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Estimates of Natural Salinity and Hydrology in a Subtropical Estuarine Ecosystem: Implications for Greater Everglades Restoration

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Disruption of the natural patterns of freshwater flow into estuarine ecosystems occurred in many locations around the world beginning in the twentieth century. To effectively restore these systems, establishing a pre-alteration perspective allows managers to develop science-based restoration targets for salinity and hydrology. This paper describes a process to develop targets based on natural hydrologic functions by coupling paleoecology and regression models using the subtropical Greater Everglades Ecosystem as an example. Paleoecological investigations characterize the circa 1900 CE (pre-alteration) salinity regime in Florida Bay based on molluscan remains in sediment cores. These paleosalinity estimates are converted into time series estimates of paleo-based salinity, stage, and flow using numeric and statistical models. Model outputs are weighted using the mean square error statistic and then combined. Results indicate that, in the absence of water management, salinity in Florida Bay would be about 3 to 9 salinity units lower than current conditions. To achieve this target, upstream freshwater levels must be about 0.25 m higher than indicated by recent observed data, with increased flow inputs to Florida Bay between 2.1 and 3.7 times existing flows. This flow deficit is comparable to the average volume of water currently being diverted from the Everglades ecosystem by water management. The products (paleo-based Florida Bay salinity and upstream hydrology) provide estimates of pre-alteration hydrology and salinity that represent target restoration conditions. This method can be applied to any estuarine ecosystem with available paleoecologic data and empirical and/or model-based hydrologic data.

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This project was funded by the USGS Greater Everglades Priority Ecosystems Science (GEPES) effort, G. Ronnie Best, Coordinator; the National Park Service (Everglades National Park) through the Critical Ecosystems Studies Initiative (CESI); and the US Army Corps of Engineers RECOVER Branch with direction from DeWitt Smith (NPS), Cheryl Buckingham (USACE) and Sue Kemp (USACE). The paleoecological portion of this work was conducted as part of National Park Service (NPS) Study number EVER-00141. Everglades National Park also provided access to and assistance with the hydrologic and salinity station data. We would like to thank Christopher Bernhardt (USGS), Thomas Cronin (USGS), and two anonymous reviewers for their thoughtful comments and suggestions, which have improved this report. Bethany Stackhouse (USGS) created the study area maps (Figs. 1 and 3). Numerous people have assisted in the collection, processing and analyses of the USGS cores and in the development of the modern analog salinity dataset including Robert Halley (retired USGS), Charles W. Holmes (retired USGS), Joel Hudley (University of North Carolina, Chapel Hill), James Murray (USGS), Bethany Stackhouse (USGS), Jeffery Stone (University of Nebraska, Lincoln), and Carleigh Trappe (former USGS contractor). Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

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Correspondence to Frank E. Marshall.

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Communicated by Nancy L. Jackson

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Marshall, F.E., Wingard, G.L. & Pitts, P.A. Estimates of Natural Salinity and Hydrology in a Subtropical Estuarine Ecosystem: Implications for Greater Everglades Restoration. Estuaries and Coasts 37, 1449–1466 (2014).

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