Which pigment is commonly used as a proxy for measuring periphyton biomass in streams?

• A. Hemoglobin
• B. Beta-carotene
• C. Chlorophyll-a
• D. Anthocyanin

Answer: (C)

Chlorophyll-a is used as the proxy because it is the primary pigment of photosynthetic algae and cyanobacteria that compose periphyton, so its amount scales with the amount of algal biomass present in the biofilm. Because chlorophyll-a is relatively consistent across different algal groups and directly tied to photosynthetic tissue, its concentration provides a reliable estimate of total periphyton biomass. In practice, researchers collect biofilm from submerged surfaces, extract the pigment with a solvent, and measure chlorophyll-a with spectrophotometry or fluorometry, often reporting it per area or per dry mass. Other pigments like beta-carotene, hemoglobin, or anthocyanin don’t track biomass as consistently across species and conditions, so they’re not used as standard proxies for stream periphyton.