Nonlinearities in phytoplankton groups across temperate high mountain lakes

1-High mountain lakes are increasingly recognized as sentinel ecosystems of global change. Monitoring phytoplankton changes or reconstructing their composition from sedimentary records can help identify systemic changes in these lakes and their catchments. 2- This study aimed to evaluate the distribution of the major phytoplankton groups in high mountain lakes across environmental gradients and identify tipping points in relative dominance. The phytoplankton groups were estimated using pigment-based chemotaxonomy in 79 lakes in the Pyrenees selected to cover the bedrock and elevation gradients. Fifty-four environment variables were considered, including in-lake and catchment descriptors. 3-Redundancy analyses showed that in-lake descriptors override the explicative capacity of landscape variables. Generalized additive models and multivariate regression trees showed that water hardness, trophic state, and food web descriptors were, in this order, the most influential factors determining ..., The study was based on a survey of 79 lakes from mid-July to the end of August 2000 across the entire range of the Pyrenees. During this period, summer stratification occurs in most lakes, and phytoplankton communities can be assumed to be in a similar successional stage. The lakes were selected to cover the main bedrock, elevation, and geographical variation within the range. Only one or, exceptionally, a few lakes were sampled in cirque basins that included many close lakes to reduce potential spatial covariance because of the proximity and also to facilitate covering the entire massif with the available resources. The environmental variables considered (54) were grouped into five categories to evaluate the partial and hierarchical influence on the phytoplankton groups. Water chemistry (15 variables) included nutrients, major ions, and DOC. The physical environment (12) was characterized by considering morphological, thermal, light, and littoral substrate characteristics. The biotic e..., , # Nonlinearities in phytoplankton groups across temperate high mountain lakes

The data file contains the phytoplankton group distribution estimated using pigment-based chemotaxonomy across 82 lakes of the Pyrenees selected to cover the bedrock and elevation gradients.

## Description of the data and file structure

The file PGMCHEMTAX-JEcol2023.xlsx contains a first raw with the variable names (19), followed by 79 raws with the data in columns. The variable names are self-descriptive, although we include a more detailed description below. There are no missing values; zeros (0) correspond to values below the detection limit of the method.

#### Variables

Lake_name: Lake name, which may differ depending on the cartographic reference used.
Latitude_N: Latitude, North
Longitude_E: Longitude, East
Altitude_m: Elevation, meters above sea level.
EMERGE_lake_code: Lake code used in the European project EMERGE.
Lake_ID: Lake identification number used in Buchaca & Catalan (2024), Journal...