Grazer control of stream algae: Modeling temperature and flood effects

A computer model for epilithic algae and grazer biomass in streams is modif ied to better predict the effects of temperature and is calibrated for diat oms and mayflies. Mayflies are predicted to maintain low diatom biomass pro vided that (1) temperatures remain within their preferred range (10-20 degr ees C); and (2) mayfly populations are not adversely affected by floods. Al gal blooms are predicted to occur in mayfly-dominated streams above 20 degr ees C-temperatures common in pasture streams over summer. We hypothesize th at mobile bed streams are susceptible to blooms during summer low flows fol lowing floods because (1) they usually lack temperature tolerant snail graz ers; and (2) mayfly recovery lags behind algal regrowth, and there is a sho rt period when algae escape from "top-down" grazer control.