The chemical composition of natural water is derived from many different sources of solutes, including gases and aerosols from the atmosphere, weathering and erosion of rocks and soil, solution or precipitation reactions occurring below the land surface, and cultural effects resulting from human activities. Broad interrelationships among these processes and their effects can be discerned by application of principles of chemical thermodynamics. Some of the processes of solution or precipitation of minerals can be closely evaluated by means of principles of chemical equilibrium, including the law of mass action and the Nernst equation. Other processes are irreversible and require consideration of reaction mechanisms and rates. The chemical composition of the crustal rocks of the Earth and the composition of the ocean and the atmosphere are significant in evaluating sources of solutes in natural freshwater. The ways in which solutes are taken up or precipitated and the amounts present in solution are influenced by many environmental factors, especially climate, structure and position of rock strata, and biochemical effects associated with life cycles of plants and animals, both microscopic and macroscopic. Taken together and in application with the further influence of the general circulation of all water in the hydrologic cycle, the chemical principles and environmental factors form a basis for the developing science of natural-water chemistry. Fundamental data used in the determination of water quality are obtained by the chemical analysis of water samples in the laboratory or onsite sensing of chemical properties in the field. Sampling is complicated by changes in the composition of moving water and by the effects of particulate suspended material. Some constituents are unstable and require onsite determination or sample preservation. Most of the constituents determined are reported in gravimetric units, usually milligrams per liter or milliequivalents

Study and Interpretation of the Chemical Characteristics of Natural Water

Fifty years of hyporheic zone research have shown the important role played by the hyporheic zone as an interface between groundwater and surface waters. However, it is only in the last two decades that what began as an empirical science has become a mechanistic science devoted to modeling studies of the complex fluid dynamical and biogeochemical mechanisms occurring in the hyporheic zone. These efforts have led to the picture of surface-subsurface water interactions as regulators of the form and function of fluvial ecosystems. Rather than being isolated systems, surface water bodies continuously interact with the subsurface. Exploration of hyporheic zone processes has led to a new appreciation of their wide reaching consequences for water quality and stream ecology. Modern research aims toward a unified approach, in which processes occurring in the hyporheic zone are key elements for the appreciation, management, and restoration of the whole river environment. In this unifying context, this review summarizes results from modeling studies and field observations about flow and transport processes in the hyporheic zone and describes the theories proposed in hydrology and fluid dynamics developed to quantitatively model and predict the hyporheic transport of water, heat, and dissolved and suspended compounds from sediment grain scale up to the watershed scale. The implications of these processes for stream biogeochemistry and ecology are also discussed.

Hyporheic flow and transport processes: Mechanisms, models, and biogeochemical implications

. Interactions between groundwater and surface water play a fundamental role in the functioning of riparian ecosystems. In the context of sustainable river basin management it is crucial to understand and quantify exchange processes between groundwater and surface water. Numerous well-known methods exist for parameter estimation and process identification in aquifers and surface waters. Only in recent years has the transition zone become a subject of major research interest; thus, the need has evolved for appropriate methods applicable in this zone. This article provides an overview of the methods that are currently applied and described in the literature for estimating fluxes at the groundwater – surface water interface. Considerations for choosing appropriate methods are given including spatial and temporal scales, uncertainties, and limitations in application. It is concluded that a multi-scale approach combining multiple measuring methods may considerably constrain estimates of fluxes between groundwater and surface water.

/pdf/measuring-methods-for-groundwater-surface-water-interactions-4pu38dqxzz.pdf

Measuring methods for groundwater – surface water interactions: a review

Although it is well known that metabolism, feeding, and behaviour of lotic organisms is influenced by various flow characteristics, hydraulic variables usually are not accurately measured in lotic ecology studies. Using an approach we call "hydraulic stream ecology", we link organismic responses to a more comprehensive treatment of the physical environment. Since a unified analytical solution for all important hydraulic variables in running waters does not exist at the moment, we advocate a simpler view of the physical system. We demonstrate methods for estimating complex hydraulic key characteristics, like turbulence in the free flow, turbulence close to the stream bottom, and the force of flow prevailing at the bottom. Calculations of these complex key characteristics require measurement of simple hydraulic characteristics like mean velocity, water surface slope, depth, bottom roughness, kinematic viscosity, and density of the water. The hydraulic environment shows characteristic patterns within whole c...

Hydraulic Stream Ecology: Observed Patterns and Potential Applications

................................................................................................................................................................... 1.0 Introduction ........................................................................................................................................................ 1.1 Model Enhancements ........................................................................................................ ................................... 2 1.2 Report Organization ............................................................................................................................... 3 1.3 Acknowledgments ........................................................................................................... .................................... 3 2.0 Theory ................................................................................................................................................................ 2.1 Background Transient Storage Models .............................................................................................. 4 2.2 Governing Differential Equations ........................................................................................................... 5 2.2.1 Processes Considered / Model Assumptions ................................................................................ .......... 5 2.2.2 Time-Variable Equations ................................................................................................. ....................... 6 2.2.3 Steady-State Equations ............................................................................................................ 7 2.3 The Conceptual System ........................................................................................................................ 8 2.4 Numerical Solution Time-Variable Equations .............................................................................. ..................... 8 2.4.1 Finite Differences ...................................................................................................................... 8 2.4.2 The Crank-Nicolson Method .................................................................................................... 10 2.4.3 Main Channel Solute Concentration ....................................................................................... . 10 2.4.4 Storage Zone and Streambed Sediment Concentrations ................................................................. 12 2.4.5 Decoupling the Main Channel, Storage Zone, and Streambed Sediment Equations ....................... 2.5 Numerical Solution Steady-State Equations ...................................................................................... 14 2.6 Boundary Conditions ....................................................................................................... .................................... 15 2.6.1 Upstream Boundary Condition ................................................................................................. 15 2.6.2 Downstream Boundary Condition ............................................................................................ 15 2.7 Parameter Estimation ...................................................................................................... ..................................... 16 3.0 User’s Guide ............................................................................................................... ..................................................... 2 3.1 Applicability ............................................................................................................. ........................................... 20 3.2 Model Features ...................................................................................................................................... 20 3.2.1 Simulation Modes: Time-Variable and Steady-State ....................................................................... 20 3.2.2 Conservative and/or Nonconservative Solutes ............................................................................. 21 3.2.3 Flow Regimes ........................................................................................................................... 21 3.2.4 Parameter Estimation using OTIS-P ........................................................................................ 22 3.3 Conceptual System, Revisited .............................................................................................................. 22 3.4 Input/Output Structure .................................................................................................... ..................................... 24 3.4.1 OTIS ........................................................................................................................................... 24 3.4.2 OTIS-P ....................................................................................................................................... 25 3.5 Input Format ........................................................................................................................................... 26 3.5.1 Units ........................................................................................................................................... 26 3.5.2 Internal Comments .................................................................................................................... 27 3.5.3 The Control File ......................................................................................................................... 27 3.5.4 The Parameter File ...................................................................................................... ............................ 29 3.5.5 The Flow File ............................................................................................................................. 35 3.5.6 The Data File (OTIS-P only) ............................................................................................. ..................... 40 3.5.7 The STARPAC Input File (OTIS-P only) .................................................................................... 41 3.6 Model Execution ..................................................................................................................................... 43 3.6.1 OTIS ........................................................................................................................................... 44 3.6.2 OTIS-P ....................................................................................................................................... 44 3.7 Output Analysis ...................................................................................................................................... 45 3.7.1 The Solute and Sorption Output Files ..................................................................................... 45 3.7.2 The Post-Processor .................................................................................................................. 46 3.7.3 Plotting Alternatives .................................................................................................................. 47 4.0 Model Applications ......................................................................................................... ................................................ 48 4.1 Application 1: Conservative Transport (OTIS) ............................................................................. ...................... 48

/pdf/one-dimensional-transport-with-inflow-and-storage-otis-a-5cges40f02.pdf

One-Dimensional Transport with Inflow and Storage (OTIS): A Solute Transport Model for Streams and Rivers

The physical characteristics of mountain streams differ from the uniform and conceptually well- defined open channels for which the analysis of solute transport has been oriented in the past and is now well understood. These physical conditions significantly influence solute transport behavior, as demonstrated by a transient storage model simulation of solute transport in a very small (0.0125 m3s−1) mountain pool-and-riffle stream. The application is to a carefully controlled and intensively monitored chloride injection experiment. The data from the experiment are not explained by the standard convection-dispersion mechanisms alone. A transient storage model, which couples dead zones with the one-dimensional convection-dispersion equation, simulates the general characteristics of the solute transport behavior and a set of simulation parameters were determined that yield an adequate fit to the data. However, considerable uncertainty remains in determining physically realistic values of these parameters. The values of the simulation parameters used are compared to values used by other authors for other streams. The comparison supports, at least qualitatively, the determined parameter values.

Simulation of solute transport in a mountain pool‐and‐riffle stream: A transient storage model

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Simulation of solute transport in a mountain pool‐and‐riffle stream: A transient storage model