Although hurricanes can damage or destroy coastal wetlands, they may play a beneficial role in reinvigorating marshes by delivering sediments that raise soil elevations and stimulate organic matter production. Hurricane Katrina altered elevation dynamics of two subsiding brackish marshes in the Mississippi River deltaic plain by adding 3 to 8 cm of sediment to the soil surface in August 2005. Soil elevations at both sites subsequently declined due to continued subsidence, but net elevation gain was still positive at both Pearl River ( 1.7 cm) and Big Branch ( 0.7 cm) marshes two years after the hurricane. At Big Branch where storm sediments had higher organic matter and water contents, post-storm elevation loss was more rapid due to initial compaction of the storm layer in combination with root-zone collapse. In contrast, elevation loss was slower at Pearl River where the storm deposit (high sand content) did not compact and the root zone did not collapse. Vegetation at both sites fully recovered within one year, and accumulation of root matter at Big Branch increased 10-fold from 2005 to 2006, suggesting that the hurricane stimulated belowground productivity. Results of this study imply that hurricane sediment may benefit subsiding marshes by slowing elevation loss. However, long-term effects of hurricane sediment on elevation dynamics will depend not only on the amount of sediment deposited, but on sediment texture and resistance to compaction as well as on changes in organic matter accumulation in the years following the hurricane.

Soil elevation affects tidal inundation period, inundation frequency, and overall hydroperiod, all of which are important ecological factors affecting species recruitment, composition, and survival in wetlands. Hurricanes can dramatically affect a site's soil elevation. We assessed the impact of Hurricane Wilma (2005) on soil elevation at a mangrove forest location along the Shark River in Everglades National Park, Florida, USA. Using multiple depth surface elevation tables (SETs) and marker horizons we measured soil accretion, erosion, and soil elevation. We partitioned the effect of Hurricane Wilma's storm deposit into four constituent soil zones: surface (accretion) zone, shallow zone (0–0.35 m), middle zone (0.35–4 m), and deep zone (4–6 m). We report expansion and contraction of each soil zone. Hurricane Wilma deposited 37.0 (± 3.0 SE) mm of material; however, the absolute soil elevation change was 42.8 mm due to expansion in the shallow soil zone. One year post-hurricane, the soil profile had lost 10.0 mm in soil elevation, with 8.5 mm of the loss due to erosion. The remaining soil elevation loss was due to compaction from shallow subsidence. We found prolific growth of new fine rootlets (209 ± 34 SE g m⁻²) in the storm deposited material suggesting that deposits may become more stable in the near future (i.e., erosion rate will decrease). Surficial erosion and belowground processes both played an important role in determining the overall soil elevation. Expansion and contraction in the shallow soil zone may be due to hydrology, and in the middle and bottom soil zones due to shallow subsidence. Findings thus far indicate that soil elevation has made substantial gains compared to site specific relative sea-level rise, but data trends suggest that belowground processes, which differ by soil zone, may come to dominate the long term ecological impact of storm deposit.

Hurricanes have shaped the structure of mangrove forests in the Everglades via wind damage, storm surges and sediment deposition. Immediate effects include changes to stem size-frequency distributions and to species relative abundance and density. Long-term impacts to mangroves are poorly understood at present. We examine impacts of Hurricane Wilma on mangroves and compare the results to findings from three previous storms (Labor Day, Donna, Andrew). Surges during Wilma destroyed ≈ 1,250 ha of mangroves and set back recovery that started following Andrew. Data from permanent plots affected by Andrew and Wilma showed no differences among species or between hurricanes for % stem mortality or % basal area lost. Hurricane damage was related to hydro-geomorphic type of forest. Basin mangroves suffered significantly more damage than riverine or island mangroves. The hurricane by forest type interaction was highly significant. Andrew did slightly more damage to island mangroves. Wilma did significantly more damage to basin forests. This is most likely a result of the larger and more spatially extensive storm surge produced by Wilma. Forest damage was not related to amount of sediment deposited. Analyses of reports from Donna and the Labor Day storm indicate that some sites have recovered following catastrophic disturbance. Other sites have been permanently converted into a different ecosystem, namely intertidal mudflats. Our results indicate that mangroves are not in a steady state as has been recently claimed.

The regularity and severity of tropical storms are major determinants controlling ecosystem structure and succession for coastal ecosystems. Hurricane landfall rates vary greatly with high and low frequency for given coastal stretches of the southeastern United States. Site-specific meteorological data of hurricane wind speeds and direction, however, are only available for select populated cities of relatively sparse distribution and inland from the coast. A spatial simulation model of hurricane circulation, HURASIM, was applied to reconstruct chronologies of hurricane wind speeds and vectors for northern Gulf coast locations derived from historical tracking data of North Atlantic tropical storms dating back to 1851. Contrasts of storm frequencies showed that tropical storm incidence is nearly double for Florida coastal ecosystems than the westernmost stretches of Texas coastline. Finer-scale spatial simulations for the north-central Gulf coast exhibited sub-regional differences in storm strength and frequency with coastal position and latitude. The overall pattern of storm incidence in the Gulf basin indicates that the disturbance regime of coastal areas varies greatly along the coast, inland from the coast, and temporally over the period of record. Field and modeling studies of coastal ecosystems will benefit from this retrospective analysis of hurricane incidence and intensity both on a local or regional basis.

The Everglades ecosystem contains the largest contiguous tract of mangrove forest outside the tropics that were also coincidentally intersected by a major Category 5 hurricane. Airborne videography was flown to capture the landscape pattern and process of forest damage in relation to storm trajectory and circulation. Two aerial video transects, representing different topographic positions, were used to quantify forest damage from video frame analysis in relation to prevailing wind force, treefall direction, and forest height. A hurricane simulation model was applied to reconstruct wind fields corresponding to the ground location of each video frame and to correlate observed treefall and destruction patterns with wind speed and direction. Mangrove forests within the storm's eyepath and in the right-side (forewind) quadrants suffered whole or partial blowdowns, while left-side (backwind) sites south of the eyewall zone incurred moderate canopy reduction and defoliation. Sites along the coastal transect sustained substantially more storm damage than sites along the inland transect which may be attributed to differences in stand exposure and/or stature. Observed treefall directions were shown to be non-random and associated with hurricane trajectory and simulated forewind azimuths. Wide-area sampling using airborne videography provided an efficient adjunct to limited ground observations and improved our spatial understanding of how hurricanes imprint landscape-scale patterns of disturbance.

The dynamics of plant regeneration via seed and vegetative spread in coastal wetlands dictate the nature of community reassembly that takes place after hurricanes or sea level rise. The objectives of my project were to evaluate the potential effects of saltwater intrusion and flooding of Hurricanes Katrina and Rita on seedling regeneration in coastal wetlands of the Gulf Coast. Specifically I tested hypotheses to determine for species in fresh, brackish and salt marshes of the Gulf Coast if 1) the pattern of seed germination and seedling recruitment differed with distance from the shoreline, and 2) seed germination and seedling recruitment for various species were reduced in higher levels of water depth and salinity. Regarding Hypothesis 1, seedling densities increased with distance from the shoreline in fresh and brackish water marshes while decreasing with distance from the shoreline in salt marshes. Also to test Hypothesis 1, I used a greenhouse seed bank assay to examine seed germination from seed banks collected at distances from the shoreline in response to various water depths and salinity levels using a nested factorial design. For all marsh types, the influence of water level and salinity on seed germination shifted with distance from the shoreline (i.e., three way interaction of the main effects of distance nested within site, water depth, and salinity). Data from the seed bank assay were also used to test Hypothesis 2. The regeneration of species from fresh, brackish, and salt marshes were reduced in conditions of high salinity and/or water, so that following hurricanes or sea level rise, seedling regeneration could be reduced. Among the species of these coastal marshes, there was some flexibility of response, so that at least some species were able to germinate in either high or low salinity. Salt marshes had a few fresher marsh species in the seed bank that would not germinate without a period of fresh water input (e.g., Sagittaria lancifolia) as well as salt water species (e.g., Avicennia germinans, Salicornia bigelovii). Nevertheless, the species richness of seeds germinating from the seed bank of freshwater marshes was reduced more than in salt marshes, indicating that freshwater marsh regeneration may be more affected by hurricanes and/or sea level rise than salt marshes. From the perspective of short-term seed germination and recruitment following hurricanes, species recruitment is dependent on the post-disturbance conditions of water and salinity.

Satellite Landsat Thematic Mapper (TM) and RADARSAT-1 (radar) satellite image data collected before and after the landfall of Hurricane Katrina in the Pearl River Wildlife Management Area on the Louisiana-Mississippi border, USA, were applied to the study of forested wetland impact and recovery. We documented the overall similarity in the radar and optical satellite mapping of impact and recovery patterns and highlighted some unique differences that could be used to provide consistent and relevant ecological monitoring. Satellite optical data transformed to a canopy foliage index (CFI) indicated a dramatic decrease in canopy cover immediately after the storm, which then recovered rapidly in the Taxodium distichum (baldcypress) and Nyssa aquatica (water tupelo) forest. Although CFI levels in early October indicated rapid foliage recovery, the abnormally high radar responses associated with the cypress forest suggested a persistent poststorm difference in canopy structure. Impact and recovery mapping results showed that even though cypress forests experienced very high wind speeds, damage was largely limited to foliage loss. Bottomland hardwoods, experiencing progressively lower wind speeds further inland, suffered impacts ranging from increased occurrences of downed trees in the south to partial foliage loss in the north. In addition, bottomland hardwood impact and recovery patterns suggested that impact severity was associated with a difference in stand structure possibly related to environmental conditions that were not revealed in the prehurricane 25-m optical and radar image analyses.

Hurricane Katrina pushed mixed Taxodium distichum forests toward a dominance of Taxodium distichum (baldcypress) and Nyssa aquatica (water tupelo) because these species had lower levels of susceptibility to wind damage than other woody species. This study documents the volume of dead versus live material of woody trees and shrubs of T. distichum swamps following Hurricane Katrina along the Gulf Coast of Mississippi and Louisiana. Pearl River Wildlife Management Area near Canton, Mississippi had the highest winds of the study areas, and these forests were located in the northeast quadrant of Hurricane Katrina (sustained wind  =  151 kph (94 mph)). Jean Lafitte National Historical Park and Preserve south of New Orleans had medium to high winds (sustained winds  =  111 kph (69 mph) at the New Orleans lakefront). Cat Island National Wildlife Refuge had a lower level of winds and was positioned on the western edge of the storm. The forests at Pearl River and to a lesser extent at Jean Lafitte had the highest amount of structural damage in the study. For Cat Island, Jean Lafitte, and Pearl River, the total volume of dead material (debris) was 50, 80, and 370 m³ ha⁻¹, respectively. The ratio of dead to live volume was 0.010, 0.082, and 0.039, respectively. For both of the dominant species, T. distichum and N. aquatica, the percentage of dead to live volume was less than 1%. Subdominant species including Acer rubrum, Liquidambar styraciflua, Quercus lyrata, and Quercus nigra were more damaged by the storm at both Pearl River and Jean Lafitte. Only branches were damaged by Hurricane Katrina at Cat Island. Shrubs such as Morella cerifera, Euonymous sp., and Vaccinium sp. were often killed by the storm, while other species such as Cephalanthus occidentalis, Forestiera acuminata, and Cornus florida were not killed. Despite the fact that Hurricane Katrina was a Category 3 storm and struck Pearl River and Jean Lafitte fairly directly, dominant species of the T. distichum swamps were relatively little affected, even though certain subdominant and shrub species were completely removed from the species composition.

We investigated variation in species resistance to hurricane winds and effects of Hurricane Rita on long-term forest dynamics using three 4-ha permanent plots in the Big Thicket of east Texas. Woody stems > 4.5 cm DBH that were severely damaged, uprooted, or snapped constituted 5% of stems at the dry upland site, 22% at the river floodplain site, and 31% at the mesic site. This variation corresponded to distance from the coast, distance from the storm track, and exposure. Nine of 27 canopy species populations showed a significantly positive relationship between mortality and DBH, and one showed a significant negative relationship. We identified 10 resistant, three intermediate, and 14 susceptible species populations. There was modest consistency in species behavior across sites, and consistency of some species between our results and the literature. Some inconsistencies can be accounted for by low vigor of some populations in our study. Relative dominance changes in the canopy and compositional trends in the small tree layer indicated that the hurricane accelerated long-term trends towards increasing dominance of shade-tolerant species at the dry and mesic sites but not at the wet site. We conclude that interspecific variation in resistance does not strongly alter temporal patterns that are based on shade tolerance and recruitment characteristics, in part because of relatively low overall damage rates.

Hurricanes can damage trees in forested wetlands, and the potential for mortality related to these storms exists due to the effects of tree damage over time. In August 1992, Hurricane Andrew passed through the forested wetlands of southern Louisiana with winds in excess of 225 kph. Although more than 78% of the basal area was destroyed in some areas, most trees greater than 2.5 cm dbh were alive and resprouting prolifically the following year (98.8%). Survival of most tree species was similarly high two years after the hurricane, but mortality rates of some species increased dramatically. For example, Populus heterophylla (swamp cottonwood) mortality increased from 7.8 to 59.2% (n  =  76) and Salix interior (sandbar willow) mortality increased from 4.5 to 57.1% (n  =  21). Stem sprouts on many up-rooted hardwood trees of other species were still alive in 1998, 6 years after the hurricane. Due to the understory tree species composition, regeneration, and high levels of resprouting, there was little change in species composition or perhaps a slight shift toward more shade and flood tolerant species six years following the hurricane event. Triadica sebifera (Chinese tallow) was found on some of the sites heavily disturbed by Hurricane Andrew, and may proliferate at the expense of native tree species.

Tropical weather disturbances are a major influence on coastal wetlands in North America. However, studies of their impact on biotic communities are rare. The abundance and species composition of amphibians and reptiles were investigated within levee, herbaceous marsh, and forested swamp habitats in southeastern Louisiana from 2002 to 2004 and again in 2005 to 2006. During the course of this study, three major hurricanes (Ivan, Katrina, and Rita) affected our study sites. This allowed us to opportunistically document the effect of major storm disturbances by comparing species richness, diversity, community assemblage, and abundance of amphibians and reptiles before and after hurricane events. We also used a previous study conducted in the same area during the late 1980's to assess long-term community composition changes. We documented the highest species richness in the forested swamp habitat (23 species), but the most diverse assemblage was found in marsh habitat (H′  =  2.082). Overall, herpetofaunal diversity decreased and evenness increased in each habitat following hurricanes Ivan and Katrina/Rita. Drastic decreases in overall abundance of amphibians occurred, while the effect on reptile abundance varied with habitat. Reduced abundance of reptiles in marsh was recorded over the course of the study, while abundances in adjacent levee habitat increased, suggesting displacement of certain reptiles from the marsh to the levee. Significant saltwater intrusion was recorded in marsh and levee habitats, but not in the forested swamp. The hurricanes altered community composition and increased species evenness within each habitat, potentially affecting long-term community dynamics and species interactions.

Understanding the consequences of hurricanes on the food resources available to neotropical-nearctic migrant songbirds may provide important insight into the effects of hurricanes on migratory populations. During autumn migration 2006 we investigated the foraging ecology of two species of insectivorous migrants, Blue-gray Gnatcatcher (Polioptila caerulea) and Yellow Warbler (Dendroica petechia), and the availability of their foraging substrates and arthropod food resources in two coastal forests in western Louisiana, which were impacted to different degrees by Hurricane Rita in autumn 2005. Both migrant species attacked prey on bark substrates significantly more frequently, and on live foliage less frequently, in severely damaged forest than in lightly damaged forest (χ² tests, P < 0.05). However, both species attacked prey on bark less than expected given its availability (i.e., migrants avoided bark), and attacked prey on live foliage more than expected given its availability (i.e., migrants selected live foliage), in severely damaged forest (χ² tests, P < 0.03). Branch-clipping revealed that arthropod biomass on live hackberry (Celtis laevigata) and sweet acacia (Acacia farnesiana) branches was significantly higher in severely damaged forest than in lightly damaged forest (Mann-Whitney test, P < 0.01). However, because live foliage was significantly less available in severely damaged forest, overall food availability for migrants was lower in severely damaged forest than in lightly damaged forest. Migrant use of, and arthropod biomass on, bark and live-foliage substrates were thus dependent on the availability of those substrates, which differed between sites as a result of hurricane-related habitat disturbance. These results demonstrate that severe hurricane disturbance reduces food availability for insectivorous songbirds during migratory stopover by reducing the availability of preferred foraging substrates.

Regeneration by seedling recruitment may be important in the long-term patterns of species composition in Taxodium forests, and most studies suggest that seedling recruitment may increase episodically following hurricanes. This study investigates the nature of regeneration in Taxodium swamps with various levels of damage by wind following Hurricane Katrina, which made landfall in August 2005 in Louisiana and Mississippi. All sites had a fairly similar range of percent canopy cover following the storms (78.9 to 92.1% canopy cover). At Cat Island, the timing of the hurricane may have contributed to low recruitment of Taxodium distichum seedlings in the growing season following the hurricanes, as based on long-term presence data from 2003 to 2007. Sites at Pearl River had the highest total tree seedling density of the three locations. Jean Lafitte had the lowest level of tree seedling and sapling density and species richness, and may have been flooded more than the other sites. The invasive species, Triadica sebifera was recruited from the seedling into the sapling class at Jean Lafitte and Pearl River during the study. Overall, the patterns of tree recruitment following the hurricane were variable and depended on location, canopy cover, and flooding.

Little is known about the effectiveness of mangroves in suppressing water level heights during landfall of tropical storms and hurricanes. Recent hurricane strikes along the Gulf Coast of the United States have impacted wetland integrity in some areas and hastened the need to understand how and to what degree coastal forested wetlands confer protection by reducing the height of peak water level. In recent years, U.S. Geological Survey Gulf Coast research projects in Florida have instrumented mangrove sites with continuous water level recorders. Our ad hoc network of water level recorders documented the rise, peak, and fall of water levels (± 0.5 hr) from two hurricane events in 2004 and 2005. Reduction of peak water level heights from relatively in-line gages associated with one storm surge event indicated that mangrove wetlands can reduce water level height by as much as 9.4 cm/km inland over intact, relatively unchannelized expanses. During the other event, reductions were slightly less for mangroves along a river corridor. Estimates of water level attenuation were within the range reported in the literature but erred on the conservative side. These synoptic data from single storm events indicate that intact mangroves may support a protective role in reducing maximum water level height associated with surge.

Conservation frequently requires the preservation or restoration of ecosystems in human-altered landscapes. Understanding these ecosystems requires matching patterns with processes at appropriate scales. On floodplains this necessitates coupling plant distributions with fine- and broad-scale hydrologic patterns. This is particularly important when target species are of conservation concern, such as the blue elderberry (Sambucus mexicana). Blue elderberry is the sole host plant for the federally threatened Valley elderberry longhorn beetle, yet controls on the shrub's distribution have largely been untested. We used nested hierarchical analyses to test hypotheses about the role of broad- and fine-scale variables structuring the distribution of elderberry in one undammed and three dammed rivers in California's Central Valley (USA). Elderberry presence across the floodplains was primarily driven by broad-scale hydrologic regime, as represented by the relative elevation, floodplain width, and lateral distance of shrubs from the stream, and secondarily by sediment texture and topography. The patchy spatial distributions of elderberry were similar among the rivers, but habitat quality characteristics (i.e., controls on abundance and size) were driven by divergent variables with high stochasticity. We can improve our understanding of species distributions and outcomes of recovery efforts by scaling floodplain conservation efforts to broad-scale hydrologic patterns and by detecting crucial variables using a multi-scale methodology. Within these relatively large, self-defined landscape units, certain precautions and the application of an adaptive management approach could be employed to address the local-scale uncertainty in large-scale conservation efforts.

Sediments in coastal wetlands host communities of phylogenetically diverse primary producers such as diatoms, cyanobacteria, and anoxygenic photosynthetic bacteria, but little is understood about spatial variation in the composition of these assemblages at the highest taxonomic levels. Using High Performance Liquid Chromatography to quantify taxon-specific pigments, I investigated habitat-linked heterogeneity in microphytobenthic biomass, composition, and diversity within two natural wetland systems from southern California and tested for differences in community structure between natural and restored ecosystems. Natural vegetated habitat at Mission Bay had higher concentrations of zeaxanthin (cyanobacteria) and bacteriochlorophyll a (anoxygenic photobacteria) than unvegetated mudflat and creek banks. Organic matter was positively correlated with the concentrations of these pigments, whereas sediment pore water salinity and sand content were generally unrelated to composition. At Tijuana Estuary, community structure was generally similar between mudflat and Spartina marsh at the natural site, but concentrations of chlorophyll a and fucoxanthin (diatoms) were higher in mudflats. Restored wetland similarity with adjacent natural habitat (age 2 yr at Tijuana Estuary and 6 yr at Mission Bay) depended on habitat type and pigment measure. Restored upper intertidal succulent marsh at Mission Bay was most divergent: it had lower microalgal biomass, a lower concentration of zeaxanthin relative to fucoxanthin, and less bacteriochlorophyll a relative to chlorophyll a than natural habitat. The results suggest that patches of prokaryotic primary producers coincide with areas of high sediment organic matter and/or hypoxia superimposed on a broadly distributed flora of diatoms across various wetland landscapes.

Hemerocallis esculenta suffered frost damage during a night of remarkably low temperatures at Sarobetsu Mire, northern Japan, on 5 June 2002. A numerical model simulation was conducted to evaluate how groundwater conditions affected the nocturnal air temperature at the mire. The numerical model developed in this study reproduced the nighttime cooling process of the air temperature profile at high resolution. The lowest water table level occurred at the site several days before 5 June. The numerical simulation suggested that if the lowest water table occurred on 5 June, under the same water table level, the minimum air temperature 0.2 m above the peat surface would have been 1.2°C higher because of the difference of volumetric water content. The rate of air temperature decrease at 0.2 m height to the water table decrease would be 0.7°C cm⁻¹. Therefore, the minimum air temperature near the peat surface of the mire is affected by both decreases in the water table level and the lowest depth prior to the observation day. Ensuring a high water table level could mitigate extreme low temperatures and frost damage at the mire.

Protection of biodiversity and restoration of species-rich plant communities rely on an adequate understanding of how diversity is regulated. We studied species diversity patterns and community assembly in a simulated three-year wetland succession using factorial combinations of two nutrient levels, two water levels, and three water level fluctuation regimes. A standard seed mixture of 23 wetland species representing a wide range of plant functional types was sown in each microcosm. We found strong and consistent effects of water depth and nutrient level on species composition, species richness, and biomass, but no clear effect of water level fluctuations. The relationship between biomass and species richness was positive in the infertile range (16 to 204 g m⁻²) but negative in the fertile range (372 to 1156 g m⁻²). This pattern is consistent with the “humped-back model”, with maximum species richness at an above ground biomass between 200 and 250 g m⁻². Increasing species richness in the low fertility range could partly be explained by limited seedling establishment in the harsh environment of nutrient poor and water logged soils. We interpret the decreasing species richness at high fertility as an effect of increasing competitive asymmetry.

We added nitrogen (N), phosphorus (P), and N P to a Zizaniopsis miliacea (Giant Cutgrass) dominated tidal freshwater marsh in Georgia USA to investigate nutrient limitation of tidal freshwater marsh primary production and invertebrate densities. After two years, aboveground biomass was significantly greater in the plots receiving N (2130 g m⁻²), and N P (2066 g m⁻²) than in the control (886 g m⁻²) and P (971 g m⁻²) only treatments. We observed no enrichment of leaf N or P in response to nutrient additions. Rather leaf N decreased and C∶N increased in plots receiving N, suggesting that leaf N was diluted by increased production of carbon laden structural components used to support increased plant height. N∶P ratios (mol∶mol) of the plant tissue were consistently < 30 (14–27) in the treatment plots, also suggesting N limitation of primary production. Total densities of benthic invertebrates and oligochaete worms (primarily Tubificidae and Lumbriculidae) were significantly greater in the N P plots than in the other treatments after two years of nutrient additions. There were no clear differences in diversity of benthic invertebrates among treatments. Our results suggest that tidal freshwater marsh primary and secondary production is limited or co-limited by N, and thus, like estuaries and salt marshes, are susceptible to N enrichment and eutrophication.

Litter accumulation within emergent macrophyte marshes may significantly influence abiotic conditions and biota but litter is rarely considered in emergent macrophyte studies. Litter is defined here as the standing and fallen dead plant material that can be collected using harvest methods in the field. Litter accumulation can be predicted by combining annual production with litter breakdown rates. Breakdown rates are typically measured using litter bag studies but these rates may also be measured using a mass-balance approach. A five year study conducted in Delta Marsh, Manitoba measured annual standing crop and harvested accumulated litter of Phragmites australis (Cav.) Trin., Typha glauca Godr., and Scolochloa festucacea (Willd.) Link. These species differ in their level of refractory material and hence the amount of litter that is expected to accumulate. Using annual estimates of standing crop and litter mass, a mass-balance model was used to estimate the litter breakdown rate for each species at three water levels. Mass-balance derived rates for Phragmites and Typha were significantly different (F_1,14  =  5.07, p  =  0.03) and also differed across water depths (F_2,14  =  4.35, p  =  0.04). For both species, predicted annual accumulation of litter tracked observed litter values. The mass-balance approach, however, was not suitable for Scolochloa because there is no litter carry over from year to year. When compared to observed litter accumulations, estimates of litter accumulation made using litter bag breakdown rates consistently overestimated annual litter accumulation. In short, breakdown rates can be estimated using a mass-balance approach and can then provide more accurate estimates of annual litter accumulation for emergent species with recalcitrant litter.

In estuarine systems, informed water resource management decisions rely, in part, on evaluating how changes in freshwater inflow and salinity affect a selected management target (i.e., habitat or organismal changes). This study examined the distribution of Spartina alterniflora and S. cynosuriodes species along the Altamaha River estuary in Georgia in association with an extensive drought, during which time freshwater inflow decreased considerably and salty water encroached into previously brackish areas. Bankside vegetation was surveyed along the length of the estuary at the beginning and end of the drought (2000, 2002), and again in 2004 after flows had increased. In addition, a removal experiment, in which one or the other plant was removed from naturally mixed communities, was conducted during the drought (2001–2002). In all surveys, S. cynosuroides densities decreased at a location that corresponded to where average high tide salinities were > 14 psu, such that the downstream border shifted from approximately 3 to 6 km from the mouth of the river between 2000 and 2002 and then back to 3 km in 2004. Although the peak density of S. alterniflora also shifted upstream between 2000 and 2002, upstream densities were high in 2004 and plant distribution did not correspond with salinity. In the removal experiment, densities and relative % cover of S. alterniflora increased in all treatments (including controls), whereas densities of S. cynosuroides remained relatively constant except in treatments where it was purposely removed. We interpret these results to suggest that S. alterniflora is a strong invader that can expand into new habitat under stressful (increased salinity, low flow) conditions, and that once it is established it can co-exist with S. cynosuroides. The more rapid response of S. cynosuroides (shifts occurred within 2 years) suggests that its downstream limit is a potential indicator of changes in inflow conditions in this system.

It is widely accepted that in coastal wetlands a negative relationship exists between plant species richness (number of species) and salinity. However, the distribution of species richness across estuarine salinity gradients has not been closely examined. We hypothesized that plant species richness in coastal marshes (i.e., wetlands dominated by herbaceous plants) is highest within the fresh-brackish transition zone (oligohaline salinity regime). The basis for this hypothesis was that salinity fluctuations between fresh and brackish salinities (i.e., 0–7 ppt) might promote coexistence of freshwater and salt-tolerant brackish marsh species, resulting in a peak in richness in the transition zone. We conducted an observational study across the fresh (< 0.5 ppt) to mesohaline (5–18 ppt) salinity gradients of the Nanticoke and Patuxent Rivers of Chesapeake Bay to describe the distribution of plant species richness across each estuarine gradient. A series of 1,000-m² plots (with nested subplots) was established along 50-km sections of each river. Our results do not conclusively support our hypothesis of a transition zone peak in richness for either river gradient. However, richness in transition zone oligohaline marshes was as high as or higher than in tidal freshwater marshes, resulting in a distinctly non-linear pattern of plant species richness along the relatively undisturbed Nanticoke River. In contrast, the more urbanized Patuxent River gradient displayed a linear decrease in plant species richness with increasing distance downstream across the estuary. Hence the non-linear pattern of plant species richness observed along the Nanticoke River may be the typical pattern in relatively undisturbed estuaries.

The floating mat fens of the Tanana Flats in interior Alaska are productive wetlands near the urban center of Fairbanks. Airboat traffic has created a network of trails through the floating vegetation mats. We established protected areas along established trails, which allowed for measurement of plant community resistance to airboat traffic and resilience following cessation of traffic. The fen plant community was resistant to airboat traffic for two growing seasons, but productivity declined dramatically by the third year. Woody plants, grasses, and most forbs were eliminated in new airboat trails. Aboveground biomass and species diversity in plots protected from airboat traffic re-grew to undisturbed levels after four years. However, woody plants and many forbs did not re-grow in protected areas. Fen vegetation was therefore not resilient following cessation of traffic, as re-grown communities differed in both plant community composition and canopy structure. The loss of woody vegetation in particular has ramifications for possible alterations of ecosystem function. Airboats also reduced the amount of live belowground biomass and changed the vertical distribution of live roots.

Most wetland maps must be updated for much of North America. High-resolution satellite images and LiDAR-based elevation data have been developed in recent years, and these may prove useful in wetland mapping. We compared the accuracy of the Wisconsin Wetland Inventory maps (WWI) to maps derived from IKONOS high resolution satellite data and LiDAR data for a 63.4 km² study area in north-central Wisconsin. One-meter, resolution merged multispectral and panchromatic IKONOS data were used with a 1-m resolution LiDAR-based digital elevation model in a manual interpretation of wetland types. IKONOS/LiDAR data were significantly more accurate (74.5% classification accuracy) than WWI data (56%) when wetlands were categorized into WWI classes. Improved accuracies were largely due to less confusion between upland and wetland classes, and generally better distinction among the various wetland classes. LiDAR data improved upland/wetland distinction, based on relative terrain heights and derived terrain-shape indices. Confusion in all classifications was particularly common among lowland coniferous species, and among evergreen shrub and moss classes.

The objective of this study was to test the ability of existing hydrogeomorphic (HGM) functional assessment models and our own proposed models to predict rates of nitrate production and removal, functions critical to water quality protection, in forested riparian wetlands in northeastern New Jersey. In particular, the relationship between rapidly measured structural indicators and complex nitrogen (N) cycling functions was evaluated as well as the ability of generalized biogeochemical models to predict rates of specific N cycling processes. Additional models were designed specifically to predict net nitrification and denitrification rates, using both rapid and non-rapid variables based on known controlling factors on these two processes. Existing models and our own rapid models were not able to describe net nitrification and denitrification rates in urban riparian wetlands. Our additional models based on non-rapid variables, quantified through long-term hydrological monitoring and laboratory analyses of soil properties, successfully described net nitrification rates, but surprisingly failed to adequately predict denitrification rates. The high variability in hydrological and soil properties and the complexity of site-specific relationships between disturbance, altered hydrology, and hydrologically driven N cycling processes in urban wetlands restricts our ability to predict denitrification rates using simple models. It is recommended that functional assessment models be designed to describe specific, process-based functions which are based on structural indicators that are well linked to process rates. These indicators should be based on measurements from at least one year of hydrological monitoring and from simple laboratory measurements of soil properties. Detailed studies of populations of wetlands may be necessary to validate specific forms of models.

To evaluate the effects of saltwater intrusion and nutrient enrichment on wetland microbial communities, we measured changes in sediment microbial structure and function in response to increased salinity and nutrients. Sediments were collected from a cypress-tupelo swamp near Lake Pontchartrain, Louisiana, USA, and maintained in microcosms treated with elevated salinity, nitrogen (N), or phosphorus (P). Impacts on bacterial community diversity and composition were determined via molecular techniques, while effects on function were assessed through measurement of extracellular enzyme activity. Salinity increased bacterial diversity, P had no effect, while N reduced diversity. Deltaproteobacteria dominated all treatments, although their representation, along with that of the Alphaproteobacteria and Planctomycetes, was reduced following N addition. P addition reduced the proportion of Alphaproteobacteria, while salinity increased the proportion of Betaproteobacteria. Exposure to elevated salinity also decreased phosphatase and N-acetlyglucosaminidase activity by almost 20%, with less effect on ß-glucosidase. P addition had no impact on extracellular enzyme activity. Overall, exposure to elevated salinity depresses microbial function and changes the sediment microbial assemblage. These wetlands are likely N-limited, and while N additions may regenerate plant communities, they also change the structure of the sediment microbial community, decreasing diversity and impacting the mineralization of other nutrients.

Wigeongrass (Ruppia maritima), a submerged aquatic plant inhabiting estuarine wetlands, is an important winter food for waterbirds along the Texas Gulf Coast. We examined availability of wigeongrass at Mad Island Wildlife Management Area, Texas, USA by estimating aboveground biomass from October through January, 1998–1999 and 2001–2002. We also used an exclosure experiment to determine the extent to which herbivory by waterbirds was responsible for depletion of wigeongrass. Aboveground biomass of wigeongrass declined an average of 189 g m⁻² and 71 g m⁻² between October and January each year. Aboveground biomass declined at a higher rate among plots exposed to herbivory compared to exclosures, and the loss of biomass attributable to foraging by waterbirds was 19%. In 1998, counts of gadwalls (Anas strepera), American wigeons (A. americana), and American coots (Fulica americana) using study ponds peaked in November and then followed a declining trend similar to availability of wigeongrass, suggesting that as wigeongrass was depleted herbivorous waterbirds moved to other habitats where food was more available.

Conservation initiatives in agricultural landscapes play an increasingly important role in ensuring the long-term persistence of amphibian biodiversity because native habitats continue to be lost to urban and commercial development. We examined larval anuran structure within seasonally inundated wetlands in four upland habitat types of southcentral Florida differing in degree of upland habitat modification for cattle ranching: native prairie at the Kissimmee Prairie Sanctuary (KPS); and improved pasture, rangeland (semi-native prairie), and woodland habitats at the MacArthur Agro-Ecology Research Center (MAERC). We sampled 24 wetlands monthly for tadpoles using throw-traps and dipnets during the 1999 wet season (June–October), recording 10,126 tadpoles of 10 species. Species richness, mean total abundance, and species abundances differed among upland habitat types. The most heavily modified habitat (pasture) had both species-poor assemblages and low tadpole abundances. Species richness in woodland, rangeland, and native prairie wetlands were similar, but woodland wetlands had higher tadpole abundances. Wetlands in the four habitats differed in the amount of nearby woodland and wetland habitats, length of hydroperiod, and percent cover of aquatic vegetation, which likely contributed to the observed amphibian richness and abundance patterns. Cattle ranches in Florida that retain a large proportion of woodland, rangeland, and temporary wetlands in the landscape are likely to contribute significantly to amphibian conservation initiatives on protected native lands.

Maximum likelihood supervised classification and post-classification change detection techniques were applied to Landsat MSS/TM images acquired in 1976, 1986, 1995, 2000, and 2005 to map land cover changes in the Small Sanjiang Plain in northeast China. A hotspots study identified land use changes in two National Nature Reserves. These were the Honghe National Nature Reserve (HNNR) and the Sanjiang National Nature Reserve (SNNR). Landscape metrics were used in both reserves to identify marsh landscape pattern dynamics. The results showed that the Small Sanjiang plain had been subject to much change. This resulted from direct and indirect impacts of human activities. Direct impacts, resulting in marsh loss, were associated with widespread reclamation for agriculture. Indirect impacts (mainly in HNNR) resulted from alterations to the marsh hydrology and this degraded the marsh ecosystem. Marsh landscape patterns changed significantly due to direct impacts in SNNR between 1976 and 1986 and again between 2000 and 2005, and, in HNNR between 1976 and 1986. Indirect impacts in HNNR after 1986 appeared to cause little change. It was concluded that effective wetland protection measures are needed, informed by the change analysis.

Vegetation structure and soil properties were measured on a sandbar, a three year old sandbar emergent marsh (SEM), and five mature Spartina alterniflora Loisel marshes located near the mouth of the Altamaha River (Georgia, USA) to determine how quickly tidal marsh vegetation and soils develop during primary succession. Those data were compared to published data collected from young (10–16 yr old) natural marshes in Virginia and young (1–28 yr old) constructed marshes in North Carolina to determine if the rate of ecosystem development is similar among tidal marshes of the southeastern US coast. Within three years of emergence, aboveground biomass of SEM was comparable to mature marshes in the area, although stem height and density were distinctly different as the SEM contained more stems that were of shorter height than mature marshes. Following colonization by vegetation, soil properties (0–30 cm) of SEM had begun to differentiate from sediments of the sandbar. Surface (0–10 cm) and subsurface (10–30 cm) soil bulk density was less, and organic carbon (C), nitrogen (N), and percent silt (0–10 cm) were greater in sediments of SEM than in the sandbar. Even so, soils of SEM contained less organic C, N, silt, and clay than mature marshes. However, accumulation rates of organic C (260 ± 40 g m⁻² yr⁻¹) and N (11 ± 3 g m⁻² yr⁻¹) in soils of SEM was 5 to 7 times greater than in mature marshes (35 ± 4 g C m⁻² yr⁻¹, 2 ± 0.2 g N m⁻² yr⁻¹). Trajectories of development for soil organic C and N pools were similar for our SEM, young natural S. alterniflora marshes in Virginia, and young constructed S. alterniflora marshes in North Carolina suggesting that soil development proceeds at similar rates for tidal marshes along much of the southeast US coast.

The flatwoods salamander (Ambystoma cingulatum) was listed as federally threatened in 1999. Alteration of habitat was considered the main threat to the species, especially the loss of habitat for larval flatwoods salamanders that develop in isolated, seasonally flooded wetlands. Our objectives were to evaluate a suite of within-pool factors (i.e., vegetation structure, water level, and an index to presence of fish) that could influence occupancy of breeding wetlands by larval flatwoods salamanders on Eglin Air Force Base in Florida, USA. We dip-netted for larval salamanders from January through March 2003–2006 and we measured a suite of vegetation characteristics in 2006–2007. Further, in 2006 we measured the level of water and relative presence of fish over the salamander breeding season. Site occupancy over the four year period was best described by a model that incorporated high herbaceous vegetation cover and open canopy cover. Detection probability was assessed, but it varied among years and was not included in the model. Our study suggests that managing the breeding habitat of flatwoods salamander for open canopies and dense herbaceous vegetation may contribute to this species' recovery.

Dryland rivers are characterized by high spatio-temporal variability in water resources, with alternating wet and dry reaches and fluctuating stream flow rates. To investigate response to this dynamic, riparian plant communities from perennial, temporally intermittent, and ephemeral-flow reaches of the Hassayampa River and an ephemeral tributary (southwestern USA) were characterized over a three year period, and soil seed banks (emergence method) were assessed. Variance through time in cover and diversity of wetland (hydric) species was lowest at perennial sites and highest at ephemeral flow sites. Wetland plants established along the active channel of the ephemeral reach following a 10-year recurrence interval flood, and compositional similarity between perennial and ephemeral sites was high during this wet year. About half of the wetland species growing at ephemeral flow sites were present in floodplain soil seed banks. Wetland species emerged from soils of the ephemeral Hassayampa River (but not of the ephemeral tributary) but their density and diversity declined with distance downstream of the perennial reach. Wetland species in the seed banks of ephemeral-flow sites were a nested subset of those at wetter sites, raising the possibility of dispersal from upstream sites. These results indicate that wetlands develop episodically on ephemeral reaches of spatially intermittent rivers of the Sonoran Desert following high winter runoff, and suggest that the wetland plants arise from local seed banks and off-site sources. The study also suggests that riverine restoration success is sensitive to location within a stream network: upon re-watering, sites closer to perennial reaches will have greater capacity to self-assemble wetland plant communities.

Low soil organic matter (SOM) levels can limit nutrient cycling and plant growth in restored wetlands. This study examined how the addition of different amounts of compost at a restoration site in Charlotte, North Carolina, affected the development of soil properties, microbial communities, and plant growth and diversity. The stream and wetland restoration was completed in July 2004 and monitored for three years. Available nitrogen (N) and phosphorus (P) increased with increasing SOM. The microbial community responded to organic matter (OM) additions with increases in both total microbial biomass and microbial activity (as measured by denitrification potential). Plant community responses were less consistent. In 2004, leaf % N significantly increased with increasing OM for two species (Pontederia cordata and Sagittaria latifolia) while two other species (Acorus calamus and Schoenoplectus tabernaemontani) showed no relationship; in 2005, however, there was no relationship for any of the species. We also found no relationship between total plant aboveground biomass and % SOM measured in 2006. We found negative relationships between species richness and % SOM in 2004 and 2006, but not in 2005. These results suggest that compost amendments are an effective method for improving soil properties, stimulating microbial communities, and can improve some ecosystem functions, such as nutrient cycling, but may have limited early effects on plant communities.

Two long-term submerged Eutric Gleysols (GLe) and two short-term flooded Eutric Fluvisols (FLe) with high organic carbon contents (C_org between 5.1 and 12.9%) were selected to characterize soil microbial communities at the Elbe River (Germany). Measurements included dehydrogenase activity (DHA), soil microbial carbon (C_mic), soil basal respiration (BR), metabolic quotient (qCO₂), C_mic/C_org ratio, and phospholipid fatty acids (PLFA). PLFA biomass, DHA, and C_mic/C_org ratios were considerable lower in GLe's than in FLe's. Whereas the BR as well as qCO₂ were higher in GLe's what seems to be an unspecific response of aerobic soil microorganisms to the long flooding period and the resulting short time for development following flooding. C_mic/C_org ratios were low in comparison to terrestrial soils. PLFA profiles were dominated by saturated fatty acids (FA). Principal component analyses (PCA) of FAs revealed clear differences among the four floodplain soils. In GLe's all fractions of PLFAs were lower than in FLe's. Polyunsaturated FA biomarkers (18:2ω6,9c) were 10 times lower in GLe's. Our results indicate that the environmental conditions in which microorganisms are exposed (i.e., long term soil inundation and anoxia) seem to be disadvantageous for fungi.

Secondarily treated municipal effluent from Breaux Bridge, Louisiana has been discharged into the Cypriere Perdue forested wetland since the early 1950s. Approximately one million gallons per day (3,785 m⁻³ day⁻¹) are discharged into the 1470 ha wetland, with average total nitrogen and phosphorus loading rates of 1.15 g N m⁻² yr⁻¹ and 0.31 g P m⁻² yr⁻¹, respectively. Vegetation and water quality of this wetland, along with a reference wetland, were monitored. Study sites were dominated by bald cypress and water tupelo, and species composition did not change significantly during the time of monitoring. Mean litterfall was higher near the effluent discharge point compared to sites located further away or the reference site. Mean stem growth was lower at the site furthest from the discharge point compared to the other sites. Nutrient concentrations measured at the site where water exits the assimilation area and at the reference site were not significantly different. Removal efficiencies for total nitrogen and phosphorus are typical of other forested wetlands receiving treated effluent in Louisiana, ranging between 65 and 90%. These results demonstrate that this wetland assimilates nutrients to background concentrations even after 60 years of operation, stimulating productivity, and causing no measurable impacts to the wetland or to the river into which the water eventually flows.

Throughout the world, many extensive wetlands, such as the Sacramento-San Joaquin Delta of California (hereafter, the Delta), have been drained for agriculture, resulting in land-surface subsidence of peat soils. The purpose of this project was to study the in situ effects of wetland drainage on the remaining peat in the Delta. Peat cores were retrieved from four drained, farmed islands and four relatively undisturbed, marsh islands. Core samples were analyzed for bulk density and percent organic carbon. Macrofossils in the peat were dated using radiocarbon age determination. The peat from the farmed islands is highly distinct from marsh island peat. Bulk density of peat from the farmed islands is generally greater than that of the marsh islands at a given organic carbon content. On the farmed islands, increased bulk density, which is an indication of compaction, decreases with depth within the unoxidized peat zone, whereas, on the marsh islands, bulk density is generally constant with depth except near the surface. Approximately 55–80% of the original peat layer on the farmed islands has been lost due to land-surface subsidence. For the center regions of the farmed islands, this translates into an estimated loss of between 2900–5700 metric tons of organic carbon/hectare. Most of the intact peat just below the currently farmed soil layer is over 4000 years old. Peat loss will continue as long as the artificial water table on the farmed islands is held below the land surface.

Hydrologic budgets for depressional wetlands require estimates of runoff from watersheds. In the Southern High Plains, where there is little elevation relief, ground surveys provide accurate watershed estimates but are time-consuming and costly. Estimates can be derived at lower cost from DEMs (Digital Elevation Models) and topographical maps, but data resolution and interpretation introduces errors. Other computational methods provide alternatives for estimating watershed area. Two computational methods based on longitudinal distances and elevations are described; minimal distance method and weighted minimal distance method. Twenty playas were ground surveyed to obtain baseline estimates of watershed area. Watershed areas for these 20 playas were also estimated using topographic maps, DEMs, and the two computational methods. The DEM method was not subsequently included in analyses because they did not have sufficient resolution. There were small differences in bias among the other methods. However, comparing the three alternative methods to ground survey estimates revealed that errors for the minimal distance method were larger than topographic map and weighted minimal distance methods. For computational accuracy, topographic map and weighted minimal distance methods are preferred. For modeling and computational ease, the weighted minimal distance method provides a simple alternative for calculating watershed area of playas.

The advancement of species poleward, due to global warming, has recently been documented worldwide. In Louisiana, Avicennia germinans (black mangrove) is moving northward into Spartina alterniflora salt marshes. Mangroves were historically restricted to southernmost islands and beaches by winter freezes; however, recently a noticeable expansion has occurred. The influence that mangroves have on ecosystem processes within Louisiana salt marshes has not been documented. Thus, this research examined the effects of mangrove expansion on sediment accretion, organic matter production and decomposition, and carbon assimilation, as well as edaphic parameters. Our results indicate that presently mangrove expansion has had no major effects on the ecosystem processes measured. Sediment accretion, belowground production, decomposition, and carbon assimilation were similar between Avicennia and Spartina. Where mangroves expanded into the surrounding salt marsh, elevation, redox potential, bulk density, and soil ammonium were slightly higher, while soil moisture and porewater salinity were somewhat lower. Because the mangroves are small in stature and areal extent, significant effects on ecosystem processes may presently be somewhat muted. However, if stands continue to grow, noted effects may occur in the future. Our research provides a baseline from which future ecosystem responses may be evaluated as mangroves in Louisiana continue to develop.