Saltmarshes in eastern Nebraska: Study characterizes some unusual wetlands

by Michael C. Gilbert, U.S. Army Corps of Engineers, Omaha District, and Randy G. Stutheit, Nebraska Game and Parks Commission

The city of Lincoln, Neb., was founded in the mid-1800s along Salt Creek. As the name of the creek implies, the potential for commercial salt production from saline wetlands played a key role in Lincoln's settlement and early history. Although other sources of salt that could be mined cheaply were found in the region, the impact of civilization on the Salt Creek wetlands continued.

During the last century, the saline marshes suffered extensive degradation through commercial and residential development, road construction, and agriculture. Today, Nebraska's eastern saline wetlands are considered to be among the most restricted and imperiled ecosystems.

Background about the wetlands

Hydrology. Eastern Nebraska saline wetlands are regionally unique, located in floodplain swales and depressions within the Salt Rock watersheds in Lancaster and southern Saunders counties. Water regimes are temporarily and seasonally flooded on saline mineral soils. Water sources are a combination of discharge from the Dakota sandstone formation aquifer, precipitation, and overbank flooding. Salts are concentrated in the soil during dry periods.

Flora. Vegetation in these wetlands is characterized by halophytes including spearscale (Atriplex subspicata), inland saltgrass (Distichlis spicata var. stricta), saltwort (Salicornia rubra) (Fig. 1 (32K)), prairie bulrush (Scirpus maritimus var. paludosus), sea blite (Suaeda depressa), and narrow-leaved cattail (Typha angustifolia). Four plant species considered rare in Nebraska are saltmarsh aster (Aster subulatus var. ligulatus), seaside heliotrope (Heliotropium curassavicum), saltwort, and Texas dropseed (Sporobolus texanus) can be found in the marshes along Salt Creek.

Fauna. The saline wetlands provide habitat for a variety of wildlife species and serve as stopover for migratory birds, particularly for shorebirds during spring, when mudflats provide abundant invertebrate foods. These wetlands also are the sole habitat for an endemic tiger beetle, Cicindela nevadica var. lincolniana (Fig. 2 (23K)).

Public awareness spawns characterization study

Since 1988, wetland inventory and public outreach efforts in Nebraska have contributed to an increased awareness of eastern Nebraska's saline wetlands and their importance. This awareness, and acknowledgement that a balanced, resource-based approach is needed for wetland survival, has stimulated public interest in preservation, resource-sensitive urban planning, cooperative wetland enhancement efforts, and mitigation banking. To ensure that information continues to contribute to the understanding of saline wetlands and to create opportunities for pro-active wetland initiatives, an updated inventory was compiled and technical value assessments of existing saline wetlands were conducted. An interagency team then designed objectives for a study to provide:

the best information available about the location of saline wetlands in Lancaster and southern Saunders counties and
a qualitative assessment of individual saline wetlands, their relative potential to maintain historic functions, and their value resulting from these functions.

The team of individuals from the Nebraska Game and Parks Commission, U.S. Army Corps of Engineers, Nebraska Department of Environmental Quality, U.S. Fish and Wildlife Service and U.S. Environmental Protection Agency identified study boundaries, established categorization criteria, and conducted individual site assessments.

Gathering mapping and site information

Distribution of saline hydric soils within the respective counties (Table 1) was used to establish study area boundaries. These data, in conjunction with existing Nebraska Game and Parks Commission wetland survey information, helped define the saline wetlands of interest ( Fig. 3 (63K)). The state wetland survey effort included both mapping products and information on critical species and plant community occurrences.

The study team was then able to prioritize site assessments for integration towards updated wetlands mapping. Digital National Wetlands Inventory data were the crucial link between field analyses and updating saline wetland inventory information. The combination of quality information prior to initiation of the resource categorization study, availability of new digital wetlands data, and field assessments focusing on critical habitat features provided the necessary components for study goals.

Evaluation criteria results in categories

Comparative site evaluations were based on the occurrence of the Salt Creek tiger beetle, presence of rare or restricted halophytes, historical significance, occurrence of halophytic associations, degree of degradation, degree of pollution, proximity to municipal or industrial solid waste disposal sites, and restoration potential. Scientists then defined four standardized wetland categories:

Category I: Site currently provides saline wetland functions of high value or has the potential to provide high values following restoration or enhancement measures. The site meets one or more of the following criteria:

Salt Creek tiger beetle present,
the presence of one or more rare or restricted halophytes
identified as having historical significance by the Nebraska State Historical Society,
contains at least one saline wetland plant association as part of the site's flora and is not highly degraded or has potential to maintain or improve saline wetland characteristics through enhancement or restoration,
contains no saline wetland plant associations but high potential exists for restoring the historic salt source.

Category II: Given current land use and degree of degradation, site currently provides limited saline wetland functions and low values. Restoration potential is low. The site meets one or more of the following criteria:

currently contaminated by hazardous or toxic waste or is/has been used for municipal or industrial solid waste disposal; has limited potential for providing high functions and values through restoration,
contains at least one saline wetland plant association as part of the site's flora and is highly degraded; has limited potential for the long-term maintenance or improvement of saline vegetative characteristics through enhancement or restoration,
contains no saline wetland plant associations and provides low functions and values due to degradation; has low potential for restoration of the historic salt source.

Category III: Site is functioning as a freshwater wetland having freshwater plant communities on a saline soil. Currently provides freshwater wetland values and no feasible restoration measures exist to reestablish the historic salt source and saline plant associations.

Category IV: Site is functioning as a freshwater wetland having freshwater plant communities on a non-saline hydric soil. Areas with insufficient data for categorization or inaccessible to the interagency work team were "NC" meaning "not categorized."

Categorization process described

The interagency work team identified some sites that had sufficient existing information on file for categorization without a field visit. All other sites were visited by team representatives prior to categorization.

Site assessments were conducted during the growing season in 1992 and 1993. Standardized field assessment forms were used. In addition, a qualitative judgment by the interagency work team about the site's degree of disturbance or restorability was noted. Consensus among the interagency work team was required in the final determination of a category designation.

Results of category designations were summarized in a database. These data were then imported as a relational table for geographic information system-based mapping. Commercially available software for digital data processing and analyses was used.

Results

Team members identified 276 wetlands with saline characteristics. More than 70 percent of these sites had sufficient data, either through documentation from the state survey or field evaluations, to allow category designations. In total, 5,644.1 acres of wetlands and deepwater habitats were identified within the study area.

Category I wetlands were the largest both in terms of number of sites and acreage. None of the sites were of historical significance. Category I wetlands comprised approximately 57 percent of the total wetlands and deepwater habitats within the study area. Category II wetlands, with 7 percent representation, were the least frequent in terms of total acreage. Category III wetlands, freshwater vegetational communities on saline soils, ranked second in terms of acreage with 11 percent of the total wetlands and deepwater habitats. Category IV wetlands account for 10 percent of the total wetland acreage and deepwater habitats within the study area. No site data for Category IV wetlands were recorded, as these freshwater vegetational communities on non-saline soils were not a focus of the study. This category did, however, represent an important component of wetlands within the study area.

Seventy-nine sites were not categorized. All were located on saline soils. The status, quality, and halophytic character of these wetlands are presently unknown. Remaining non-saline wetlands and deepwater habitats within the study area are associated with rivers and lakes. Federal, state, and local agencies are currently using the study results in zoning applications, initiation of private mitigation banks, wetland acquisition, and day-to-day Section 404 permit reviews. The results of this study are available in computer mapping/database format. These data can be used in future applications for trend analysis, land use planning, and as a mechanism for prioritization of restoration sites. To maximize utility in these applications, digital data for land use classes, watershed units, and soils could be incorporated into future geographic information system analyses.

Additional information about the Nebraska eastern saline wetlands categorization project may be obtained by contacting Mike Gilbert at (402) 221-3057 or Randy Stutheit at (402) 471-5584.

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