New Mexico Geological Society Annual Spring Meeting — Abstracts

Climate is one of several important variables that influences the formation of soils. Recent documented increases in desertification threaten to significantly alter the environment of many soils, probably on a global scale. Therefore, it is important to understand how anticipated climate change (e.g. global warning) will specifically affect soil environments. The evaluation of soils along the elevation gradient is one effective way to study climate's influence on soil formation. The transitional climate regime of the semi-arid southwest in southcentral New Mexico on the southeast edge of the Rio Grande rift provides an opportunity to closely examine a soil climosequence following the "state factor" strategy of Jenny (1941, 1980). Studies of two soils forming on fluvial terraces in the Palo Duro drainage basin, estimated to be of early Holocene age, help determine the effect of a spatial change in climate on soil development. One site occurs at an elevation of approximately 1,830 meters, where mean annual precipitation is (MAP) is 29.35 mm and mean annual temperature (MAT) is 19.14°C. The second site occurs at an elevation of approximately 1,422 meters and here, MAP is 18.65 mm and MAT is 21.95°C. The soils profile associated with the site at the highest elevation is characterized by the presence of a non-calcareous argillic horizon from a depth of 5 cm to 30 cm, and calcium carbonate begins to accumulate at a depth of 30 cm and continues to the bottom of the pit at 136 cm. In contrast to this soil, pedogenic carbonate has accumulated throughout the soil profile starting at the lower elevation site; its morphology is stage II (Gile et aI., 1966) and no argillic horizon is present.

It is unlikely that the small difference in the present-day climate at the two sites can account for the observed differences in these two soils. There are many alternative explanation for the differences. It is possible that the time period of the meteorological data collected does not clearly establish the longer term contrast in climate between the two sites. There have been many climate changes in the Holocene that could be responsible for the observed changes. A stronger climatic gradient could produce greater temperature and precipitation differences. A greater difference in the climatic gradient could account for the differences in the depth of calcium carbonate, clay accumulations, and soluble salts. Climate depends upon many complex responses and invokes many dependent relationships, for example, the positive feedback between vegetation and climate, and the effect of the amount of vegetation and the production of carbonic acid. It is possible that the contrasts observed are due to the positive vegetation feedback since the "higher" elevation site has 70% vegetation cover and the "lower" site has 20% vegetation cover. The influx of dust also should be investigated to determine its influence of the water balance in the soils. Future studies investigating the various possible complex responses should also conducted to aid in future studies of the influences of climate changes on soil development.