Chlorophyll and Productivity in a Mountain River1

Chlorophyll was sampled on the shallow, rocky, canyon section of Logan River—a swift, clear, calcareous mountain river in the Middle Rocky Mountains of northern Utah. Chlorophyll extractions were made by immersing entire rocks supporting algae in acetone. The average quantity of chlorophyll per m 2 of bottom of the canyon section of Logan River was 0.30 grams. Downstream supplementary stations supported 3 to 4 times as much chlorophyll as the canyon section. No significant difference existed between means of chlorophyll samples in fall and late winter and between the upstream and downstream portions of the canyon section. Annual gross primary production equal to about 1.2 kg per m 2 was estimated from the relation of chlorophyll to photosynthesis in light and dark jar experiments. A standing crop of 25 grams of dry plant biomass per m 2 was determined from the chlorophyll dry weight ratio of samples of the community. Average standing crops (dry wt.) of insects and fish were 5 and 1.6 per cent, respectively, of the producer biomass or average standing crop of algae. Production of chlorophyll on artificial substrata (concrete rocks) showed no close relationship with either insolation or water movement within the range of values encountered in the Logan River.