Cyanobacterial Occurrence and Bloom Development in Oligotrophic Adirondack Lakes Active

Problem



Harmful algal blooms (HABs) are increasingly a global concern because HABs pose a threat to human and ecosystem health and cause economic damages. HABs are a concern in waterbodies used for drinking-water supply and recreation in New York State. Toxins produced by some species of cyanobacteria (called cyanotoxins) can cause acute and chronic illnesses in humans. Aquatic ecosystem health also is affected by cyanotoxins, as well as low dissolved oxygen concentrations and changes in aquatic food webs caused by an over-abundance of cyanobacteria.

Cyanobacterial HABs are typically considered to be a symptom of eutrophication. However, oligotrophic lakes worldwide, including those in the Adirondack Region of New York, also are experiencing cyanobacterial blooms. As such, some of the most pristine lakes in New York are now threatened by HABs. Once Adirondack lakes experience blooms, they appear to be more likely to experience them again in the future.



Objectives



The goal of this effort is to better understand the occurrence, through assessments of phytoplankton community assemblages, of potentially toxic cyanobacteria in oligotrophic lakes. This study will: 1) describe the contribution of toxic and non-toxic cyanobacteria to the overall phytoplankton community in  oligotrophic lakes; 2) determine if there are differences in cyanobacterial communities between lakes that have and have not had documented blooms; and 3) indicate whether bottom sediments in lakes that have had documented blooms are enriched with cyanobacterial resting stages (e.g. akinetes).



Approach



Oligotrophic lakes in the Adirondacks and northeastern New York will be identified and grouped according to whether they have had documented cyanobacterial blooms. Water-quality conditions will be compared between the two groups using existing NYSDEC datasets. A subset of 2-3 lakes from each group will be selected for a focused data collection effort during 2021; lakes that are being sampled as part of DEC lake monitoring programs during 2021 will be given priority in the selection process.

 

Each lake (4-6 total) will be sampled at the beginning (June-July), middle (August-September), and end (October-November) of the 2021 cyanobacterial bloom season in New York. During each lake visit, water and bottom sediment samples will be collected from open-water and near shore areas (total of 24-36 samples for water and sediment analyses). In lakes that have experienced blooms, near shore areas will be selected based on locations of reported blooms. In lakes that have not experienced blooms, near shore areas will be selected based on the location of recreational areas and access points. When observed, additional surface grab samples will be collected from cyanobacterial blooms.

 

At each sample location vertical profiles of light, temperature, dissolved oxygen, pH, specific conductance, turbidity, and algal and dissolved organic matter fluorescence will be measured. Secchi depth will also be measured. Integrated photic zone samples will be collected using a pump. All discrete water-quality samples will be analyzed for: phytoplankton community composition, with an emphasis on cyanobacteria; 16S rRNA sequencing; and qPCR for cyanotoxin synthetase gene targets (anatoxin-a, cylindrospermopsin, microcystin, and saxitoxin). A subset of samples will be analyzed for cyanotoxins based on the results of other analyses.

 

Surficial bottom sediments (approximately the top 3 centimeters) will also be collected at each sample location. Sediment samples will be analyzed for: cyanobacterial akinetes and remnants; 16S rRNA sequencing; and qPCR for cyanotoxin synthetase gene targets (anatoxin-a, cylindrospermopsin, microcystin, and saxitoxin). In addition, bottom sediment samples will be cultured to identify the presence of cyanobacteria that do not have akinetes or remnants identifiable through microscopy.

 

Traditional microscopy will be used for identification and enumeration of phytoplankton and cyanobacterial akinetes. Genetic analyses and cyanobacterial cultures will more fully characterize cyanobacterial community composition and the potential for cyanotoxin production than can be achieved through microscopy alone and may help elucidate subtle differences between lakes that have and have not experienced blooms. Spatial and seasonal differences in cyanobacterial communities between lakes that have and have not experienced blooms will be evaluated. Cyanobacterial akinetes and remnants, and culturable cyanobacteria, in near-surface bottom sediments will provide an indication of the differences between potential seed banks and source areas in lakes that have and have not experienced blooms.