Abstrato

Anthropogenic changes in water storage in peat deposit in intramountain Orawa-Nowy Targ Basin (Western Carpathians)

Adam Lajczak

 The aim of the presentation is to evaluate the scale of changes in water storage in peat deposit in the Orawa-Nowy Targ Basin
(643 km2) off the western Carpathians (European mountain range), influenced by human activity since the middle ages till 2015.
The basin is covered by fluvioglacial fans rich in groundwater and stores large amounts of water in vast peatbogs, especially
raised bogs. The peatbogs occur at the altitude from 592 to 770 m a.s.l. (metres above sea level) since the middle ages the
peatbogs in this basin have been degraded by human impact, mainly due to peat exploitation and drainage by dense network of
ditches. After 1990 shrinkage of the limit of peatbog domes slowed down or even stopped and draining ditches are not cleaned
which causes increasing irrigation of post-peat areas. Contemporary limit of individual peatbogs and their elements (i.e. reduced
domes, post-peat areas, isolated peat patches) in the basin was determined based on data from aerial laser scanning LiDAR (Light
Detection and Ranging) and additionally from peatbogs mapping. Former limit of peatbogs was assessed on the basis of historical
maps (18th-20th centuries) and mapping of remnants of peat deposit. Using drilling methods, the thickness of peat deposit was
measured within each peatbog in the period from August to October (relatively dry deposit). In order to determine the amount of
water in peat, four raised bogs and four fens, assumed as representative for the area studied, were sampled in 2008-2015 from
May to October (every two months). Using Kopecky`s cells (0.25 dm3), 540 peat samples were taken at the profile depth every 50
cm, which were the bases to calculate capillary capacity of peat in volume version Pwv [%]. Water resources in peatbogs both
current and those probable existing before the beginning of the intensive human impact in the basin were estimated based on the
appropriate volume of peat deposits and values of capillary water volume of peat Pwv [%]. Finally, maximal amount of water
which may be stored in domes (now in residual domes and post-peat areas) and fens was estimated. In the past probable total
amount of water which might have been permanently stored in fens in the basin was estimated to 32 million m3, and in the raised
bog domes 139 million m3 (together 171 million m3). Total amount of water which is currently stored in fens in the basin is
estimated to 15.1 million m3, in raised bog domes to 45.2 million m3, and in post-peat areas to 2.1 million m3 (total volume of
water is 62.4 million m3). In relation to the whole area of the basin, the index of water retention of peatbogs reaches 10 cm and at
the end of the middle ages this index was probably 27 cm. The fastest rate of water loss in peats occurred 50-150 years ago.