Abstract
The community structures of phytoplankton are important factors and indicators of lake water quality. Harmful algal blooms severely impact water supply, recreational activities and wildlife habitat. This study aimed to examine the phytoplankton composition and variations using microscopy, and identify harmful Cyanobacteria in weekly samples taken from four sites at Harsha Lake in southwest Ohio. Over the course of the summer in 2015, the phytoplankton of Harsha Lake consisted mainly of 13 taxa belonging to Bacillariophyta, Chlorophyta, Cryptophyta, Cyanobacteria, Dinophyta and Euglenophyta. Their significant successions started with Bacillariophyta and/or Chlorophyta, then bloomed with Cyanobacteria and ended with Chlorophyta and/or Dinophyta. Cyanobacteria members: Microcystis, Planktothrix, Dolichospermum, Aphanizomenon, Cylindrospermopsis, and Oscillatoria from the Cyanophyceae were identified to be dominant genera. These organisms varied spatially and temporally in similar patterns along with the variations of nutrients and formed the summer bloom with the total biomasses ranging from 0.01 to 114.89 mg L−1 with mean of 22.88 mg L−1. M. aeruginosa and P. rubescens were revealed as the microcystin producers, while A. circinalis and Aphanizomenon sp. were identified as a saxitoxin producer through cloning and sequencing PCR products of mcyA, mcyE and sxtA genes. The biomasses of phytoplankton, Cyanobacteria and Microcystis were positively correlated to nutrients, especially to total nitrogen. The total ELISA measurement for microcystin positively correlated with Cyanobacteria (R2 = 0.66, P < 0.0001), Microcystis (R2 = 0.64, P < 0.0001) and phytoplankton (R2 = 0.59, P < 0.0001). The basic information on the occurrence and biomasses of Cyanobacteria and total phytoplankton, and the analysis for toxic species, which were the first report for the inland water in Ohio, USA, will document the succession patterns of phytoplankton and toxin production over a season and provide data to predict risk occurrence to both human and ecological factors.
Highlights
Investigation of phytoplankton by direct microscopy yields information of biomass and species compositions, which has long been used in lake studies [1], such information is often of considerable significance in the monitoring of lake water quality [2]
This study aimed to examine the phytoplankton composition and variations using microscopy, and identify harmful Cyanobacteria in weekly samples taken from four sites at Harsha Lake in southwest Ohio
During the entire sampling period, the phytoplankton of Harsha Lake consisted mainly of 13 genera belonging to Bacillariophyta (Cyclotella, Melosira and Synedra), Chlorophyta (Chlamydomonas and Pediastrum), Cryptophyta (Cryptomonas), Cyanobacteria (Aphanizomenon, Dolichospermum, Microcystis and Oscillatoria), Dinophyta (Ceratium and Peridinium) and Euglenophyta (Euglena), and their total biomass varied from 2.06 to 122.72 mg L−1 with a mean of 34.12 mg L−1 (Table 3)
Summary
Investigation of phytoplankton by direct microscopy yields information of biomass and species compositions, which has long been used in lake studies [1], such information is often of considerable significance in the monitoring of lake water quality [2]. Over the past 10 years, HABs have been increasing in Ohio inland lake waters [6]. HABs and associated toxins are a major water-quality issue in Lake Erie, and in the other inland lakes in Ohio. Phytoplankton are an important basal resource to heterotrophic organisms in lakes, and their growth, succession and community structures determine the potential productivity of the ecosystem [11] as well as the status of the ecosystem and water quality. The purpose of this investigation was to examine phytoplankton composition with emphasis on Cyanobacteria, community succession and HAB toxic species and to explore the relationships between the variations of phytoplankton and HABs, and biomasses and nutrients
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