Water Conservation Area Research Articles

Spatial Distribution of Alligator Holes in the Central Everglades

Alligator holes are a key feature of Everglades marshes that provide refugia and foraging sites for a wide range of species. We investigated the spatial pattern of alligator holes in Water Conservation Area 3, a part of the central Everglades, and examined associations among alligator holes, canals, and hydrology. There were fewer alligator holes within 1000 m of canals than expected, supporting the hypothesis that Alligator mississippiensis (American Alligator) are using canals as aquatic refugia rather than creating or maintaining alligator holes in the marsh. In addition, density of holes was associated with hydrology; specifically, areas that were drier had more than twice as many alligator holes than areas that were wetter. Analyses from this study provide a baseline for evaluating changes in location and density of alligator holes in response to canal removal and hydrologic changes that will occur as part of Everglades restoration.

Multi-temporal monitoring of wetland water levels in the Florida Everglades using interferometric synthetic aperture radar (InSAR)

Interferometric synthetic aperture radar (InSAR) techniques can successfully detect phase variations related to the water level changes in wetlands and produce spatially detailed high-resolution maps of water level changes. Despite the vast details, the usefulness of the wetland InSAR observations is rather limited, because hydrologists and water resources managers need information on absolute water level values and not on relative water level changes. We present an InSAR technique called Small Temporal Baseline Subset (STBAS) for monitoring absolute water level time series using radar interferograms acquired successively over wetlands. The method uses stage (water level) observation for calibrating the relative InSAR observations and tying them to the stage's vertical datum. We tested the STBAS technique with two-year long Radarsat-1 data acquired during 2006–2008 over the Water Conservation Area 1 (WCA1) in the Everglades wetlands, south Florida (USA). The InSAR-derived water level data were calibrated using 13 stage stations located in the study area to generate 28 successive high spatial resolution maps (50 m pixel resolution) of absolute water levels. We evaluate the quality of the STBAS technique using a root mean square error (RMSE) criterion of the difference between InSAR observations and stage measurements. The average RMSE is 6.6 cm, which provides an uncertainty estimation of the STBAS technique to monitor absolute water levels. About half of the uncertainties are attributed to the accuracy of the InSAR technique to detect relative water levels. The other half reflects uncertainties derived from tying the relative levels to the stage stations' datum.

The efficiency of a risk reduction program for debris-flow disasters – a case study of the Songhe community in Taiwan

Abstract. A risk reduction program was developed after debris-flow disaster analysis is conducted using mitigation structures, evacuation measures and community restrained expansion strategy. The risk assessment method delineates hazard zones and analyzes vulnerability and the resilient capacity of an affected area, allowing the prediction of losses of properties and lives, and the corresponding risk. It can also be used to evaluate performance of a risk reduction program. The proposed method was applied to the Songhe community as a case study to assess debris-flow risk and performance of reduction programs consisting of mitigation structures, evacuation measures and a restrained expansion strategy. Total annual risk decreased to $0.01 million from $0.72 million for the No. 1 Torrent and to $0.36 million from $1.22 million for the No. 2 Torrent after mitigation structures were installed, and evacuation measures were implemented based on restrained expansion. Although mitigation structures are costly, they can reduce the size of hazard zones. Delimitating the Designated Soil and Water Conservation Area restrains community expansion and decreases possible losses. Although evacuation measures cannot reduce the size of hazard zones, they effectively increase the resilient capacity of residents. The benefit-cost ratio for mitigation structures exceeds 1.0 for both torrents with an average of 3.87; the benefit-cost ratio for evacuation measures is markedly greater than 1.0. Combining mitigation structures and evacuation measures increases the total benefit with a benefit-cost ratio of 4.38. Analytical results showed that the risk reduction program is cost-effective.

Influence of soil and water conservation measures on reducing in frequency of hyperconcentrated flows in the Wudinghe River basin

Based on data of SSC, precipitation, sand-dust storms and area of soil and water conservation, a study has been made of the temporal variation in the frequency of hyperconcentrated flows in the Wudinghe River, a major tributary of the Yellow River, China. The results showed that the decreasing trend in the frequency of hyperconcentrated flows (Fh) was significant. High-flow season precipitation (P6–9) decreased slightly, and annual number of sand-dust storm days (Dss) decreased markedly. Correlation analysis shows that the variation in P6–9 had little influence on the decreasing Fh, but the decreasing Dss had significant influence on the decreasing Fh. The 5-year moving average of the frequency of hyperconcentrated flows (Fh,5m) was closely correlated with the area of land terracing, the area of the land created by check dams, the area of tree planting and the area of grass planting. The results of the present study show that the frequency of hyperconcentrated flows can be significantly reduced by soil and water conservation measures. Thus, these results may be useful for decision making for the management of sediment-related disasters in the Wudinghe River basin and in the Yellow River basin.

Spatially distributed modeling of surface water flow dynamics in the Everglades ridge and slough landscape

Summary A two-dimensional, spatially distributed flow dynamics model was developed and tested for a 1.5 by 4 km area of the patterned ridge and slough landscape of the Florida Everglades. This model is intended to support a deepened understanding of the system ecohydrological dynamics, and provide a useful tool for management decision support. The model was constructed with a fine enough mesh structure to ensure proper representation of ridge and slough topographic detail as well as capture local hydrologic influences. Upstream and downstream stage data collected near the study area in central Water Conservation Area 3A were used to establish the initial and boundary conditions. Water velocities measured in the ridges and sloughs over a 3-year period were used to calibrate and verify the model. Hydraulic resistance was computed using a power-law relationship with water depth. The simulated water levels, water depths, and flow velocities showed good agreement with the 3-year field-monitored data with percent model errors of approximately 4%, 12%, and 10%, respectively. Computed differences in hydraulic resistance between ridge and slough were reduced significantly during the storm season compared to the dry season. This suggests that more solute and suspended solid mass can be redistributed from the sloughs to the ridges in particular during wet seasons, due to the weakened heterogeneity of hydraulic resistance during high flows.

COMPOSITION OF EXTRACELLULAR POLYMERIC SUBSTANCES FROM PERIPHYTON ASSEMBLAGES IN THE FLORIDA EVERGLADES1

In wetland habitats, periphyton is a common component of open‐water areas with species assemblage determined by local water quality. Extracellular polymeric substances (EPS) secreted by algae and bacteria give structure to periphyton, and differences in EPS chemistry affect the functional roles of these polymers. The Florida Everglades provide a unique opportunity to study compositional differences of EPS from distinctive algal assemblages that characterize areas of differing water chemistry. Water conservation area (WCA)‐1 is a soft‐water impoundment; periphyton was loosely associated with Utricularia stems and amorphous in structure, with a diverse desmid and diatom assemblage, and varying cyanobacterial abundance. Extracellular polymers were abundant and were loosely cell‐associated sheaths and slime layers in addition to tightly cell‐associated capsules. The EPS were complex heteropolysaccharides with significant saccharide residues of glucose, xylose, arabinose, and fucose. Carboxylic acids were also prominent, while ester sulfates and proteins were small components. Structured, cohesive cyanobacteria‐dominated periphyton was observed in WCA‐2A, a minerotrophic impoundment, and filaments were heavily encrusted with calcium carbonate and detrital matter. EPS were primarily cell‐associated sheaths, and polymer residues were dominated by glucose, xylose, fucose, and galactose, with uronic acids also a significant component of the polymers. Principal components analysis revealed that periphyton community assemblage determined the monosaccharide composition of EPS, which ultimately determines a range of biogeochemical processes within the periphyton.

Water budget model for a remnant northern Everglades wetland

The Arthur R. Marshall Loxahatchee National Wildlife Refuge overlays Water Conservation Area 1, a 580 km2 freshwater wetland remnant of the northern Everglades in Palm Beach County, Florida, USA. Changes in water quantity and quality have impacted the Refuge ecosystem. Ensuring appropriate management to maximize benefits for wildlife while meeting flood control and water supply needs is a refuge priority. The Simple Refuge Stage Model described herein supports these management decisions. The two-compartment model with a daily time step predicts temporal variations of water level in the refuge rim canal and interior marsh, based on observed inflows, outflows, precipitation and evapotranspiration. The model was used to evaluate various water management scenarios. The modelling approach applied herein may have utility in managing other wetland systems where over-bank flooding is a dominant mechanism, affecting hydrology and water quality.

Analisis Kesesuaian Lahan Wilayah Pesisir Kota Bengkulu melalui Perancangan Model Spasial dan Sistem Informasi Geografis (SIG)

This research is aimed to alocate land management and use coastal and ocean area Sub-Province base on digital through Geographical Information System (GIS). This research was done in the coastal area Kota Bengkulu, through spatial alocate analysis and land suitability analysis for brackish water fish ponds, maritime tourism and conservation areas. Approach used in this research is spatial analysis to parameter/variable and land suitability criteria consist of element abiotik, biotik, culture, and spatial use (RTRW). Land suitability analysis is done by using SIG through overlay technique. Result of research indicate that from 7 sub district of coastal area of exist in Kota Bengkulu, land suitability (S1) for brackish water fish ponds are found in sub-district Muara Bangkahulu and Kampung Melayu. Land suitability (S1) for the maritime tourism are found in sub-district Teluk Segara and Ratu Samban, while Land suitability (S1) for conservation area of are found in sub-district Kampung Melayu.

Spatial monitoring of a non‐stationary soil property: phosphorus in a Florida water conservation area

SummaryEcological restoration plans in the Florida Everglades require detailed information about the status and change of the nutrient content of the soil. The soil total phosphorus (TP) content is of particular importance as the system is naturally P limited and the TP enrichment has led to changes in the wetland vegetation communities. One way to provide the relevant information is by geostatistical prediction from sampled data. However, conventional geostatistical models assume that properties being monitored are realizations of second‐order stationary random functions. The assumption of second‐order stationarity is not appropriate for soil TP in Water Conservation Area 1 (WCA‐1) of the Florida Everglades because the mean and variance of soil TP are larger at sites adjacent to the canals which bound WCA‐1 and deliver P to the system than at sites in the interior of the region.We develop a novel linear mixed‐model framework for spatial monitoring of a property for which this assumption is not valid. Specifically we use this non‐stationary model to map the status and change of TP within WCA‐1 from surveys carried out in 1991 and 2003. We fit the parameters of the model by residual maximum likelihood (REML) and compare the effectiveness of this non‐stationary model with the conventional stationary model.Conventional second‐order stationary models fail to represent accurately the large uncertainty in predictions of TP adjacent to the canals. The non‐stationary model predicts an invading front of P entering the interior of the region which is not evident in the predictions from the stationary model. Tests on the log‐likelihood and the standardized squared prediction error of the fitted models provide further evidence in favour of the non‐stationary model.The sampling intensity required to ensure a certain precision of TP predictions varies across WCA‐1 with the variance of TP. Therefore we apply a spatial simulated annealing optimization algorithm to design future monitoring surveys based upon our non‐stationary model which ensure that the status and change are efficiently and effectively predicted across the region.

Nutrient and growth responses of cattail (Typha domingensis) to redox intensity and phosphate availability

In the Florida Everglades, the expansion of cattail (Typha domingensis) into areas once dominated by sawgrass (Cladium jamaicense) has been attributed to altered hydrology and phosphorus (P) enrichment. The objective of this study was to quantify the interactive effects of P availability and soil redox potential (Eh) on the growth and nutrient responses of Typha, which may help to explain its expansion. The study examined the growth and nutrient responses of Typha to the interactive effects of P availability (10, 80 and 500 microg P L(-1)) and Eh level (-150, +150 and +600 mV). Plants were grown hydroponically in a factorial experiment using titanium (Ti(3+)) citrate as a redox buffer. Relative growth rate, elongation, root-supported tissue/root ratio, leaf length, lateral root length and biomass, as well as tissue nutrient concentrations, were all adversely affected by low Eh conditions. P availability compensated for the negative effect of low Eh for all these variables except that low P stimulated root length and nutrient use efficiency. The most growth-promoting treatment combination was 500 microg P L(-1)/ + 600 mV. These results, plus previous data on Cladium responses to P/Eh combinations, document that high P availability and low Eh should benefit Typha more than Cladium as the growth and tissue nutrients of the former species responded more to excess P, even under highly reduced conditions. Therefore, the interactive effects of P enrichment and Eh appear to be linked to the expansion of Typha in the Everglades Water Conservation Area 2A, where both low Eh and enhanced phosphate availability have co-occurred during recent decades.

Microbial Indicators of Eutrophication in Everglades Wetlands

Nutrient loading has been implicated as a major cause of ecological changes in Everglades wetlands. The main objective of this study was to assess changes in microbial indicators in response to nutrient loading across the Everglades landscape. Soil chemical, physical, and microbial properties were measured for nutrient‐impacted and oligotrophic sites within Water Conservation Area (WCA)‐1, WCA‐2a, WCA‐3a, and Taylor Slough of Everglades National Park. Impacts of nutrient loading were most evident by the development of gradients in floc and soil total P from peripheral to interior areas of all wetlands following the paths of surface water flow. Floc was more responsive to nutrient loading than the underlying soil. The sensitive indicators of eutrophication were floc and soil total P, microbial biomass P, and mineralized P. Total P averaged 185 and 140% greater for nutrient‐impacted than oligotrophic areas for floc and soil (0–3 cm), respectively. Microbial biomass P averaged 97 and 52% higher at nutrient‐impacted than oligotrophic areas for floc and soil, respectively. Mineralized P was the most sensitive indicator of eutrophication, being 689 and 135% higher at nutrient‐impacted than oligotrophic areas for floc and soil, respectively. Microbial indicators in WCA‐3a and Taylor Slough were more responsive to nutrient loading than in WCA‐1 and WCA‐2a, which received higher P loads. Delineation of nutrient‐impacted and oligotrophic areas in Everglades wetlands may serve as a baseline to assess future impacts of eutrophication. The consistent pattern in the response of microbial processes to nutrient loading across the range of conditions in different Everglades wetlands demonstrates their suitability as sensitive indicators of eutrophication.

Integrating spectral indices into prediction models of soil phosphorus in a subtropical wetland

Remote sensing, in combination with multivariate geostatistical methods, has the potential to improve the prediction of soil properties at landscape scales. In the Everglades region, and particularly in Water Conservation Area 2A (WCA-2A), phosphorus enrichment has drawn a lot of attention and has led to an extensive documentation of different aspects of the degradation of the system. This study presents a hybrid geospatial modeling approach to predict soil total phosphorus (TP) using remotely-sensed data and ancillary landscape properties as supporting variables. Two remote sensors, Landsat 7 Enhanced Thematic Mapper (ETM)+ and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), were used to investigate relationships between spectral data and indices and soil TP. A variation of a vegetation index (Normalized Difference Vegetation Index – NDVI green) was found to be the most effective in predicting floc TP values, due to its capacity to capture small variations in chlorophyll a that are associated to TP levels in periphyton, especially in aquatic/non-impacted areas. On the other hand, NDVI, a more traditionally used vegetation index, was still a good indicator of TP variability, particularly in the soil surface layer, due to its stronger relationship with impacted areas dominated by cattail ( Typha domingensis Pers.). Findings from this study indicate that: a) remote sensing can play an important role in optimizing monitoring of environmental variables, particularly below-ground properties of floc and soils; b) because of limitations about the numbers and frequency of soil samples that can be taken, the combination of remote sensing and geostatistics could represent a non-invasive and cost-effective method to monitor soil nutrient status in complex wetland systems, and c) variations of traditional remote sensing indices such as NDVI can be used to better capture the spatial variability associated with soil and periphyton TP.

Multi‐state succession in wetlands: a novel use of state and transition models

The complexity of ecosystems and mechanisms of succession are often simplified by linear and mathematical models used to understand and predict system behavior. Such models often do not incorporate multivariate, nonlinear feedbacks in pattern and process that include multiple scales of organization inherent within real-world systems. Wetlands are ecosystems with unique, nonlinear patterns of succession due to the regular, but often inconstant, presence of water on the landscape. We develop a general, nonspatial state and transition (S and T) succession conceptual model for wetlands and apply the general framework by creating annotated succession/management models and hypotheses for use in impact analysis on a portion of an imperiled wetland. The S and T models for our study area, Water Conservation Area 3A South (WCA3), Florida, U.S.A., included hydrologic and peat depth values from multivariate analyses and classification and regression trees. We used the freeware Vegetation Dynamics Development Tool as an exploratory application to evaluate our S and T models with different management actions (equal chance [a control condition], deeper conditions, dry conditions, and increased hydrologic range) for three communities: slough, sawgrass (Cladium jamaicense), and wet prairie. Deeper conditions and increased hydrologic range behaved similarly, with the transition of community states to deeper states, particularly for sawgrass and slough. Hydrology is the primary mechanism for multi-state transitions within our study period, and we show both an immediate and lagged effect on vegetation, depending on community state. We consider these S and T succession models as a fraction of the framework for the Everglades. They are hypotheses for use in adaptive management, represent the community response to hydrology, and illustrate which aspects of hydrologic variability are important to community structure. We intend for these models to act as a foundation for further restoration management and experimentation which will refine transition and threshold concepts.

δ 13C, δ 15N, carbon, nitrogen and phosphorus as indicators of plant ecophysiology and organic matter pathways in Everglades deep slough, Florida, USA

Historically, the Florida Everglades was characterized by a corrugated landscape of shorter hydroperiod, elevated sawgrass ( Cladium jamaicense) ridges and longer hydroperiod, deep water slough communities. Drainage and compartmentalization of the Everglades have fundamentally altered this pattern, and sawgrass ridge communities have expanded at the expense of deep water slough communities throughout much of the landscape. In this study we provide a simple isotopic and nutrient characterization of major components of the slough ecosystem to elucidate physiological and nutrient differences among species and to suggest pathways for organic matter decomposition that contribute to peat development in deep water sloughs. We examined carbon (C) and nitrogen (N) isotopes and C, N and phosphorus (P) concentrations of the floating-leaved macrophytes Nymphaea odorata and Nymphoides aquatica, the emergent macrophyte Eleocharis elongata, and the submerged species Utricularia foliosa and Utricularia purpurea, as well as soil and flocculent material from the southern Water Conservation Area 3-A. Flocculent material and soils had the highest N content (4.5 ± 0.2%) and U. foliosa and N. odorata had the highest P content (0.13 ± 0.01% to 0.12 ± 0.01%). The range for δ 15N average ± SE values was 5.81 ± 0.29‰ ( U. foliosa) to −1.84 ± 0.63‰ ( N. odorata), while the range for δ 13C values was −23.83 ± 0.12‰ ( N. odorata) to −29.28 ± 0.34‰ ( U. purpurea). Differences of up to 10‰ in C isotopic values of U. foliosa and N. odorata suggest fundamental physiological differences between these species. Along a degradation continuum, enrichment of 13C and 15N and extent of decomposition was negatively related to phosphorus concentrations. A two end-member 13C mixing model suggested that Utricularia species were the primary organic source for flocculent materials, whereas organic matter derived from root decomposition of N. odorata contributed to the progressively enriched δ 13C values found with depth in soils. These results illustrate the fundamentally important roles of Nymphaea and Utricularia species in ecosystem dynamics of deep water sloughs.

Effects of Burn Temperature on Ash Nutrient Forms and Availability from Cattail (Typha domingensis) and Sawgrass (Cladium jamaicense) in the Florida Everglades

Plant ash derived from fire plays an important role in nutrient balance and cycling in ecosystems. Factors that determine the composition and availability of ash nutrients include fire intensity (burn temperature and duration), plant species, habitat nutrient enrichment, and leaf type (live or dead leaf). We used laboratory simulation methods to evaluate temperature effects on nutrient composition and metals in the residual ash of sawgrass (Cladium jamaicense) and cattail (Typha domingensis), particularly on post-fire phosphorus (P) availability in plant ash. Live and dead leaf samples were collected from Water Conservation Area 2A in the northern Everglades along a soil P gradient, where prescribed fire may be used to accelerate recovery of this unique ecosystem. Significant decreases in total carbon and total nitrogen were detected with increasing fire temperature. Organic matter combustion was nearly complete at temperatures > or = 450 degrees C. HCl-extractable P (average, 50% of total P in the ash) and NH(4)Cl-extractable P (average, 33% of total P in the ash) were the predominant P fractions for laboratory-burned ash. Although a low-intensity fire could induce an elevation of P availability, an intense fire generally resulted in decreased water-soluble P. Significant differences in nutrient compositions were observed between species, habitat nutrient status, and leaf types. More labile inorganic P remained in sawgrass ash than in cattail ash; hence, sawgrass ash has a greater potential to release available P than cattail. Fire intensity affected plant ash nutrient composition, particularly P availability, and the effects varied with plant species and leaf type. Therefore, it is important to consider fire intensity and vegetation community when using a prescribed fire for ecosystem management.

Soil Total Mercury Concentrations across the Greater Everglades

Elevated Hg concentrations in the Everglades pose ecological and human health risks. We mapped soil total Hg concentrations per mass (THgM) and area (THgA) across the Everglades, and investigated relationships with soil properties (total P [TP] and organic matter content), community type, and hydrologic compartmentalization. Samples (n = 600) from surface soils (0–10 cm) were selected from a population of 1405 sites spanning the Everglades. Overall, 168 sites had THgM levels >0.2 mg kg−1; interpolation suggests that 23% of the Greater Everglades exceeds this threshold. Hot spots (>0.4 mg kg−1) were observed in eastern Water Conservation Area (WCA) 1 and west‐central WCA3A; parts of WCA2A, WCA3AN, and WCA3B were locally high. Despite significant global differences in THgM among plant communities, differences evaluated using paired proximate sites were not significant, suggesting that large spatial scale depositional gradients govern ecosystem storage. Median THgA was 1.89 mg m−2 (range 0.07–12.05 mg m−2), representing approximately 100 yr of atmospheric deposition at contemporary rates (∼19 μg m−2 yr−1). Correlation between TP and THgM was positive in unimpacted areas (TP < 500 mg kg−1, r = 0.69), but negative in impacted areas (TP > 500 mg kg−1, r = ‐0.47), probably due to accelerated peat accretion rates in P‐enriched areas. Moreover, while reverse correlation with distance from a canal for THgM (0.70) and TP (−0.77) supports Hg enrichment via atmospheric deposition, THgM hotspots in WCA3AS, WCA1, and the Holeyland and Rotenberger tracts are suggestive of local enrichment mechanisms. Finally, despite dramatic regional emissions declines, the estimated mass of Hg in surface soils across the Everglades has increased ∼20% (11,000 vs. 13,100 kg) since 1996; while the statistical significance of this change is unknown, it provides a useful benchmark for future surveys.

Estimating transition probabilities among Everglades wetland communities using multistate models

In this study we were able to provide the first estimates of transition probabilities of wet prairie and slough vegetative communities in Water Conservation Area 3A (WCA3A) of the Florida Everglades and to identify the hydrologic variables that determine these transitions. These estimates can be used in management models aimed at restoring proportions of wet prairie and slough habitats to historical levels in the Everglades. To determine what was driving the transitions between wet prairie and slough communities we evaluated three hypotheses: seasonality, impoundment, and wet and dry year cycles using likelihood-based multistate models to determine the main driver of wet prairie conversion in WCA3A. The most parsimonious model included the effect of wet and dry year cycles on vegetative community conversions. Several ecologists have noted wet prairie conversion in southern WCA3A but these are the first estimates of transition probabilities among these community types. In addition, to being useful for management of the Everglades we believe that our framework can be used to address management questions in other ecosystems.

Multistate Succession in Wetlands

Example of an emergent slough with Crinum americanum (Southern swamp lily), Water Conservation Area 3A South in the Everglades, Florida, USA. Slough/sawgrass complex in Water Conservation Area 3A South. . Wetlands are an ecosystem with unique, nonlinear patterns of succession due to the regular, but often inconstant presence of water on the landscape. To address this, we developed general, nonspatial state and transition succession models (S and T) for wetlands, and within this framework, created succession/management models for use in restoration of the Everglades, Florida. Our study area, Water Conservation 3A South, has been impounded for over 40 years, and the resultant ponding has affected its unique vegetation community composition and patterns, particularly emergent sloughs/wet prairies and the sawgrass ridge and slough landscape. We sampled transects across community ecotones to provide baseline information and create S and T models that address the effect of hydrology on the succession of vegetation communities. Setting out to sample wetland vegetation in Water Conservation Area 3A South. These photographs illustrate the article “Multi-state succession in wetlands: a novel use of state and transition models” by Christa L. Zweig and Wiley M. Kitchens, tentatively scheduled to appear in Ecology in 2009.

Seasonal variation in seed bank composition and its interaction with nutrient enrichment in the Everglades wetlands

In the Florida Everglades, nutrient enrichment from agricultural outflow and the change in hydrology have collectively contributed to the expansion of cattails ( Typha spp.). To assess the effectiveness of prescribed fire in controlling cattails and to predict vegetation dynamics after the fire, it is important to understand the seasonal variation of the soil seed bank and how the seed bank is affected by nutrient enrichment and fire. This paper investigates the effects of season, nutrient enrichment, and fire on soil seed bank species composition, richness, and density along a nutrient gradient in Water Conservation Area 2A (WCA 2A) of the Florida Everglades. Species richness was significantly affected by nutrient enrichment and season but not their interaction. Total seed density, however, was significantly affected by the interaction between nutrient enrichment and season. Yet, at species level, the relationship between seed density, nutrient enrichment and season varied. The highest seed density of cattail occurred in summer at highly enriched sites, but that of sawgrass occurred in fall regardless of enrichment; the seed density of water lily was very low regardless of season and nutrient enrichment, and the highest Amarathus seed density occurred at highly enriched sites year round. Moreover, germination timing differed greatly among species. While cattail seeds had a short incubation period and started to germinate 2–3 days after initiation of the germination assay, sawgrass seeds generally started to germinate 4 weeks later. Further, both the prescribed summer fire at the highly enriched site and the natural winter fire at the moderately enriched site reduced the seed density of cattail but not of sawgrass. Our results suggest that fire application for vegetation recovery in WCA 2A would benefit from explicitly considering seasonal dynamics of the seed bank.

Estimation of Crayfish Abundance and Size-structure in Diets of White Ibis Chicks

Abstract We investigated the use of crayfish gastroliths and exoskeleton pieces for quantifying crayfish abundance and size-structure in diets of White Ibis (Eudocimus albus) chicks in the Everglades. We then quantified crayfish and fish abundance from various small hard parts and intact fish heads in 23 boluses, taken from two nesting colonies in Water Conservation Area 3 (WCA 3) and Arthur R. Marshall Loxahatchee National Wildlife Refuge (Lox) in the Florida Everglades during May 2006. We determined that using gastroliths to estimate crayfish numbers in boluses had significant drawbacks; only a small fraction of field-caught crayfish bear gastroliths and the two crayfish species in the Everglades differ in percentage bearing gastroliths. In contrast, counts of crayfish rostrums and chelae pairs gave simple and similar estimates of crayfish in the boluses. The two colonies had strikingly different diets in May 2006; New Colony 3 (Lox) boluses were dominated by crayfish while birds from the Alley North (W...