An important pathway of atrazine degradation in perfusion systems of three soils was chemical hydrolysis to hydroxyatrazine. Ultraviolet spectrophotometric analyses of the perfusates showed the presence and accumulation of hydroxyatrazine. Atrazine degradation followed first‐order kinetics in soil‐free, sterilized soil and perfusion systems. An increased rate of atrazine hydrolysis in an acid soil was consistent with the effect of pH on hydrolysis. No microbial degradation of atrazine was detected following inoculation of a soil‐free atrazine medium with perfusates. An increased rate of hydrolysis in the presence of sterilized soil was postulated to result from soil adsorption of atrazine. Soil pH and organic matter content largely controlled the rate of atrazine hydrolysis; for soils of similar pH, atrazine degradation rates increased with increased atrazine adsorption.

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The amounts and forms of inorganic and organic phosphate (P) in lake sediments are discussed in relation to sediment composition and properties. The ability of noncalcareous and calcareous sediments to sorb and desorb added P in the laboratory and in the lake environment is interpreted in terms of the amounts and reactivities of sediment components involved in the sorption of P; emphasis is placed on the role of an Fe‐rich gel complex. Factors controlling the chemical mobility and biological availability of sediment inorganic and organic P are considered. Whether sediments act as a P source or sink is determined by sediment composition and limnological conditions. The factors involved in the interchange of P between the sediment interstitial water and the overlying water column are reviewed. The role of P in lake eutrophication is discussed briefly.

Interpretation of the potential bioavailability of phosphorus forms and fractions indicates some of the P entering lakes may have a limited effect on lake productivity. Some P sources, such as land runoff, are often high in particulate P, significant portions of which cannot be utilized in the growth of algae and higher plants. Based on existing information (mostly from Great Lakes studies), potentially bioavailable P in tributaries generally does not exceed 60% of the total P and is often considerably less. Potentially bioavailable P is shown to correspond to the dissolved reactive P (DRP) plus the fraction of particulate inorganic P obtained by extraction with 0.1N NaOH. Whether potentially bioavailable particulate P actually becomes available in a receiving water depends on factors such as the receiving‐water DRP concentration and the position (location) of the particle in the water. A mathematical model, combining two classical modeling approaches, is used to illustrate the importance of positional limitation. Consideration of bioavailability in eutrophication‐control strategies should lead to more cost‐effective management.