Experimental Evidence of the Tolerance to Chlorate of the Aquatic Macrophyte Egeria densa in a Ramsar Wetland in Southern Chile

Abstract

In 2004, a massive die-off of the aquatic macrophyte Egeria densa occurred in a Ramsar wetland in southern Chile. In 2004, a pulp mill started its operations upstream from the wetland. Chlorate, a chemical compound found in pulp mill effluent, was one of the suspected causes of the observed ecosystem-level changes. The hypothesis was that high concentrations of chlorate in the wetland caused a massive die-off of the large populations of Egeria densa in this ecosystem. In this study several experimental efforts were aimed to understanding the potential effect of chlorate on E. densa. Plants were exposed to different doses of chlorate for variable periods in a large mesocosm array and several morphometric endpoints were quantified. Additionally, an ecotoxicological assay was implemented providing the first insight into the tolerance to chlorate of this aquatic plant. Both mesocosm and ecotoxicological evidences suggest that E. densa is tolerant to fairly high levels of chlorate (i.e. EC50 in the order of 1000 mg/L), at least three orders of magnitude larger than the highest concentration recorded in the wetland. Our results provide evidence that should guide the efforts of understanding the real causes of this environmental change.