Seasonality and distribution of epilithic diatoms, macroalgae and macrophytes in a spring-fed stream system in Ontario, Canada

A study of the epilithic diatom, macroalgal and macrophyte communities from a spring-fed stream in Ontario, Canada was undertaken from September 1996 to July 1997. The relative abundance of the epilithic diatom flora, percent cover of macroalgal and macrophyte taxa, and several physical and chemical stream conditions were monitored along a 20-m stretch at each of four site s, approximately every 2 months. Several stream conditions were relatively constant over the sampling period (pH, maximum width and maximum depth), wh ile others exhibited a distinct seasonal pattern (water temperature, specif ic conductance and daylength) and some fluctuated strongly with no discerna ble seasonal pattern (turbidity, current velocity). A total of 124 taxa wer e identified from the four sites, including 79 epilithic diatoms, three mac roalgal diatom species (large gelatinous masses), one cyanobacterium, two r ed algae, eight green algae, one chrysophyte alga, one tribophyte alga, thr ee mosses, three horsetails and 23 angiosperm taxa. Species richness was po sitively correlated to stream channel maximum width and depth, indicating t hat the total number of species tends to increase in a downstream direction . Distribution of several diatom and macroalgal species was significantly c orrelated to stream conditions (e.g. Gomphonema parvulum and Phormidium sub fuscum with current velocity); however, the vast majority of species did no t display seasonal variation in abundance that could be explained by change s in stream conditions. Many of the taxa identified from Blue Springs Creek are common elsewhere in North America.