Aerial photograph time series and UAS Remote Sensing application to study rapid ecosystem change of palsa mires in Fennoscandinavia.
Abstract
Palsas (peat-covered mounds with perennially frozen cores) occur in the narrow circumpolar zone of sporadic permafrost in the northern hemisphere. Previous studies have shown palsa mounds melting and collapsing as a result of warming climate and increasing precipitation. In Fennoscandia, palsas are likely to disappear almost completely by the middle of this century.
Aerial photo time series allow tracking areal changes of palsas in Finnish Lapland from ca. 1960s. Aerial photos reveal that about 50% of palsas have disappeared in many locations in Finnish Lapland 1960-2016. Since 2016 we have collected data with Unmanned Aerial Systems (UAS) from 10 separate palsa mires twice annually (mid June and late August flying campaigns). The ultra-high spatial resolution of UAS orthophotos and Digital Elevation Models (DEM) allow accurate detection of boundaries between palsa mounds and surrounding mire, which is often hindered by shrubs and other vegetation. New data improves our knowledge about palsas' decay rate, extent and topographical heterogeneity. The UAS time series (2016-2018) from several study sites showed ca. 2-18 % decrease in areal extent of many palsa mounds. In summer 2018 field work in two large palsa mire complexes were conducted, we collected 12 km2 of multispectral UAS data acquired, several hundred active layer measurements, vegetation mapping and GHG measurements on different mire surfaces were collected (e.g. palsa, open mire, overgrown thermokarst ponds). One of the clearest sign of palsa disappearance are thermokarst ponds that appear as palsa's melts. Thermokarst ponds are rather fast overgrown by sphagnum moss and grass species ( mainly Sphagnum riparium and Eriophorum russeolum). These revegetated thermokarst ponds are clearly visible in new and old aerial photos as whitish and roundish objects. By investigating these forms from old and new aerial photos we can estimate distribution and amount of palsas about 50-100 years pre 1960's. All these remote sensing and field data indicate that decay of palsa mounds is faster than expected. Signs of decay are clear in most of palsas and just a few new palsa embryos have been detected.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B33K2816K
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCESDE: 0480 Remote sensing;
- BIOGEOSCIENCESDE: 1640 Remote sensing;
- GLOBAL CHANGE