Land-sea mercury transport through a modified watershed, SE Brazil.

Abstract

iver management has altered the land–sea transport of water, sediments, and chemicalcompounds with profound impacts on the structure of continental and costal ecosystems.Understanding riverine transport across modified watersheds allow for better assessmentof the influence of river management on material fluxes to coastal waters. Here, we assessthe quantitative and qualitative aspects of mercury (Hg) transport across a modifiedwatershed by diversion of Paraı ́ba do Sul River waters into Sepetiba Bay, Brazil. Wemeasured concentrations and speciation of Hg in water samples collected at sites withinthe modified watershed. These data, together with water discharge and sediment load fromnumerical models and measurements were used to estimate mass balances. In theSepetiba watershed, mercury is mainly associated with suspended sediments (90%) andtherefore Hg flux displayed the characteristic trend of downstream reduction due totrapping efficiency of particulate load by successive reservoirs. The mass balance suggeststhat the major source of mercury to Sepetiba Bay is the erosion of soil-derived particlesfrom the drainage basin rather than mercury diverted from Paraı ́ba do Sul River watershed