Hydrologic regimes play a major role in determining the biotic composition, structure, and function of aquatic, wetland, and riparian ecosystems. But human land and water uses are substantially altering hydrologic regimes around the world. Improved quantitative evaluations of human‐induced hydrologic changes are needed to advance research on the biotic implications of hydrologic alteration and to support ecosystem management and restoration plans. We propose a method for assessing the degree of hydrologic alteration attributable to human influence within an ecosystem. This method, referred to as the “Indicators of Hydrologic Alteration,” is based upon an analysis of hydrologic data available either from existing measurement points within an ecosystem (such as at stream gauges or wells) or model‐generated data. We use 32 parameters, organized into five groups, to statistically characterize hydrologic variation within each year. These 32 parameters provide information on ecologically significant features of surface and ground water regimes influencing aquatic, wetland, and riparian ecosystems. We then assess the hydrologic perturbations associated with activities such as dam operations, flow diversion, groundwater pumping, or intensive land‐use conversion by comparing measures of central tendency and dispersion for each parameter between user‐defined “pre‐impact” and “post‐impact” time frames, generating 64 Indicators of Hydrologic Alteration. This method is intended for use with other ecosystem metrics in inventories of ecosystem integrity, in planning ecosystem management activities, and in setting and measuring progress toward conservation or restoration goals.
1. This paper introduces a new approach for setting streamflow‐based river ecosystem management targets and this method is called the ‘Range of Variability Approach’ (RVA). The proposed approach derives from aquatic ecology theory concerning the critical role of hydrological variability, and associated characteristics of timing, frequency, duration, and rates of change, in sustaining aquatic ecosystems. The method is intended for application on rivers wherein the conservation of native aquatic biodiversity and protection of natural ecosystem functions are primary river management objectives.
2. The RVA uses as its starting point either measured or synthesized daily streamflow values from a period during which human perturbations to the hydrological regime were negligible. This streamflow record is then characterized using thirty‐two different hydrological parameters, using methods defined in Richter et al. (1996). Using the RVA, a range of variation in each of the thirty‐two parameters, e.g. the values at ± 1 standard deviation from the mean or the twenty‐fifth to seventy‐fifth percentile range, are selected as initial flow management targets.
3. The RVA targets are intended to guide the design of river management strategies (e.g. reservoir operations rules, catchment restoration) that will lead to attainment of these targets on an annual basis. The RVA will enable river managers to define and adopt readily interim management targets before conclusive, long‐term ecosystem research results are available. The RVA targets and management strategies should be adaptively refined as suggested by research results and as needed to sustain native aquatic ecosystem biodiversity and integrity.
Two ecologically and morphologically divergent species of the Gasterosteus aculeatus (threespine stickleback) species complex occur in Enos Lake, Vancouver Island, British Columbia. The limnetic species swims in open water most of the time and feeds on plankton, and the benthic species lives near the shore in a structurally complex environment where it eats larger benthic prey. Based on design criteria inferred from hydrodynamic considerations, from other fishes, or from other populations of Gasterosteus, and on ecological differences between the two species, we expected that limnetic sticklebacks would have a more fusiform body, longer pectoral fins and snout, and larger eyes. Although some of these expected differences had been observed in a previous study of this species pair, others were verified for the first time in this study. Shape divergence between our samples results both from allometric trends coupled with differences in overall mean size and from size-free shape differences. Standard length is a poor proxy for general size (i.e., the first principal component of the morphometric variables) because several major features which differ between the species are dorsoventrally oriented. The marked morphometric divergence between these species has probably evolved within about the past 13 000 years, since deglaciation of Vancouver Island.
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