Paleoecology Study: Preliminary results of calibration sets and soil cores from WCA-2A.

By: Dr. Sherri Cooper

Introduction

The Florida Everglades provide a unique opportunity to study the effects of multiple stressors on a wetland ecosystem. The Everglades have experienced major anthropogenic changes in both hydrology and nutrient inputs over the past 100 years. Although there is much ongoing research of this wetland, the status of the ecosystem before human intervention, and the relative effects of nutrients and hydrology on changing vegetation and water quality are not well understood.

In the last several decades, nitrogen and phosphorus enriched agricultural drainage has been pumped into the northern water conservation areas from the Everglades Agricultural Area. The bulk of the nutrients are discharged into water conservation Area 1 (WCA-1) and WCA –2A, creating a phosphorus gradient of enrichment. Concentrations of phosphorus are highest near the Hillsboro canal, which runs along the northern boundary of WA-2A and where several gates are located that allow discharges into WCA-2A. Phosphorus levels in the water column and soils decrease in the downstream of southerly direction. Along with e P enrichment in the northern part of WCA-2A, there has been a shift in plant species composition to southern cattail from the native sawgrass communities. There have also been major changes to the hydrology of the system, but these are not as well understood.

Paleoecology

Paleoecological methods can provide a wealth of information about the Everglades ecosystem related to the effects of the two fundamental environmental variables of hydroperiod and nutrient conditions. Pollen, seed, and phytolith analyses of dated sediments or soils can provide information on plant community development and changes through time. Other paleoecological methods such as diatom stratigraphy, chrysophyte cyst abundance, charcoal analysis of sediments, organic carbon and nutrient analysis of sediments or soils, and measurement of various metals (including heavy metal accumulation in the peat soils ) can be used to characterize the original ecosystem, and investigate both the direct and long-term trends resulting from changing environmental variables due to climate and human intervention.

Research on the history of plant communities and other ecosystem indicators in the Everglades is needed for determining the communities that were present prior to canal development and drainage alterations, their responses to climate variables before human intervention, and for determining the effects of anthropogenic influences on the communities. Specifically, the histories of flooding frequency, water depth, nutrient availability, and fire frequency in the Florida Everglades are being investigated in this paleoecological study. The history of nutrient effects and hydrology of the Everglades can be addressed by researching fossil indicators through calibration sets of surface samples, and in dated soil cores.

Geochemical parameters such as carbon (C), nitrogen (N), phosphorus (P), and metals and fossil pollen have already been used in the Everglades study for indicating nutrient fluxes, water quality, soil quality, vegetation history and microbial influences. These, along with biogenic silica (BSi) analyses, will be important indicators to compare with additional biological data such as siliceous microfossil abundance (including diatoms, phytoliths, chrysophtye cysts and sponge spicules). All of these indicators will be used in developing transfer functions for environmental variables by canonical correlations, and other statistical analysis. These transfer functions are then used when comparing calibration sets from existing environments to down-core changes in microfossils.

Diatoms

Diatoms are particularly useful for paleoecological research cause of a species specific silica shell (frustule) that is often preserved in the stratigraphic record. Presence of absence of individual species and diatom community structure can be interpreted as indicators of eutrophication (nutrients), hydroperiod, pH, and salinity changes. Researchers have developed transfer functions using diatoms to predict P concentrations in lakes, and downcore (back in time) in lakes sediments. Diatoms contribute as a dominant algae group in the periphyton of the Everglades.

Objectives of Paleoecological Studies

The goal of this paleoecological study of the Florida Everglades is to re-create the history of vegetation cover, water quality and water depths in areas of the Everglades that have experienced human impacts. Nutrient enriched agricultural drainage and changes in hydroperiod and water levels have been implicated in changes through time in areas of the northern Everglades that receive runoff from the Everglades Agricultural Area.

The two objectives of this sub project are 1.) to calibrate indicators such as pollen, seeds and diatoms to current areas of different nutrient inputs (and across nutrient gradients), different vegetation cover, and different hydrology patterns; and 2) to analyze sediment cores from different areas of the Everglades (primarily WCA-2A and –3A) to determine historical vegetation cover and water quality changes trough time over the past 100-500 years in relation to historical changes in anthropogenic influence to the areas, including changes in the fire history of the Everglades. These analyses will provide of the relative effects of multiple stressors on this aquatic ecosystem.

Discussion of Preliminary Results

The results so far indicate that there are major changes in fossil indicators across the nutrient gradient in WCA-2A that are related to changes in soil Phosphorus as well as other nutrients, and possibly hydrology patterns. Continued work on calibration sets will help to elucidate relative effects of these different stressors on this wetland ecosystem, and allow more detailed interpretation of the historical record found in peat cores from this area.