To identify mineral alterations which might occur in stream environments, predominantly illitic soil clays were equilibrated in bottom sediment environments under natural and laboratory conditions for 217 and 98 days, respectively. Changes occurring after 217 days on the bottom of the Auglaize River, Ohio, consisted of a reduction in carbonate content, a decrease in particle size, and a slight loss of Al and Si; however, no significant changes in basal spacings were observed.

Clays equilibrated in river water under laboratory conditions at 4° and 25°C in CO2, N2, or air atmospheres showed only an increase in oxalate-extractable iron. The concentrations of Al, Si, Fe, Mn, K, and Ca in solution above the clays varied with the atmosphere and temperature. The concentrations of Fe, Al, and Si in solution may have been influenced by the dissolution of amorphous Al-Fe-Si compounds. Therefore, the mineralogical differences between soils in the watershed and sediments in the drainage system can not be attributed to mineralogical transformations during residence in the drainage system.

The paper is devoted to mathematical modelling and numerical computations of anonstationaryfree boundary problem. The model is based on processes of molecular diffusion ofsomeproducts of chemical decomposition of a solid organic substance concentrated inbottom sediments.It takes into account non-stationary multi-component and multi-stage chemicaldecomposition oforganic substances and the processes of sorption desorption under aerobic andanaerobic conditions.Such a model allows one to obtain quantitative estimates of incoming soluteorganicsubstances of anthropogenic origin having different molecular weights from thebottom sedimentsinto water and to study the influence of seasonal variations of theconcentration of solute oxygenin the near-bottom water on the direction of exchange processes in the system“waterbottom”.
Identification of parameters of the mathematical model with the use ofexperimental data andwith the employment of a priori information of the model's structure is carriedout. Comparisonof the numerical simulations with experimental data is conducted to the end ofverification ofefficiency and plausibility of the proposed mathematical model of secondarypollution. It impliesassessment of water quality on account of the processes of exchange in thesystem “waterbottom”.The results of computations of non-stationary fluxes at the boundary“waterbottom” are analyzed.A model example is used to estimate the potentials of the biogenic load on thewater reservoir.