|projects > spatial and temporal patterns and ecological effects of canal-water intrusion into the A.R.M. Loxahatchee national wildlife refuge > work plan
U.S. Geological Survey, Greater Everglades Priority Ecosystems Science (GE PES)
Fiscal Year 2007 Study Work Plan
Study Title: Spatial and temporal patterns and ecological effects of canal-water intrusion into the A.R.M. Loxahatchee National Wildlife Refuge
Overview & Objective(s): Alterations to ground-water and surface-water hydrology and 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 interior of the Loxahatchee National Wildlife Refuge largely has 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.
Specific Relevance to Major Unanswered Questions and Information Needs Identified: 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 (P) impacts on Everglades populations and processes have been extensively studied, the ecological effects of other major water quality changes remain poorly understood. This study will improve understanding of the effects of elevated 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 documents spatial and temporal 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.
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 cooperation with the USFWS and 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. Laboratory nutrient and stable isotope analyses have been completed and data interpretation and manuscript preparation are underway.
A 12-station transect monitoring network was established in May 2004 along gradients of canal influence across the central Refuge, and measurements of water, soil, and plant chemistry and periphyton and macrophyte communities began in August 2004. This sampling has documented mineral gradients extending as much as 5 km into the Refuge as a result of canal-water intrusion. These gradients are associated with predictable shifts in slough and wet prairie (SWP) vegetation and a decline in the extent of these habitats with increasing canal influence. A transect-wide sawgrass decomposition experiment was initiated in August 2004. Preliminary results indicate that litter decomposition and nutrient mineralization are affected by water and litter chemistry as well as by local differences in hydrology among sampling sites.
Sampling began in 2005 to document natural spatial variation in Refuge mineral and nutrient chemistry. Soil and vegetation samples were collected from major habitat types including slough-wet prairies, sawgrass stands, and tree islands and analyzed for total mineral and nutrient concentrations. Ion-exchange membranes were incubated at the same locations to estimate levels of bioavailable minerals and nutrients. Total soil concentrations of selected elements such as P and Mg tended to be higher on tree islands than in surrounding slough-wet prairie habitats, suggesting that tree islands may be a source of various elements to adjacent aquatic habitats. However, ion-exchange membranes showed no difference in the availability of these elements in soils of different habitats. Additional measurements of nutrient availability are planned for FY07 to augment initial results.
A field fertilization experiment consisting of 15 walled plots (3.7 m x 1.2 m) was constructed during the fall of 2004 to quantify chemical and biological responses to mineral enrichment. Monthly dosing of these plots was initiated in March 2005. 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. Soil, porewater and plant chemistry and periphyton and plant community composition were monitored in these plots during FY05 and FY06. Available data show small increases in soil mineral content and availability and more pronounced changes in porewater chemistry in response to increased mineral loading. Vegetation chemistry and species composition did not respond to mineral loading during the first year of dosing.
Laboratory bioassays were initiated during FY05 to understand microbial and plant responses to nutrient and mineral gradients in the Refuge. Aerobic microbial respiration was found to be strongly C limited across these gradients, with no evidence of P or mineral effects. The response of a common interior slough-wet prairie macrophyte, Xyris ambigua, to nutrient and mineral enrichment was assessed in a series of laboratory experiments. Selective enrichment with common limiting nutrients (N, P, and/or K) elicited no significant growth response. Enrichment with an artificial canal-water (mineral) solution significantly reduced the growth rate of this species. Germination of this species from interior soil samples and initial seedling growth also declined with increasing mineral levels. The negative response of this species to mineral enrichment may explain its distribution in the Refuge, where it is restricted to the soft-water interior. A second experiment conducted during FY06 examined sawgrass responses to mineral enrichment. Sawgrass seedlings grown in different soil types and mineral treatments exhibited faster growth in response to both elevated soil P and higher loading of minerals compared to untreated soil from an interior (low P and mineral content) slough. Plant responses observed in these experiments are consistent with vegetation patterns documented along canal gradients in the Refuge.
A document was prepared that reviews ecological effects of mineral enrichment in peatlands and contains preliminary data from this GE PES project to indicate effects of increased mineral loading from canals on Everglades biota and processes. A draft document was prepared and reviewed by Refuge staff and a revised version was distributed for external peer review. The final document will be released as an USGS open-file report in FY07.
Recent Products: Results from this project were presented at the National Conference on Ecosystem Restoration in Orlando in December 2004 and at the Greater Everglades Ecosystem Restoration Conference in Orlando in June 2006. Preliminary findings also were presented at the annual A.R.M. Loxahatchee NWR science workshop in Delray Beach in May 2006. Three manuscripts were prepared using data from this project. These manuscripts will be submitted to peer-review journals in FY07.
Planned Products: An open-file report, peer-review manuscripts, and technical presentations (2 already scheduled for FY07).
Title of Task 1: Continue monitoring water and soil chemistry along canal-water gradients
Task Summary and Objectives: The Refuge has established a conductivity monitoring network to document spatial and temporal patterns of canal-water intrusion. Twelve of these monitoring sites, which are located along an east-west gradient of canal influence in the central Refuge, were selected for more intensive sampling, including characterization of soil and porewater nutrients, decomposition rates, and periphyton and plant communities. The objective of this sampling is to understand ecological changes associated with different levels of canal influence.
Work to be undertaken during the proposal year and a description of the methods and procedures:
Dataloggers will continue to be deployed to obtain nearly continuous measurements of surface-water conductivity. The Refuge will continue monthly water-quality sampling. Final soil and porewater chemistry measurements at these sites will focus on sulfur chemistry and include measurements of sulfate and sulfide concentrations as well as porewater redox and soil sulfur. These measurements will be combined with a laboratory experiment (see Task 8) to assess the extent of sulfate contamination along this gradient and the spatial relationship between sulfate loading and sulfate reduction.
This task supports efforts under the A.R.M. Loxahatchee National Wildlife Refuge Enhanced Water Quality Monitoring and Research Plan. This task also will provide information to support other tasks focusing on the ecological effects of water-quality changes caused by canal-water intrusion on Refuge resources.
Specific Task Product(s): These data will be used to help explain chemical and vegetation patterns already documented across this gradient and will be included in reports and peer-review manuscripts containing those data. The Refuge also is including this information in their Enhanced Water Quality Monitoring database.
Title of Task 2: Field experiment to quantify changes in litter decomposition and nutrient flux rates along canal-water gradients
Task Summary and Objectives: Sawgrass litter was collected from all 12 transect stations in May 2004, air dried and weighed in the lab, and used to fill mesh bags that were returned to the sites in August. Litter collected from each site was returned to the same site to measure site-specific decomposition (loss of mass) and nutrient recycling (loss of N and P content) rates over a 3-year period. Litter from the lowest conductivity site (LOX8), which is believed to have the lowest nutrient content (to be determined in the lab) due to the lack of canal influence, also was placed at 4 other sites with increasing levels of canal influence to assess the effect of water chemistry (i.e., increasing nutrient concentrations) on decomposition rates. Finally, litter from these other four sites was placed at LOX8 to assess the influence of litter chemistry (i.e., increasing nutrient content related to canal-water intrusion) on these rates. Sawgrass decomposition rates are typically quite slow, and it will be 1-2 years before patterns will emerge from this study. In order to obtain a "quick and dirty" assessment of the effects of canal-water intrusion on potential decomposition rates, strips of standardized cotton (i.e., cellulose) fabric were deployed in sawgrass and slough habitats in August 2004. This procedure has been widely used for this same purpose in other wetland studies. The hypothesis being tested is that increasing levels of canal influence (i.e., higher conductivity) result in faster rates of decomposition and N and P recycling as a result of increased nutrient inputs.
Work to be undertaken during the proposal year and a description of the methods and procedures: 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.
Specific Task Product(s): Results will be compiled into the final project report, which will then be converted into a peer-review manuscript. Results may also be included in scientific presentations.
Title of Task 3: Habitat sampling to establish the range of natural variation in soil mineral and nutrient chemistry in the Refuge
Task Summary and Objectives: This task was initiated in FY06 based on questions and hypotheses generated during the preparation of the open-file report described in Task 9. Specifically, it was hypothesized that soil concentrations and availability of elements such as P and Ca exhibit spatial variation in the Refuge interior as a result of local differences in hydrology and vegetation. The magnitude of this variation likely is small compared to changes in soil chemistry across canal gradients near the Refuge perimeter, but may be important in terms of understanding natural sources and sinks for limiting nutrients and minerals within this spatially heterogeneous wetland. Prior to the initiation of this task, most sampling for soil chemistry had been conducted in SWP habitats. This task extended this sampling to other common habitats such as sawgrass and tree islands.
Work to be undertaken during the proposal year and a description of the methods and procedures: Site sampled for total soil and plant-tissue nutrients in FY06 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 FY06.
Specific Task Product(s): Results will be presented in the final project report and also in a peer-review manuscript that will include data for this task from FY06. Results may also be included in scientific presentations.
Title of Task 4: Field experiment to quantify ecological effects of additions of high conductivity waters to the Refuge interior
Task Summary and Objectives: Controlled mineral additions are being performed at a minimally impacted location in the Refuge interior to experimentally determine effects of varying levels and durations of canal-water intrusion on marsh processes and vegetation patterns. The information gained from this experiment will be critical to establishing cause-effect relationships between canal-water intrusion and ecological changes. Fifteen experimental plots 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.
Work to be undertaken during the proposal year and a description of the methods and procedures: 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 FY05 will continue. Microbial enzyme measurements initiated in collaboration with investigators from the SFWMD will be completed.
Specific Task Product(s): Data collection and analysis will be completed in FY07. Results will be presented in the final report and then as a peer-review manuscript. Data will also be used in various scientific presentations planned for FY07 and beyond.
Title of Task 5: Laboratory experiments to determine the effects of water chemistry and hydrology on soil phosphorus retention and release
Task Summary and Objectives: The effects of canal-water intrusion on P cycling rates at interior Refuge locations will be examined using a series of laboratory incubations beginning in FY06. This work was originally slated to begin in FY05 but was postponed in order to begin preparation of a report on peatland responses to increased mineral loading at the request of the Refuge. The occurrence of temporarily elevated P concentrations or "excursions" at some interior Refuge locations in recent years is of concern to Refuge and water managers. One hypothesis to be tested here is that interior sites with elevated conductivity levels exhibit greater P limitation and, therefore, tighter P cycling than low conductivity sites. If true, this would explain the tendency for P excursions to occur at the most interior (lowest conductivity) locations. It also is likely that hydrology (e.g., flooded vs. saturated vs. drying soil conditions) affects the potential for soil P release.
Work to be undertaken during the proposal year and a description of the methods and procedures: 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.
This task will provide critical information on how hydrologic and water quality changes affect microbial processes that retain and release P from Refuge sediments, which likely represents the primary source of water-column P in interior areas. The findings of this work will allow the Refuge and other environmental managers to better understand the natural and human factors that affect surface-water P concentrations within the Refuge.
Specific Task Product(s): Results from this task will be presented in the final project report and in a peer-review manuscript.
Title of Task 6: Field and laboratory experiments to determine the effect of canal-water pulses on mineral and nutrient accumulation in the Refuge interior
Task Summary and Objectives: Results of the synoptic survey (FY04) indicated that nutrient levels in the surface soil-litter layer may be a more sensitive indicator of the effects of canal-water intrusion on Refuge chemistry compared with routine measurements of water chemistry. This is especially true for areas that receive periodic pulses of canal water rather than continuous exposure. At such sites, elevated nutrient levels may persist in the surface soils despite a rapid return of surface-water chemistry to ambient conditions. Experiments will be performed to assess the potential for surface soils to accumulate P and non-P nutrients (e.g., Ca, K, N, S) in response to pulsed vs. continuous exposure to canal water. These experiments will test the perception that transient water-quality excursions (e.g., temporarily elevated concentrations of P or other nutrients) in the Refuge interior have no lasting effect on marsh biogeochemistry. Initial experiments during FY06 showed various patterns of accumulation for different elements. Additional experiments will be designed in FY07 to better understand accumulation mechanisms and the ecological significance of this enrichment.
Work to be undertaken during the proposal year and a description of the methods and procedures: 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.
Specific Task Product(s): Results will be included in the final project report and combined with FY06 data in a peer-review manuscript.
Title of Task 7: Scoping study to assess the efficacy of different geochemical methods for reconstructing historic water quality conditions across the Refuge
Task Summary and Objectives: This scoping study involves the measurement of changes in chemical constituents through time in soil cores as a means of reconstructing historic water quality conditions in the Refuge. Wetland soils often provide a record of past environmental conditions through storage of chemical (inorganic and organic) and biological (pollen, shells) markers. Interpretation of this record often is not straightforward and may be hampered by an absence of modern analog studies, and resetting of chemical signals by diagenetic processes. Nevertheless, paleoecological studies have frequently been successful at providing important information on past conditions. Such information can provide managers with concrete goals for restoring and maintaining water quality.
Work to be undertaken during the proposal year and a description of the methods and procedures: Laboratory processing of soil cores collected during FY06 will be completed early in FY07.
Specific Task Product(s): Results will be included in the final project report and will include an assessment of the efficacy of these geochemical methods to improve understanding of past water quality conditions in the Refuge. Depending on the results, these data may be published as a peer-review paper.
Title of Task 8: Laboratory experiment: influence of P enrichment on sulfate reduction in Refuge soils
Task Summary and Objectives: Sulfate data collected across canal gradients indicates that porewater sulfate levels are higher at the interior end of these gradients where sulfate loads are low (but still elevated) than in areas near the canals where sulfate loads are highest. This pattern in turn suggests that the zone of sulfate reduction in the Refuge is more restricted than that for sulfate enrichment. Field sampling proposed in Task 1 will better document sulfate concentrations and reduction rates across canal gradients and, if this sampling confirms the patterns just described, then a laboratory experiment will be performed to test a hypothesis concerning the processes that limit the spatial extent of sulfate reduction across canal gradients. Specifically, we hypothesize that the soil redox conditions necessary to favor sulfate reduction are generated only in the presence of sufficient enrichment with P, which is a primary nutrient limiting microbial respiration and growth. Phosphorus enrichment may stimulate aerobic (as well as anaerobic) microbial respiration, resulting in increased oxygen consumption in the soil and the onset of anoxic conditions and lower soil redox. The zone of P enrichment in the Refuge is smaller than the zone of sulfate enrichment and, if our hypothesis is correct, then this may explain why the zone of sulfate reduction is limited as well.
Work to be undertaken during the proposal year and a description of the methods and procedures: The design of laboratory experiments during FY07 is underway. 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 design based on initial findings.
Specific Task Product(s): Results of this experiment will help to explain patterns of sulfate accumulation and reduction across canal gradients. Findings will be combined with those for Task 1 as a section in the final project report. Results also may be included in peer review manuscripts and in scientific presentations.
Title of Task 9: Complete report on peatland mineral chemistry and continue data integration and synthesis
Task Summary and Objectives: Increased attention will focus on entering, interpreting, and disseminating data in peer-review manuscripts and scientific presentations. At the request of the Refuge, a document is being prepared that reviews available information on the ecological importance of mineral chemistry in peatlands and available evidence for the ecological effects of shifts in mineral chemistry in the Everglades. This document is currently undergoing internal USGS review and will be formatted and disseminated as an official USGS report.
Work to be undertaken during the proposal year and a description of the methods and procedures: The primary goal of this task is to complete a draft document for external peer review by December 2006 and provide a final version in the form of an electronic USGS open-file report by the end of February 2007. Data entry, QA/QC, and analysis of other data from this project will continue. Submission of peer-review publications and presentations at scientific meetings are also planned for FY07.
Specific Task Product(s): Open-file report, peer-review publications, scientific presentations
U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 04 September, 2013 @ 02:09 PM(KP)