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|projects > effects of water hardness on slough-wet prairie plant communities of 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: Effects of water hardness on slough-wet prairie plant communities of the A.R.M. Loxahatchee National Wildlife Refuge
Overview & Objective(s): Alterations to ground-water and surface-water hydrology and water chemistry in south Florida have contributed to increased flows of mineral-rich (i.e., hard water) canal water into historically rainfall-driven (soft water) areas of the Everglades. The interior of the A.R.M. Loxahatchee National Wildlife Refuge largely has retained its historic low conductivity or "soft-water" condition due to its relative isolation from canal flows. However, recent sampling by USGS and the Refuge has shown that canal influences on water quality extend several km into the Refuge in some areas, and Refuge scientists and managers have expressed concern that these influences may increase depending upon future changes in water management operations. Intrusion of canal waters into the Refuge increase the availability of phosphorus (P), the primary limiting plant nutrient in the Everglades, as well as concentrations of major mineral ions such as Ca2+, Mg2+, and SO42-. While the ecological effects of P enrichment on the Everglades is fairly well understood, potential impacts caused by increased mineral concentrations in this soft-water wetland are largely unknown. Understanding the types and magnitude of these impacts is particularly important given that the area of the Refuge exposed to mineral enrichment is much greater than that exposed to P enrichment.
The objective of this project is to determine the effects of increased flows of mineral-rich canal water on the aquatic plant community of the Refuge interior. Slough-wet prairie (SWP) habitats are a major landscape feature in the Refuge, and several SWP plant species may be adapted to the soft-water conditions in the Refuge interior. Increased mineral loads to the Refuge may result in a shift towards a more species-poor and spatially homogeneous community. In addition, there is a small amount of evidence to suggest that mineral enrichment may favor the growth and expansion of sawgrass and a consequent decline in the coverage of SWP habitats. A survey across existing mineral gradients will be performed to document patterns of vegetation change and their relation to changes in water hardness and other (e.g. soil P and hydrology) environmental factors. Laboratory and field experiments will test these correlative relationships to determine the relative importance of increasing water hardness as a cause of observed vegetation changes across canal gradients.
Specific Relevance to Major Unanswered Questions and Information Needs Identified: A major DOI concern is that the quality of water supplied for Everglades hydrologic restoration be acceptable to achieve desired community and functional responses (DOI Science Plan, pg. 16). Considerable research has focused on the response of native vegetation communities to excess P loading. However, despite the known importance of mineral gradients in determining vegetation patterns in other peatlands, little attention has been paid to the effects of mineral-rich canal flows into the historically rainfall-driven and more mineral poor Everglades. The potential for increased intrusion of canal water into the Refuge as a result of CERP and related water management activities is of particular concern given that the Refuge represents perhaps the best remaining example of the historic soft-water Everglades (Science Plan, pg. 44). Gradient studies and other research are needed to understand the ecological effects of canal-water intrusion on native communities in the Refuge in order to make informed management decisions (Science Plan, pg. 45).
The proposed research, which will document wetland vegetation changes across gradients of canal influence and determine the cause of these changes using controlled experiments, directly supports DOI and Refuge priorities just described. Study results will provide Refuge management with a clearer understanding of the nature and extent of vegetation changes caused by increased intrusion and the specific environmental factors contributing to such change. This information will support the development of science-based operational targets for water management activities that affect the Refuge to achieve a balance between the need to improve water deliveries while not harming existing Refuge resources. Information on the environmental requirements of native vegetation gained from this study will also provide a basis for management efforts to restore and conserve the natural diversity and abundance of Refuge biota as described in the Refuge's 2000 Comprehensive Conservation Plan.
Status: The vegetation survey (Task 1) was conducted in October 2006. Thirty permanent monitoring stations (including both EVPA and EWQM sites) were selected for sampling. Vegetation composition was recorded in 24 1 m2 plots along a transect established near the water-quality monitoring site. Water depth and specific conductance were recorded. Duplicate soil cores (0-10 cm) were collected and currently are being processed for total and extractable nutrients and minerals.
Construction of walled plots for the field dosing experiment (Task 2) began in November 2006 and will be completed in January 2007. Baseline vegetation and soil measurements will be performed in these plots and dosing will begin in February 2007.
Planned Products: Planned products for FY07 include 2 technical presentations on the results of initial field and laboratory work as part of a special symposium entitled "Everglades Water Quality: On the Critical Path to Restoration" to be held at the 2007 annual meeting of the North American Benthological Society in June 2007. If requested, initial findings also will be presented to Refuge staff and other interested parties at the annual A.R.M. Loxahatchee National Wildlife Refuge Science Workshop in May 2007.
Title of Task 1: Field survey (gradient study)
Task Summary and Objectives:
Work to be undertaken during the proposal year and a description of the methods and procedures: The Refuge will be surveyed during fall of FY06 to determine the distribution of common SWP plant species and the extent of SWP habitat with respect to water and soil chemistry. Thirty locations will be selected that encompass a range of hydrology and water chemistry. Severely overdrained areas at the north end of the Refuge, deepwater areas at the south end, and highly enriched cattail area near canals will be excluded as vegetation in these areas is clearly driven by hydrology and/or P.
The frequency of occurrence of common SWP species will be determined in 24 1-m2 quadrats placed at roughly 2-m intervals along a transect across the center of this habitat. An additional 5 minutes will be spent surveying the site to detect species present in lower abundance. Voucher specimens will be collected and repeat visits will be made later in the year to assure accurate taxonomic identifications. Aerial photography of the Refuge obtained by Palm Beach County in 2004 will be used to determine the percent coverage of SWP (as opposed to sawgrass, tree island, and brush) habitat at each site. Water depths and soil and water chemistry (pH, surface-water conductivity, soil Ca and total and extractable P and N concentrations) also will be measured at each site. Additional water chemistry data will be obtained from monthly water-quality monitoring trips conducted at each site by the Refuge and SFWMD.
Data will be analyzed using simple correlations, multiple regressions, and multivariate analysis to identify patterns of species distributions and habitat cover with respect to chemical variables and depth. These analyses will generate testable hypotheses concerning the importance of water hardness vs. other environmental factors in determining the size and vegetation composition of SWP habitats.
Specific Task Product(s): These data will be used to assess the relative importance of changes in hydrology, mineral chemistry, and nutrient availability in determining vegetation patterns across canal gradients in the Refuge. Results will be presented as part of a special symposium entitled "Everglades Water Quality: On the Critical Path to Restoration" to be held at the 2007 annual meeting of the North American Benthological Society in June 2007.
Title of Task 2: Effects of mineral and P enrichment on sawgrass and SWP communities and cover
Task Summary and Objectives: Field surveys in the Refuge have found that certain SWP plant species are common in the Refuge interior and absent from areas near the perimeter that are affected by canal-water intrusion. Phosphorus enrichment has been shown to influence SWP plant distributions across canal gradients in other parts of the Everglades. Available evidence from studies based in the Refuge indicates that mineral enrichment also may be an important factor limiting the distribution of certain species to the soft-water interior. Additional studies (see description in Task 3 below) also suggest that these water-quality changes stimulate the growth of sawgrass and promote its encroachment on SWP habitats. A controlled field enrichment experiment will be conducted to simultaneously measure the response of interior SWP plant species and sawgrass stands to mineral and/or P enrichment to better understand how different water-quality constituents affect plant community composition and habitat coverage.
Work to be undertaken during the proposal year and a description of the methods and procedures: Sets of 4 walled enclosures (2.5 m x 1.25 m) will be established at 3 locations (for a total of 12 enclosures) near an interior monitoring station (LOX8) in the Refuge. Enclosures will be located in the transition zone between sawgrass and SWP habitats such that approximately half of each enclosure is within each habitat. Vegetation composition and tissue chemistry will be measured in each enclosure during February 2007. Once this baseline assessment is completed, enclosures will be enriched with one of the following substances: 1) no enrichment (control); 2) crushed limerock (mineral, pH treatment); 3) slow release P fertilizer (nutrient enrichment); 4) both limerock and P enrichment. Each treatment will be applied to 1 enclosure in each set for a total of 3 replicates per enrichment treatment. Surface soils will be collected from each enclosure 1 month after the first dose is applied and processed to determine pH, mineral content, and available P. Additional doses will be applied quarterly or more frequently as required to maintain elevated levels of these chemical parameters in applicable treatments. Vegetation responses will be measured after 6 months and every 6 months thereafter. Dosing will continue through FY08.
Specific Task Product(s): Results from this experiment will be used to test the following hypotheses: 1) those generated from Task 1 concerning responses of SWP species to specific changes in water quality across canal gradients; and, 2) that sawgrass growth and expansion is stimulated by both mineral and P enrichment. Task products will include scientific presentations and a peer-review manuscript.
Title of Task 3: Laboratory experiment to determine the effects of increased mineral and P loading on sawgrass growth in sloughs
Task Summary and Objectives: Results from a previous laboratory experiment indicate that mineral enrichment of Refuge soils enhances the growth of sawgrass. These data also suggest that mineral and P enrichment in combination provides even greater growth stimulation. Field measurements show an increase in sawgrass cover and a decline in SWP cover with increasing mineral and P loading across canal gradients in the Refuge, suggesting that canal-water intrusion promotes the expansion of sawgrass into SWP communities. However, this relationship may be a consequence of historical vegetation patterns or environmental factors unrelated to water chemistry. The experiment described for this task will provide needed information to further test the hypothesis that both mineral and P enrichment stimulate the growth of sawgrass growing in SWP soils.
Work to be undertaken during the proposal year and a description of the methods and procedures: Sawgrass seeds from a common seed source will be germinated in the laboratory. While still small (~2-3 cm high), seedlings will be transplanted to small pots containing 500 g of soil from an interior slough in the Refuge. Initially, soils will be amended with a mineral solution containing major ions in the same proportions as found in canal water and with P in different combinations. Plants will be grown for 3 months under a temperature and photoperiod indicative of spring-time conditions in south Florida and watered 1-2 times each week with the same solutions used for soil amendment. The growth rate (increase in height) of replicate plants in each treatment will be measured over a 3-month period and final biomass will be determined. Initial and final soil pH and nutrient and mineral chemistry will be measured.
Specific Task Product(s): Results of this experiment will be used in combination with the field experiment proposed in Task 2 to provide further evidence to determine the effects of canal-water intrusion on sawgrass growth and expansion in the Refuge. Data from this experiment will be combined with those from an earlier experiment and presented as part of a special symposium entitled "Everglades Water Quality: On the Critical Path to Restoration" to be held at the 2007 annual meeting of the North American Benthological Society in June 2007. Other products from this task will include a peer-review manuscript.
Title of Task 4: Response of a submerged aquatic plant, Eriocaulon compressum, to mineral enrichment
Task Summary and Objectives: The macrophyte Eriocaulon compressum is a common aquatic species in the Refuge interior and exhibits broad hydrologic tolerances as it is found submerged in deeper water sloughs as well as on peat pop-ups with moist to saturated soils. This species is rare in parts of the Refuge affected by canal intrusion and appears to be restricted to shorter hydroperiod habitats in these areas. Many species of the genus Eriocaulon are indicative of soft-water conditions in wetlands and other aquatic habitats. It is also known that E. compressum relies strictly on CO2 as an inorganic carbon source for photosynthesis. This requirement alone would restrict this species to waters with lower pH - conditions under which CO2 is the predominant dissolved inorganic carbon form - when it is growing submerged.
Based on the above information, an experiment was designed to test several hypotheses concerning the distribution of E. compressum with respect to mineral gradients in the Refuge:
1) The growth of Eriocaulon is inhibited in soils with high mineral content;
2) The growth of Eriocaulon is inhibited when submerged in water with high mineral content;
3) The growth of Eriocaulon is more specifically inhibited by the absence of CO2 in waters with high mineral content due to the associated high pH.
This last hypothesis would explain why Eriocaulon can be found in shorter hydroperiod habitats in canal-influenced portions of the Refuge where it is rarely submerged and, therefore, is not isolated from the atmospheric CO2 source).
Work to be undertaken during the proposal year and a description of the methods and procedures: Twenty-four E. compressum plants of similar size will be collected from a peat pop-up at an interior location in the Refuge. Plants will be shipped overnight to the laboratory and weighed to obtain initial wet weights. Twelve plants will be potted in interior slough soil (low mineral content) in deep plastic containers and the remaining 12 will be planted in soils from a canal-influenced slough (higher mineral content). Plants of each soil treatment will be subjected to the following hydrologic treatments (4 replicate plants each): 1) watering to maintain saturated conditions; 2) watering to maintain flooding approximately 1/2 way up the above-ground portion of the plant; 3) flooding to submerge the plant under several cm of water. Plants grown in low mineral soils will be watered weekly with mineral-poor water from the same collection site. Plants grown in higher mineral soils will receive the same water that has been amended with a mineral solution to approximate 50% of the ionic strength of canal water, a mineral content that periodically occurs in sloughs near the Refuge perimeter in response to canal-water intrusion. Plants in flooded treatments will be acclimated gradually by raising water levels a few cm each week. Thus, for example, it will take about 5 weeks to completely flood plants in the submerged treatment.
Plants will be grown for 3 months under a temperature and photoperiod indicative of spring-time conditions in south Florida. Water pH and conductivity will be monitored weekly in each flooded container and concentrations of major cations and anions (mineral content) will be measured every 2-3 weeks. Care will be taken to avoid excessively high mineral concentrations by adding unamended interior slough water or distilled water as needed to account for evaporation. Plant height and diameter will be monitored for 3 months. The extent of browning of each plant also will be measured as an indicator of stress. At the end of the experiment, plants will be harvested to measure final biomass and tissue chemistry. Final water and soil mineral concentrations and pH will be measured.
Specific Task Product(s): Results of this experiment will provide evidence for the sensitivity of this common Refuge plant species to increased mineral loading from canals and insight into the specific mechanisms underlying this sensitivity. These data will be combined with information on spatial distribution and environmental relationships for this species obtained in Task 1 in a peer-review journal publication.
Title of Task 5: Response of the floating aquatic plant, Nymphoides aquaticum, to mineral enrichment
Task Summary and Objectives: The floating macrophyte Nymphoides aquaticum is common in areas of the Everglades with softer water such as the Refuge and parts of the interior of WCA 3A. It is a common species in the Refuge interior but is absent from areas near the perimeter that are affected by canal intrusion. A laboratory experiment will be conducted to assess the sensitivity of this species to elevated mineral and P concentrations found near the perimeter.
Work to be undertaken during the proposal year and a description of the methods and procedures: Several plants of N. aquaticum will be collected from an interior slough in the Refuge during February 2007. Collection of this species at this time of the year is facilitated by the abundance of small, free-floating specimens produced asexually by fragmentation. Plants will be shipped overnight to the laboratory, weighed to obtain initial wet weights, and measured for leaf number and size. Soils from an interior (low mineral content) and perimeter (high mineral content) slough will be combined in the following wet-weight ratios and used to fill the bottom of replicate containers: 1) 100%L:0%H; 2) 75%L:25%H; 3) 50%L:50%H; 4) 25%L:75%H; 5) 0%L:100%H. Soils in these respective treatments will be flooded with water from an interior location that has been amended with minerals to achieve 0, 25, 50, 75, or 100% of the increased ionic strength of canal water over interior surface water. Additional treatments will combine selected mineral treatments with P enrichment. A seedling will be placed in each container and allowed to grow and root for 3 months under a temperature and photoperiod indicative of spring-time conditions in south Florida. Water specific conductance and pH will be monitored weekly and water mineral and P chemistry will be measured every 2-3 weeks. Leaf number and size will be measured monthly. At the end of the experiment, plants will be harvested to determine final biomass and tissue chemistry. Final soil and water chemistry will be measured.
Specific Task Product(s): The results of this experiment will provide evidence for the sensitivity of this common Refuge plant species to increased mineral and P loading from canals. These data will be combined with information on spatial distribution and environmental relationships for this species obtained in Task 1 in a peer-review journal publication.
Title of Task 6: Competition Experiment
Task Summary and Objectives: Vegetation patterns across environmental gradients result from differential species tolerances to abiotic conditions and from species interactions such as competition. Single-species laboratory experiments such as those described in Task 4 and Task 5 provide information on the tolerances of individual SWP species to changes in soil and water chemistry but do not address the role of competitive interactions in determining species' distributions across water-quality gradients in the Refuge. For example, it is possible that certain interior SWP species are tolerant of changes in water-quality across canal gradients but are absent from perimeter sloughs due to competition from other species that are stimulated by mineral and/or nutrient enrichment. An outdoor microcosm experiment will be conducted to determine the relative importance of abiotic conditions and competition in determining growth rates of selected interior and perimeter SWP taxa.
Work to be undertaken during the proposal year and a description of the methods and procedures: This experiment is currently being designed, but anticipated methods are as follows. Large (e.g., 20 L) pots will be filled with soils from either an interior (low minerals and nutrients) or perimeter (high minerals and nutrients) SWP. Pots of each soil type will be planted with dominant interior (Xyris, Eriocaulon, Nymphoides) and perimeter (Eleocharis cellulosa) SWP taxa either separately or in combination. Replicate pots of each soil-plant treatment will be maintained under either slightly flooded (e.g., 10 cm) conditions that are representative of interior SWPs or under deeper and fluctuating water depths (e.g., 10-30+ cm) that are more representative of perimeter SWPs. The experiment will be maintained in large water troughs at Refuge headquarters for a minimum of 12 months, and plant growth and survival will be measured quarterly. Initial and final soil and plant-tissue chemistry will be measured.
Specific Task Product(s): This experiment will provide data to determine the importance of competitive exclusion in determining SWP species' distributions across canal gradients. In combination with information on biotic-abiotic relationships from other tasks, these results will improve understanding of the ecological effects of canal-water intrusion on Refuge vegetation. Task products will include scientific presentations and a peer-review manuscript.
U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 04 September, 2013 @ 02:09 PM(KP)
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