Salicornia virginica (common pickleweed) is the dominant vascular plant of many saline marshes of the US west coast, yet little is known about seasonal patterns or abiotic factors controlling it. In a southern California salt marsh, quarterly sampling revealed strong seasonal trends, with 2x greater S. virginica biomass in summer than in winter. Tissue nitrogen (N) and phosphorus (P) concentrations were highest in winter and lower in spring and summer, suggesting a dilution of nutrients as plants accumulated biomass during the growing season. Despite high sediment nutrient levels in this marsh, an experiment examining N and P effects still found strong S. virginica responses to N applied biweekly for >1 year. Increases in succulent tissue biomass after N addition were first seen in April 1998 (after fertilization for 11 months); two-fold increases in biomass and the number of branches resulted by the end of the experiment in August 1998. Addition of N increased N concentration in the woody tissues when sampled in August. The N:P ratio increased with N addition beginning in winter (7 months after fertilization began) and continuing through the remainder of the experiment. Effects of P addition were less marked, as adding P did not result in biomass responses; however, it did influence tissue nutrient levels. These amendments increased P concentrations in the woody tissue in August 1998. In contrast to N amendments, which did not affect root nutrient concentrations, P addition led to increases in P content of root tissues in the latter portion of the growing season. These data suggest that increases in nutrients (especially N, but also P) can lead to large changes in S. virginica characteristics even in estuaries with high sediment nutrient levels.

Terracing is a relatively new wetland-restoration technique used to convert shallow subtidal bottom to marsh. This method uses existing bottom sediments to form terraces or ridges at marsh elevation. A terrace field is constructed by arranging these ridges in some pattern that maximizes intertidal edge and minimizes fetch between ridges; the intertidal area is planted with marsh vegetation. We examined the habitat value of terracing for fishery species at Sabine National Wildlife Refuge, Louisiana (USA) in spring and fall 1999 by quantifying and comparing nekton densities in a 9-yr-old terrace field and nearby reference area using a 1-m² drop sampler. Decapod crustaceans were more abundant than fishes, composing 62% and 95% of all organisms we collected in spring and fall, respectively. White shrimp Litopenaeus setiferus, daggerblade grass shrimp Palaemonetes pugio, blue crab Callinectes sapidus, and brown shrimp Farfantepenaeus aztecus accounted for 94% of all crustaceans, whereas 60% of all fishes were gulf menhaden Brevoortia patronus. Mean densities of white shrimp (fall), daggerblade grass shrimp, blue crab, and brown shrimp (spring) were significantly greater in terrace marsh than on non-vegetated bottom in the reference pond. Densities of most nekton on non-vegetated bottom were similar in the terrace field and the reference pond, but gulf menhaden and white shrimp had higher densities at terrace pond sites and brown shrimp (spring) were more abundant at reference pond sites. The pattern for biomass was similar to that for density in that the mean biomass of most species was significantly greater at terrace marsh sites than reference pond sites and similar at terrace and reference pond sites. Terrace marsh, however, was not functionally equivalent to natural marsh, as mean densities of daggerblade grass shrimp (fall), brown shrimp (spring), and blue crab and mean biomass of white shrimp (fall), striped mullet Mugil cephalus (spring), and spotted seatrout Cynoscion nebulosus (fall) were greater at reference marsh sites than terrace marsh sites. Using these density and biomass patterns and the percentage of marsh and pond area in the terrace field, we concluded that terrace fields support higher standing crops of most fishery species compared with shallow marsh ponds of similar size. Future restoration projects could include design changes to increase the proportion of marsh in a terrace field and enhance the habitat value of marsh terraces for fishery species.

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.

Plant decomposition and litter accumulation are important components of wetland functions, yet they have rarely been evaluated in created wetlands. In this study, eleven 20-yr and six 2-yr-old depressional wetlands, the most common type of created wetlands, were investigated. We measured plant decomposition as mass loss over 507 days for both age classes and litter accumulation as litter (detritus) mass present in the 20-yr-old wetlands. The wetlands were all created via excavation and contained shallow facultative wetland and deeper obligate wetland plant communities that were often dominated by Scirpus cyperinus and Typha latifolia, respectively. In the decomposition study, stems and leaves from each species were harvested from an adjacent 20-yr-old wetland site and placed in separate plastic mesh bags. Bags were deployed in March 1994 and were recovered after 2, 161, 258, 364, and 507 days. In the litter accumulation study, plant litter that accumulated on top of alluvium was harvested in 0.25-m² plots adjacent to decomposition bags. Several environmental variables were measured in the 20-yr-old wetlands, including live standing crop biomass (peak aboveground biomass) in 1993 and 1994, nutrient concentrations (in water, soil, and plant tissues), and hydrologic parameters. Decomposition was faster in 20-yr-old wetlands (76% of mass remaining) than in 2-yr-old wetlands (85%) but was well below most literature estimates for comparable species in natural wetlands (53%). Decomposition of S. cyperinus was slower than that for T. latifolia in all 17 wetlands. In the 20-yr-old wetlands, hydrologic variables were important for decomposition of both species. Masses of litter that accumulated during the 20 years since excavation were greater among facultative wetland (764 g/m²) than in obligate wetland communities (368 g/m²). Accumulated litter mass in the facultative wetland community was positively correlated with the S. cyperinus percentage of total live standing crop biomass. Accumulated litter mass in the obligate wetland community was positively correlated with drawdown duration and litter C:N ratios. Decomposition functions of these wetlands are still developing 20 years after creation.

The interaction between plant growth and nutrient availability is an important aspect of vegetation dynamics in wetlands. In this study, seedlings of Typha domingensis were used to assay the nutrient availability of fire-disturbed Florida Everglades soils. Seedlings were planted in soils that had been naturally muck- (MB), surface- (SB), or non-burned (NB) and that showed significant differences in concentrations of inorganic:total phosphorus according to fire severity. After two months of growth, plant height, number of leaves, culm diameter, number of rhizomes, length of rhizomes, live leaf biomass, and above- and below-ground biomass were greatest in MB seedlings. In addition, root architecture and biomass allocation were influenced by soil type. Seedlings from NB and SB soils developed thinner roots with numerous root hairs and had higher percentages of below-ground biomass. In contrast, seedlings grown in muck-burned soils developed large rhizomes in addition to thicker, hairless roots while allocating proportionally more biomass to aboveground parts. Tissue nutrient analyses showed that both experimental and field-harvested plants grown in MB soils contained significantly more phosphorus than plants from SB or NB soils. Typha domingensis has displaced plant communities in areas of the Everglades that receive nutrient-enriched agricultural runoff. However, this study suggests that establishment and expansion of this species also may occur in overdrained regions of the Everglades where muck fires are a frequent occurrence. In addition to creating an opening in the landscape, muck fires increase the bioavailability of soil phosphorus, thus providing a competitive advantage for T. domingensis.

As in many areas of western North America, flood irrigation for hay production has created many wetlands in the Laramie Basin, Wyoming. Since the early 1900s, water from mountain snowmelt has reached wetlands via ditches and as interflow and ground water percolating from flooded fields and unlined ditches. Such systems are viewed as inefficient for irrigation and other human uses because they reduce the volume and increase the salinity of downstream flows. Increasing irrigation efficiency by lining ditches or installing sprinklers would decrease wetland habitat, but such effects are seldom considered. To assess potential impacts of increased irrigation efficiency, we determined how flood irrigation affects the hydrology and types of wetlands in the Laramie Basin. For 74 wetlands with 80 total inflows, just 14% of inflows were as surface flow from natural stream channels. In contrast, 65% of inflows were directly from irrigation: 30% as surface flow from ditches and 35% as interflow percolating from ditches and irrigated fields. Fifteen percent of inflows were as surface flow from other wetlands, and 6% of inflows were from ground water with unknown recharge source (probably either natural streams or irrigation). In this year of high water availability (1999), wetlands receiving surface water generally were fresh or oligosaline regardless of whether that flow was from natural streams, other wetlands, or ditches (mean ± 1 SD = 3.28 ± 5.07 mS/cm, median = 1.60, range 0.07–22.10). In contrast, wetlands receiving water as interflow percolating from ditches or irrigated fields, or as ground water with unknown recharge source, were more likely to have conductivities of mesosaline or higher (mean ± 1 SD = 22.45 ± 32.71 mS/cm, median = 9.08, range 0.60–112.00). Conductivity of surface water in the 74 wetlands (mS/cm) ranged from fresh (0.07) to hypersaline (112.00), with a mean of 10.89 ± 22.80 (SD) and median of 2.60; this range of salinity corresponds to substantial variation in wetland community structure. In the Laramie Basin and similar areas, flood irrigation is critical to the existence, hydrology, and community types of most wetlands, and these effects should be considered in plans to increase irrigation efficiency.

Sediment cores, representing a range of watershed characteristics and anthropogenic impacts, were collected in 11 subalpine marshes in the Lake Tahoe basin, USA and vicinity in order to trace the effect of anthropogenic impacts on sedimentation and sediment accumulation rates. Cores were ²¹⁰Pb-dated using a CRS model, and these data were used to calculate sedimentation rates and sediment accumulation rates, which were compared with environmental variables. Age-depth profiles indicated that sedimentation rates changed at different times in different marshes, and we separated sediment cores into two parts to show sediment characteristic and sediment-accumulation-rate changes. Ranges of dry mass accumulation rates and sedimentation rates were 0.081–1.356 kg m⁻² yr⁻¹ and 0.94–4.64 mm yr⁻¹ in the upper core and 0.094–0.563 kg m⁻² yr⁻¹ and 0.57–1.75 mm yr⁻¹ in the lower core. In general, the cores showed recent increases in sediment accumulation rates. Species composition was related to water quality, with the dominant species changing in a predictable series with decreasing water quality: Nuphar, Nuphar and Carex/Scirpus, Eleocharis, Potamogeton, Ranunculus, and Chara. The effect of a rough road used for timber transport was observed as the change of sediment accumulation rates in Upper Grass Lake. Sediment accumulation rates since the improvement of the rough road decreased to ca. 80 % of those prior to the improvement. Road-salt use was related to relatively high water cation concentrations and conductivity in Meyers Grade Marsh adjacent to Hwy 50. Increased lead accumulation rates and concentrations in more recent sediments at Meyers Grade Marsh and Snow Creek reflect the increasing use of fossil fueled vehicles in this region. Urbanization and animal farming were related to increased N and P concentrations in marsh water. The number of exotic plant species within a marsh was highly correlated with water quality and C and N accumulation rates. This study showed that 8 of the 11 marshes studied are in relatively undisturbed condition, while the remaining 3 have been heavily impacted. Urbanization and increased recreation facilities, and activities are important anthropogenic impacts on subalpine marshes. This study suggests that pristine subalpine marshes be protected from increasing human activities and that marshes impacted by rough roads can be restored to pristine conditions.

Black willow (Salix nigra) is a well-known pioneer species of disturbed riparian areas. It competes for nutrients, light, and water, but it may also act as a “nurse” crop, providing shelter for other species from high light and temperature; so, the overall effect on species planted under a willow canopy could be positive or negative. This experiment examined the response of container-grown seedlings of four tree species outplanted into three habitats: 1) an existing willow stand, 2) a similar habitat, but with the willow canopy removed, and 3) an adjacent grass-dominated area free of willow. After three years, survival rates of overcup oak (Quercus lyrata), baldcypress (Taxodium distichum), and water hickory (Carya aquatica) were not reduced under the willow canopy relative to the other two treatments. Laurel oak (Q. laurifolia) was killed by several floods during the first growing season. Height of baldcypress seedlings planted under a willow canopy was less than for seedlings where the willow had been removed. Water hickory and overcup oak height were not affected by the willow canopy. Elevation of the planting sites, indicating probable soil wetness, was a good indicator of survival when used in conjunction with the species flood-tolerance. The existing willow stand was not detrimental to survival of three of the outplanted tree species. Thus, willow removal is unnecessary for successful outplanting, saving time and money.

Portions of the northern Everglades of Florida, USA have become enriched with phosphorous and have responded with increased plant productivity and increased litter decomposition rates. Many lakes respond to eutrophication with decreased redox potential in sediments. The objective of this study was to determine if there were differences in soil redox potential along a nutrient-enrichment gradient in the Everglades marshes. We measured redox potential, the depth at which iron reduction occurs as determined by steel rod oxidation, and the oxidation state of exchangeable iron along the gradient. The results of redox potentials at fixed depths, redox-potential profiles, and rusting of steel rods all suggest that iron-reducing conditions exist beneath the surface of the sediment in both the unenriched and enriched areas and that differences between the enriched, cattail-invaded area and the unenriched sawgrass areas are either not significant or, in the case of the redox profiles from 20- to 40-cm depth in the soil, of borderline significance and small magnitude (< about 50 mV). The lack of large differences also suggests that reduction of the soil redox potential by eutrophication is not a significant factor influencing the competition between sawgrass and the invading cattail or other biogeochemical differences that have been observed along this gradient.

Standpipe piezometers are often used in wetland hydrologic studies for measuring pore-water pressures and, therefore, hydraulic heads. Here, we consider the errors associated with the use of simple standpipe piezometers in wetland soils. The performance of two typical piezometer designs was assessed. Rather than measure the performance of the piezometer designs in the field, we modelled their response to computer-generated changes in pore-water pressures for three ‘model’ floodplain soils. We showed that for some piezometer design/soil-type combinations, standpipe piezometers can be in considerable error. Greatest errors were found where the less efficient of the two piezometer designs (standpipe inside diameter = 5 cm, outside diameter of intake = 5.6 cm, intake length = 5 cm) was in a poorly permeable silt deposit (hydraulic conductivity = 6 cm d⁻¹) overlain by a permeable sand (hydraulic conductivity = 210 cm d⁻¹). If undetected, these errors could lead wetland researchers and/or consultants to make erroneous conclusions about both patterns and rates of ground-water flow in wetland soils. In field investigations, we recommend that selective use is made of rapidly responding piezometers, such as closed hydraulic piezometers, so that the performance of standpipe piezometers can be assessed.

In this study, we hypothesized that the primary variable determining species responses and interactions within wet/mesic riparian meadows in central Nevada, USA was the water table but that the direct and indirect effects of livestock grazing modified both species responses and interactions. We tested this hypothesis for two widespread riparian species, Carex nebrascensis and Poa pratensis ssp. pratensis, that co-occur but have maximum expression at different water tables. Carex nebrascensis has widely spread tillers typical of ‘guerilla’ plant architecture, while P. pratensis has closely spaced and compact tillers typical of ‘phalanx’ plant architecture. Individuals of both species were grown at mid- and low water tables with or without neighbors and were either clipped or not clipped at the end of the first growing season. For the study site with the most complete record, mean water-table depth during the growing season (May through August) on the mid sites was −32 cm in year 1 and −7cm in year 2. Water-table depth on the low sites was −69 cm in year 1 and −31 cm in year 2. Plant survival, tillering, biomass, and seed production over a 2-yr period were used to quantify the species responses. Water table had no effect on tillering or biomass of C. nebrascensis, indicating that it is adapted for growth and persistence over the range of water tables examined. In contrast, growth and tillering of P. pratensis was severely restricted at more shallow water tables. Poa pratensis had about 50% fewer tillers and lower biomass (9.0 vs 46.5 g) for neighbor-removed plots on mid- than low-water-table sites at one of the study meadows. Further, tiller numbers of P. pratensis increased over time on the low-water-table plots, but decreased on the mid-water-table plots. Clipping had no effect on the survival, tillering, or growth of either species. The clipping treatment may not have removed sufficient leaf mass or may have been applied too near the end of the growing season to elicit a response. Neighborhood removal resulted in a 3- to 10-fold increase in tillering and higher plant mass (1.3 vs. 9.5 g) for C. nebrascensis. Poa pratensis showed an even greater response to neighbor removal. Tillering was 6- to 100-fold greater and mass was 15 to 50 times greater on neighbor removed than neighbor-intact plots. Comparisons between single species and mixed species plots indicated that there was an interaction between the species that limited tiller production in C. nebrascensis. These results indicate that P. pratensis, the ‘phalanx’ species, is capable of more rapidly responding to disturbances that remove neighbors and increase available space than C. nebrascensis, the ‘guerilla’ species. Contrary to previous studies, the interactions between the two species do not seem to be related to plant architecture and can be best attributed to generally greater growth rates and increased competitive ability for P. pratensis at lower water tables. Grazing may further alter the relative competitive ability of the two species in favor of P. pratensis.

The extent of endomycorrhizal colonization of Dasiphora floribunda was measured in 8 calcareous wetlands in eastern New York State, USA. Environmental parameters (pH, conductivity, water-table depth, soil moisture, soil organic matter, soil NH₄ , soil available P, and porewater DIP) varied among wetlands. Soil available P was relatively low and ranged from 2.52 to 15.74 mg-P gdw⁻¹ in all 8 wetlands. Contrary to expectation, the extent of endomycorrhizal colonization of D. floribunda did not vary among calcareous wetlands of different soil phosphorus or moisture status. Mycorrhizal colonization of D. floribunda ranged from 66.7 to 91.7%, with an average of 78.1 ± 7.7%. Although environmental parameters were only measured once, these results suggest that soil available P and soil moisture, used to predict variation of endomycorrhizal colonization of other wetland plants, are not useful for predicting the extent of endomycorrhizal colonization of D. floribunda. We propose that calcareous wetlands in eastern New York are an endpoint on a continuum of wetland types where P availability is so low that variation of P status among calcareous wetlands is not ecologically significant in the regulation of endomycorrhizal colonization.

Because germination requirements of the exotic saltcedar (Tamarix ramosissima) and native cottonwood (Populus deltoides subsp. wislizenii) are similar, efforts to establish cottonwoods often result in concurrent establishment of saltcedars. We evaluated the success of fall flooding to reduce saltcedar seedling density in the Rio Grande floodplain of central New Mexico, USA. We also evaluated the effects of flooding on cottonwood seedlings. Six- to 8-week-old saltcedars and cottonwoods and 4-week-old saltcedars were completely submerged for a 30 day period from late August to late September. Effects of submergence were compared to a no submergence (control) treatment. Survival of 6- to 8-week-old saltcedar was 43.5 ± 5.61% in the submerged treatment and 66.25 ± 4.85% in the control. Survival of 4-week-old saltcedar was 2.0 ± 2.0% and 65.75 ± 8.74%, respectively, in submerged and control treatments. Cottonwood did not survive in the submergence treatment and 78.5 ± 10.4% in the control. Because of the high mortality of cottonwood in response to complete submergence, flooding saltcedar seedlings may not be desirable when submergence of cottonwood seedlings will also occur.

Salt cedar (Tamarix ramossisima), an invasive species, has become a dominant shrub along many streams of the southwestern United States, where it has replaced many native species such as Fremont cottonwood (Populus fremontii). We examined whether the successful invasion of this exotic shrub alters stream leaf litter decomposition rates and affects the aquatic macroinvertebrates that are dependent on leaf litter as a food source. With an in-stream leaf pack experiment, we found that faster decomposition of salt cedar litter was associated with a two-fold decrease in macroinvertebrate richness and a four-fold decrease in overall macroinvertebrate abundance, relative to native Fremont cottonwood. Macroinvertebrate communities were also significa ntly different on the two food sources through time. These studies demonstrate that invasion by salt cedar affects leaf litter quality, which in turn affects stream macroinvertebrates. Such impacts on the primary consumers and food web structure could affect higher trophic levels.