Statistics and Data Analysis in Geology

Livestock grazing is the most widespread land management practice in western North America. Seventy percent of the western United States is grazed, including wilderness areas, wildlife refuges, national forests, and even some national parks. The ecological costs of this nearly ubiquitous form of land use can be dramatic. Examples of such costs include loss of biodiversity; lowering of population densities for a wide variety of taxa; disruption of ecosystem functions, including nutrient cycling and succession; change in community organization; and change in the physical characteristics of both terrestrial and aquatic habitats. Because livestock congregate in riparian ecosystems, which are among the biologically richest habitats in arid and semiarid regions, the ecological costs of grazing are magnified in these sites. Range science has traditionally been laden with economic assumptions favoring resource use. Conservation biologists are encouraged to contribute to the ongoing social and scientific dialogue on grazing issues.



El pastoreo de ganado es la practica de manejo de la tierra mas ampliamente utilizada en el oeste de Norte America. El setenta por ciento del oeste de Estados Unidos se utiliza para pastoreo, incluyendo areas silvestres, refugios de vida silvestre, bosques nacionales e inclusive algunos parques nacionales. El costo ecologico de esta forma ubicua de uso de la tierra puede ser dramatico. Ejemplos de este costo incluyen perdida de la biodiversidad; decrecimiento de las densidades de poblacion para una amplia variedad de taxones; alteraciones en las funciones del ecosistem, incluyendo ciclos de nutrientes y sucesiones; cambios en la organizacion de la comunidad y cambios en las caracteristicas fisicas de habitas terrestres y acuaticos. Dado que el ganado se congrega en ecosistemas riberenos, los cuales estan entre los habitas biologicamente mas ricos dentro de las regiones aridas y semi-aridas, los costos ecologicos del pastoreo se magnifican en estos sitios. Tradicionalmente, la ciencia de pastizales, ha estado cargada de suposiciones economicas que favorecen el uso del recurso. Se alienta a los biologos conservacionistas a contribuir al dialogo social y cientifico en los problemas del pastoreo.

https://www.jstor.org/stable/pdfplus/2386504.pdf

Ecological Costs of Livestock Grazing in Western North America

Baselevel is the imaginary horizontal level or surface to which sub-aerial erosion proceeds. It is sea level. Controversy surrounds the effect of baselevel change on river behavior, the rejuvenation of landscapes, and the delivery of sediment to the shelf-slope depositional system. The effect of baselevel change depends upon many factors, such as rate of change, amount of change, direction of change, river character, and dynamics and erodibility of the sediment source area. In most cases the effects of baselevel change will be moderate, and they can be accommodated by changes of channel pattern, width, depth, and roughness. Therefore, the delivery of large amounts of sediment to a shoreline or continental shelf probably reflects not only baselevel lowering, but significant uplift of the sediment-source area and perhaps climate change.

River Response to Baselevel Change: Implications for Sequence Stratigraphy

Reciprocal interactions and adjustments between fluvial landforms and vegetation dynamics in river corridors: A review of complementary approaches

The sequence stratigraphy of fluvial depositional systems: the role of floodplain sediment storage

Precipitation history and ecosystem response to multidecadal precipitation variability in the Mojave Desert region, 1893-2001

During the first 40 years of the twentieth century, erosion was the dominant geomorphic process affecting the morphology of the Little Colorado River channel. The discharge regimen was one of frequent large floods and high annual discharge that created a wide sandy channel free of vegetation. In the 1940s and early 1950s, average annual precipitation declined, reducing annual discharge to about 57% of that of the preceding period as well as reducing the frequency of large floods. The channel adjusted to the new hydrologic regimen by reducing its width. Parts of the channel were frequently dry, and riparian vegetation, primarily nonnative salt cedar, became established on the higher channel surfaces. Precipitation and discharge thereafter increased and aggradation by overbank deposition was the primary geomorphic process, as indicated by accretion of 2 to 5 m of flood-plain alluvium between 1952 and 1978. Events of 1980, however, suggest that the flood plain has ceased to accrete, although climate has not fluctuated. The flood plain has probably reached a critical height above the channel, beyond which further accretion is unlikely under the existing discharge regimen. The recent history of the Little Colorado broadly suggests that flood-plain development was initiated by climatically induced hydrologic fluctuations. Flood-plain deposits in the stratigraphic column of such ephemeral streams may record repeated adjustments to altered hydrologic conditions.

Climate and ephemeral-stream processes: Twentieth-century geomorphology and alluvial stratigraphy of the Little Colorado River, Arizona

Modern alluvial history of the Paria Rver drainage basin, southern Utah

Valley-fill alluvium deposited from ca. A.D. 1400 to 1880 is widespread in tributaries of the Paria River and is largely coincident with the Little Ice Age epoch of global climate variability. Previous work showed that alluvium of this age is a mappable stratigraphic unit in many of the larger alluvial valleys of the southern Colorado Plateau. The alluvium is bounded by two disconformities resulting from prehistoric and historic arroyo cutting at ca. A.D. 1200–1400 and 1860–1910, respectively. The fill forms a terrace in the axial valleys of major through-flowing streams. This terrace and underlying deposits are continuous and interfinger with sediment in numerous small tributary valleys that head at the base of hillslopes of sparsely vegetated, weakly consolidated bedrock, suggesting that eroded bedrock was an important source of alluvium along with in-channel and other sources. Paleoclimatic and high-resolution paleoflood studies indicate that valley-fill alluviation occurred during a long-term decrease in the frequency of large, destructive floods. Aggradation of the valleys ended about A.D. 1880, if not two decades earlier, with the beginning of historic arroyo cutting. This shift from deposition to valley entrenchment near the close of the Little Ice Age generally coincided with the beginning of an episode of the largest floods in the preceding 400–500 yr, which was probably caused by an increased recurrence and intensity of flood-producing El Nino events beginning at ca. A.D. 1870.

Valley-fill alluviation during the Little Ice Age (ca. A.D. 1400–1880), Paria River basin and southern Colorado Plateau, United States

Rainfall during the warm season (June 15–October 15) is the most important of the year in terms of flood generation and erosion in rivers of the southern Colorado Plateau. Fluvial erosion of the plateau decreased substantially in the 1930s to early 1940s, although the cause of this change has not been linked to variation of warm-season rainfall. This study shows that a decrease of warmseason rainfall frequency was coincident with and probably caused the decreased erosion by reducing the probability of large floods. Warm-season rainfall results from isolated thunderstorms associated with the Southwestern monsoon and from dissipating tropical cyclones and (or) cutoff low-pressure systems that produce widespread, general rainfall. Warm-season rainfall is typically normal to above normal during warm El Nino-Southern Oscillation (ENSO) conditions. A network of 24 long-term precipitation gages was used to develop an index of standardized rainfall anomalies for the southern Colorado Plateau for the period 1900–85. The index shows that the occurrence of anomalously dry years increased and the occurrence of anomalously wet years decreased after the early 1930s, although 1939–41, 1972, and 1980–84 were anomalously wet. The decrease in warm-season rainfall after the early 1930s is related to a decrease in rainfall from dissipating tropical cyclones, shifts in the incidence of meridional circulation in the upper atmosphere, and variability of ENSO conditions.

http://archive.li.suu.edu/docs/ms130/AB/hereford.pdf

Richard Hereford

Papers

Precipitation history and ecosystem response to multidecadal precipitation variability in the Mojave Desert region, 1893-2001

Climate and ephemeral-stream processes: Twentieth-century geomorphology and alluvial stratigraphy of the Little Colorado River, Arizona

Modern alluvial history of the Paria Rver drainage basin, southern Utah

Valley-fill alluviation during the Little Ice Age (ca. A.D. 1400–1880), Paria River basin and southern Colorado Plateau, United States

Historic variation of warm-season rainfall, Southern Colorado Plateau, Southwestern U.S.A.