Biological Assessment, Emergency Actions to Stabilize Quitobaquito Pond, Part II: Renovating the Southeast Corner

Organ Pipe Cactus National Monument

Quitobaquito Pond lies on the international border near the southwestern corner of Organ Pipe Cactus National Monument and is comprised of multiple special-status cultural and natural resources, including the endangered Quitobaquito (aka Sonoyta) pupfish (Cyprinodon eremus) and the Sonoyta mud turtle (Kinosternon sonoriensis longifemorale), a candidate species. In 2006 and 2007, the surface elevation of Quitobaquito Pond fell to low levels, unprecedented in the history of the pond since it was dredged and deepened in 1962. These drops in water level were presaged by a smaller reduction in midsummer 2005. Normally averaging about 25" to 42" deep and about 29,000 ft2 in surface area, by late 2007 the pond had fallen to 23.25" below the outflow pipe, and was 70% of its normal surface area. This loss of surface area and total water volume presented threats to the Quitobaquito pupfish, Sonoyta mud turtle, and the natural and cultural resources. Initial evaluations and management actions assumed the water deficit was caused by long-term drought affecting spring discharge, and overdue maintenance of the spring collection system. While those factors contributed to diminished water supply, by late 2007 additional evaluation and water loss indicated loss of water from the pond itself, over and above normal evapotranspiration. A leak in the retaining berm forming the pond, or elsewhere in the pond margin or bottom, was strongly suspected. In the effort to understand and rectify the low-water situation at Quitobaquito, in 2006 through 2009 ORPI undertook multiple management actions, assessed results of inspections and monitoring, and consulted with experts, partners, and interested parties. These actions included renovating the northeast spring, increasing emergent plant management, repairing the stream channel, evacuating pupfish and mud turtles, installing a diaphragm wall in the retaining bermtrucking water to supplement the pond, and others. All these actions ameliorated the situation to a certain extent. However, the March 2009 water-hauling project had two purposes: 1) To raise the pond level in a controlled, closely measured fashion to evaluate its water-holding integrity, and: 2) To supplement the pond prior to the upcoming warm-dry months of midsummer. That effort demonstrated that a large-scale leak from the pond was still active, causing the unexplained loss of 9 to 14 g/m. While large volumes of water clearly were lost in short time periods, evidence of the escaped water has never been found adjacent to or near the pond. The lost water appears to be going straight down into the earth, leaving no evidence as localized damp areas or lush plant growth. The retaining berm remained a highly suspect area, particularly in the areas of the southeast corner, the leaning cottonwood, and other areas where larger trees had been rooted in the berm. In midsummer 2009, nontoxic tracer dye was used in the pond to attempt to determine the leak location. Effectiveness of this technique was probably compromised somewhat by extremely shallow water, breezy conditions, and up to 16" of organic detritus and mud overlaying the pond bottom. However, after four trials, the most consistent dye movement observed was toward the southeastern corner. Based on these observations and other circumstantial evidence, the NPS elected to carry out a renovation limited to the southeast corner. First, extensive bulrush encroachment was removed from the inner face of the retaining berm and pond bank. Then, approximately 4,500 ft2 of the southeast corner was isolated from the rest of the pond, by constructing a temporary coffer dam. The southeast corner was then emptied of water, mud, and detritus. The retaining berm was widened inward approximately 4 feet, using compacted clean fill material. A bentonite wall was built into the center of this enlargement of the berm. Finally, the pond bottom was covered with compacted bentonite and fill mixture.

Biological Assessment, Emergency Actions to Stabilize Quitobaquito Pond, Part II: Renovating the Southeast Corner

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