202 4 Cuarta Modificación del Estudio de Impacto Ambiental Las Bambas Wetland 5,54 4,36 1,18 58,03 202 5 Cuarta Modificación Del EIA-D de La Unidad Minera La Arena Wetland 2,85 4,79 1,94 3,79 202 6 EIA Proyecto Trapiche Wetland 4,68 3,76 0,92 47,57 Polylepis Forest 57,50 50,00 7,50 2,68 Chachacom o Forest 74,50 41,00 33,5 10,96 Lake 5,81 0,06 5,75 47 719 m3 Source: SENACE These cases show, at least, that (i) activation of the Environmental Offset Plan (PCA) is being formally required in fragile ecosystems (wetlands) and (ii) there is administrative traceability (approved IGA). However, the public information reviewed does not always make it possible to close the loop toward measurable net gain, because it often does not include (or does not standardize) the full set of condition/EV metrics, the final area to be offset, additionality, and post-implementation monitoring results. The analysis of the case studies was structured around a logical sequence that links application of the mitigation hierarchy, quantification of residual impact and the design of offset measures. First, after the documented application of prevention, minimization and restoration measures, significant residual impacts on fragile ecosystems—mainly wetlands—were identified, which formally triggered the regulatory requirement for Environmental Offset Plans (PCA) within the approved environmental management instruments. For each case, the biophysical characterization of the impacted ecosystem made it possible to estimate a pre-impact ecological value (EV0), using the indicators defined in MINAM’s ecosystem guides. In parallel, selection of the receiving ecosystem for the offset was based on functional and structural equivalence criteria, considering attributes such as hydrology, vegetation structure and anthropogenic pressures, from which the ecological value of the ecosystem to be offset (EV) was estimated. The difference between both values (ΔEV) represents the expected ecological gain of the PCA and is the central metric for evaluating whether the offset is oriented toward no net loss or toward net gain of biodiversity. This gain, together with the initial condition of the receiving ecosystem, 151
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