produced across the entire unsaturated peat profile, whereas temperature and hourly flux data appear to suggest that CO₂ fluxes are controlled by very near surface peat. We explore how temperature‐, moisture‐ and gas transport‐related mechanisms could cause mean CO₂ emissions to increase linearly with water table depth and also have a large diurnal cycle.     

Effects of enhanced UV-B radiation on production-related properties of a Sphagnum fuscum dominated subarctic bog

1. The aim of the study was to investigate effects of enhanced UV-B radiation on the balance between biomass production and decay in an ombrotrophic bog which is dominated by one species of Sphagnum ( S. fuscum). This paper concerns production.
2. Enhanced UV-B radiation (simulating 15% ozone depletion under clear sky conditions) was applied by means of fluorescent tubes during two growing seasons.
3. In S. fuscum, shoot density, mass relations and length increment over time were measured and productivity was estimated. Pigment concentration, rates of dark respiration and maximum net photosynthesis were recorded.
4. Sphagnum fuscum productivity was not changed by enhanced UV-B radiation while properties determining production were highly influenced although in opposite directions.
5. Height increment was decreased by 20% in the first growing season and by 31% in the second growing season under enhanced UV-B radiation. After two growing seasons spatial shoot density was decreased by 8% by enhanced UV-B radiation. The shoots became stunted as capitulum dry mass and stem dry mass per unit length were increased by 21 and 17%, respectively, under enhanced UV-B radiation.
6. Dark respiration was significantly decreased by 31% after growth under enhanced UV-B radiation.
7. The UV-B induced change in shoot biometry together with the reduced spatial shoot density involve potential long-term effects on peat structure with possible feedback on productivity, decomposition and the strength of the system as a carbon sink.