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This chapter describes work on a stochastic soil moisture model that has been used to investigate the relationship between the hydrologic and vegetation dynamics ecohydrology in water-controlled ecosystems. Such systems are complex evolving structures whose characteristics and dynamic properties depend on many links between climate, soil, and vegetation. After a discussion of the soil water balance and a brief account of rainfall modeling, infiltration, and runoff, evapotranspiration and drainage are sketched. The probabilistic modeling of the soil moisture process and of long-term water balance are discussed, followed by minimalist modeling of soil moisture dynamics. The chapter concludes with a brief account of plant water stress, with an application to the Kalahari precipitation gradient.

Themes that characterise urban wetlands in this century are: an association with human activities, especially development, education, and culture; invasive species management; migratory species feeding and breeding grounds; recognition by international environmental agreements; restored or constructed wetlands; and a role in providing for a focus of sustainability in the urban system. The chapter sets those themes in the context of the emerging paradigm of ecohydrology and the application of the ecosystem approach of the convention on biological diversity. For wetlands, especially in an urban context, understanding the linkage between ecology and hydrology — ecohydrology — is an important new way of thinking. Four key points that define ecohydrology are: understanding that ecosystem change is inevitable, and the role of people in managing change; integrating water and biodiversity science at management relevant spatial and temporal scales; understanding the role of ecosystem services; and defining and understanding the links between green and blue water. The role of blue and green water in an urban setting is also linked with human generated grey and black water, and linkages between these waters result in a range of semi-natural and artificial (or constructed) wetland ecosystems in urban landscapes. Human health in urban areas also depends on having well-functioning and well-managed ecosystems to provide a range of ecosystem services that support both human health, but also the health (functioning) of other ecosystems and their components. The chapter also identifies ten urgently needed research directions.

Chemical equilibria in surface waters stem from complex interactions between physical background and living components of ecosystems. Catchments differ in geological background, climate, and land use; their run-off bears a distinctive chemical ‘fingerprint’. This chapter illustrates how the monitoring of standard parameters, such as oxygen, pH, conductivity, major ions, nutrients, and carbon, can lead to an interpretation of key aspects of the functioning of major ecosystem processes and how chemical constituents may affect the distribution of aquatic organisms. This requires understanding principles that underlie available measurement techniques and it demands a certain familiarity with the intrinsic variability of parameter values and of their chemical interaction. It is not required that field scientists be able to conduct detailed chemical assessments, but all should be able to collect samples yielding high-quality data. Therefore, detailed advice on chemical monitoring practice is provided, including sample collection, filtering, sample processing, and is discussed with the context of several case studies.

This chapter explores the ecohydrology of tamarisk, with particular emphasis on water use, salt tolerance, potential for salinizing flood plains, drought tolerance and rooting depths, and ecological interactions with native plants on western rivers. It presents the working hypothesis that tamarisk is adapted to water stress, with low to moderate water use that tends to replace mesic vegetation when conditions on flow-regulated rivers become unsuitable for those species, rather than as an invasive species that displaces and out-competes native species under all conditions. It includes data on the annualized rates of evapotranspiration, transpiration, and stomatal conductance by tamarisk stands on western US rivers. It also cites the lack of evidence that simply removing tamarisk from a riverbank will improve salinity or allow native mesic vegetation to return.