Grundkartering och bedömning av vattentäktspotential i fem åländska sjöar

D4 Published development or research report or study


Internal Authors/Editors


Publication Details

List of Authors: Hans-Peter Huhtala
Publisher: Åbo Akademi, Husö biologiska station
Publication year: 2017
Start page: 1
End page: 35
ISBN: 978-952-12-3657-0


Abstract

In the summer of 2017 five lakes (Storträsk, Toböle träsk, Borgsjön,
Inre fjärden, Södra Långsjön) in the Åland Islands were surveyed to
determine their potential for water extraction. The lakes were surveyed
by mapping vegetation and by examining the benthic fauna and fish
stocks. Of the studied lakes, two (Toböle träsk, Borgsjön) are used for
water extraction to supply drinking water, and one (Storträsk) is used
to water nearby farmland. Water extraction can affect water levels in
lakes, especially under drought conditions with low levels of
precipitation and runoff. Loss of water volume can lead to loss of
species richness and to higher concentrations of nutrients and of
fish-stocks in the lake. In determining the potential for water
extraction, a rudimentary “water budget” was calculated based on data on
annual catchment runoff and precipitation. The buffer potential of the
catchment area was also evaluated using data to assess its composition,
focusing mainly on the proportion of woodland and farmland found in the
area, but also on areas assumed to have a low retention rate of water.
The potential for water extraction varied in the lakes, and all had
associating factors that made the lakes suboptimal. Based on the
estimated water budgets the lakes currently used for drinking water
extraction (Toböle träsk, Borgsjön) had water budgets suboptimal for
water extraction. Toböle träsk was determined to have potential for a
modest increase of extraction if precipitation levels were average, but
should see no increase in extraction during dry periods, whereas
Borgsjön should see no further increase during normal or dry years. Of
the lakes that were found to be suitable for water extraction based on
their water budgets, two (Storträsk, Södra Långsjön) were able to
support notable volumes and one (Inre fjärden) a more modest rate of
extraction. The ecological survey produced more nuanced results. All
were found to have features potentially sensitive to effects of water
extraction, but two of the lakes (Storträsk, Södra Långsjön) were
determined to be especially vulnerable to water extraction. Storträsk
was extremely shallow and had populations of Charophytes that could
readily be exposed or replaced by other species if water levels drop,
while Södra Långsjön was determined to be ecologically exceptional with
its large population of Isoetids, which are vulnerable to water level
fluctuations. The other lakes (Toböle träsk, Borgsjön, Inre fjärden)
were found to have features potentially sensitive to the effects of
water extraction, but to a more modest degree. The catchment areas of
the studied lakes were all majority woodland, and only one had a
significant proportion of farmland (Storträsk).


Last updated on 2019-08-12 at 02:49