THE FIRST ACTIVE ACID SULFATE SOIL FOUND OUTSIDE THE BALTIC BASIN, IN VISKA VALLEY WEST COAST OF SWEDEN
Abstract
Acid sulfate (AS) soils are naturally formed but are responsible for environmental problem
due to its low pH. Drainage of active AS soils can lead to mobilization of harmful metals and
a severe pH drop in nearby aquatic environments, which in turn may harm the ecological
conditions. Most AS soil in Sweden has been found mainly along the northeast coast, and this
area has received much research attention. A few discoveries have also been made in
Mälardalen and Skåne. Recently, during a geological survey by the Geological Survey of
Sweden (SGU) in the Viska Valley in Halland, old drilling profiles were found that showed
sulfide-rich layers that hinted about the possible existence of AS soil. Focusing on the Viska
Valley, this project aims to investigate the existence of AS soil in southwestern Sweden and
find clues about its formational environment. Electrical Resistivity Tomography’s (ERT)
suitability was evaluated as a method for locating AS soil on the west coast, and the ERT data
was compared to the old drilling profiles. This study together with another master thesis
study in Falkenberg was carried out during September 2019 to June 2020 in collaboration
with SGU. Sampling sites were determined based on the old drilling data and SGU’s soil
map. Samples were collected by using an Edelmann drill and brought to the laboratory for
oxidation and further analyses, including grain-size distribution, metal-, sulfur- and organic
content. Two ERT-measurements were made along one of the drilling profiles. This study is
the first that proves the existence of AS soil outside the Baltic basin. In two areas of the
valley, AS soil was found, one which was active and one potential, both in post-glacial gyttja
clay covered by floodplain sediments. The gyttja clay is believed to have formed during the
Tapes transgression when the valley consisted of a fjord-like bay, protected from wind and
currents with saltwater input from Kattegat. The data from the ERT measurements displayed
anomalies where the AS soil was found, but the information is not sufficient to determine
with certainty whether the layer of AS soil is present. However, the study made
simultaneously in Falkenberg showed more optimistic results with the ERT, which suggests
that it may be an appropriate method with different electrode spacing and a larger number of
measurements. This study only covers a small area of the Viska Valley, and most likely it is
possible to find more AS-soil in the area as well on the entire west coast in areas that were
below the highest coastline.
Degree
Student essay
Collections
View/ Open
Date
2023-09-15Author
Bergström, Johanna
Keywords
Acid sulfate soil
AS soil
ERT measurements
resistivity
Baltic basin
Swedish west coast
acidification
Tapes transgression
Series/Report no.
B1273
Language
eng