14 research outputs found
Freezing and thawing processes
Seasonally frozen soil strongly influences runoff and
erosion on large areas of land around the world. In
many areas, rain or snowmelt on seasonally frozen
soil is the single leading cause of severe runoff and
erosion events. As soils freeze, ice blocks the soil
pores, greatly diminishing the permeability of the
soil. This is aggravated by the tendency of water to
migrate to the freezing front, causing elevated ice
content and frost heav
Ecosystem modeling: supermodel or coupling approach?
Non-Peer Reviewe
Freezing and thawing processes
Seasonally frozen soil strongly influences runoff and
erosion on large areas of land around the world. In
many areas, rain or snowmelt on seasonally frozen
soil is the single leading cause of severe runoff and
erosion events. As soils freeze, ice blocks the soil
pores, greatly diminishing the permeability of the
soil. This is aggravated by the tendency of water to
migrate to the freezing front, causing elevated ice
content and frost heav
Long-term water balance and conceptual model of a semi-arid mountainous catchment
Long-term water balance investigations are needed to better understand hydrologic systems, especially semi-arid mountainous catchments. These systems exhibit considerable interannual variability in precipitation as well as spatial variation in snow accumulation, soils, and vegetation. This study extended a previous 10-year water balance based on measurements and model simulations to 24 years for the Upper Sheep Creek (USC) catchment, a 26 ha, snow-fed, semi-arid rangeland headwater drainage within the Reynolds Creek Experimental Watershed in southwestern Idaho, USA. Additional analyses afforded by the additional years of data demonstrated that the variability between streamflow and annual precipitation (r2 = 0.54) could be explained by the timing of precipitation and antecedent moisture conditions. Winter–spring precipitation and soil moisture deficit at the beginning of the water year accounted for 83% of the variability in streamflow, which was almost as accurate as applying the more complex physically- based Simultaneous Heat and Water (SHAW) numerical model (r2 = 0.85) over the three dominant land cover classes. A conceptual model was formulated based on field observations, numerical simulations and previous studies. Winter precipitation and spring snowmelt must first replenish the deficit within the soil water profile and ground water system before water is delivered to the stream. During this period, surface water and ground water are tightly coupled and their interaction is critical to streamflow generation. Shortly after snow ablation, however, water flux in the root zone becomes decoupled from the ground water system and subsequent precipitation does little to contribute to streamflow for the current year, but serves to offset ET and the soil moisture deficit at the beginning of the following year. This study demonstrates the merits of long-term catchment-scale research to improve our understanding of how climate and land cover interact to control hydrologic dynamics in complex mountainous terrain
Temporal Variability in Microclimatic Conditions for Grass Germination and Emergence in the Sagebrush Steppe
Sagebrush steppe ecosystems in the western United States are characterized by harsh environmental conditions with high annual and seasonal variability in both precipitation and temperature. Environmental variability contributes to widespread failure in establishing stands of desired species on degraded and invaded landscapes. To characterize seasonal microclimatic patterns and planting date effects on restoration outcomes, we evaluated long-term simulations of seed germination response of cheatgrass (Bromus tectorum L.), bottlebrush squirreltail (Elymus elymoides [Raf] Swezey), and Idaho fescue (Festuca idahoensis Elmer) to annual patterns of soil temperature and moisture. Extremely high annual variability in both the conditions favorable for germination and patterns of post-germination drought and thermal stress make it difficult to justify general inferences about seedbed treatment and planting date effects from individual, short-term field studies. We discuss the interpretation of individual-year and seasonal plant establishment factors and offer a mechanistic model for interpreting planting date and year effects on initial seedling establishment. Historical ranking and mechanistic descriptions of individual-year seedbed conditions may allow for expanded inferences through meta-analysis of limited-term field experiments. © 2015 Published by Elsevier Inc. on behalf of The Society for Range Management.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information