Gregory B. Pasternack

Volcanic lake systematics II. Chemical constraints

Abstract A database of 373 lake water analyses from the published literature was compiled and used to explore the geochemical systematics of volcanic lakes. Binary correlations and principal component analysis indicate strong internal coherence among most chemical parameters. Compositional variations are influenced by the flux of magmatic volatiles and/or deep hydrothermal fluids. The chemistry of the fluid entering a lake may be dominated by a high-temperature volcanic gas component or by a lower-temperature fluid that has interacted extensively with volcanic rocks. Precipitation of minerals like gypsum and silica can strongly affect the concentrations of Ca and Si in some lakes. A much less concentrated geothermal input fluid provides the mineralized components of some more dilute lakes. Temporal variations in dilution and evaporation rates ultimately control absolute concentrations of dissolved constituents, but not conservative element ratios. Most volcanic lake waters, and presumably their deep hydrothermal fluid inputs, classify as immature acid fluids that have not equilibrated with common secondary silicates such as clays or zeolites. Many such fluids may have equilibrated with secondary minerals earlier in their history but were re-acidified by mixing with fresh volcanic fluids. We use the concept of ‘degree of neutralization’ as a new parameter to characterize these acid fluids. This leads to a classification of gas-dominated versus rock-dominated lake waters. A further classification is based on a cluster analysis and a hydrothermal speedometer concept which uses the degree of silica equilibration of a fluid during cooling and dilution to evaluate the rate of fluid equilibration in volcano-hydrothermal systems.

Flow convergence routing hypothesis for pool‐riffle maintenance in alluvial rivers

[1] The velocity reversal hypothesis is commonly cited as a mechanism for the maintenance of pool-riffle morphology. Although this hypothesis is based on the magnitude of mean flow parameters, recent studies have suggested that mean parameters are not sufficient to explain the dominant processes in many pool-riffle sequences. In this study, two- and three-dimensional models are applied to simulate flow in the pool-riffle sequence on Dry Creek, California, where the velocity reversal hypothesis was first proposed. These simulations provide an opportunity to evaluate the hydrodynamics underlying the observed reversals in near-bed and section-averaged velocity and are used to investigate the influence of secondary currents, the advection of momentum, and cross-stream flow variability. The simulation results support the occurrence of a reversal in mean velocity and mean shear stress with increasing discharge. However, the results indicate that the effects of flow convergence due to an upstream constriction and the routing of flow through the system are more significant in influencing pool-riffle morphology than the occurrence of a mean velocity reversal. The hypothesis of flow convergence routing is introduced as a more meaningful explanation of the mechanisms acting to maintain pool-riffle morphology.

Spawning habitat rehabilitation ‐I. Conceptual approach and methods

Abstract Altered sediment and flow regimes in regulated rivers limit available spawning habitat for many fishes, especially salmonids. Mitigation efforts include spawning habitat rehabilitation and dam‐removal, but often neglect conceptual or predictive models of hydrogeomorphic and ecological processes. Complete restoration of processes necessary for maintaining spawning habitat is often unrealistic in regulated rivers. However, we present a framework for spawning habitat rehabilitation based on the premise that certain ecologic functions and geomorphic processes can be restored in a manner that facilitates testing of underlying scientific theories. SHIRA (Spawning Habitat Integrated Rehabilitation Approach) provides a science‐based, systematic framework for reach‐scale rehabilitation of salmonid spawning habitat in regulated rivers. This approach is driven by a mix of field data, conceptual models and numerical models to provide predictive and explanatory insight into the rehabilitation process. Conceptual models are advocated for developing multiple design scenarios and explicit hypotheses about hydrogeomorphic processes and ecologic functions provided by said designs. Hydrodynamic, habitat suitability and sediment entrainment models that test the potential validity of design hypotheses prior to construction are reviewed. It is presumed that the added insight would improve the outcome of rehabilitation projects and test underlying scientific theories against the rigors of real‐world uncertainties.

Sedimentation Cycles in a River-Mouth Tidal Freshwater Marsh

Tidal freshwater marshes are critical buffers that exist at the interface between watersheds and estuaries. Little is known about the physical dynamics of tidal freshwater marsh evolution. Over a 21-mo period, July 1995 to March 1997, measurements were made of biweekly sediment deposition at 23 locations in a 3.8-ha tidal freshwater marsh in the Bush River subestuary of the upper Chesapeake Bay. Biweekly accumulation showed high spatial and temporal variability, ranging from −0.28 g cm−2 to 1.15 g cm−2. Spatial variability is accounted for by habitat differences including plant associations, elevation, and hydrology. Temporal variability is accounted for by interannual climate variability, the growth cycles of marsh plants, stream-marsh interactions, forest-marsh interactions, and animal activity.

Spawning habitat rehabilitation ‐ II. Using hypothesis development and testing in design, Mokelumne river, California, U.S.A.

Abstract Rehabilitation of salmonid spawning habitat in regulated rivers through spawning bed enhancement is commonly used to mitigate altered sediment and flow regimes and associated declines in salmonid communities. Partial design‐phase predictive results are reported from the application of SHIRA (Spawning Habitat Integrated Rehabilitation Approach) on the lower Mokelumne River, California. The primary management goal of the project was to improve habitat for spawning and incubation life stages of fall‐run chinook salmon (Oncorhynchus tshawytscha). In the summer of 2001, we conducted a pre‐project appraisal followed by development and testing of 12 design scenarios. A subsample of eight design hypotheses, used in three of the design scenarios, is presented. Hydrodynamic, habitat suitability and sediment entrainment model results were used to test five of the eight design hypotheses. Two of the three hypotheses not tested were due to inadequate data on flow boundary conditions at high discharges. In September 2001, the project was constructed in a 152 m reach of the LMR from a final design based on all eight of the design hypotheses presented. Transparent hypothesis development and testing in design is emphasized as opposed to declaring success or failure from an ongoing long‐term monitoring campaign of the case study presented.

Does the river run wild? Assessing chaos in hydrological systems

Abstract The standing debate over whether hydrological systems are deterministic or stochastic has been taken to a new level by controversial applications of chaos mathematics. This paper reviews the procedure, constraints, and past usage of a popular chaos time series analysis method, correlation integral analysis, in hydrology and adds a new analysis of daily streamflow from a pristine watershed. Significant problems with the use of correlation integral analysis (CIA) were found to include a continued reliance on the original algorithm even though it was corrected subsequently and failure to consider the physics underlying mathematical results. The new analysis of daily streamflow reported here found no attractor with D ⩽5. Phase randomization of the Fourier Transform of streamflow was used to provide a better stochastic surrogate than an Autoregressive Moving Average (ARMA) model or gaussian noise for distinguishing between chaotic and stochastic dynamics.

Hydrogen peroxide treatment effects on the particle size distribution of alluvial and marsh sediments

Pretreatment of sediment with hydrogen peroxide to remove organic constituents and aid deflocculation is a common component of particle size analyses of terrestrial and marine sediments. This study quantitatively determined the effect of a range of treatment levels on particle size distribution among four sediment types representing a range of mineral/organic particle size distributions, organic content and particle characterisation (charcoal or detrital plant material). The hypothesis was that complete removal of organic particles would lead to improved repeatability of results for a given sample and treatment level. Repeatability was assessed with a coefficient of variance calculation and a comparison of particle size distribution patterns within and across treatments. The effect of treatment levels on commonly used distribution descriptors (e.g. texture ratios and measures of central tendency) were then examined for each sample. Samples characterised primarily by detrital material responded most readily to treatment, whereas charcoal-dominated samples required higher levels of treatment to achieve increased repeatability and disappearance of large organic particles. Certain distribution descriptors, such as modal analysis, were found to be more resilient to organic particle presence, although amplitude of the organic distribution and the degree of overlap with the inorganic signal in some cases obscured even this metric. Thus, final treatment recommendations are based on sample characteristics and the types of distribution descriptors used in a study.

The effects of wildfire on the sediment yield of a coastal California watershed

The occurrence of two wildfi res separated by 31 yr in the chaparral-dominated Arroyo Seco watershed (293 km 2 ) of California provides a unique opportunity to evaluate the effects of wildfi re on suspended-sediment yield. Here, we compile discharge and suspended-sediment sampling data from before and after the fi res and show that the effects of the postfi re responses differed markedly. The 1977 Marble Cone wildfi re was followed by an exceptionally wet winter, which resulted in concentrations and fl uxes of both fi ne and coarse suspended sediment that were ~35 times greater than average (sediment yield during the 1978 water year was 11,000 t/km 2 /yr). We suggest that the combined 1977–1978 fi re and fl ood had a recurrence interval of greater than 1000 yr. In contrast, the 2008 Basin Complex wildfi re was followed by a drier than normal year, and although suspended-sediment fl uxes and concentrations were signifi cantly elevated compared to those expected for unburned conditions, the sediment yield during the 2009 water year was less than 1% of the post–Marble Cone wildfi re yield. After the fi rst postfi re winters, sediment concentrations and yield decreased with time toward prefi re relationships and continued to have signifi cant rainfall dependence. We hypothesize that the differences in sediment yield were related to precipitationenhanced hillslope erosion processes, such as rilling and mass movements. The millennialscale effects of wildfi re on sediment yield were explored further using Monte Carlo simulations, and these analyses suggest that infrequent wildfi res followed by flincrease long-term suspended-sediment fl markedly. Thus, we suggest that the current approach of estimating sediment yield from sediment rating curves and discharge data— without including periodic perturbations from wildfi res—may grossly underestimate actual sediment yields.

Optimizing placement of beacons and data loggers in a sensor network - a case study

Localization and clustering of sensor nodes are important services in a sensor network since the nodes are typically deployed in an ad-hoc manner into an infrastructure-less terrain. When beacons are used for localization, there are two critical design issues: 1) to maximize the lifetime of the beacons and 2) to maximize the coverage area. With clustering, the goal is to minimize the energy dissipation of the sensor network. In this paper, we consider the placement of beacons and data loggers (that act as cluster heads) in the Cosumnes River Preserve, which is a joint collaborative restoration project between the Cosumnes Research Consortium at University of California at Davis (UCD) and The Nature Conservancy. Currently, there are many types of sensors deployed in the preserve which are wired to data loggers. Our objective is to determine the minimum number and placement of beacons and data loggers for wireless sensors deployed in the preserve. We formulated an optimization problem which is solved by integer linear program (ILP).

Biogeomorphology of an upper Chesapeake Bay river-mouth tidal freshwater marsh.

Field mapping and monitoring of vegetation, sedimentation patterns, substrate characteristics, and geomorphology in the Bush River tributary to upper Chesapeake Bay has been conducted since 1991 to ascertain the process-morphology dynamics in a tidal freshwater marsh. Nine plant associations from 5 distinct marsh habitats were identified by clustering species abundance measurements from 115 quadrats throughout an 84-hectare area. High spatial variability in physical habitat conditions such as summer-average sediment deposition, summer-average organic content, and surface-sediment grain size distributions were explainable using combinations of independent variables, including elevation, plant distributions, and distances to the tidal inlet and an adjacent stream. Sedimentation and vegetation were both observed to show a predictable response to disturbance by animal activity.