Transient Alterations in Streamwater Quality Induced by Pollution Incidents: Interim Losses Calculations and Compensation Alternatives Based on Habitat Equivalency Analysis

Pollution incidents cause transient water quality alterations during the passage of contaminants' plume along watercourses, with plume passage period and contaminants' concentrations modelled by advection-dispersion equations. Despite being transient, water quality alterations can impose many impacts on the streamwater ecosystem services. This study proposes two frameworks based on Habitat Equivalency Analysis to be applied during assessments of streamwaters' pollution incidents and respective compensation panoramas: (1) Streamwater interim loss framework, to calculate interim loss debits caused by transient alterations in the streamwater quality; (2) Total credit framework, to calculate streamwater credits generated by improvements in selected watercourse's streamwater quality, produced by wastewater treatment plants in this study. The amount of credits calculated in the selected watercourses assists in the proposal of suitable compensatory remediation projects to offset interim losses. Frameworks' calculations are founded on IVA, a water quality index for protection of aquatic life and aquatic communities. Frameworks' calculations depend on three parameters: IVA, watercourses fluxes and the present value multiplier. The frameworks were calculated in Delta IVAxL, unit defined by multiplying sensed alterations in streamwater quality (as Delta IVA) and streamwater flux, in liters (L). The frameworks were applied to two major streamwater pollution incidents in Brazil, caused by the dam collapses of Mariana and Brumadinho, suggesting suitable compensatory remediations' projects for the respective streamwater interim losses. Depending on the selected project, Brumadinho compensation period varied from 2 to 5 years, with estimated costs in the 2020 Int.$ 5.7-18.7M range; Mariana compensation period varied from 8 to 20 years, with estimated costs in the 2020 Int.$ 16.7-58.1M range. Based on Brumadinho compensatory remediation projects, an average water pollution environmental damage value per interim loss was calculated, 1.17E-4 2020 Int.$/Delta IVAxL, which might be useful in comparing streamwater pollution evaluations around the world.