Salinity Concentration Monitoring of Fresh Water Holes

in the Florida Keys.

This SOKD project began in late March 2019 and is being done in collaboration with SOKD volunteers, the USFWS/Florida Keys National Wildlife Refuges, and Boy Scouts of America.

Fresh water sources for Florida Keys wildlife are important resources whose availability varies with the region’s distinct wet and dry seasons, and may become quite limited during extended periods of draught.  In the middle and lower Keys such sources are comprised of natural depressions holding rain water, artificial or man-enhanced depressions (e.g. mosquito ditches and dug-out ponds) some of which are connected to subterranean freshwater lenses, and small and large solution holes.

“Salinity” in water is a term combining the concentration of ions such as sodium, magnesium, potassium and a few others. The salinity of sea water world-wide is 35-38 parts per thousand (ppt). The salinity of the human body (and most mammals) is around 9 ppt. The very large difference makes drinking sea water (for even short periods of time) lethal to humans. Some animals (e.g. sea gulls) have evolved unique mechanisms to drink sea water and extract the excess salt through glands that mammals don’t have.  A researcher studying Key Deer in the 1970s observed them drinking from water sources having salinities in the 12-13 ppt range.  He proposed that they have developed an increased tolerance for salinity in their drinkable water supply.

The importance of awareness of the palatability state of the various sources throughout the year has been long recognized by the Refuge.  In the past, regular field monitoring for water salinity was conducted. Presently, there is no regular, high-frequency, long-term fresh water monitoring program in-place that spans the entire multi-island Key Deer habitat range. This project aims to provide continuous valid scientific data about the status of water availability to wildlife throughout islands spanning from No Name to Sugarloaf Keys.  The data are made available to Refuge management and related state and federal agencies, as well as the public.  The salinity data are regularly collected by a group of trained volunteers permanently residing in the Keys, and the project is managed by SOKD using internal financial resources.  The project utilizes a broad network of sampling sites, some of which are on non-refuge lands and some of which lie within the Refuge.

In addition to providing spatially detailed and comprehensive data on drinking water availability to wildlife in the middle Keys, this project provides the opportunity to conduct research on several related topics: 1) Using rain gauges on multiple islands and locations, the project will allow the study of how rainfall volumes affect the various water sources – e.g. how much rainfall is required to bring a particular source back to wildlife-usable range.  This will, in turn, allow better understanding and estimation of water resource availability in the future; 2) Using trail cameras at selected water sources, this project will aim to provide direct video evidence of the deer’s (and potentially other wildlife’s) acceptance of the different salinity concentrations as the water sources cycle through their annual range, thus providing updated data on what salinities are acceptable to the deer.