Eutrophication Risk Index (ERI) for the Cerrado and Caatinga: Modeling Scenarios for 2030 and 2040

To assist in mapping Water Pollution Risk (WPR), we developed the Eutrophication Risk Index (ERI). This index is designed to assess and predict the vulnerability of water bodies to eutrophication, a process driven by excessive nutrient accumulation—particularly nitrogen and phosphorus—resulting in uncontrolled algal growth. The ERI helps identify at-risk areas and supports the development of more effective mitigation strategies aimed at preserving water quality and sustaining aquatic ecosystems.

The proposed Eutrophication Risk Index (ERI) specifically accounts for human pressures on aquatic ecosystems. The ERI is determined by the phosphorus contribution to aquatic environments, derived from urban effluents and the excess nutrients (phosphorus and nitrogen) applied to the soil, measured in tons per hectare per year (Ton ha⁻¹ year⁻¹). To calculate the ERI for the Cerrado and Caatinga, we employed an equation with two main components: one concerning nutrient loss from agricultural systems and the other related to nutrient loss in wastewater.

Nutrient Loss in Agricultural Areas:Nutrient loss from agricultural areas was estimated using a spatially explicit soil nutrient balance model, incorporating secondary data sources and land use and land cover maps of the study area. For this analysis, we assumed that the nutrient balance in the soil is the difference between total inputs (IN) and total outputs (OUT), where IN includes chemical and organic fertilizers and OUT represents agricultural products. A positive nutrient balance, or surplus, indicates potential nutrient loss that could impact adjacent ecosystems. In our calculations, we also considered phosphorus saturation levels as a risk factor for phosphorus loss, alongside soil types.

Nutrient Loss in Wastewater:Nutrient loss in wastewater was based on data from the National Water and Sanitation Agency. This method considers the nutrient content in untreated wastewater and in effluents from wastewater treatment plants. We assumed a constant treatment efficiency of 30%, although this value may be optimistic given the primary effluent treatment processes in Brazil. For future assessments, local data on sewage treatment plants could be incorporated into the calculations if available during the project's execution.

This dataset includes empirical data and model simulations developed under the NEXUS project (https://nexus.ccst.inpe.br/), which analyzed the interrelationship and challenges of agricultural production, energy, and water resource use in the Caatinga and Cerrado regions. Conducted between 2018 and 2024, the NEXUS project employed a participatory multiscale approach, combining qualitative and quantitative methods from natural and social sciences. Over its six-year duration, the project engaged more than one hundred stakeholders from various sectors, producing diagnostics and scenarios for sustainable futures in these biomes.

Scenarios Descriptions:The “Green Transition” scenario aligns with the dominant sustainability narrative in the business sector, focusing on efficiency gains and technological solutions (e.g., low-carbon agriculture, energy transition led by large corporations) to address environmental challenges. This scenario envisions agricultural production concentrated in highly productive areas, facilitating the restoration of natural vegetation and fostering an increasingly urban future.

Conversely, the “Lives in Balance” scenario reflects the aspirations and struggles of social movements and traditional communities for recognition and the coexistence of diverse ways of life. It advocates transforming production systems, particularly through decentralized food and energy production, and emphasizes strengthening family farming and agroecological systems.

AcknowledgementsThe authors would like to thank the NEXUS Project, funded by the São Paulo Research Foundation – FAPESP (grants 2022/00917-0 and 2017/22269-2), and the Coordination for the Improvement of Higher Education Personnel (CAPES) for their support to Marcela Miranda through the National Postdoctoral Program (grants 88882.317530/2019-1 and 1732909/2017-2).