Aquatic Habitats In Sustainable Urban Water Management

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Urban aquatic habitats: characteristics and functioning 11 Table 2.1 Physical features of aquatic habitats being affected by human pressures in urban catchments Flow regime Physical habitat Chemical Variables Food (energy) Biotic structure (water quality) sources interactions • water depth • flow velocity • flow variability • discharge • flood magnitude • flood frequency • drought frequency • habitat diversity • habitat connectivity • channel sinuosity • siltation • sedimentation pattern • bank stability • substrate type • plant cover • nutrients • thermal regime • toxins • pseudohormones • salinity • turbidity • oxygen concentration •pH • primary production of algae and macrophytes • energy • particulate organic matter • aquatic and terrestrial invertebrates • species structure (invasions of exotics) • endemic species • threatened, endangered, sensitive species • species richness • trophic structure • age and genetic structure • predation • competition Source: Lapiǹska, 2004; Karr et al., 1986, modified. ● Specific pollutants (pollution by all priority substances identified as being discharged into the body of water; pollution by other substances identified as being discharged in significant quantities into the body of water). The assessment of the physical quality of habitats is based on the quality and degree of change of the above factors shown in Figure 2.1 and listed in the EU WFD, usually in comparison to reference (natural/un-impacted) conditions. It should be also understood that any modification of the physical characteristics of a habitat is followed by changes in the aquatic biota’s structure and performance. Therefore a proper assessment of freshwater ecosystems quality goes beyond physical characteristics. It should also include the assessment of the biotic compartment, which is usually based on relevant biotic indices (see Chapter 5 for a more detailed discussion). 2.2 HUMAN MODIFICATIONS OF AQUATIC HABITATS The characteristics of aquatic habitats presented in the above section are also reflected in the classification of major human pressures to which they are exposed (see Table 2.1). Aquatic habitats in urban areas are particularly exposed to these pressures. The primary factors of habitat deterioration are water quality decline and flow alternations, which are particularly pronounced in urban catchments. The broad range of chemicals from point and diffused sources include toxic substances and carcinogens, fertilizers, pesticides, herbicides, household hazardous wastes, oils, anti-freeze, heavy metals, pet and yard wastes, and pseudo-hormones (see Chapter 8 for a more detailed discussion of these issues and the related potential risks for urban populations). Simultaneously, the natural heterogeneity of habitats is often degraded or destroyed. In many cities, aquatic habitats
12 Aquatic habitats in sustainable urban water management are included in the urban drainage system, receiving and disposing of stormwater. The structure of aquatic habitats is adapted for these purposes by such measures as canalization, lining with concrete slabs, water intakes, and damming, among others. These modifications induce the impacts described in the later sections, as well as changes in habitat characteristics. 2.2.1 Flow regime There is a general agreement that flow regime controls, to a great extent, affects the development of the physical habitat structure in non-channelized rivers, with respect to both macro- and micro-habitat features, while creating variable conditions for the associated aquatic life. Analysis of flow regimes should focus on the aspects that are most important for creating and maintaining the habitat’s physical structure and supporting the requirements of aquatic organisms during various life stages. High flows are important for stream geomorph-ology, bed erosion and sediment transport; affect fish migration; and create periodical connectivity between the river and its floodplains, thereby providing additional spawning grounds for biota and juvenile rearing (Horner et al., 1994; Poff et al., 1997). Low flows usually have a greater impact on water quality, for example by lowering dissolved oxygen (DO), increasing temperature or increasing concentrations of many pollutants (Spence et al., 1996). Moreover, in the case of long-lasting and deep droughts, low flows may also set limits on the proper functioning of the ecological processes in river ecosystems. Urbanization greatly affects the hydrological cycle and by extension the flow regime as well. Such changes are summarized by Roesner et al., (2005) as more frequent and higher flows, increased duration of geomorphically significant flows (MacRae, 1997), flashier/less predictable flows (Henshaw and Booth, 2000), altered timing and rate of change relative to riparian and floodplain connections (Poff et al., 1997), altered duration of low-flow periods (Finkenbine et al., 2000), and conversion of subsurface distributed discharge (interflow) to surface point discharge (Booth and Henshaw, 2001). The management of urban habitats usually implies high levels of flow control, particularly intermediate and large-scale flood flows, and river channelization. This limits the active role of flow regime in the creation of habitat diversity. Modification of the flow regime causes changes in the sediment transport and stream geomorphology. The isolation of surface water bodies from ground waters and floodplains reduces water storage capacity and results in dramatic changes of discharge patterns. This increases freshwater ecosystems’ susceptibility to droughts, and short and extremely high peak flows impact their stability. Frequently, magnitude and irregularity of events change environmental templates, creating conditions unsuitable for the inhabiting organisms. Intended or unintended modifications of flow regime should be examined for key features of the creation and maintenance of the habitat’s physical structure, supporting the requirements of aquatic organisms during various life stages. In some climates, there are also intermittent streams (often described by such terms as arroyos, wadis or torrents), which flow only during a part of the year. Nevertheless these streams are also ecologically important and can be characterized by special biological assemblages (algae, bryophytes, invertebrates and amphibians) that are indicative of the degree of hydrologic permanence. Finally, there are also ephemeral streams, which form only during and after rainfall. A similar classification could be used for impoundments with intermittent water storage.
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62 Aquatic habitats in sustainable
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Chapter 5 Aquatic habitat rehabilit
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surface run-off from urban catchmen
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9.2 MODDERGAT RIVER REHABILITATION
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9.5 INTEGRATING ECOLOGICAL AND HYDR
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9.8 INTEGRATED MANAGEMENT OF AQUATI
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BLACK SEA Built-up Areas in 1955 Bu
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Index absorbing capacity 95, 96, 97
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Index 227 hard path for water 33, 4
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Index 229 urban drainage 49-59, 65,
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Plate 25 BLACK SEA Built-up Areas i
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Aquatic Habitats In Sustainable Urban Water Management

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