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Abstract:
Productivity of attached algae is limited by macronutrients such as nitrogen and phosphorus when light is saturating. Attached algae can supplement the available dissolved inorganic nutrient pool through the production of intracellular and extracellular enzymes in order to sequester otherwise bio-unavailable forms of nitrogen and phosphorus. Increased cation concentration can potentially stimulate attached algal productivity through increased enzyme activity and increased nutrient uptake efficiency. We conducted a full factorial laboratory experiment to test the effects of increased cation concentration, measured as specific conductance, and phosphorus source (inorganic or organic) on productivity of algae collected from Lake Tahoe and Lake Tanganyika. We manipulated cation concentration using commercially available lake salts, primarily magnesium, calcium, and potassium. Algal dry mass and productivity were significantly higher in the elevated conductivity treatments regardless of whether the phosphorus provided was in organic or inorganic form. No difference in dry mass was observed between phosphorus source and lake of origin but inorganic phosphorus treatments had significantly higher productivity. Our findings suggest that increased specific conductance in nutrient limited conditions can stimulate attached algal biomass and productivity.