Garth van der Kamp

Water and solute transfer between a prairie wetland and adjacent uplands, 1. Water balance

The hydrology and water quality of lakes and wetlands are controlled by the exchange of water and solutes with adjacent uplands. We studied a small catchment in Saskatchewan, Canada, to evaluate the mechanisms of water and solute transfer between the wetland and the surrounding upland. Detailed measurements of hydrologic processes (precipitation, runoff, evapotranspiration, and subsurface flow) and chloride distribution are combined to improve the estimate of the transfer flux. This paper describes hydrologic processes and Part 2 describes the solute transport processes. Large snowmelt runoff occurs in the catchment, which transfer 30–60% of winter precipitation on the upland into the wetland to form a pond in the center. Snowmelt water and summer precipitation infiltrate under the central pond. Infiltration accounts for 75% of water leaving the central pond and evapotranspiration accounts for 25%. Most of the infiltrated water flows laterally in the shallow subsurface to the wet margin of the pond and further to the upland, where it is consumed by evapotranspiration without recharging deep groundwater. The net recharge rate of the aquifer underlying the catchment is only 1–3 mm year−1. Snowmelt runoff transfers water from the upland to the wetland, and shallow subsurface flow transfers water in the opposite direction. When the two processes are combined, they provide the paths for cyclic transport of solutes.

Water and solute transfer between a prairie wetland and adjacent uplands, 2. Chloride cycle

The quality of water in lakes and wetlands depends on the exchange of solutes with adjacent uplands. In many prairie wetlands, the input of water is dominated by snowmelt runoff and the outputis dominated by groundwater flow. We use chloride as a tracer to quantify the mass transfer processes associated with surface runoff and groundwater flow between a wetland in Saskatchewan, Canada and the surrounding upland. Snowmelt runoff transports 4–5 kg yr−1 of chloride from the upland to the wetland. Most of this chloride infiltrates under the wetland and moves laterally to the upland with shallow groundwater. Under the upland, chloride moves upward in the vadose zone with soil water, and accumulates near the surface as water is consumed by evapotranspiration. Part of this chloride mixes with snowmelt runoff and moves back to the wetland Therefore, chloride is cycled between the wetland and the upland at an approximate rate of 5 kg yr−1. The chloride cycle occurs within 5–6 m of the ground surface. A small amount of chloride escapes from the cycle with the downward flow of groundwater into the deep aquifer. The estimated flux of chloride leaving the cycle is 0.1-0.6 kg yr−1, which is of the same order of magnitude as the rate at which the catchment receives atmospheric deposition of chloride. Because the atmospheric input is reasonably well known over the prairie region, the concentration of chloride in groundwater under recharge wetlands can be used to estimate the recharge rate of deep aquifers.

Hydrology of Prairie Wetlands: Understanding the Integrated Surface-Water and Groundwater Processes

Wetland managers and policy makers need to make decisions based on a sound scientific understanding of hydrological and ecological functions of wetlands. This article presents an overview of the hydrology of prairie wetlands intended for managers, policy makers, and researchers new to this field (e.g., graduate students), and a quantitative conceptual framework for understanding the hydrological functions of prairie wetlands and their responses to changes in climate and land use. The existence of prairie wetlands in the semi-arid environment of the Prairie-Pothole Region (PPR) depends on the lateral inputs of runoff water from their catchments because mean annual potential evaporation exceeds precipitation in the PPR. Therefore, it is critically important to consider wetlands and catchments as highly integrated hydrological units. The water balance of individual wetlands is strongly influenced by runoff from the catchment and the exchange of groundwater between the central pond and its moist margin. Land-use practices in the catchment have a sensitive effect on runoff and hence the water balance. Surface and subsurface storage and connectivity among individual wetlands controls the diversity of pond permanence within a wetland complex, resulting in a variety of eco-hydrological functionalities necessary for maintaining the integrity of prairie-wetland ecosystems.

USE OF SOLUTE MASS BALANCE TO QUANTIFY GEOCHEMICAL PROCESSES IN A PRAIRIE RECHARGE WETLAND

In the northern prairie region of North America, there are millions of small seasonal wetlands. The aquatic ecology of these wetlands is partly controlled by the salinity of the wetland pond water, which affects the vegetation and invertebrate communities. The objective of this study was to identify the key geochemical processes affecting water chemistry in prairie wetlands. We used the combined water and solute mass balance approach to quantify the rates of geochemical reactions in a typical prairie recharge wetland in Saskatchewan, Canada. Sulfate reduction, carbonate mineral dissolution, and processes adding carbon dioxide to the pond were identified as the key geochemical reactions. Sulfate reduction removed more sulfate from the pond than infiltration in each of the four years examined. The average rate of sulfate reduction, 0.07 g m−2 d−1, was greatest in spring and decreased during the year. Reduced sulfate remains in the sediments but is re-oxidized when the pond dries out and is dissolved into the pond water and sediment pore water when the pond re-floods. X-ray diffraction analyses of wetland soil and mass balance calculations indicate magnesium-calcite is dissolved into the pond water in the spring and precipitates out of solution later in the year, and dissolves into the pond the following year.

Theory for the effects of free gas in subsea formations on tidal pore pressure variations and seafloor displacements

Loading of the seafloor by regional-scale pressure variations, such as those imposed by ocean tides, is supported by both the rock matrix and interstitial fluid. The nature of the partitioning of the support between the two depends primarily on the compressibility of the fluid and the compressibility and fluid-transport properties of the rock matrix. In this paper, we examine theoretically the influence of free gas on pore fluid compressibility, on the nature of time-dependent load partitioning, and on the consequent vertical rock deformation and seafloor displacement. An example is the gas trapped below deep-sea gas hydrate. We have derived an expression for the steady state compressibility of pore fluid considering the influence of gas solubility in water. The effect of gas solubility is seen to be important at low, such as tidal, loading frequencies and thus must be included when observations of tidally induced pore fluid pressure variations or seafloor displacements are used to constrain gas content. For very low gas concentrations ng (much less than 0.1%), the steady state fluid compressibility can be enhanced by gas solution/dissolution over the loading cycle by several factors at high ambient pressure and more than an order of magnitude at low ambient pressures ( 2%, the fluid compressibility increases sensitively with ng and greatly affects the tidal response of the pore fluid pressure regardless of the solubility. Thus, with careful experimental design, tidally induced pore pressure variations may be used to detect very small amounts of free gas and constrain the quantity if ng > 2%. This method is complementary to using acoustic velocity to constrain the quantity of free gas, which works well in the ng = 0.2–2% range. We have also given an expression for the vertical deformation of subsea formations and hence of the seafloor displacement under tidal loading. The presence of free gas enhances tidally induced seafloor displacement, but the maximum effect is limited by the compressibility of the matrix frame. Given relatively low frame compressibility, tidally induced seafloor displacement is small, of the order of 1 mm, which is presently difficult to detect at tidal frequencies.

10 – Water Level Changes in Ponds and Lakes: The Hydrological Processes

Lakes and ponds occur in a wide range of depths, sizes, and permanence—from deep lakes having a permanent body of surface water to shallow ponds having water for only a few weeks each year. These factors also vary within each lake or pond, resulting in diverse communities of aquatic plants growing in various patterns. Certain types of plants require relatively high water levels, while others cannot tolerate standing water. Therefore, water level change is considered to be a disturbance to many aquatic plants. Water level changes in ponds and lakes occur because of the water input exceeding output or vice versa. Because hydrological processes control inputs and outputs, understanding the water level changes and resulting ecological responses requires understanding the individual processes. It is particularly important to realize the intimate link between lakes and their catchments. Disturbance in the catchment, such as major land use change, can cause a dramatic change in hydrological processes, which ultimately affects the lake water level. This fact is clearly demonstrated in this chapter, in the case study of prairie wetlands, where grassing the uplands resulted in the drying out of wetlands. It is expected that collaborative research on ecohydrology is helpful in observing hydrological processes and ecological responses simultaneously, and to develop coupled models for the prediction of ecosystem responses to land use and climate changes.

Use of tensiometer response time to determine the hydraulic conductivity of unsaturated soil

The response time of tensiometers is controlled by the soil hydraulic conductivity when the flow resistance of the porous cup is sufficiently small. Therefore, we can determine the hydraulic conductivity of unsaturated soils from the response of a tensiometer to an artificially-induced perturbation ofpressure. We evaluated a practical procedure to determine the conductivity by numerical simulations and by laboratory and field tests. The data can be analyzed by a simple graphical technique based on the linear slug test equation because nonlinear dependence ofhydraulic conductivity on matric potential head is not significant when the head perturbation is small (<0.5 m). Using readily available equipment, a field tensiometer response test generally takes less than 1 h. Tests can be repeated over time to determine the in situ relationship between hydraulic conductivity and matric potential. The estimated conductivity is sensitive to the disturbance of the soil in close proximity to the porous cup. To improve the reliability of response tests, new methods need to be developed to install tensiometers with minimum soil disturbance. Despite the problem of soil disturbance, the tensiometer response test is an attractive method in clay-rich soils where other field methods are not easily applicable.

On the changes in long-term streamflow regimes in the North American Prairies

ABSTRACT Climate change/variability accompanied by anthropogenic activities can alter the runoff response of landscapes. In this study we investigate the integrated impacts of precipitation change/variability and landscape changes, specifically wetland drainage practices, on streamflow regimes in wetland-dominated landscapes in the Assiniboine and Saskatchewan River basins of the North American Prairies. Precipitation and streamflow metrics were examined for gradual (trend type) and abrupt (shift type) changes using the modified Mann-Kendall trend test and a Bayesian change point detection methodology. Results of statistical analyses indicate that precipitation metrics did not experience statistically significant increasing or decreasing changes and there was no statistical evidence of streamflow regime change over the study area except for one of the smaller watersheds. The absence of widespread streamflow and precipitation changes suggests that wetland drainage did not lead to detectable changes in streamflow metrics over most of the Canadian portion of the Prairies between 1967 and 2007. Editor Z.W. Kundzewicz Associate editor None assigned

Prairie Pothole Wetlands – Suggestions for Practical and Objective Definitions and Terminology

Prairie pothole wetlands are subject to large year-to-year and decadal variability of precipitation, resulting in large variations in ponded area, plant communities and ecological functionality that obscure trends in wetland conditions caused by changes in climate and land use. Descriptions and analyses of these variations and trends require practical and objective definitions of pothole wetlands that can be used to establish the boundaries of individual wetlands, detect long-term changes of these boundaries, and distinguish wetlands from lakes and from small non-wetland depressions. The boundaries of prairie pothole wetlands should ideally be defined on the basis of wetland soils, which are more stable and persistent than vegetation and ponded water. The latter are necessarily used as indicators of wetland conditions through time because they are amenable to remote sensing and regional wetland inventories. However, the relationships between wetland ponds, vegetation and soil zones need improved documentation. Wetlands are persistent and stable landscape features (unless they are drained or filled). Some ecological functions of wetlands such as waterbird habitat may be seasonal, but other important hydrological and biochemical functions act year-round whether or not a pond is present. Phrases such as “seasonal wetland” that refer to the duration of ponded water should be avoided and terms such as “wetland”, “depression” and “pond” should be used with clear definitions that are accepted across the wetland disciplines. Commonly used wetland classifications based on vegetation zones and duration and salinity of ponds should incorporate reference to the decadal-scale time period for which the descriptions apply.

Progress in Scientific Studies of Groundwater in the Hydrologic Cycle in Canada, 2003-2007

This paper summarizes recent progress in Canadian groundwater hydrology, focussing on scientific studies of groundwater in relation to the hydrologic cycle, excluding studies that deal primarily with groundwater contamination, water resource evaluation, and engineering applications. Within the scope of this limited survey, major research interests appear to be in groundwater-surface water interaction, groundwater recharge and its sensitivity to climate change, regional hydrogeology, hydrogeophysics, and the development of sophisticated numerical models that integrate subsurface and surface hydrology.