The research objective was to study temporal and spatial relations between specific phosphorus species as well as to examine total phosphorus content in the bottom sediments of an anthropogenic, hypertrophic limnic ecosystem Rybnik Reservoir, functioning under thermal pollution conditions. The chemical extraction procedure for the speciation of bioavailable phosphorus forms was used. It was found that available algae phosphorus was the most dominant phosphorus species in both sediment layers (83%), while the lower share was readily desorbed phosphorus form (0.1%). The phosphorus species concentrations depended on the organic matter concentration. The differences between phosphorus species contents in the upper (5 cm) and lower (15–20 cm) sediment core layers were low. The biologically active sediment layer extended from the sediment surface to at least 20 cm depth of the sediment core. Distributions of the concentrations within the year and at specific sampling points resulted from the variability observed for particular points and transformation intensity. Furthermore in the following study, the reaction rate constant for the increase and decrease in the concentrations of the phosphorus species in sediments was given. It was indicated that the speed of the phosphorus species transformations was affected by the environment temperature. In the heated water discharge zone (water temp. 17–35°C) the concentrations of selected speciation phosphorus forms increased more than in the dam zone (5–25°C). It was also found that the abundance of the bottom sediments with phosphorus species was related to the oblong and transverse asymmetry of reservoir depth.
The sorption isotherm and sorption kinetics of NH4+ by the Fen River reservoir sediment were investigated for a better understanding of the NH4+ sorption characteristics and parameters. The results showed that Q (adsorption content) increased with the increase of Ceq (equilibrium concentration), sorption isotherms could be described by Freundlich equation (R2 from 0.97 to 0.99). Cation exchange capacity (CEC) had a significant correlation with the parameters K and n (R2 was 0.85 and 0.95, respectively). The ENC0 (Ceq as Q was zero) of S1, S2, S3 and S4 was 1.25, 0.57, 1.15 and 1.14 mg L-1, respectively, and they were less than the NH4+ concentrations in reservoir water. The sediments released NH4+ to the Fen River reservoir water and acted as a pollution source, in the form of complex and heterogeneous adsorbents. The NH4+ adsorption kinetic process was composed of ‘fast’ and ‘slow’ reaction patterns and could be fitted using both Elovich equation and Pseudo second-equation. More than one-step may be involved in the NH4+ sorption processes, and interior diffusion was not dominant ion action.