Challenges and Opportunities in the Hydrologic Sciences (2012) / Chapter Skim
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4 Clean Water for People and Ecosystems
4 Clean Water for People and Ecosystems
Pages 123-154
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From page 123... ...
Ensuring clean water for the future requires an ability to understand, predict, and manage changes in water quality. INTRODUCTION As the "lifeblood" of the planet and the universal solvent, water transports vast quantities of dissolved chemicals and suspended matter through the biosphere.
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From page 124... ...
. Supplying clean water to the growing human population will require much greater water reuse and water treatment than in the past.
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From page 125... ...
The flow of water and dissolved or suspended mass fluxes can vary many orders of magnitude over spatial scales ranging from centimeters to kilometers. It is unrealistic to expect that every detail of heterogeneity can be measured and cataloged to further understanding; useful scientific theories, after all, are ones that capture the essence of phenomena simply by setting aside unnecessary
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From page 126... ...
Given the importance of groundwater as a source of potable water and in recharging surface water systems, continued improvements in understanding fluxes and transformations in such connected networks should be pursued and will require much new work. Oftentimes, this understanding is derived from research conducted at experiment sites (Box 4-1)
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From page 127... ...
Groundwater age therefore has an age distribution that represents, on the one extreme, the fast flow paths through the high-conductivity, well-connected portions of the system, and on the other extreme, the slow flow paths through the often nonaquifer portions of the system. The age distribution is rich with information about the complexity of the surrounding flow regime, the presence of preferential flow paths, different scales of heterogeneity, and slow mass exchange between the fast and slow parts of the system.
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From page 128... ...
. The key questions and hypotheses emerging from these research activities include the following: Are small-scale preferential flow paths resulting from varia tions in hydraulic conductivity (K)
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From page 129... ...
CLEAN WATER FOR PEOPLE AND ECOSYSTEMS 129 b c trench source release. (The two-dimensional contour map is constructed from the peak concentrations at each multilevel sampler location from the MADE-3 test.)
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From page 130... ...
How much of the spatiotemporal heterogeneity in linked hydrologicalbiogeochemical cycling must be understood to estimate, model, and predict net watershed solute export? The increasing ability to monitor chemical and biological conditions in R02116 real time is revealing previously unknown temporal trends that in turn push Figure 4-2 the boundaries of process understanding.
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From page 131... ...
What variables control the occurrence and magnitude of hot spots in terrestrial, riparian, and hyporheic zones? Can knowledge about the joint distribution of organic carbon and fast flow paths be used to infer the major control points for ecosystem biogeochemical reactions?
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From page 132... ...
For example, synthetic aperture radar derived vegetative cover and inundation for a reach of the Solimões River in the central Amazon Basin, Brazil, is shown in Figure 4-3. On a much smaller scale, microelectrode profiles illustrate the variability of oxygen, iron, and manganese concentrations in co-located sediment profiles (Figure 4-4)
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From page 133... ...
CLEAN WATER FOR PEOPLE AND ECOSYSTEMS 133 FIGURE 4-4 Voltammetric profiles indicate significant variability in speciation in wetland soils 2 cm apart in sediment cores collected on the same day in Jug Bay, Maryland. SOURCE: Reprinted, with permission, from Ma et al.
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From page 134... ...
Recent research has highlighted that bedload sediment composition and mass flux in a river basin might be set by not only the channel network structure, but also, to a large degree, the sediment size and composition supplied from upstream hillslopes. This dynamic connectivity between channels and their surroundings is not unique to erosional systems; in fact, it is even more pronounced in net depositional systems such as deltaic networks.
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From page 135... ...
CLEAN WATER FOR PEOPLE AND ECOSYSTEMS 135 FIGURE 4-7The terrain complexity in a deltaic system of channels modulates complex interactions between water, earth, and biota for which predictive models are lacking. This picture shows the elevation analysis of LiDAR data from the Wax Lake Delta, Louisiana, with the distribution of total area (hectares)
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From page 136... ...
The idea that clean water is accessed only upstream from
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From page 137... ...
Symbols are graduated in size and color to indicate higher arsenic concentration. Arsenic concentration varies spatially because of complex inter R02116 relationships among hydrologic flow paths, sediment structure, organic carbon, and pumping.
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From page 138... ...
The list of contaminants of emerging concern known to be present in natural waters is quite large, ranging from hormonally active agents to caffeine. With development of new chemicals and their subsequent introduction to the water cycle, this list continues to grow.
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From page 139... ...
CLEAN WATER FOR PEOPLE AND ECOSYSTEMS 139 FIGURE 4-9 Increase in the concentration of chloride in streams and rivers in rural areas in the northeastern United States. SOURCE: Reprinted, with permission, from Kaushal et al.
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From page 140... ...
. How do anthropogenic changes in land use alter water flow paths that in turn impact other elemental fluxes and water quality?
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From page 141... ...
contaminants of concern? Which R02116 contaminants of emerging concern are bioavailable and which may Figure 4-10 and how do these processes bioaccumulate, interact with hydrologic processes to affect bitmapped, uneditable the evolution of water quality?
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From page 142... ...
This knowledge will inform changes in policy that will be needed to protect water quality in the future. How do alterations in water flow paths affect temperature and contaminant regimes of freshwater ecosystems?
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CLEAN WATER FOR PEOPLE AND ECOSYSTEMS 143 FIGURE 4-11 Diel (24-hour) cycles in streamflow, temperature, and pH, and dissolved arsenic (As)
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From page 144... ...
Similarly, the energy required for transportation, to generate electricity, or to provide clean water for 9 billion people is enormous. And all of these demands should be considered against the backdrop of a changing climate, providing yet another challenge to maintaining adequate water quality for humans and ecosystems.
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From page 145... ...
An opportunity exists to probe the geochemical phenomena associated with changing urban flow paths, i.e., stormwater. Knowledge exists in this area.
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From page 146... ...
Under predevelopment conditions, the groundwater systems flowed from recharge areas to natural discharge areas, providing an exit for dissolved salt. However, when overdraft occurs and the pumped groundwater is reapplied to the land for irrigation, a closed hydrologic basin is potentially created whereby shallow groundwater of lesser quality (for example, elevated salinity)
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How can the hydrologic sciences inform solutions to the "water-energy nexus"? Water and energy are mutually dependent resources.
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, research efforts to provide the scientific understanding of how harnessing the natural power of water disrupts the water cycle and alters water quality will become a priority. What are the related changes in FIGURE 4-13 Federal Energy Regulatory Commission (FERC)
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From page 149... ...
Carbon sequestration in deep geologic formations has the potential to affect groundwater quality. What are the water quality tradeoffs associated with various carbon sequestration strategies?
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From page 150... ...
Low flows in surface waters can also further exacerbate problems of low oxygen and alter the toxicity of contaminants. This concept has a variety of consequences that expand into the realm of Water and Life, because low flow shrinks habitat for aquatic species and increases the contaminant concentration and, in turn, exposure.
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From page 151... ...
Thus, while the hydrologic sciences are critical to the resolution of the issues discussed in this report, it will be interdisciplinary teams of researchers, including not only physical, chemical, and biological scientists, but also social scientists, that produce useful scientific results. Ongoing consultations with those who build and maintain infrastructure are essential.
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From page 152... ...
2006. Motivation of synthesis, with an example on groundwater quality sustainability.
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From page 153... ...
2006. Do gravel bed river size distributions record channel network structure?
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