Laurentian Great Lakes Phytoplankton and Their Water Quality Characteristics, Including a Diatom-Based Model for Paleoreconstruction of Phosphorus Euan D. Reavie 1 *, Adam J. Heathcote 2 , Victoria L. Shaw Chraı¨bi 3 1 Center for Water and the Environment, Natural Resources Research Institute, University of Minnesota Duluth, Duluth, Minnesota, United States of America, 2 Groupe de Recherche Interuniversitaire en Limnologie, De ´partement des Sciences Biologiques, Universite ´ du Que ´bec a ` Montre ´al, Montre ´al, Que ´bec, Canada, 3 Department of Earth and Atmospheric Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska, United States of America Abstract Recent shifts in water quality and food web characteristics driven by anthropogenic impacts on the Laurentian Great Lakes warranted an examination of pelagic primary producers as tracers of environmental change. The distributions of the 263 common phytoplankton taxa were related to water quality variables to determine taxon-specific responses that may be useful in indicator models. A detailed checklist of taxa and their environmental optima are provided. Multivariate analyses indicated a strong relationship between total phosphorus (TP) and patterns in the diatom assemblages across the Great Lakes. Of the 118 common diatom taxa, 90 (76%) had a directional response along the TP gradient. We further evaluated a diatom-based transfer function for TP based on the weighted-average abundance of taxa, assuming unimodal distributions along the TP gradient. The r 2 between observed and inferred TP in the training dataset was 0.79. Substantial spatial and environmental autocorrelation within the training set of samples justified the need for further model validation. A randomization procedure indicated that the actual transfer function consistently performed better than functions based on reshuffled environmental data. Further, TP was minimally confounded by other environmental variables, as indicated by the relatively large amount of unique variance in the diatoms explained by TP. We demonstrated the effectiveness of the transfer function by hindcasting TP concentrations using fossil diatom assemblages in a Lake Superior sediment core. Passive, multivariate analysis of the fossil samples against the training set indicated that phosphorus was a strong determinant of historical diatom assemblages, verifying that the transfer function was suited to reconstruct past TP in Lake Superior. Collectively, these results showed that phytoplankton coefficients for water quality can be robust indicators of Great Lakes pelagic condition. The diatom-based transfer function can be used in lake management when retrospective data are needed for tracking long-term degradation, remediation and trajectories. Citation: Reavie ED, Heathcote AJ, Shaw Chraı ¨bi VL (2014) Laurentian Great Lakes Phytoplankton and Their Water Quality Characteristics, Including a Diatom- Based Model for Paleoreconstruction of Phosphorus. PLoS ONE 9(8): e104705. doi:10.1371/journal.pone.0104705 Editor: Francois G. Schmitt, CNRS, France Received February 21, 2014; Accepted July 16, 2014; Published August 8, 2014 Copyright: ß 2014 Reavie et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This research was largely supported by grants to E. Reavie from the U.S. Environmental Protection Agency under Cooperative Agreements GL- 00E23101 and GL-00E00790-2. This document has not been subjected to the Agency’s required peer and policy review and therefore does not necessarily reflect the view of the Agency, and no official endorsement should be inferred. Sedimentary assemblages from Lake Superior were collected and assessed under research sponsored by the Minnesota Sea Grant College Program supported by the NOAA office of Sea Grant, United States Department of Commerce, under grant No. R/CC-01-10. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * Email: ereavie@d.umn.edu Introduction Recent trends from monitoring data demonstrate rapid changes in the Laurentian Great Lakes system associated with anthropo- genic drivers. Most notably, changes in the water quality [1], phytoplankton (unpublished data), zooplankton [2] and benthos [3] collectively confirm or suggest detriments associated with invasive species, nutrient imbalances and climate. While algal abundances have been inordinately low in some regions (e.g., Lake Huron; unpublished data), new eutrophication problems have also manifested as substantial algal blooms (e.g., [4]). Such quantitative assessments of environmental problems have been valuable to support lake management [5] because they provide information on the abundance of various organisms, traits that are critical to understanding and managing food webs. However, taxon-specific evaluations of pelagic indicators in the Great Lakes are lacking. In addition to these more intuitive evaluations of organism numbers and biomass, taxon-specific ecological data can provide additional tools to inform management [6]. Developing effective indicators of ecological condition requires that they be calibrated to identify their responses to important environmental stressors [7]. The main goals of calibration are to identify environmental characteristics of potential indicator taxa so that they may be subsequently used to infer condition. Assem- blages of algae, which are physiologically subject to water quality, have the potential to provide time-integrated inferences of limnological conditions. Such bioindicators are particularly needed to monitor the impacts of human activities that are increasing nutrient supplies to water bodies, introducing non- native species, and changing climate. Great Lakes coastal algae, particularly diatoms, have been shown to provide a more temporally integrated assessment of water quality conditions than discrete water quality measurements [8], but similar indicators PLOS ONE | www.plosone.org 1 August 2014 | Volume 9 | Issue 8 | e104705