Published by Springer Verlag
Print ISSN: 0277-5212
Evapotranspiration determined using the energy-budget method at a semi-permanent prairie-pothole wetland in east-central North Dakota, USA was compared with 12 other commonly used methods. The Priestley-Taylor and deBruin-Keijman methods compared best with the energy-budget values; mean differences were less than 0.1 mm d−1, and standard deviations were less than 0.3 mm d−1. Both methods require measurement of air temperature, net radiation, and heat storage in the wetland water. The Penman, Jensen-Haise, and Brutsaert-Stricker methods provided the next-best values for evapotranspiration relative to the energy-budget method. The mass-transfer, deBruin, and Stephens-Stewart methods provided the worst comparisons; the mass-transfer and deBruin comparisons with energy-budget values indicated a large standard deviation, and the deBruin and Stephens-Stewart comparisons indicated a large bias. The Jensen-Haise method proved to be cost effective, providing relatively accurate comparisons with the energy-budget method (mean difference=0.44 mm d−1, standard deviation=0.42 mm d−1) and requiring only measurements of air temperature and solar radiation. The Mather (Thornthwaite) method is the simplest, requiring only measurement of air temperature, and it provided values that compared relatively well with energy-budget values (mean difference=0.47 mm d−1, standard deviation=0.56 mm d−1). Modifications were made to several of the methods to make them more suitable for use in prairie wetlands. The modified Makkink, Jensen-Haise, and Stephens-Stewart methods all provided results that were nearly as close to energy-budget values as were the Priestley-Taylor and deBruin-Keijman methods, and all three of these modified methods only require measurements of air temperature and solar radiation. The modified Hamon method provided values that were within 20 percent of energy-budget values during 95 percent of the comparison periods, and it only requires measurement of air temperature. The mass-transfer coefficient, associated with the commonly used mass-transfer method, varied seasonally, with the largest values occurring during summer.
Congressional policymaking has a significant impact on the management of wetlands in the United States. Both the congressional committees and witnesses who participate in hearings play significant roles in helping define wetland policy. This research examines congressional 240 hearings and 1569 witnesses who testified from 1789 to 1995 on wetlands. Based on key issues from witnesses and the committees who set the agenda, the findings show that three distinct eras exist in wetland policymaking in Congress. Era I (1789–1945) was characterized by a dominant monopoly of agricultural and development issues in congressional policymaking. Agricultural committees dominated in framing the debate by controlling the hearings and legislative discussion of issues during this time period. A significant break-up of these dominant agricultural issues occurred in Era II from 1946–1965 with the early beginning of public attention to environmental issues and the start of scientific investigation into wetlands. However, since Era III, which began in 1966, wetland policymaking in Congress has been highly conflictual, with no single committee or witness dominating. The growth of wetland science and continued public interest in wetlands presents a challenge to the dominant agricultural and development interests that once controlled congressional policymaking. Unlike in Era I, wetland monopoly that controls the issue. Wetland policy debates no longer focus solely on agricultural concerns but have expanded and been re-defined to include issues such as leisure, environmental protection, private property, and economics. Chi Square tests and a regression analysis demonstrate the strong relationship among hearings, venues, and witnesses. A major conclusion drawn from the study is that congressional wetland policymaking is a more open and democratic process than in earlier eras.
Greentree reservoir (GTR) management is a common waterfowl habitat management technique used in both the northeastern and southeastern United States. However, this management technique is controversial because greentree reservoir management can cause changes in forest composition and structure. We studied the effects of GTR management at the Montezuma National Wildlife Refuge in central New York by comparing vegetation in permanent plots in two GTRs and a natural forest wetland over 30-year period (preflood and 2 years and 18 years after flood cessation). We detected long-term effects of GTR management on vegetation composition and structure. Red maple and green ash remained the dominant overstory species, but density of green ash saplings was higher (P=0.026) in a natural forested wetland (300 trees/ha) compared to the two GTRs (30–90 trees/ha). Age determinations of several green ash saplings suggest these changes were likely caused by reduced regeneration in the GTRs. Mortality of green ash seedlings in 1996 was greatest in a GTR flooded for 1 year (60%) versus an unflooded GTR (12%) and a natural forested wetland (27%). Overall, shrub density was similar 18 years post-flooding and preflooding, but several species had lower densities (P=0.001–0.031) than a natural forested wetland. Shannon-Weiner diversity index (1.8–2.0) and richness (29–31) of herbaceous species were similar among all sites 18 years after flood cessation. However, two species of fern remained at lower densities (P=0.0001–0.026), while three herbaceous species remained at higher densities (P=0.0001–0.015) 18 years after flood cessation as compared to preflood densities and densities in a natural forested wetland. It is unknown after which year of flooding these changes occurred, but 12 years of GTR management did cause long-term effects on the forest community.
Top: The Peace-Athabasca Delta watershed and study area. Bottom: Location of the randomly chosen air photos. The vertical and horizontal lines delimit the four quadrants.
Comparison of means N and medians m of four cover types for six vintages. Lines are spline fits. Note the differences in vertical scale.  
Median and range of percent cover values for the 24 study areas, two analyst teams, and three air photo vintages. 
Comparison of water conditions at the confluence of the Prairie River and Lake Claire in 1927 (top) and 1955 (bottom). In 1927, the basin near photo center was open-drainage, open water. In 1955, the same basin was a semi-restricted emergent marsh. Note the Potamogeton beds in Lake Claire in bottom photo. National Air PhotoLibrary photos, 1927: 617-28, 1955: 15172-20.  
Percent cover of wet (all marshes + water) and dry (willows + forests) communities, 1927–2001. Dots are percent cover on 24 air photo study areas (except for 1927 where n510). Line is a LOWESS regression; overlapping data points are jittered.  
This study examined landscape change in the Peace-Athabasca Delta, northern Alberta, Canada. The proportion of the landscape covered by ten habitat types was determined for five vintages of air photos (1945–2001) from 24 randomly chosen study areas. To test for reproducibility, three vintages were analyzed by two independent teams, neither of which knew the dates or locations of air photos. Their results were highly correlated. Comparison with another air photo study focused in the southeastern delta revealed good agreement. Analysis of oblique air photos extended the reconstruction back to 1927. Of four cover types (water, marshes, willows, forests), only water differed significantly in area between vintages. Cover trends for the most general of types (wet communities and dry communities) indicated drying from 1927 to 2001. This trend may be due to multidecadal geomorphic evolution and climate change. Currently, the changes are statistically non-significant, but nevertheless may inform about the long-term future of the ecosystem. Large spatial and temporal variation in landscape cover is characteristic of the system. The types and ranges of change in the delta’s vegetation post-Bennett Dam (1968) do not appear unusual relative to pre-Bennett Dam change. A multi-decadal perspective is necessary to encompass normal oscillations in abundance. Key to understanding change in the delta is to think at multiple scales and to remain aware that trends or patterns are scale-dependent. The delta may not be predictable on the meso-scales relevant to society and management.
Landscape Change Detection Results in San Dieguito Lagoon, California, with Landscape Class (w wetland; nw non-wetland) Indicated for the Four-date Study.
Aerial photographs of San Dieguito Lagoon used in wetlands change analysis: 1928 and 1945 panchromatic photography; 1975 and 1994 color infrared photography. 
This study analyzed change of a coastal wetland using remote sensing, image processing, and GIS techniques. Aerial photographs from 1928, 1945, 1975, and 1994 were acquired for San Dieguito Lagoon, in San Diego County, California, USA. The photographs were scanned and the landscape classified as wetland or non-wetland. A GIS model quantified and indicated trends in wetland change. Results show that, in 1928, 50% (366 ha) of the study area was comprised of wetlands. By 1994, the total wetland area decreased to 15% (109 ha) of the study site area. The annualized loss reveals a continual decrease in the rate of loss over all three time periods, which corresponds to the national decline in the rate of wetland loss. The greatest loss rate occurred from 1928 to 1945 (3% per year), and the lowest rate of loss occurred from 1975 to 1994 (0.3% per year).
Alkaline wetland beaches provide crucial habitat for breeding piping plovers (Charadrius melodus) in the northern Great Plains of the United States and Canada. Vegetation encroachment has been identified as a potential threat that decreases alkaline beach habitat availability, but the long-term status of these breeding habitats has not been evaluated. We measured vegetation changes at two North Dakota alkaline wetland complexes from 1938 to 1997. Total beach habitat, including lower beaches that were impacted by flooding, varied substantially among years based on changes in surface-water levels. Quantities of upper-beach habitats, which were not affected by inundation, were negatively correlated with precipitation amounts during the previous five-year periods. We measured declines in upper-beach habitat averaging 0.89 ha/yr and 0.20ha/yr at our two wetland complexes from 1938 to 1997, suggesting that long-term changes in factors other than precipitation (e.g., ground-water hydrology, livestock grazing intensity, or fire frequency) may be negatively affecting beach availability. Vegetation reduction may be critical to long-term recovery of threatened piping plovers in the Great Plains.
Summary statistics for 1950 photo plots from Loxahatchee National Wildlife Refuge. Orientation is 0 to 180 degrees, with 0 north and 180 south.
Summary statistics for 1991 photo plots from Loxahatchee National Wildlife Refuge. Orientation is 0 to 180 degrees, with 0 north and 180 south.
Hydrology data for hydrology zones in Loxahatchee National Wildlife Refuge that contained photo plots.
Size, shape, orientation, and distribution of tree islands in a remnant of northern Everglades wetland were examined from 1950 and 1991 aerial photography. The objectives were to quantify the patterns of tree islands in Loxahatchee National Wildlife Refuge, to determine if the patterns of tree islands had changed between the two dates, and to relate the tree island patterns to modeled pre-and post-drainage hydrologic patterns. There was considerable variation in the patterns of tree islands spatially and temporally Changes in the size and shape of tree islands from 1950 to 1991 are consistent with changes in the modeled pre-and post-drainage hydrologic patterns. Photo plots along the edges of the refuge, where hydroperiods are longer and depths deeper than they were historically, show a decrease in tree island size and in overall area of tree islands in the plots. Photo plots in the interior, where hydroperiods are shorter than they were pre-drainage, show an increase in tree island area. Overall, there is a tendency for more tree islands to be irregularly shaped in the 1991 photo plots than in the 1950 plots, a reflection of the loss of water flow, reduction of pulse magnitude, and the ponding of water along the perimeter dikes. This study illustrates the importance of considering long-term changes in hydroperiod, depths, and water flows in the restoration of this area.
We examined historical patterns of land use of depression wetlands (Carolina bay and bay-like wetlands) to determine if a relationship between vegetative successional changes over a 41-year period and previous human disturbances (primarily agricultural) could be established. Land cover was interpreted from 1951 (black and white) and 1992 (false color infrared) aerial photography of the Savannah River Site (a 780 km2 federal nuclear facility in which wetlands have been relatively undisturbed since 1951). Patterns of change from one land cover to another were detected by constructing a series of frequency tables. About one fourth of the 299 wetlands identified were either pasture or cultivated in 1951, and the majority had been ditched for drainage. Agriculturally disturbed wetlands primarily became mixed hardwood/pine or were converted to pine plantations by 1992; however, no successional differences between wetlands that were cultivated versus pasture were detectable. The type of land use of many of the depression wetlands prior to 1951 probably was determined by physical characteristics of the wetlands (e.g., topographic position, size, and hydrologic features). Thus, in many cases, separation of recovery trajectories from other successional pathways, initial hydrogeomorphic differences, and/or continued human influences is not possible in this study. However, from this change-detection study, we recognize that many of the currently protected depression wetlands at SRS were disturbed by agricultural practices or were impacted by hydrologic alterations prior to 1951, implying considerable resilience in the recovery toward a functioning wetland condition if hydrologic regimes are restored. A significant finding of this study is the relative stability of herb-dominated bays, which indicates that this vegetation type is not necessarily a successional continuum toward an eventual hardwood forest, at least in the temporal scale of the study. Thus, we suggest that management prescriptions for the restoration/conservation of herb-dominated wetlands should incorporate concepts of temporal stability within a framework of cyclical hydrologic and vegetation changes.
Tangxunhu wetland is one of China’s largest freshwater lakes and plays a significant role in the sustainable development of the city of Wuhan. Based on terrain maps, TM images, and statistical data from 1953 to 2005, the spatial characters and changing features of Tangxunhu wetland were quantitatively assessed by calculating the landscape metrics of shape index (SI), fractal dimension (D), and stability index (S). The results showed that Tangxunhu wetland had meandrous development over the past 53 years, withSI, D, and S decreasing from 1953 to 1967, increasing from 1967 to 2000, and then decreasing again from 2000 to 2005.SI, D, andS were lowest in 1967, indicating maximuminstability, but highest in 2000, indicating maximum stability. These changes in Tangxunhu wetland were associated with various natural, social, and economic factors. Key Wordsfractal dimension-Geographic Information System (GIS)-landscape ecology-shape index-stability index-sustainable development
Historically, anthropogenic activities have contributed to the direct loss of wetland area, mostly due to agriculture and urban land uses. Urbanization also indirectly impacts wetlands at a landscape scale through altered wetland hydrology and change in the spatial configuration of wetlands in a watershed. In addition, beaver (Castor canadensis) create and modify wetlands in a landscape. Because of recent increases in urbanization and rising beaver populations, a raster-based geographic information system (GIS) was used to analyze the combined effects of humans and beavers on wetland area and types in the Chickahominy River watershed from 1953 to 1994. Results of the study revealed that 29% of the land changed during the 41-year study period, and wetland conversion constituted 7% of the total change. The major reason for wetland loss was the construction of two large water-supply reservoirs in the watershed, and most of the remaining wetland loss was due to urbanization. Wetland functions vary depending on wetland type, and the results of this study showed that 90% of the change in wetlands from 1953 to 1994 was a result of shifting between wetland types. Beaver-modified wetlands increased 274%, and beaver activity was responsible for 23% of the wetland change.
Marshes in the Sanjiang Plain of Northeast China have undergone dramatic loss and fragmentation over the past decades. This paper analyzed the loss and fragmentation of these marshes for the period 1954–2005 using historical land-cover information and remote sensing data. In 1954, marshes covered one-third of the total land area but have decreased by 77% over the 50year period. Results showed two distinct periods of impact: 1954–1986 and 1987–2005. In the earlier period, the number of marsh patches fell from 4,799 to 1,476 (−69.2%), and total marsh area decreased from 35,270km2 to 13,893km2 (−60.6%). In the latter period, the number of marshes declined from 1,476 to 1,037 (−29.7%), and the total area decreased from 13,893km2 to 8,100km2 (−41.7%). The rapid decrease in the number and area of marshes during 1954–1986 was largely attributed to extensive agricultural reclamation under the “Food First” agricultural policy. This resulted in many negative ecological consequences. In contrast, the slower reduction of marsh areas during 1987–2005 was due to the implementation of governmental policies for protecting and restoring marshes. Increasing air temperature would otherwise have enhanced crop yields and stimulated the conversion of marsh into crops. KeywordsAgriculture–Climatic changes–Marsh loss–Policy–Remote sensing
A waterfowl habitat development project along 7.5 miles (12.07 km) of stream was evaluated after 27 years. There was a modest 12% net increase in wetlands in impounded areas, but much of the wetland vegetation changed from seasonally flooded, nonpersistent and persistent emergents to shallow, open-water areas. An unimpounded, downstream reference area had drier plant communities, probably resulting from reduced flooding. The loss of shallow vegetated wetlands could have significant impacts on both water quality functions and waterbird populations. The overall project goal of increasing numbers and diversity of waterfowl was met, but waterfowl numbers and species composition changed more because of transplanting and nest-box programs than habitat modifications. Although impacts on birds of shallow wetlands such as rails and songbirds were not quantitatively assessed, it is likely that the numbers of such birds were reduced because their preferred habitats were reduced markedly. Use of smaller lateral impoundments and increased management for emergents would diversity waterbird populations and increase dabbling duck production.
The Louisiana coastal marshes form some of the most extensive wetlands within the continental United States. The problem of land loss in these coastal marshes is well-documented, but very little is known about possible changes in vegetation composition that might be associated with this loss. We analyzed vegetation data collected from 1968 to 1992 in the tidal wetlands of Terrebonne parish and described five vegetation types that occur in this region. Our data did not show the predicted change to more salt-tolerant vegetation. This is probably due to the influence of the Atchafalaya River in the study area. However, we documented a large change in the dominant vegetation of the fresh marsh.Panicum hemitomon-dominated marshes occupied 51% of the study area in 1968 and only 14% in 1992. This vegetation type was replaced withEleocharis baldwinii-dominated marshes (3% in 1968 to 41% in 1992). This change occurred adjacent to an area of significant conversion to open water. Based on limited available data from the literature, we evaluated three potential driving factors in this change-grazing, water-level increase, and water quality-but could not determine the cause of change definitively.
Wetlands provide a range of critically important ecosystem services. However, a lack of reliable wetland data limits the efficacy of wetland management in remote mountainous areas. To optimize the management of wetlands in the vicinity of Mount Everest we created a new classification system for high alpine wetlands. Object-oriented image classifications and geographical information systems were used to extract wetland information for 1976, 1988, and 2006 from remote sensing data and field surveys. The results show that total area of wetlands in the vicinity of Mount Everest in 2006 was 1663.5km2 mainly found 4100–4800m above sea level. Wetlands had changed, and the changing area (expansion and contraction) added up to 94.5km2 or 5.6% from 1976–2006. Temporal-spatial variation in wetlands and land cover imply that regressive succession has occurred in some areas. Natural driving forces are key factors. Data suggest that creation of the Mount Qomolangma (Everest) National Nature Preserve in 1988 positively impacted wetland conservation. KeywordsLands cover change–Qomolangma–Remote sensing–Tibetan Plateau
The interaction of ground water with prairie wetlands in the Cottonwood Lake area has been the focus of research by the U.S. Geological Survey and the U.S. Fish and Wildlife Service since 1977. During this time, climatic conditions at the site ranged from near the driest to near the wettest of the century. Water levels in wetlands and in water-table wells throughout the study area responded to these changing climate conditions in a variety of ways. The topographically highest wetlands recharged ground water whenever they received water from precipitation. The wetland of principal interest, Wetland P1, which is at an intermediate altitude, received ground-water discharge much of the time, but it also had transpiration-induced seepage from it along parts of its perimeter during all but the wettest year. The large fluctuations of the water table in response to recharge and transpiration reflect the ease with which water moves vertically through the fractured till. Lateral movement of ground water is much slower; pore-water moves vertically through the fractured till. Lateral movement of ground water is much slower; pore-water velocities are generally less than 3 m yr−1. The water supply to the wetlands is largely from precipitation during fall, winter, and spring. During these periods, precipitation either falls directly on the wetland, or precipitation that falls on the upland runs over frozen soils or saturated soils into the wetland. The average ratio of stage rise to total overwinter precipitation was 2.59 for the 12-year study period. After plants leaf out, precipitation generally results in much lower rises of the wetland water level. The average ratio of stage rise to over-summer precipitation was less than 1.0.
Sultan Marshes, an important ecosystem and wildlife refuge in the Develi Basin in Turkey, originally included two lakes and two freshwater marshes, with a total surface area of 176 km2, surrounded by wet meadows and salt steppes. The Develi Irrigation Project changed the Sultan Marshes severely starting in 1988 by diverting surface and ground-water flows from the wetlands. Water diversions caused more than 1 m decline in water levels in the lakes and marshes. Spatial changes in the Sultan Marshes ecosystem with time were analyzed using Landsat images from 1980, 1987, 2000, and 2003 that were transformed into five information classes (water, marsh, agriculture, dry lake, and steppe) by unsupervised classification. Changes were identified by a post-classification change detection method. Classification accuracies were 89% to 93%, and accuracies of the change maps were 80% to 85%. The analysis showed that lake surface areas decreased by 93% from 1980 to 2003. Yay Lake was almost completely dry in 2003. The marshes receded more than 50%, and the surrounding steppe expanded into the lakes and marshes. Agriculture expanded in the western and eastern parts (Kepir Marshes) of the study area. Although the years 2000 and 2003 had lower than average annual precipitation, and lower annual precipitation than in 1980 and 1987, the changes in Sultan Marshes are so large that they cannot be solely attributed to weather fluctuations. Surface water diversions and increased use of spring waters and ground water are responsible for the changes.
A two-stage, stratified, systematic sample design was implemented in the Willamette Valley, Oregon, USA, to quantify wetland and land-use changes from the 1980s to the 1990s. The Stage 1 sample (n=711) was drawn from public land survey sections and was stratified by land use and runoff potential. The Stage II sample (n=114) re-sampled the Stage I sample stratified by the amount of hydric soils identified in the Stage 1 sample. Wetland and upland classes were delineated on large-scale aerial photographs, digitized into ARC/Info coverages, and compared to quantify land-cover changes. Total loss of wetlands to uplands during the study period was about 3,800 ha, representing a 2.1 percent wetland loss from the 1980s. The net loss after adjusting for wetland gains was about 2,750 ha. During the study period, 70 percent of the wetland loss was associated with agriculture, six percent was lost to urbanization, and 24 percent was lost to other changes. The loss of wetlands to agriculture and the conversion of wetland types was consistent with a pronounced climatic component related to below-normal precipitation from 1985 to 1994, although continued installation of tile drains and expansion of irrigated agriculture also may have contributed to the changes. The loss of wetlands to agriculture raised questions regarding the effectiveness of current agricultural wetland policy, which appears ill-prepared to protect small wetlands or to deal with loss of wetlands from intensified use of existing farmland. This study identified a larger number and area of wetlands compared with national wetland surveys because of the larger scale data used in this study, the nature of the strata used in the statistical design, and the inclusion of palustrine farmed wetlands in the landuse classification.
Species composition, basal area, and density of wetland sites in Louisiana and South Carolina in 1987 and 1999.
Paired plots were established across a soil moisture gradient (dry, periodically flooded, flooded) in three forested wetland watersheds in Louisiana and South Carolina, USA in 1986–1987. All trees greater than 10-cm diameter at breast height were tagged and measured annually through 1999 to determine density, basal area changes, ingrowth, and mortality. A greater number of tree species was found in South Carolina dry and periodically flooded sites than in Louisiana. Flooded sites in both states were dominated by water tupelo (Nyssa aquatica) and baldcypress (Taxodium distichum). The overall trend in density in both states was flooded > periodically flooded > dry. From 1987 to 1999, density decreased in all of the Louisiana sites except one, while in South Carolina, density remained the same or increased in four of the sites and decreased in the other four. The greatest changes in density occurred in those sites where water-level changes were occurring and in areas where storm winds struck. Basal area in 1987 was similar in both states, ranging from 20.8 to 55.2 m2/ha in Louisiana and 24.0 to 49.5 m2/ha in South Carolina. Flooded sites had the greatest basal area, and periodically flooded and dry sites had similar basal areas. Mortality rates in Louisiana and South Carolina forested wetlands are typically low (around 2%/year) in areas that have not been altered hydrologically. Annual mortality in Louisiana plots with increased water levels rose from 4% in 1987 to 16% in 1997. Wind storm events significantly increased mortality rates, and mortality rates remained high for years after the event, as damaged trees died. Of special concern are areas like the Verret Basin site where the exotic, invasive species Chinese tallow (Sapium sebiferum) invaded after Hurricane Andrew and has the potential to become a dominant canopy tree in the future.
Properties of 7 wetland sediments used in sorption-desorption experiment.
Rate of 2,4-D desorption from sediments within 2 hours after sorption as a function of sediment organic carbon content at 5 and 25uC. Regression lines reflect an average across initial 2,4-D concentrations. Sediment 4 (organic matter 5 3.8%) was excluded because replicates demonstrated large variations in desorption results, relative to other sediments.
Sediment properties and 2,4-D sorption coefficients for 41 wetland sediments collected from Alberta, Saskatchewan, and Manitoba, Canada.
Freundlich sorption coefficient, Kf, and Freundlich sorption constant, 1/n, for selected sediments.
The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is among the most frequently detected pesticides in the water-column of surface waters in Canada. Bottom sediments (0 to 15 cm) were collected in 41 wetlands across the prairie region of Canada and analyzed for organic carbon content (OC), pH, and texture. Using batch equilibrium experiments at 5 and 25°C, the herbicide sorption coefficient, Kd, was determined for 41 sediments, along with more comprehensive herbicide sorption and desorption isotherms for 7 of these 41 sediments. The 2,4-D Kd was positively correlated with OC and negatively correlated with sediment pH. A small (3%) significant increase in the 2,4-D Kd occurred when the temperature was at 25°C rather than 5°C. Desorption rates were faster for sediments with ≤ 2.4% OC and exhibited little or no hysteresis, compared to sediments with ≥ 5.9% OC that consistently exhibited hysteresis. We conclude that bottom sediments could serve as a source of 2,4-D to the water-column regardless of water temperature (5 to 25°C). However, the potential for accumulation of 2,4-D in wetland sediments would be small because between 62 and 100% of the 2,4-D sorbed by sediments was released after 8 hours.
A recent conflict between Lebanon and Israel began July 12, 2006, and ended August 14, 2006, with one of the hardest hit regions being the Tyre or Sour area. There was concern about environmental damage to one of the most prominent environmental sites in the region, the Tyre Coast Nature Reserve (TCNR) and the artesian springs within it. The recharge zone of these springs lies to the east of the TCNR in an area that was subject to severe bombing. The main objective of this study was to assess the impact of the bombing on the water quality of these springs by comparing water quality data collected before the July war with those collected shortly after the cessation of hostilities. The physicochemical characteristics of the water samples were mostly within normal ranges. However, a spike in the concentrations of nickel and chromium did appear in one post-conflict sample. Therefore, to ascertain that no permanent contamination has occurred, continuous monitoring of the artesian springs and the receiving portion of the Mediterranean should be carried out.
Finding environmental constraints on the establishment in salt marshes of Phragmites australis may help elucidate human activities that facilitated its invasion. We tested the effects of rhizome burial, salinity, anoxia, and sulfides on emergence, survival, growth, biomass production, and spread. In greenhouse and field experiments, rhizome burial facilitated initial emergence in well-drained soils. Rhizome emergence was prohibited in poorly drained treatments, regardless of salinity or sulfide concentrations. Emergence in well-drained treatments was not affected by salinity or sulfides, but survival, growth, and biomass storage of the culms and rhizomes were diminished in salt treatments. Combined with other studies, these results indicate that Phragmites invasion is a multi-stage process, with emergence constrained by poor drainage and survival constrained by lack of burial opportunities and salinity. These conditions constrain early stages of the invasion only, as later stages of the invasion can spread into anoxic and high salinity areas. These results also suggest that the process of invasion is facilitated by different human activities at different stages. Emergence is facilitated by soil disturbance, rhizome burial, and altered drainage. Survival through the first season can be facilitated through activities that lower porewater salinity.
In the past 100 years, the hydrology and nutrient levels of the Florida Everglades, USA, have been drastically altered by a system of canals and dikes and urban and agricultural development. Levels of soil total phosphorus (TP) have become elevated in the northern part of Water Conservation Area 2A (WCA-2A). Vegetation community changes in the past 20 years in this impacted area are characterized by the invasion ofTypha domingensis into historicallyCladium jamaicense marshes and aquatic slough communities. The objective of this study was to calibrate modern pollen assemblage data from surface soil samples with soil nutrient data and observed macrophyte changes across a TP gradient at 31 sites in WCA-2A. Soil TP, nitrogen, carbon, biogenic silica, and calcium analyses of soils were included in the study. Modern pollen distribution corresponds to living macrophyte community variation along a TP gradient in WCA-2A. Pollen assemblages associated with three major marsh types in WCA-2A (Typha-dominated,Cladium-dominated, mixedTypha-Cladium) can be defined. Multivariate statistics show that the parameters measured explain about half of the variance in pollen data. TP was the only parameter measured that explains a significant amount of the variation. The remaining chemical variables tested were not significant. Clearly, other environmental factors not measured for this study also affect distributions. Although not analyzed statistically, hydrology patterns in WCA-2A probably play an important role based on pollen cluster analysis. A weighted averaging (WA) regression model for TP from the pollen assemblages has a high correlation coefficient (r2=0.76) between observed and inferred values. This model can be used to estimate present plant community structure based on soil TP content in WCA-2A (e.g., optimal TP levels for specific taxa) and past TP levels based on pollen assemblages found in dated soil core subsamples. moreover, historical plant community assemblages can be reconstructed from pollen profiles. Such reconstructions are essential to the restoration of the Everglades.
The Santa Margarita River is one of the few remaining free-flowing river systems on the Southern California coastal plain, and it provides one of the most expansive, unspoiled riparian habitats in Southern California. There is concern among resource managers that the cumulative impacts associated with rapid development of the upper watershed will degrade the ecological integrity of the entire watershed. In response to this concern, we assessed the impacts of development projects in this watershed, which were subject to regulation under Section 404 of the Clean Water Act. Cumulative impacts were assessed by comparing the conditions present at each project site prior to issuance of the Section 404 permit to conditions present after issuance of the permit. Changes between pre- and post-project site conditions were evaluated using a semantic categorization for the following six criteria: endangered species habitat, structural diversity, spatial diversity, undeveloped open space, linear contiguity, and adjacent habitat. The impact assessment showed that although the Section 404 permit program has attenuated project impacts, it has failed at minimizing cumulative impacts. Projects permitted under Section 404 contributed to the disruption of movement corridors linking the habitats of the upper and lower watershed and resulted in extensive floodplain encroachment, which may have hydrologic as well as ecological implications. More importantly, this assessment identified the types of activities and habitat functions that should be addressed during revisions in permitting procedures and should be emphasized in the watershed planning process. These conclusions will be incorporated into an ongoing Advanced Identification study sponsored by the U.S. Environmental Protection Agency and U.S. Army Corps of Engineers to develop a management plan for the Santa Margarita Watershed.
In order to receive a Department of Army permit to discharge dredged or fill material into “waters of the United States,” including wetlands, a permit applicant may have to clearly demonstrate that the proposed discharge is unavoidable and the least environmentally-damaging practicable alternative. Failure to do so as required under EPA’s 404(b)(1) Guidelines (40 CFR 230) may result in permit denial. Generally, the practicable alternative that involves the least amount of filled “waters” will be considered the least damaging; practicable alternatives that avoid “special aquatic sites” such as wetlands are always presumed to be less damaging environmentally than those that do not. “Practicable” alternatives are not unreasonably costly, but may produce less return on investment than is desired by the permit applicant. Such alternatives are considered available if they are owned by the applicant or if they can be obtained, utilized, expanded, or managed during the planning and permitting phases of the proposed project. In order for the analysis of alternatives to be useful to the permitting process, the project purpose must be defined generically, and separate analyses may be required for each component of a multiple-purpose project. The geographic scope of analysis must remain broad enough to reasonably consider all environmentally-preferable sites where the basic project purpose could be achieved. We conclude that an alternative analysis, performed properly and early in the project formulation stage can reduce project costs, increase certainty, and most importantly, result in avoidance and protection of valuable wetland resources.
Over the past 200 years, an estimated 53% (about 47 million ha) of the original wetlands in the conterminous United States have been lost, mainly as a result of various human activities. Despite the importance of wetlands (particularly along the coast), and a longstanding federal policy framework meant to protect their integrity, the cumulative impact on these natural systems over large areas is poorly understood. We address this lack of research by mapping and conducting descriptive spatial analyses of federal wetland alteration permits (pursuant to section 404 of the Clean Water Act) across 85 watersheds in Florida and coastal Texas from 1991 to 2003. Results show that more than half of the permits issued in both states (60%) fell under the Nationwide permitting category. Permits issued in Texas were typically located outside of urban areas (78%) and outside 100-year floodplains (61%). More than half of permits issued in Florida were within urban areas (57%) and outside of 100-year floodplains (51%). The most affected wetlands types were estuarine in Texas (47%) and palustrine in Florida (55%). We expect that an additional outcome of this work will be an increased awareness of the cumulative depletion of wetlands and loss of ecological services in these urbanized areas, perhaps leading to increased conservation efforts.
Information was complied on permits issued under Section 404 of the Clean Water Act for alteration of freshwater wetlands from January 1982-August 1987 in Louisiana, Alabama, and Mississippi. The location, area, wetland type, and other data describing the impacted and compensatory (i.e., created, restored, and preserved) wetlands were compiled and analyzed. Trends in Louisiana, the state with the most permits issued, were emphasized, and a synopsis of the results from Alabama and Mississippi is presented for comparison. The objective of the study was to uncover patterns and trends in Section 404 permitting in the three states to document the effects of the permit decisions. Only the information contained in the permit record was compiled and analyzed. No judgment was made concerning compliance with the terms of the permits or whether the compensatory wetland replaced the ecological functions of the wetland destroyed. Neither could be determined from the permit record. In Louisiana, 226 permits were issued, resulting in a potential loss of over 10,000 hectares of primarily forested wetlands. Compensatory mitigation was required in 93 permits (41%); however, only 8% of the total area impacted by all permits issued was compensated. Over 50% of the wetlands impacted were less than or equal to 4 hectares in size. Permitted activities occurred throughout Louisiana, but the majority were located along the Gulf coast and the Mississippi and Atchafalaya Rivers. Food chain support and wildlife habitat were the most commonly listed impacted functions in the permit record. Specific objectives for the mitigation projects were not documented. Only 10% of the compensatory wetlands were monitored by at least one site visit. The Section 404 permitting program could be evaluated more effectively if record-keeping was standardized. The accuracy and thoroughness of this report was affected by poor record-keeping and inconcise permit language. Requirements for follow-up monitoring and increasing the specificity of the information contained in the permits would provide information on the impacts to wetlands and their functions to be considered in future permit decisions.
Lake Chicot, in south central Louisiana, USA, was created in 1943 by the impoundment of Chicot Bayou. Extensive establishment of woody seedlings occurred in the lake during a 1.5 year period, including the growing seasons of both 1986 and 1987, when the reservoir was drained for repair work on the dam. Study plots were established in September 1986 to document woody vegetation establishment and to provide a baseline by which to monitor survival and growth after flooding resumed.Taxodium distichum seedlings were the dominant species after one growing season, with a maximum density of 50 seedlings/m2, an average of about 2/m2, and an average height of 75 cm. The lake was reflooded at the end of 1987, bringing water depths at the study plots up to about 1.4 m. Temporary drawdowns were again conducted during the fall of 1992 and 1996. In December 1992, the site was revisited, new plots established, and saplings counted and measured. There was an average of 2.1T. distichum stems/m2, and the average height was 315 cm. After the 1996 growing season, there was still an average of about 1.9 stems/m2, and the average height had increased to 476 cm. Preservation ofT. distichum forests in relatively shallow but continuously flooded areas such as Lake Chicot may be a simple matter of draining the lake after a good seed crop and maintaining the drawdown long enough for the seedlings to grow taller than the typical growing season water level. In the case of Lake Chicot, this period was two growing seasons. This action will mimic natural, drought-related drawdowns of the lake and will allow the seedlings to establish themselves and grow tall enough to survive normal lake water levels.
We examined data collected on fish assemblage structure among three differing floodplain types (broad, moderate, and narrow) during the 1993 flood in the unimpounded reach of the upper Mississippi River. This 500 year flood event provided a unique opportunity to investigate fish-floodplain function because the main river channel is otherwise typically disjunct from approximately 82% of its floodplain by an extensive levee system. Fishes were sampled during three separate periods, and 42 species of adult and young-of-the-year (YOY) fishes were captured. Analysis of similarity (ANOSIM) revealed a significant and distinguishable difference between both adult and YOY assemblage structure among the three floodplain types. Analysis of variance revealed that Secchi transparency, turbidity, water velocity, and dissolved oxygen were significantly different among the floodplain types. However, only depth of gear deployment and Secchi transparency were significantly correlated with adult assemblage structure. None of these variables were significantly correlated with YOY assemblage structure. The numerically abundant families (adult and YOY catches combined) on the floodplain included Centrarchidae, Ictularidae, and Cyprinidae. Both native and non-native fishes were captured on the floodplain, and several of the numerically abundant species that were captured on the floodplain peaked in catch-per-unit-effort 1–3 years after the 1993 flood event. This suggests that some species may have used flooded terrestrial habitat for spawning, feeding, or both. The findings from our study provide much needed insight into fish-floodplain function in a temperate, channelized river system and suggest that lateral connectivity of the main river channel to less degraded reaches of its floodplain should become a management priority not only to maintain faunal biodiversity but also potentially reduce the impacts of non-native species in large river systems.
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.
Drainage ditches and ground-water gradients in abandoned agricultural sapric peatlands (mucklands) produce distinctive vegetation patterns. Ditches in abandoned mucklands were ineffective in creating ground-water depression in adjacent soil, while ditches in a newly-cleared muckland were effective in doing so. Upon abandonment, drainage ditches are subject to bank erosion and sedimentation. Coupled with years of soil subsidence and an altered hydrologic regime, ditches lose effectiveness in draining and function merely as small-scale topographic depressions, providing linear zones of seasonally high water levels. Species are distributed on abandoned mucklands in association with soil moisture conditions induced by topographic variation at both small (i.e., ditches) and larger (i.e., site-wide) spatial scales. Vegetation that is usually restricted to moist or saturated soils had greater cover closer to or within drainage ditches or in other topographically low areas, while species with low fidelity to saturated soil dominated the remaining drier areas. Some shrub species had slightly greater stem densities either within or immediately adjacent to ditches, resulting in a “parallel” distribution (i.e., illustrating ditch fidelity). Species having higher affinity to lower soil moisture conditions, such as quaking aspen (Populus tremuloides), showed significantly greater stem density in areas farther away from ditches. Ground-water levels are of primary importance in affecting distribution patterns on naturally revegetating, abandoned agricultural mucklands. The accuracy of the wetland indicator status for woody and herbaceous species encountered on these abandoned mucklands is supported quantitatively by direct gradient analysis. The functioning of existing drainage ditch systems should be assessed prior to any mitigation or restoration activities.
Water table levels at the Cacouna bog (dashed line represents the average site water table). The ‘ threshold ’ level (> − 0.4 m) identifies water table levels which are generally suitable for moss survival at the Cacouna bog (Price and Whitehead 2001). Water table levels near to (7 m upslope; grey) and far from (153 m upslope, black) a peat dam illustrate the non-uniform rise of water table levels following rewetting. Black bars represent precipitation (P) 
Artificial drainage networks established throughout peatlands during the peat extraction process often remain active following abandonment, maintaining a water table relatively far from the surface of the peat, and hindering the survival and reestablishment of Sphagnum mosses. As an initial restoration effort, the primary drainage network of an abandoned cutover peatland was blocked with a series of peat dams, consequently reducing the runoff efficiency and causing the site-average water table to rise by 32cm. Higher water tables and a blocked drainage network resulted in increased runoff variability, dependent upon antecedent conditions (capacity to retain additional water on-site), and event-based precipitation dynamics. Evapotranspiration (ET) rates were 25% higher following rewetting (3.6mmday−1) compared to pre-restoration ET rates of 2.7mmday−1. Total storage changes were restricted following rewetting, as a factor of the reduced runoff losses limiting water table drawdown, thereby constraining peat compression and preventing undue drying of the unsaturated zone. An average surface level rebound of 3cm was observed, increasing the mean hydraulic conductivity by an order of magnitude. Changes to the system hydrology following restoration efforts produced hydrological conditions more favourable for the recolonization of Sphagnum mosses. KeywordsHydraulic conductivity–Peat–Rewetting– Sphagnum moss–Water balance
We examined plant recruitment from two soil seed banks used in the freshwater wetland restoration of an abandoned sand mine in South Brunswick, New Jersey. One seed bank was already present at the mine prior to restoration; the other was imported from a nearby wetland to be destroyed by road development. We also investigated the effects of pH and water regime on recruitment in a greenhouse study and assessed plant recruitment at the restoration site during the first growing season. Multivariate analysis of recruitment in greenhouse communities revealed differential responses of the two seed banks to pH and water regime treatments. In the wetland soil, species richness and plant density responded favorably to inundation and increased pH treatments. In the mine soil, species richness and density were greatest with non-inundated and unadjusted pH conditions. The imported seed bank was characterized by greater species richness (n=21) than the mine seed bank (n=14). Mean recruit density was also greater in the wetland soil (263.6 individuals/m2) than the mine soil (60.1 individuals/m2). Recruits unique to the imported wetland seed bank included a significant proportion of obligate wetland species (52.4%). More species were censused in the field study (82) compared to the greenhouse study (24), with 23.2% of species present in both studies. A lower proportion of obligate wetland species (24.0%) was present in the field. The imported wetland seed bank was the major contributor to species richness and plant density, indicating that the use of imported soils as an amendment may enhance success of wetland restoration projects.
After 30 years of abandonment, a block-cut peatland near Cacouna, Quebec, Canada, has naturally regenerated Sphagnum mosses on <10% of its area, typical for these disturbed systems. Distinct hydrologic conditions were observed where Sphagnum has successfully recolonized, providing a basis for establishing thresholds that can be targeted by peatland restoration managers. Sites where Sphagnum mosses recolonized were characterized by high water table (mean−24.9±14.3 cm), soil moisture (ϕ) > 50%, and soil-water pressure (Ψ)≥ 100 mb. These hydrologic indicators were spatially organized according to the morphology of block- cut trenches, which typically include raised baulks, shallow ditches, and the convex skag (unused turf) deposits along the central axis of the trench. Topographically low areas like the shallow ditches (D) and lower parts of the skag (LS) adjacent to the ditches maintained ϕ and Ψ > 50% and − 100 mb, respectively, for 100% of the summer period. About 83% of all Sphagnum recolonization that occurred in the study trench did so in these areas. In more raised areas like the mid- and center portion of the skag, ϕ and Ψ eventually fell below these thresholds, and these areas generally did not support Sphagnum, except in a few localized microtopographic depressions in the lower (downslope) end of the trench. While this lower end of the trench had all the Sphagnum species that were present in the trench, even there it was only 38% of the total area. It seems that even short periods of low Ψ may restrict Sphagnum reestablishment in an otherwise favorably wet site.
Early attempts at peatland restoration have been aimed mostly at rewetting the peat, which alone has proven inadequate to ensure good regeneration ofSphagnum mosses.Sphagnum mosses can be actively reintroduced by scatteringSphagnum fragments (diaspores) on bare peat surfaces and by sheltering them against desiccation. The present study aims at refining the restoration techniques to reintroduceSphagnum where the surface conditions of cutover peatlands are too harsh for naturalSphagnum establishment. The objective is to increase local moisture conditions of the peat by reprofiling the surface to invert the camber created during drainage operations.Sphagnum diaspores were spread in the concavity. Reprofiling fields increasedSphagnum establishment compared to control sites. The addition of two plastic sheets on the edge of the field reduced evaporation and directed precipitation towards the middle of the field. When they were combined with reprofiling, there was a further increase in the establishment success ofSphagnum.
Cranberry agriculture is a major land use in parts of the New Jersey Pinelands, USA. We compared the composition of genus-level macroinvertebrate assemblages collected from three habitats (muck, vegetated muck, and woody debris) in 12 New Jersey Pinelands blackwater streams draining forest, abandoned-cranberry bogs, and active-cranberry bogs and evaluated whether variations in macroinvertebrate assemblages were related to differences in land uses within the associated drainage basins. All 12 streams were relatively slow moving and acidic, with low conductance values and dissolved-oxygen concentrations. Muck was the dominant substrate at most stream sites. Many of the taxa that we encountered are adapted to lentic habitats, slow-moving lotic habitats, or low-oxygen environments. Macroinvertebrate composition differed significantly between the active-cranberry streams and the other two stream types and was associated with a complex environmental gradient represented by variations in dissolved oxygen, temperature, specific conductance, stream width, and woody debris. Overall, the effect of stream type appeared to overshadow that of the three different habitats. Although we cannot conclude that subtle between-site differences in dissolved oxygen were responsible for variations in community composition, many of the genera associated with the forest and abandoned-bog/active-cranberry ends of the community gradient are reported to have contrasting tolerances to low-oxygen levels. The relationship between reduced canopy cover and both lower woody-debris cover and higher stream temperatures, which can influence dissolved-oxygen levels, was most likely related to forest-canopy removal associated with historic- and active-cranberry agriculture.
During 1991 and 1992, we studied 92 wetlands, including open water (ponds) and emergent communities, created as a result of Wyoming Abandoned Mine Lands’ (AML) reclamation efforts in northeast Wyoming. Through these activities, over 300 wetlands were filled, reclaimed, created, or otherwise modified. For mitigation purposes, wetlands to be filled or modified were first evaluated using a Wetland Habitat Value (WHV) Model. Using the model, wetland losses were mitigated by increasing the WHV of some wetlands or by creating new wetlands elsewhere. We evaluated model performance in offsetting wetland loss and how well the model predicted waterfowl use. We also compared post-reclamation wetland sizes to those predicted by engineering plans and submitted for Section 404 permit approval. In our study, predicted WHVs were overestimated at 100% of the wetlands for which pre-reclamation WHVs were available (n=8). The most commonly overestimated variables were size, fraction of emergent cover, adjacent upland cover, and the number of bays and peninsulas. We obtained pre-construction size estimates for 64 of the original 80 wetlands. Fifty-five of 64 wetlands were smaller than pre-reclamation engineering goals. The WHV Model accurately predicted use of wetlands by migrating and breeding Canada geese (Branta canadensis), migrating dabbling ducks, and migrating diving ducks. Future users of the model must be careful not to overestimate results of planned mitigation efforts. Predicted size of constructed wetlands may be commonly overestimated; this possibility should be considered in mitigation plans, especially those involving wetland destruction.
We monitored 35 temporary wetlands in a ridge region (Rothrock State Forest=1991-R) of central Pennsylvania in 1991 and 15 temporary wetlands in each of three regions across a ridge (Rothrock State Forest=1992-R), plateau (Allegheny Front=1992-A), and valley (Barrens area, State Game lands=1992-B) landscape in central Pennsylvania in 1992 in order to identify correlations among several abiotic variables and breeding success of three amphibians (wood frogs—Rana sylvatica, Jefferson salamanders—Ambystoma jeffersonianum, and spotted salamanders—A. maculatum). The number of egg masses deposited byA. jeffersonianum was correlated positively with pH (1991-R, 1992-R) and alkalinity (1991-R) and negatively with [Al] (1991-R). Egg deposition byA. maculatum was correlated positively with pH (1991-R) and pond volume (1991-R, 1992-B) and negatively with total cations (Na, K, Mg, Ca, specific conductance) (1991-R) and [Si] (1992-B). Egg deposition byR. sylvatica was correlated positively with pond volume (1991-R, 1992-R) and dissolved organic carbon (1991-R). Three days following a rain event of 1.9 cm in April, 1991, the pH in four of nine ponds was significantly lower than three and five days prior to the rainfall. There were differences among some of the three regions in pond pH, [K], [Ca], [Al], [ortho-P], [dissolved organic carbon], alkalinity, [Zn], volume, and the number of egg masses ofR. sylvatica andA. maculatum, suggesting that temporary ponds are rather heterogeneous in their abiotic and biotic characteristics. There are landscapescale patterns (ridge, valley, plateau) that are especially deserving of additional study. Amphibian breeding success in temporary ponds of central Pennsylvania can be predicted in part by abiotic conditions such as pH, [Al], [total cations], [dissolved organic carbon], [Si], and pond volume. Further work is needed to determine which of these variables are causally linked to amphibian breeding and why there is variation among sites and years in the degree of correlation among abiotic and biotic variables.
Annual production of vegetation is an important indicator of various ecosystem processes in coastal marshes; many factors, both biotic and abiotic, can influence production of aboveground biomass. Using a 14-year data set, we evaluated the relative influence of 38 biotic and abiotic factors on annual aboveground biomass of an intermediate coastal marsh on the upper Gulf Coast of Texas. We used visual obstruction (VO) measurements as a surrogate variable in a prediction model to estimate available aboveground biomass in the marsh. Available biomass was greatest (3.34 kg/m2) when sampling site was flooded. Plant growth form, type of animal present, and composition of the ground cover influenced biomass of the marsh. Presence of insects was related to biomass (regression beta weight = 0.28), uniquely accounting for 7.6% of the incremental variance in biomass. The presence of moderate amounts of litter was also related to available biomass (beta weight = 0.86). Soil capping had little or no influence on aboveground biomass. Implementing standard protocols for long-term vegetation monitoring can be cost and time intensive. Our results suggest quantitative measurement of VO and qualitative observation of few variables (standing water, insects, and litter) measured annually can yield a reasonable assessment of aboveground biomass of intermediate coastal marshes.
Fish that co-occur in intertidal salt marshes in coastal Virginia showed some interspecific differences in tolerance to abiotic stresses. This is noteworthy since these sympatric fish would appear to be adapted to and constrained by similar environmental conditions. In preliminary acute range-finding tests, there were significant overall differences among three species in tolerance to high temperature, low pH, and hyposaline transfer. There were also significant differences between species in median lethal high temperatures (two species) and low pH (five species) at 96 h. The 96 h pH50 in sea water was especially divergent, withMenidia beryllina being the least tolerant (pH50=4.62) andFundulus luciae the most tolerant (pH50=3.60). The hierarchy of tolerance among species was not consistent across all abiotic stresses. The growth ofLucania parva orFundulus heteroclitus was not generally affected by salinities of 3.5–35 ppt or 0–35 ppt, respectively. These results suggest that selective pressures on each species have resulted in different suites of physiological adaptations to resist spatial and/or temporal changes in the abiotic environment. Such differences in tolerance might affect competitive and/or predaceous interactions among these fishes in a varying abiotic environment. The physiological tolerances of each species and the effects of any such differences on the fish assemblage of intertidal marshes need to be studied further. The indirect effects of variations in abiotic factors on fish may also be considerable.
The above-ground net primary production (NPP) and litter fall of five peatlands (bog, poor fen, wooded moderate-rich fen, lacustrine sedge fen, and extreme-rich fen) representing the bog-rich fen gradient in central Alberta, Canada were measured during two growing seasons. Total above-ground NPP increased along the gradient from the bog to moderate-rich fen and then decreased in the sedge and extreme-rich fens. Above-ground NPP in the bog (264–297 g·m−2·yr−1) was low compared to other North American bogs, while the Alberta fens had intermediate values of NPP (214–360 g·m−2·yr−1) compared to other North American fens. Moss NPP was lowest in the sedge fen but did not differ significantly between the other peatlands. Vascular plant NPP was highest in the poor fen, moderate-rich fen, and sedge fen and lowest in the bog and extreme-rich fen. Herb NPP tended to increase along the bog-rich fen gradient, while shrub NPP tended to decrease along the gradient. Litter fall was greatest in the poor and moderate-rich fens and lowest in the sedge and extreme-rich fens.
Percentage cover of bog and fen species comprising at least 2% plot area or 2% of ANPP (Table 1) for the final year of treatment 1997. The genus Rhynchospora is also separated into flowering R. alba and flowering R. fusca. The non-flowering Rhynchospora is listed as Rhynchospora spp. C represents control plots; LNLP represents low N and
Above-ground net primary production by treatment for 1997 bog functional groups. Control indicates no nutrients, LNLP indicates low N and low P, HNHP indicates high N and high P, etc. Fertilizer codes with the addition of 'L' indicate lime addition as well. Error bars represent standard error, n 2. Bryophyte values that similar (LSD p 0.05) are represented by bars having the same letters (ab series). Shrub values that are similar (LSD p 0.05) are represented by bars having the same letters (xy series). There were no significant fertilizerlime differences in graminoid response.  
Above-ground net primary production by treatment for 1997 fen functional groups. Control indicates no nutrients, LNLP indicates low N and low P, HNHP indicates high N and high P, etc. Fertilizer codes with the addition of 'L' indicate lime addition as well. Error bars represent standard error, n 2. Graminoid values that similar (LSD p 0.05) are represented by bars having the same letters (ab series). There were no significant fertilizerlime differences in 1997 shrub response.
Nutrient limitation is often assumed to be similar among the species of a plant community. However, limitation can differ among ecosystems and among life forms and individual species within a particular ecosystem. Peatlands have some of the lowest nutrient availabilities and highest acidities among wetland types, but the relative roles of nutrient limitation and pH stress in structuring peatland plant communities are unknown. Accordingly, we measured changes in above-ground net primary production (ANPP) and percent cover of plants to additions of low levels of N, P, and calcium carbonate in a bog and fen in northern Minnesota, USA. Plots were treated for three years with a combination of 2 or 6 g N m-2 yr-1 as ammonium, 0.67 or 2 g P m-2 yr-1, and/or calcium carbonate to raise the pH of the bog from 3.8 to 4.9 and the pH of the fen from 4.9 to 6.4. In the bog, the low N treatment increased ANPP, whereas the high N treatment inhibited ANPP. Lime addition also stimulated ANPP. The whole-community bog response was largely due to bryophytes, which accounted for 76% of ANPP on average. However, the productivity of the shrub community (18% of total ANPP) increased with P additions but only during the third year of fertilizer application. Productivity of the bog graminoids did not respond significantly to any addition. Fen ANPP was stimulated by P addition, but the effect was isolated to graminoids (95% of total ANPP), and this was largely due to the response of Carex exilis. Our results suggest that low nutrient availability does not necessarily imply nutrient limitation of peatland plant communities. Furthermore, life forms and individual species responded differently, indicating that there are several levels of nutrient limitation within each peatland community. In particular, bog Sphagnum mosses appear to have a very low tolerance for N. Production and community structure were controlled by N-availability and pH in the bog and by P-availability in the fen.
In this work, we propose a new tagging technique to evaluate NAPP in Scirpus giganteus (bulrush), a species commonly found in freshwater marshes of South America. Through this method, a total mean NAPP of 1514.12±305.11 gm−2 year−1 (C.V.=20%) was obtained by a combination of tagging and harvesting entire mats. A maximum living biomass of 1063.60±362.06 g m−2 (C.V.=34%) was registered in February (late summer), which would be the estimation of the total annual NAPP using the traditional peak standing crop method and gives an underestimation of NAPP because it neither considers mortality before the peak biomass is attained, nor does it include any production after peak. As there are no statistically significant changes in the mean living biomass on different sampling dates (df=9, F=2.22, p>0.10), which is an expected situation in a species that grows through the whole year, methods based on changes in living and dead biomass are difficult to apply. The proposed tagging method gives an estimate of NAPP for a species on which more widely used procedures cannot be applied. Moreover, the tagging technique may be applicable for a great number of emergent wetland plants showing similar growth forms.
In order to determine whether nitrogen (N) or phosphorus (P) limits aboveground plant growth in peatlands in Alberta, we fertilized one bog, two fens, and two marshes with N and P at a ratio of 7∶1 (Redfield ratio of these two elemental nutrients in aquatic plants) as well as with water without either fertilizer in 1994. The response of aboveground plant production to N or P was species-specific and varied among the sites. In the bog,Smilacina trifolia, a herb, showed significant increases in net primary production (NPP) after fertilization with N plus water and the addition of water, whileAndromeda polifolia only showed significant increases in NPP after fertilization with N plus water.Ledum groenlandicum, an ericaceous shrub, showed significant decreases in NPP after additions of N plus water, P plus water, and water, whileOxycoccus quadripetalus, another ericaceous shrub, also showed significant decreases of NPP after additions of N plus water and water.Sphagnum fuscum (moss) NPP increased significantly after the additions of water and decreased significantly after the additions of N plus water and P plus water. In the fens and marshes, onlyCarex spp. in the lacustrine sedge fen showed a significant increase in NPP after the addition of N. Vascular NPP (shrubs and herbs combined) did not increase significantly in any of the five peatlands. Total NPP (moss, herb, and shrub strata combined) increased significantly only in the bog after the addition of water due to the dominance of the moss stratum in that site. In the bog, moss growth was limited by water, and herb and shrub growth responses to N and P fertilization were species-specific. Neither N nor P limited aboveground plant production in the fens and marshes.
Sediment filtration potential is well known as a key function of riparian forests; however, the capacity of riparian ecosystems to accumulate sediment without degradation is unclear. This study examined the effects of sediment deposition on productivity, vegetation composition, and structure in riparian forests of ephemeral streams at Fort Benning, Georgia, USA. Sedimentation occurs at Ft. Benning as a result of erosion from unpaved roads situated in sandy soils along slopes and ridges. Seven ephemeral streams were selected to represent a range of sediment deposition rates, and another two were selected as reference catchments. Within all nine catchments, paired plots were established with one plot being delineated in an upper portion of the catchment and another lower, nearer to the ephemeral stream. Upper plots of disturbed catchments showed evidence of sediment accumulation, such as buried tree bases and alluvial fans, while lower plots lacked those indications. Aboveground net primary productivity (ANPP), litterfall nutrient contents, leaf area index (LAI), species composition, and stand structure were compared within and among catchments. Decreases in litterfall, woody increment, ANPP, and LAI were observed with sediment accumulation rates near 0.2 cm yr−1, and an equilibrium response appeared to be reached near 0.5 cm yr−1. Nutrient contents of litterfall followed a similar pattern. Changes in species composition and structure were also observed. In general, reference catchments and lower plots were associated with closed overstory canopies, whereas upper plots had more overstory mortality and heavier densities of saplings and seedlings of shade-intolerant species. These results suggest that sedimentation rates commonly occurring in some riparian forests may alter productivity, structure, and composition. Consequently, riparian functions that are closely linked to forest integrity may be jeopardized as well.
Top-cited authors
Patrick Megonigal
  • Smithsonian Institution
Scott Bridgham
  • University of Oregon
Douglas A. Wilcox
  • State University of New York -- Brockport
Stewart Rood
  • University of Lethbridge
Curtis Richardson
  • Duke University