Journal of Water Resource and Protection, 2019, 11, 810-829 http://www.scirp.org/journal/jwarp ISSN Online: 1945-3108 ISSN Print: 1945-3094 DOI: 10.4236/jwarp.2019.116049 Jun. 30, 2019 810 Journal of Water Resource and Protection Evaluation of Size Structure in Freshwater Cyanobacterial Populations: Methods to Quantify Risk Associated with Changes in Biomass and Microcystin Concentrations Nancy J. Leland 1 , James F. Haney 2 , Kristin Conte 3 , Karen Malkus-Benjamin 4 , Bryan Horsely 5 1 Lim-Tex, North Andover, MA, USA 2 Department of Zoology, University of New Hampshire, Durham, NH, USA 3 Manchester Water Works, Manchester, NH, USA 4 Town of Barnstable, Barnstable, MA, USA 5 Association to Preserve Cape Cod, Dennis, MA, USA Abstract Cyanobacterial populations in surface waters, including drinking water supplies and recreational waters, represent an ever present challenge for resource man- agers. As communities continuously respond to external and internal processes, dynamic profiles of composition, dominance, growth and toxigenicity emerge. In this study measures of size structure and biomass, quantified using light mi- croscopy and fluorometry, were used to estimate microcystin concentrations through linear regression analysis. Toxigenic profiles using cyanobacterial bio- mass were developed for lakes dominated by Microcystis spp. and Dolichos- permum spp., influenced by both genus-specific pigment concentrations as well as microcystin concentrations. Community composition (Log %MIC) and bio- mass were used to describe microcystin concentrations in mixed assemblages, where composition was the first input variable. The accessory photopigment phycocyanin was used to describe the linear relationship between the daily growth and net microcystin production rates in the bloom-forming Micro- cystis spp. samples, suggesting that this size-fractionated sample may provide indications of potential toxigenicity in the whole lake water sample. Future investigations using fluorometric evaluation of cyanobacterial populations could provide additional applications and metrics for use by resource man- agers to quantify risk association with elevated cyanotoxin concentrations. Keywords Microcystis, Dolichospermum, Phycocyanin, Microcystins, Growth Rates How to cite this paper: Leland, N.J., Ha- ney, J.F., Conte, K., Malkus-Benjamin, K. and Horsely, B. (2019) Evaluation of Size Structure in Freshwater Cyanobacterial Pop- ulations: Methods to Quantify Risk Asso- ciated with Changes in Biomass and Micro- cystin Concentrations. Journal of Water Resource and Protection, 11, 810-829. https://doi.org/10.4236/jwarp.2019.116049 Received: May 26, 2019 Accepted: June 27, 2019 Published: June 30, 2019 Copyright © 2019 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access