EFFECTS OF NUTRIENT ENRICHMENT AND FLOOD FREQUENCY ON PERIPHYTON BIOMASS IN NORTHERN OZARK STREAMS

Ambient nutrient concentrations (TN and TP) and periphyton biomass (Chl a) were measured every 2 wk during March-November in 1985 and 1986 at 22 sites on 12 streams in the northern Ozarks, Missouri. Benthic Chl a was positively correlated in both years with log TN (R2 = 0.58, 0.60) and with log TP (R2 = 0.47, 0.60). When sites were grouped by the degree of enrichment and plotted over time, benthic Chl a decreased at all sites after flood events but rebounded more rapidly at highly enriched sites. Differences in recovery following flooding were most obvious in fall 1986, when both high and moderately enriched sites exhibited similar biomass accrual patterns, reaching mean benthic Chl a of 397.4 and 321.1 mg.m2, respectively, within 42 d after a catastrophic flood. In contrast, average benthic Chl a at nutrient-poor sites reached a maximum level of 76.8 mg.m-2 within 28 d after flooding, suggesting that maximum standing crops are influenced by both nutrient supply and the length of the flood-free period.