Inclusion of ecosystem concepts in integrated management of river resources

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1 Integrated Water Resources Management (Proceedings of a symposium held al Davis. California. April 2000). IAHS Publ. no Inclusion of ecosystem concepts in integrated management of river resources TON SNELDER, BARRY BIGGS & MARK WEATHERHEAD National Institute of Water and Atmospheric Research, PO Box 8602, Riccarton, Christchurch, New Zealand [email protected] Abstract Integrated environmental management (IEM) attempts to bring together knowledge of biophysical processes with regulatory mechanisms and the aspirations of society in environmental decision making. In general it is the ecosystem processes, which can be defined at any scale or level of complexity, that correspond most closely with valued natural resources and ecosystem services. This paper discusses how reductive analysis can be assisted by physical classification of ecosystems into management units. We illustrate the process of analysis using the example of issues associated with elevated nutrient concentrations in the rivers of the Canterbury region of the South Island of New Zealand. Key words classification; ecosystem management; GIS; integrated environmental management; New Zealand; rivers; scale INTRODUCTION Integrated environmental management (IEM) planning attempts to define how to coordinate human activities to achieve a broad range of goals for the sustained provision of natural resources and ecosystem services (Cairns, 1991). Good IEM planning must fulfil four criteria: it must be comprehensive, interconnective, goal orientated and reductive (Born & Sonzogni, 1995). It must be sufficiently comprehensive to take a large-scale view of existing and future environmental problems and interconnective to recognize that issues emerge from the interactions between socioeconomic and institutional factors as well as between component parts of the ecosystem. A goal orientation seeks to define how conflicting use of resources and ecosystem services will be accommodated. IEM must also be reductive and acknowledge the need to develop responses that accommodate complexity and deal with the most important interconnections within management units in a coherent and consistent manner. In our view, the reductive component of IEM is best achieved by organizing the factors that affect processes that define the ecosystem and its valued attributes in an hierarchical fashion, to provide a context for understanding the system at appropriate spatial scales. In this way planning exercises can move logically from broad-scale comprehensive goals to increasingly specific, issue-orientated objectives for managing natural resources and ecosystem services.

2 380 Ton Snelder et al. DEFINING ECOSYSTEM PROPERTIES AND PROCESSES Ecosystems can be classified according to the physical factors that provide the context for their ecological processes. Our approach emphasizes the use of models to link physical factors to properties via processes at different levels of detail. This allows analysis to interpret patterns of processes and properties at scales that are appropriate to the planning process. For planning at regional scales we believe it is also necessary to be able to group and map environments into management units that share processes and other properties, and ultimately have similar goals and issues. Issues can be identified as comprehensive wholes by reconciling scales of modelled processes with descriptions of natural resources and ecosystem services. The link from ecosystems to management units then comes at the level of processes that support ecosystem properties. RIVER CLASSIFICATION SYSTEM We have developed a GIS-based classification of the rivers of the Canterbury region of the South Island at a scale of 1: (Snelder et al., 1999). The choice of controlling factors was therefore restricted to those that could be determined at any location from data available to GIS. For this paper, we are concerned with only four controlling factors: climate, source of flow, geology and land cover. In our classification, climate remains constant at the scale of a region, and is not therefore an important factor in distinguishing rivers within a region. All controlling factors are subdivided into various categories. For example, source of flow categorizes catchments according to the interaction of topography and climate. The categories recognize that hydrological response of a catchment is mediated by storage such as snow pack and reservoirs such as lakes and groundwater. The catchment of a river at any point is potentially comprised of different combinations of these factors. The classification for each factor is based on rules that assign a category based on the dominant influence at each section in the river network. Within a region these physical categories correlate with many other ecosystem properties such as flood frequency, nutrient regime and biotic communities. An important concept that underpins our classification system is that of the river continuum (Vannote et al., 1980). This concept recognizes that the physical variables at any point in a river reflect the integrated effect of controlling factors in the catchment above that point. Classification therefore changes moving down the river system as the proportions of various controlling factors change. Tributary streams may therefore have very different classifications to the main stems they meet, and tributaries may collectively change the classification ofthe main stem. IEM REDUCTIVE ANALYSIS Our approach to analysis of regional-scale environmental issues can be summarized as five steps (iteration between steps is generally necessary).

3 Inclusion of ecosystem concepts in integrated management of river resources 381 Establish the environmental goals These goals are broad descriptions of natural resources and ecosystem services that management seeks to sustain. This first step identifies perceived issues based on conflicts between resource use and other valued ecosystem properties. Develop an environmental context There are two components in this step. First, a model is developed of the important ecological processes involved in the issue. Second, the region is subdivided using the river environment classification system into management units that we expect to contrast significantly in terms of the processes involved in the issue and implications for managing these. Identify vulnerable environmental values Strategic reduction of the issue is encouraged at this step by focusing on the most vulnerable ecosystem properties. We use the management units that are defined by the classification system to constrain variance in the range of ecosystem properties and therefore provide a realistic set of potential values. Vulnerability is the combination of the significance of values and how susceptible the ecological processes that support these values are to changes caused by use of ecosystem services (Udo de Haes & Klijn, 1994). Define the severity and extent of the issue Issues are defined where the use of natural resources may affect the vulnerability of other valued ecosystem properties. The severity and extent of the issue is assessed against a set of criteria. The criteria are measures of system state variables (e.g. water quality) that will sustain the vulnerable values at a specified level of protection. Environments are evaluated against these criteria enabling information about the extent and severity of the issue to be generated. Develop options for management Management objectives are actions that are aimed at achieving specific levels of protection for values. This step is therefore linked to the establishment of criteria and recognizes that objectives may vary depending on the levels of protection that are desired. The final selection of management objectives involves value judgements that must be considered through the political processes. EXAMPLE: NUTRIENT ENRICHMENT IN RIVERS OF THE CANTERBURY REGION In the Canterbury region of the South Island of New Zealand nutrient enrichment of rivers is due principally to nonpoint sources resulting from intensification of pastoral land use. These rivers support many values, which may conflict with the service of assimilating nutrients. In this example, we consider the conflict between nutrient assimilation and one particular value, a trout fishery. Some increase in nutrients in rivers can be a subsidy to the ecosystem and increase its productivity. Excess nutrients, however, adversely affects trout numbers by promoting high algal biomass causing fluctuations in dissolved oxygen and ph levels, and smothering invertebrate habitat thereby reducing food supply. Establish environmental goals Manage the effects of nutrients so that the trout fishery is sustained. Defining the environmental context The most important ecological process in relation to nutrient supply is the production of plant biomass. We model plant biomass as a function of nutrient supply and time available for growth, which is determined by

4 382 Ton Snelder et al Table 1 Flood disturbance-nutrient supply matrix defined by the river environment classification system. Management units Controlling factors: Ecological matrix: Flow source Geology Land cover Disturbance Nutrient supply Glacial mountain G H N High Low Mountain M H N High Low Hill natural H H N Medium Low Hill pasture H H P Medium Medium Plains hard sedimentary L H P Low Medium Volcanic pasture L V P Low High Plains soft sedimentary L S P Low High Key:Source of flow: glacial mountain G, mountain M, hill H, low elevation L. Geology: hard sedimentary H, soft sedimentary S, volcanic V. Land cover: pasture P, natural N. the disturbance due to floods (Biggs, 2000a). These processes can be defined using patterns provided by the catchment scale controlling factors: source of flow, geology and land cover from our classification. Source of flow separates rivers into different classes, which correlate with the frequency of flood disturbance, broad scale sediment supply and to some extent, nutrient supply. Catchment geology and land cover (and its correlate, land use) contain more specific correlates with nutrient supply. Hard indurated sediments (greywacke) result in low nutrients, whereas volcanic and soft Tertiary sediments result in higher nutrient supply. Natural land covers such as alpine tussock (native grass species) and hill forests result in low nutrient supply whereas pastoral land cover increases the supply of nutrients. The classification system was used to group and map the region's rivers into seven major management units that describe a disturbance-nutrient supply matrix to enable prediction of algal biomass (Table 1). Identify the vulnerable environmental values The management units were used to define environments that have potential habitat for brown trout. Brown trout are potentially abundant in all Canterbury River environments except those with soft sedimentary and volcanic geology, which do not provide the substrates required for spawning. Establish extent and severity of the issue Our criteria for plant biomass for the protection of trout are based on an allowable maximum chlorophyll-a concentration of 200 mg m"~ that marks the boundary between mesotrophic and eutrophic ecosystem states (Dodds et al., 1998). The criteria for phosphorus and nitrogen concentrations that will maintain rivers at the oligotrophic/mesotrophic and mesotrophic/eutrophic thresholds are based on Biggs (2000b). Nutrient criteria that define the trophic thresholds are therefore defined for different flood frequencies, which determine the time available for growth (Fig. 1). To assess the nutrient status of rivers with respect to these criteria we constrain the variance in water quality data collected from 500 sites across the whole region by grouping the sites on the basis of the management units in Table 1. Data collected from sites in each management unit was analysed collectively and used to represent nutrient levels in each management unit (Fig. 1). Figure 1 indicates that nutrient criteria are not exceeded in glacial mountain, mountain and hill natural management units. The criteria for nitrogen are exceeded in the hill pasture

5 Inclusion of ecosystem concepts in integrated management of river resources 383 High Flood Frequency Medium Flood Frequency Management Units Fig. 1 Box and whisker plots for soluble nitrogen and dissolved reactive phosphorus data collected from the seven management units compared to nutrient criteria. The white boxes are management units where criteria are not exceeded, the grey boxes are management units where criteria are exceeded for one nutrient, and the hatched boxes are management units where the criteria for both nutrients are exceeded. \ t v V X *or H - vis ^ À N 30 Kilometers /Ax [ I Lakes /\y A Glacial mountain /%/ Mountain A / Hill natural A / Hill pasture A Plains hard sedimentary " / / Plains soft sedimentary Volcanic pasture Fig. 2 Classification of rivers of the Canterbury region into seven management units describing an ecological matrix containing interactions between flood disturbance and nutrient supply.

6 384 Ton Snelder et al. management unit, meaning these rivers are susceptible to increases in phosphorus. Both criteria are exceeded in all plains and volcanic pasture management units indicating they are already potentially eup-ophic. The classification system is used to map these results to show the extent of the issue (Fig. 2). Developing options for management The results suggest that the vulnerable fish values in glacial mountain, mountain and hill natural river management units are not compromised by excessive nutrient levels. In the plains rivers the nutrient levels greatly exceed the criteria. These rivers are characterized by low gradient meandering streams and lack of flood disturbance. Excessive plant biomass is a common issue in these management units. However, controlling biomass by restricting nutrients is an unlikely objective in these systems, as it would probably preclude intensive fanning activities. An alternative management approach is to restrict plant growth by reducing light in the stream channel. This is likely to be the most effective option for managing eutrophication in these management units. In contrast to the plains rivers, the hill pasture rivers have high nitrogen levels and are therefore susceptible to inputs of phosphorus. Management objectives are best directed at reducing phosphorus inputs to rivers by managing activities such as fertilizer application rates in the pastoral catchments of this management unit. CONCLUSION The example demonstrates a number of uses for river ecosystem classification that are based on physical controlling factors, for planning and management. Definition of seven broad river environment classes, which differ in their ecological processes and values, assisted the analysis of the nutrient issue. Defining these management units gives specific geographic boundaries and meaning to ecosystem processes and the values involved. This assists planning by allowing ecosystem state to be visualized as a dynamic balance between the use of natural resources and other ecosystem values (Holling, 1995). This reduces the potential for planning exercises to focus on either optimizing the use of natural resources, or promoting a purely conservative retention of the status quo (Brown & MacLeod, 1996). Definition of management units also assists with monitoring the implementation of plans as it provides a context for data interpretation and state of the environment reporting, the results of which can be fed back into new planning cycles. We conclude that IEM is improved by defining river environment classes for management that are based on factors that provide a context for understanding ecosystem properties. Furthermore, these classes can be linked to abstract models that represent ecological processes at scales and levels of detail that are relevant to the objectives of management. Acknowledgements We are grateful to the New Zealand Ministry for the Environment for funding and the Canterbury Regional Council for data, advice and peer review. We also thank Ian Hawes for review comments on the manuscript. This paper has greatly benefited from research carried out under contracts C01519 and C01813 (Environmental Hydrology and Hydraulics) funded by the New Zealand Foundation for Research, Science and Technology.

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