| Summary: | In order to determine effects of the chemistry of inflow waters on organic productivity in small fishing impoundments, water samples were collected from streams tributary to 12. lakes located in . northern and southern Arizona. The relative magnitude of productivity in the impoundments was determined from gross primary productivity measurements or from growth rates of fingerling trout. Other possible sources of nutrient salts and differences in the chemical composition of streams during different flood stages were investigated. Increasing concentrations of alkalinity, expressed as calcium carbonate, total phosphate and nitrate, were found to favor increased lake productivity although their effects were regulated to some degree by the morphological characteristics of the lake basin. The physical and geological features of a lake's watershed were dominant factors determining the chemical quality of waters flowing into the lake. Water draining sedimentary rocks, especially those containing limestone, generally contained higher concentrations of dissolved salts than that which drained igneous and metamorphic rock formations. Water from watersheds with very steep slopes, regardless of the geological formations, however, were found to contain very low concentrations of dissolved minerals.
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