The Coastal Plainer: Fall 2011

Evaluation of Astatula Sand in the South-Central Florida Ridge

By the Tavares MLRA Team: Julie Ruh, Alison Steglich, and Manuel Matos

The evaluation of Astatula sand evolved from an agreement signed by the USDA Forest Service and the USDA Natural Resources Conservation Service on April 15, 2010. The agreement called for an update of the soils information for the Ocala National Forest (ONF), which is located in parts of Lake, Marion, and Putnam Counties. Astatula sand covers 184,979 acres, or 51 percent, of the ONF.

Across MLRA 154 (the South-Central Florida Ridge), Astatula sand covers 276,687 acres (fig. 1). Map units consisting of Astatula sand have been mapped in five soil survey areas. The units used different slope phases (0 to 5, 0 to 8, 5 to 8, 5 to 12, and 8 to 17 percent slopes), different map unit designs, and, in some cases, different water table depths, polygon densities, polygon sizes, and ecological communities.

The objectives of the evaluation are to create a consistent map unit design, improve map unit composition, improve the tabular data, delineate better slope classes, and create ecological site descriptions.

The soils of the Astatula series are classified as hyperthermic, uncoated Typic Quartzipsamments. These soils are very deep, excessively drained, and located on broad ridges adjacent to sinks and small lakes (https://soilseries.sc.egov.usda.gov/OSD_Docs/A/ASTATULA.html). These soils formed in sandy marine, eolian, or fluvial sediments. They are considered limited for supporting production of specialty crops and have very low natural fertility. This series, however, supports the largest sand pine ecosystem in the world. The Sand Pine Scrub ecological community is one of the oldest ecosystem types in Florida, and 40 to 60 percent of the plants and animals are considered endemic species. Additional information about this unique ecological community is available at http://www.ocala.com/article/20080218/NEWS/802180315.

With newer soil-science technology playing a significant role, the Tavares MLRA team is putting considerable effort into completing the Astatula sand update project. The team received training with ground-penetrating radar (GPR) early in 2011. Most of the field data collection for the project consisted of running transects (sometimes miles long) with the GPR to dissect the units across the landscape (fig. 2). The data was verified by taking full pedon descriptions at various points throughout the transects. In the office, the team used the ArcGIS Soil Resource Inventory Tool (SRITB) to digitize the SSURGO data, the National Soils Information System (NASIS) to update the tabular data, and the Lidar Enhanced Soil Survey (LESS) model to accurately delineate slope breaks that represented actual landforms.

One of the major findings of the survey was the recognition of unique geology and landforms within the delineations of Astatula sand. For decades, the geology and landforms have been subject to controversy between scientists. Two main landforms were identified. The first consists of sandy marine and eolian sediments over loamy marine sediments. The second consists of deep, sandy marine and eolian sediments. The update project is differentiating the two geological areas with well-documented, specific data regarding composition.

On the first landform, Astatula sand formed in sandy marine and eolian sediments over loamy marine sediments. The loamy marine sediments are also known as the Cypresshead Formation (fig. 3). This landform can be described as having broad ridges with long slopes located toward the west of the ridge. The abrupt textural contact between the sandy marine sediments and the Cypresshead Formation indicates a break in the geologic material. The material differs in particle size (sand over sandy loam and sandy clay loam), distribution, and mineralogy (siliceous over siliceous-kaolinitic-iron oxide). Based on studies by the University of Florida, the top of the Cypresshead Formation exhibits evidence of clay movement that represents a horizon associated with an older, eroded soil.

On the second landform, Astatula sand formed in deep, sandy marine and eolian sediments (beaches, ridges, and dunes of the Quaternary to Pleistocene/Holocene). This landform can be described as having transverse dune patterns with short slopes located toward the east of the ridge.

The work of the Tavares MLRA team using GPR, ArcGIS technology, soils data, and geology data has made the Astatula sand update move swiftly. The team anticipates delivery of the updated project by the scheduled due date (December 31, 2011). The data should be available from the Soil Data Mart and Web Soil Survey by the beginning of the second quarter of fiscal year 2012.

Figure 1.—Distribution of Astatula sand in the South-Central Florida Ridge.

Figure 2.—Ashlyn Smith-Sawka, student intern, reviewing GPR data.

Figure 3.—Borrow pit showing Astatula sand over the Cypresshead Formation.

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