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projects > spatial and temporal patterns and ecological effects of canal-water intrusion into the A.R.M. Loxahatchee National Wildlife Refuge > project summary

Project Summary Sheet

U.S. Geological Survey, Greater Everglades Priority Ecosystems Science (GE PES) Initiative

Fiscal Year 2006 Study Summary Report

Study Title: Spatial and temporal patterns and ecological effects of canal-water intrusion into the A.R.M. Loxahatchee National Wildlife Refuge
Study Start Date: February 2004   Study End Date: February 2007
Web Sites: n/a
Location (Subregions, Counties, Park or Refuge): A.R.M. Loxahatchee National Wildlife Refuge
Funding Source: USGS Greater Everglades Priority Ecosystems Science (GE PES) Initiative
Principal Investigator(s): Paul McCormick,, 304.724.4478, Carol Kendall, 650.329.5603
Supporting Organizations: A.R.M. Loxahatchee National Wildlife Refuge
Associated / Linked Studies: A.R.M. Loxahatchee National Wildlife Refuge Enhanced Water Quality Monitoring and Research Plan

Overview & Objective(s): 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.

This study is part of a coordinated effort between USGS and the Refuge to understand causes and predict patterns of canal-water intrusion and to assess effects on sensitive wetland biota and functions. Research was initiated in FY04 to (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.


A synoptic survey of water, vegetation, and soil chemistry was performed at 130 stations across the Refuge in February 2004. The results of this task are described in earlier summary reports.

A 12-station transect monitoring network was established along a canal-water gradient in May 2004. Measurements of water chemistry and soil and plant nutrients at these stations began in August 2004. A transect-wide decomposition experiment was also initiated in August 2004 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. Findings to date show that a gradient of conductivity and associated mineral constituents is maintained across the Refuge, with highest levels near the western perimeter of the Refuge where most canal-water intrusion occurs. Changes in the species composition of slough-wet prairie (SWP) vegetation and the cover of SWP and sawgrass habitats occur across this gradient, and the results of associated laboratory experiments suggest that at least some of this vegetation change is attributable to increased mineral loading from canal waters. Decomposition rates also show some correlation with this gradient, but may be more strongly related to hydroperiod than to water chemistry changes.

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 enclosures located along a sawgrass-slough fringe are being dosed monthly with a solution that mimics the composition of major ions responsible for the high conductivity of canal water. Sampling conducted during the first year of dosing found accumulation of certain mineral elements in surface soils in enclosures exposed to the highest doses. Dosing had little effect on macrophyte mineral chemistry and no effects of species composition during the first year of the experiment.

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. Initial experiments found that the response of selected plant species to controlled mineral loading was consistent with their occurrence across mineral gradients in the Refuge.

Recent Products: An oral presentation summarizing the results of transect sampling and associated experimental work was delivered at the Greater Everglades Ecosystem Restoration Conference in Orlando in June 2006. A second presentation summarizing study findings to date was presented at the A.R.M. Loxahatchee National Wildlife Refuge Annual Science Workshop in May 2006. A draft white paper summarizing literature on the effects of mineral loading on the Everglades and other peatlands and incorporating available results from this study was completed in July 2006 and is currently being reviewed by DOI staff. A peer-review manuscript presenting the results of stable isotope analyses from the 2004 synoptic survey is undergoing internal review and will be submitted to a scientific journal in September 2006.

Planned Products: Reports, peer-review manuscripts, and technical presentations will result from this study. Two manuscript detailing findings from the synoptic survey and laboratory experiments are currently in preparation.

Specific Relevance to Information Needs Identified in DOI's Science Plan in Support of Ecosystem Restoration, Preservation, and Protection in South Florida (DOI's Everglades Science Plan) [The Science Plan is posted on SOFIA's Web site:]: 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 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. Thus, this project directly supports DOI's science program to "support the assessment and management of contaminants that could be introduced into the system as an indirect effect of water engineering projects".

This study supports the Arthur R. Marshall Loxahatchee NWR Internal Canal Structures Project as it helps understand spatiotemporal patterns and ecological effects on Refuge resources of changing water quality and its relation to restoration activities. This project will provide answers to 3 of the 4 major unanswered questions for the Refuge in the DOI Science Plan by addressing: (1) links between hydrology, water quality, and ecology; (2) ecological responses to hydrologic change; and (3) water quality criteria that must be achieved for agricultural and urban water diverted into the Refuge. Results of this study are also relevant to projects in other areas of the Everglades that may be affected by changing water quality as a result of increasing canal-water inputs including the Water Conservation Area 3 Decompartmentalization and Sheetflow Enhancement Project.

Information gained from this study will support the Landscape Scale Modeling Project as it: (1) provides data to improve the accuracy and precision of hydrologic models for the Refuge; (2) provides data that facilitate the simulation of nutrient transport and biogeochemical cycling in the soil and water column; (3) facilitates Everglades Landscape Model (ELM) development by providing data on how periphyton respond to changes in water quality, which can be incorporated into the model to improve its accuracy in predicting landscape responses to different water management scenarios; and (4) facilitates Regional Simulation Model (RSM) ecological module development by providing data on how biota respond to water quality changes produced by restoration efforts.

Key Findings

  1. Surface-water conductivity levels provide a clear indication of the location and timing of canal-water intrusion into the Refuge.
  2. Concentrations of phosphorus, sulfur, calcium, and other macronutrients in soils and plants are positively correlated with canal-water influence among sites within the Refuge.
  3. Soil concentrations of uranium, a chemical marker of canal-water influence, are positively correlated with conductivity and nutrient levels and may provide a useful tracer of the movement of suspended materials in canal water into the Refuge
  4. Biota show large changes in carbon (d13C) and nitrogen (d15N) isotope compositions with distance from the canal, suggesting that these chemical measures will be a useful environmental marker of changes in food web dynamics related to canal-water intrusion.
  5. Initial results of laboratory experiments suggest that common wetland plant species in the Refuge interior exhibit a broad range of tolerances to increasing conductivity. Certain species appear to require soft-water conditions, while others exhibit no measurable response to elevated conductivity.

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