ERTS-I: A New Window on Our Planet

GEOLOGICAL SURVEY PROFESSIONAL PAPER 929
RICHARD S. WILLIAMS, JR. and WILLIAM D. CARTER, EDITORS
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1976

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Excerpt: ECOLOGICAL MODEL IN FLORIDA

By Aaron L. Higer, A. Eugene Coker, and Edwin H. Cordes,
U.S. Geological Survey

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Thousands of years of seasonally fluctuating water supply, punctuated periodically by drought or unseasonally heavy rain, have resulted in a natural balance of plant and animal communities in south Florida. Water fluctuations, together with fires and hurricanes, contributed to the shaping of the ecological communities, that is, the tree islands (composed of woody vegetation) and grassland communities (wet prairies and sawgrass marshes). This natural ecological balance, however, is now influenced by a modified water regime, altered by water control within the Kissimmee-Okeechobee-Everglades watershed for flood control, crop irrigation, and coastal urban use (fig. 96). The Central and Southern Florida Flood Control District manages this watershed that contains more than 22,500 km of canals and levees.

An effect of water deficiencies in Everglades National Park is the failure of wood storks to form rookeries. Wood storks nest in winter at the inner edge of the mangrove belt in the Everglades National Park in south Dade and north Monroe Counties. According to John Ogden, an ornithologist of the National Park Service (written commun., l973), the wood storks were successful in forming rookeries in 1959,1960, and 1961 but failed for 5 successive years (1962-66), when low rainfall in south Florida resulted in prolonged drought in the park.

The success or failure of wood stork rookeries is a significant index of hydrologic conditions in the park. Wood stork studies in Everglades National Park by the National Park Service suggested a working hypothesis for establishing the water conditions of Shark River Slough, the largest freshwater course in the park, needed for successful formation of these rookeries. An annual prediction of success or failure of the rookeries at the inner edge of the mangrove belt could be made in November, which marks the beginning of the dry season and precedes the height of rookery formation by approximately 2 mo. The prediction can be based on recorded water-level measurements together with a synoptic view of the spatial distribution of surface water. bath available from ERTS data, and on the density of small aquatic animals collected in quantitative traps.

The ecological model is designed to relate the wildlife in the Shark River Slough to the availability of food and water (fig. 97) (Higer and others, 1973). In an on-going study with the National Park Service, more than 50,000 aquatic animals have been captured and tagged. The species numbers and hydrologic data are entered into a digital computer program that provides statistical summaries of species distributions and water depths at point locations in the slough. Time-variant synoptic displays using ERTS imagery taken concurrently with stage and rainfall data presently being collected from DCS (figs. 98, 99) may provide the following information to develop an ecological model (Higer and others, 1974):

1. Knowledge of the quantity of water stored in the slough.
2. Knowledge of the spatial distribution of water in the slough as it relates to available food for the bird rookeries (fig. 100).
3. Quantitative hydrologic data that allows management to know where and when to increase water into the slough from the upstream water storage areas.
4. Ability to predict the number of aquatic animals in the slough and the success or failure of the rookeries, based on conditions of the hydrologic regime.

FIGURE 96. Color composite ERTS-I image mosaic of the State of Florida prepared by the General Electric Co.. Beltsville, Md., in cooperation with the US. Geological Survey. Water Resources Division. Miami, Fla., the Central and Southern Florida Flood Control District, and NASA. [larger image]

Sufficient water must be maintained in the Shark River Slough of the Everglades National Park to preserve the aquatic community and the several bird and mammal species that feed primarily on fish. The amount and time of water releases to the park are a resource-management decision based on very limited information on the water storage that may be available to the north of the park. Small-scale thematic maps of water levels provide an accurate evaluation of water distribution. A gradual reduction of water levels before the birds start nesting would result in the concentration of fish in the Shark River Slough that may ensure adequate food for successful hatches of several rare and endangered bird species.

FIGURE 97 (left). Wildlife ecological model of the Shark River Slough, Fla. [larger image] FIGURE 98 (right). Data collection platform in the Everglades National Park in south Florida used in the ecological model study. [larger image]

 

FIGURE 99 (left). Surface-water storage model of the Shark River Slough, Fla. [larger image] FIGURE 100 (right). Wood storks nesting in the Everglades National Park, south Florida. [larger image]