A Survey of the Invasive Aquatic and Riparian Plants of the Lower Rio Grande, 2004
ENGINEER RESEARCH AND DEVELOPMENT CENTER VICKSBURG MS ENVIRONMENTAL LAB
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Hydrilla has exhibited extensive range expansion along the Rio Grande since it was first discovered in early 1990 and is now found in areas far removed from the original infestation in Brownsville, TX. Hydrilla, a nonindigenous aquatic plant species, has been implicated in restricted water delivery, inaccurate water accounting, and an overall breakdown of system maintenance. The presence of hydrilla also has had a decided impact on native flora by the formation of extensive monocultures in many areas. In 2004, surveys were conducted starting below Amistad Reservoir to immediately below Falcon Reservoir to assess the distribution and expansion of hydrilla infestations and document the presence of other invasive aquatic and riparian plant species. A total of seven nonindigenous plant species were observed. Hydrilla infestations that were originally discovered during 2003 had increased in size through localized stolon expansion. Also, new hydrilla sites were discovered in 2004, including several directly below Amistad Reservoir. No hydrilla was discovered immediately south of Laredo however, hydrilla infestations had dramatically increased below Falcon Reservoir. Giant cane continues to spread down river, even displacing well-established common cane. While no new Eurasian watermilfoil sites were discovered in 2004, existing infestations near Del Rio remain stable, extending bank-to-bank and considerable distances down the river. Eurasian watermilfoil fragments, which could lead to the formation of new infestations downstream, were observed in the river. Numerous new sites of parrotfeather, elephant-ear and salt cedar were found during the 2004 survey, and all sites identified in 2003 had increased in localized spread. One endangered wetland plant species, Corrells false dragonhead Physostegia correllii, was tentatively identified.
- Hydrology, Limnology and Potamology