USING WATER ISOTOPES, NUTRIENTS, AND WATER LEVEL DATA TO EVALUATE THE HYDROLOGIC INTERACTIONS BETWEEN A CONSTRUCTED WETLAND AND SURROUNDING URBANIZED AREAS

Pondhawk Natural Area (PNA) has exhibited hydric conditions in the past, but an increase in groundwater use and the introduction of canals led to the disappearance of the wetland in the 1950s. In 2010, Palm Beach County reconstructed the wetland to reverse some of the negative changes that had occurred to PNA’s hydrology and wetland dependent ecosystems. In addition to the wetland reconstruction, recent nearby land development, construction of ponds, and installation of municipal wells have all caused significant changes to the local hydrology. This research aims to identify the effects of these land use changes and water diversions on the wetlands and how those effects vary seasonally by characterizing the exchanges of water between the wetland, groundwater, adjacent lakes and municipal wells throughout the year. Weekly sampling began in March of 2015 and will continue through summer 2016. Data collection has included water sampling and monitoring of water levels from the wetland, two monitoring wells, two man-made lakes, and a canal. The water samples are being analyzed for stable isotopes of water and nutrients. Basic principles of mass balance will be applied to the data, allowing for an estimation of water exchanges between the sampled locations. Weekly monitoring of water levels in the wells has allowed for the determination of groundwater flow directions. The data collected thus far has begun to show trends and clarify the local hydrology. There is significant temporal variability on the site. Between March and October 2015, the water table elevation increased by a meter. During that same time period, both water level and isotope data show that the wetland progressed from a discharge to a flow-through and then to a recharge wetland. This research will help determine what data is most useful for assessing the local hydrology and thus will inform plans for long term monitoring. Further data collection will also help determine to what degree the hydrologic variability is controlled by rainfall versus human water diversions, including groundwater pumping and manipulation of canal water levels. The information gained from this study will be valuable to managers in deciding what policies to set in order to maintain adequate water levels in the wetland to support the native vegetation communities.