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Trace Elements in Lakes Located in an Agricultural-Forest Catchment: A Case Study of Lake Raczyńskie, Poland
The enrichment of bottom sediments with trace elements due to anthropogenic factors is of growing concern worldwide. With the development of industry, agriculture, and urbanization, the risk of freshwater contamination with trace elements is increasing. As trace elements are poorly soluble in water, they have a tendency to accumulate in bottom sediments. The study focused on the evaluation of the trace element contents in the surface layer of bottom sediments of Lake Raczyńskie, located in Poland, and assessing the risks posed by these sediments. The pollution of bottom sediments was estimated based on the index of the geo-accumulation (Igeo), enrichment factor (EF), Nemerow multi-factor index (Pn), and pollution load index (PLI). The assessment of environmental risk was evaluated by the potential ecological risk index (RI) and mean PEL quotient method. The results obtained showed that the average contents of Cd, Cu, Ni, Pb, and Zn exceeded the national geochemical background values (Bn), indicating possible enrichment of bottom sediments due to human activity. Only for Mn were the observed contents below the Bn. This evaluation was confirmed by the PLI and Pn values, which indicated sediment pollution from anthropogenic sources. However, the risk assessment by RI and mean PEL showed a low risk of contamination. The results of principal component analysis (PCA) and values of Igeo and EF suggested that Cd, Cu, Mn, and Zn mainly originate from geogenic sources, while Ni and Pb probably come from an unrecognized anthropogenic source. The distribution of Cd, Mn, and Ni depended on the contents of silt and clay fractions. Additionally, organic carbon influenced Cu, Mn, Ni, and Zn contents in bottom sediments.
The Role of Stand Age in Soil Carbon Dynamics in Afforested Post-Agricultural Ecosystems: The Case of Scots Pine Forests in Dfb-Climate Zone
Land use changes inevitably lead to changes in the carbon stocks stored in the soil. However, despite numerous studies investigating soil organic carbon (SOC) dynamics following the afforestation of post-agricultural lands, findings remain diverse and often inconclusive. In this study, the effect of stand age on the carbon content and stock in Scots pine (Pinus sylvestris) stands located in the Dfb-climate zone was investigated. Five research plots, characterized by similar soil types, geological structures, and tree cover, but differing in stand age (14-, 27-, 37-, 55-, 90-year-old stands), were selected. Additionally, one plot was located at arable soil as a reference. The soil was sampled from both organic and mineral horizons. The content of organic carbon in the organic horizion increased with years that passed from afforestation and amounted to 234.0, 251.6, 255.0, 265.0 and 293.0 g·kg−1 in 14-, 27-, 37-, 55- and 90-year-old stands, respectively. Such a pattern was also observed in the upper mineral horizons where the contents of SOC gradually increased from 7.27 g·kg−1 up to 17.1 g·kg−1. In the organic horizon, the stock of OC increased significantly with stand age up to 55 years after afforestation, while in the former plough layer, SOC stocks were found to slowly increase with stand age. The afforested soils, with the organic horizon, reached levels of carbon stocks observed on arable land after 17 years. Notably, the SOC stock in the mineral A horizon reach this level after 83 years. The obtained results indicate that in the years immediately following afforestation, SOC content is notably higher in arable soils compared to forest soils. However, as stand age increases, the SOC contents of upper horizons in forest soils surpass those of comparable agricultural soils. The observed SOC variability pinpoints the necessity of long-term monitoring in forest ecosystems in order to better understand the temporal dynamics of carbon turnover and to optimize afforestation strategies for long-term carbon sequestration.