Impact-recovery patterns of water quality in temporary wetlands after fire retardant pollution

Abstract

Fire retardants, which are used in wildland fire prevention and extinguishing operations, can cause eutrophi cation of surface waters. We measured water quality in artificially constructed outdoor ponds over three hydrological cycles to determine impact-recovery trajectories in retardant-contaminated, temporary wetlands. We used a multiple before–after control–impact (MBACI) design to determine the effects of application rates that are used in grasslands (1 L·m–2) and scrublands (3 L·m–2). Retardant application caused a significant increase in the trophic status of the ponds in the postcontamination period (second and third hydrological cycle) relative to the precontamination period (first hydrological cycle). The retardant clearly affected nutrients and indirectly affected chlorophyll a, pH, dissolved oxygen, and Secchi transparency, resulting in a shift from clear water to turbid water stable states. Univariate analyses showed that water quality variables showed distinct recovery trajectories, as influenced by natural, seasonal changes (chiefly water level fluctuations). Nonmetric, multidimensional scaling analyses suggest that water quality did not return to precontamination levels after two hydrological cycles in the retardant-treated ponds. Water quality affected by retardant contamination appeared to maintain wetlands in hysteresis for at least two hydrological cycles and prevented them from returning to the clear water, submerged macrophyte-dominated state.