Impaired water quality in a small stream was related to autumn leaf fall from riparian vegetation. Dissolved oxygen and pH decreased, and water color, specific conductance, iron, manganese, and bicarbonate values increased as the rate of leaf fall increased. Similar quality changes occurred in laboratory cultures of tree leaves in filtered stream water, but the five leaf species studied produced widely differing results. Stream quality improved rapidly following cha inel flushing by storm flow. Organic loading by tree litter can exert significant control on water composition, especially during low flow.Previous studies have demonstrated impaired water quality resulting from dissolution of leaf litter in pooled streams. The present report relates quality changes in a small stream to the quantity of leaf fall from riparian vegetation. A concurrent study of water-quality effects of tree leaves in laboratory tanks helps to interpret the field observations.The autumn shedding of leaves from deciduous forests may produce organic loading of otherwise unpolluted streams. The annual chemical quality cycle in small streams such as the North Fork of Quantico Creek may be generalized as low concentrations of solutes during the relatively high stream flows in winter and spring when runoff predominates over ground water inflow, middle values of solute concentration in summer showing the relative increase of ground water over runoff, and high concentrations of solutes during the autumn when most of the flow derives from ground water. Streams are at annual low flows in autumn over much of the United Slates, and the dissolved solids concentration is normally the highest for the rear. During the autumn lov, flow period, the capacity oí streams to assimilate organic material also is lower than at any other time of year. Depletion of dissolved oxygen ny decomposing litter often results in fid. kill., de-creases in bottom fauna, and m nuisance rdors from tinaeiohic decomposition. The mass of material Use'1 causes aes'het-v ueterao! "Po". and water treatment yobiems, clogging of water '•'e. tm.eiit filters in oarticulnr.OOciac , . Technology

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For most natural water, a large sample is required to provide the 3 grams of carbon needed for a carbon-14 determination. A field procedure for isolating total dissolved-carbonate species is described. Carbon dioxide gas is evolved by adding sulfuric acid to the water sample; the gas is then collected in a sodium hydroxide trap by recycling in a closed system. The trap is then transported to the dating laboratory where the carbon-14 is counted.

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