Assessment of natural resource conditions in and adjacent to Biscayne National Park. Natural Resource Report NPS/BISC/NRR—2012/598

This report is an assessment of the conditions of natural resources in Biscayne National Park (BNP) based on the compilation, review and evaluation of existing information on the Park’s natural resources. This review evaluates threats and stressors, and is intended to improve understanding of BNP resources to help guide Park management to address the identified threats, which are supported by enhanced data collection, research and assessment efforts. The report is focused on broad resource components, namely terrestrial resources and aquatic systems including: wetlands, canals, bay waters, marine/reef areas and ground waters. Biotic and abiotic resource components are considered in the review.

Vegetation:environment relationships and water management in Shark Slough, Everglades National Park

The hydrologic regime of Shark Slough, the most extensive long hydroperiod marsh in Everglades National Park, is largely controlled by the location, volume, and timing of water delivered to it through several control structures from Water Conservation Areas north of the Park. Where natural or anthropogenic barriers to water flow are present, water management practices in this highly regulated system may result in an uneven distribution of water in the marsh, which may impact regional vegetation patterns. In this paper, we use data from 569 sampling locations along five cross-Slough transects to examine regional vegetation distribution, and to test and describe the association of marsh vegetation with several hydrologic and edaphic parameters. Analysis of vegetation:environment relationships yielded estimates of both mean and variance in soil depth, as well as annual hydroperiod, mean water depth, and 30-day maximum water depth within each cover type during the 1990’s. We found that rank abundances of the three major marsh cover types (Tall Sawgrass, Sparse Sawgrass, and Spikerush Marsh) were identical in all portions of Shark Slough, but regional trends in the relative abundance of individual communities were present. Analysis also indicated clear and consistent differences in the hydrologic regime of three marsh cover types, with hydroperiod and water depths increasing in the order Tall Sawgrass , Sparse Sawgrass , Spikerush Marsh. In contrast, soil depth decreased in the same order. Locally, these differences were quite subtle; within a management unit of Shark Slough, mean annual values for the two water depth parameters varied less than 15 cm among types, and hydroperiods varied by 65 days or less. More significantly, regional variation in hydrology equaled or exceeded the variation attributable to cover type within a small area. For instance, estimated hydroperiods for Tall Sawgrass in Northern Shark Slough were longer than for Spikerush Marsh in any of the other regions. Although some of this regional variation may reflect a natural gradient within the Slough, a large proportion is the result of compartmentalization due to current water management practices within the marsh.We conclude that hydroperiod or water depth are the most important influences on vegetation within management units, and attribute larger scale differences in vegetation pattern to the interactions among soil development, hydrology and fire regime in this pivotal portion of Everglades.

A 2,500-year record of environmental change in Highlands Hammock State Park (Central Florida, U.S.A.) inferred from siliceous microfossils

Analysis of siliceous microfossils of a 79 cm long peat sediment core from Highlands Hammock State Park, Florida, revealed distinct changes in the local hydrology during the past 2,500 years. The coring site is a seasonally inundated forest where water availability is directly influenced by precipitation. Diatoms, chrysophyte statospores, sponge remains and phytoliths were counted in 25 samples throughout the core. Based on the relative abundance of diatom species, the record was subdivided into four diatom assemblage zones, which mainly reflect the hydrological state of the study site. An age-depth relationship based on radiocarbon measurements of eight samples reveals a basal age of the core of approximately 2,500 cal. yrs. BP. Two significant changes of diatom assemblage composition were found that could be linked to both, natural and anthropogenic influences. At 700 cal. yrs. BP, the diatom record documents a shift from tychoplanktonicAulacoseira species to epiphytic Eunotia species, indicating a shortening of the hydroperiod, i.e. the time period during which a wetland is covered by water. This transition was interpreted as being triggered by natural climate change. In the middle of the twentieth century a second major turnover took place, at that time however, as a result of human impact on the park hydrology through the construction of dams and canals close to the study site.

Water Quality and Wet Season Diatom Assemblage Characteristics from the Tamiami Trail Pilot Swales Sites (Everglades National Park, Florida, USA)

A pivotal component of hydrological restoration of the Florida Everglades is the improvement of water conveyance to Everglades National Park by the degradation of the current network of canals, roadways and levees. The Tamiami Trail (L29) road/canal complex represents a major barrier to natural water flows into the park and a variety of modification options for flow improvement are currently being explored, including the installation of spreader swales immediately downstream of culverts conveying water under Tamiami Trail from the L29 canal into Everglades National Park. In this study, we evaluated water column chemistry and wet-season diatom community structure to provide baseline information for use in future monitoring activities related to the proposed Tamiami Trail modifications. Water chemistry showed pronounced fluctuations in response to precipitation and anthropogenically mediated hydrological events. Differences in water quality variables among sites were dampened during periods of inundation, and became more pronounced during periods of low canal stage, suggesting the importance of small-scale mechanisms related to isolation of habitat patches. Diatom assemblages were unexpectedly speciose (127 taxa in 40 samples) compared to typical Everglades assemblages, and spatially heterogeneous in sites associated with concentric areas of dense vegetation immediately downstream of culverts. We also observed significant compositional dissimilarities among transects, indicating that culvert pool and north transect assemblages were substantially influenced by propagule input from the canal and areas to the north, while south transect sites were compositionally similar to typical sawgrass prairie diatom communities. Central transect sites were compositionally intermediate to their north and south counterparts. We propose that the position and spatial extent of this “transitional assemblage” is a sensitive indicator of subtle environmental change related to Tamiami Trail modifications.

Recent Fish Introductions Into Everglades National Park: An Unforeseen Consequence of Water Management?

Non-native fishes present a management challenge to maintaining Everglades National Park (ENP) in a natural state. We summarized data from long-term fish monitoring studies in ENP and reviewed the timing of introductions relative to water-management changes. Beginning in the early 1950s, management actions have added canals, altered wetland habitats by flooding and drainage, and changed inflows into ENP, particularly in the Taylor Slough/C-111 basin and Rocky Glades. The first non-native fishes likely entered ENP by the late 1960s, but species numbers increased sharply in the early 1980s when new water-management actions were implemented. After 1999, eight non-native species and three native species, all previously recorded outside of Park boundaries, were found for the first time in ENP. Several of these incursions occurred following structural and operational changes that redirected water deliveries to wetlands open to the eastern boundary canals. Once established, control non-native fishes in Everglades wetlands is difficult; therefore, preventing introductions is key to their management. Integrating actions that minimize the spread of non-native species into protected natural areas into the adaptive management process for planning, development, and operation of water-management features may help to achieve the full suite of objectives for Everglades restoration.

Evidence of Recent Phosphorus Enrichment in Surface Soils of Taylor Slough and Northeast Everglades National Park

Everglades National Park (ENP) is the last hydrologic unit in the series of impounded marsh units that make up the present-day Everglades. The ENP receives water from upstream Water Conservation Areas via canals and water control structures that are highly regulated for flood control, water supply, wildlife management, concerns about poor water quality and the potential for downstream ecosystem degradation. Recent surveys of surface soils in ENP, designed for random sampling for spatial analysis of soil nutrients, did not sample proximate to inflow structures and thus did not detect increased soil phosphorus associated with these water conveyances. This study specifically addressed these areas in a focused sampling effort at three key inflow points in northeast ENP which revealed elevated soil TP proximate to inflows. Two transects extending down Shark River Slough and one down Taylor Slough (a natural watershed of particular ecological value) were found to have soil TP levels in excess of 500 mg kg−1—a threshold above which P enrichment is indicated. These findings suggest the negative impact of elevated water (P) from surface flows and support the assertion that significant soil TP enrichment is occurring in Taylor Slough and other areas of northeastern ENP.