The Cladocera as Hydrological Indicators in Subarctic Peatlands in Northern Finnish Lapland.

Long term hydrology in pristine areas (e.g. subarctic Scandinavia) are mostly driven by climatic forcing. Peatlands, which cover over 35% of Finnish Lapland, can be studied to establish reliable records of past environmental conditions. However, the shifts in hydrological conditions are not always easily interpreted due to various microhabitats in peatlands and the wide hydrological tolerance of some plant species. Here, we present the first results regarding the applicability of cladocerans as additional proxies to establish hydrological reconstructions in wet peatland systems.

We used plant macrofossil analysis and cladoceran subfossil analysis to reveal the dynamics of hydrological conditions in two peatlands in Northern Finnish Lapland during the past 2 millennia. Standard paleolimnological and paleoecological methods were used to retrieve and treat the samples.

In Kaamanen peatland, there was a clear directional change towards high cladoceran diversity and species richness accompanied by increased abundance of wet peatland plant species from 2700 cal.BP to 1135 cal.BP. In Iitto peatland, similar trend towards wetter conditions was detected in between 465 cal.BP and 245 cal.BP. In both sites, the cladoceran remains disappear abruptly due to drier conditions, palsa mound formation and loss of aquatic habitat.

In Kaamanen, the wetter conditions, which was detected in plant community was in good agreement with known climatic shifts as the lake levels and flooding intensity has increased during that time period due to increased effective moisture. The prolonged or stronger flooding has probably resulted in larger and deeper pools in fens thus enabling rich cladoceran community to thrive. In Iitto, the adjacent large river system and steep morphology of catchment are contributing to more fluctuating conditions, which is reflected in large amount of cladoceran resting eggs in samples. The reason for wetter conditions is difficult to interpret, but it could be related to the Little Ice Age and cool temperatures during that time period.

Rich cladoceran species assemblages occurred together with known historical climate trends as well as with wet peatland plant assemblages. The cladoceran analysis may thus provide a useful additional proxy for interpretation of water conditions in subarctic peatlands.