Local shallow groundwater drawdown and baseflow cessation due to regional groundwater pumping. In Lowrance, R. (Ed.), Riparian Ecosystems and Buffers: Multi-Scale Structure, Function, and Management

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Numerous studies have shown that stream water and shallow groundwater are tightly linked in alluvial settings, and that changes in stream stage are propagated rapidly across alluvial aquifers (Castro and Hornberger 1991, Sophocleous 1991). Thus, many researchers have assumed that stream stages approximate water tables in alluvial aquifers (Auble et al. 1994, Stromberg and Patten 1996). This assumption is valid in some cases but invalid in other cases, particularly in arid basin terrain and more humid mountain terrain. Even when this assumption is valid, this relationship only implies correlation and not causation so the potential effects of stream flow alterations on shallow groundwater and associated riparian vegetation remain unknown.
The Great Valley Sequence of Upper Jurassic to Upper Cretaceous strata is composed of clastic detritus eroded from the Sierran-Klamath belt, which was the site of a late Mesozoic magmatic arc. The sequence accumulated mainly as a prismatic wedge of turbidites in an asymmetric trough within the arc-trench gap. Stratigraphic variations in detrital sandstone mineralogy define five petrologic intervals, or nearly synchronous petrofacies, useful for regional correlation. By contrast, local lithofacies are markedly lenticular. The clastic debris in the sequence was derived mainly from volcanic and plutonic rocks in varying proportions. The parameters used to define the petrofacies include: (a) content of quartzose grains (Q), feldspar grains (F), and unstable lithic fragments (L) expressed as volumetric percentages of the Q-F-L population; (b) ratios of plagioclase to total feldspar (P/F) and volcanic rock fragments to total unstable lithic fragments (V/L), and (c) content of mica (M) expressed as volumetric percentage of framework sand grains. The most distinctive characteristics of the petrofacies recognized, and their approximate time-stratigraphic spans, are as follows: (1) Stony Creek (Tithonian-Neocomian): quartz-poor and feldspatholithic sandstones with high P/F, high V/L, low M; (2) Lodoga (Aptian-Albian): quartz-rich sandstones with high P/F; (3) Boxer (Cenomanian): two distinct variants with moderate P/F, one quartz-rich and the other quartz-poor and feldspatholithic; (4) Cortina (Turonian-Coniacian): two similar variants with moderate P/F, one with Q-F-L proportions nearly equal and the other quartz-poor and feld-spatholithic; (5) Rumsey (Santonian-Campanian): quartz-rich lithofeldspathic with low P/F and high M. The nature of the petrofacies and their age can be related to the petrology and timing of dated intrusive episodes with inferred volcanic accompaniments in the Sierra Nevada. The Stony Creek petrofacies contains mainly volcanic debris erupted during the Yosemite magmatic epoch, and the overlying Lodoga petrofacies contains mainly plutonic debris emplaced during the same epoch, but only exposed to erosion by subsequent dissection. The Boxer and Cortina petrofacies contain mixed and intercalated volcanic and plutonic debris derived mainly from rocks erupted or emplaced during the Huntington Lake magmatic epoch. The slight differences between the Boxer and Cortina petrofacies may indicate that plutonic contributions were partly from older rocks for the Boxer, but volcanic contributions were essentially the same for both. The Rumsey facies contains mainly plutonic debris, with subordinate volcanic debris, derived from igneous rocks of the Cathedral Range magmatic epoch. Except locally or slightly, petrofacies boundaries do not transgress time-stratigraphic boundaries in the region. A close linkage among major magmatic, tectonic, and depositional events in arc-trench systems is implied.
Data from two headwater streams in southern Ontario provide support for conceptual models that suggest that hyporheic zone influence on stream nutrient retention is determined by the extent of surface-groundwater exchange and subsurface chemical transformation rates. The hyporheic zone (>10% stream water) was delineated by a chemical mixing equation using differences in background stream and groundwater chloride concentrations and by injections of chloride to stream flow. Good agreement between the two methods confirmed that the extent of stream-groundwater exchanges can be successfully estimated using background conservative ions as a tracer technique. During low stream flows in May-October the depth of the hyporheic zone was 2-15 cm in a 12-m sand-bottom pool, debris dam, pool reach of Glen Major stream and 15-20 cm in a 16-m gravel riffle reach of Duffin Creek. Differences between observed NO3 concentrations and concentrations predicted from background chloride indicated depletion of NO3 in the hyporheic zone at a few locations in Glen Major and at 5-10 cm depth throughout the Duffin Creek reach. NO3 and NH4 injected into stream water were reactive at only a few hyporheic sites in the streams. Upstream-downstream comparisons during injections indicated that stream retention was minor.
RESEARCH based on stable isotope variations in natural compounds is expanding in scientific fields such as geochemistry, hydrology, environmental studies and biochemistry. However, intercomparison of results obtained in different laboratories is often not fully reliable and therefore to improve the intercalibration of deuterium and 18O measurements in natural waters, two water standards have been distributed by the International Atomic Energy Agency since 1968. The two standards, called V-SMOW (Vienna Standard Mean Ocean Water) and SLAP (Standard Light Antarctic Precipitation), were prepared, following a recommendation by an Advisory Group Meeting convened by the IAEA in 1966. Information on the two standards is given here.
To evaluate the abundance of Tricolored Blackbirds (Agelaius tricolor), the schedule of breeding throughout the Central Valley of California was determined in four years (1992-1994, 1997). By the end of April in 1994, all observed Tricolored Blackbirds were in the immediate vicinity of active breeding colonies. Only one colony of 600 birds was established in the Sacramento Valley north of Sacramento County. During late May and early June, more than 170,000 individuals settled in the Sacramento Valley, while attendance at colonies in the San Joaquin Valley was declining. Most breeding birds colo-nizing the Sacramento Valley in May and June probably already had completed nesting efforts elsewhere. This suggests that Tricolored Blackbirds are itinerant breeders. Surveys, conducted after initial settlement and before substantial movements from one breeding area to another occur, have the potential to estimate overall numbers. Inclusion of late season breeding colonies in estimates of overall abundance would result in substantial overestimates of the global population. Local and regional declines in the number of breeding Tricolored Blackbirds of an order of magnitude or more resemble population collapses but probably are attributable to itinerant breeding.
The High Plains aquifer underlying the semiarid Southern High Plains of Texas and New Mexico, USA was used to illustrate solute and isotopic methods for evaluating recharge fluxes, runoff, and spatial and temporal distribution of recharge. The chloride mass-balance method can provide, under certain conditions, a time-integrated technique for evaluation of recharge flux to regional aquifers that is independent of physical parameters. Applying this method to the High Plains aquifer of the Southern High Plains suggests that recharge flux is approximately 2% of precipitation, or approximately 11 ± 2 mm/y, consistent with previous estimates based on a variety of physically based measurements. The method is useful because long-term average precipitation and chloride concentrations in rain and ground water have less uncertainty and are generally less expensive to acquire than physically based parameters commonly used in analyzing recharge. Spatial and temporal distribution of recharge was evaluated by use of δ2H, δ18O, and tritium concentrations in both ground water and the unsaturated zone. Analyses suggest that nearly half of the recharge to the Southern High Plains occurs as piston flow through playa basin floors that occupy approximately 6% of the area, and that macropore recharge may be important in the remaining recharge. Tritium and chloride concentrations in the unsaturated zone were used in a new equation developed to quantify runoff. Using this equation and data from a representative basin, runoff was found to be 24 ± 3 mm/y; that is in close agreement with values obtained from water-balance measurements on experimental watersheds in the area. Such geochemical estimates are possible because tritium is used to calculate a recharge flux that is independent of precipitation and runoff, whereas recharge flux based on chloride concentration in the unsaturated zone is dependent upon the amount of runoff. The difference between these two estimates yields the amount of runoff to the basin.
In this study, we identify the origin of shallow ground water that supports regionally unique plant and wildlife habitats in a riparian and reservoir-fringe system using isotopic and chemical procedures. This study was conducted where Little Stony Creek flows into East Park Reservoir on the east front of the Coast Range, northern California. Little Stony Creek water, Hyphus Creek water, Franciscan Complex regional ground water, Great Valley Group regional ground water, and local shallow ground water were collected during wet and dry seasons and were analyzed for deuterium, oxygen-18, temperature, pH, redox potential, conductivity, and major cation and anion concentrations. Turnover in the local flow system is rapid indicating that local shallow ground water is dependent on recent recharge. Local shallow ground water is recharged primarily by Little Stony Creek water and Franciscan Complex ground water. In the wet season, Little Stony Creek is the more prominent source of local shallow ground water, and the ratio of Little Stony Creek water to Franciscan Complex ground water decreases with distance from the channel. In the dry season, Franciscan Complex ground water is the more prominent source of local shallow ground water, and the ratio of Little Stony Creek water to Franciscan Complex ground water decreases with distance down the valley. Franciscan Complex ground water discharges to local shallow ground water throughout the year, primarily because the local flow system is a regional low that lies perpendicular to the Franciscan Complex ground water flowpath. Little Stony Creek is a more prominent source of ground water in the wet season than in the dry season because Little Stony Creek flows continuously through the alluvial reach in the wet season and intermittently through the alluvial reach in the dry season. Extensive ground water withdrawals from the Franciscan Complex flow system could reduce the amount of water available to the local flow system, particularly during the dry season, and could substantially reduce the geographic extent of the regionally unique plant and wildlife habitats.
The relationship between deuterium and oxygen-18 concentrations in natural meteoric waters from many parts of the world has been determined with a mass spectrometer. The isotopic enrichments, relative to ocean water, display a linear correlation over the entire range for waters which have not undergone excessive evaporation.
The Franciscan Assemblage and Related Rocks in Northern California
  • Jr Blake
  • D L Jones
Blake, Jr., M.C. and D.L. Jones, 1981. The Franciscan Assemblage and Related Rocks in Northern California. In The Geotectonic Development of California, ed. W.G. Ernst, 306-328. Prentice-Hall, Englewood Cliffs, New Jersey.
Great Valley Group (Sequence)
  • R V Ingersoll
  • W R Dickinson
Ingersoll, R.V. and W.R. Dickinson, 1990. Great Valley Group (Sequence), Sacramento Valley, California. In Sacramento Valley Symposium and Guidebook, ed. R.V. Ingersoll and T.H. Nilsen, 183-215. The Pacific Section, Society of Economic Paleontologists and Mineralogists, Los Angeles, California.
Oxygen and Hydrogen Isotopes in the Hydrologic Cycle
  • J R Gat
Gat, J.R., 1996. Oxygen and Hydrogen Isotopes in the Hydrologic Cycle. Annual Review of Earth and Planetary Sciences 24:225-262.
Personal Communication to Author
  • W Dunn
Dunn, W., 2000. Personal Communication to Author, Stonyford, CA, September 28.