Catchment characteristics and their long-term effects on lateral and vertical peat accumulation in boreal and boreonemoral landscapes : a comparison between mire-catchment interactions in the Sävar Rising Mire Chronosequence in Westrobothnia and the Forsmark area in Uppland

Sammanfattning

Minerogenic mires (fens) are often found in depressions in the landscape and their surface vegetation is, unlike that of ombrogenic mires (bogs), in contact with groundwater either from the underlying mineral soil or from the upslope catchment area. The catchment area drains the surface and brings water with solutes to the mires. This, together with upwelling of groundwater into the peat column, feeds the mire vegetation. In this way the catchment area influences the productivity, peat accumulation and expansion rates of minerogenic mires. Substances harmful to humans may be transported to a mire either from groundwater upwelling, surface water from the catchment area, or deposited from the atmosphere. These substances could theoretically be diluted by water or other substances that are transported from the catchment area to the mire. This literature review compares long-term mire development and possible dilution effects in the mire recipients under different catchment settings for two areas representing different biomes: coastal areas of northern Uppland (Forsmark area; FM in the boreonemoral zone of central Sweden), and the coastal areas of Westrobothnia (Sävar Rising Coastline Mire Chronosequence; SMC in the boreal zone of northern Sweden). Both areas are found below the highest coastline and are characterized by relatively high isostatic rebound. Apart from differences in climatic settings, quaternary deposits differ between the areas, as Uppland is characterized by calcite rich till and clay sediments, while the SMC is dominated by till and post-glacial silt, clay and sand. It was found that mire lateral expansion after initiation was widespread in the SMC, while mires in the FM seem to be more restricted to the basin they were originally formed in. This likely reflects the mire initiation type (in the FM a higher proportion is believed to originate from terrestrialized lakes compared to primary mire formation), and climatic differences between the areas (which cause differences in the hydrologic balances), since topographically the lower-sloping FM should offer suitable conditions for lateral expansion. In both areas, the increment in peat depth, and in the SMC also the lateral expansion of peat, was rapid during the first ca 1 000–2 000 years, where after the expansion rates levelled off. In both mire areas, catchments are still influencing the elemental composition of surface peat, even though mires in the SMC are supported by somewhat larger catchment-to-mire areas compared to mires in the FM. The smaller catchment areas in the FM compared to the SMC may lead to a lower dilution of harmful substances, if the mire surfaces of the FM receive such substances through groundwater upwelling. Apart from the catchment-to-mire area ratio, catchment slope and wetness were found to be important for the transport of water and solutes to the mires, where a higher slope was found to co-vary with higher peat elemental concentrations. The slope of the catchment area, and especially the slope by the mire margins, will also control the possibilities of a mire to expand laterally, since a steep mire-surrounding catchment area will be unfavorable for lateral expansion.

Nyckelord

Catchment hydrology; Peat depth; Minerogenic mire; Landscape development; Biogeochemistry; Radionuclides

Publicerad i

SKB technical report
2024, nummer: TR-24-04
Utgivare: Svensk Kärnbränslehantering AB

SLU författare

• Ehnvall, Betty

  • Institutionen för vatten och miljö, Sveriges lantbruksuniversitet
    

UKÄ forskningsämne

Fysisk geografi

Permanent länk till denna sida (URI)

https://res.slu.se/id/publ/140084