Artikkelit jotka sisältää sanan 'Accumulation'

The carbon pool of surface layers (up to 500 years old) in 73 boreal mires was investigated in order to assess its significance in the carbon cycle. Peat columns were collected from mires of varying depth, age and degree of natural state in the aapa mire and raised bog regions and coastal mires of southern and central Finland and Russian Karelia. The quantities of carbon sequestered during recent centuries and over the entire lifetimes of the mires were determined using a total of 367 dates (186 14C AMS and 181 conventional dates) and age-depth models derived from bulk density measurements. Particular attention was paid to accumulation over the last 100 and 300 years, as these periods encompass the best estimates of the acrotelm age across the range of sites investigated. The average carbon pool of layers younger than 300 years was determined as 101 ± 8 tonnes ha-1 in the aapa mire region, 115 ± 9 tonnes ha-1 in the raised bog region and 184 ± 20 tonnes ha-1 in coastal mires. Overall, the mean carbon pool of layers younger than 300 years was calculated to be 121 ± 7 tonnes ha-1 (range 44–259 tonnes ha-1) and of layers younger than 100 years 63 ± 4 tonnes ha-1 (range 17–141 tonnes ha-1). The size and dynamics of the carbon pool represented by these surface layers depends upon the mire site type, vegetation and natural state; variations reflect differences in plant communities as well as factors that affect biomass production and decay rates. The high carbon accumulation in surface layers is temporary and mainly related to the development of the mire. The surface layers are still undergoing a rapid carbon cycle. A relatively rapid accumulation and turnover of carbon is taking place in surface layers (<300 years) in the same way as in a growing forest. Therefore, this "pre-peat" in the surface layers of mires should be distinguished as a separate class from the peat underneath. Our results indicate how important it is to understand the carbon accumulation rates of surface layers and the long-term dynamics of mire carbon accumulation in order to set the current flux estimates in perspective.

• Mäkilä, Geological Survey of Finland, P.O. Box, 96, 02151 Espoo, Finland Sähköposti: ei.tietoa@nn.oo
• Goslar, Sähköposti: ei.tietoa@nn.oo

Studies of mire hydrology and carbon accumulation have shown 1) an exponential increase in the rate of horizontal water movement with increasing height of the water table, and 2) a curvilinear relationship between the water table elevation and carbon accumulation rate, with a single maximum. Equations for these relationships suggest that optimal carbon accumulation will occur where the water table is at moderate depth and the surface has little microtopography. Wet conditions tend to enhance microtopographic relief by differential peat accumulation, while dry conditions tend to reduce relief. For mires with abundant dry microsites, increasing the water supply typically increases the rate of carbon accumulation, but this effect could be transient because microtopographic relief may also increase and have a negative effect on carbon accumulation. The runoff-inhibiting nature of ridge and hollow patterns makes patterned mires especially vulnerable to loss of carbon fixation ability with increasing wetness. While dry periods often cause peat loss in the short term, over the long term their effect may be positive because they hinder the formation of strong microtopography. This helps explain why high peat accumulation rates and some of the world’s most extensive peatlands occur in continental regions with a marginally adequate moisture supply.

• Swanson, USDA Forest Service, PO Box 907, Baker City, OR 97814 USA Sähköposti: ei.tietoa@nn.oo

Two charcoal layers, originating from two forest fires, were found at between 7 and 58 cm in the peat of Lakkasuo mire. Using dendro-chronological techniques and fire scars on Scots pine {Pinus sylvestris L.) stumps, the date when these two layers was deposited could be estimated. The earlier fire swept over the mire about 1780 A.D. and the later fire, which seems to have been limited to the eastern part of Lakkasuo, occurred in 1845 A.D. Knowing the thickness of the peat layer above the dated charcoal layers, its bulk density and carbon content, the rate of carbon accumulation during the last 212-147 years could therefore be calculated for different site types in the Lakkasuo mire complex. These values ranging from 39.8 to 80.7 g C m-2 a-1. can be compared to those (28.5-42.8 g C m-2 a-1 ) 0f the peat layer down to a still older fire horizon dated using the AMS radiocarbon "wiggle matching" technique at 1040 ± 90 B.P. Keywords: Carbon accumulation, charcoal, dating, dendrochronology, fire

• Alm, Department of Biology, University of Joensuu, P.O. Box 111, FIN-80100 Joensuu, Finland Sähköposti: ei.tietoa@nn.oo
• Tolonen, Sähköposti: ei.tietoa@nn.oo
• Vasander, Sähköposti: ei.tietoa@nn.oo

We determined the rate elements are sequestered in hummock peat of an ombrotrophic bog. The peat below 65 cm was radiocarbon dated and the upper 65 cm was dated using the acid insoluble ash (AIA) content and Polytrichum strictum growth increments. Peat produced during the last 9 yrs contains roughly all the N, P, Ca, and Mg, and about twice the K, deposited during this period. However, these nutrients are depleted from older peat at rates that depends on mineralization and adsorption properties of the ions. Changes in inorganic chemistry occur mostly while peat is in the acrotelm. Therefore, only peat in the catotelm will show the true accumulation rate of elements. In peat below 65 cm, the annual accumulation rate, as a percent of the present annual input, is: N-38, K-2.5, P-18, Na-1.5, Ca-3, Mg-51 and S-3.5%. Dust fall increased 4-fold about 500 yrs ago and has remained at this level. Therefore, the annual accumulation of elements in peat below 65 cm, or older than 522 yrs, presumably underestimates present accumulation in the catotelm of soil-derived elements, especially Ca and P, and elements that have increased due to pollution such as N and S. This increased dust fall probably changed the floristic composition of the vegetation as well as production and decay. Keywords: Accumulation, dating, element retention, input changes, nutrient dynamics

• Damman, Department of Ecology and Evolutionary Biology, University of Connecticut, 75 N. Eagleville Road, Storrs, CT 06269-3042, USA Sähköposti: ei.tietoa@nn.oo
• Tolonen, Sähköposti: ei.tietoa@nn.oo
• Sallantaus, Sähköposti: ei.tietoa@nn.oo

• Väliranta, Environmental Change Research Unit (ECRU), Ekosysteemit ja ympäristö tutkimusohjelma; Helsinki Institute of Sustainability Science (HELSUS) Sähköposti: minna.valiranta@helsinki.fi
• Piilo, Environmental Change Research Unit (ECRU), Ekosysteemit ja ympäristö tutkimusohjelma; Helsinki Institute of Sustainability Science (HELSUS) Sähköposti: sanna.piilo@helsinki.fi
• Zhang, Institute for Atmospheric and Earth System Research (INAR), Fysiikan laitos, Helsingin yliopisto Sähköposti: hui.zhang@helsinki.fi