ABSTRACT The exceptional groundwater community inhabiting the karstic Edwards-Trinity Aquifer system in central Texas has inspired generations of biologists seeking to understand diversification in an extreme environment. Since the late 1990s, molecular genetic tools have increasingly been used to uncover hidden diversity and infer the evolutionary history of groundwater species inhabiting the Edwards-Trinity system. The field of phylogeography—the study of the spatial distribution of genealogical lineages within and among intraspecific populations and closely related species—has provided unparalleled insight into patterns of Edwards-Trinity groundwater biodiversity. Similar to other global groundwater biodiversity hotspots, phylogeographic studies in the Edwards-Trinity Aquifer system have documented exceptionally high levels of endemism and strong population structure due to isolation across naturally fragmented habitat. Cryptic species (two or more morphologically similar but genetically distinct species) have been discovered in a number of phylogeographic investigations, including Eurycea salamanders, Dionda minnows, and Stygobromus amphipods. A number of these species are threatened or endangered with extinction due to habitat loss and degradation resulting from urbanization. Accurately delimiting species boundaries has had significant implications for biodiversity and groundwater conservation in the Edwards-Trinity region because the Endangered Species Act has been used to regulate unrestricted groundwater withdrawal in the eastern Edwards Aquifer where listed species are found. New developments in deoxyribonucleic acid (DNA) sequencing technology coupled with advancements in model-based inference will provide powerful tools for furthering our understanding of Edwards-Trinity biodiversity and predicting its response to a rapidly changing environment.

Dammed rivers are subject to changes in their flow, water-quality, and sediment regimes. Each of these changes may contribute to diminished aquatic habitat quality and quantity. Of the three factors, an altered sediment regime is a particularly unyielding challenge on many dammed rivers. The magnitude of the challenge is illustrated on the Lower Missouri River, where the largest water storage system in North America has decreased the downriver suspended-sediment load to 0.2%–17% of pre-dam loads. In response to the altered sediment regime, the Lower Missouri River channel has incised as much as 3.5 m just downstream of Gavins Point Dam, although the bed has been stable to slightly aggrading at other locations farther downstream. Effects of channel engineering and commercial dredging are superimposed on the broad-scale adjustments to the altered sediment regime. The altered sediment regime and geomorphic adjustments constrain restoration and management opportunities. Incision and aggradation limit some objectives of flow-regime management: In incising river segments, ecologically desirable reconnection of the floodplain requires discharges that are beyond operational limits, whereas in aggrading river segments, small spring pulses may inundate or saturate low-lying farmlands. Lack of sediment in the incising river segment downstream of Gavins Point Dam also limits sustainable restoration of sand-bar habitat for bird species listed under the Endangered Species Act. Creation of new shallow-water habitat for native fishes involves taking sediment out of floodplain storage and reintroducing most or all of it to the river, raising concerns about increased sediment, nutrient, and contaminant loads. Calculations indicate that effects of individual restoration projects are small relative to background loads, but cumulative effects may depend on sequence and locations of projects. An understanding of current and historical sediment fluxes, and how they vary along the river, provides a quantitative basis for defining management constraints and identifying opportunities.

ABSTRACT The Edwards Aquifer Authority (EAA) was established in 1996 after lawsuits that were filed for the protection of endangered species in Comal and San Marcos Springs revealed the need for aquifer management. Several events set the stage for water management in Texas and the creation of the EAA. The EAA succeeded the Edwards Underground Water District, which was formed after the 1951–1956 drought of record. The EAA was eventually granted regulatory responsibilities, including issuing permits for wells, setting limits on groundwater pumpage, and development of a habitat conservation plan to protect endangered species.

Abstract U.S. military installations increasingly have become de facto bioreserves as the result of legacy and current land uses, urbanization, and historical siting of installations. The relative value of military lands as bioreserves compared to land holdings of other federal agencies is not proportional to total land area. Ironically, a significant reason that U.S. military installations have become important bioreserves is that they were not established with the purpose of conserving or extracting natural resources. This historical factor has resulted in a broad representation of U.S. ecoregions on military lands and largely has shielded those lands from the habitat loss and degradation that has occurred in surrounding regions due to urbanization, agricultural development, and other non-military land uses. Fort Hood, Texas, is used as a case study to illustrate the characteristics of military installations that fit the model for bioreserves as areas for conservation of biological resources and processes in the context of human use of the environment. A major current challenge for management of natural resources on military lands is that the value of U.S. military lands as bioreserves is increasing as surrounding habitats and natural communities continue to be degraded.

ABSTRACT The Edwards Aquifer supports an important ecosystem with rarely seen faunas that have unique adaptations to a dark and thermally stable environment. We tallied over 60 species of aquifer-adapted (stygobitic) species in the Edwards Aquifer, and 30 more in other Texas aquifers, including snails, flatworms, worms, crustaceans, mites, and beetles. Exploration and research continue, with nine new species described in the last two years. Vertebrate species include Eurycea salamanders and ictalurid catfish, including a blind species ( Prietella phreatophila ) recorded for the first time in the United States from the Edwards–Trinity Plateau Aquifer in 2016. Contributing to the stygobite diversity are ten state or federally listed species, including the Texas blind salamander ( Eurycea rathbuni ), which was one of the first species to be listed as endangered by the U.S. Fish and Wildlife Service (USFWS) in 1970. Major springs of the Edwards (Balcones fault zone), Edwards–Trinity Plateau, Trinity, and other aquifers are under constant threat of drying due to aquifer overdraft and climate change. These springs provide habitat for 26 state or federally listed spring-adapted species. Aquifer species in general are known to provide ecosystem services, including water purification, nutrient cycling, and biological indication; however, the function and biology of these species in central Texas have not been studied. Considering the Edwards Aquifer ranks among the top aquifers in the world for number of species, the gaps in understanding remain enormous.

ABSTRACT The Edwards Aquifer Habitat Conservation Plan (EAHCP) protects the federally listed species in the Comal and San Marcos Springs. The plan was developed through the Edwards Aquifer Recovery Implementation Program, a consensus-based process involving a diverse body of stakeholders including industries, agricultural users, municipalities, water purveyors, river authorities, environmental organizations, four state agencies, and downstream interests. Since 2013, the partners of the EAHCP have implemented a multifaceted program mainly focused on spring-flow protection and habitat improvements to ensure the persistence of the covered species and to create more certainty in the region’s water supplies.