William Orem
A survey across existing mineral gradients will be performed to document patterns of vegetation change and their relationship to changes in water hardness and other 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.
The objective of this project is to determine the effects of increased flows of mineral-rich water on the aquatic plant community of the Refuge interior. Slough-wet prairie (SWP) habitats area 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 the SWP habitats.
U.S. Department of Agriculture - Natural Resources Conservation Service (NRCS) Department of the Interior - U.S. Geological Survey Department of Commerce - National Oceanic and Atmospheric Administration (NOAA) Environmental Protection Agency (EPA) Smithsonian Institution - National Museum of Natural History (NMNH)
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.
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.
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.
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.
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.
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.
U.S. Department of the Interior, U.S. Geological Survey
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