Blue Earth Experience

PRE-RESTORATION CONDITION

The wetlands restoration site is situated on the floodplain of the Rio Chama. The site was heavily grazed by domestic livestock. Prior to restoration work, there were no jurisdictional wetlands present at the site. A shallow swale conveyed storm-water runoff from a culvert at U.S. Highway 285 south across the eastern portion of the site. The swale contained remnant stands of intensively-browsed coyote willow (Salix exigua) and scattered clumps of marshy spike-rush (Eleocharis palustris), which were cropped close to the ground.

A mature cottonwood bosque occupied the eastern quarter of the site adjacent to the Rio Chama. The bosque had no understory except for scattered saplings of Russian olive (Eleaegnus angustifolia). A level field of upland grasses and forbs occupied the western three-quarters of the site. Common wetland plants along the Rio Chama included Torrey's rush (Juncus torreyi), jointed rush (J. articulatus), hardstem bulrush (Schoenoplectus acutus), three-square bulrush (S. pungens), softstem bulrush (S. tabernaemontani), woolly sedge (Carex pellita), and alkali sacaton (Sporobolus airoides).

RESTORATION DESIGN AND IMPLEMENTATION

A detailed set of restoration design plans was developed, which included specifications for monitoring and maintenance as well as measureable success criteria for the project. The main feature of the restoration plan was excavation of shallow depressions on the flooplain, which were designed to intercept shallow groundwater. Perimeter fencing was constructed around the site to exclude trespass livestock.

The plan also specified planting of herbaceous and woody wetland vegetation. Twenty-seven species were planted at the site in varying numbers. Ten of the planted species were common at or in the immediate vicinity of the restoration site.

RESULTS

Eleven of the 27 species (41%) planted in 2003 were recorded at the restoration site in 2004. Ten of these were species that existed at or near the site prior to restoration. In 2005, only 8 of the 27 planted species (30%) were recorded at the site, all of which were common at the site prior to restoration. Vegetation cover developed quickly at the restoration site. Average plant cover was 76.9% in 2004 and increased to 92.3% in 2005. Most of the plant cover consisted of perennial plant species and was dominated by hydrophytes.

Plant species diversity decreased slightly and dominance increased slightly from 2004 to 2005. The five most frequently encountered species in 2005 were muskgrass, alkali sacaton, softstem bulrush, coyote willow, and narrowleaf cattail. In 2004, the five most abundant species were muskgrass, marshy spike-rush, hardstem bulrush, Rio Grande cottonwood, and three-square bulrush.

INTRODUCTION

The Griego Wetlands Restoration project was developed by the New Mexico Department of Transportation (NMDOT) as off-site compensatory mitigation for unauthorized wetland impacts that occurred at the U.S. Highway 84/285 bridge crossing of the Pojoaque River in 1999. The U.S. Army Corps of Engineers required mitigation for unauthorized fills placed in jurisdictional wetlands along the Pojoaque River. On-site mitigation of the filled wetlands was not possible.

The NMDOT contracted Blue Earth Ecological Consultants, Inc. (Blue Earth) to develop a wetlands restoration plan for a 0.55 ha (1.37 ac) site owned by the agency and located on the west side of the Rio Chama at the U.S. 285 bridge crossing in Rio Arriba County. To develop the restoration plan, Blue Earth conducted a topographic survey of the site, assessed existing flora, placed several piezometers to measure depth to ground water, and conducted a field review of nearby wetland sites. The final wetland restoration design was completed in March 2003. The design involved excavation of shallow depressions on the floodplain, interception of shallow ground water to create areas with saturated or inundated soils, use of a storm-water runoff channel to convey water to the site, and planting of native herbaceous and woody wetland plants.

CONCLUSIONS

1) The project achieved the objectives. Success criteria were achieved in the first year following restoration and were sustained through the second year. Cover in both years was well above the success criteria of 65% and cover by hydrophytic plant species exceeded 90% of total cover in both years.

2) Vegetation developed rapidly after restoration, and its composition and structure has remained stable through the second post-restoration year. These findings are consistent with wetland development at other restoration sites where rapid colonization (e.g. Kellogg and Bridgham, 2002) was followed by relatively stable community structure (e.g. Atkinson et al., 2005).

3) Pre-restoration assessment of seed bank and hydrology is essential. Initial colonization by wetland plants was primarily a function of the existing seed bank, species present in the remnant wetland found in the drainage swale, and seed dispersal. Planting of the site appears to have had relatively little influence on the plant community that has developed (Pittenger and Mullins, 2004). In particular, natural establishment of cottonwood was orders of magnitude higher than establishment of the plant by pole plantings at the site. Consequently, planting or seeding may be unnecessary at sites where appropriate hydrologic conditions can be restored and that also have a diverse assemblage of wetland plants at or adjacent to the site (Brown, 1998).

Atkinson, R. B., J. E. Perry, and J. Cairns, Jr. 2005. Vegetation communities of 20-year-old created depressional wetlands. Wetlands Ecology and Management 13(4): 469-478.

Brown, S. C. 1998. Remnant seed banks and vegetation as predictors of restored marsh vegetation. Canadian Journal of Botany 76: 620-629.

Kellogg, C. H. and S. D. Bridgham. 2002. Colonization during early succession of restored freshwater marshes. Canadian Journal of Botany 80(2): 176-185.

Pittenger, J. S. and J. F. Mullins. 2004. 2004 Monitoring Report for the Thomas L. Griego Wetlands Restoration Project, Rio Arriba County, New Mexico. Report prepared for the New Mexico Department of Transportation and the U.S. Army Corps of Engineers by Blue Earth Ecological Consultants, Inc., Santa Fe, New Mexico.