LIMNOLOGICAL EFFECTS OF ORGANIC EXTRACTS OF LITTER IN A SOUTHWESTERN IMPOUNDMENT

Watershed litter in semiarid southeastern Arizona is relatively unleached, and the accumulation of a year or more is occasionally delivered to lakes within the first few days of the summer rainy season. Pena Blanca Lake received at least 750 g/m 2 of oak litter during the summer of 1959. About 329 kg cal/m 2 were delivered to the lake in oak litter extracts of which 26% were probably from carbohydrates, 54% from phenolic compounds, and 20% from unidentified compounds. Oak leaf extracts were experimentally effective as an energy source for microorganisms used as food by filter‐feeding organisms ( Xenopus laevis ) and snails. Efficiency of the extract‐microorganisms‐Xenopus and snail food chain was 3.28%. Based on an estimated ecological efficiency of 0.56% for the food chain: litter extract‐microorganisms‐zooplankton‐young Micropterus salmoides, Micropterus biomass production may have been increased 0.4 g/m 2 by organic components in oak litter extracts contributed to Pena Blanca Lake in 1959. This increase represents 16.7% of the average annual fish harvest for 1959, 1960, and 1961.