Hydrologic Changes over 60 Years (1959-2019) in an Old-Growth Bald Cypress Swamp on a Rapidly Developing Landscape by Shawn E. Clem and Michael J. Duever

National Audubon Society’s Corkscrew Swamp Sanctuary (Naples, Florida, USA), an ecological relic of Old Florida, protects the largest remaining old-growth bald cypress swamp in the world. A 60-year record of daily water level measurements revealed substantial changes in Corkscrew Swamp’s hydrology as agricultural and residential development have grown to dominate the landscape surrounding the sanctuary. Between 1959 and 2019, surface water data indicate no decadal change in the timing or magnitude of peak wet season water levels or in the hydroperiods (days inundated per water year) of upland hammock and pine forests or wet prairies. Despite little change in rainfall patterns between the 1960s and 2010s, hydroperiods decreased 29% in marshes, 18% in old-growth bald cypress, and 17% in ponds, with the most notable change occurring between the 1990s and 2000s. Average dry season water level recession rate (decrease in water level over time) was 6.3 mm/d in the 2000s and 5.7 mm/d in the 2010s, 47% and 32% higher, respectively, than those seen in earlier decades. Analyses of groundwater data indicated a similar dry season decline between the 1990s and 2000s to that seen in surface water. Analyses of cumulative hydroperiod in surface and groundwater suggested markedly drier conditions began in the 2006 water year. While causes of the observed hydrologic changes are uncertain, likely interacting causes include reduced upstream wet season surface and groundwater storage, increased residential and agricultural extraction, increased downstream drainage, and increased evapotranspiration rates across the region as more deeply-rooted shrubs and trees replace more shallowly-rooted herbaceous plant communities. We discuss significant implications for plant and animal communities, particularly the historic Corkscrew wood stork colony, and discuss the role of long-term hydrologic monitoring for detecting and documenting ecological change.