Stream biomonitoring at an agricultural test site using benthic algae

The percent cover and composition of benthic macroalgal growths and the str ucture of epilithic diatom communities were analyzed in 1995 at four sites in a stream flowing through a cultivated field near Kintore, Ontario, Canad a. The dominant epilithic diatom taxa did not differ greatly among sites. H owever, a correspondence analysis of the diatoms sampled monthly between Ju ly and September separated an upstream site from those receiving agricultur al runoff. Sites downstream of agricultural inputs showed an increase in th e cover of Cladophora glomerata (L.) Kutz and other green algae, and in gen eral a reduction in the cover of diatoms and crusts dominated by Oscillator iaceae (aff. Oscillatoria sp.) and the red alga Audouinella violacea (Kutz. ) Hamel. In particular, there was a positive correlation between the cover of Cladophora and nitrate concentration.