Improving Rainfall Effectiveness on Rangeland

6 pp., 1 graph, 1 table, 3 illustrationsRainfall is a major limiting factor for livestock production on Texas rangelands. This publication explains how to more effectively use water for forage production on rangelands, and how to reduce runoff, evaporation, soil erosion and undesirable weeds and brush

Effectiveness of Native Species Buffer Zones for Nonstructural Treatment of Urban Runoff

A field study was conducted to determine the influences of vegetation composition, buffer width, and infiltration rate on the effectiveness of native vegetation buffer zones as nonstructural treatments of urban runoff with respect to increasing water quality. The field site was in Austin, Texas with runoff originating in a parking lot with a drainage area of approximately one hectare. The soil was a shallow, well-drained clay overlying limestone. Twelve constituents were measured; fecal streptococci, fecal coliforms, dissolved nitrate, total nitrate, dissolved total phosphorus, total phosphorus, dissolved ammonia, total ammonia, dissolved total Kjeldahl nitrogen, total Kjeldahl nitrogen, total lead, and total suspended solids. Four different vegetation compositions were used as treatments; wooded areas, wooded areas cleared, native grasses mowed, and native grasses unmowed. The vegetation in the mowed and unmowed areas was primarily composed of Johnson grass (Sorghum halepense), Bermuda grass (Cynodon dactylon) and mixed legumes. The wooded area was dominated by common red cedar (Juniperus virginiana) with scattered live oak (Quercus virginiana) and Ashe juniper (Juniperus ashei). The ground cover was juniper litter and scattered Texas wintergrass (Stipa leucotricha). Only total suspended solids, total lead, total Kjeldahl nitrogen, total nitrate, total phosphorus, dissolved nitrate, and dissolved total phosphorus were influenced at the 0.10 significance level by vegetation composition and buffer width. For pollutants affected by vegetation composition, the wooded areas had the highest mean concentrations of pollutants. The mowed and unmowed areas generally had the lowest concentrations of pollutants. For this application of buffer strips, it was found that as buffer width increased, the pollutant concentration also increased. Other researchers have reported decreasing pollutant concentrations. One explanation is that this is caused by excess transport capacity associated with the runoff entering the buffer strip. As the runoff moved though the buffer strip, pollutants were detached and transported through the buffer strip. If the buffer strip is sufficiently wide, an equilibrium between detachment and transport capacity may be reached and a decrease in pollutant concentration may be seen subsequently. A physically-based model was developed to simulate sediment yield through the buffer strips studied. The model has a stochastic pollutant concentration input generator. Transport capacity is computed using the Yalin equation. Detachment and deposition are computed using a modified version of the Universal Soil Loss Equation. The model was used to simulate this field study. The model did not simulate individual rainfall events well. The model predicted the long-term average results of this field study with concentrations increasing with buffer width. The coefficient of determination for observed concentrations compared to average predicted concentrations was 0.90

Sagebrush-Obligate Passerine Response to Ecological Site Characteristics

Adoption of ecological sites as monitoring and management units by a variety of land users has prompted discussion of their benefits for wildlife habitat management. Density and occurrence of shrub-steppe passerines are often related to key habitat characteristics such as plant species composition, cover, and structure. Until recently, ecological sites have not been tested as units for monitoring and management of passerines. We conducted a study implementing ecological sites as management units and used passerines as indicators of potential use of these sites. Ecological site characteristics and three sagebrush-obligate passerines were quantified on ecological sites at and near Browns Park National Wildlife Refuge in Colorado. In 2006 and 2007, we surveyed passerines and site characteristics using standard techniques within 101, 100-m radius plots. Density of Brewer’s sparrow (Spizella breweri) and occurrence of Brewer’s sparrow, sage sparrow (Amphispiza belli), and sage thrasher (Oreoscoptes montanu) were estimated for six ecological sites and then related to site characteristics. For example, Brewer’s sparrow densities were greatest (3.0 birds/ha) on a Loamy Fine Sand Ecological Site containing taller vegetation than vegetation for other ecological sites. Scientific literature commonly associates Brewer’s sparrows with sagebrush (Artemisia tridentata) presence, but on ecological sites at Browns Park Brewer’s densities are related more to vegetative structure rather than species composition. Results show there are links between passerine populations and ecological sites; a relationship which provides a meaningful foundation in developing long-term monitoring protocols and enhancing management decisions to favor sagebrush-obligate passerines

The spread of marine anoxia on the northern Tethys margin during the Paleocene-Eocene Thermal Maximum

Records of the paleoenvironmental changes that occurred during the Paleocene-Eocene Thermal Maximum (PETM) are preserved in sedimentary rocks along the margins of the former Tethys Ocean and Peri-Tethys. This paper presents new geochemical data that constrain paleoproductivity, sediment delivery, and seawater redox conditions, from three sites that were located in the Peri-Tethys region. Trace and major element, iron speciation, and biomarker data indicate that water column anoxia was established during episodes when inputs of land-derived higher plant organic carbon and highly weathered detrital clays and silts became relatively higher. Anoxic conditions are likely to have been initially caused by two primary processes: (i) oxygen consumption by high rates of marine productivity, initially stimulated by the rapid delivery of terrestrially derived organic matter and nutrients, and (ii) phosphorus regeneration from seafloor sediments. The role of the latter process requires further investigation before its influence on the spread of deoxygenated seawater during the PETM can be properly discerned. Other oxygen-forcing processes, such as temperature/salinity-driven water column stratification and/or methane oxidation, are considered to have been relatively less important in the study region. Organic carbon enrichments occur only during the initial stages of the PETM as defined by the negative carbon isotope excursions at each site. The lack of observed terminal stage organic carbon enrichment does not support a link between PETM climate recovery and the sequestration of excess atmospheric CO2 as organic carbon in this region; such a feedback may, however, have been important in the early stages of the PETM

Hydrologic interrelationships with vegetation and soil as affected by selected livestock grazing systems and climate on the Edwards Plateau

Typescript (photocopy).The effects of grazing systems and climate on rangeland hydrology, soil and vegetation were assessed over a six year period at the Texas Agricultural Research Station, located 56 km southwest of Sonora on the Edwards Plateau, Texas. Bimonthly estimates of infiltration rate and sediment production in midgrass and shortgrass dominated interspaces were obtained using a mobile-drip-type rainfall simulator. Soil and vegetation parameters were also measured for each simulated rainfall plot. Permanent point-frame plots, vegetation line transects, pasture-wide soil samples and natural runoff were also used to verify the trends obtained on the simulated rainfall plots. Data were collected in pastures that were grazed under moderate continuous (MCG), heavy continuous (HCG), high-intensity low-frequency (HILF), and short duration (SDG) systems, and in a livestock exclosure (LEX). The pastures were stocked with a combination of cattle, sheep and goats at a ratio of 50:25:25, respectively. Total organic cover and clay content of the surface soil were the most influential factors of the infiltration rate model 2 (multiple regression model r^2 =.98). Cover breaks raindrop and thus protects surface soil structure. Clay content was associated with aspects of soil structure such as bulk density (r=-.77) and aggregate stability (r=.41). Sediment production estimation (multiple 2 regression model, r^2 = .96) was influenced most by midgrass cover and litter biomass. Bunchgrass and litter both acted as barriers that inhibited sediment transport. The MCG, HILF and LEX pastures demonstrated the ability to recover from droughts and maintain or improve infiltration rates, sediment production rates and midgrass relative dominance. Infiltration rates and midgrass dominance significantly decreased and sheet erosion significantly increased on the HCG and SDG pastures stocked 1.75 times the moderate rate. Changes in the HCG and SDG pastures were most pronounced during drought. The observed rate of recovery for the HCG and SDG systems was much slower than the moderately grazed MCG and HILF systems and the ungrazed LEX pasture. Infiltration rate was seasonally cyclic in the HCG and SDG pastures but was not in the MCG or LEX pastures

Hydrologic interrelationships with vegetation and soil as affected by selected livestock grazing systems and climate on the Edwards Plateau

Typescript (photocopy).The effects of grazing systems and climate on rangeland hydrology, soil and vegetation were assessed over a six year period at the Texas Agricultural Research Station, located 56 km southwest of Sonora on the Edwards Plateau, Texas. Bimonthly estimates of infiltration rate and sediment production in midgrass and shortgrass dominated interspaces were obtained using a mobile-drip-type rainfall simulator. Soil and vegetation parameters were also measured for each simulated rainfall plot. Permanent point-frame plots, vegetation line transects, pasture-wide soil samples and natural runoff were also used to verify the trends obtained on the simulated rainfall plots. Data were collected in pastures that were grazed under moderate continuous (MCG), heavy continuous (HCG), high-intensity low-frequency (HILF), and short duration (SDG) systems, and in a livestock exclosure (LEX). The pastures were stocked with a combination of cattle, sheep and goats at a ratio of 50:25:25, respectively. Total organic cover and clay content of the surface soil were the most influential factors of the infiltration rate model 2 (multiple regression model r^2 =.98). Cover breaks raindrop and thus protects surface soil structure. Clay content was associated with aspects of soil structure such as bulk density (r=-.77) and aggregate stability (r=.41). Sediment production estimation (multiple 2 regression model, r^2 = .96) was influenced most by midgrass cover and litter biomass. Bunchgrass and litter both acted as barriers that inhibited sediment transport. The MCG, HILF and LEX pastures demonstrated the ability to recover from droughts and maintain or improve infiltration rates, sediment production rates and midgrass relative dominance. Infiltration rates and midgrass dominance significantly decreased and sheet erosion significantly increased on the HCG and SDG pastures stocked 1.75 times the moderate rate. Changes in the HCG and SDG pastures were most pronounced during drought. The observed rate of recovery for the HCG and SDG systems was much slower than the moderately grazed MCG and HILF systems and the ungrazed LEX pasture. Infiltration rate was seasonally cyclic in the HCG and SDG pastures but was not in the MCG or LEX pastures