Methods

Site Desciption

The site choosen for this study was the flats area in and around Cedar Key, Florida (Fig 1). These area is a drowned penensula that is disected by channels. The flats are, on average, a few inches below mean low water (MLW). On extreme low tides, mean low low water (MLLW) or below, the flats are exposed (Fig 2). The flats are vegetated by submerged aquatic vegetation. Specifically, three species of these seagrasses dominate the landscape: Halodule wrightii, Syrigodium filimore, and Thalassia testudium (Fig 3). Aerial photography shows these vegetated flats appear to be mostly stable since 1961 and are the most likely places to observe post-depositional alterations of the soil (pedogenesis). The slightly drier sand bars and beaches are unvegetated (Fig 4), as are the mud flats (Fig 5) that occur in and around the salt marsh communities of the area. Within the study area, exists a wide variety of landforms and vegetation covers.

Fig 1. Site map of the study area located near Cedar Key, Fl.

Fig 2. Grass flat exposed on an extreme low tide. This happens a few times a month for a duration of a few hours

Fig 3. Seagrasses

Fig 4. Unvegetated, sandy areas

Fig 5. Unvegetated flats (mud flats)

Basemap Creation

Creating basemaps is a necessary part of this study. Aerial photography must be obtained. Prints and negatives must be scanned and rectified in a manner appropriate for mapping soils (i.e. 1:12,000). Satellite imagery must be obtained at low tide, cloud free days during the late fall when the balance between seagrass biomass and water clarity is at a maximum.

Aerial Photography
Black and white aerial photographs from 1961, 1974, and 1989 in addition to true color from 2001 were obtained, scanned, and rectified to the State Plane North (Feet) HARN projection. The 2001 photographs were rectified first and the black and whites were image-to-image recitfied using the 2001 as the source (Fig 6).

Fig 6.

Satellite Imagery
Using tide models, three late fall Landsat 7 ETM scenes with minimal cloud cover were identified as possible low tide scenes. These three scenes were aquired and one of the scenes shows a majority of the seagrass beds to be exposed on an extremely low tide (Fig 7).

Fig 7.

Map Units
Based on Photo tone, map units were drawn on a 1:12,000 poster printed from the 2001 aerial photography (Fig 8 and 9). These lines were then heads-up digitized using Arcview 3.2. In the future, the process will be repeated using satellite imagery to determine if the larger pixel size (30 m) of the Landsat scene allows for similar precision compared to aerial photography (1 m pixels).

Fig 8.

Fig 9.

Sampling Design

This project attempts to answer questions across the borders of pedology, geology, and marine ecology. Necessarily, each questions requires aproach to sampling.

Formation of A horizons in vegetated areas
In the future several epipedons of vegetated areas will be extracted using a russian auguer (Fig 10). From there, the A horizon can be sampled in 1 cm intervals to determine whether carbon and biogenic silica distribution with depth.

Fig 10.