Abstract
Trophic state indexes (TSI) guide management strategies regarding eutrophication control worldwide. Such indexes usually consider chlorophyll-a (Chl-a), total phosphorus (TP), and Secchi disk depth (SDD) as independent variables for estimating aquatic productivity and the degree of impairment. TSIs for each of these components are frequently averaged to produce a single TSI value associated with a trophic state classification (e.g., oligotrophic, mesotrophic, or eutrophic). The potential divergence among equations and classification systems originally developed for temperate lakes or tropical/subtropical reservoirs might be particularly relevant in the tropics, where there is a lack of data and the use of equations originally developed for temperate systems may be inappropriate. We calculated two widely used TSIs for temperate lakes (TSItemp) or tropical reservoirs (TSItrop) and explored the deviations among TSI components in Brazilian reservoirs. When applied to our tropical/subtropical reservoirs, the TSItemp provided a conservative approach, with lower limits anticipating increasing trophic state classification. TSI components for Chl-a and SDD significantly deviated for both sets of equations, and these discrepancies were related to turbidity, water temperature, and cyanobacterial biomass. For TSItemp, but not for TSItrop, TSI values in relation to Chl-a and TP were also significantly different. All such deviations have important management implications especially when Chl-a, TP, and SDD are averaged in a single TSI, representing loss of information and less useful trophic state classifications. Our results demonstrate that tropical water bodies may respond to drivers of eutrophication differently than temperate systems, highlighting the need for more data to better inform management of these understudied ecosystems. As managers collect data from more tropical water bodies, regional models may offer even better understanding of factors influencing trophic state.
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Data Availability
The full dataset used in this paper is electronically available as Online Supplementary Material.
Change history
09 October 2021
A Correction to this paper has been published: https://doi.org/10.1007/s00267-021-01544-0
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Acknowledgements
The authors thank FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) for funding DGF Cunha and NR Finkler (Grants #2018/21412-9 and #2018/13171-1). We also thank CETESB (Companhia Ambiental do Estado de São Paulo) for the dataset used in this paper, which is publicly available at the InfoÁguas Sytem: https://cetesb.sp.gov.br/infoaguas. Two anonymous reviewers and the associate editor provided helpful comments to improve the manuscript.
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This study was partially funded by FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) under the Grant Agreements #2018/21412-9 and #2018/13171-1.
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All authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by DGFC, NRF, MCL, MdCC, WKD, and REC. The first draft of the manuscript was written by DGFC and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
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Cunha, D.G.F., Finkler, N.R., Lamparelli, M.C. et al. Characterizing Trophic State in Tropical/Subtropical Reservoirs: Deviations among Indexes in the Lower Latitudes. Environmental Management 68, 491–504 (2021). https://doi.org/10.1007/s00267-021-01521-7
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DOI: https://doi.org/10.1007/s00267-021-01521-7