Harpeth Conservancy 2019 Algal Toxin Survey

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Water full of algae laps along the Sewell's Point shore on the St. Lucie River under an Ocean Boulevard bridge.

Introduction

Phosphorus and nitrogen are essential nutrients for plant and algal growth in aquatic habitats.  Elevated levels of phosphorus and nitrogen caused by nutrient pollutionmaylead to the growth and occurrence of algal blooms, which is the rapid growth of aquatic or marine algae.  Algal blooms have a multitude of impacts to human and environmental health including: (1) contribute to low oxygen conditions in aquatic habitats, (2) outcompete native algae andvegetation for resources, and (3) produce toxins that are hazardous to human and animal health.  This report focuses on toxin produced by algae.  Algal toxins are produced by cyanobacteria, which are classified as bacteria but commonly referred to as blue-green algae –toxin produced by cyanobacteria will be referred to as cyanotoxin.Microcystin is a common cyanotoxin and is produced by a variety of cyanobacterial species most notably Microcystis aeruginosa

 

The U.S. Environmental Protection Agency has determined that nutrient pollution, and thus the conditions to cause algal blooms, occurs in all 50 U.S. states.  Unfortunately, in a 2019 report by the National Resources Defense Council (NRDC), 15 of the 50 U.S. states lack any cyanobacteria or cyanotoxin data collected by the state – Tennessee being one of the 15.The Harpeth Conservancy in partnership with Jefferson G. Lebkuecher, Ph.D. at Austin Peay University performed an algal composition survey within the Harpeth River in 2017.  Several cyanobacteria genera were identified in the Harpeth River that are known cyanotoxin producers such as Microcystis, Oscillatoria, andPhomidium.  These results in conjunction with the NRDC report led to a second survey for microsystin in the Harpeth watershed between September and October 2019.  The authors are not aware of any data available for concentrations of microcystin within the Harpeth watershed.

Materials and Methods

Water samples (n = 18) were collected between September 14th and October 2nd, 2019 at various locations within the Harpeth watershed (Table 1).  Both Harpeth River mainstem and tributaries were represented within the sampling locations.  Locations were selected based on ease-of-access and whether algae was present regardless of it being within the water column or as a benthic scum.  Locations with more visible algal growth were given priority as cyanotoxin would be more likely to be present and/or detected.

Water samples (n = 18) were collected between September 14th and October 2nd, 2019 at various locations within the Harpeth watershed (Table 1).  Both Harpeth River mainstem and tributaries were represented within the sampling locations.  Locations were selected based on ease-of-access and whether algae was present regardless of it being within the water column or as a benthic scum.  Locations with more visible algal growth were given priority as cyanotoxin would be more likely to be present and/or detected.

Frozen samples were transported in a cooler to the Environmental Sciences Department at Tennessee State University for analysis.  Each sample was analyzed for microcystins/nodularins (µg/L; EPA Method 546) using an Abraxis, Inc (Warminster, PA) ELISA kit (Item #: 520011-OH).  It is important to note that this analysis is for research purposes only and are not part of a USGS or State study, or from a certified lab.

Results and Discussion

Table 1 contains location description, date, and concentration of microcystin (µg/L) for each sample.  A non-detect result indicates that values were below the detection limit of 0.150 µg/L.  Highlighted rows indicate the detection of microcystin above the detection limit.  The tributary by Bailey Rd. (0.44 µg/L) and Trace Creek (0.24 µg/L) both had detectable quantities of microcystin.  Latitude and longitude values are reported for each location (Table 1) and mapped within the Harpeth River watershed (Fig. 1).

Table 1: Location, date, and concentration of microcystin (µg/L) for each site sampled between September 14th and October 2nd.
Figure 1: Location of each sampling location (green dot) and corresponding value for microcystin concentration (µg/L). The map also depicts the Harpeth River watershed (blue shaded region), major roadways (black lines), and major waterways (blue lines) within the watershed.

Sampling locations were primarily selected to be within the main channel (n = 14) of the Harpeth River due to the likelihood of recreational use compared to the smaller tributaries (n = 4) within the watershed.  Two of the four samples that exhibited measurable concentrations of microcystin were collected from smaller tributaries within the Harpeth River watershed.  While smaller tributaries may offer a higher likelihood to detect microcystin given that dilution would be at a minimum, larger rivers such as the Ohio River have experienced algal blooms and microcystin values >1,000 µg/L in a 2019 algal bloom.  Photos from select sites are included in Appendix A and B.

The U.S. EPA recommends that a 4 µg/L microcystin threshold should be the maximum exposure limit for recreational activities.  For the minimum drinking water threshold for microcystin levels in tap water, the EPA states, “10-day Health Advisory of 0.3 µg/L is considered protective of non-carcinogenic adverse health effects for bottlefed infants and young children of pre-school age over a ten-day exposure to microcystins in drinking water.”  The levels of microcystin found in the Harpeth are lower than those recommended for recreational exposure and so no immediate health concerns were documented.  However, the presence of toxin producing algae indicates that under deleterious conditions (or worst-case scenarios), toxin production could increase.  Additional monitoring particularly in tributaries should be considered especially during late summer months when water temperatures are high and drought conditions exist.

Acknowledgements

Thanks to our partner Thomas Byl and the Environmental Sciences Department at Tennessee State University for performing the laboratory work necessary to analyze the water samples for microcystin.