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(1) document spatial and temporal patterns of canal-water intrusion into the Refuge; (2) quantify nutrient concentrations and shifts in the nature and degree of nutrient limitation along canal-water gradients; (3) quantify changes in key microbial, periphyton, and plant processes along these gradients; (4) link changes in biota and process rates to water chemistry changes caused by canal-water intrusion through field experimentation.
William, Paul McCormick Orem, 200810, Spatial and temporal patterns and ecological effects of canal-water intrusion into the A.R.M. Loxahatchee National Wildlife Refuge: Hydrogeology Journal v. 117.
Jud Harvey and Carol Kendall also worked on this project
703 648-6273 (voice)
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Alterations to groundwater and surface-water hydrology and water chemistry in south Florida have contributed to increased flows of mineral-rich (i.e., high conductivity) canal water into historically rainfall-driven (low conductivity) areas of the Everglades. The Loxahatchee National Wildlife Refuge has largely retained its historic low conductivity or "soft-water" condition, which supports a characteristic periphyton community, wetland plant species that may also be adapted to soft-water conditions, and lower rates of key ecosystem processes (e.g., decomposition) than in areas of the Everglades exposed to canal discharges. Recent monitoring data indicate a trend towards increased intrusion of canal water into the Refuge interior, but the causes (e.g., changing water management strategies, weather patterns) and magnitude of ecological effects resulting from this intrusion are not clear.
Projects that improve the quantity, timing, and distribution of water supplies to the natural system are at the core of Everglades restoration efforts. This study addresses a major Department of Interior (DOI) concern that the quality of water available for these projects may be inadequate to support natural ecosystem functioning. While phosphorus impacts on Everglades populations and processes have been extensively studied, the environmental effects of other major water quality changes remain poorly understood. This study will improve understanding of the effects of elevated marsh concentrations of water quality constituents other than P resulting from increased supplies of canal water to the natural system.
A field dosing experiment was initiated in March 2005 to quantify changes in soil, microbial, and vegetation characteristics in response to elevated conductivity produced by canal-water intrusion into the Refuge. Fifteen experimental plots along a sawgrass-slough fringe have been dosed monthly since March 2005 with a mineral solution containing the major ions Ca2+, Cl-, K+, Mg2+, HCO3-, Na+ and SO42- in a ratio similar to that for canal water. Triplicate plots are being dosed with a mineral solution to produce mineral pulses that approximate 0 (control), 12, 25, and 50% of canal mineral levels.
A series of laboratory experiments began in January 2005 to better understand and predict effects of changing water quality on key vegetation communities and microbial processes in the Refuge.
The last set of decomposition bags will be collected in August 2007 (36 months of incubation). Additional bags placed at two sites to determine effects of hydroperiod on decomposition rates also will be collected at this time (22 months of incubation). Samples will be processed in the laboratory to measure rates of plant mass and nutrient loss.
Site sampled for total soil and plant-tissue nutrients in FY 2006 will be re-visited and additional samples will be collected to measure concentration of extractable nutrients and minerals, including N, P, Ca, K, Mg, iron (Fe), and aluminum (Al). These data will complement total soil elemental concentrations measured in FY 2006.
Monthly dosing will continue with the assistance of Refuge staff. Measurements of soil, porewater, and vegetation mineral accumulation and macrophyte and periphyton composition begun in FY 2005 will continue. Microbial enzyme measurements initiated in collaboration with investigators from the SFWMD will be completed.
Controlled laboratory experiments are being conducted to measure P fluxes from soils from different transect sites under different hydrologic and water quality conditions. In phase 1, soil cores from selected transect sites will be incubated in the laboratory under different hydrologic conditions to measure levels of potentially bioavailable P. Replicate soil cores will be incubated under flooded, saturated, and drained conditions for an extended period (1-2 months). Incubation chambers will then be replenished with fresh low-P water and filtered to measure release of soluble reactive P (SRP).
In phase 2, soils from a minimally impacted location will be incubated in water containing different conductivity levels (i.e., a laboratory solution containing major ions at concentrations similar to those in canal waters) but the same background concentration of P. Initially, small soil samples will be incubated in test tubes for short periods (several days), drained and then agitated in distilled water, and filtered to measure SRP. Longer term experiments will involve incubating larger soil cores in the same water quality treatments and then treating them as described for phase 1 experiments. Microbial respiration and biomass will also be measured to understand the role of microbial activity in P release.
In phase 3, soil cores from the same minimally impacted location will be exposed to low P waters of varying conductivity prior to replenishment with waters containing a specified concentration of SRP. Incubation containers will be slowly shaken (minimum speed for shaker table) for a 24-h period and rates of SRP loss will be measured via periodic sampling. Microbial respiration and biomass will also be measured to understand the role of microbial activity in P retention.
The design of a laboratory experiment during FY07 is underway. Cores containing the surface soil-litter layer (0-10 cm depth) from a location in the Refuge interior will be incubated in the presence of surface-water containing different concentrations of major mineral ions in proportions similar to those documented across canal gradients. Elemental accumulation and availability in the litter layer will be tracked. After several weeks of mineral enrichment, remaining cores will be exposed to mineral-poor water from the Refuge interior and the retention of different elements will continue to be monitored.
Laboratory processing of soil cores collected during FY06 will be completed early in FY07.
In an initial experiment, replicate soil cores or slurries will be incubated in the laboratory in the presence of elevated sulfate and/or phosphate concentrations. Sediment oxygen demand, soil redox and sulfide levels will be monitored in each treatment to track general microbial activity and the activity of sulfate reducing bacteria. A second experiment will be designed based on initial findings.
Person who carried out this activity:
561 682-2866 (voice)
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Harvey, Judson W. McCormick, Paul V., 200902, Groundwater's significance to changing hydrology, water chemistry, and biological communities of a floodplain ecosystem: Hydrogeology Journal v. 17, n. 1, Springer-Verlag, Dordrecht, The Netherlands.
The article was originally published in the Hydrogeology Journal.
Chang, C. C. Y. McCormick, P. V.; Newman, 2009, Isotopic indicators of environmental change in a subtropical wetland: Ecological Indicators v. 9, n. 5, p. 825-836, Elsevier Science B. V., Amsterdam, The Netherlands.
The full article is available via journal subscription or single article purchase. The abstract may be viewed on the Science Direct website by selecting the volume and issue number.
A Refuge-wide synoptic survey of surface-water conductivity and marsh soil and plant nutrient levels at 130 sites was completed. Additional samples were collected at each site to assess whether stable isotope compositions of soil and vegetation and soil uranium concentrations could provide useful environmental markers of the extent and effects of canal-water intrusion.
A 12-station transect monitoring network was established along a canal-water gradient. Measurements at these stations included water chemistry and soil and plant nutrients. A transect-wide decomposition experiment was also initiated to measure changes in organic matter mineralization rates and nutrient storage along the gradient. Nearly continuous monitoring of conductivity began at several sites in December 2004 and is now being conducted at all sites as water levels allow. Periodic periphyton sampling began in March 2005 and a detailed characterization of vegetation along this canal-water gradient began in the summer of 2005.
The Refuge has established a conductivity monitoring network to document spatial and temporal patterns of canal-water intrusion. Twelve of these monitoring sites, located along an east-west gradient of canal influence across the center of the Refuge, were selected for more intensive sampling, including characterization of soil and porewater nutrients, nutrient cycling rates, and periphyton and plant communities and productivity.
Are there legal restrictions on access or use of the data?
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727 803-8747 ext 3028 (voice)
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