RELATIONSHIP BETWEEN SOIL WATER RETENTION AND SOIL ORGANIC MATTER CONTENT WITHIN XERIC VEGETATION COMMUNITIES IN BOCA RATON, FL

In Palm Beach County, FL., declining water tables are significantly below pre-development levels due to drainage activities and groundwater withdrawals. In Boca Raton, FL., where the groundwater is shallow, xeric vegetation communities, such as oak hammock and upland scrub, are the first to be impacted by groundwater withdrawal. Soil moisture is dynamic and one of the key factors in ecosystem health. Complex interactions between infiltration, precipitation, evaporation, root uptake, and soil drainage impacts water stress in vegetation. One factor that influences soil water storage capacity is soil organic matter (SOM); SOM increases the ability to retain water, storing it for later use. At several urban preserves in Palm Beach County, managers are attempting to maintain native xeric vegetation communities on disturbed soil or fill, and little is known about the SOM content of these soils and the role it plays in soil-moisture-plant dynamics. This study examines whether there is any correlation between SOM content and volumetric water content (VWC) with respect to three vegetation communities: 1) managed grasslands, 2) native oak hammock, and 3) native upland scrub. Soil cores from each vegetation site were collected using a manual hand auger at depths of 2ft (near the root zone), 4ft below the surface and 6in above the water table (about 5.5ft to 6.5ft below surface). An organic-rich horizon was observed at 4ft below the surface at study sites 2 and 3. Percent SOM near the root zone was determined by a loss-on-ignition (LOI) method and VWC was obtained from soil moisture probes buried at 2ft beneath land surface. Average percent SOM near the root zone was compared with average and time-series VWC. Average percent SOM was 0.2%, 0.2%, and 0.4% and average VWC was 0.07m³m^-3, 0.06 m³m^-3, and 0.07m³m^-3 at vegetation sites 1, 2, and 3, respectively. Since there is little variation in SOM and VWC between sites, SOM contents will be compared to range in VWC and lag time in the VWC hydrograph to determine if there are any correlations between OM content and soil moisture. These results will shed light on the combined role of OM and soil moisture in maintaining native xeric vegetation in disturbed areas.