Project Summary Sheet

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, pmccormick@usgs.gov, 304.724.4478, Carol Kendall ckendall@usgs.gov, 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. Synoptic surveys, monitoring along canal-water gradients, and field experimentation were initiated in FY04 with the following objectives:

(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.

Status: A Refuge-wide synoptic survey of surface-water conductivity and soil and plant nutrient levels at 130 sites was completed in February 2004 in coordination with the SFWMD. 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 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.

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 to assess ecological effects will begin in September 2005.

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. Short-term incubations are being conducted to identify how water-chemistry changes caused by canal-water intrusion affect plant and microbial growth rates and related processes.

Recent Products: An oral presentation and a poster summarizing the results of the synoptic survey (Task 1) were delivered at the National Conference on Ecosystem Restoration in Orlando in December 2004.

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. A white paper is also being prepared to synthesize available information on potential and measured ecological effects of mineral enrichment in the Everglades.

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) [Page numbers listed below are from the DOI Everglades Science Plan. The Science Plan is posted on SOFIA's Web site: http://sofia.usgs.gov/publications/reports/doi-science-plan/]:

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 (p. 14). 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” (p. 17).

This study supports the Arthur R. Marshall Loxahatchee NWR Internal Canal Structures Project (p. 39) 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 (p. 37) 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 (p. 66).

Information gained from this study will support the Landscape Scale Modeling Project (p. 81) 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 (p. 81); (3) facilitates Everglades Landscape Model (ELM) development (p. 82) 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 (p. 82) 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.