Lake water and sediments chemistry data along with temporal data on environmental drivers

Increasing iron (Fe) concentrations are found in lakes on a wide
geographical scale but exact causes are still debated. The observed trends
might result from increased Fe loading from the terrestrial catchment, but
also from changes in how Fe distributes between the water column and the
sediments. To get a better understanding of the causes we investigated
whether there has been any change in the sediment formation of Fe sulfides
(FeS) as an Fe sink in response to declining atmospheric sulfur (S)
deposition during recent decades. For our study, we chose Lake Bolmen in
southern Sweden, a lake for which we confirmed that Fe concentrations in
the water column have strongly increased along with water color during
1966 to 2018. Our investigations showed that Fe accumulation and
speciation varied independently of S accumulation patterns in the Lake
Bolmen sediment record. Thus, we were not able to relate the positive
trend in Fe concentrations to reduced FeS binding in the sediments.
Furthermore, we found that Fe accumulation rates increased along with lake
Fe concentrations, indicating that increased catchment loading rather than
a change in the distribution between the sediments and the water column
has driven the increase in Fe concentrations. The increased loading may be
due to land-use change in the form of an extensive expansion of coniferous
forest during the past century. Altered forest management practices and
increased precipitation may have led to enhanced weathering and erosion of
organic soil layers under aging coniferous forest.