Ciénaga

Ciénaga

A ciénega (also spelled ciénaga) is a wetland system unique to the American Southwest and Northern Mexico. Ciénagas are alkaline, freshwater, spongy, wet meadows with shallow-gradient, permanently saturated soils in otherwise arid landscapes that often occupy nearly the entire widths of valley bottoms. That description satisfies historic, pre-damaged ciénagas, although few can be described that way now. Incised ciénagas are common today. Ciénagas are usually associated with seeps or springs, found in canyon headwaters or along margins of streams. Ciénagas often occur because the geomorphology forces water to the surface, over large areas, not merely through a single pool or channel. In a healthy ciénaga, water slowly migrates through long, wide-scale mats of thick, sponge-like wetland sod. Ciénaga soils are squishy, permanently saturated, highly organic, black in color or anaerobic. Highly adapted sedges, rushes and reeds are the dominant plants, with succession plants—Goodding's willow, Fremont cottonwoods and scattered Arizona walnuts—found on drier margins, down-valley in healthy ciénagas where water goes underground or along the banks of incised ciénagas. Ciénagas are not considered true swamps due to their lack of trees, which will drown in historic ciénagas. However, trees do grow in many damaged or drained ciénagas, making the distinction less clear. The distribution and conservation status of ciénegas of Arizona and adjacent New Mexico were first inventoried and assessed systematically in 1985.[1] Characterized by slow-moving, broad flows through extensive emergent vegetation, intact ciénegas were then rare, but reviews of historic accounts of the surface waters and landscapes of that region indicated they were previously extensive. Broadscale incision of ciénegas and conversion of large segments of former ciénegas to ephemeral surface flows through deeply incised former ciénega-formed soils, was hypothesized to have occurred predominantly in the late 1800s as a result of overgrazing, water diversions, and changing climates. More recent updates and geographically broadened inventories and status assessments of ciénegas now extend throughout Arizona and New Mexico eastward into Texas and south into Chihuahua and Sonora (México).[2][3][4][5][6] Though often diverse local factors have clearly played major roles in altering some former ciénegas, the hypothesis of ongoing region-wide erosion since arrival of Europeans, and subsequent alteration of the land and aquifers (including more recent pumping of them), has been generally supported. "Since the late 1800s, natural wetlands in arid and semi-arid desert grasslands of the American Southwest and Northern Mexico have largely disappeared.".[7] Historic ciénegas are now deeply entrenched and generally dry, or left with far less-permanent, often now ephemeral water. Broad grasslands adjacent to former ciénegas, once supported by shallow and stable groundwater maintained by ciénegas, are gone, replaced largely by mesquite and other arid-land vegetation, sometimes with narrow, remnant ciénegas persisting in deeply incised channels. Additional resources about ciénegas are available,[8] including an extensive bibliography of relevant literature.[9]