OLIGOTREND, a global database of multi-decadal chlorophyll a and water quality time series for rivers, lakes, and estuaries

Abstract

Reversed eutrophication, called oligotrophication, has been widely documented globally over the last 30 years in rivers, lakes, and estuaries. However, the absence of a comprehensive and harmonized dataset has hindered a deeper understanding of its ecological consequences. To address this data gap, we developed the OLIGOTREND database, which contains multi-decadal time series of chlorophyll a, nutrients (nitrogen and phosphorus), and related physicochemical parameters, totalling 4.3 million observations. These data originate from 1894 unique monitoring locations across estuaries (n = 238), lakes (687), and rivers (969). Most time series cover the period from 1986–2022 and comprise at least 15 years of chlorophyll a observations. Each location is associated with catchment and hydroclimatic attributes. Trend and breakpoint analyses were applied to all time series. Chlorophyll a showed temporally variable and ecosystem-specific responses to nutrient declines with an overall declining trend for 18 % of the time series, contrasting greatly with a majority of declining trends for nutrient concentrations. We harmonized the database to ensure reproducibility and ease of access and support future updates and contributions. Available at https://doi.org/10.6073/pasta/a7ad060a4dbc4e7dfcb763a794506524 (Minaudo and Benito, 2024), the OLIGOTREND database supports collaborative efforts aimed at further advancing our understanding of biogeochemical and biological mechanisms underlining oligotrophication and ecological impacts of global long-term environmental change.