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    Depth-dependent predictability of soil temperature under Mediterranean climatic conditions: a frequency-based perspective
    (Springer Wien, 2026) Guleryuz, Didem; Yildirim, Umit; Guler, Cuneyt
    Soil-temperature predictability is inherently depth-dependent because atmospheric forcing is progressively attenuated and transformed into smoother, lower-frequency thermal dynamics with increasing depth. Under Mediterranean climatic conditions, where pronounced seasonality and strong surface forcing coexist, this depth-dependent transformation provides an informative basis for evaluating model behaviour. This study examines soil-temperature prediction at depths of 5, 10, 20, 50, and 100 cm using a multivariate dataset comprising 5,285 retained daily observations from the Mersin meteorological station on T & uuml;rkiye's eastern Mediterranean coast. Precipitation, air temperature, relative humidity, wind speed, and evaporation were used as predictors. Support vector regression, random forest, and LightGBM were evaluated using R & sup2;, RMSE, and MAE. All three models performed strongly in the near-surface layers, with test R & sup2; values ranging from 0.948 to 0.954 at depths of 5-20 cm. Predictive performance declined with increasing depth as short-period variability weakened and the thermal signal became smoother and more seasonally structured. RF and LightGBM showed a greater numerical decline at 50-100 cm, whereas SVR achieved test R & sup2; values of 0.923 at 50 cm and 0.847 at 100 cm; however, inter-model differences remained modest and were interpreted descriptively. Lomb-Scargle spectral analysis, applied using the actual observation dates, indicated that short-period variability became relatively less pronounced with depth while seasonal-scale and low-frequency components remained prominent. Overall, the findings suggest that soil-temperature prediction should be interpreted in relation to depth-dependent temporal signal characteristics rather than as a search for a universally superior algorithm.
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    Pollution Source and Soil Quality Assessments of Heavily Contaminated Soils by Selected Potentially Toxic Elements in a Human-Degraded Wetland Area
    (Mdpi, 2024) Kurt, Mehmet Ali; Yalcin, Sezen; Guler, Cuneyt; Guven, Onur; Yildirim, Umit
    Wetlands are transitional between terrestrial and aquatic environments and have essential ecological functions. Unfortunately, due to anthropogenic activities and climate change, the area covered by wetlands is gradually decreasing worldwide, causing deterioration and loss of their critical and vital ecological functions. One of these degraded wetlands is the H & uuml;rmet & ccedil;i Sazl & imath;& gbreve;& imath;, a nationally important wetland located in the Kayseri Province of Turkey. This study aims to determine the spatial and vertical (depth profile) distribution and the sources of the potentially toxic elements (PTEs) As, Cd, Pb, and Zn in the soils around the H & uuml;rmet & ccedil;i Sazl & imath;& gbreve;& imath; Wetland (HSW) and to evaluate environmental risk factors using various soil quality indicators. According to the results obtained, it was determined that some parts of the wetland soils were significantly polluted in terms of As, Cd, Pb, and Zn. The concentrations (in mg/kg) of these PTEs in the soil around the wetland ranged between 9.12 and 273.9 for As, 0.38 and 1119.46 for Cd, 3.59 and 1807.66 for Pb, and 41.68 and 77,287.5 for Zn. Several soil quality indicators, including the Enrichment Factor (EF), Contamination Factor (CF), Ecological Risk Index (ERI), and Potential Ecological Risk Index (RI), were calculated to determine the quality and pollution levels of the collected soil samples. According to the calculated RI values, 70 out of 77 sites sampled in the area around the HSW are in the High Risk class in terms of all studied PTEs. The soil profile samples indicated that the topsoil (0-50 cm) was heavily contaminated by all PTEs, particularly near a zinc processing plant established in 1976. In addition, parts of the wetland further away from the Zn processing plant were also affected by arsenic pollution from geogenic sources, which can be associated with Plio-Quaternary volcanic activity in the region.