Late Holocene hydrologic and climatic variability in the Walker Lake basin, Nevada and California

Oxygen and carbon isotopic measurements of the total inorganic carbon (TIC) fraction of sediments from Walker Lake (Nevada, USA) were completed at a decadal-scale resolution spanning the last ∼3000 years. On the basis of radiocarbon dating of the total organic fraction of cored sediments, the late Holocene isotope record recorded a relatively dry climate in Period LH-1 (1000 BC to AD 800), a relatively wet climate punctuated by a few severe droughts in Period LH-2 (AD 800 to 1900), and an anthropogenical perturbation era (L14-h: 1900–2000). Relative high accumulation rates in Period LH-2 (AD 800 to 1900) provided detailed information on climatic and hydrologic variability in this region. Coupled with the tree-ring-based Sacramento River flow record, the radiocarbon-based age model was refined for the interval of AD 800 through 1900. A high-resolution (3.5 year per sample) TIC δ18O record spanning the last 1200 years was generated to reflect fluctuations in winter snowfall of the Sierra Nevada. This TIC δ18O record shows two prolonged droughts that occurred during the Medieval Warm Epoch, which are chronologically well consistent with previous findings (STINF, 1994). Time series analyses on the TIC δ18O and the Sacramento River flow records reveal that interdecadal and centennial modes of climate variability persisted over the last millennium. PDO-like interdecadal oscillations that centered in the periods of 50–90 yr were almost in phase with thermal fluctuations in ocean climate of the California Current, suggesting that indedacadal climate oscillations in the Sierra Nevada were intimately linked with the Pacific dynamics. The underlying centennial to multicentennial variability corresponding to the Medieval Warm Epoch and the Little Ice Age comprise the major share of total variance. In addition, the TIC δ18O record of Walker Lake is visually well correlated with the polar ice-core-based cosmogenic nuclide production and the Rice Lake Mg/Ca records. This suggests that at least some centennial oscillations in winter precipitation of the Sierra Nevada were associated with solar activity over the last millennium

Chemical and Isotopic Evaluation of Sulfur Sources and Cycling in the Pecos River, New Mexico, USA

The use of stable isotopes in studies of watershed biogeochemical processes has increased greatly throughout the last several decades. Much of the sulfur cycling research has addressed the influence of changes in atmospheric acid deposition on sulfur dynamics in temperate ecosystems. Little is known about sulfur cycling in dryland ecosystems such as those in the American Southwest. To identify the sources and assess the cycling of sulfur in dryland ecosystems, chemical and isotopic compositions of water were measured on samples collected from the Pecos River (New Mexico, USA) during a reconnaissance survey in spring 2010. Based on the chemical and isotopic results, the Pecos River is readily divided into an upper basin of 6,000 km2 above Santa Rosa Lake and a lower basin of 44,000 km2 above Red Bluff Reservoir in western Texas. The upper basin contains river water with low concentrations of chloride (3 mg/L) and sulfate (13 mg/L), low values of δD (− 87‰) and δ18O (− 12.3‰), and low δ34S (− 4.3‰) and δ18O values (2.6‰) of dissolved sulfate (δ34SSO4 and δ18OSO4). Three different sources contributing to the pool of dissolved sulfate are identified, namely the oxidation of sulfide minerals, the soil processing of atmospheric sulfate, and the dissolution of ancient evaporites. The relative contributions of the three different sulfate sources change from reach to reach. Sulfate from evaporite dissolution primarily of Permian age dominates in the lower reaches while sulfate from sulfide oxidation dominates in the upper part of the Pecos River. Despite significant lithologic variations across the lower basin, δ34SSO4 values of river water are quite constant, with an average value of 11.8‰. In contrast, a 5‰ decrease was observed in δ18OSO4 values of river water between upstream and downstream reaches of the lower Pecos River, indicating that 63% of the dissolved sulfate had been recycled. Surprisingly, most of the sulfur cycling observed occurs in two small irrigation districts (the Fort Sumner Irrigation District and the Carlsbad Irrigation District), whereas there is only a minimal decrease (0.7‰) in δ18OSO4 in the largest irrigation district (the Pecos Valley Artesian Conservancy District). This study implies that the influence of land use activities on sulfur cycling may be more profound than previously thought

Characteristics of Oxygen-18 and Deuterium Composition in Waters from the Pecos River in American Southwest

The Pecos River, situated in eastern New Mexico and western Texas, receives snowmelt from winter storms in the headwater region of the southern Rocky Mountains and runoff from warm-season monsoonal rainfall in the lower valley. The isotopic composition of the two water sources differs from each other due to their different geographical origins in the Pacific North and the Gulf of Mexico. To better assess the physical features of the Pecos River, oxygen and hydrogen isotopic compositions (δ18O and δD), major ion concentrations, and other physical variables (e.g., water temperature and electrical conductivity) were measured on water samples collected from the main stem and its selected tributaries during a growing season (March, May, and July) in 2005. The results of this work indicate that stream water from the Pecos River contains a relatively large magnitude of variations in δ18O and δD, with δ18O ranging from − 8.9‰ to 3.6‰ and δD from − 64.5‰ to 1.6‰. The average value of δ18O is around − 3‰, which is significantly larger than that of the snowmelt but almost identical to that of the Mexican monsoonal rainfall. On the other hand, the average value of δD is around − 30‰, which is significantly larger than that of the snowmelt but lower than that of the Mexican monsoonal rainfall. Application of a dual isotope index, deuterium excess (d-excess), allows us to assess the relative contribution of various hydrologic components and processes that shape the stream hydrology of the Pecos River. The river water from the upper valley is characterized by relatively low values of δ18O and δD and relatively high values of d-excess (d = 10‰), documenting the isotopic fingerprint of the snowmelt. The middle basin is topographically gentle and its water quality has been severely affected by anthropogenic disturbances (e.g., water impoundments and diversions). As a result, chemical and isotopic composition of the water from the middle basin is highly variable, depending on its time, location, and degree of disturbances. Both δ18O and δD increase significantly from upstream to downstream and from cold to warm seasons because of evaporation-induced isotopic enrichments. The average δ18O value of the heavy-isotope-enriched waters from the middle basin is identical to that of the waters from the lower valley. In contrast, d-excess of the waters from the middle basin usually is negative, and substantially lower than that of the waters from the lower valley. Using a simple d-excess based hydrologic model, we estimated that there was up to 85% of stream flow which was derived from local freshwater sources (mainly from the Mexican monsoonal rainfall) in the lower valley and that there was up to 33% of stream water which was lost through evaporation occurring in stream channels and fields of the middle basin. Additionally, the correlation of d-excess and electrical conductivity further highlights the role of evaporative enrichments in regulating stream chemistry and isotope hydrology. This study demonstrates the usefulness of combined isotopic and geochemical data, especially the applicability of d-excess, for watershed baseline assessments

Dominant Processes Controlling Water Chemistry of the Pecos River in American Southwest

Here we show an analysis of river flow and water chemistry data from eleven gauging stations along the Pecos River in eastern New Mexico and western Texas, with time spanning 1959–2002. Analysis of spatial relationship between the long-term average flow and total dissolved solids (TDS) concentration allows us to illuminate four major processes controlling river chemistry, namely saline water addition, evaporative concentration with salt gain or loss, dilution with salt gain or loss, and salt storage. Of the 10 river reaches studied, six reaches exhibit the process dominated by evaporative concentration or freshwater dilution with little change in salt load. Four reaches show considerable salt gains or losses that are induced by surfaceground water interactions. This analysis suggests that the evaporative concentration and freshwater dilution are the prevailing mechanisms, but local processes (e.g., variations in hydrologic flowpath and lithologic formation) also play an important role in regulating the hydrochemistry of the Pecos River

Influence of the Pacific Decadal Oscillation on Hydrochemistry of the Rio Grande, USA, and Mexico

The hydrochemistry has been examined using the major element composition of river water at 12 gauging stations along the Rio Grande. As the Rio Grande Basin consists of two watersheds that have different hydrologic and climatic regimes, two chloride concentration records from the El Paso and Falcon Dam gauging stations have been extracted to reflect long-term variability in river chemistry of the upper and lower basins over the last 50–70 years. Both records contain decadal variability in chloride concentration but are different in nature. The chloride concentration record from the upper basin displays a distinct pattern of decadal variability similar to the Pacific Decadal Oscillation (PDO). This indicates the chloride concentration at El Paso is largely determined by the amount of stream discharge of the upper basin that is associated with the PDO. Conversely, there is no such pattern of decadal variability in the chloride concentration record from the lower basin though several of the chloride concentration maxima coincide with minima in the PDO index. Instead, the chloride concentration record from the lower basin contains a progressively increasing trend of chloride concentration from 1970 to 1990, suggesting that anthropogenic disturbances (e.g., dam constructions and increased irrigation demands) may also play a role in intervening long-term changes in river chemistry

Characteristics of Oxygen-18 and Deuterium Composition in Waters from the Pecos River in American Southwest

The Pecos River, situated in eastern New Mexico and western Texas, receives snowmelt from winter storms in the headwater region of the southern Rocky Mountains and runoff from warm-season monsoonal rainfall in the lower valley. The isotopic composition of the two water sources differs from each other due to their different geographical origins in the Pacific North and the Gulf of Mexico. To better assess the physical features of the Pecos River, oxygen and hydrogen isotopic compositions (δ18O and δD), major ion concentrations, and other physical variables (e.g., water temperature and electrical conductivity) were measured on water samples collected from the main stem and its selected tributaries during a growing season (March, May, and July) in 2005. The results of this work indicate that stream water from the Pecos River contains a relatively large magnitude of variations in δ18O and δD, with δ18O ranging from − 8.9‰ to 3.6‰ and δD from − 64.5‰ to 1.6‰. The average value of δ18O is around − 3‰, which is significantly larger than that of the snowmelt but almost identical to that of the Mexican monsoonal rainfall. On the other hand, the average value of δD is around − 30‰, which is significantly larger than that of the snowmelt but lower than that of the Mexican monsoonal rainfall. Application of a dual isotope index, deuterium excess (d-excess), allows us to assess the relative contribution of various hydrologic components and processes that shape the stream hydrology of the Pecos River. The river water from the upper valley is characterized by relatively low values of δ18O and δD and relatively high values of d-excess (d = 10‰), documenting the isotopic fingerprint of the snowmelt. The middle basin is topographically gentle and its water quality has been severely affected by anthropogenic disturbances (e.g., water impoundments and diversions). As a result, chemical and isotopic composition of the water from the middle basin is highly variable, depending on its time, location, and degree of disturbances. Both δ18O and δD increase significantly from upstream to downstream and from cold to warm seasons because of evaporation-induced isotopic enrichments. The average δ18O value of the heavy-isotope-enriched waters from the middle basin is identical to that of the waters from the lower valley. In contrast, d-excess of the waters from the middle basin usually is negative, and substantially lower than that of the waters from the lower valley. Using a simple d-excess based hydrologic model, we estimated that there was up to 85% of stream flow which was derived from local freshwater sources (mainly from the Mexican monsoonal rainfall) in the lower valley and that there was up to 33% of stream water which was lost through evaporation occurring in stream channels and fields of the middle basin. Additionally, the correlation of d-excess and electrical conductivity further highlights the role of evaporative enrichments in regulating stream chemistry and isotope hydrology. This study demonstrates the usefulness of combined isotopic and geochemical data, especially the applicability of d-excess, for watershed baseline assessments

Climate Change from Oxygen Isotopic Variation of Pore Water from Sediments in Punderson Lake, Northeast Ohio

The environment in Ohio has changed over time. The hydroclimate, which is the climate of the water, shows changes from the Industrial Revolution to the present. Evidence for these changes can be found in levels of δ18O and δ2H isotopes in the layers of sediment and water in the lakes of Northeast Ohio. Mass spectrometry can be used to test the levels of δ18O and δ2H isotopes from pore water samples within sediment cores. In this study, surface soil and water samples were collected from cores in Punderson Lake at Punderson State Park in Newbury, Ohio. Pore water was extracted from the sediment core every centimeter. Next the oxygen isotope composition (δ18O) and the levels of δ2H of the pore water in the sediment layers were measured using a Picarro Cavity Ringdown Spectrometer. A record of the δ18O and δ2H of Punderson Lake was then recorded to determine the climate variability over a period of approximately 350 years. Changes in the δ18O and δ2H of lake water can be used to see changes in precipitation and water balance. Determining past climate and hydroclimate changes can help us predict future changes in the climate of Northeast Ohio.https://engagedscholarship.csuohio.edu/u_poster_2013/1012/thumbnail.jp

Analytical Solutions for Vertical Flow in Unsaturated, Rooted Soils with Variable Surface Fluxes

Analytical solutions to Richards\u27 equation have been derived to describe the distribution of pressure head, water content, and fluid flow for rooted, homogeneous soils with varying surface fluxes. The solutions assume that (i) the constitutive relations for the hydraulic conductivity and water content as function of the pressure head are exponential, (ii) the initial water content distribution is a steady-state distribution, and (iii) the root water uptake is a function of depth. Three simple forms of root water uptake are considered, that is, uniform, stepwise, and exponential functional forms. The lower boundary of the rooted soil profile studied is a water table, while at the upper boundary time-dependent surface fluxes are specified, either infiltration or evaporation. Application of the Kirchhoff transformation allows us to linearize Richards\u27 equation and derive exact solutions. The steady-state solution is given in a closed form and the transient solution has the form of an infinite series. The solutions are used to simulate the hydraulic behavior of the rooted soils under different conditions of root uptake and surface flux. The restricted assumptions for the solutions may limit the applicability, but the solutions are relatively flexible and easy to implement compared to other analytical and numerical schemes. The analytical solutions provide a reliable and convenient means for evaluating the accuracy of various numerical schemes, which usually require sophisticated algorithms to overcome convergence and mass balance problems

Changes in Major Element Hydrochemistry of the Pecos River in the American Southwest Since 1935

The Pecos River, situated in eastern New Mexico and western Texas, receives water from a drainage area of 91 000 km2. There are primarily two major water inputs, namely snowmelt from winter storms in the headwater region of the southern Rocky Mountains and runoff from warm-season monsoonal rainfall in the lower valley. The Pecos River suffers from high levels of total dissolved solids (TDS \u3e5000 mg L−1) under normal flow conditions. This not only poses serious problems for agricultural irrigation and safe drinking water supply, but also results in a permanent loss of biodiversity. This study examines changes in stream flow and water chemistry of the Pecos River over the last 70 a to better understand the long-term variability in stream salinity and the role of agricultural practices in salt transfer. A TDS record from the lower Pecos River near Langtry (Texas) back to 1935 was extracted to show a distinct pattern of decadal variability similar to the Pacific Decadal Oscillation (PDO), in which stream salinity is overall above average when the PDO is in positive (warm) phase and below average when the PDO is in negative (cold) phase. This is due to: (1) the dissolved salts contributed to the river are largely from dissolution of NaCl and CaSO4-bearing minerals (e.g., halite and gypsum) in the upper basin, (2) the amount of the dissolved salts that reach the lower basin is mainly determined by the stream flow yield in the upper basin and (3) the stream flow yield from the upper basin is positively correlated with the PDO index. This further attests that large-scale climatic oscillation is the major source of long-term changes in stream flow and salinity of the Pecos River. On the other hand, there is also a strong indication that the rate of salt export has been affected by reservoir operations and water diversions for agricultural practices

Simple Methods for Estimating Outflow Salinity from Inflow and Reservoir Storage

Reservoir storage reduces fluctuation in streamflow salinity, as inflow blends with stored water. This process is directly relevant to reservoir management, yet the methods for predicting outflow salinity from inflow and storage data are not adequately addressed. This study examined three simple methods for estimating outflow salinity on a monthly time step. The first method applies when inflow approximately equals outflow. The second method is applicable to changing reservoir storage. The third method utilizes a two-layer model in which evaporative concentration is assumed to occur in the top layer. The third method requires the full account of the water balance, including evaporation and percolation losses. All three methods require reservoir storage blend with inflow in a stepwise manner. Outflow salinity was then computed monthly as a moving average. These methods were applied to high and low storage periods up to two years at three large reservoirs (Elephant Butte, Amistad, and Falcon) located along the Rio Grande. All of the equations tested provided good estimates of outflow salinity with the standard errors of estimate ranging from 5 to 10%. When a matching factor (accounting for ungauged inflow and water levels) was used in the first or the second method, they provided the estimate of monthly outflow salinity just as accurately as did the two-layer model. The accuracy of prediction, especially by the third method, can be improved if the initial reservoir salt storage is assessed with greater accuracy. Although the third method is more descriptive, the first two methods are also useful when detailed water balance data are not available