Showing papers in "Wetlands in 2003"
TL;DR: Geographic isolated wetlands as discussed by the authors are naturally formed or the result of human action, such as pothole wetlands, playas, and sinkhole wetlands, which are not confined to basins, as some occur on broad flats and others form on slopes.
Abstract: While many wetlands form along floodplains of rivers, streams, lakes, and estuaries, others have developed in depressions far removed from such waters. Depressional wetlands completely surrounded by upland have traditionally been called ''isolated wetlands.'' Isolated wetlands are not confined to basins, as some occur on broad flats and others form on slopes. The term ''geographically isolated wetlands'' better describes these wetlands, since many are hydrologically connected to other wetlands and waterbodies through ground-water flows or by intermittent overflows (spillovers). Numerous types of geographically isolated wetlands occur throughout the United States. They may be naturally formed or the result of human action. Naturally formed types include prairie pothole wetlands, playas, Nebraska's Rainwater Basin and Sandhills wetlands, West Coast vernal pools, sinkhole wetlands, Carolina bays, interdunal and intradunal wetlands, desert springs, terminal basins in the Great Basin, and kettle-hole bogs in glaciated regions. Human-caused isolated types may be intentionally built, such as ponds designed for various purposes and wetlands built on mined lands, or they may be accidentially created (e.g., natural wetlands that were once connected to rivers and streams but are now isolated by roads, railroads, and other development or isolated by altered river hydrology). Many of the functions and benefits attributed to non-isolated wetlands are present in isolated wetlands.
386 citations
TL;DR: In this article, Tiner's (2003b) definition as wetlands that are completely surrounded by upland is revisited, and the authors suggest that isolation not be viewed discretely but be considered within an isolation-connectivity continuum.
Abstract: The recent U.S. Supreme Court case of Solid Waste Agency of Northern Cook County v. U.S. Army Corps of Engineers (SWANCC) has had profound implications on the legal status of isolated wetlands. As a result, policymakers need ecological information on the definition and functions of isolated wetlands to respond to this decision. The term “isolated wetlands” is of fairly recent usage and has been poorly defined. In response, I recommend Tiner’s (2003b) definition as wetlands “that are completely surrounded by upland.” Isolation needs to be considered with respect to specific processes and functions. I suggest that isolation not be viewed discretely but be considered within an isolation-connectivity continuum. Isolation has a fundamental influence on the way water enters and leaves a wetland. This consequently affects any wetland function that depends on water as a vector (e.g., pollutant transport and certain types of dispersal). These wetlands can also have a high level of endemism, extensive plant zonation, and high biodiversity. Isolated wetlands, however, do not represent ecologically isolated habitat for many organisms. I conclude that the effect of isolation may not be as significant as the term “isolated wetlands” suggests: many of the biological features of isolated wetlands may result from environmental conditions that also occur in nonisolated wetlands. As a result of SWANCC, assessment methods are needed that can help regulators distinguish between jurisdictional and non-jurisdictional isolated wetlands. I propose that the merger of simple, source-sink-transport vector concepts with landscape-level assessment methods could be useful in this regard. I point to the need for documented examples of organisms that spend most of their lives in waters of the U.S. but also require isolated wetlands. I conclude that wetland science would benefit from the development of a comprehensive view of isolation as a formative process across different regional wetland types.
252 citations
TL;DR: Fens are among the most floristically diverse of all wetland types, supporting a large number of rare and uncommon bryophytes and vascular plant species, as well as uncommon animals including mammals, reptiles, land snails, butterflies, skippers, and dragonflies as discussed by the authors.
Abstract: The term fen has been variously used by peatland ecologists, ground-water hydrologists, and vegetation scientists. The common denominator among all types of fens is recognition of the importance of ground-water discharge, especially mineral-rich ground water, in determining fen hydrology, chemistry, and vegetation, in contrast to wetlands whose characteristics are determined primarily by precipitation or surface-water inputs. Thus, fens tend to occur where climate and hydrogeologic setting sustain flows to the planrooting zone of mineral-rich ground water. In the United States, these areas include the glaciated Midwest and Northeast, as well as portions of the Appalachian Mountains and mountainous West. Individually and collectively, fens are among the most floristically diverse of all wetland types, supporting a large number of rare and uncommon bryophytes and vascular plant species, as well as uncommon animals including mammals, reptiles, land snails, butterflies, skippers, and dragonflies. Several species listed under the federal Endangered Species Act inhabit or use fens. Fens also help maintain stream water quality through denitrification and phosphorus sorption. Few estimates of loss and current extent exist, but where estimates are available, they indicate extensive loss, fragmentation, and degradation. Cultural eutrophication threatens the biological and functional integrity of remaining fens because, along with mineral-rich water, low availability of nitrogen and phosphorus controls many of their distinctive characteristics. Because they occur where ground water discharges to the surface, fens are isolated from neither ground water nor surface water. However, the majority of fens develop in headwater areas and could be defined as “isolated” for jurisdictional purposes because of their distance from navigable-in-fact waters. If so defined, the critical roles that fens play in maintaining biological diversity and stream water quality are at risk regarding federal jurisdiction over “isolated waters” because of the 2001 U.S. Supreme Court ruling in the case of Solid Waste Agency of Northern Cook County v. U.S. Army Corps of Engineers.
189 citations
TL;DR: In this paper, a vegetation map was tested for classification accuracy with a pre-existing detailed GIS wetland vegetation database compiled by manual interpretation of 1∶40,000-scale color infrared (CIR) aerial photographs.
Abstract: Data acquired by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) with 224 bands, each with 0.01-μm spectral resolution and 20-meter spatial resolution, were used to produce a vegetation map for a portion of Everglades National Park, Florida, USA. The vegetation map was tested for classification accuracy with a pre-existing detailed GIS wetland vegetation database compiled by manual interpretation of 1∶40,000-scale color infrared (CIR) aerial photographs. Although the accuracy varied greatly for different classes, ranging from 40 percent for scrub red mangroves (Rhizophora mangle) to 100 percent for spike rush (Eleocharis cellulosa) prairies, the Everglades communities generally were successfully identified, averaging 66 percent correct for all classes. In addition, the hyperspectral image data proved suitable for detecting the invasive exotic species lather leaf (Colubrina asiatica) that is sometimes difficult to differentiate on aerial photographs. The findings from this study have implications for operational uses of spaceborne hyperspectral image data that are now becoming available. Practical limitations of using such image data for wetland vegetation mapping include inadequate spatial resolution, complexity of image processing procedures, and lack of stereo viewing.
188 citations
TL;DR: In this article, the authors show that terrestrial habitats associated with isolated wetlands are essential elements for enhancing biodiversity, and recognize that these terrestrial habitats can be used to enhance biodiversity in southern wetlands.
Abstract: A wetland ecosystem, no matter how small or isolated, includes biotic and abiotic features that interact to promote biodiversity at larger landscape scales. Isolated wetlands, in particular, harbor a significant portion of regional fauna and are often critical habitats for maintaining herpetofaunal biodiversity in southern wetlands. Long-term research on isolated wetlands reveals that two terrestrial habitats contiguous with the wetland—the terrestrial periphery and terrestrial corridors that connect isolated wetlands—are vital for much of the animal community. The U.S. Supreme Court’s ruling on the SWANCC decision has severely threatened the continued existence of such wetlands and their associated animals. Recognition that terrestrial habitats associated with isolated wetlands are essential elements for enhancing biodiversity could garner support from regulators, resource managers, and the general public in strengthening wetlands protection.
187 citations
TL;DR: Vernal pools are ecosystems that have evolved in a balance between isolation and connectedness as discussed by the authors, and are particularly abundant on the Pacific Coast and in various forms in the glaciated landscapes of the north and northeast.
Abstract: Vernal pools, broadly defined as ephemeral wetlands that predictably form in permanent basins during the cooler part of the year but which dry during the summer months, are distributed throughout the world. In the U. S., they are particularly abundant on the Pacific Coast and in various forms in the glaciated landscapes of the north and northeast. Vernal pools are ecosystems that have evolved in a balance between isolation and connectedness. Because of isolation at several scales, the vernal pools biota includes many regionally endemic species. Because of connectedness, vernal pools also share many taxa with continent-spanning distributions at the generic and species level. Vernal pools serve an important local biodiversity function because of their connection to surrounding terrestrial habitats. Along with other ephemeral wetlands, they are the primary habitat for animal species that require relatively predator-free pools for feeding or breeding, including many amphibians. The recent U. S. Supreme Court decision (SWANCC), which deemed “isolated” wetlands to be outside the class of “waters of the United States,” places some significant but unknown proportion of vernal pools at risk. In the worst case, the consequences could be immediate reductions in biodiversity at a local level, and regional reductions over longer periods of time. Ideally, federal law should be rewritten to establish unambiguously the value of ephemeral wetlands. It will also be necessary for conservationists to educate the public and to bring the issue of vernal pool protection to the notice of their local and state governments.
180 citations
TL;DR: Experimental evidence indicates that mangrove roots and debris provide refuge for small nekton from predators, thus enhancing overall survival, and meta-analyses for density and survival data suggest lower densities may be typical of mangroves when compared to segrass, coral reef, marsh, and non-vegetated habitats.
Abstract: The term nursery implies a special place for juvenile nekton (fishes and decapod crustaceans) where density, survival, and growth of juveniles and movement to adult habitat are enhanced over those in adjoining juvenile habitat types. We reviewed recent literature concerning these four topics and conducted meta-analyses for density and survival data. Most studies of mangroves as nurseries have addressed only occurrence or density of fishes or decapods, have not used quantitative sampling methods, and have not compared alternate habitats. Comparison of nekton densities among alternate habitats suggests that, at times, lower densities may be typical of mangroves when compared to segrass, coral reef, marsh, and non-vegetated habitats. There is little direct consumption of mangrove detritus by nekton. C, N, and S isotope studies reveal little retention of mangrove production by higher consumers. Densities of prey for transient fishes and decapods may be greater within mangroves than elsewhere, but there has been no verification that food availability affects growth or survival. Experimental evidence indicates that mangrove roots and debris provide refuge for small nekton from predators, thus enhancing overall survival. There is no evidence that more individuals move to adult habitats from mangroves than from alternate inshore habitats. There is an obvious need to devise appropriate experiments to test the nursery functions of mangroves. Such data may then be one more reason to add support for mangrove conservation and preservation.
178 citations
TL;DR: In this article, the authors evaluated the effects of sediment burial on emergence of plants and invertebrates in a prairie environment and found that sediment entering wetlands from agricultural erosion may also hamper successional changes throughout interannual climate cycles.
Abstract: Intensive agricultural activities near prairie wetlands may result in excessive sediment loads, which may bury seed and invertebrate egg banks that are important for maintenance and cycling of biotic communities during wet/dry cycles. We evaluated effects of sediment burial on emergence of plants and invertebrates from seed and invertebrate egg banks. Sediment-load experiments indicated that burial depths of 0.5 cm caused a 91.7% reduction in total seedling emergence and a 99.7% reduction in total invertebrate emergence. Results of our burial experiments corroborated prior research on seedling emergence. However, our study demonstrated that invertebrate emergence is also highly susceptible to the effects of burial. Our research suggests that sediment entering wetlands from agricultural erosion may also hamper successional changes throughout interannual climate cycles. Land-management strategies need to be implemented that will prevent erosion of cropland top soil from entering wetlands.
176 citations
TL;DR: Open Grounds Farm (OGF) is an 18,220-ha row-crop farm located in the lower Neuse River Estuary, North Carolina, USA, where a wetland was constructed to remove nutrients (N and Phosphorus), sediment, and pathogens in surface water draining from a 971-ha area of OGF as discussed by the authors.
Abstract: Constructed wetlands are recognized as a means to improve water quality through nitrogen (N) removal. Water-quality concerns in the N-sensitive Neuse River Estuary, North Carolina, USA, have necessitated enactment of a 30% reduction, in nitrogen (N) loading accompanied by an N loading cap. Open Grounds Farm (OGF) is an 18,220-ha row-crop farm located in the lower Neuse River Estuary. In 1999, a wetland was constructed to remove nutrients (N and Phosphorus), sediment, and pathogens in surface water draining from a 971-ha area of OGF. The wetland site is 5.1 ha of alternating segments of emergent marsh and open water. Nitrogen removal from the wetland via denitrification was measured monthly by analysis of dissolved nitrogen, oxygen, and argon in laboratory incubated sediment chambers using a Membrane Inlet Mass Spectrometer (MIMS). Nitrate concentration appeared to be the primary variable controlling denitrification rates. Spatial and temporal variability in rates of denitrification were investigated, including pre- and post- N loading events. Following rainfall, there was a 400% increase in denitrification rates in response to increased inorganic N loading. Nutrient loads entering and leaving the wetland were determined from nutrient analysis (twice monthly), intensive precipitation event sampling, and continuous flow measurements at the entrance and exit of the, wetland. Results indicated that the wetland received variable N loading (1-1,720 kg N per month) and had variable N removal via denitrification (8-81 kg N per month). Denitrification was an important mechanism for N removal.
164 citations
TL;DR: In this article, the authors observed spillage into and out of a North Dakota wetland during two field visits and found that specific conductance may have increased at the site by as much as 614 μS cm−1 due to spillage from the upslope wetland.
Abstract: A number of studies have noted the occurrence of intermittent surface-water connections between depressional wetlands in general and prairie potholes in particular. Yet, the ecological implications of such connections remain largely unexplored. In 1995, we observed spillage into and out of a North Dakota wetland during two field visits. Between May 3 and May 26, there was a positive relationship between specific conductance and water level at this site, suggesting an external source of dissolved ions. We estimated that specific conductance may have increased at the site by as much as 614 μS cm−1 due to spillage from the upslope wetland. Based on a spatial analysis that compared National Wetlands Inventory maps with 1996 color infrared imagery, we estimated that 28% of the area’s wetlands had a temporary surface water connection to at least one other wetland at that time, including one complex of 14 interconnected wetlands. These results indicate that the connectivity observed in 1995 was not confined to the two wetlands nor to that single year. The degree of connectivity we observed would be expected to occur during the wetter portions of the region’s 20-year wet-dry cycle. We hypothesize that intermittent surface-water connections between wetlands occur throughout the prairie pothole region. Given patterns in relief and precipitation, these connections most likely would have occurred in the eastern portion of the prairie pothole region. However, wetland drainage may have altered historical patterns. The implication of these spatial and temporal trends is that surface-water connections between depressional wetlands should be viewed as a probability event that has some distribution over time and space. We refer to connections that are impermanent, temporally discontinuous, or sporadic as temporal connectivity. The most intriguing feature of these temporary connections may be that they could affect biodiversity or population dynamics through transport of individuals or reproductive bodies. Research is needed to determine whether these connections actually cause these biological effects and to characterize the distribution and effects of this phenomenon.
150 citations
TL;DR: The concept of hydrologic isolation was introduced in this article, where the authors show that the degree that isolated wetlands are connected through the ground-water system to other surface-water bodies depends to a large extent on the rate that ground water moves and the rate of hydrological stresses can be transmitted through the water system.
Abstract: Wetlands that are not connected by streams to other surface-water bodies are considered to be isolated. Although the definition is based on surface-water connections to other water bodies, isolated wetlands commonly are integral parts of extensive ground-water flow systems, and isolated wetlands can spill over their surface divides into adjacent surface-water bodies during periods of abundant precipitation and high water levels. Thus, characteristics of ground-water flow and atmospheric-water flow affect the isolation of wetlands. In general, the degree that isolated wetlands are connected through the ground-water system to other surface-water bodies depends to a large extent on the rate that ground water moves and the rate that hydrologic stresses can be transmitted through the ground-water system. Water that seeps from an isolated wetland into a gravel aquifer can travel many kilometers through the ground-water system in one year. In contrast, water that seeps from an isolated wetland into a clayey or silty substrate may travel less than one meter in one year. For wetlands that can spill over their surface watersheds during periods of wet climate conditions, their isolation is related to the height to a spill elevation above normal wetland water level and the recurrence interval of various magnitudes of precipitation. The concepts presented in this paper indicate that the entire hydrologic system needs to be considered in establishing a definition of hydrologic isolation.
TL;DR: In this paper, structural characteristics of the created and natural salt marshes were compared using the line-intercept technique, and organic matter (OM) was measured in 1996 and 2002, while bulk density and soil particle size distribution were determined in 2002 only.
Abstract: The use of dredge material is a well-known technique for creating or restoring salt marshes that is expected to become more common along the Gulf of Mexico coast in the future. However, the effectiveness of this restoration method is still questioned. Wetland structural characteristics were compared between four created and three natural salt marshes in southwest Louisiana, USA. The created marshes, formed by the pumping of dredge material into formerly open water areas, represent a chronosequence, ranging in age from 3 to 19 years. Vegetation and soil structural factors were compared to determine whether the created marshes become more similar over time to the natural salt marshes. Vegetation surveys were conducted in 1997, 2000, and 2002 using the line-intercept technique. Site elevations were measured in 2000. Organic matter (OM) was measured in 1996 and 2002, while bulk density and soil particle-size distribution were determined in 2002 only. The natural marshes were dominated by Spartina alterniflora, as were the oldest created marshes; these marshes had the lowest mean site elevations ( 35 cm NGVD) and became dominated by high marsh (S. patens, Distichlis spicata) and shrub (Baccharis halimifolia, Iva frutescens) species. The higher elevation marsh seems to be following a different plant successional trajectory than the other marshes, indicating a relationship between marsh elevation and species composition. The soils in both the created and natural marshes contain high levels of clays (30–65 %), with sand comprising < 1 % of the soil distribution. OM was significantly greater and bulk density significantly lower in two of the natural marshes when compared to the created marshes. The oldest created marsh had significantly greater OM than the younger created marshes, but it may still take several decades before equivalency is reached with the natural marshes. Vegetation structural characteristics in the created marshes take only a few years to become similar to those in the natural marshes, just so long as the marshes are formed at a proper elevation. This agrees with other studies from North Carolina and Texas. However, it will take several decades for the soil characteristics to reach equivalency with the natural marshes, if they ever will.
TL;DR: The lower species richness, greater compositional variability, and lack of a distinctive flora support the hypothesis that dispersal limitation is the primary cause of the differences between the vegetation in restored and natural wetlands.
Abstract: Hundreds of wetlands comprising thousands of hectares have been restored in the Midwestern United States. In nearly all cases, restoration consisted of simply restoring wetland hydrology. For this reason, the success of these restorations relies on natural colonization. We compared the structure and composition of the vegetation in two types of wetlands: 10 natural wetlands and 17 five-to-seven-year-old restored wetlands. The overall vegetative composition of restored wetlands was different from that of natural wetlands. Restored wetland flora was formed from a subset of species found in natural wetlands. The species restricted to natural wetlands tended to be native perennials and were evenly represented along the elevational gradient. The few species that were restricted to restored wetlands were largely mudflat annuals whose presence is more indicative of the presence of more unvegetated habitat in restored wetlands than of the presence of a distinctive restored wetlands flora. In addition, restored wetlands had lower vegetative cover and species richness than natural wetlands. Both wetland types had similar numbers of exotic species at the whole wetland (4.4 species per wetland) and quadrat scale (1.5 species m2), and dominance of exotics increased with elevation. The lower species richness, greater compositional variability, and lack of a distinctive flora support the hypothesis that dispersal limitation is the primary cause of the differences between the vegetation in restored and natural wetlands.
TL;DR: Control of E. angustifolia is likely to be most promising where natural river flow regimes remain relatively intact, and the success of this species is at least partly due to its ability to take advantage of the reduced levels of physical disturbance that characterize riparian habitats downstream from dams.
Abstract: Elaeagnus angustifolia (Russian olive) is an alien tree that is increasingly common in riparian habitats of western North America. This paper reviews the pertinent scientific literature in order to determine the status ofE. angustifolia as a riparian invader and to suggest ecological reasons for its success.Elaeagnus angustifolia meets the biogeographic, spread, and impact criteria for invasive species. Ecological characteristics likely enabling its invasiveness include adaptation to the physical environmental conditions that characterize semi-arid riparian habitats, lack of intense pressure from herbivores, and tolerance of the competitive effects of established vegetation. We believe that the success of this species is at least partly due to its ability to take advantage of the reduced levels of physical disturbance that characterize riparian habitats downstream from dams. Control ofE. angustifolia is likely to be most promising where natural river flow regimes remain relatively intact.
TL;DR: Carolina bays, depression wetlands of the southeastern United States Coastal Plain, are "islands" of high species richness within the upland landscape and are the major breeding habitat for numerous amphibians.
Abstract: Carolina bays, depression wetlands of the southeastern United States Coastal Plain, are “islands” of high species richness within the upland landscape and are the major breeding habitat for numerous amphibians. The 2001 Supreme Court decision that removes isolated wetlands from protection under the Clean Water Act has potential for great losses of these wetland ecosystems. Most Carolina bays are not naturally connected with stream drainages or other water bodies, and their hydrology is driven primarily by rainfall and evapotranspiration. Their potential interaction with shallow ground water is not well-understood. Water levels in these wetlands may vary seasonally and across years from inundated to dry, and organisms inhabiting Carolina bays must be adapted to fluctuating and often unpredictable hydrologic conditions. The ecological importance of these wetlands as habitats for species that require an aquatic environment for a part of their life cycle has been well-documented. Many Carolina bays have been drained and converted to agriculture or other uses, and many of the smaller bays have been poorly inventoried and mapped. If these wetlands are not protected in the future, a major source of biological diversity in the southeastern United States will be lost.
TL;DR: Water quality characteristics of isolated wetlands are highly variable and depend primarily on the sources of water, substrate characteristics, and land uses associated with the wetland watershed as mentioned in this paper, and it is difficult to identify any general pattern of water quality characteristics within or between isolated wetlands in the three hydrogeomorphic classes.
Abstract: Isolated wetlands occur in many hydrogeomorphic settings, and while the appear to be physically isolated from other water bodies, they are almost never completely decoupled from surface-water or ground-water systems. In this paper, we examine water-quality data for isolated wetlands in three hydrogeomorphic classes (depressions, slopes, flats). Some isolated wetlands are dominated by atmospheric exchanges and have little ground-water or surface-water connections with adjacent systems. Other isolated wetlands are dominated by ground-water inputs and have intermittent or continuous hydrologic connections to adjacent systems. Water-quality characteristics of isolated wetlands are highly variable and depend primarily on the sources of water, substrate characteristics, and land uses associated with the wetland watershed. We were unable to identify any general pattern of water-quality characteristics within or between isolated wetlands in the three hydrogeomorphic classes. Alteration of hydrologic conditions (e.g., ditching, filling), however, usually results in increased nutrient export to downstream systems. From a water-quality perspective, we conclude that so-called isolated wetlands are rarely isolated, and isolation is a term that is not very useful from an ecosystem perspective. Isolated wetlands are nutrient sinks and, because most are hydrologically connected to other waters and wetlands, the loss of isolated wetlands would potentially have negative impacts on the water quality of downstream systems.
TL;DR: A survey of 304 vernal pools in southern, central, and northern Maine, USA was conducted to assess pool physical characteristics, landscape setting, and presence of pool-breeding amphibians for the purpose of guiding potential pool conservation strategies as discussed by the authors.
Abstract: Vernal pools in northeastern North America are typically seasonal woodland pools that support breeding populations of amphibians and invertebrates dependent upon fishless environments for successful reproduction. A survey of 304 vernal pools in southern, central, and northern Maine, USA was conducted to assess pool physical characteristics, landscape setting, and presence of pool-breeding amphibians for the purpose of guiding potential pool conservation strategies. In particular, information on reproductive effort by pool-breeding amphibians was used to assess the statewide applicability of the Maine Natural Resources Protection Act’s proposed definition of Significant Vernal Pool, a category of Significant Wildlife Habitats that allows closer environmental review of proposed impacts to vernal pools. The results of our study show regional differences in pool characteristics and amphibian usage. Defining “significance” based on number of egg masses and diversity of vernal pool indicator species is a useful tool but should be considered in the context of such landscape characteristics as availability of suitable terrestrial habitat and distribution of other breeding habitats and wetlands.
TL;DR: Moderate and highly invasive species are distinct from less invasive species in terms of ecophysiology in both wetland types, subject to the species' varying tolerances for salinity.
Abstract: We compared the ecophysiological performance of four dominant, perennial plant species of tidal marshes of northeastern North America (Phragmites australis, Typha angustifolia, Spartina alterniflora, and Leersia oryzoides), asking whether species that fall along a continuum of invasiveness vary consistently in terms of primary productivity, growth, biomass allocation, phenology, maximal photosynthetic rate, leaf turnover, tissue nutrient and chlorophyll content, and water use. During 1999, we examined plants growing at two brackish marshes and two freshwater tidal marshes in southern Connecticut, USA. Phragmites and Typha consistently exceeded the other two species in both marsh types in terms of ramet biomass, standing crop, length of the growing season, standing leaf area, leaf longevity, and total chlorophyll. Typha, Phrag- mites, and Spartina showed similar maximal photosynthetic rates across marsh types, significantly greater than the P max observed in Leersia. Foliar nitrogen was significantly greater in Phragmites than in all other species, suggesting that this species accrues nutrients more efficiently. Phragmites and Typha populations did not differ in a number of characters between freshwater and brackish marshes, indicating low sensitivity to exposure to moderate salinity levels. A principle components analysis placed Phragmites and Typha close to each other and more distant from Spartina and Leersia along axes describing components of competitive ability and photosynthetic performance. Thus, moderately and highly invasive species are distinct from less invasive species in terms of ecophysiology in both wetland types. As Phragmites australis and Typha an- gustifolia displace other plant species in marshes, they will likely influence the carbon- and nitrogen-cycling functions of wetlands, subject to the species' varying tolerances for salinity.
TL;DR: In this article, the authors evaluated the potential development of a macroinvertebrate Index of Biotic Integrity (IBI) for Prairie Pothole Region wetlands, using redundancy analysis (RDA) to identify the influences of fish, and temporal and spatial variation on the macroinvetertebrate community.
Abstract: To evaluate the potential development of a macroinvertebrate Index of Biotic Integrity (IBI) for Prairie Pothole Region wetlands, we sampled the aquatic macroinvertebrate and fish communities in 24 semipermanent wetlands located throughout central North Dakota. Wetland basins were selected to encompass a range of surrounding land-use, ranging from 100% grassland to 100% cropland. We used redundancy analysis (RDA) to identify the influences of fish, and temporal and spatial variation on the macroinvertebrate community. We also used RDA to look for relationships between wetland macroinvertebrate communities and land-use. Seventeen potential invertebrate metrics were tested by graphical analyses. We identified a strong influence on the macroinvertebrate community due to the presence of fish. A number of invertebrate taxa decreased in abundance as the summer progressed, and there was noticeable variation in the invertebrate community among individual wetlands of the region. However, we detected no strong relationships between the varying degrees of agricultural land-use in the wetland catchments and the invertebrate community. Consequently, we were unable to identify and effective IBI metrics indicative of land-use disturbance. Lack of correspondence between land-use and macroinvertebrates in this habitat is most likely due to a high degree of natural disturbance (e.g., presence of fish, temporal changes) and a low diversity community of resilient taxa in Prairie Pothole Region wetlands.
TL;DR: In this article, cattle were stocked at four treatment levels on improved and semi-native pastures in south-central Florida, USA, and the results showed that cattle stocking had little significant effect on water column nutrient concentration or invertebrate community structure.
Abstract: Responses of wetland abiotic variables and aquatic invertebrate community structure to cattle stocking density, pasture type, and dominant vegetation were evaluated in subtropical pastures. Cattle were stocked at four treatment levels on improved (fertilized) and semi-native (unfertilized) pastures in south-central Florida, USA. Improved pasture wetlands were dominated either byPanicum hemitomon (maidencane) or by a mixture ofPolygonum spp. (smartweed) andJuncus effusus; semi-native pasture wetlands were dominated mainly by maidencane. Cattle stocking density had few significant effects on water-column nutrient concentration or invertebrate community structure. However, water-column nutrient concentrations were significantly greater in the wetlands on improved pastures compared to semi-native pastures. Invertebrate richness and diversity were greater in wetlands on semi-native pastures than on improved pastures, despite lower nutrient concentrations in the former. Overall, the cattle stocking treatment had little impact on invertebrate community structure in these systems relative to prior pasture land use. However, vegetation type influenced invertebrate communities and explained some of the differences between pasture types. Seminative (lower nutrient) wetland pastures dominated by maidencane had significantly greater invertebrate richness and diversity than improved (higher nutrient) wetland pastures dominated by mixed vegetation but showed no difference when compared to improved wetland pastures dominated by maidencane. Chironomids were the dominant invertebrate in wetlands of both pasture types. Correspondence analysis revealed that ostracods and Culicidae larvae might be useful as bioindicators of subtropical wetlands that are experiencing cultural eutrophication.
TL;DR: Although summer flow patterns during the first year of growth strongly influenced species composition of seedling cohorts, low seedling densities and high overwinter mortality likely reduce the long-term impacts of initial cohort differences on successional trajectories.
Abstract: In riparian ecosystems, river flow is the dominant driver influencing ecological process and pattern, including the recruitment of riparian tree species. In a four-year field study (1997–2000) of seedling recruitment on sandbars in the Wisconsin River, I evaluated the hypothesis that the timing of seed dispersal and river flow interact to determine the annual composition of pioneer tree seedling cohorts. In the final three years of the study (1998–2000), growing season flow pulses strongly influenced the species composition and density of new seedling cohorts. Mortality rates of new seedlings exceeded 90% during the 1998 and 1999 flow pulses, and species composition shifted to dominance by Acer saccharinum following the 1999 flow pulse. Different species dominated the cohort of each year: in 1997, 83% of new seedlings were Betula nigra; in 1998, 63% were Salix spp. (S. nigra 39%, S. exigua ssp. interior 24%); in 1999, 89% were Acer saccharinum; and in 2000, 71% were S. exigua and 23% were Betula nigra. Cohorts retained their initial differences in species composition for at least one year after establishment. The three years (1998–2000) with summer flow pulses produced very low end-of-the-growing-season densities of new seedlings (<0.1 seedlings/m2 on random plots), and subsequent mortality in the first year after establishment further reduced seedling numbers by 53–94% on monitored plots. Thus, although summer flow patterns during the first year of growth strongly influenced species composition of seedling cohorts, low seedling densities and high overwinter mortality likely reduce the long-term impacts of initial cohort differences on successional trajectories.
TL;DR: In this article, the U.S. Fish and Wildlife Service (FWS) used geographic information system (GIS) technology to analyze existing digital data to predict the extent of isolated wetlands in 72 study areas.
Abstract: In preparing a major report on geographically isolated wetlands, the U.S. Fish and Wildlife Service (FWS) initiated a study of the extent of these wetlands across the country. The FWS used geographic information system (GIS) technology to analyze existing digital data (e.g., National Wetlands Inventory data and U.S. Geological Survey hydrologic data) to predict the extent of isolated wetlands in 72 study areas. Study sites included areas where specific types of “isolated” wetlands (e.g., Prairie Pothole marshes, playas, Rainwater Basin marshes and meadows, terminal basins, sinkhole wetlands, Carolina bays, and West Coast vernal pools) were known to occur, as well as areas from other physiographic regions. In total, these sites represented a broad cross-section of America's landscape. Although intended to show examples of the extent of isolated wetlands across the country, the study was not designed to generate statistically significant estimates of isolated wetlands for the nation. As expected, t...
TL;DR: It is suggested that species show differential accumulation and release of N and P and may influence the overall potential of a wetland to retain agricultural nutrients.
Abstract: Riparian wetlands have a demonstrated ability to filter and control nitrogen (N) and phosphorus (P) movement into streams and other bodies of water; few studies, however, have examined the roles that individual plant species serve in sequestering N and P pollutants. We evaluated the potential for growth and consequent N and P accumulation by five species of wetland perennials. We planted blocks consisting of 900-cm2 plots of each species at 11 sites within a riparian wetland that receives large inputs of agricultural runoff. Plant shoots and roots were collected at the time of peak standing crop to determine net accumulation of biomass, N, and P for one growing season. A portion of the plant shoots was placed in decomposition litterbags in the field to determine biomass, N, and P losses for 60, 120, and 150 days. Of the five species, bur reed (Sparganium americanum) had the greatest aboveground accumulation of N and P but had the lowest belowground accumulation values. In contrast, woolgrass (Sci...
TL;DR: A restriction fragment length polymorphism (RFLP) assay was developed to distinguish native, non-native, and Gulf Coast type populations of Phragmites from each other.
Abstract: The common reed,Phragmites australis, is a common feature in wetlands across North America. Recent studies have suggested that the widespread invasions of this species may be due to the introduction of a non-native strain from EurAsia. Since native population types is needed to facilitate management of ulations are also found, a method for distinguishing population persist in many areas where introduced populations are also found, a method for distinguishing population types is needed to facilitate management of the species. A restriction fragment length polymorphism (RFLP) assay was developed to distinguish native, non-native, and Gulf Coast type populations ofPhragmites from each other. Two amplified non-coding chloroplast DNA regions are each cut with one restriction enzyme, allowing the distinction of native, non-native and Gulf Coast haplotypes from each other. When used together, these cut sites provide a low cost, rapid way of determining the origin ofPhragmites populations.
TL;DR: In this paper, the distribution and determinants of marsh vegetation along the major distributary channel system of southern Africa's largest wetland, the Okavango Delta, using a large, inter-disciplinary data set.
Abstract: This study investigated the distribution and determinants of marsh vegetation along the major distributary channel system of southern Africa’s largest wetland, the Okavango Delta, using a large, inter-disciplinary data set. Eight communities were recognized, dominated respectively by Pennisetum glaucocladum, Phragmites mauritianus, Cyperus papyrus, Cyperus papyrus/Miscanthus junceus, Miscanthus junceus, Imperata cylindrica, Pycreus nitidus and a mixed bog community. The Pennisetum glaucocladum community is situated in the Panhandle (a narrow valley reach at the head of the fan) on elevated scroll bars that are flooded seasonally for short periods (days to weeks). The Phragmites mauritianus community occurs largely in the Panhandle where channel margins have high clay contents and where soils are seasonally flooded for moderate periods (months). Fires are widespread in the Panhandle, but both Pennisetum glaucocladum and Phragmites mauritianus are stoloniferous, and meristems occur below the soil surface and are protected from fire. In contrast, the rhizomatous sedge C. papyrus dominates in situations where meristems are permanently submerged, and therefore protected from fire, such as areas of open channel water where current velocities are sufficiently low to enable the extension of C. papyrus into the channel. This situation exists where channel avulsion has recently taken place or where discharge is reduced by water loss from the channel by overspill. The semi-floating habit of C. papyrus in the channel fringe results in high hydraulic conductivities, which promotes water loss from channels and leads to sediment deposition within channels. Miscanthus junceus occurs in areas where the nutrient status of water is low, seasonal changes in water level are small, and the average water level is approximately constant over decadal time scales. It occurs some distance from the channel on the upper reaches of the Delta and progressively closer to the channel downstream such that it is the dominant channel fringe species in the distal reaches. This pattern, where a community occurs progressively closer to the channel downstream is similar for communities dominated by Imperata cylindrica and Pycreus nitidus suggesting that environmental gradients (probably nutrient supply) perpendicular to the channel axis are steep and that they are mirrored by long-range environmental gradients downstream. An analysis of hydraulic characteristics of this distributary river system illustrates that channel width varies most with variation in discharge, while channel depth and current velocity are relatively constant over the range of discharges in the study area. Since channel width is primarily a consequence of vegetation processes in the channel margin, especially the growth of the giant sedge C. papyrus it is clear that channel hydraulics are affected largely by vegetation.
TL;DR: The 2001 U.S. Supreme Court decision in Solid Waste Agency of Northern Cook County (SWANCC) held that isolated intrastate non-navigable waters could not be protected under the Clean Water Act (CWA) based on the presence of migratory birds as mentioned in this paper.
Abstract: The 2001 U.S. Supreme Court’s decision in Solid Waste Agency of Northern Cook County (SWANCC) held that isolated intrastate non-navigable waters could not be protected under the Clean Water Act (CWA) based on the presence of migratory birds. SWANCC represented a major reinterpretation of the CWA by re-emphasizing the importance of navigability in the definition of “waters of the United States” protected by the statute. The decision also implied that isolated waters might be “waters of the United States” where they had a “significant nexus” to navigable waters. Understanding the significance of SWANCC requires a historical look at the geographic scope of federal laws and regulations protecting surface waters. The concept of navigability had been prominent in the Rivers and Harbors Act of 1899, but the principal implementation focus for the CWA after its enactment in 1972 and prior to SWANCC had been on the hydrologic cycle and the relevance of links to interstate commerce for determining what waters were protected under the CWA. In upcoming years and months, the geographic jurisdiction of the CWA will continue to be debated in the courts, within Federal agencies, and by the public. Aquatic resource science will play a key role in helping ensure that the CWA is implemented in a scientifically defensible manner, consistent with SWANCC. One area in need of particular emphasis is additional research on the ways in which isolated waters help ensure the physical, chemical, and biological integrity of navigable waters and their tributaries. It is this question—the “significant nexus” between an intrastate non-navigable isolated water and the rest of the aquatic ecosystem—that will likely determine whether the water will be protected by the CWA.
TL;DR: The initial stages of seed-bank and vegetation development were documented in a newly created tidal freshwater wetland where donor soils were not applied as discussed by the authors, and subsequent changes were rapid, with colonization and complete plant cover occurring within one year.
Abstract: The initial stages of seed-bank and vegetation development were documented in a newly created tidal freshwater wetland where donor soils were not applied. The 32.3-ha site adjacent to the Delaware River in New Jersey, USA was completed in stages from November 1993 to November 1994. Objectives of the study were to determine characteristics of the seed bank and vegetation and to monitor spatial and temporal changes. The study was carried out from 1995 to 1999 using three sites (North, East, and South Marshes) and three elevation locations (1 m from a tidal channel, midpoint, and 1 m from the upland edge). Development of the seed bank and vegetation demonstrated tremendous colonization potential derived from regional and local sources. Colonization and complete plant cover occurred within one year, and subsequent changes were rapid. Individual species behaved uniquely regarding colonization time, duration, and decline in both the seed bank and vegetation. Large seed banks of some species were present even after decline in the vegetation. Overall, the seed bank was large, small-seeded and persistent, and diverse. A total of 177 species occurred in soil seed bank and 92 in field vegetation samples, with 72 contributing to cover. Seedbank densities (mean±SE/m2) ranged from 450±152 to 394,600±29,950. Species richness (species/ sample) ranged from 3.3±1.2 to 32.3±1.8. Density and species richness were clearly reduced by inundation and were lowest in channel edge samples and in the first year (1995). Cover species richness ranged from 1.6±0.2 to 7.3±0.6 per quadrat. Complexity of the vegetation increased over time, with lowest diversity along the channels. The 1995 site differences, with greatest densities and species richness in the East Marsh, could be related to site history (timing of construction). Species similarity between the seed bank and vegetation ranged from 11 to 53% and showed no site, location, or temporal pattern. However, similarity between sites of the seed bank and vegetation increased from 1995 to 1998. Several New Jersey State rare or threatened species, as well as invasive species, were present. Results indicated that it is ecologically feasible to create a wetland adjacent to a tidal freshwater river without use of donor soil and that transplantation had not been necessary.
TL;DR: This article examined whether landscape variables influenced the initial colonization of 22 constructed ponds and conducted a long-term study of changes in species richness and community composition in ten constructed and ten reference ponds over seven breeding seasons.
Abstract: Although amphibians are increasingly being used to assess ecosystem function of compensatory wetlands, there are almost no long-term studies of responses to ecological restoration. Consequently, much uncertainty exists about the appropriate timeframes and best criteria for evaluating responses to wetland restoration. We studied aspects of pond colonization and long-term community dynamics in ponds created at a mitigation site in western North Carolina. We examined whether landscape variables influenced the initial colonization of 22 constructed ponds and conducted a long-term study of changes in species richness and community composition in ten constructed and ten reference ponds over seven breeding seasons. During the first year of pond filling, species richness and the number of egg masses of the wood frog (Rana sylvatica) and spotted salamander (Ambystoma maculatum) were positively correlated with pond size, depth, and hydroperiod but independent of distance to the nearest forest, paved road, or source pond. The ten constructed ponds in the long-term study first filled in 1996 and were larger, deeper, warmer, more oxygen-rich, and of longer seasonal hydroperiod than reference ponds. Seven species bred in the constructed ponds during the first year of filling, and species richness reached equilibrium within two years of initial pond filling. Most species colonized constructed ponds rapidly, but frequency of use by eastern newts (Notophthalmus viridescens) increased slowly over five years. Constructed ponds supported significantly more species than reference ponds, and the annual turnover rate of breeding populations was approximately 25% for both pond types. Our data suggest that post-restoration monitoring for 2–3 years may be sufficient to characterize species and communities that will utilize ponds for the first decade or so after pond creation.
TL;DR: An 8-yr study to examine the demographic responses of the wood frog and spotted salamander to wetland creation at a mitigation bank in western North Carolina, it is still uncertain that site restoration will achieve the goal of increasing breeding populations above pre-restoration levels.
Abstract: Although regulatory, agencies in the USA typically require 3–5 yr of post-restoration monitoring of biotic responses to wetland mitigation, many researchers have argued that longer time frames are needed to assess population responses adequately. We conducted an 8-yr study to examine the demographic responses of the wood frog (Rana sylvatica) and spotted salamander (Ambystoma maculatum) to wetland creation at a mitigation bank in western North Carolina. Our primary goals were to compare juvenile output in ten reference and ten constructed ponds and to assess the overall change in breeding population size in response to site restoration. We used annual censuses of egg masses to assess changes in breeding population size and used estimates of larval population size at hatching and the initiation of metamorphosis to assess embryonic and larval survival. Adults of both species bred in most constructed ponds within a few months after filling in 1996. Estimated juvenile production from 1996 to 2002 did not differ significantly between pond types for either species. The percentage of both constructed and reference ponds that produced juveniles decreased markedly from 1996 to 1998 and remained low through 2002. The decrease in juvenile output was mostly associated with reduced larval survival rather than increased embryonic mortality across years. Drought and outbreaks of a pathogen (Ranavirus) were the primary causes of low juvenile production from 1998 to 2002. The overall breeding population of R. sylvatica increased markedly in 1999–2000 following a large recruitment of juveniles from constructed ponds in 1996–1997. With the onset of drought and ranaviral infections, the population declined to levels in 2002 that were at or below 1995 pre-restoration numbers. Despite site perturbations, the breeding population of A. maculatum remained relatively stable from 1995 to 2002, a phenomenon that may reflect selection for delayed reproduction and iteroparity in this species. Although we have monitored R. sylvatica and A. maculatum for seven breeding seasons after the creation of seasonal wetlands, we are still uncertain that site restoration will achieve the goal of increasing breeding populations above pre-restoration levels. Because amphibians have significant population lags and are sensitive to site perturbations, monitoring that exceeds five years may be required to assess demographic responses to site restoration adequately.
TL;DR: In this paper, the authors reviewed the state of our scientific understanding of isolated wetlands, based on the major findings of papers contributed to this special issue of Wetlands, and recommended that geographically isolated wetlands be defined as "wetlands that are completely surrounded by upland", as proposed by Tiner, for the purposes of scientific studies.
Abstract: In Solid Waste Agency of Northern Cook County v. U.S. Army Corps of Engineers (SWANCC), the U.S. Supreme Court held that isolated, intrastate, non-navigable waters could not be protected under the Clean Water Act based solely on their use by migratory birds. The SWANCC decision has created a need to compile and make available scientific information for post-SWANCC policy development. In response, this article reviews the state of our scientific understanding of isolated wetlands, based on the major findings of papers contributed to this special issue of Wetlands. Because the term “isolated wetland” has not been used consistently in the scientific literature, we recommend that geographically isolated wetlands be defined as “wetlands that are completely surrounded by upland,” as proposed by Tiner, for the purposes of scientific studies. Geographically isolated wetlands are not homogeneous but have a broad range of functional response, partly due to their occurrence over a wide range of climatic and geologic settings. One major question addressed through this special issue is the role that isolation plays in the function of geographically isolated wetlands. It appears that isolation is not a primary factor and that many of the functions performed by isolated wetlands are also performed by non-isolated wetlands and non-wetland ecosystems. Variability in moisture conditions plays an important role in the function of many geographically isolated wetlands. However, hydrologic isolation may affect moisture conditions, and biotic isolation could be important for certain populations. Depending on the factor being considered, geographically isolated wetlands are not entirely isolated but are better viewed as occurring within an isolation-connectivity continuum that has both hydrologic and biotic expressions. The juxtaposition of isolation and connectivity occurring in geographically isolated wetlands may represent a semi-isolated state that uniquely shapes these wetlands and their functions. Comprehensive data, designating the number, total area, and functional classification of isolated wetlands, would provide the foundation for monitoring impacts to isolated wetlands. Studies are needed to examine and quantify how isolated wetlands, wetland complexes, and other potentially impacted waters contribute hydrologically, chemically, and biologically to waters of the U.S. Methods to assess and map the degree of connectivity between geographically isolated wetlands and waters of the U.S., based on ground-water travel time, recurrence frequency of intermittent surface-water connections, and home ranges of species that require both types of waters, could be useful for regulators. Whatever policies are developed, scientific input and technical information will continue to play a crucial role in the policy and regulatory arena. Maintaining and enhancing the dialogue among wetland scientists, policy-makers, and regulators will ensure that critical information is developed and communicated and also continue to invigorate wetland science.