Expert Report

Each report is produced by a committee of experts selected by the Academy to address a particular statement of task and is subject to a rigorous, independent peer review; while the reports represent views of the committee, they also are endorsed by the Academy. Learn more on our expert consensus reports.

The St. Johns River Water Management District in east-central Florida is weighing potential effects on wetland ecosystems of a proposed withdrawal of 262 million gallons of water per day from the river for future public water supply. The District's Water Supply Impact Study draws on data and analyses from seven scientific workgroups: hydrology/hydrodynamics, wetlands, biogeochemistry, plankton, benthos, submersed aquatic vegetation, and fish. The District has asked the National Research Council to review scientific aspects of the study and provide ongoing advice. This report points to progress the District has made in response to recommendations offered in August 2009, such as developing detailed conceptual models to show linkages and paths of activity in the effects of water withdrawal and to help integrate efforts of the workgroups. Individual workgroups have also acted on recommendations; some have initiated new studies to fill gaps in their analyses, improved their methods, and resolved many earlier concerns. For example, the Plankton Workgroup has implemented a water quality simulation model that integrates data from three groups. The report identifies those efforts that have not adequately addressed specific issues and recommends further improvements.

Key Messages

  • As recommended, the District has assembled water budgets for some areas of the floodplain, has begun to analyze return flows of water after withdrawals from the St. John's River, and is developing measures for determining what floodplain areas would be thoroughly dewatered as a result of withdrawals of river water.
  • Some workgroups have initiated new studies to fill gaps in their analyses, improved their methods, and resolved many earlier concerns. The Plankton Workgroup has implemented a water quality simulation model that integrates data from three groups. The Fish Workgroup has clarified the sampling schedule and the data to be collected and has largely resolved concerns about monitoring changes in salinity.
  • The District has not adequately addressed biogeochemistry concerns regarding analyses of changes in nutrient loadings. District scientists plan to develop nutrient budgets for the river and some subcomponents. Important factors remain to be addressed in those analyses.
  • The District has not made clear its assumptions and its planned methodology for developing a GIS model to identify sensitive wetland areas. For example, information on how data layers in the model will be weighted has not been presented for review.
  • The St. Johns River Water Management District is making significant progress in response to recommendations the National Research Council offered in August 2009. For example, the District's science workgroups are developing detailed conceptual models to show linkages and paths of activity in the effects of water withdrawal. These conceptual models will help integrate their efforts.