Ciénega

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A restored cienega in Balmorhea State Park

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.

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.

Current state[edit]

Undamaged ciénagas, essentially nonexistent today,[citation needed] were characterized by a slow-moving, broad flow through extensive emergent vegetation as just described. But today,[when?] 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."[1]

Properties[edit]

Ciénegas occur at intermediate elevations (1000-2000 m) and are characterized by saturated, reducing soils with reliable water supply via seepage. Sedges, rushes, and grasses are the dominant plants, with a few trees that can withstand saturated soils, such as willows. Ciénegas trap organic matter from their surroundings, and are thus highly productive ecosystems.[2]

The structure of a natural ciénega is influenced by long-term climatic cycles of wet and dry periods. During dry periods, falling water tables lead to a reduction in vegetation. Prolonged wet periods lead to increased vegetation and trapping of sediment, while brief periods of high rainfall may lead to carving of gullies. Runaway gully growth, as can occur when vegetation is artificially removed (e.g., by overgrazing), can lead to channelization and loss of the ciénega.[3]

Importance and conservation[edit]

As a primary source of water in arid environments, ciénegas support a broad range of terrestrial life, including numerous endangered species. For instance, in Arizona, 19% of threatened, endangered, or candidate threatened or endangered species are directly associated with ciénegas.[4] Ciénegas also purify surface water and mitigate flooding when heavy precipitation occurs, and help to cycle nutrients between water and soil.[4] Humans have also long relied on the water provided by ciénegas: Indigenous Americans used ciénegas for water and hunting grounds, and a majority of pre-historic agricultural settlements occurred in the vicinity of ciénegas.[5] Indigenous inhabitants of the American Southwest also gave spiritual significance to ciénegas and local watering holes.[6]

The decline of ciénegas has been caused largely by changes in land use, primarily overgrazing (which removes water-absorbing vegetation) and overexploitation of ground water for agriculture and urban use.[2][4] Direct removal of vegetation from the vicinity of wetlands has also been a cause of ciénega loss,[7] as has the extirpation of beaver from the region.[8] Preservation of existing ciénegas, and restoration of degraded ciénegas, depends on reversing these trends in land use and preventing their recurrence in the vicinity of ciénegas. This preservation is complicated by the fact that a majority of ciénegas are found on privately-owned land, most of which does not have binding conservation agreements or easements in place.[4]

Occurrence[edit]

It is likely that there were many hundreds of long lost ciénagas when the Southwest was Indian country, although there are only 155 identified or named ciénagas since the European arrival in the entire International Four Corners Region of the Southwest — that is, Arizona and New Mexico in the United States and Chihuahua and Sonora in Mexico.[9] As shown in Table 2 below, fewer than half (44%) of known ciénagas are functional or restorable, while 56% have no potential for restoration or are dead.

State Number of Ciénagas
Arizona, USA 66
New Mexico, USA 61
Sonora, MX 20
Texas, USA 4
Chihuahua, MX 3
Coahuila, MX 1
TOTAL 155
Condition of Ciénagas Number of Ciénagas Percent of Total Number
Functional 40 26%
Restorable 28 18%
Severely Damaged 18 12%
Dead 69 44%
TOTAL 155 100%
Table 1. Distribution of Known Ciénagas by State in the US and Mexico Table 2. Current Condition of Known Ciénagas

In late 2018, as part of his effort to create a wetland action plan for the state of New Mexico, retired former New Mexico botanist Robert Sivinski discovered via satellite an additional 119 small ciénagas in New Mexico.[10] This surprising number of previously unidentified or unstudied ciénagas suggests there may be more to be found. A working ciénaga inventory is maintained at the University of Texas Austin with access to numerous papers, google maps and other ciénaga materials: [1]

See also[edit]

  • La Cienega
  • Dry lake – Basin or depression that formerly contained a standing surface water body
  • Salt pan (geology) – Flat expanse of ground covered with salt and other minerals
  • Oasis – Isolated source of fresh water in a desert
  • Grass valley – Meadow within a forested and relatively small drainage basin

References[edit]

  1. ^ Minckley and Brunelle (2007). "Paleohydrology and Growth of a Desert Ciénega". Journal of Arid Environments. 69 (3): 420–431. Bibcode:2007JArEn..69..420M. doi:10.1016/j.jaridenv.2006.10.014.
  2. ^ a b Hendrickson, D.A.; Minckley, W.L. (1984). "Ciénegas: Vanishing Climax Communities of the American Southwest". Desert Plants. 6: 131–175.
  3. ^ Lisenby, P.E.; Tooth, S.; Ralph, T.J. (2019). "Product vs. process? The role of geomorphology in wetland characterization". Science of the Total Environment. 663: 980–991. doi:10.1016/j.scitotenv.2019.01.399.
  4. ^ a b c d Minckley, T.A.; Turner, D.S. (2013). "The relevance of wetland conservation in arid regions: A re-examination of vanishing communities in the American Southwest". Journal of Arid Environments. 88: 213–221.
  5. ^ Bahre, Conrad Joseph (1991). A Legacy of Change: Historic Human Impact on Vegetation of the Arizona Borderlands. Tucson: University of Arizona Press.
  6. ^ Childs, Craig (2001). The Secret Knowledge of Water, Discovering the Essence of the American Desert. New York, Boston, London: Back Bay Books.
  7. ^ Hendrickson, D.A.; Kubly, D.M. (1984). "Desert waters: Past, present, and future". The Nature Conservancy News. 34: 6–12.
  8. ^ McNamee, Gregory (1994). Gila, The Life and Death of an American River. New York: Orian Books.
  9. ^ Cole and Cole (2015). "An Overview of Aridland Cienagas with Proposals for the Classification, Restoration, and Preservation". New Mexico Botanist (Special Issue, No. 4).
  10. ^ Sivinski, Robert (December 2018). "Wetlands Action Plan, Arid-land Spring Cienegas of New Mexico". New Mexico Environment Department, Surface Water Quality Bureau.