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Why is this study important?
It represents a critical first step in characterizing the streamflow requirements of habitat and wildlife along the Verde River.
Haney, J.A., Turner, D.S., Springer, A.E., Stromberg, J.C., Stevens, L.E., Pearthree, P.A., and Supplee, V., 2008, Ecological Implications of Verde River flows: A report by the Arizona Water Institute, The Nature Conservancy, and the Verde River Basin Partnership, 122 p. The Verde River is an essential element of life in central Arizona for both its natural and human communities. Apparent conflicts have developed, however, between human demands for water and those of the plants and animals that use the river. Such issues are not unique to the Verde, and experience in watersheds around the world has shown that water conflicts can be reduced or resolved through better understanding. To the extent that land and water managers understand the physical processes involved and the character of various water demands, they can work for solutions that better meet the needs of the Verde’s ecosystem and the human communities within it. The study is represents an initial step in describing the needs of the plant and animal communities that depend on water in the Verde River. It is intended to fill a gap in the discussions of Verde water management. By highlighting the basic needs of the Verde River ecosystem, it shows areas of overlap with human demands and can be used to refine the sense of trade-offs in management decisions. The Verde River Ecological Flows study was a collaborative effort, sponsored by the Arizona Water Institute, The Nature Conservancy, and the Verde River Basin Partnership, and involving experts from fifteen agencies, universities, and other organizations.
Summary of Results
This study identifies where the scientific information is clear about the types and scope of change that would result from changes in surface and groundwater conditions on the Verde River, and where additional scientific studies are needed to resolve particular issues. There is clear scientific evidence that the plants and animals in and along the banks of the Verde River depend on river flows, and would be affected if these flows diminish. Reduced base flow would alter aquatic habitat, reducing or removing populations of some fish and other animals and plants dependent on open water conditions for at least part of their life cycles. In addition, if base flow were to decrease and stream reaches changed from perennial to intermittent, the water table in the stream aquifer would show increased seasonal and year-to-year fluctuations, and the average annual depth from the land surface to the zone of saturation would increase. Riparian forest response to streamflow regime and depth-to-groundwater fluctuations have been extensively studied in southwestern rivers. Based on these studies, experts predicted: 1) declines in cottonwood and willow abundance; 2) decreases in structural diversity; and 3) increases in non-native species such as tamarisk. Such vegetation changes would likely cause shifts in the bird community, with reductions or loss of some species. Thresholds for some species have not been adequately quantified for the Verde River through scientific study. To capture the state of our knowledge and facilitate the needed research, subject experts reviewed the available science and developed hypotheses on the ecological responses of species to changing river and groundwater levels. When refined with adequate data, these hypotheses will provide advance warning of potential species loss from the river system in time to prevent it. The effects of reduced base flow would differ according to the local hydrologic and geomorphic conditions. Base flow in the upper Verde River is smaller than in the Verde Valley, so the same volume of water removed from the river would remove a greater proportion of streamflow in the upper reach than in the Verde Valley. Thus, ecological impact may be larger in the upper reach. However, water use and land use are complex in the Verde Valley. Workshop participants identified several studies that would address this information gap.
A Research Agenda for the Future
A major goal of the Verde River Ecological Flows workshop was to identify critical gaps in our knowledge, and to develop a prioritized research agenda to fill those gaps. The experts stressed that data collection needs to be integrated among the physical- and biological-science disciplines. Priority research goals include better characterization of the river and its floodplain with representative cross sections and longitudinal profiles, development of information on the flood stage that can be expected with various flow levels, and documentation of the depth to groundwater at representative study sites. Biological research priorities include measuring vegetation attributes at the same representative sites, and quantifying fish habitat availability as it relates to stream flow. Results from such integrated data collection should provide the essential platform for quantifying the responses of plants and animals to changes in river flow. CLICK HERE TO READ THE FULL REPORT
