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.A more detailed description of the dataset can be found in the uploaded README file.The dataset contains data on water chemistry and the chemical composition of sediments in Lake Bolmen, southern Sweden. The water chemistry data that was used to analyze temporal changes in iron, water color, sulfate and pH in the three main inflows to Lake Bolmen and in the lake outflow was collected by two monitoring initiatives. Samples were analyzed by standard limnological methods. Sediment samples were collected in 2015 using a gravity corer in the deepest lake basin at 35 m depth. One sediment core was sliced and the freezedried subsamples were used for 210Pb dating and analyzed for several elements. An intact frozen sediment core was scanned with a XRF analyzer and subsamples were analyzed with X-ray absorption spectroscopy (XAS). The iron K-edge X-ray absorption spectra were further analyzed with linear combination fitting and first shell analyses to receive information on iron speciation in the lake sediments