Status review of construction, native species introductions, and operation of an endangered species refugium channel, Phantom Lake Spring, Texas

Revisión del estado de construcción, introducción de especies nativas, y operación de un canal de refugio de especies en peligro, Phantom Lake Spring, Texas

KEYWORDS: Cyprinodon elegans; Gambusia nobilis; Phantom Lake Spring; Texas; refugium

CLAVES: Cyprinodon elegans; Gambusia nobilis; Phantom Lake Spring; Texas; refugio

ABSTRACT

Two endangered fish species, Comanche Springs pupfish Cyprinodon elegans and Pecos gambusia Gambusia nobilis historically occupied Phantom Lake Spring, Texas. In spring, 1993, construction commenced for a fish refugium channel below Phantom Lake Spring. The Rio Grande Fishes Recovery Team monitored construction, native species introductions, and operation of the refugium channel during 1993. Discussion will include review of refugium design, construction activities, introduction of native plants, invertebrates and fishes, and initial monitoring of the colonization by native species within the refugium.

RESUMEN

Dos especies de peces en peligro, Comanche Springs pupfish Cyprinodon elegans y Pecos gambusia Gambusia nobilis históricamente ocupaban el Phantom Lake Spring, Texas. En la primavera de 1993, inició la construcción de un canal de refugio para peces, abajo del Phantom Lake Spring. El Equipo de Recuperación del Río Grande monitoreó la construcción, introducción de peces nativos, y la operación del canal del refugio durante 1993. La discusión incluirá un repaso del diseño del refugio, actividades de construcción, introducción de plantas nativas, peces e invertebrados, y el monitoreo inicial de la colonización por peces nativos en el refugio.

CONTRIBUTED PAPER

Phantom Lake Springs are located approximately 6 km west of Toyahvale, Texas, near the border of Jeff Davis and Reeves counties. The springs emerge from a limestone bluff and immediately are channeled into a Bureau of Reclamation (Reclamation) irrigation canal. At elevation 1,080 m, these springs, part of the complex of springs surrounding the Balmorhea area, are most vulnerable to human- induced aquifer decline (Brune 1981). Since discharge recordings were initiated in the early 1930's, Phantom Lake Springs have exhibited a steadily- declining discharge.

Phantom Lake Springs historically discharged into a small, shallow cienega before returning underground via a limestone cavern. The waters of Phantom Lake Springs supported a unique fish fauna and invertebrate assemblage and, according to archeological inventory data, attracted Native Americans who utilized the surrounding vegetation and abundant wildlife (Charles, 1993).

Anglo- American water development in the Balmorhea area began in the 1870's when irrigated food crops were produced for the military at Ft. Davis (Water and Power Resources Service, 1981). Later, in 1914, the Reeves County Water Improvement District #1 (District) was formed, consolidating numerous local canal companies. In 1946, Reclamation began reconstructing the District's facilities, including initiating the construction of the Phantom Lake Canal (Water and Power Resources Service, 1981). As part of the agreement to reconstruct and upgrade various District facilities, Reclamation received ownership of a 7.11 ha property surrounding Phantom Lake Springs, which includes the springhead, and approximately 200 m of canal.

The existing canal immediately below the springhead, with vertical, concrete walls, provides minimal shallow water habitat or structural cover for most aquatic species. Endemic species, including the federally endangered Comanche Springs pupfish Cyprinodon elegans and Pecos gambusia Gambusia nobilis, are found in reduced numbers within the Reclamation property, and were the main focus of a Rio Grande Fishes Recovery Team (Recovery Team) effort to design, construct, and monitor a native fish refugium channel at Phantom Lake Springs. The Recovery Plans for each of these endangered species suggest that a refugium be constructed at Phantom Lake Springs to enhance habitat conditions (Rio Grande Fishes Recovery Team 1981; 1983). The purpose of the project was to establish an off- canal facility that would transport flows via a protected, structurally diverse channel. The channel would serve as a refugium for listed aquatic species and associated unique invertebrate fauna, and would be protected from invasion from undesirable species via screening of the inlet structure and creation of a waterfall at the outlet structure.

Methods and Materials

Reclamation planners initially negotiated with the District to ensure project compatibility with District irrigation needs and water rights. A field review, consisting of Recovery Team and District personnel, visited the Phantom Lake Springs property on August 31, 1991, discussed project scope, and conducted preliminary engineering surveys. Subsequently, the Recovery Team developed guidelines for design of the facility. These included creating a protected refugium channel with mesohabitat heterogeneity, facility operation capability over a variety of spring discharges, ability to manipulate water elevations in the refugium over a range of flows, and establishment of a cross- sectional channel profile that maximized shallow water habitat at all flows while still providing faster velocity habitats.

Reclamation staff provided engineering design and specifications for the project. A contractor was selected to conduct the construction of the refugium. National Environmental Policy Act and Endangered Species Act compliance were performed by Reclamation. Funding was secured through Public Law 102- 27, Emergency Drought Assistance Act.

Results and Discussion

In spring, 1992, a fence was constructed around the entire Reclamation property to preclude livestock and human use and protect the endangered fish refugium. Texas Parks and Wildlife Department (TPWD) personnel will regularly monitor the integrity of this feature.

Construction for the refugium channel commenced in February, 1993. A 110 m channel was excavated parallel to the existing canal and lined with a low density polyethylene liner to minimize water loss (Figure 1). Native materials from the channel excavation were used to create habitat features. Construction of the refugium occurred without disturbance of the existing canal and its resident aquatic population until water was initially diverted into the refugium. Two large (10 m long x 8 m wide) and two smaller pools (10 m long x 5 m wide) were formed, with intervening run habitat. Terraces were constructed at 150 mm vertical intervals on all cross sections, yielding extensive shallow habitats at all water elevations. Engineering estimates indicate that, for flows up to 0.3 m3/s (11 cfs), evaporative losses are less in the refugium than the irrigation canal.

Figure 1.Phantom Lake Springs Endangered Fish Refugium Plan.

Water was initially diverted from the existing canal into the refugium via a stoplog weir on June 7, 1993. Total refugium flow capacity is approximately 0.4 m3/s (13 cfs). Spring discharge above that capacity will spill into the existing canal and the cienega. The refugium outlet structure is comprised of an adjustable aluminum "Cipoletti" weir. This weir allows manipulation of water velocity and elevation within the refugium. The weir was also constructed at an elevation higher than the downstream canal, creating a waterfall to restrict upstream fish movements. A stoplog weir was also placed in the lower irrigation canal to allow dewatering of the canal between the refugium channel's inlet and outlet structures.

Reclamation biologists observed the initial refugium filling activities, and, once water elevation had stabilized, began transferring aquatic vegetation and associated invertebrates into the refugium channel. Reclamation personnel manipulated the elevation of the facility to determine, at the existing spring discharge of approximately 0.1 m3/s (4 cfs), a suitable velocity to protect the unstable substrate. It was immediately discovered that excessive velocities could be produced within the refugium that cause significant head- cutting of substrate in the lower refugium and threatened to impact the refugium's integrity. A locking mechanism was therefore placed on the weir to restrict manipulation of elevation. Biologists have subsequently maintained the weir at a higher setting to provide maximum wetted habitat areas and reduced channel velocities.

The waterfall, while apparently creating a barrier to centrarchid and ictalurid migration into the refugium, was unsuccessful in restricting movements of Mexican tetra Astyanax mexicanus into the refugium. Astyanax mexicanus were attracted to the increased downstream velocities created by the waterfall, and were observed readily leaping waterfall elevations of up to approximately 500 mm. A floating, self cleaning fish barrier, constructed of cross- laid PVC pipe, was subsequently installed below the waterfall and apparently has successfully restricted movements of A. mexicanus.

On September 20 and 21, 1993, members of the Recovery Team seined the lower canal areas and collected Cyprinodon elegans and Gambusia nobilis for transfer into the refugium. A total of approximately 135 G. nobilis and 2 C. elegans were collected. Biologists carefully introduced these fish into refugium pool habitat, while lightly disturbing the substrate in an effort to increase water turbidity and thereby reduce possible A. mexicanus harassment and/or predation. After release, G. nobilis were seen utilizing the abundant aquatic vegetation that had colonized after the early summer vegetation introduction. Overhanging riparian grasses have also colonized the refugium's bank and appear to increase habitat diversity and overhead cover for fish introduced into the refugium. Specimens of the Reeves County snail Cochliopa texana and diminutive amphipod Gammarus hyalelloides were captured within the refugium during fish introductions, indicating invertebrates had begun colonization of the newly created habitats.

Because few C. elegans were collected in the Phantom Lake Springs area, the Recovery Team decided to introduce a stock of C. elegans that are currently held at Uvalde National Fish Hatchery. Personnel from TPWD were contacted to conduct genetic analysis of this hatchery stock. This study subsequently determined that the hatchery stock C. elegans were suitable for introduction. On October 14, 1993, 109 C. elegans were introduced into various pools, utilizing the same methods as above. These fish have been observed utilizing faster velocity waters throughout the refugium. Numerous C. elegans have since been observed downstream in the main canal and perhaps migrated out of the refugium.

A cooperative agreement was developed between Reclamation and Texas A&M University (TAMU) in fall, 1993, for aquatic monitoring studies. Under this agreement, researchers from TAMU will sample Phantom Lake Springs on a quarterly basis for two years, monitoring habitat condition, fish abundance and microhabitat use, and water quality. Results of these monitoring efforts will indicate the success of this project and help determine future operational guidelines.

Restoration of altered aquatic habitat and associated species is often a complex, controversial issue, especially when water rights and deliveries to users are impacted. However, as this project has indicated, affording protection to aquatic species can be accomplished without significant reduction in water deliveries to downstream users. Reductions in water during delivery to irrigators generally occur in two ways, seepage and evaporation. Evaporation can be somewhat controlled via shading of water by riparian vegetation, creation of a narrowed channel and increasing velocity. Seepage can be controlled by installation of a membrane or clay liner or concrete channel. Phantom Lake Springs refugium designs incorporated all these water saving methods. Historically, the District had resisted major modifications to the existing water distribution system. However, after negotiations to explain the water- saving measures being proposed for the refugium, District membership has not objected to restoration activities at Phantom Lake Springs. Flexible membrane liners have wide application to aquatic habitat restoration projects, are fairly cost effective, and should be considered for future restoration activities. Membrane liners provide reliable containment and seepage control for conservation of water. In contrast, traditional liner materials, such as clay and concrete, are not as reliable, and concrete is expensive and difficult to install. Membranes are conducive to areas of potential differential settlement, whereas concrete or clay liners usually fail. Concrete and clay liners can lose much of their barrier properties in the long run due to the absence of elasticity, difficulties of proper compaction, weathering effects, and root growth.

Membrane liners are composed of many different materials including hypalon, polyvinyl chloride (PVC), high and low density polyethylene (HDPE and LDPE), and recycled rubber (ethylene propylene diene monomer - EPDM), just to name a few. The composition of the membrane, and related manufacturing practices, determine strength, elasticity, durability, and chemical, microorganism and ultra violet resistance. In many cases the material can be manufactured to select colors and textures. Textured liners are usually more expensive, but allow better stability of surface materials on steeper slopes (smooth liners should not be used for steep slopes or cover materials may slump). The following is presented as a general guideline for 30 mil membrane liners:

Material Qualities Cost/ft2

Hypalon Extremely durable, UV light resistant $1.00

PVC Somewhat durable, decay resistant $0.35

LDPE Smooth Flexible, durable, UV resistant $0.50

Textured Flexible, durable, UV resistant $0.60

EPDM Short life, decay- prone, light sensitive $0.30

Installation of a liner is relatively easy; with most materials, reliable seams can be achieved in the field, and various shapes and patterns can be achieved. Membranes can be covered with soil to allow vegetative growth to enhance slope stability and provide for erosion control.

Costs for design and construction of the refugium channel at Phantom Lake Springs were more expensive than anticipated. Much of the excessive cost can be attributed to government overhead and personnel costs, and extra cost required by law during government contracting. Remote worksite location, uniqueness of the work, including modification of existing concrete canal, and contract modifications also increased overall costs. However, it is hoped that overall benefits to the aquatic resource, especially provision of an additional refugium for C. elegans, G. nobilis, and associated invertebrates, outweigh monetary considerations.

Literature

Brune, G. 1981. Springs of Texas, Volume I. Branch- Smith, Inc. Ft. Worth, TX.

Charles, M.C. 1993 (draft). Archeological evaluation and testing, Site 41JD63, Phantom Lake Springs, Jeff Davis County, Texas. Contract Report 8- CS- 40- 06920 for Bureau of Reclamation. Complete Archeological Service Associates, Cortez, CO.

Rio Grande Fishes Recovery Team. 1981. Recovery plan for the Comanche Springs pupfish. U.S. Fish and Wildlife Service, Albuquerque, NM.

Rio Grande Fishes Recovery Team. 1983. Recovery plan for the Pecos gambusia Gambusia nobilis. U.S. Fish and Wildlife Service, Albuquerque, NM.

Water and Power Resources Service. 1981. Project Data. U.S. Department of the Interior, Denver, CO.

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