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projects > development and stability of everglades tree islands, ridge and slough, and marl prairies > work plan

Project Work Plan

U.S. Geological Survey Greater Everglades Science Initiative (Place-Based Studies)

Fiscal Year 2004 Project Work Plan

A. GENERAL INFORMATION:

Project Title: Development and Stability of Everglades Tree Islands, Ridge and Slough, and Marl Prairies
Project Start Date: 10/01/00 Project End Date: 9/30/06
Project Funding: USGS Place-Based Studies Initiative
Principal Investigator: Debra A. Willard
Email address: dwillard@usgs.gov
Phone: 703-648-5320 Fax: 703-648-6953
Mail address: U.S. Geological Survey, 926A National Center, Reston, VA 20192

Other Investigator(s): William H. Orem
Email address: borem@usgs.gov
Phone: 703-648-6273 Fax: 703-648-6419
Mail address: U.S. Geological Survey, 956 National Center, Reston, VA 20192

Project Summary: Everglades restoration planning requires an understanding of the impact of natural and human-induced environmental change on wetland stability, and this project focuses specifically on three wetland types: tree islands, the sawgrass ridge and slough system, and marl prairies. For each of these, restoration targets are being proposed, although varying amounts of data exist on their predrainage extent and ecosystem dynamics. This project applies methods and databases developed in this project and the previous "Ecosystem History of the Everglades" project to improve our understanding of the response of these key wetland types to climatic variation and human alteration of water quantity and quality.

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 also 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 expanded to include examination of the Ridge and Slough system. Although several hypotheses exist regarding the genesis of Everglades ridge and slough structure, little data have been generated to verify any of these hypotheses. Similarly, it has been suggested that sawgrass ridges are expanding at the expense of adjacent sloughs, eventually resulting in loss of the ridge and slough structure and development of broad expanses of sawgrass similar to those present in much of WCA 2A. Performance targets for peat accretion rates in each subenvironment also are being considered for CERP efforts, although there is little scientific basis for such targets. Analyses of surface sediments from ridges and sloughs indicate that their pollen assemblages are distinctive and may be used to identify ridge vs slough habitat in sediment cores. The project will use well-dated pollen records from transects across ridge and slough systems to identify the timing of ridge and slough formation and document 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 FY03-04, we shall begin research designed to determine the predrainage extent and vegetational composition 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. Use of well-dated 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 integrates 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 and longevity of sawgrass ridges and sloughs, determine whether they represent initial sites of tree-island formation, 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.

Integration of paleoecological (pollen, seed, charcoal analysis) and geochemical methods with research by colleagues on bedrock mapping, vegetational surveys, ecological analyses, hydrologic monitoring and modeling will improve our understanding of ecosystem response to specific environmental changes. Analyses are performed on sediment cores, which are sampled at 1-2 cm increments for analysis of paleoenvironmental proxies. 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 (mollusks, ostracodes, charophytes), and seeds. 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, tree-island health will form the basis for one or more performance measures. Our results provide regional data on the condition of tree islands before and after 20th century changes to Everglades hydrology and therefore provide baseline data for 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 areas of the oldest, thickest peats. Our results also indicate regional differences in response to hydrologic changes. Whereas many tree islands in the central Everglades have become smaller due to artificially high water levels, those in the southern Everglades appear to have become larger. These data allow prediction of regional patterns of tree island response 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 and other biomarkers in dated cores from tree islands provide useful proxies for historical wading bird populations. 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 and 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 because 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.

Collaborators:
Florida, State Agencies, Florida Fish and Wildlife Conservation Commission
Contact: T. Towles, M. Poole
Department of Interior, Fish and Wildlife Service, Loxahatchee National Wildlife Refuge
Contact: L. Brandt
Department of Interior, U.S. Fish and Wildlife Service
Contact: L. Heisler
Florida, Rotenburger and Holeyland Wildlife Management Areas
Department of Interior, National Park Service, Everglades National Park
Contact: T. Armentano, S. Mitchell
Department of Interior, National Park Service, Big Cypress National Preserve
Contact: J. Snyder

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, Big Cypress National Preserve.

B. WORK PLAN

Title of Task 1: Response of Everglades Tree Islands to Environmental Forcing Factors
Task Funding: USGS Place-Based Studies Initiative
Task Leaders: Debra A. Willard
Phone: 703-648-5320
FAX: 703-648-6953
Task Status (proposed or active): Active
Task priority: High
Time Frame for Task 1: FY03-05
Task Personnel: Debra Willard, William Orem, Christopher Bernhardt, Margo Corum, Charles Holmes, Bryan Landacre, Harry Lerch, Marci Marot, Thomas Sheehan

Task Summary and Objectives:

Tree islands in the Water Conservation Areas (WCAs), Loxahatchee NWR, Everglades National Park (ENP) and Big Cypress National Preserve 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 biomarkers, therefore, 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 FY03-04, 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 History Biomarkers (Analytical work in FY03-04, 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 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. 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. 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: Temporal and Spatial Stability of the Ridge and Slough System
Task Funding: USGS Place-Based Studies Initiative
Task Leaders: Debra A. Willard
Phone: 703-648-5320
FAX: 703-648-6953
Task Status (proposed or active): Active
Task priority: High
Time Frame for Task 1: FY03-06
Task Personnel: Debra Willard, Christopher Bernhardt, Charles Holmes, Bryan Landacre, Marci Marot, Thomas Sheehan

Task Summary and Objectives:

The hypothesis that sawgrass ridge size is changing in response to hydrologic modifications is tested by collection of sediment cores in transects across both "pristine" and altered 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 position, shape, and size and 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. The transects analyzed to date indicate that the ridge and slough structure has been in place throughout the history of the sites, with changes tied both to global climatic fluctuations and local hydrologic changes. The position of the ridge/slough ecotone has fluctuated since the 1950s; analysis at additional sites is necessary to determine whether changes are consistent throughout the region or locally variable.

Work to be undertaken during the proposal year and a description of the methods and procedures:

Sampling FY03-05; analytical work FY03-05; publications FY04-05; synopsis FY06. In FY04-05, 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.

Planned Outreach: See task 1

Title of Task 3: Temporal and Spatial Stability of Marl Prairie Habitat
Task Funding: USGS Place-Based Studies Initiative
Task Leaders: Debra A. Willard
Phone: 703-648-5320
FAX: 703-648-6953
Task Status (proposed or active): Active
Task priority: Medium
Time Frame for Task 1: FY03-06
Task Personnel: Debra Willard, Christopher Bernhardt, Charles Holmes, Bryan Landacre, Marci Marot, Thomas Sheehan

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 proposed a pilot study to determine the predrainage extent of marl prairies. Due to funding restrictions on travel, this field work may not occur in FY03, and we propose undertaking it early in FY04. 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

C. BRIEF DESCRIPTION ON HOW PROJECT TASKS SUPPORT THE DOI AND USGS EVERGLADES RESTORATION SCIENCE PLANS

Study areas described in all three tasks have been identified as important vegetation types for landscape modeling in DOI and USGS Science Objectives. The tasks provide data on the structure and function of the natural (predrainage) systems and their response to 20th century hydrologic changes; this information provides a basis to predict their response to different restoration scenarios. The tasks are particularly relevant to issues related to decompartmentalization of WCA 3; they illustrate the impact of water impoundment on tree islands in southern WCA 3A and of water diversion from tree islands and modern marl prairies in the southern Everglades. Studies of transects across sawgrass ridges and sloughs provide evidence for the timing and causes of changes in these features. Geochemical analyses of phosphorus and organic markers of wading bird populations may provide insights in changes in locations of wading bird colonies throughout the region.



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