Martin C. Thoms

An ecosystem approach for determining environmental water allocations in Australian dryland river systems: the role of geomorphology

The allocation of water for environmental purposes is a key management issue in many dryland regions. Many different methods have been developed for determining environmental water requirements but these are not directly applicable to dryland rivers because of inherent flow and habitat variability. An ecosystem approach for determining environmental water allocations in dryland regions is presented in this paper. This four-step process involves (1) a hierarchical characterisation of the river system, to assess what mesohabitats are present and where they are located; (2) the determination of flows that would inundate these habitats and perform other key ecological processes; (3) hydrological analyses in which the key hydrological signatures of the river are identified and the impact of water resource development on these is determined; and (4) the derivation of a water management decision tree that enables managers to allocate water to consumptive users during individual flood pulses (events). It is recommended that the flood pulse should be the focus for environmental flow management in dryland regions. If rivers are indeed nested hierarchies, then a change in hydrological behaviour at the scale of a flood pulse will, with time, extend throughout the hydrological hierarchy. Current environmental flow management strategies in dryland river systems are essentially focused at the flow regime and history scale; this is inappropriate given the inherent flow variability of these systems. The ecosystem approach is outlined for the Condamine-Balonne River, a large dryland system in Australia.

Ecogeomorphology of Altered Riverine Landscapes: Implications for Biocomplexity Tenets

Existing theories are used to predict responses to anthropogenic changes in riverine ecosystems, but explicit hypotheses on ecosystem behavior in altered landscapes have not been incorporated into these models. This chapter describes the types of responses expected in altered riverine ecosystems as defined by the tenets of the RES. Disturbances changing attributes in one domain will alter attributes of others through secondary or tertiary mechanisms. This chapter addresses broad changes in the nature of riverine ecosystems through direct actions on attributes and provides examples of deviations from expected patterns. The tenets of the riverine ecosystem synthesis (RES) are presented by considering how they can be used to predict changes/responses from population to landscape levels. The tenets provide a framework for applying the RES in situations encountered in altered systems and for understanding how changes in the characteristics of an FPZ influence ecosystem structure and function independent of location along a longitudinal gradient of a riverine ecosystem. A goal of this chapter is to provide key policy makers and river managers with better tools for environmental management and rehabilitation of riverine landscapes.

Hierarchical Patch Dynamics in Riverine Landscapes

Understanding the nature of changes in biocomplexity from headwaters to a river mouth is an important path toward developing a conceptually cohesive model of riverine ecosystem structure and function. This chapter discusses another major component of model—aquatic applications of the Hierarchical patch dynamics (HPD) model.. The original, terrestrial-based HPD model integrates a general theory of spatial heterogeneity (patch dynamics) with hierarchy theory by expressing relationships among pattern, process, and scale in a landscape context. This chapter describes the meaning of patch. A patch is as a spatial unit differing from its reference background in nature and appearance, a depiction that could also be applied to temporal patches. The size of a patch is scale-, organismal-, and process-dependent and can vary greatly in temporal dimension and size (e.g., an individual rock to a river segment or a floodscape area). The HPD model is composed of five principal elements. First, ecological systems are viewed as ‘nested, discontinuous hierarchies of patch mosaics.’ Second, the dynamics of ecological systems are derived from a composite of intra- and inter-patch dynamics. Third, pattern and process are interlinked and scale-dependent. Various processes (e.g., nutrient spiraling) may create, modify, or eliminate patterns at certain spatial and temporal scales, while at the same time certain spatial and temporal patterns (e.g., differences in flow characteristics) can substantially alter ecological processes. Fourth, nonequilibrial conditions and stochastic processes play a dominant role in the so-called “ecosystem stability.” Fifth, a quasi-equilibrial, metastable state can develop at one hierarchical level through incorporation of multiple; nonequilibrial patches from the adjacent lower level.

Introduction to the Riverine Ecosystem Synthesis

This chapter provides an overview of the Riverine Ecosystem Synthesis (RES), which is an integrated model derived from aspects of other aquatic and terrestrial models proposed from 1980 to 2007, combined with the perspectives on functional process zones (FPZs) and other aspects of riverine biocomplexity. The RES pertains to the entire riverine landscape, which includes both the floodscape and the riverscape. This contrasts with many lotic models whose primary emphasis or support focuses on main channel systems within headwaters. This synthesis, which incorporates the ecosystem consequences of spatiotemporal variability across mostly longitudinal and lateral dimensions, has three broad components: a fundamental, physical model describing the hierarchical patchy arrangement of riverine landscapes within longitudinal and lateral dimensions based primarily on hydrogeomorphology and emphasizing a new geomorphic division (an FPZ) between the reach and the valley scale; ecological implications of the physical model in terms of an expandable set of 17 general to specific (testable) hypotheses, or model tenets, on biocomplexity, which is applicable in some form to both pristine and altered riverine landscapes; a framework for studying, managing, and rehabilitating riverine landscapes through the use of the hierarchical physical model and aquatic applications of the terrestrially derived hierarchical patch dynamics (HPD) model. The goal is to provide a framework for the development of a cohesive theory of riverine ecosystems over time rather than to produce a finished product. This chapter draws upon three primary components of river science that contribute to the study of riverine landscapes: lotic ecology, landscape ecology, and fluvial geomorphology.

Historical and Recent Perspectives on Riverine Concepts

This chapter gives a broad overview of the riverine ecosystem synthesis (RES) by exploring the nature and applications of all prominent riverine theories published even in the last few decades. Consequently, the focus and analysis of the review is only on those hypotheses, models, theories, and paradigms that address large-scale spatial patterns affecting the structure and function of riverine ecosystems and ecological regulation of communities at smaller spatiotemporal scales. At the larger spatial scale, this chapter concentrates the analysis on two (longitudinal and lateral) of the four recognized dimensions of rivers. It briefly covers briefly covers vertical dimension because less controversy seems to exist among stream ecologists about processes and patterns operating in this dimension. The fourth dimension, which involves temporal phenomena, is the longitudinal dimension that alludes to patterns and processes occurring along discharge and altitudinal gradients from headwaters downstream to the river mouth. And by the lateral dimension, this chapter refers to similarities and differences in communities from the main channel through slackwaters (riverscape) to the floodplains (floodscape). At smaller spatial scales, theories debating which biotic and/or abiotic factors regulate community structure and the importance of temporal phenomena are discussed. The review of selective aspects of other models is tailored to that synthesis and its specific contribution toward conceptual cohesiveness.

Practical Applications of the Riverine Ecosystem Synthesis in Management and Conservation Settings

The importance of river classification in conservation planning and management is widely recognized. The river characterization approach presented in this chapter as part of the riverine ecosystem synthesis (RES) provides an excellent framework to classify riverine landscapes at various scales. By focusing on the scale of FPZs, scientists, river managers, and people interested in river rehabilitation will be operating at a scale that is appropriate for entire river networks. The identification and mapping of FPZs can provide a framework for conservation planning and prioritization of management activities within river networks. Interdisciplinary research in river ecosystems is a relatively young endeavor and one that is fraught with problems—linking across scales and integrating different disciplinary approaches and conceptual tools. Frameworks are useful tools for achieving this because they help define the bounds for the selection and solution of problems. They also indicate the role of empirical assumptions, carry the structural assumptions, show how facts, hypotheses, models, and expectations are linked, and indicate the scope at which a generalization or model applies. The RES provides such an integrative framework for the study of entire riverine landscapes. A framework is neither a model nor a theory because models describe how things work and theories explain phenomena. In contrast, a conceptual framework helps to order phenomena and materials, thereby revealing patterns.

Defining the Hydrogeomorphic Character of a Riverine Ecosystem

Hydrogeomorphic patches and their resultant processes play important roles in riverine landscapes. They provide physical habitat and act as ecological disturbances, among other things. River networks are complex systems that need to be interpreted within their local and historical context. Attention to identifying and characterizing FPZs within the context of river networks will improve our knowledge of riverine landscapes. At this scale, river networks are a mosaic of patches that do not simply reflect a continuum of river zones. This chapter delves into the messy business of methods—the how tos of determining the character of river networks. It cautions against a focus on seeking the single method that can be applied to any situation. The options presented in this chapter provide various approaches that can be applied to particular situations. It demonstrates that FPZs can be identified equally as well via data collected at larger or smaller scales. Characterizations that highlight specific aspects of the linkages between channel networks and resultant processes are likely to be most useful, but careless application of any characterization may prove misleading—no characterization can substitute for an alert, intelligent, and well-trained observer.

Ecological Implications of the Riverine Ecosystem Synthesis: Some Proposed Biocomplexity Tenets (Hypotheses)

A major component of the riverine ecosystem synthesis (RES) is an expandable set of 17 biocomplexity tenets or hypotheses. These model tenets are developed both to illustrate some implications of the RES to broad areas of riverine ecology and to offer possible future research avenues in riverine ecology from headwaters to great rivers and throughout the riverine landscape. This chapter presents the 17 biocomplexity tenets that describe the predicted functioning of epigean portions of riverine ecosystems on ecological timescales from species to landscape levels. The ideas about FPZs and ecogeomorphology into these tenets are integrated where they are applicable. The model tenets are divided into three somewhat arbitrary and overlapping categories. The first set of tenets concerns factors influencing species distributions or, in effect, composition of the species pool within a single riverine ecosystem. The next category on community regulation relates to factors controlling species diversity, abundance, and trophic position within the assemblage of species potentially present in the environment. Both density-independent and dependent factors are included. The final cluster of tenets covers processes at the ecosystem and riverine landscape levels. All the model tenets are based on the assumption that riverine ecosystems around the world are pristine or at least have not been modified sufficiently to alter their basic community properties and ecosystem functioning.

The Spatial Arrangement of River Systems: The Emergence of Hydrogeomorphic Patches

A diverse array of physical structures may exist between and within riverine landscapes. Broad-scale patterns in the spatial arrangement of riverine landscapes are observed despite variations in the influence of independent catchment and channel variables. Rivers are continually evolving in response to longer-term natural disturbances, shorter-term pulsed or ramped human interventions, and high magnitude, low-frequency episodic events. Responses may be cyclic, nonlinear, and/or lagged, and the effects of single or multiple disturbance may overlap and interact, thereby increasing the probability of alternative states in river systems. This view of riverine landscapes moves away from notions of equilibrium and cyclic behavior as a means to explain nonlinear relationships and stochasticity. Recent views of river systems emphasize the importance of scale and their hierarchical organization, acknowledging both top-down constraints and the emergent features of bottom up influences. Contrasting views of the clinal and patch approach to the spatial arrangement and behavior of riverine landscapes reflect the differences between Darwinian and Newtonian approaches to science in some way. The former embraces the principles of complexity, contingency, and interdependence, while the latter strives for simplification, ideal systems, and predictive understanding. This chapter discusses concepts and theoretical approaches to the spatial arrangement of riverine landscapes. Following this, a review of the river characterization is presented. In particular, the results of a meta-analysis of the more commonly used river characterization schemes are presented. A characterization scheme for riverine landscapes then presented, and its application demonstrated with two case studies: the Murray–Darling Basin, Australia, and some of the rivers in the Kingdom of Lesotho, Africa.