William H Orem
Tree islands are considered key indicators of the health of the Everglades ecosystem because of their sensitivity to both flooding and drought conditions. Tree islands also act as a sink for nutrients in the ecosystem and may play an important role in regulating nutrient dynamics. Although management strategies to restore and even create tree islands are being formulated, published data on their age, developmental history, geochemistry, and response to hydrologic alterations is limited. This project addresses these issues by integrating floral and geochemical data with geologic and vegetational mapping activities to establish the timing of tree-island formation and impacts of both flooding and droughts on tree islands throughout the Everglades. These data are used to assess the depth and period of flooding that tree islands can tolerate before degradation begins. We are also studying the role of tree islands in the geochemical budget of nutrients in the Everglades and investigating the use of sediment phosphorous as a tracer of historic bird populations in the Everglades.
In FY 2003, the project expanded to include examination of the Ridge and Slough system. Resource managers have hypothesized that sawgrass ridges are expanding at the expense of adjacent sloughs; continuation of this trend would result in loss of the ridge and slough structure and development of broad expanses of sawgrass. In addition, performance targets for peat accretion rates in each subenvironment are being considered for CERP efforts, although there is little scientific basis for such targets. Initial analyses of sediment cores from sawgrass ridges and adjacent sloughs indicates that it is possible to distinguish the assemblages in sediment cores. The project will use well-dated pollen records from transects across ridge and slough systems to identify changes in spatial extent of sawgrass ridges and sloughs in both 'pristine' and disturbed areas. These data will be used to: determine the longevity of the features; document changes in spatial extent of sawgrass ridges and sloughs; determine past rates of peat accretion in ridges vs. sloughs; determine whether sawgrass ridges are analogs for sites of tree-island formation; and assess the response of ridges and sloughs to natural and anthropogenic hydrologic changes.
In Fy 2003-2004 we began research to determine the predrainage extent of marl prairies, particularly in the western Everglades. Marl prairies, with relatively shallow water depths and short hydroperiods, are characterized by a greater abundance of graminoid species compared to sawgrass marshes. Use of well-dated pollen cores to determine the distribution of marl prairies over the past 150 years will facilitate prediction of the impacts of different restoration schemes on this critical region.
Assistance with the previous phase of the project was provided by: Lorraine Heisler, Tim Towles: Florida Game and Fresh-Water Fish Commission. Scientific collaboration and logistic support and elevation and vegetation data from tree islands and guidance in tree-island selection.
Fred Sklar, Susan Newman, Tom Fontaine, Ken Rutchey, Yegang Wu, Steve Krupa, Cindy Bevier, Jeff Giddings: South Florida Water Management District. Scientific collaboration and logistic support, elevation and vegetation data from tree islands and guidance in tree-island selection, and data on ground-water/surface water interactions and cores with lithologic description of underlying bedrock
Laura Brandt: Loxahatchee National Wildlife Refuge. Scientific collaboration and guidance on tree-island selection, vegetation data.
Tom Armentano, David Jones: Everglades National Park. Scientific collaboration on tropical hammocks in Everglades National Park.
David L. Dilcher: Florida Museum of Natural History. Scientific collaboration and vegetational reconstruction and evaluation of Late Holocene CO2 concentrations.
Willard, D. A., Lerch, H. E., Bates, A. L., Boylan, A., Corum, M.
Sklar, F and van der Val, A., editors
Holmes, Charles W.
Weimer, Lisa M.
Weimer, Lisa M., Riegel, W. L.
Holmes, C. W., Korvela, M. S., Mason, D., Murray, J. B., Orem, W. H., Towles, T.
Sklar, Fred H. and van der Valk Arnold G., editors
Orem, W. H.
Pielke, Roger A., Sr., Steyaert, Louis T., Willard, Debra A.
Paleoenvironmental reconstructions will be based on analysis of sediment core samples collected in transects along the length and breadth of selected tree islands. Integration of geochronologic and vegetational data from each island will identify phases in development of tree-island vegetation from the original marsh/slough communities as well as the timing of tree-island formation. Comparison of these patterns among different types of tree islands across the region will establish whether common regional patterns of development exist. Through analysis of transects of cores collected along the length of the island, we will document the timing of tree-island head and tail formation and determine whether they formed synchronously or whether tree-island heads formed before tails. Such information is critical to evaluate hypotheses that tails formed due to accumulation of debris behind the head (hydrodynamic hypothesis), due to chemical/nutrient enrichment from the head (chemo-hydrodynamic hypothesis), or due to hydrologic controls tied to climatic and environmental changes. An understanding of processes governing head and tail formation is necessary for development of plans to restore and create tree islands.
Transects of sediment cores also will be collected across the breadth of tree-island heads from marsh to marsh to compare long-term vegetational and geochemical patterns on and off the island. These will include cores for solid phase paleoecology, geochemistry, and dating as well as cores for pore-water geochemical studies. Wells are being installed on heads and adjacent marshes of two to three tree islands by SFWMD for monitoring of groundwater discharge on and around tree-island heads. During the drilling of each well, thirty-foot long cores of the underlying limestone will be obtained. In collaboration with personnel at SFWMD, we will describe the lithology of these cores and determine wheter the limestone composition is different under the heads compared to the surrounding marsh. Also, SFWMD and FGFC are collecting data across these transects on sediment depth to bedrock to determine whether topographic highs underlie the islands.
Initial geochemical and biological data from tree-island cores in WCA 3B indicates correlations between specific vegetational assemblages and elevated phosphorus levels in the tail and marsh. Regional sampling of tree islands will establish whether this is a common pattern on Everglades tree islands or a local phenomenon. The source of phosphorus is unclear, but bird guano is a likely source (Powell, et al, 1991). We will examine the sources of phosphorus to the tree islands through tracer and isotope studies of sediment cores collected on the islands and from guano and sediment cores collected from extant bird rookeries in the Everglades. Another possible source is upwelling ground water; analysis of samples from wells installed on key islands by SFWMD will clarify the relative roles of wading birds and upwelling ground water in phosphorus enrichment of tree-island sediments.
Sustained high water levels during the last few decades have resulted in degradation and loss of tree islands in much of WCA 2A. Determination of vegetational patterns on drowned and healthy islands should help establish the sequence of vegetational changes during tree-island drowning and provide useful data to aid restoration efforts on specific tree islands. Integration of these long-term patterns with ongoing mapping of bedrock topography and vegetation will facilitate development of models of tree-island formation and evolution. An understanding the role of various environmental parameters in controlling plant community composition and geochemistry, in both healthy and degraded islands, is critical in determining appropriate management strategies to sustain tree islands, restore degraded islands, establish appropriate monitoring strategies, and evaluate the feasibility of creating tree islands.
Field work included in March - Collected transects of cores on 6 islands in WCA 3A, including a declining rookery island near the L67 canal; collected cores on 2 islands in Loxahatchee NWR and in August - Collected transects of cores on 4 islands in Everglades National Park and 1 declining tree island in WCA 2A
Preliminary palynological analysis of cores from island sampled in FY 1999
Geochemical analyses on cores from FY 1999 and some from this year
Dating of cores collected this year
In FY 2003 the project expanded to include examination of hte Ridge and Slough system. The hypothesis that sawgrass ridges are expanding in size will be tested by collection of sediment cores in transects across ridges and sloughs. Pollen analysis combined with radiometric dating (lead -210, cesium-137) of closely spaced cores across the ridge/slough ecotone will be used to reconstruct the position of the ecotone at selected time slices. This will facilitate reconstruction of sawgrass ridge size as well as clarify whether the ridges have been stationary or migrate through time. We also will document sedimentation rates in the two environments to test the hypothesis that peat accretion rates are higher on sawgrass ridges than sloughs.
In FY 2003, we will complete pollen and geochronologic analyses of cores collected in 'pristine' transects during FY 2002. We will identify the position of the sawgrass ridge/slough ecotone at selected time slices to document changes in sawgrass ridge size and determine whether the position of sawgrass ridges and sloughs has been stable over long time periods. Transects of sediment cores across ridges and sloughs will be designed in consultation with McVoy (SFWMD), with closest spacing of cores across the ecotone. Pollen analysis will be used for vegetational reconstruction, and radiometric dating (lead-210, cesium-137: Holmes, USGS, St. Petersburg) will be used for age control in cores as well as to document differences in sediment accumulation rates in the two environments.
Tree islands in the Water Conservation Areas (WCAs), Loxahatchee NWR, and Everglades National Park (ENP) were selected for study in consultation with scientists at South Florida Water Management District (SFWMD), the Florida Fish and Wildlife Conservation Commission, Loxahatchee NWR, and ENP. These islands were picked to maximize regional coverage and include several different types of islands, including fixed, tear-drop shaped tree islands, pop-up islands, bay heads, willow heads, and cypress domes. Paleoenvironmental reconstructions of patterns of tree island development are based on analysis of sediment cores collected in transects along the length and breadth of tree islands and adjacent marshes and sloughs. Comparison of these patterns among different tree island types throughout the region will establish whether common regional patterns of development exist and the relative roles of climate and local factors in governing tree-island development.
Work planned for FY 2003 includes 1. Completion of the survey of pollen/geochemistry of Everglades tree islands (sampling to be completed this year and 2. Coring of tree islands in Taylor Slough area of Everglades National Park, lost tree islands in WCA 2, strand islands in western WCA 3 and WCA 1. For most sites, piston coring techniques used in previous studies will be employed. On dry tree-island heads, vibracoring techniques will be used. Pollen analysis will be incorporated in all analyzed cores; on tree island heads and near tails, analysis of seeds will be used to improve estimates of species composition and biodiversity. Analysis of total and organic C, total N, total P, and total S in sediments using Leco elemental analyzer (C,N,S) and colorimetric analysis for total P. Phosphorus speciation studies in selected cores using published methods. Pore water analysis for nutrients, anions, sulfur species, conductivity, pH, alkalinity, and cations, at selected sites. Pore waters obtained by whole core squeezing method. Redox sensitive chemical species in porewater analyzed by electrochemistry in field. Nutrients, anions, and cations analyzed by colorimetric methods, ion chromatography, and ICP/MS at labs in Reston, VA.
Wading Bird History Biomarkers analytical work is planned for FY 2003 and FY 2004. High phosphorus levels on tree islands and in tree island tails are likely a result of guano deposition from bird rookeries. Downcore changes in total phosphorus concentrations and other markers of wading birds in dated cores from tree islands, thus, may be useful indicators of wading bird history. We will investigate the utility of phosphorus as a marker of wading bird history, and look for other organic markers of wading birds, through analysis of fresh wading bird guano, and sediment cores. Organic geochemical studies will involve standard solvent extraction of guano samples (obtained from D. Gawlik, SFWMD) and sediments, followed by isolation procedures (column chromatography), and GC and GC/MS fro analysis. Facilities and analytical equipment for this work is located at USGS labs in Reston, VA. Changes in total phosphorus and organic markers of bird guano downcore will provide historical perspective on changes in wading bird populations on tree islands throughout the ecosystem. Correlation of wading bird history with historical palynological results from studies by Willard may allow interpretation of what environmental factors influenced historical changes in wading bird populations. This will provide managers with a better understanding of how proposed changes to the ecosystem in CERP may affect wading bird populations.
In FY 2003, we propose a pilot study to determine the predrainage extent of marl prairies. Marl prairies, with relatively shallow water depths and short hydroperiods, are characterized by a greater abundance of graminoid species compared to sawgrass marshes, and earlier analyses indicate that they are distinguishable in the pollen record. However, sediments in marl prairies typically are very thin, and it is necessary to collect cores in dissolution holes to acquire sufficiently long records. Earlier research has indicated that lead-210 concentrations in sediment cores from dissolution holes are altered by lead-210 associated with ground water, and cesium-137 migrates throughout the core in association with organic matter. Therefore short-lived radioisotopes produce unreliable age models, and geochronology will have to rely on radiocarbon analysis of bomb carbon (carbon released since nuclear testing in the last few decades). This year, we plan to determine the best approaches to dating such cores before beginning a larger scale effort in out years.
Response of Everglades tree islands to environmental forcing factors
Complete survey of pollen/geochemistry of Everglades tree islands (sampling completed in FY03-04, analytical work in FY03-04, publications in FY03 and FY04, synopsis completed in FY04-05). Coring of cypress strands and domes in Big Cypress and western WCA 3A, lost tree islands in WCA 2A, and strand islands in WCA 1. For most sites, piston coring techniques used in previous studies will be employed; where necessary, vibracoring techniques will be used. Pollen analysis will be incorporated in all analyzed cores. Analysis of total and organic C, total N, total P, and total S in sediments using Leco elemental analyzer (C,N,S) and colorimetric analysis for total P. Phosphorus speciation studies in selected cores using published methods. Pore water analysis for nutrients, anions, sulfur species, conductivity, pH, alkalinity, and cations, at selected sites. Pore waters obtained by whole core squeezing method. Redox sensitive chemical species in porewater analyzed by electrochemistry in field. Nutrients, anions, and cations analyzed by colorimetric methods, ion chromatography, and ICP/MS at labs in Reston, VA.
Wading bird biomarkers: We will continue analyses of fresh wading bird guano for phorphorus and other organic markers and apply results to sediment core interpretation. Organic geochemical studies will involve standard solvent extraction of guano samples (obtained from D. Gawlik, SFWMD) and sediments, followed by isolation procedures (column chromatography), and GC and GC/MS analysis. Facilities and analytical equipment for this work are located at USGS labs in Reston, VA.
Ridge and Slough System temporal and spatial stability
We will focus on degraded sawgrass ridge/slough systems identified using historic photographs. Transects of cores will be collected in these regions to document their early to mid-20th century extent and the timing of their alteration. Sites will be selected in collaboration with C. McVoy (SFWMD) and T. Smith (USGS) to determine the most appropriate sites to examine past degradation of the habitat. Pollen analysis will be used for vegetational reconstruction, and radiometric dating (lead-210, cesium-137) by C. Holmes (USGS) will be used for age control in cores as well as to document differences in sediment accumulation rates in the two environments.
marl prairie habitat temporal and spatial stability
In FY03, we proposed a pilot study to determine the predrainage extent of marl prairies. Marl prairies, with relatively shallow water depths and short hydroperiods, are characterized by a greater abundance of graminoid species compared to sawgrass marshes, and earlier analyses indicate that they are distinguishable in the pollen record. However, sediments in marl prairies typically are very thin, and it is necessary to collect cores in dissolution holes to acquire sufficiently long records. Earlier research has indicated that lead-210 concentrations in sediment cores from dissolution holes are altered by lead-210 associated with ground water, and cesium-137 migrates throughout the core in association with organic matter. Therefore short-lived radioisotopes produce unreliable age models, and geochronology will have to rely on radiocarbon analysis of bomb carbon (carbon released since nuclear testing in the last few decades). This year, we plan to determine the best approaches to dating such cores before beginning a larger scale effort in out years.
U.S. Department of the Interior, U.S. Geological Survey, Center for
Coastal Geology
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