Abraham E. Springer

Degassing of mantle-derived CO2 and He from springs in the southern Colorado Plateau region - Neotectonic connections and implications for groundwater systems

Groundwaters of the southern Colorado Plateau–Arizona Transition Zone region are a heterogeneous mixture of chemically diverse waters including meteoric (epigenic) fluids, karst-aquifer waters, and deeply sourced (endogenic) fluids. We investigate the composition of travertine-depositing CO 2 -rich springs to determine the origin, transport, and mixing of these various components. The San Francisco Mountain recharge area has little surface flow. Instead, waters discharge through major springs hundreds of kilometers away. About 70% (9340 L/s) of the total recharge (13,500 L/s) discharges 100 km to the north in the incised aquifer system at Grand Canyon. Most of this water (85%; 8070 L/s) emerges through two travertine-depositing karst spring systems: Blue Springs (6230 L/s) and Havasu Springs (1840 L/s). About 30% of recharge (4150 L/s) flows to the south and discharges along NW-striking faults in the Arizona Transition Zone, forming the base flow for the Verde River. Geochemical data define regional mixing trends between meteoric recharge and different endogenic end members that range from bicarbonate waters to sulfate waters. Water quality in the region is dictated by the percentage and character of the endogenic inputs that cause a measurable degradation of groundwater quality for water supply. Sources for the high CO 2 include dissolution of limestone and dolostone (C carb ) and “external carbon” (C external ). C external is computed as the bicarbonate alkalinity (dissolved inorganic carbon [DIC]) minus the C carb (C external = DIC - C carb ). C external is deconvolved using carbon isotopes into biogenically derived sedimentary carbon (C organic ) and deep CO 2 inputs (C endogenic ). Measured δ 13 C values are −17‰ to +3‰ versus Pee Dee Belemnite (PDB). Assuming δ 13 C carb = +2‰, δ 13 C organic = −28‰, and δ 13 C endogenic = −5‰, water chemistry mixing models indicate that an average of 42% of the total DIC comes from dissolution of carbonate rocks, 25% from organic carbon, including soil-respired CO 2 ,and 33% from deep (endogenic) sources. Helium isotope values ( 3 He/ 4 He) in gases dissolved in spring waters in the southern Colorado Plateau region range from 0.10 to 1.16 R A (relative to air) indicating that a significant component of the deeply derived fluid is from the mantle (mean of 5% asthenospheric or 10% subcontinental lithospheric mantle source). Measured CO 2 / 3 He ratios of 2 × 10 9 to 1.4 × 10 13 are adjusted by removing the proportion of CO 2 from C carb and C organic to give values 10 for all but four samples. Various mixing models using CO 2 / 3 He suggest that the mantle-derived components of the CO 2 load are highly variable from spring to spring and may make up an average of ~10% of the total CO 2 load of the regional springs. Fluid-rock interactions involving endogenic fluids are suggested by 87 Sr/ 86 Sr, δ 18 O, and other tracers. The endogenic CO 2 component, multiplied by discharge for each spring, yields an integrated annual flux of deeply derived CO 2 to the groundwater system of ~1.4 × 10 9 mol/yr. This CO 2 emission from the Colorado Plateau region reflects a complex tectonic evolution involving Laramide hydration of the lithosphere above the Farallon slab, addition of fluids from mid-Tertiary mantle tectonism during slab removal, and ongoing fluid movement induced by neotectonic small-scale asthenospheric convection.

PLANNED FLOODING AND COLORADO RIVER RIPARIAN TRADE‐OFFS DOWNSTREAM FROM GLEN CANYON DAM, ARIZONA

Regulated river restoration through planned flooding involves trade-offs be- tween aquatic and terrestrial components, between relict pre-dam and novel post-dam re- sources and processes, and between management of individual resources and ecosystem characteristics. We review the terrestrial (wetland and riparian) impacts of a 1274 m 3 /s test flood conducted by the U.S. Bureau of Reclamation in March/April 1996, which was designed to improve understanding of sediment transport and management downstream from Glen Canyon Dam in the Colorado River ecosystem. The test flood successfully restored sandbars throughout the river corridor and was timed to prevent direct impacts to species of concern. A total of 1275 endangered Kanab ambersnail (Oxyloma haydeni kan- abensis) were translocated above the flood zone at Vaseys Paradise spring, and an estimated 10.7% of the total snail habitat and 7.7% of the total snail population were lost to the flood. The test flood scoured channel margin wetlands, including potential foraging habitats of endangered Southwestern Willow Flycatcher (Empidonax traillii extimus). It also buried ground-covering riparian vegetation under .1 m of fine sand but only slightly altered woody sandbar vegetation and some return-current channel marshes. Pre-flood control ef- forts and appropriate flood timing limited recruitment of four common nonnative perennial plant species. Slight impacts on ethnobotanical resources were detected .430 km down- stream, but those plant assemblages recovered rapidly. Careful design of planned flood hydrograph shape and seasonal timing is required to mitigate terrestrial impacts during efforts to restore essential fluvial geomorphic and aquatic habitats in regulated river eco- systems.

Coupling groundwater and riparian vegetation models to assess effects of reservoir releases

Although riparian areas in the arid southwestern United States are critical for maintaining species diversity, their extent and health have been declining since Euro-American settlement. The purpose of this study was to develop a methodology to evaluate the potential for riparian vegetation restoration and groundwater recharge. A numerical groundwater flow model was coupled with a conceptual riparian vegetation model to predict hydrologic conditions favorable to maintaining riparian vegetation downstream of a reservoir. A Geographic Information System (GIS) was used for this one-way coupling. Constant and seasonally varying releases from the dam were simulated using volumes anticipated to be permitted by a regional water supplier. Simulations indicated that seasonally variable releases would produce surface flow 5.4–8.5 km below the dam in a previously dry reach. Using depth to groundwater simulations from the numerical flow model with conceptual models of depths to water necessary for maintenance of riparian vegetation, the GIS analysis predicted a 5- to 6.5-fold increase in the area capable of sustaining riparian vegetation.

Semi‐Arid Aquifer Responses to Forest Restoration Treatments and Climate Change

The purpose of this study was to develop an interpretive groundwater-flow model to assess the impacts that planned forest restoration treatments and anticipated climate change will have on large regional, deep (>400 m), semi-arid aquifers. Simulations were conducted to examine how tree basal area reductions impact groundwater recharge from historic conditions to 2099. Novel spatial analyses were conducted to determine areas and rates of potential increases in groundwater recharge. Changes in recharge were applied to the model by identifying zones of basal area reduction from planned forest restoration treatments and applying recharge-change factors to these zones. Over a 10-year period of forest restoration treatment, a 2.8% increase in recharge to one adjacent groundwater basin (the Verde Valley sub-basin) was estimated, compared to conditions that existed from 2000 to 2005. However, this increase in recharge was assumed to quickly decline after treatment due to regrowth of vegetation and forest underbrush and their associated increased evapotranspiration. Furthermore, simulated increases in groundwater recharge were masked by decreases in water levels, stream baseflow, and groundwater storage resulting from surface water diversions and groundwater pumping. These results indicate that there is an imbalance between water supply and demand in this regional, semi-arid aquifer. Current water management practices may not be sustainable into the far future and comprehensive action should be taken to minimize this water budget imbalance.

Have wet meadow restoration projects in the Southwestern U.S. been effective in restoring geomorphology, hydrology, soils, and plant species composition?

BackgroundWet meadows occur in numerous locations throughout the American Southwest, but in many cases have become heavily degraded. Among other things they have frequently been overgrazed and have had roads built through them, which have affected the hydrology of these wetland ecosystems.Because of the important hydrologic and ecological functions they are believed to perform, there is currently significant interest in wet meadow restoration. Several restoration projects have been completed recently or are underway in the region, sometimes at considerable expense and with minimal monitoring. The objective of this review was to evaluate the effects of wet meadow restoration projects in the southwestern United States on geomorphology, hydrology, soils and plant species composition. A secondary objective was to determine the effects of wet meadow restoration projects on wildlife.MethodsElectronic databases, internet search engines, websites and personal contacts were used to find articles of relevance to this review. Articles were filtered by title, abstract and full text. Summary information for each of the articles remaining after the filtering process was compiled and used to assess the quality of the evidence presented using two different approaches.ResultsOur searches yielded 48 articles, of which 25 were published in peer-reviewed journals, 14 were monitoring or project reports, and 9 were published in conference proceedings or are unpublished theses or manuscripts.A total of 26 operational-scale restoration projects were identified. A wide range of restoration techniques were employed, ranging from small-scale manipulations of stream channels (e.g., riffle structures) to large scale pond-and-plug projects. Other common restoration techniques included fencing to exclude livestock (and sometimes also native ungulates), other forms of grazing management, seeding, and transplanting seedlings.Most of the articles reported that restoration was fully or partially effective, at least in the short-term. However, the relative lack of high quality quantitative data, and especially data extending more than two years after project implementation, greatly limits our ability to determine how effective restoration has truly been in practice.ConclusionsWhile caution is warranted due to data quality limitations, progress has been made over the past 20 years in wet meadow restoration. In particular, important contributions have been made in restoring the highly degraded wet meadow systems that are characterized by deep, wide and relatively straight gullies. There is evidence, for example, that the pond-and-plug approach is an effective technique for restoring many aspects of these systems, albeit at the cost of creating new features (ponds) that are not necessarily natural features of wet meadows.There is a need to allocate additional effort to project documentation, including better-designed and longer-lasting monitoring programs. One approach that might help is for practitioners to work with scientists from government agencies, local universities and colleges, and other organizations. When this type of collaboration has happened in the past it appears to have been effective. Many important lessons could have been learned, and mistakes avoided, if more effort had been put into documenting both successes and failures of past projects.

Local vs. Regional Groundwater Flow Delineation from Stable Isotopes at Western North America Springs

The recharge location for many springs is unknown because they can be sourced from proximal, shallow, atmospheric sources or long-traveled, deep, regional aquifers. The stable isotope (18 O and 2 H) geochemistry of springs water can provide cost-effective indications of relative flow path distance without the expense of drilling boreholes, conducting geophysical studies, or building groundwater flow models. Locally sourced springs generally have an isotopic signature similar to local precipitation for that region and elevation. Springs with a very different isotopic composition than local meteoric inputs likely have non-local recharge, representing a regional source. We tested this local vs. regional flow derived hypothesis with data from a new, large springs isotopic database from studies across Western North America in Arizona, Nevada, and Alberta. The combination of location-specific precipitation data with stable isotopic groundwater data provides an effective method for flow path determination at springs. We found springs in Arizona issue from a mix of regional and local recharge sources. These springs have a weak elevation trend across 1588 m of elevation where higher elevation springs are only slightly more depleted than low elevation springs with a δ18 O variation of 5.9‰. Springs sampled in Nevada showed a strong elevation-isotope relationship with high-elevation sites discharging depleted waters and lower elevation springs issuing enriched waters; only a 2.6‰ difference exists in 18 O values over an elevation range of more than 1500 m. Albertas springs are mostly sourced from local flow systems and show a moderate elevation trend of 1200 m, but the largest range in δ18 O, 7.1‰.

Springs ecosystem distribution and density for improving stewardship

Springs support some of the most diverse and unique ecosystems on Earth, but their stewardship has been hindered by the lack of knowledge of the distribution and density of springs across landscapes. Death Valley National Park (DEVA) and the State of Arizona in the USA are 2 landscapes for which significant knowledge exists about the distribution and density of springs. We used data on springs in DEVA to test the application of accumulation curves for estimating spring density. We used a spring-specific database in Arizona as an example of how to compile geospatial information for a large landscape. In both landscapes, springs are nonrandomly distributed because they emerge in topographically and geologically complex terrain and in clusters of multiple sources. Thus, estimates of their density depend on the spatial scale of inquiry and the extent to which sources are considered independent. For example, based on the current inventory, density in DEVA is estimated to be 0.033 to 0.074 springs/km2 depending on whether springs are defined as individual orifices or as complexes (groups of related spring orifices). The best data for springs as individual orifices yield an estimated 0.035 springs/km2 in Arizona. These densities are based on current data sets, and an unknown number of springs remain unmapped in both landscapes. To predict the total number of springs in DEVA, we used a modified density accumulation curve, involving the number of springs detected in surveys over the past century. The analysis indicated that undocumented springs may exist across the landscape. Knowledge of the distribution and density of the springs can help land and resource managers develop unbiased prioritizations of spring ecosystems for stewardship actions. Management actions could benefit further from an understanding of the emergence environment of a complex of springs, instead of each emergence point of a spring in a complex.

Groundwater Dependent Ecosystems: Classification, Identification Techniques and Threats

This chapter begins by briefly discussing the three major classes of groundwater dependent ecosystems (GDEs), namely: (I) GDEs that reside within groundwater (e.g. karsts; stygofauna); (II) GDEs requiring the surface expression of groundwater (e.g. springs; wetlands); and (III) GDEs dependent upon sub-surface availability of groundwater within the rooting depth of vegetation (e.g. woodlands; riparian forests). We then discuss a range of techniques available for identifying the location of GDEs in a landscape, with a primary focus of class III GDEs and a secondary focus of class II GDEs. These techniques include inferential methodologies, using hydrological, geochemical and geomorphological indicators, biotic assemblages, historical documentation, and remote sensing methodologies. Techniques available to quantify groundwater use by GDEs are briefly described, including application of simple modelling tools, remote sensing methods and complex modelling applications. This chapter also outlines the contemporary threats to the persistence of GDEs across the world. This involves a description of the “natural” hydrological attributes relevant to GDEs and the processes that lead to disturbances to natural hydrological attributes as a result of human activities (e.g. groundwater extraction). Two cases studies, (1) Class III: terrestrial vegetation and (2) Class II: springs, are discussed in relation to these issues.