Abstract
Phytoplankton bloom monitoring in freshwaters is a challenging task, particularly when biomass is dominated by buoyant cyanobacterial communities that present complex spatiotemporal patterns. Increases in bloom frequency or intensity and their earlier onset in spring were shown to be linked to multiple anthropogenic disturbances, including climate change. The aim of the present study was to describe the phenology of phytoplankton blooms and its potential link with morphological, physiographic, anthropogenic, and climatic characteristics of the lakes and their watershed. The spatiotemporal dynamics of near-surface blooms were studied on 580 lakes in southern Quebec (Eastern Canada) over a 17-year period by analyzing chlorophyll-a concentrations gathered from MODIS (Moderate Resolution Imaging Spectroradiometer) satellite images. Results show a significant increase by 23% in bloom frequency across all studied lakes between 2000 and 2016. The first blooms of the year appeared increasingly early over this period but only by 3 days (median date changing from 6 June to 3 June). Results also indicate that high biomass values are often reached, but the problem is seldom extended to the entire lake surface. The canonical correlation analysis between phenological variables and environmental variables shows that higher frequency and intensity of phytoplankton blooms and earlier onset date occurred for smaller watersheds and higher degree-days, lake surface area, and proportion of urban zones. This study provides a regional picture of lake trophic state over a wide variety of lacustrine environments in Quebec, a detailed phenology allowing to go beyond local biomass assessments, and the first steps on the development of an approach exploiting regional trends for local pattern assessments.
Highlights
IntroductionCyanobacteria threaten the ecological integrity of some of the world’s most important lake environments, including Lake Erie [1], Lake Ontario [2], Lake Taihu [3], Lake Okeechobee [4], and Lake Victoria [5]
The marked increase in freshwater algal blooms is of major interest to governments and public health agencies responsible for maintaining the ecological services provided by these systems.Cyanobacteria threaten the ecological integrity of some of the world’s most important lake environments, including Lake Erie [1], Lake Ontario [2], Lake Taihu [3], Lake Okeechobee [4], and Lake Victoria [5].Their increasing frequency and sustained presence affect the structure and functioning of aquatic food webs [6], limit recreational activities [7], and threaten drinking water sources [8]
This study presents the spatiotemporal dynamics of phytoplankton blooms over 580 lakes in southern Quebec between 2000 and 2016, and their potential relationships with physiographic, morphological, and climatic descriptors prevailing on the lakes and their watersheds
Summary
Cyanobacteria threaten the ecological integrity of some of the world’s most important lake environments, including Lake Erie [1], Lake Ontario [2], Lake Taihu [3], Lake Okeechobee [4], and Lake Victoria [5]. Their increasing frequency and sustained presence affect the structure and functioning of aquatic food webs [6], limit recreational activities [7], and threaten drinking water sources [8]. The N:P ratio is used as an indicator of the occurrence of cyanobacterial [27,28,29]
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