Supplement 1. Data on phytoplankton species richness and environmental variables used in this study.

File List EPAdata.txt Description The EPAdata.txt file is a tab-delimited ASCII file. The file contains data on phytoplankton species richness and environmental variables of 540 lakes and reservoirs distributed across the continental USA. The lakes and reservoirs were sampled from 1973–1975 as part of the National Eutrophication Survey conducted by the U.S. EPA. Column definitions and checksum values: Name of waterbody State Type of waterbody (lake or reservoir) Latitude, SUM = 20585.85475 Longitude, SUM = -51798.3929 Altitude (in km), SUM = 304.5463 Lake area (in km²), SUM = 25453.51 Lake depth (in m), SUM = 4945.149999 Number of sampling days, SUM = 1592 Chlorophyll concentration (in μg/L), SUM = 11718.22239 Total nitrogen (in mg/L), SUM = 705.6529752 Total phosphorus (in mg/L), SUM = 70.3631407 Temperature (in °C), SUM = 10188.35764 Secchi depth (in m), SUM = 885.1552689 Species richness (number of phytoplankton species), SUM = 15875 There are no missing values.