Estuaries along the southwest coast of ENP receive the majority of surface water from the Shark River Slough. The slough is a broad southwest-trending arc of continuous wetland, dotted throughout with numerous tree islands (Schomer and Drew, 1982). The southwest coast of ENP is recognized as an important part of the Everglades system, and information on the timing and magnitude of discharge and nutrient flux is required to assess existing water management practices and to document changes brought about by rehabilitation efforts in the Everglades. Data described in this report are available from the USGS National Water Information System (NWIS). Additional data are available from the ENP Marsh and Marine Monitoring Network, the USGS mangrove dynamics stations, the Southeast Environmental Research Program water-quality monitoring program, and other ecological studies. Discharge data for this area of ENP were previously collected by the USGS between 1960-1967, and are available in out-of-print reports (U.S. Geological Survey, 1970, 1975).

Purpose and Scope

Figure 1. Location of USGS discharge stations, Everglades National Park rainfall stations, and S-12-A, B, C, and D structure locations. [larger image]

Acknowledgments

Thanks are extended to DeWitt Smith, Tom Smith, numerous Dutch exchange students, Kevin Kotun, and others at the Everglades National Park Research Station who helped accomplish this study. Special thanks to Gordon Anderson of USGS, Miami for assisting with numerous field trips, arranging for exchange students to assist with field trips, and as a valuable source of information about the southwest coast study area.

Description of Study Area

The west coast of ENP is a subtropical mangrove forest and wetland area with many stream channels, lagoons, and back bays interwoven through the mangrove forests. Red mangroves dominate the land margins adjacent to the streams. Some mangroves are approximately 60 ft in height along the banks of the Shark and Harney Rivers closer to the Gulf of Mexico.

The headwaters of the five streams selected for this study are located near Lake Okeechobee and are influenced by rain events and water control structures located along the Tamiami Trail (U.S. Highway 41) (fig. 1). Drainage basin boundaries of the rivers are indeterminate due to a lack of elevation data and the flatness of the terrain. Drainage basin boundaries of these rivers within ENP have been estimated based on aerial photographs and the alignment of vegetation in satellite imagery. Within the ENP, the river basins overlap. As water in the Shark River Slough flows towards the southwest coast, distinct stream channels form and transport the water to back-country bays and the Gulf of Mexico.

The Everglades basin has a tropical savanna to subtropical climate characterized by a relatively long dry season (November to April) and a wet season (May to October) (Hela, 1952; Fernald and Patton, 1984). Annual rainfall typically ranges from 48 to 60 in., with approximately 80 percent occurring during the wet season (Schomer and Drew, 1982). Additionally, longer-term (greater than 5 years) rainfall averages exhibit a bimodal distribution pattern with a peak in May-June and a second peak in September-October (Thomas, 1974). Rainfall data collected by ENP personnel between 1996 and 2001 continue to exhibit the bimodal pattern. Average temperatures typically range from the mid-60s in the winter to low-90s (degrees Fahrenheit) in the summer (Schomer and Drew, 1982).

Figure 2. Location of USGS discharge stations. [larger image]

Discharge and nutrient monitoring stations (fig. 2) were established in the Broad, Harney, and Shark Rivers between October 1996 and January 1997, and were discontinued in March 2001. Additional discharge and nutrient monitoring stations were established in Lostmans Creek and North River between January and April 1999 and were discontinued in March and May 2001 respectively. "Left and right bank" and "edge of water" terms used in the following station descriptions refer to their location when viewed looking downstream (direction of positive discharge or flow towards the Gulf of Mexico).

The Lostmans Creek station is the northernmost station (fig. 2, table 1). The station is approximately 13 river miles from the Gulf of Mexico and about 1 mi upstream of Big Lostmans Bay. Both riverbanks are lined with mostly red mangroves, which are 5 to 15 ft tall. The river is approximately 300 ft wide at the station, with depths ranging from about 3 ft at the edges to about 6 ft near the center of the river at mean high tide. Normal tidal range is less than 1 ft, and velocities are less than 1 ft/s during flood or ebb tides. The left and right river edges are nearly vertical and composed of peat and fine mud. The river bottom consists of soft mud near the banks, grading to hard-packed mud littered with mollusk shells near the center of the river. Underwater visibility is usually about 4 to 6 ft.

The Broad River station is located approximately 10 river miles upstream from the Gulf of Mexico, about 1 mi upstream from Broad River Bay (fig. 2, table 1). Both riverbanks are lined mostly with red mangroves of 8 to 16 ft height. The river is approximately 200 ft wide at the station, with depths ranging from about 6 ft at the river edges to about 8 ft near the center. Riverbanks are vertical and consist of peat and fine sediments. The river bottom is covered with mud near the edges (approximately 1 to 3 ft from the edges) transitioning to exposed limestone with ridges, holes, and pinnacles less than 1/2 ft in elevation. Occasional small limestone spires and mollusk-encrusted limestone are distributed across the river bottom. Underwater visibility is usually 6 to 8 ft.

The Harney River station is located approximately 5 river miles from the Gulf of Mexico and about 1,800 ft downstream of the North Harney and Harney River confluence (fig. 2, table 1). Riverbanks are lined mostly with red mangroves of spectacular heights, some more than 60 ft. The river is approximately 350 ft wide with depths ranging from 0 ft at the right bank, sloping rapidly to about 13 ft near the center. The river bottom then gradually slopes up to about 9 ft at the vertical left bank. The sloped right bank is a sand beach about 10 to 20 ft wide at low tide, grading to muddy sediments as the water deepens. Within 50 ft of the right bank, these sediments transition to exposed limestone that extends across the river to within about 40 ft of the left bank. Near the left bank, the river bottom is composed of muddy sediments with a vertical peat bank. Most of the bottom at this station is exposed limestone with ridges, holes, and pinnacles less than 1/2 ft in elevation. Mollusks cover much of the exposed limestone bottom. Underwater visibility is usually between 2 and 4 ft.

The Shark River station is located approximately 6 river miles upstream from the Gulf of Mexico and about 1,000 ft downstream of Gunboat Island (fig. 2, table 1). The riverbanks are lined mostly with red mangroves of moderate heights (30 to 40 ft). The river is approximately 400 ft wide, with depths ranging from 7 ft at the right bank sloping to 8 or 9 ft near the center and gradually decreasing in depth back to 7 ft at the left bank. Both banks are nearly vertical and consist of peat. Some areas of mud are located along the river bottom within 1 to 3 ft from the riverbanks. The remaining cross section is exposed limestone with ridges, holes, and pinnacles approximately 1 ft in elevation. Mollusks are attached to the exposed limestone bottom. Underwater visibility is usually 6 to 8 ft.

The North River station is located approximately 4 river miles upstream from Whitewater Bay and about 16 mi from the Gulf of Mexico (fig. 2, table 1). Riverbanks are lined mostly with red mangroves of relatively short stature, with heights of only 5 to 8 ft. The river is approximately 250 ft wide with depths ranging from 4 ft at the right bank to 5 ft near the center of the river, and gradually decreasing in depth up to 3 ft at the left bank. Both riverbank edges are vertical and composed of peat and fine sediments. The bottom is composed of packed mud over harder bottom. The bottom of the river near the center is composed of fine sediments having a "pudding-like" consistency. Underwater visibility is usually between 2 and 4 ft.