MEETING SUMMARY

On July 11, 1996 the National Biological Service's Midwest Science Center hosted a meeting at the Fort Brown Holiday Inn, Brownsville, Texas to identify research and information needs on Lower Rio Grande Valley resacas (oxbow lakes which have formed in historic floodplain channels of the Rio Grande river). The goal was to provide a forum for representatives of management and research to discuss what information presently exists for resacas and what new information is needed. As a result of these discussions, it is anticipated that agencies will collaborate on projects to address these needs. Information from this meeting should be useful to participants and others in focusing present efforts and for developing multi-agency proposals in response to funding opportunities.

Representatives from the following entities attended: U.S. Fish and Wildlife Service (USFWS), U.S. Geological Survey (USGS), National Biological Service (NBS), Texas Health Department (THD), Texas Natural Resources Conservation Commission (TNRCC), Texas Parks and Wildlife Department (TPW), City of Brownsville-Engineering, University of Texas-Brownsville, University of Texas-Pan American, National Audubon Society.

Distribution and Location:

Resacas are numerous throughout the lower Rio Grande Valley. The City of Brownsville alone is estimated to have a total 3500 acres of resaca habitat (ranging in size from <1 acre to several acres) distributed across the city. Resacas are found in urban, residential, and commercial areas as well as on protected wildlife refuges. Increased development in the Rio Grande Valley has elevated land containing resacas to prime real estate. Mapping of the resacas for use with GIS databases would be a valuable management and planning tool.

Biology:

Most of the Lower Rio Grande Valley falls into the Matamoran province which is characterized by more lush vegetation than surrounding regions north or south. Resacas may be the key to the high biodiversity found in this region as they provide the major source of fresh surface water outside of the Rio Grande river proper. They provide wetland, riparian, and aquatic habitat for a variety of fish (Rio Grande Cichlid and Amazon molly), amphibians (e.g. Rio Grande Siren), reptiles (Diamondback Water Snake), birds and invertebrates. Some of these species are at the northern or southern extremes of their range. Waterfowl such as the black belly whistling duck and least grebe are reported to use resacas. The Rio Grande Valley is renown as a great "birding" area and resacas contribute by providing key habitat for two migrating bird flyways. The role that resacas may play in providing habitat within "corridors" for such species as the ocelot needs to be assessed.

Hydrology:

Dams and levees for flood control and water storage along the Rio Grande River have severed the natural connection between the river and most of the resacas. Today, resacas are typically filled by pumping Rio Grande water, rainfall, or input of irrigation return flows. All of the resacas within the City of Brownsville are connected to receive storm drain discharge and some provide drinking water. As well, many resacas are themselves connected to one another. An understanding of the hydrological dynamics of these systems is needed particularly to understand sediment transport into and out of resacas relative to contaminant loads sediment may be carrying.

Contaminant Impacts:

As integral parts of the urban stormwater drainage system in Brownsville and other Valley cities, the resacas may be subject to urban non-point source pollution such as pesticides (e.g. chlordane), automotive oil, grease and metals, fertilizers, sewage, and dissolved salts. Runoff to resacas is also a potential problem in rural areas. In addition, there are concerns about illegal dumping into resacas and suitability of existing water standards. If contaminants are a problem in the mainstem Rio Grande River, they may also be a problem for those resacas receiving river water.

Non-contaminant Impacts:

Non-contaminant impacts to the resacas include loss of riparian habitat and natural vegetation as a result of urbanization. Manipulation of resacas in urban areas may also have changed aquatic communities through the loss of flood/drought cycles, restrictions to fish movements, changes in water flow patterns, connecting of individual resacas, and bank erosion due to stormwater control projects.

Recreational Use:

The Texas Parks and Wildlife Department has attempted to develop resacas for use in urban fishing programs, but public perception is that they are polluted. TPW needs information about the safety of the resacas for fishing and human consumption of fish. With this information, TPW will begin an aggressive public education program about fishing in resacas. TPW has already begun educating the public about the issues relative to resacas.

Major studies:

TPW has some fish community surveys done relative to sport fishing on resacas.

THD samples fish tissue (filets) for residues yearly and have data from 1970-1994. USFWS has some data on contaminants in resacas on refuge lands and is interested in studying effects on key species such as the recently reintroduced aplomado falcon. TPW and NBS will initiate a study on Brownsville resacas during the summer of 1996 to assess contaminant exposure of fish. Federal and state cooperation will continue into the fall to study resacas on the USFWS Santa Ana refuge and possibly include collaboration with colleagues in Mexico to study resacas in Matamoros, Mexico.

Monitoring:

TNRCC supports volunteer water monitoring groups such as Texas Watch, which has an EPA-approved quality assurance program, throughout the Valley. Currently, TNRCC is administering grants for two non-point source studies on resacas. TNRCC is also considering establishing monitoring stations on selected resacas.