Effect of Discharge Rate on Biotic and Abiotic Chemical Flux in an Acidified Stream

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Abstract
Acidity of Norris Brook, a mountain stream in the Hubbard Brook Experimental Forest, New Hampshire, was manipulated to estimate the effects on biotic and abiotic chemical flux during high (spring) and low (summer) discharge periods. Sulfuric acid was added to maintain the pH near 4.0 from April to September 1977. Al, Ca, Mg, and K were mobilized into streamwater with concentrations progressively increasing downstream, as a result of increased H+concentration. Concentrations of Na and NO3were not affected by the acidification. Dissolved organic carbon concentrations decreased downstream during periods of high discharge but did not change significantly during low flow. During storms, Al, Ca, Mg, and K increased in concentration below the acid addition as well as in the reference reach of the stream. Net flux of dissolved Al in streamwater was significant during both high- and low-discharge periods. Net flux of Al in invertebrate biomass was significantly increased only during high flow but was insignificant when compared with the amount in the dissolved form. Net flux of N was significant only in biomass of invertebrates at high discharge. Significance of flux of N in biota was totally overshadowed by transport (flux) of dissolved N (as NO3and NH4) during storms.