Biological Resources in Big Bend National Park

To complete this assessment and provide the information needed by Park staff, TXWSC scientists

• Provided Big Bend National Park as well as policy makers, regulators, and non-governmental organizations in Texas and Mexico with baseline data and supporting interpretations on the occurrence and distribution of instream and riparian-zone biological resources of the Rio Grande in reaches within and adjacent to Big Bend National Park. 
   
• Established benchmark monitoring stations on the Rio Grande in Big Bend National Park to assess the status and trends of instream and riparian-zone biological resources in relation to differences in channel habitat, instream flow, and water quality. 
   
• Selected one or more aquatic and riparian indicator species and associated instream habitat as ecosystem surrogates to use in predictive modeling directed toward developing an understanding of the effects of reduced instream flows and related habitat loss, and water-quality degradation on the stream ecosystem. 

Background

Big Bend National Park administers 240 miles of the Rio Grande including the reach downstream from the park designated the Rio Grande Wild and Scenic River. The Texas Parks and Wildlife Department administers 60 miles of the Rio Grande and Big Bend State Park adjacent to and upstream of the National Park. The Rio Grande represents the Chihuahuan Desert's most extensive aquatic and associated riparian environments. Increased pollution and loss of instream flow threaten floral and faunal populations in the Big Bend area of the Rio Grande. The Rio Grande is subject to increasing pollution from upstream urban and agricultural sources in the United States and Mexico. Increased industrialization on both sides of the border upstream of Big Bend National Park resulting from the North American Free Trade Agreement has increased the discharge of urban and industrial wastes and runoff into the Rio Grande. Dams and diversions on the Rio Grande have reduced the river to a vestige of its historical flow. Mexico's Rio Conchos, the primary Rio Grande tributary upstream of Big Bend, has in recent decades contributed 85 percent of the instream flow through Big Bend National Park, Big Bend Ranch State Park, and the Rio Grande Wild and Scenic River. However, the Rio Conchos is rapidly being developed for water supply by Mexico. Six dams are on the Rio Conchos and tributaries, and more are planned. 

Park managers are engaged in local, regional, and international dialogues to maintain and improve the ecological integrity of the Rio Grande at Big Bend. The Texas Natural Resources Conservation Commission, the International Boundary and Water Commission, and the U.S. Environmental Protection Agency have responsibility for water quality and water flow in this region. Park managers participate in working groups with these agencies and the Border XXI Environmental Side Agreement working group, a consortium of U.S. Federal agencies formed to address environemntal issues associated with the international boundary between the United States and Mexico. National Park Service efforts to obtain water quality and proposed flows necessary to sustain park aquatic resources are fundamentally thwarted without quantitative data regarding status and needs of affected faunal groups and species. 

Increased pollution, flow loss, and the invasion of exotic species have degraded the Rio Grande's aquatic resources in the Big Bend region of Texas. Seven native fish species have been extirpated. Of the remaining native fish species, one is Federally endangered and two are Federally listed as species of concern. Aquatic invertebrates, essential to ecosystem health, have not been assessed. No thorough mussel survey has been done; five Rio Grande mussel species have not been documented alive since the 1970's. The effects of upstream diversions from the Rio Grande on instream and riparian vegetation and biological resources of the river in the Big Bend National Park have not been established.