The earth’s surface is comprised of 71% water and south Florida is no different. Everglades National Park is comprised of a wide array of ecological systems, but nearly 100% of them are dependent on water. There is no portion of the Everglades more dependent on water for its productivity and more particular, freshwater, than Florida Bay. Florida Bay is dependent on a consistent source of freshwater to provide a variety of species varying salinities for their life cycle. These salinities should range from completely fresh at 0 Practical Salinity Units (PSU’s) to 32 PSU’s. Over the last several decades, the delivery of freshwater has been inconsistent and has been disparate with the paleo (i.e. historical) record. In some instances, this inconsistency has allowed for ecological system alterations that have caused negative impacts. One of the many alterations that has occurred is an increase in the density of turtle grass in the coastal bights of Florida Bay and more specifically, Garfield Bight. These bights would, based on the historical record, be comprised primarily of shoal grass.
Changes in freshwater inflow affect the salinity regimes in Florida Bay. Low freshwater inputs leading to increased salinity disturb the recruitment of various prey species and the sportfish that depend on them. For example, shrimp have the potential to determine the success or failure of trout fishing. Over the course of the past 6 months, reports of the loss of significant portions of seagrass in Florida Bay have become part of common water related discussions. This problem did not start 6 months ago, but actually in December 2014. The salinity in Garfield Bight began the dry season that month at approximately 30 practical salinity units, which was close to normal PSU ranges in the open ocean of 32-36. Scientific research indicates an annual average of 28 PSU’s for Garfield Bight. At this same time, the water level gauges in the Northeast Shark River Slough (NSRS, a natural wet prairie which is a conduit of fresh water for the southern portion of Everglades National Park) were at approximately 7’ above mean sea level (NGVD, or National Geodetic Vertical Datum). Over the following 6 months, from January 2015 through June 2015, the water level gauge in NSRS began to fall and the salinity in Garfield Bight began to climb. By June of last year, the water level gauge in the NSRS had dropped 2.5’ and by the following month the salinity in Garfield Bight had climbed to 72 PSU, or more than twice the salinity of open ocean seawater.
Due to many input stressors of heat, calm weather, natural topographic landscape fracturing in Florida Bay created by Snake Bight, lack of rain throughout the dry season and into the rainy season, and the increase in salinity, hydrogen sulfides formed. Hydrogen sulfides are extremely harmful to seagrass and more particularly turtle grass, the same turtle grass that had colonized in high density into Garfield Bight due to two decades of continued water delivery inconsistencies since the crash in the bay in 1987. This accumulated hydrogen sulfide along with other environmental stressors are what brought about the first waves of seagrass die-off’s, which were evidenced by the dense surface mats of floating dead seagrass throughout the central part of the Bay, particularly in Rankin and Johnson Key Basins. Current conditions mirror a similar event in 1987 which persisted for many years and further impacted Florida Bay, primarily due to the proliferation of dense plumes of algae.
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