—Samuel Rajasekhar, Idea Integration
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A primary objective of the Indian River Lagoon (IRL) Surface Water Improvement and Management (SWIM) Plan is to protect and restore seagrasses, a key resource. Seagrasses are a good indicator of the overall health of the lagoon ecosystem. For example, expansion of seagrass into deeper water indicates improvement in water quality/clarity/salinity. The IRL SWIM Plan directs the South Florida and St. Johns River Water Management Districts to map seagrasses in the Indian River Lagoon at 2–3 year intervals. Seagrass mapping is based on the interpretation of aerial photographs. Only a single photo interpreter maps seagrass at any given area at any time. In 2006, two photo interpreters using softcopy stereoscopic techniques, each digitized seagrass polygons three times from a sample set of five aerial photographs within St. Joseph's Sound/Clear Water Harbor, and Tampa Bay. From the resultant shape files, variation in polygon area and was calculated indicating variation in area was slight, perhaps due to gains & losses canceling each other. Variation in spatial placement of the individual line segments, especially the deep edge was measured using GIS techniques. Results indicate variation in deep edge was much higher as gains and losses do not compensate for each other. On average, mapped seagrass deep edge can vary by several meters. This could affect the deep edge calculations in locations where the bottom slope is even moderately steep.