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<p>The Diatom-based transfer function model is a robust tool for inferring past water phosphorus concentrations, particularly in highly impacted water ecosystems where information on pre-disturbance conditions is often lacking. Although well studied in natural reservoirs, especially in temperate regions, there is a notable gap in our understanding of its efficiency in man-made tropical reservoirs. To address this gap, our study focuses on the development of a robust diatom-based transfer function model, specifically applied to infer past water phosphorus concentrations in the Guarapiranga Reservoir in Brazil (from 1919 to 2010). To provide a reliable, predictive ability, we integrated limnological and biological data from surface sediment diatom assemblages from across 33 reservoirs, covering a trophic gradient from ultraoligotrophic to hypereutrophic conditions. The regression and calibration steps involved 63 diatom species from 112 sample units, resulting in a good predictive calibration model (r<sup>2</sup> = 0.84). Species were categorized into three trophic groups (oligotrophic, mesotrophic, and eutrophic) based on their optimal conditions and tolerance to TP concentrations. The Weighted Averaging (WA(tol)) model, employing inverse tolerance weighting, demonstrate effectiveness (RMSE of 16.71&#xa0;µg TP L<sup>−1</sup>). Applying this model to a core from the Guarapiranga Reservoir provided a quantitative reconstruction of phosphorus concentrations over approximately 91&#xa0;years, with 24 species from the calibration set contributing to TP reconstruction. The reference values (19&#xa0;µg TP L<sup>−1</sup>, oligotrophic) and pre-eutrophication phosphorus thresholds (around 26&#xa0;µg TP L<sup>−1</sup>, mesotrophic) established by the model were aligned with previously known qualitative paleoenvironmental reconstructions for the reservoir. This comprehensive understanding of the total phosphorus conditions at baseline before the onset of eutrophication is essential for establishing effective conservation and recovery goals. Thus, this model has emerged as an indispensable auxiliary tool for environmental management measures, contributing to the historical understanding of eutrophication and supporting the effective formulation of management and restoration plans.</p>

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Diatom transfer-function of total phosphorus in an urban water supply reservoir in Brazil: inference of baseline conditions for tropical reservoirs

  • 期刊论文

  • 发表日期：

    2025年6月11日

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  • Angela Maria da Silva-Lehmkuhl,
  • Luciane Fontana,
  • Denise C. Bicudo

摘要

The Diatom-based transfer function model is a robust tool for inferring past water phosphorus concentrations, particularly in highly impacted water ecosystems where information on pre-disturbance conditions is often lacking. Although well studied in natural reservoirs, especially in temperate regions, there is a notable gap in our understanding of its efficiency in man-made tropical reservoirs. To address this gap, our study focuses on the development of a robust diatom-based transfer function model, specifically applied to infer past water phosphorus concentrations in the Guarapiranga Reservoir in Brazil (from 1919 to 2010). To provide a reliable, predictive ability, we integrated limnological and biological data from surface sediment diatom assemblages from across 33 reservoirs, covering a trophic gradient from ultraoligotrophic to hypereutrophic conditions. The regression and calibration steps involved 63 diatom species from 112 sample units, resulting in a good predictive calibration model (r2 = 0.84). Species were categorized into three trophic groups (oligotrophic, mesotrophic, and eutrophic) based on their optimal conditions and tolerance to TP concentrations. The Weighted Averaging (WA(tol)) model, employing inverse tolerance weighting, demonstrate effectiveness (RMSE of 16.71 µg TP L−1). Applying this model to a core from the Guarapiranga Reservoir provided a quantitative reconstruction of phosphorus concentrations over approximately 91 years, with 24 species from the calibration set contributing to TP reconstruction. The reference values (19 µg TP L−1, oligotrophic) and pre-eutrophication phosphorus thresholds (around 26 µg TP L−1, mesotrophic) established by the model were aligned with previously known qualitative paleoenvironmental reconstructions for the reservoir. This comprehensive understanding of the total phosphorus conditions at baseline before the onset of eutrophication is essential for establishing effective conservation and recovery goals. Thus, this model has emerged as an indispensable auxiliary tool for environmental management measures, contributing to the historical understanding of eutrophication and supporting the effective formulation of management and restoration plans.