Autotrophic Production in Carnation Creek, a Coastal Rainforest Stream on Vancouver Island, British Columbia

Abstract

Attached algal growth in Carnation Creek and its estuary were monitored in 1974 and 1975 as part of the Carnation Creek Experimental Watershed Project. Net production on the estuary was 17.8 μg organic matter (org)∙cm−2∙day−1, and in Carnation Creek the average was 3.4 μg org∙cm−2∙day−1. Algal growth in Ritherdon Creek, located in an adjacent logged watershed, was slightly higher (4.6 μg org∙cm−2∙day−1) than the Carnation Creek average. In a streamside nutrient enrichment experiment, nitrate and phosphate concentrations in one trough were increased to twice the normal Carnation Creek values present in the control. In 35 days the nutrient-enriched trough had a total algal volume 3 times that of the control. It is suggested that extremely low nutrient concentrations (especially phosphate), and secondarily, poor light conditions under the canopy, are responsible for the paucity of algal growth in Carnation Creek. Major loss of algae from the system is caused by periodic freshets which scour the stream bed. Losses by grazing herbivorous insects were considered negligible. Dominant diatoms in Carnation Creek were Achnanthes minutissima, Synedra ulna, Hannaea arcus, Diatoma hiemale, and Eunotia pectinalis. Ulothrix sp., Draparnaldia sp., and Mougeotia sp. were the dominant filamentous green algae. Net production and algal biomass (chlorophyll a) in Carnation Creek are among the lowest ever reported in the literature.