In Situ Observation of Whole Lake Gross Primary Productivity: Response to and Recovery from Copper Algaecide Application

Abstract

The fortuitous presence of in situ equipment capable of high-resolution (time/space) measures of O 2 and total dissolved inorganic carbon (TDIC) enabled the response and recovery of a small pond to copper algaecide application to be monitored. Algaecide application to the pond significantly impacted the gross primary productivity (GPP) of the pond over a timescale of less than 4 days. By day 3-4 (postapplication), GPP had recovered to preherbicide levels and net ecosystem productivity (NEP) returned to a positive value. This indicated a timescale for copper algaecide impact on GPP of the order 1ϩ day and duration of impact of the order 3 days. Observed timescales for GPP recovery (3-4 days) indicate that algaecide effectiveness is not significantly controlled by mixing processes in this pond but is most likely influenced by the rate of removal of Cu to the sediment and the rate of Cu release from the chelating agent in K-tea. Observed recovery timescales for GPP (3-4 days) occurring during minimal inflow also indicate that significant nutrient recycling (internal loading) occurs to fuel the recovery of GPP. Thus, as an agent for the overall reduction in primary productivity of a polymictic pond ecosystem, a single copper application may not have a significant long-term impact on primary productivity.