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4: Environmental Health and Degradation

Kim H. Haag, U.S. Geological Survey, Florida Integrated Science Center, Tampa, Florida

The ecology, water quality, and hydrology were compared in 10 freshwater marsh and cypress wetlands in the northern Tampa Bay area. The hydrology of marsh and cypress wetlands is directly affected by rainfall patterns, and since the early 1970s it has been affected by development, particularly ground-water withdrawals. Withdrawal of ground water in regional well fields has lowered the water levels in the Floridan aquifer. As a consequence, water levels in many wetlands have declined, and the frequency, duration, and areal extent of seasonal flooding have decreased. Augmentation of some marsh and cypress wetlands with ground water has been used to mitigate the effects of ground-water withdrawals in well fields, causing changes in wetland hydrology, water quality, and ecology.

The hydrology of augmented wetlands differed from natural wetlands in several fundamental aspects, including the size of the flooded areas, residence times of water in the wetlands, leakage rates, the magnitude of runoff, and the water-table configuration. The relatively constant flooded area in three of the four augmented wetlands was well within the wetland perimeter, leaving the remainder of the wetland bottom subject to invasion by upland vegetation. However, perennial standing water in augmented wetlands increased their primary productivity compared to natural wetlands, as indicated by the higher periphyton and vegetation biomass. The greater primary productivity of the augmented wetlands, combined with infrequent drying, probably accelerated the accumulation of organic material in all but one augmented wetland, which repeatedly dried out.

The wetlands augmented with ground water were ecologically similar to the natural wetlands in many respects. Most of the biotic community measures in the augmented wetlands, including abundance, taxa richness, and diversity, were within the existing range for natural wetlands of the same type (marsh or cypress). The distribution of wetland periphyton species was related to pH and conductivity, but differences related to nutrient concentrations were not distinct. Biomass of herbaceous vegetation was higher in augmented wetlands, and may be related to availability of nutrients released from the accumulated partially decayed vegetation. The relative abundance of plant types (obligate, facultative wet, facultative) was not substantially different among wetland groups (augmented or natural), most likely because many of these plants have broad tolerances for water depth and occur across a gradient of hydrologic conditions. The occurrence of snails and mussels was confined to augmented wetlands where the concentration of calcium carbonate was sufficient for shell formation. With the exception of one augmented marsh (where snails were abundant), the biomass and density of macroinvertebrates at augmented sites was within the range found at natural wetlands.

The variability of periphyton, herbaceous vegetation, and macroinvertebrates in wetlands is inherently high, and ecological comparisons of natural and augmented marsh and cypress wetlands would improve if a larger population of wetlands were available for study.

Contact Information: Kim H. Haag, U.S. Geological Survey, Florida Integrated Science Center, The University Center for Business, 10500 University Center Drive, Suite 215, Tampa, FL 35512; phone: 813-975-8620; email: khhaag@usgs.gov

Andy O’Reilly1, Marty Wanielista2, and Keith Loftin3

1 U.S. Geological Survey, Florida Integrated Science Center, Orlando, Florida
2 University of Central Florida, Stormwater Management Academy, Orlando, Florida
3 U.S. Geological Survey, Organic Geochemistry Research Laboratory, Lawrence, Kansas

As the demand for fresh water increases in central Florida to meet both public supply and irrigation needs, stormwater is increasingly being managed as a resource to help offset possible future declines in aquifer water levels. Water quality is an important consideration when using stormwater for recharge or reuse. A constituent of recent concern is cyanobacteria (popularly known as blue-green algae) because some of these can produce toxins (cyanotoxins) that are detrimental to animal and human health. Microcystins are the most commonly found type of cyanotoxin in Florida and have been detected in a variety of rivers, natural lakes, and stormwater ponds. Microcystin-containing genera of cyanobacteria retain the toxin within healthy cells; toxin is released when cells lyse. Once released into the water, the dissolved microcystins can potentially move with the prevailing hydraulic gradient through the water-body bed sediments and into adjacent aquifers. Little is known about the transport and fate of microcystin in soil and ground water. Microcystin that reaches the ground-water flow system could adversely impact the quality of water withdrawn for irrigation as well as drinking water purposes. The potential for transport of microcystin in soil and ground water is being investigated by using laboratory soil column experiments.

The first soil column experiment was performed using microcystin-LR (MC-LR) and a clean sand media. Natural stormwater spiked to yield a MC-LR concentration of 4 mg/L was continuously applied to 2 (duplicate) columns (5 feet tall and 12-inch diameter) for 75 hours. Samples were collected from 6 sampling ports (0.5, 1, 1.5, 2, 3, and 4.5 feet deep) on each column in addition to the ponded water at the top of each column. Sampling time intervals ranged from 0.5 to 14 hours; a total of 120 samples were collected. These samples were quantitatively analyzed using enzyme-linked immunosorbent assay (ELISA) to provide an estimate of the degree of microcystin attenuation/degradation in ground water. Microcystin removal efficiencies up to 30% in one column and 70% in the second column were identified. Clear breakthrough curves were identified at the shallowest sampling port. Analysis of these data indicated that the microcystin was likely moving at or slightly slower than the pore-water velocity, suggesting adsorption was minimal. Substantial degradation of microcystin (likely microbiologically mediated) occurred after breakthrough at each sampling port. A subset of samples is being analyzed with liquid chromatography tandem mass spectrometry (LC/MS/MS) to confirm results by ELISA. A second soil column experiment is planned to further investigate the potential for microcystin degradation over a longer time period.

Contact Information: Andy O’Reilly, U.S. Geological Survey, Florida Integrated Science Center, 12703 Research Parkway, Orlando, FL 32826; phone: 407-803-5525; email: aoreilly@usgs.gov