This morning’s Arizona Daily Star‘s front page article by Tony Davis tells us that Governor Ducey is asking the Federal EPA to revise the rules that determine which streams are protected as “waters of the U.S.”
Apparently, real estate developers are unhappy because they have to treat ephemeral streams in the same manner they treat streams that carry water all year. That is, they have to get the permits required by the Clean Water Act even if there is no water in the stream most of the year. How sad. They can’t fill those dry ditches or streams without doing some paperwork. As, Davis points out aquifer protection is an issue and the state claims they will continue to protect the washes that are involved aquifer.
However, there is an another issue here – biodiversity of the desert, in this case, the Sonoran, Mojave, and Chihuahuan deserts.
Ephemeral streams (washes or arroyos) are abundant in Arizona, yet we know little about how their vegetation differs from surrounding terrestrial zones and about their projected response to regional warming and drying. Stomberg et al. (2017) assessed plant communities at seven ephemeral streams (and terrestrial zones) distributed among three climatic settings in Arizona. Compared to terrestrial zones, riparian zones had a similar herbaceous cover but greater woody vegetation volume. They supported more plant species, with several woody taxa restricted to the ephemeral zone (consistent with the idea that herbaceous plants are rain-dependent while riparian trees rely on runoff stored in stream sediments). Their herbaceous communities had high compositional overlap with terrestrial zones and therefore ephemeral streams may sustain regional diversity as droughts intensify. Desert Wash habitats are characterized by the presence of arborescent, often spiny, shrubs generally associated with intermittent streams (washes) or drier bajadas (alluvial deposits adjacent to washes), especially in the Sonoran Desert. Thus, washes and arroyos help maintain the biodiversity of the desert.
The structure of the vegetation in desert washes also differs from the surrounding desert. The following information is from Laudenslayer (n.d.). The plants comprising Desert Wash habitats are taller and denser than those in the surrounding desert habitats. Heights of desert wash plants usually do not exceed 5 m however, some mesquite stands are as tall as 9 m. The height of wash vegetation usually is proportional to the size of the arroyo. Washes in northern deserts not bounded by arborescent shrubs should be considered taller examples of the surrounding habitat (e.g., Sagebrush).
Desert Wash habitats in the south exhibit a more diverse vertical structure than do those in the north. The composition of desert wash plant assemblages depends on variables such as latitude, elevation, and precipitation. Generally, washes in the south are more diverse in plant species composition and vertical structure than washes to the north. Canopy species typically found in washes include blue palo verde, littleleaf paloverde, desert ironwood, smoketree, catclaw acacia, mesquite, screwbean mesquite, and tamarisk. Plants of the subcanopy include desert broom, crucillo, Anderson’s wolfberry, arrowweed, desert willow, as well as small individuals belonging to the dominant canopy species. Ground cover plants include white brittlebush, Opuntia, snakeweed, goldenbush, saltbush, bursage, desert lavender as well as a variety of forbs and grasses.
Given this information, the vegetation along desert washes is obviously valuable wildlife habitat.
Laudenslayer WE. (nd). California Wildlife Habitat Relationships System California Department of Fish and Game California Interagency Wildlife Task Group < file:///C:/Users/John/Dropbox/BiogeographyTT/DSW.pdf>
Stromberg JC, Setaro DL, Gallo EL, Lohse KA, Meixner T. 2017. Riparian vegetation of ephemeral streams. Journal of Arid Environments. 138:27-37.