Calcium Significance to Fish and Aquatic Life
Various investigators have indicated that calcium chloride and nitrate in soft water could be toxic to fish at concentrations between 300 and 1000 mg/L as calcium. In higher concentrations of calcium chloride (2,500 to 4,000 mg/L of calcium) in various waters, fish have been shown to survive three days.
The application of lime to soft water lakes has increased their productivity. Presumably, productivity rose by raising the alkalinity and providing larger reservoirs of available bicarbonates. The hypolimneon concentration can be on the order of twice that at the surface and is rather uniform throughout the lake stratum. Biologically, low calcium concentration lakes usually contain less living matter per unit area than high calcium concentration lakes.
The total estimated biomass of plant substances in certain medium calcium concentration lakes were found to be three to five times that of low calcium concentration lakes. The animal mass, not counting fish, was as much as triple that of the low calcium concentration lakes. The total mass of organisms may be greatest in rich lakes. Medium lakes often harbor a greater variety of kinds of plants and animals.
Additionally, low concentration lakes generally support a unique assemblage of species even though they are a quantitatively meager mass of organisms.