effect of chronic exposure to phosphorus-inactivation agents on freshwater biota

The phosphorus (P)-inactivation agents alum or modified zeolite (Aqual-P™) are used in eutrophic lake remediation. Lake managers must evaluate the benefits of P-removal against potential adverse effects on lake biota. Laboratory mesocosms were used to determine whether a 2 month exposure to alum or Aqual-P had lethal or sublethal effects on native benthic-dwelling macroinvertebrates or fish. The P-inactivation agents were applied while the organisms were present to evaluate both acute- and longer-term effects. A gradient of doses up to 344 g alum m⁻² (>7 mm capping layer thickness) and a single 200 g Aqual-P m⁻² dose were applied with no detectable acute effects on survival or behaviour. After 2 months, there was no significant effect of alum or Aqual-P on the survival or growth of the crayfish, mussels or fish, but aluminium accumulation was measurable in some treatments. Fingernail clams were held in a sub-mesocosm to prevent predation, which resulted in exposure to intact capping layers. The highest alum dose significantly decreased fingernail clam survival and reburial rates, while 200 g Aqual-P m⁻² caused highly variable survival. Our findings can be used by lake managers to assist the selection of site-specific application rates for these P-inactivation agents.