Nine phyto-ashes from the biomass combustion of birch (Betula), oak (Quercus), red oak (Quercus rubra), horbeam (Carpinus), pine (Pinus sylvestris), poplar (Populus), maple (Acer), oilseed rape straw (Brassica napus) and wheat straw (Triticum aestivum) were blended with a biogas digestate at 1:1 mass ratio to give nine organic-mineral soil improvers. The concept of the research was to outline an eco-friendly and low cost soil improver for remediating degraded lands. These (i.e. phyto-ashes, improvers and the biogas digestate) were applied (0, 5, 10, 20, 40 t·ha^-1) to a soil metallurgically contaminated with Cu, Zn, Pb and Cd. Of several tested parameters, pH changes revealed that organic-mineral soil improvers may efficiently replace (linear R²>0.90****, P<0.001) phyto-ashes in soil remedial goals. Buffering properties expressed by the cation exchange capacity (CEC) improved progressively: 29, 52, 71, 100% (phyto-ash treatments) and: 18, 37, 44, 73% (improvers treatments) for the rates 5, 10, 20, 40 t·ha^-1, respectively as referred to the control CEC. The Dynamic Remediation Efficiency (DRE) indices for Cu, Zn, Pb, Cd revealed metal-specific geochemical reactions initiated by phyto-ashes, improvers and biogas digestate. The rates 5.0–10.0 t·ha^-1 for phyto-ashes and about 20 t·ha^-1 for improvers [1:1, i.e. Phyto-ash:Biogas digestate] are recommended. For biogas digestate, the rates 10–20 t·ha^-1 were found more efficient.

The main goal of the presented research was to investigate spatial distribution of surface sediments and to recognize relationships between chemical composition of water and sediments in a coastal Lake Sarbsko (northern Poland). The Lake Sarbsko is a freshwater basin. The water column is well oxygenated and waters exhibit only minor spatial variability of chemical composition indicating rapid and good mixing. Surface sediments of Lake Sarbsko are strongly diversified with respect to chemical composition. The sediments of Lake Sarbsko are characterized by elevated content of terrigenous silica indicating enhanced input of clastic material from the watershed and/or increased dynamics of the lake waters. Moreover, SiO2ter is strongly negatively correlated with SiO2biog, organic matter and element contents, which argues for diluting effect of the former towards authigenic components of sediments. Basically, terrigenous silica (quartz) content is highest in the lake shores and declines towards the lake center. Biogenic silica, organic matter and most of elements display reversed tendency. CaCO3 was encountered in three isolated areas, where it co-occurs with FeS. It is anticipated that precipitation of calcite in Lake Sarbsko resulted from postdepositional processes. Spatial distribution of Fe, Mn, Ca, Mg, Na and K in Lake Sarbsko is also governed by their geochemical affinities to organic matter (Fe), Fe/Mn oxides (Fe, Mn), sulphides (Fe), clay minerals (Na, K, Mg, Mn) and carbonates (Ca, Mn).