Rich in history, the Guana ecosystem is a fundamental part of the northeast Florida community, especially popular for outdoor recreational activities including bird watching, paddle sports, fishing, and waterfowl hunting. The headwaters of the Guana River originate in Ponte Vedra Beach and the river system runs parallel to the Tolomato River, with the two rivers joining 7 miles north of the St. Augustine Inlet.
In 1957, the Florida Fish and Wildlife Conservation Commission (FWC) constructed a water control structure, Guana Dam, in the Guana River to create suitable conditions for duck hunting. The impoundment formed by Guana Dam is referred to as Guana Lake and encompasses 2,400 acres of wetlands, including brackish and freshwater grasses. To this day, Guana Lake is still managed by FWC.
The Guana River was once a praised harvest area for shellfish, but due to decreased water quality and human health risks, Florida’s Department of Agriculture and Consumer Services has restricted harvest since the mid-1980s. Through efforts by members of the Oyster and Water Quality Task Force (OWQTF) of the Guana, Tolomato, and Matanzas Rivers, it was realized that a lack of regular sampling has led to a scarcity of knowledge about current water quality conditions in the Guana ecosystem.
Inspired by momentous community interest and a common research priority, multiple sponsors including the Audubon Society and the Friends of the GTM Research Reserve, generously funded water quality sampling and subsequent laboratory analyses for a one-year pilot study, which began in July 2017. Monthly sampling, a collaboration between GTMNERR and Northeast Florida Aquatic Preserves, occurred during high outgoing tides at sites within the Guana Lake and Guana River.
The pilot study was featured in the September 2018 edition of the Estuary Examiner, GTM Research Reserve’s quarterly newsletter. Read the article here!
Map of sampling sites during the one-year pilot water quality study in the Guana system. Created by Michael Dickson
The average concentrations of nutrients and chlorophyll
a were concerning at some sites. When comparing these sites to the GTMNERR SWMP station at Pine Island, the site in the middle of Guana River was comparable. Pine Island is a good reference site because it is nearby in the Tolomato River and data go back to 2003.
Average concentrations of nutrient analyses of the one-year pilot study of water quality in the Guana system (July 2017-June 2018). Averages are calculated using geometric means. Guana Lake sites (Micklers, Lake Middle, and Lake South) are Class III estuarine waters. Guana River sites (River North and Guana River) are Class II estuarine waters. Waterbody classification determines the water quality threshold values.
Bacterial levels at the stations generally did not exceed the water quality standards for their associated waterbody. However, high levels were observed in months following large rainfall events, such as Hurricane Irma in the October 2017 sampling event.
Fecal coliform data from one-year pilot study of water quality in the Guana system. Horizontal lines represent threshold levels. Dashed line (43 MPN/100mL): no more than 10% of samples may exceed this value. Solid line (14 MPN/100mL) is median value.
Enterococcus data from one-year pilot study of water quality in the Guana system. Horizontal lines represent threshold levels. Dashed line (35 MPN): Geometric mean (min 10 samples) in any 30-day period. Solid line (130 MPN): No more than 10% of samples
Where are we now and what is next?
Florida’s DEP assesses water quality in state waterbodies every 5 years. (More info on the assessment process can be found here.) DEP could only use data prior to July 2017 for that assessment and had insufficient data to assess Guana waterbodies. Because of the 5-year cycle, DEP was not considering sampling Guana waterbodies this year to be a high priority, but we reached out and shared our recent concerning results.
We have now partnered with DEP, Northeast Florida Aquatic Preserves, and FWC to continue monthly sampling at the five original stations as well as five additional stations five times per year. Additionally, we will also be collecting genetic samples to determine if bacteria are from human or non-human sources. It is also possible to determine the specific animal sources (dog, deer, pig, gull, etc.), which will inform more specific management practices.
Collecting baseline data and further investigating the potential sources (and quantity) of nutrients into the Guana system will further our understanding of eutrophication using an impounded estuarine system. Guana is an ideal system to study the effects and sources of eutrophication due to the clear input (water control structure at Mickler Road) and output (Guana Dam) points and a gradient of land development from north to south throughout the watershed. Stay tuned for more information as we continue sampling. We also plan to seek funding for a hydrodynamic study and a graduate research assistant.
Interested in data from the Guana Water Quality Project?
Contact Research Director, Nikki Dix (Nikki.Dix@FloridaDEP.gov) for information.