Technical Report


Irrigated Wetlands Of The Colorado Plateau: Information Synthesis And Habitat Evaluation Method Public Deposited

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  • Wetlands of the Colorado Plateau that receive water from irrigation can, by their functions, support several societal values. For example, their capacity for removing nitrate and perhaps pesticides from nonpoint source runoff might be considerable. However, relatively little research has been conducted in irrigated wetlands, and their ability to alter water quality in particular remains relatively unknown. Much more documentation exists concerning the importance of irrigated wetlands as habitat. About 72% of all reptiles, 77% of all amphibian species, 80% of all mammals, and 90% of all bird species which occur regularly in the Colorado Plateau region routinely use irrigated wetlands and riparian areas. About 30% of the region's bird species use wetlands and other aquatic areas to the exclusion of upland habitats. Wetland and riparian habitats also support a disproportionate number of species that are of concern because they migrate to neotropical areas, have small continental populations, or are declining. Virtually all wetland and riparian habitats in agricultural areas of the Colorado Plateau are sustained to some degree by runoff and seepage from irrigation. No single characteristic (i.e., "indicator") reliably predicts which irrigated wetlands comprise the best habitat. Rather, habitat quality is associated with various combinations of the conditions of several indicators, at several scales. The most predictive indicators are probably patch size, water regime, vegetation form and species, aquatic organism abundance, and landscape context. However, attempts to identify indicators of "good" irrigated wetland habitat encounter a problem of defining "good for which species?" The importance of each indicator, or of each unique combination of indicator conditions, depends on the values placed on the species associated with it. Many indicator conditions are ideal for only a few species, but if these species are particularly valued (e.g., because they are regionally rare, declining, or hunted), then the indicator conditions can be considered important. To help address the need for an explicit, integrated, local-scale approach to biodiversity assessment, this report introduces a new procedure for rapidly evaluating wetland and riparian habitat. In contrast to existing methods, it does not require the user to judge a habitat based on the habitat's suitability for just a few "indicator species." Rather, the procedure addresses the question, "good for which species" by estimating explicitly the quality of a habitat for all wetland/riparian species of the region's most diverse vertebrate taxonomic group -- birds. The procedure estimates the number of species likely to occur regularly in a particular wetland and uses this to assign importance to the wetland. The user can employ the procedure to evaluate a wetland using any subset of the species, and to select combinations of wetlands that will maximize avian diversity at local and regional scales. The procedure's emphasis on biodiversity and an ecosystems approach is consistent with current shifts in scientific thinking and the mandates and operations of many resource agencies. The procedure requires less than 30 minutes per wetland to implement. Information from systematic field testing has been used to improve the procedure and its supporting database. Additional validation, by comparing evaluation scores with actual species richness as measured by direct multitemporal surveys of birds and other vertebrates, is desirable.
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  • Preparation of this document was supported by EPA’s Wetlands Research Program through contract #68- C8-0006 to ManTech Environmental Technology, Inc.
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