What makes the desert bloom? The contributions of dust and crusts to soil fertility on the Colorado Plateau
Wildland Shrub Synposium: Shrubland Ecosystem Genetics and Biodiversity
U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station
Eolian dust (windblown silt and clay) and biological soil crusts are both important to ecosystem functioning of arid lands. Dust furnishes essential nutrients, influences hydrology, contrib-utes to soil formation, and renders surfaces vulnerable to erosion. Biological soil crusts contribute directly to soil fertility by fixing carbon and nitrogen, and indirectly by trapping newly-deposited dust and stabilizing already-present soil. Results from crust-stabi-lized, unconsolidated sandy sediments on prominent rock exposures and grasslands show dust inputs have significantly increased all bio-essential nutrients in soils of SE Utah, including P, K, Mg, Na, and Ca. As plants can be P and K-limited in these soils, dust may be essential for plant growth. Evidence for eolian dust comes from magnetic, chemical, and mineralogic properties of the soils that contrast greatly with those of local bedrock. For example, magne-tite, which formed originally in igneous rocks, is common in soils but absent in the local sedimentary bedrock. In view of the regional geology, particle-size distribution of soils, and patterns of proper-ties, the magnetite represents long-distance transport of eolian dust. Dust in the biological soil crusts, when compared to underlying sediment, shows higher magnetite, Zr, and Zr/Ti, suggesting that dust sources have changed over the past few decades. It is suggested that recent human disturbance in areas surrounding the Colorado Plateau may be responsible for this change in dust source. Because most of the fertility in these soils is due to dust input, it is of concern to land managers when soil loss via wind and water erosion exceeds this input. Ever-increasing use of these desert landscapes by recre-ation, military and agricultural activities generally destroys the biological soil crusts that are critical for nitrogen, carbon, and soil stability. Thus, increased erosion, and reduced dust retention, may be a result of these activities.
Belnap, J., Reynolds, R. L., Reheis, M., and Phillips, S. L., 2001, What makes the desert bloom? The contributions of dust and crusts to soil fertility on the Colorado Plateau, in McArthur, E. D., and Fairbanks, D. J., eds., 11th Wildland Shrub Synposium: Shrubland Ecosystem Genetics and Biodiversity, June 13-15, 2000, Provo, Utah, Proceedings No. RMRS-P-21: Ogden, Utah, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, p. 147- 153.