projects > evolution of everglades tree islands > work plan
Project Work Plan
Greater Everglades Science Program: Place-Based Studies
Project Work Plan FY 2003
A. GENERAL INFORMATION:
Project Title: Development and Stability of Everglades Tree Islands, Ridge and Slough, and Marl Prairies
Project Summary: Understanding the impact of natural and human-induced environmental change on the stability of Everglades wetlands is a critical need for restoration planning. This project has focused on tree-island development and stability and is proposing similar pilot studies in two other systems: the sawgrass ridge and slough system and marl prairies. For each of these, restoration targets are being proposed, even though little data exists on their predrainage extent. In the following, we outline proposals for pilot studies to address these key restoration issues.
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, the published data on their age, developmental history, geochemistry, and response to hydrologic alterations is limited. To address these issues, this project integrates 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. In particular, we hope to test hypotheses on the amount of flooding that tree islands can tolerate before degradation begins. We also will study the role of tree islands in the geochemical budget of nutrients in the Everglades and investigate the use of sediment phosphorous as a tracer of historic bird populations in the Everglades.
In FY03, the project is expanding 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 1) test the hypothesis of ridge expansion in the past century and 2) to compare peat accretion rates in the two subenvironments.
In FY03, we propose a pilot study 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.
Project Objectives and Strategy: This project aims to integrate the vegetational and geochemical history of tree islands with hydrologic studies and mapping of current vegetation, topography and lithology of underlying limestone to understand how environmental parameters have influenced tree-island development. Specific goals of this project include: document the timing of tree-island formation across the region; establish patterns of vegetational development and geochemical changes on the islands; compare development of different types of tree islands; develop a model of tree-island formation that may be used in restoration of degraded islands and, possibly, creation of new islands; and determine the duration of flooding or drought that tree islands can tolerate before changes in aerial extent occur. The project also aims to determine past distribution of sawgrass ridges and sloughs, identify times of ridge expansion and contraction, and estimate natural and postdrainage peat accretion rates in sawgrass ridges and sloughs. In marl prairies systems, the project aims to reconstruct the predrainage distribution of marl prairies and document their response to 20th century hydrologic changes.
We interate paleoecological (pollen, seed, charcoal analysis) and geochemical methods with work by colleagues on bedrock mapping, vegetational surveys, ecological analyses, hydrologic monitoring and modeling to understand how each system has responded to various environmental changes, whether induced by natural climate variability or water management practices. Analyses are performed on sediment cores, typically collected with a piston coring device; these cores are sampled at 1-2 cm increments, which then are divided for analysis of different components. Reconstructions of past vegetation, hydroperiod, and water depth are based on statistical comparison of down-core pollen assemblages with a calibration set of >200 surface samples; this allows identification of close analogs for fossil assemblages. Where marl layers are present, sediments also will be examined for the presence of calcareous microfossils such as mollusks and ostracodes. Analysis of total and organic C, total N, total P, and total S will be performed, along with pore water analysis for nutrients, anions, sulfur species, conductivity, pH, alkalinity, and cations, at selected sites.
Potential Impacts and Major Products: Because tree islands are influenced directly by water-management practices, one likely performance measure for restoration success involves tree-island health. Our results provide regional data on the condition of tree islands before and after 20th century changes to Everglades hydrology and therefore may be used to set restoration targets. This information feeds into validation of the Natural Systems Model during assessment of ecological impacts of plans being considered by the Comprehensive Everglades Restoration Project (CERP).
This research provides a regional perspective for identification of common patterns of tree-island development. Preliminary results suggest a gradient in timing of tree-island formation, with the oldest tree islands in the north. Our results also indicate regional differences in response to hydrologic changes. Whereas many tree islands in the northern Everglades have become smaller due to artificially high water levels, those in the southern Everglades appear to have become larger. These allow prediction of spatial changes after restoration of appropriate water supply.
The role of tree islands in nutrient cycling within the greater Everglades ecosystem is virtually unknown. Basic data on the nutrient geochemistry of tree islands within the context of the surrounding slough and marsh system will provide managers with the information necessary for integrating tree islands into a nutrient model for the ecosystem. In addition, profiles of phosphorus in dated cores from tree islands may provide a useful proxy for historical wading bird populations in the ecosystem. Although it generally is accepted that wading bird populations in the Everglades have declined dramatically over the last 100 years, the reasons for this decline still are unclear. An understanding of historical trends in wading bird populations will provide information on what environmental factors are most important. It also will provide a basis for managers to manipulate the conditions within the ecosystem to maximize the potential for recovery of wading bird populations.
Very little scientific evidence exists on the natural extent of sawgrass ridges and sloughs; however, performance measures already are being established for peat accretion rates and relative spatial extent of the two sub-environments. The proposed research is designed to document changes in size of each as well as to estimate differences in peat accretion rates. The paleoecological approach will provide these estimates more quickly and in a greater number of ridge/slough systems than monitoring efforts peat accretion rates are very low. Suggested time frames for acquire estimates of sedimentation rates using monitoring techniques have been on the order of a decade, when restoration will likely be in the early construction phases.
Clients: South Florida Water Management District; U.S. Fish and Wildlife Service, Arthur R. Marshall Loxahatchee National Wildlife Refuge; National Park Service, Everglades National Park
B. WORK PLAN
Title of Task 1: Response of Everglades Tree Islands to Environmental Forcing Factors
Task Summary and Objectives: Tree islands in the Water Conservation Areas (WCAs), Loxahatchee NWR, and Everglades National Park (ENP) are 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 are 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.
Initial geochemical and biological data from tree-island cores in WCAs 2 and 3 indicate correlations between specific vegetational assemblages and elevated phosphorus levels on the tree island. 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 examine the sources of phosphorus 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, whereas tree islands in ENP appear to have become larger due to decreased water supply. Reconstruction of changes in size in comparison with historic records of water flow will provide critical information on the impact of altered hydrology on tree island size.
Work to be undertaken during the proposal year and a description of the methods and procedures: Complete survey of pollen/ /geochemistry of Everglades tree islands (sampling completed in FY03, analytical work in FY03 and FY04, publications in FY03 and FY04, synopsis completed in FY04). 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 in FY03 and FY04, publications in FY03 and FY04). 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.
Planned Outreach: Posting of databases (tree island geochemical database) on Sofia website. Fact Sheet: Everglades Tree Islands-Evolution and Disappearance Correspondence with interested parties in south Florida (technology transfer, information transfer) Presentations as requested at workshops and public forums on Everglades tree island topics. Peer-reviewed papers.
Title of Task 2: Spatial Stability of the Ridge and Slough System
Task Summary and Objectives: 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.
Work to be undertaken during the proposal year and a description of the methods and procedures: Sampling (FY03-04; analytical work FY03-05; publications FY04-05; synopsis FY06). In FY03, we will complete pollen and geochronologic analyses of cores collected in "pristine" transects during FY02. 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.
Planned Outreach: See task 1
Title of Task 3: Stability of Marl Prairie Habitat
Task Summary and Objectives: Although several restoration schemes for the western Everglades are being considered, very little information (scientific or anecdotal) exists on the predrainage spatial extent of the marl prairies that exist in the Rattlesnake Ridge area. We propose a sampling program to reconstruct the predrainage distribution of western Everglades marl prairies over the past 100-150 years. The project also would analyze selected sites in the eastern marl prairies; in that region, historical and anecdotal records extend as far back as the 1930s, and results could be used to cross-check interpretations for the western region. The goal of the task is to document the distribution of graminoid-dominated marl prairies pre-and post-drainage. 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.
Work to be undertaken during the proposal year and a description of the methods and procedures: In FY03, 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.
Planned Outreach: See task 1