Springs ecosystem distribution and density for improving stewardship and springs as sources of temperate and tropical perennial streams

摘要

Springs support some of the most diverse and unique ecosystems on Earth. Stewardship of springs ecosystems has been hindered by the lack of knowledge of the distribution and density of springs across landscapes. Death Valley National Park and the State of Arizona in the U.S. are examples of two landscapes with significant knowledge about the distribution and density of springs. Springs data in Death Valley National Park are used to test the application of accumulation curves of spring's density. A spring's specific database of Arizona is used as an example of how to accumulate geospatial information for a large landscape. In both landscapes, springs are highly non-randomly distributed due to emergence in topographically and geologically complex terrain. In addition, springs emerge in clusters of multiple sources; therefore, density depends on the spatial scale of inquiry and the extent to which sources are considered independent. For example, the current inventory of Death Valley National Park estimates springs density between 0.033 - 0.074 springs/km2 depending on how springs are defined, either as individual spring orifices or springs complexes - represented as groups of related springs orifices. When considering springs as individual orifices, the best data estimates that Arizona has a density of 0.035 springs/km 2. These densities are only representative of current datasets because an unknown number of springs remain unmapped in both landscapes. To predict the total number of springs in Death Valley, we used a modified density accumulation curve, involving the number of springs detected in surveys over the past century. This analysis indicates that there may still be additional undocumented springs across the landscape. Knowledge of the distribution and density of the springs across a landscape can assist land and resource managers develop unbiased prioritizations of springs ecosystems for stewardship actions.;Groundwater and surface water supply the vast majority of global freshwater sources. Groundwater discharge serves as a major contributor to surface waters, and may have a growing role as climate change alters global sources of freshwater. Groundwater sources are increasingly threatened by a worldwide boom in groundwater extraction, especially in arid regions of low recharge. The limited surface waters of the arid southwestern U.S. support municipal and agricultural demands and are hotspots of biological diversity. Sources of perennial surface water in the Southwest are threatened by diversions, increased groundwater pumping and prolonged drought. This study investigates groundwater as a source to rivers globally and as sources of perennially flowing steams in Arizona to focus attention on monitoring and preservation of these endangered resources.;A literature review of the world's 20 largest rivers indicates that each has groundwater contributions. A GIS analysis of The Nature Conservancy's mapping of perennial streams and the Springs Stewardship Institute's springs distribution highlights insufficiencies of springs inventories and stream mapping as many perennially flowing streams have no identified groundwater source, defined here as a spring. Through detailed analysis of the Verde River watershed, we found that 80% of perennial streams have mapped groundwater sources and that 55% of perennial streams were misclassified according to the existing perennial streams data set, with many perennial streams over estimated in length.