Cultural and Natural Resources at Lake Amistad National Recreation Area
From mid-May through early July I conducted my internship at Lake Amistad National Recreation Area outside of Del Rio, Texas. My internship was with the resource management division of the park, where I participated in activities ranging from archaeological surveys of the region’s rock art, digitization of historic photos, educational seminars held for the local schools, to field work with the environmental management crew. During my internship, the nature of my work changed on a daily basis as I was tasked out to meet different needs in the department. This proved to be a highly educational and enjoyable experience, as I was able to expand my knowledge and understanding of the various aspects of park management. Any week could involve activities ranging from shovel testing, archaeological survey work, water quality analysis, day hikes to plot spring water sources, and archival projects in the office. In the following sections I will provide an example of the archaeological survey work in which I participated, and then describe what I learned about ecological concerns particular to the reservoir.
Rock Art in the Canyonlands
In early June, the National Park Service undertook a project in concert with Texas Tech University and the Shumla School for Archeological Research to survey and document an archaeological site in a rock shelter in Rattlesnake Canyon near Langtry, TX. The reasoning behind this effort is that the art within the cave is rapidly deteriorating. Comparisons of the shelter today with illustrations made of it by Olea Forrest Kirkland in the 1930s reveal evidence of this deterioration, which is all the more noteworthy considering that the images are perhaps as much as 5000 years old. The flooding of the region following the construction of Amistad Dam in the 1960’s has dramatically increased the humidity and led to frequent flooding in the otherwise dry floor of Rattlesnake canyon. Previous floods have deposited sediment on the painted wall of the cave, obscuring much of the lower portion of the wall and scouring away some of the images. Additional impacts of the environmental changes include flaking of the limestone surface, called spalling or exfoliation.
The shallow rock shelter contains an elaborate mural of painted figures stretching approximately 60m long and 3m high covering the interior wall of the shelter (see fig. 1). The art present here is defined as “Pecos River Style” and dates back to 2500 B.C.E. The elaborate murals incorporate a variety of colors and figure styles to illustrate stories of both the physical and spiritual worlds. Dr. Carolyn Boyd of the SHUMLA school divides the figures into 3 primary catagories; anthropomorphic (human like), zoomorphic (animal-like), or enigmatic (unidentifiable or non-living items i.e. serpentine lines or depictions of the sun). Many of the images and stories portrayed on these murals can be found in other locations all around the Lower Pecos Valley. Rattlesnake Canyon is one of the most densely decorated sites in the region, more than 300 figures had been documented as of 6/4/2014 and likely many more were found during the course of the survey project.
The canyon itself is accessible by water during periods when the lake is full, but there is no easement to allow road access for vehicles. Permission has to be obtained from the owners of the adjacent property in order to cross from highway 90 to the canyon. From the road it is a 20 minute drive over rough terrain, and even the 4 wheel drive vehicles find it a challenge. After having reached the rim of the canyon we abandoned the vehicles and conducted the rest of our trek on foot. The shelter being documented is about 2 miles down the steep, rocky canyon from this access point. The gear, including water, documentation materials, scaffolding, photography equipment and the 40lb Total Data System (TDS) had to be hiked into and out of the canyon, some of it daily.
After hiking down the canyon and climbing up to the cave a daily briefing was conducted and individual tasks were assigned. Most of the staff of 8-10 people spent the day writing descriptions of the figures painted on the walls, using cameras with a special filtering program called D-stretch installed that filters and sharpens various colors to allow the viewer to see details that might be to faint to see with the naked eye. These figure descriptions include the nature if the figure; anthropomorphic, zoomorphic, or enigmatic, its position on the wall, other figures it interacts or intersects with and its size and color scheme. Other members of the crew were involved in photographic documentation and surveying using the TDS, which records precise GPS coordinates and 3 dimensional positions on the wall. This data was later used to create an interactive 3D digital rendering of the cave for academic use and posterity.
Lake Ecology and Invasive Species
In addition to the archaeological work, the biology team also had several projects in which I was able to participate. The current focus of the team is the application of preventative measures that will keep an invasive species of bivalves from colonizing the lake.
Zebra Mussels are a small, but very hearty species of bivalve native to southeast Russia, discovered in the Great Lakes in 1988. They can survive in a broad range of climates and water types, and habitable temperatures ranging from 32-88 °F. The free-floating larval stage lasts up to one month and provides ample time for the transportation of the microscopic larvae to new ecosystems via live wells, bait buckets, bilges or any other places where water can be trapped on a boat. The frequent migration of boats -often cross-country- due to fishing competitions means that Zebra mussels can be easily imported from an infested lake or river if care is not taken to decontaminate all equipment between lakes.
Zebra mussels, like all invasive species, effect changes on new ecosystems. The high rate of reproduction coupled with the efficiency of their filter-feeding deprives native filter-feeders of their food source. Not only does this activity reduce the concentration of zooplankton -a primary food source of larval fish- but the increased water clarity also allows greater penetration of sunlight, which leads to over-production of aquatic vegetation.
In addition to the ecological impacts, the economy suffers from the infestation as well. Reductions in quality and quantity of fish affect commercial and game fishing, while colonies of mature Zebra mussels adhere to both hard and soft substrates, clogging water intake systems and damaging property.
There is no efficient way of eliminating an extant infestation. Chlorination, thermal shock, or lowering of dissolved oxygen concentrations are effective in small, enclosed systems, but non-target organisms may also be eradicated by these measures. To date, the National Park Service can only hope to delay infestation as long as possible, but there seems to be no real way to prevent introduction in the long-term.
Efforts are being taken at Amistad to educate the public about Zebra mussels, and implement inspection and pressure washing stations for boaters coming in from other lakes. The main obstacle here is the sheer number of access points for boaters, which means that they could easily bypass these inspection stations if they wished to, making compliance purely voluntary at this time.
While working with the biology team and the Texas Commission on Environmental Quality I frequently participated in excursions for conducting water quality testing, inspection of monitoring stations, collection of water samples for lab-testing, and full days spent at the docks inspecting debris recovered from the marina floor by the dive teams (see fig. 2). At this time no Zebra Mussels have been found at Lake Amistad there is hope that the climate and relative warmth of the water there may prevent this species from flourishing as it does in northern lakes. The work I was able to participate in with the biology team, Joanny Guindin and Wendy Weckesser in particular, has sparked a renewed interest in environmental geography and resource management, which intend to pursue as a grad student at Texas State University.
Conclusion
Although I was offered a position with the NPS at Lake Amistad, I do not feel that it would be the right choice for me personally. I will be looking for a position closer to home. Perhaps a position with Texas Parks and Wildlife or a local government agency will more easily accommodate my to return to Texas State in the fall of 2015 for graduate school. However, I do intend to return to Lake Amistad for a week in August to continue working on a model earth oven that I was constructing for the 2014 Archaeology Fair, and hopefully spend more time in the field with the Biology team.