South Florida Natural Resource Center

Homestead, FL, United States

South Florida Natural Resource Center

Homestead, FL, United States
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Rosentreter J.A.,Southern Cross University of Australia | Maher D.T.,Southern Cross University of Australia | Ho D.T.,University of Hawaii at Manoa | Call M.,Southern Cross University of Australia | And 2 more authors.
Limnology and Oceanography | Year: 2017

Gas transfer velocities (k) of CO2 and CH4 were determined from 209 deployments of a newly designed floating chamber in six mangrove dominated estuaries in Australia and the United States to estimate mangrove system specific k. k600-CO2 and k600-CH4 (k normalized to the Schmidt number of 600) varied greatly within and between mangrove creeks, ranging from 0.9 cm h−1 to 28.3 cm h−1. The gas transfer velocity correlated well with current velocity at all study sites suggesting current generated turbulence was the main driver controlling k. An empirical relationship that accounts for current velocity and a linearly additive contribution of wind speed and water depth was a good predictor of k600-CO2 (R2 = 0.67) and k600-CH4 (R2 = 0.57) in the mangrove creeks in Australia. In a side-by-side study, good agreement was found between k determined from this new floating chamber and a 3He/SF6 dual tracer release experiment (∼5% discrepancy). k600-CH4 correlated well with k600-CO2 (R2 = 0.81), however, k600-CH4 was on average 1.2 times higher than k600-CO2, most likely reflecting a microbubble flux contribution. The microbubble flux contributed up to 73% of the total CH4 flux and was best predicted by a model that included CH4 supersaturation, temperature, and current velocity. A large overestimation was found for both CO2 and CH4 fluxes when calculated using empirically derived k models from previous studies in estuaries. The high temporal and spatial variabilities of kCO2 and kCH4 highlights the importance of site specific transfer velocity measurements in dynamic ecosystems such as mangrove estuaries. © 2016 Association for the Sciences of Limnology and Oceanography

Yagci A.L.,NASA | Santanello J.A.,NASA | Jones J.W.,U.S. Geological Survey | Barr J.,South Florida Natural Resource Center
International Journal of Remote Sensing | Year: 2017

A remote-sensing-based model to estimate evaporative fraction (EF)–the ratio of latent heat (LE; energy equivalent of evapotranspiration –ET–) to total available energy–from easily obtainable remotely-sensed and meteorological parameters is presented. This research specifically addresses the shortcomings of existing ET retrieval methods such as calibration requirements of extensive accurate in situ micrometeorological and flux tower observations or of a large set of coarse-resolution or model-derived input datasets. The trapezoid model is capable of generating spatially varying EF maps from standard products such as land surface temperature (Ts) normalized difference vegetation index (NDVI) and daily maximum air temperature ((Ta)). The 2009 model results were validated at an eddy-covariance tower (Fluxnet ID: US-Skr) in the Everglades using (Ts) and NDVI products from Landsat as well as the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors. Results indicate that the model accuracy is within the range of instrument uncertainty, and is dependent on the spatial resolution and selection of end-members (i.e. wet/dry edge). The most accurate results were achieved with the (Ts) from Landsat relative to the (Ts) from the MODIS flown on the Terra and Aqua platforms due to the fine spatial resolution of Landsat (30 m). The bias, mean absolute percentage error and root mean square percentage error were as low as 2.9% (3.0%), 9.8% (13.3%), and 12.1% (16.1%) for Landsat-based (MODIS-based) EF estimates, respectively. Overall, this methodology shows promise for bridging the gap between temporally limited ET estimates at Landsat scales and more complex and difficult to constrain global ET remote-sensing models. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

D'Odorico P.,University of Virginia | He Y.,University of Virginia | Collins S.,University of New Mexico | De Wekker S.F.J.,University of Virginia | And 3 more authors.
Global Ecology and Biogeography | Year: 2013

Aim: Climatic conditions exert a strong control on the geographic distribution of many woodland-to-grassland transition zones (or 'tree lines'). Because woody plants have, in general, a weaker cold tolerance than herbaceous vegetation, their altitudinal or latitudinal limits are strongly controlled by cold sensitivity. While temperature controls on the dynamics of woodland-grassland ecotones are relatively well established, the ability of woody plants to modify their microclimate and to create habitat for seedling establishment and growth may involve a variety of processes that are still not completely understood. Here we investigate feedbacks between vegetation and microclimatic conditions in the proximity to woodland-grassland ecotones. Location: We concentrate on arctic and alpine tree lines, the transition between mangrove forests and salt marshes in coastal ecosystems, and the shift from shrubland to grassland along temperature gradients in arid landscapes. Methods: We review the major abiotic and biotic mechanisms underlying the ability of woody plants to alter the nocturnal microclimate by increasing the temperatures they are exposed to. Results: We find that in many arctic, alpine, desert and coastal landscapes the presence of trees or shrubs causes nocturnal warming thereby favouring the establishment and survival of woody plants. Main conclusion: Because of this feedback, trees and shrubs may establish in areas that would be otherwise unsuitable for their survival. Thus, in grassland-woodland transition zones both vegetation covers may be (alternative) stable states of the landscape, thereby affecting the way tree lines may migrate in response to regional and global climate change. This article is a U.S. Government work and is in the public domain in the USA.

Barr J.G.,South Florida Natural Resource Center | Fuentes J.D.,Pennsylvania State University | Delonge M.S.,University of California at Berkeley | O'Halloran T.L.,Sweet Briar College | And 2 more authors.
Biogeosciences | Year: 2013

Mangrove forests are ecosystems susceptible to changing water levels and temperatures due to climate change as well as perturbations resulting from tropical storms. Numerical models can be used to project mangrove forest responses to regional and global environmental changes, and the reliability of these models depends on surface energy balance closure. However, for tidal ecosystems, the surface energy balance is complex because the energy transport associated with tidal activity remains poorly understood. This study aimed to quantify impacts of tidal flows on energy dynamics within a mangrove ecosystem. To address the research objective, an intensive 10-day study was conducted in a mangrove forest located along the Shark River in the Everglades National Park, FL, USA. Forest-atmosphere turbulent exchanges of energy were quantified with an eddy covariance system installed on a 30-m-tall flux tower. Energy transport associated with tidal activity was calculated based on a coupled mass and energy balance approach. The mass balance included tidal flows and accumulation of water on the forest floor. The energy balance included temporal changes in enthalpy, resulting from tidal flows and temperature changes in the water column. By serving as a net sink or a source of available energy, flood waters reduced the impact of high radiational loads on the mangrove forest. Also, the regression slope of available energy versus sink terms increased from 0.730 to 0.754 and from 0.798 to 0.857, including total enthalpy change in the water column in the surface energy balance for 30-min periods and daily daytime sums, respectively. Results indicated that tidal inundation provides an important mechanism for heat removal and that tidal exchange should be considered in surface energy budgets of coastal ecosystems. Results also demonstrated the importance of including tidal energy advection in mangrove biophysical models that are used for predicting ecosystem response to changing climate and regional freshwater management practices. © Author(s) 2013.

D'Odorico P.,University of Virginia | Engel V.,South Florida Natural Resource Center | Carr J.A.,University of Virginia | Oberbauer S.F.,Florida International University | And 2 more authors.
Ecosystems | Year: 2011

Mosaic freshwater landscapes exhibit tree-dominated patches -or tree islands-interspersed in a background of marshes and wet prairies. In the Florida Everglades, these patterned landscapes provide habitat for a variety of plant and animal species and are hotspots of biodiversity. Even though the emergence of patchy freshwater systems has been associated with climate histories, fluctuating hydrologic conditions, and internal feedbacks, a process-based quantitative understanding of the underlying dynamics is still missing. Here, we develop a mechanistic framework that relates the dynamics of vegetation, nutrients and soil accretion/loss through ecogeomorphic feedbacks and interactions with hydrologic drivers. We show that the stable coexistence of tree islands and marshes results as an effect of their both being (meta-) stable states of the system. However, tree islands are found to have only a limited resilience, in that changes in hydrologic conditions or vegetation cover may cause an abrupt shift to a stable marsh state. The inherent non-linear and discontinuous dynamics determining the stability and resilience of tree islands should be accounted for in efforts aiming at the management, conservation and restoration of these features. © 2011 Springer Science+Business Media, LLC (outside of USA).

Onorato D.P.,Florida Fish And Wildlife Conservation Commission | Criffield M.,Florida Fish And Wildlife Conservation Commission | Lotz M.,Florida Fish And Wildlife Conservation Commission | Cunningham M.,Florida Fish And Wildlife Conservation Commission | And 4 more authors.
Animal Conservation | Year: 2011

Decisions regarding landscape management, restoration and land acquisition typically depend on land managers' interpretation of how wildlife selects habitat. Such assessments are particularly important for umbrella species like the endangered Florida panther Puma concolor coryi, whose survival requires vast wildlands. Some interpretations of habitat selection by panthers have been criticized for using only morning locations in defining habitat use. We assessed habitat selection using a Euclidean distance analysis and location data collected throughout the diel period from GPS collars deployed on 20 independent Florida panthers. We corroborated aspects of earlier analyses by demonstrating the selection of forested habitats by panthers. We also confirmed the selection of open habitats (i.e. marsh-shrub-swamps, prairie grasslands), a novel result. Habitat selection did not vary by sex or season but varied by time of day. Panthers were located closer to wetland forests in the daytime and used prairie grasslands more at night. Our assessment of the effect of patch size on selection of forest habitat revealed that panthers were not solely reliant on large patches (>500ha) but utilized patches of all sizes (≤1, >5-10, >1000ha, etc.). Our results emphasize the importance of collecting panther location data throughout the diel period when assessing habitat selection. Conservation strategies for panthers should consider a mosaic of habitats, a methodology that will protect other sensitive flora and fauna in South Florida. © 2010 The Authors. Animal Conservation © 2010 The Zoological Society of London.

Barr J.G.,South Florida Natural Resource Center | DeLonge M.S.,University of California at Berkeley | Fuentes J.D.,Pennsylvania State University
Journal of Geophysical Research: Atmospheres | Year: 2014

Diurnal and seasonal controls on water vapor fluxes were investigated in a subtropical mangrove forest in Everglades National Park, Florida. Energy partitioning between sensible and latent heat fluxes was highly variable during the 2004-2005 study period. During the dry season, the mangrove forest behaved akin to a semiarid ecosystem as most of the available energy was partitioned into sensible heat, which gave Bowen ratio values exceeding 1.0 and minimum latent heat fluxes of 5 MJ d-1. In contrast, during the wet season the mangrove forest acted as a well-watered, broadleaved deciduous forest, with Bowen ratio values of 0.25 and latent heat fluxes reaching 18 MJ d-1. During the dry season, high salinity levels (> 30 parts per thousand, ppt) caused evapotranspiration to decline and correspondingly resulted in reduced canopy conductance. From multiple linear regression, daily average canopy conductance to water vapor declined with increasing salinity, vapor pressure deficit, and daily sums of solar irradiance but increased with air temperature and friction velocity. Using these relationships, appropriately modified Penman-Monteith and Priestley-Taylor models reliably reproduced seasonal trends in daily evapotranspiration. Such numerical models, using site-specific parameters, are crucial for constructing seasonal water budgets, constraining hydrological models, and driving regional climate models over mangrove forests. Key Points Forests partitioned energy like semi-arid environments during the dry seasonIncreased salinity reduced evapotranspiration (ET) by as much as 26%Site-specific models reproduced seasonal rates of ET in mangrove forests. ©2014. American Geophysical Union. All Rights Reserved.

Barr J.G.,South Florida Natural Resource Center | Engel V.,U.S. Geological Survey | Fuentes J.D.,Pennsylvania State University | Fuller D.O.,University of Miami | Kwon H.,Chonbuk National University
Biogeosciences | Year: 2013

Despite the importance of mangrove ecosystems in the global carbon budget, the relationships between environmental drivers and carbon dynamics in these forests remain poorly understood. This limited understanding is partly a result of the challenges associated with in situ flux studies. Tower-based CO 2 eddy covariance (EC) systems are installed in only a few mangrove forests worldwide, and the longest EC record from the Florida Everglades contains less than 9 years of observations. A primary goal of the present study was to develop a methodology to estimate canopy-scale photosynthetic light use efficiency in this forest. These tower-based observations represent a basis for associating CO2 fluxes with canopy light use properties, and thus provide the means for utilizing satellite-based reflectance data for larger scale investigations. We present a model for mangrove canopy light use efficiency utilizing the enhanced green vegetation index (EVI) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) that is capable of predicting changes in mangrove forest CO2 fluxes caused by a hurricane disturbance and changes in regional environmental conditions, including temperature and salinity. Model parameters are solved for in a Bayesian framework. The model structure requires estimates of ecosystem respiration (RE), and we present the first ever tower-based estimates of mangrove forest RE derived from nighttime CO2 fluxes. Our investigation is also the first to show the effects of salinity on mangrove forest CO2 uptake, which declines 5% per each 10 parts per thousand (ppt) increase in salinity. Light use efficiency in this forest declines with increasing daily photosyn-thetic active radiation, which is an important departure from the assumption of constant light use efficiency typically applied in satellite-driven models. The model developed here provides a framework for estimating CO2 uptake by these forests from reflectance data and information about environmental conditions. © Author(s) 2013.

O'Halloran T.L.,Oregon State University | Law B.E.,Oregon State University | Goulden M.L.,University of California at Irvine | Wang Z.,Boston University | And 7 more authors.
Global Change Biology | Year: 2012

Forest disturbances are major sources of carbon dioxide to the atmosphere, and therefore impact global climate. Biogeophysical attributes, such as surface albedo (reflectivity), further control the climate-regulating properties of forests. Using both tower-based and remotely sensed data sets, we show that natural disturbances from wildfire, beetle outbreaks, and hurricane wind throw can significantly alter surface albedo, and the associated radiative forcing either offsets or enhances the CO 2 forcing caused by reducing ecosystem carbon sequestration over multiple years. In the examined cases, the radiative forcing from albedo change is on the same order of magnitude as the CO 2 forcing. The net radiative forcing resulting from these two factors leads to a local heating effect in a hurricane-damaged mangrove forest in the subtropics, and a cooling effect following wildfire and mountain pine beetle attack in boreal forests with winter snow. Although natural forest disturbances currently represent less than half of gross forest cover loss, that area will probably increase in the future under climate change, making it imperative to represent these processes accurately in global climate models. © 2011 Blackwell Publishing Ltd.

Barr J.G.,South Florida Natural Resource Center | Engel V.,South Florida Natural Resource Center | Smith T.J.,U.S. Geological Survey | Fuentes J.D.,Pennsylvania State University
Agricultural and Forest Meteorology | Year: 2012

Eddy covariance (EC) estimates of carbon dioxide (CO 2) fluxes and energy balance are examined to investigate the functional responses of a mature mangrove forest to a disturbance generated by Hurricane Wilma on October 24, 2005 in the Florida Everglades. At the EC site, high winds from the hurricane caused nearly 100% defoliation in the upper canopy and widespread tree mortality. Soil temperatures down to -50cm increased, and air temperature lapse rates within the forest canopy switched from statically stable to statically unstable conditions following the disturbance. Unstable conditions allowed more efficient transport of water vapor and CO 2 from the surface up to the upper canopy layer. Significant increases in latent heat fluxes (LE) and nighttime net ecosystem exchange (NEE) were also observed and sensible heat fluxes (H) as a proportion of net radiation decreased significantly in response to the disturbance. Many of these impacts persisted through much of the study period through 2009. However, local albedo and MODIS (Moderate Resolution Imaging Spectro-radiometer) data (the Enhanced Vegetation Index) indicated a substantial proportion of active leaf area recovered before the EC measurements began 1year after the storm. Observed changes in the vertical distribution and the degree of clumping in newly emerged leaves may have affected the energy balance. Direct comparisons of daytime NEE values from before the storm and after our measurements resumed did not show substantial or consistent differences that could be attributed to the disturbance. Regression analyses on seasonal time scales were required to differentiate the storm's impact on monthly average daytime NEE from the changes caused by interannual variability in other environmental drivers. The effects of the storm were apparent on annual time scales, and CO 2 uptake remained approximately 250gCm -2yr -1 lower in 2009 compared to the average annual values measured in 2004-2005. Dry season CO 2 uptake was relatively more affected by the disturbance than wet season values. Complex leaf regeneration dynamics on damaged trees during ecosystem recovery are hypothesized to lead to the variable dry versus wet season impacts on daytime NEE. In contrast, nighttime CO 2 release (i.e., nighttime respiration) was consistently and significantly greater, possibly as a result of the enhanced decomposition of litter and coarse woody debris generated by the storm, and this effect was most apparent in the wet seasons compared to the dry seasons. The largest pre- and post-storm differences in NEE coincided roughly with the delayed peak in cumulative mortality of stems in 2007-2008. Across the hurricane-impacted region, cumulative tree mortality rates were also closely correlated with declines in peat surface elevation. Mangrove forest-atmosphere interactions are interpreted with respect to the damage and recovery of stand dynamics and soil accretion processes following the hurricane. © 2011.

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