Cienega

A ciénega (also spelled ciénaga) is a wetland system unique to the American Southwest. Ciénagas are alkaline, freshwater, spongy, wet meadows with shallow-gradient, permanently saturated soils in otherwise arid landscapes that often occupied 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. Although trees drown in historic ciénagas — that’s why “swamp” is a common erroneous description; swamps have trees — these woody plants now occupy many damaged or drained ciénagas.

Undamaged ciénagas, essentially nonexistent today, were characterized by a slow-moving, broad flow through extensive emergent vegetation as just described. But today, the ongoing region-wide erosion that followed the arrival of Europeans in the American Southwest and the subsequent misuse of the land by settlers firmly entrenched water flow between vertical walls, resulting in an ever-worsening incision process, a drawdown of local water tables and the drying up of most marshland environments, leaving behind scarcely few undamaged ciénagas. Many that remain today look and function like a creek: narrow, incised and continuing to degrade. "Since the late 1800s, natural wetlands in arid and semi-arid desert grasslands of the American Southwest and Northern Mexico have largely disappeared."

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Wikipedia