A novel zooplankton-based environmental monitoring tool for coastal impacted areas: The case of the Doce River dam rupture

Abstract

Zooplankton monitoring has been carried out in the Doce River region since 2015, when the Fundão mine dam ruptured and its tailings reached the coast. It is considered the biggest environmental disaster in Brazilian history. Here, we present an update on the zooplankton community scenario and introduce the novel Prevalence of Bioindicator Groups (PBG) index. It uses bioindicator taxa (Paracalanus cf parvus and Oikopleura spp) to assess inorganic pollution in the water. We measured salinity, temperature, river flow and wave energy and sampled quarterly for metal(loid) elements, suspended particulate matter, organic matter, and chlorophyll-a concentrations in the water along with zooplankton vertical sampling. Shannon diversity and Pielou evenness indexes were negatively correlated with the Doce River flow. They reached the lowest mean values during the three first wet periods of January 2019, 2020, and 2021, with significantly different values from the dry periods. PBG variation was better explained by concentrations of Cr, Co, Ni, Cu and Pb and by the percentage of organic matter. An apparent improvement in the zooplankton community was detected based on diversity, evenness and PBG values comparing the first years of monitoring (first to third) with the last years (fourth and fifth), which could be linked to the reduction of metal bioavailability in the water. It is still unclear whether this improvement represents a linear trend or a fluctuation caused by extreme local oceanographic events. Either way, PBG indicate that the environment is still far from recovering to its pre-dam rupture status and proven to be useful as a complementary tool for metal(loid) impact monitoring.