Search

We analyzed the transverse pattern of vegetation along a reach of the Fremont River in Capitol Reef National Park, Utah, USA using models that support both delineation of wetland extent and projection of the changes in wetland area resulting from upstream hydrologic alteration. We linked stage-discharge relations developed by a hydraulic model to a flow-duration curve derived from the flow history in order to calculate the inundation duration of 361 plots (0.5 x 2 m). Logistic regression was used to relate plant species occurrence in plots to inundation duration. A weighted average of the wetland indicator values of species was used to characterize plots as Aquatic, Wetland, Transitional, or Upland. Finally, we assessed how alterations in the flow duration curve would change the relative widths of these four zones. The wetland indicator values of species and the wetland prevalence index scores of plots were strongly correlated with inundation duration. Our results support the concept that plants classified as wetland species typically occur on sites inundated at least two weeks every two years. The portion of the riparian zone along the high-gradient study reach of the Fremont River that satisfied the vegetation criterion for a regulatory wetland was narrow (2 m wide). Both the unvegetated Aquatic zone (7.8 m) and the Transitional zone (8 m) were substantially wider. The Transitional zone included the maxima of several species and was, therefore, not merely a combination of elements of the Wetland and Upland zones. Multiplicative increases or decreases in streamflow regime produced a wetter, or drier, bottomland vegetation, respectively. Systematic reductions in flow variability reduced the width of both the Wetland and Transitional zones and increased the width of the Upland zone. Our approach is widely applicable to inform water management decisions involving changes in flow regime. [ABSTRACT FROM AUTHOR]

The relation between the occurrence of riverine wetlands in floodplains along a humid to semiarid climatic continuum was studied in two regions. The first included 36 mid-reach streams from Colorado to Iowa, USA, a region with a broad range of PET ratios (potential evapotranspiration/precipitation) from 0.70 to 1.75. The second region included 16 headwater streams in eastern North Carolina with PET ratios ranging from 0.67 to 0.83. Wetland boundaries were identified in the field along transects perpendicular to the floodplain. The width of jurisdictional wetlands was compared with flood-prone width (FPW) and expressed as a percent. An increase in PET ratio corresponded to an exponential decrease in the percentage of the FPW that is wetland. Soil texture, duration of overbank flow, and stream order did not correlate with percentage of FPW that was wetland. Streams with a PET ratio greater than 0.98 did not have wetlands associated with them. Greater channel cross-sectional areas correlated positively with greater wetland widths in both study regions. Overbank flow did not appear to contribute to wetland prevalence. Supplemental ground-water sources, however, as indicated by greater base flows, could not be ruled out as sources contributing to wetland occurrence. [ABSTRACT FROM AUTHOR]

For two years, we measured soil moisture, pH, salinity, and ion concentrations bimonthly from 55 vegetation plots in six Mediterranean salt marshes of SE Spain. Edaphic characteristics during dry and wet seasons were compared within six selected plant communities. The dominant species in each of these communities were Suaeda vera, Lygeum spartum, Limonium sp, Sarcocornia fruticosa, Halocnemum strobilaceum, andArthrocnemum macrostachyum. Although soil salt concentrations were lower during the wet season, different patterns of temporal variation in total dissolved salts, sodium adsorption ratio, Cl-, Na+, K+, Ca2+, and Mg2+ were observed in the soils occupied by different plant communities. The variation patterns for SO42- werethe same in all plant communities. The Ca2+/Mg2+, Ca2+/Na+, and SO42-/Cl- ratios increased during the wet season because of the more pronounced decrease in Cl-, Na+, and Mg2+ concentrations relative to Ca2+, and SO42-. Canonical correspondence analysis (CCA) related the species distribution with certain soil conditions. The edaphic variables that best explained the data were maximum soil moisture, mean K+/Na+ ratio, mean Ca2+/Mg2+ ratio, maximum pH, and maximum K+. Two different environments were identified: dry salt marsh and wet salt marsh. To examine soil ionic gradients in these two environments, two further CCA were applied. The variables that best explained soil-vegetation relationships in the dry salt marsh were mean K+/Na+ ratio, mean Ca2+/Mg2+ ratio, maximum K+, and minimum Ca2+/Na+ ratio. Some representative dry salt marsh specieswere Lygeum spartum, Atriplex glauca, Suaeda vera, and Frankenia corymbosa. The variables explaining the data set in the wet salt marsh were maximum sodium adsorption ratio, maximum Mg2+ content, mean Ca2+ content, and mean Ca2+/Mg2+ ratio. Species such as Arthrocnemum macrostachyum, Sarcocornia fruticosa, Juncus maritimus, and Tamarix boveana w [ABSTRACT FROM AUTHOR]