Limiting nutrients for periphyton growth in sub-alpine, forest, agricultural and urban streams

1. Nutrient-diffusing artificial substrata were used in summer and autumn to assess limiting nutrients for periphytic algal growth in streams draining sub-alpine, forested, agricultural and urban catchments in eastern Victoria, Australia. 2. Chlorophyll a density was primarily limited by nitrogen in most cases; often phosphorus was secondarily limiting. One sub-alpine, one forest and one agricultural stream were primarily phosphorus limited in at least one season. Added trace elements and vitamins did not increase chlorophyll density. 3. The dominant filamentous algal genera did not differ greatly between various nutrient enrichments. However, the relative abundance of Stigeodanium spp. was sometimes increased on substrata containing the limiting nutrient. 4. The results suggest that nutrient limitation is a widespread phenomenon in Victorian streams, and that limiting nutrients can be inferred from stream-water nitrogen to phosphorus ratios in many instances.