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 (TSI_temp) or tropical reservoirs (TSI_trop) and explored the deviations among TSI components in Brazilian reservoirs. When applied to our tropical/subtropical reservoirs, the TSI_temp 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 TSI_temp, but not for TSI_trop, 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.

营养状态指数 (TSI) 指导全球富营养化控制的管理策略。此类指标通常将叶绿素 a (Chl-a)、总磷 (TP) 和 Secchi 圆盘深度 (SDD) 作为估计水生生产力和损害程度的独立变量。这些成分中的每一个的 TSI 经常被平均以产生与营养状态分类（例如，贫营养、中营养或富营养）相关的单个 TSI 值。最初为温带湖泊或热带/亚热带水库开发的方程和分类系统之间的潜在分歧在热带地区可能特别相关，因为那里缺乏数据，使用最初为温带系统开发的方程可能不合适。我们计算了两种广泛使用的温带湖泊 TSI (TSI_temp ) 或热带水库 (TSI _trop ) 并探索了巴西水库中 TSI 组件之间的偏差。当应用于我们的热带/亚热带水库时，TSI_温度提供了一种保守的方法，下限预计会增加营养状态分类。Chl-a 和 SDD 的 TSI 成分在两组方程中都有显着偏差，这些差异与浊度、水温和蓝藻生物量有关。对于 TSI _temp，但不适用于 TSI _trop，与 Chl-a 和 TP 相关的 TSI 值也有显着差异。所有这些偏差都具有重要的管理意义，尤其是当 Chl-a、TP 和 SDD 在单个 TSI 中取平均值时，代表信息丢失和不太有用的营养状态分类。我们的研究结果表明，热带水体对富营养化驱动因素的反应可能与温带系统不同，这凸显了需要更多数据来更好地为这些未充分研究的生态系统的管理提供信息。随着管理人员从更多热带水体收集数据，区域模型可以更好地了解影响营养状态的因素。