Hydrological characterization of watersheds in the Blue Nile Basin, Ethiopia

Thirty-two watersheds (31–4350 km2), in the Blue Nile Basin, Ethiopia, were hydrologically characterized with data from a study of water and land resources by the US Department of Interior, Bureau of Reclamation (USBR) published in 1964. The USBR document contains data on flow, topography, geology, soil type, and land use for the period 1959 to 1963. The aim of the study was to identify watershed variables best explaining the variation in the hydrological regime, with a special focus on low flows. Moreover, this study aimed to identify variables that may be susceptible to management policies for developing and securing water resources in dry periods. Principal Component Analysis (PCA) and Partial Least Square (PLS) were used to analyze the relationship between five hydrologic response variables (total flow, high flow, low flow, runoff coefficient, low flow index) and 30 potential explanatory watershed variables. The explanatory watershed variables were classified into three groups: land use, climate and topography as well as geology and soil type. Each of the three groups had almost equal influence on the variation in hydrologic variables (R2 values ranging from 0.3 to 0.4). Specific variables from within each of the three groups of explanatory variables were better in explaining the variation. Low flow and low flow index were positively correlated to land use types woodland, dense wet forest and savannah grassland, whereas grazing land and bush land were negatively correlated. We concluded that extra care for preserving low flow should be taken on tuffs/basalts which comprise 52% of the Blue Nile Basin. Land use management plans should recognize that woodland, dense wet forest and savannah grassland can promote higher low flows, while grazing land diminishes low flows

Cattle Grazing Preferences, Animal Performance, and Harvest Management Effects among Diploid and Tetraploid Cultivars of Annual Ryegrass

Incremental gains in productivity from new forages are likely to be very small in developed countries like the USA where forage research is highly advanced, thus animals must be used in determining their value. Three experiments were conducted. Experiment I evaluated grazing preference of cattle and its relationship with morphological and chemical characteristics. Treatments were two diploid cultivars ‘Marshall’ and ‘Gulf’ and two tetraploid cultivars ‘Maximus’ and ‘Nelson’ arranged in a 4 × 4 Latin square design experiment. Animal preference was based on herbage disappearance, the Chesson-Manly index, and animal grazing time. Both herbage disappearance (1400 vs. 890 kg ha-1) and Chesson-Manly index (8.1 vs. 5.8%) were greater for tetraploid than diploid cultivars. Experiment II quantified forage and animal response of a tetraploid (Maximus) vs. a diploid (Marshall) annual ryegrass. Three stocking rates (SR), 3.75, 5, or 7.5 animals ha-1, were imposed on the two cultivars in a 3 × 2 factorial of a CRD experiment with two replications. Angus cross-bred heifers (initial BW = 240 kg) were used. There was no cultivar effect or any interactions on ADG or herbage mass (HM). Both ADG (1.22 kg d-1 at low SR to 0.98 kg d-1 at high SR) and HM (3.8 Mg ha-1 at low SR to 2.5 Mg ha-1 at high SR) had a linear response to SR. Experiment III quantified forage production, morphological characteristics, and nutritive value between a tetraploid (Maximus) vs. a diploid (Marshall) annual ryegrass cultivar harvested at three different leaf stages 2-, 3-, and 4-leaves tiller-1 and two stubble heights 5 and 10 cm. Treatments were arranged in a 3 × 2 × 2 factorial of a RCBD experiment with four replications. In 2011, there was a linear increase in forage harvested from 2-leaf (7.3 Mg DM ha-1) to 4-leaf stage (8.8 Mg DM ha-1) and in 2012 the response was quadratic with the highest forage harvested at 2- and 4-leaf stages (7.6 Mg DM ha-1). These results indicate that cultivars of annual ryegrass varied in their responses to grazing preference, grazing management, and defoliation management based on leaf stage

Cattle Grazing Preferences, Animal Performance, and Harvest Management Effects among Diploid and Tetraploid Cultivars of Annual Ryegrass

Incremental gains in productivity from new forages are likely to be very small in developed countries like the USA where forage research is highly advanced, thus animals must be used in determining their value. Three experiments were conducted. Experiment I evaluated grazing preference of cattle and its relationship with morphological and chemical characteristics. Treatments were two diploid cultivars ‘Marshall’ and ‘Gulf’ and two tetraploid cultivars ‘Maximus’ and ‘Nelson’ arranged in a 4 × 4 Latin square design experiment. Animal preference was based on herbage disappearance, the Chesson-Manly index, and animal grazing time. Both herbage disappearance (1400 vs. 890 kg ha-1) and Chesson-Manly index (8.1 vs. 5.8%) were greater for tetraploid than diploid cultivars. Experiment II quantified forage and animal response of a tetraploid (Maximus) vs. a diploid (Marshall) annual ryegrass. Three stocking rates (SR), 3.75, 5, or 7.5 animals ha-1, were imposed on the two cultivars in a 3 × 2 factorial of a CRD experiment with two replications. Angus cross-bred heifers (initial BW = 240 kg) were used. There was no cultivar effect or any interactions on ADG or herbage mass (HM). Both ADG (1.22 kg d-1 at low SR to 0.98 kg d-1 at high SR) and HM (3.8 Mg ha-1 at low SR to 2.5 Mg ha-1 at high SR) had a linear response to SR. Experiment III quantified forage production, morphological characteristics, and nutritive value between a tetraploid (Maximus) vs. a diploid (Marshall) annual ryegrass cultivar harvested at three different leaf stages 2-, 3-, and 4-leaves tiller-1 and two stubble heights 5 and 10 cm. Treatments were arranged in a 3 × 2 × 2 factorial of a RCBD experiment with four replications. In 2011, there was a linear increase in forage harvested from 2-leaf (7.3 Mg DM ha-1) to 4-leaf stage (8.8 Mg DM ha-1) and in 2012 the response was quadratic with the highest forage harvested at 2- and 4-leaf stages (7.6 Mg DM ha-1). These results indicate that cultivars of annual ryegrass varied in their responses to grazing preference, grazing management, and defoliation management based on leaf stage

A Novel Approach to Grass-Legume Management

A 2-yr grazing study quantified pasture and animal responses of four forage systems (FS) grazed at two stocking rates (SR; 3 or 6 animals ha-1). Using „Marshall? annual ryegrass (Lolium multiflorum Lam.) and „Durana? white clover (Trifolium repens L.), FS treatments included spatially separated grass and legumes within the same paddock (SS), monoculture grass (MG), monoculture legume (ML), and a binary grass and legume mixture (MIX). Annual herbage mass (HM) was similar among FS at high SR (1900 kg ha-1), but at low SR, grass plots had greater HM (2900 vs. 2000 kg ha-1) than plots of legume monocultures. Animals on SS (1.12 kg) had greater average daily gain (ADG) than ML (0.97 kg), but neither was different from MG (1.08 kg) or MIX (1.00 kg). Low SR animals had greater ADG than high SR (1.09 vs. 0.99 kg). These results indicate that SS grazing system can improve pasture productivity

Frozen reaction fronts in steady flows: a burning-invariant-manifold perspective

The dynamics of fronts, such as chemical reaction fronts, propagating in two-dimensional fluid flows can be remarkably rich and varied. For time-invariant flows, the front dynamics may simplify, settling in to a steady state in which the reacted domain is static, and the front appears "frozen". Our central result is that these frozen fronts in the two-dimensional fluid are composed of segments of burning invariant manifolds---invariant manifolds of front-element dynamics in $xy\theta$-space, where $\theta$ is the front orientation. Burning invariant manifolds (BIMs) have been identified previously as important local barriers to front propagation in fluid flows. The relevance of BIMs for frozen fronts rests in their ability, under appropriate conditions, to form global barriers, separating reacted domains from nonreacted domains for all time. The second main result of this paper is an understanding of bifurcations that lead from a nonfrozen state to a frozen state, as well as bifurcations that change the topological structure of the frozen front. Though the primary results of this study apply to general fluid flows, our analysis focuses on a chain of vortices in a channel flow with an imposed wind. For this system, we present both experimental and numerical studies that support the theoretical analysis developed here.Comment: 21 pages, 30 figure

Summer Rains and Dry Seasons in the Upper Blue Nile Basin: The Predictability of Half a Century of Past and Future Spatiotemporal Patterns

peer-reviewedDuring the last 100 years the Ethiopian upper Blue Nile Basin (BNB) has undergone major changes in land use, and is now potentially facing changes in climate. Rainfall over BNB supplies over two-thirds of the water to the Nile and supports a large local population living mainly on subsistence agriculture. Regional food security is sensitive to both the amount and timing of rain and is already an important political challenge that will be further complicated if scenarios of climate change are realized. In this study a simple spatial model of the timing and duration of summer rains (Kiremt) and dry season (Bega), and annual rain over the upper BNB was established from observed data between 1952 and 2004. The model was used to explore potential impacts of climate change on these rains, using a down-scaled ECHAM5/MP1-OM scenario between 2050 and 2100. Over the observed period the amount, onset and duration of Kiremt rains and rain-free Bega days have exhibited a consistent spatial pattern. The spatially averaged annual rainfall was 1490 mm of which 93% was Kiremt rain. The average Kiremt rain and number of rainy days was higher in the southwest (322 days) and decreased towards the north (136 days). Under the 2050–2100 scenario, the annual mean rainfall is predicted to increase by 6% and maintain the same spatial pattern as in the past. A larger change in annual rainfall is expected in the southwest (ca. +130 mm) with a gradually smaller change towards the north (ca. +70 mm). Results highlight the need to account for the characteristic spatiotemporal zonation when planning water management and climate adaptation within the upper BNB. The presented simple spatial resolved models of the presence of Kiremt and annual total rainfall could be used as a baseline for such long-term planning.Swedish International Development Cooperation Agenc

The zero-sum game of pathway optimization: Emerging paradigms for tuning gene expression

With increasing price volatility and growing awareness of the lack of sustainability of traditional chemical synthesis, microbial chemical production has been tapped as a promising renewable alternative for the generation of diverse, stereospecific compounds. Nonetheless, many attempts to generate them are not yet economically viable. Due to the zero-sum nature of microbial resources, traditional strategies of pathway optimization are attaining minimal returns. This result is in part a consequence of the gross changes in host physiology resulting from such efforts and underscores the need for more precise and subtle forms of gene modulation. In this review, we describe alternative strategies and emerging paradigms to address this problem and highlight potential solutions from the emerging field of synthetic biology.National Science Foundation (U.S.) (Synthetic Biology Engineering Research Center (SynBERC), grant number EEC-0540879)National Science Foundation (U.S.) (NSF CAREER Award (grant number CBET-0954986))Natural Sciences and Engineering Research Council of Canada (Fellowship

A method to estimate trends in distributions of 1 min rain rates from numerical weather prediction data

It is known that the rain rate exceeded 0.01% of the time in the UK has experienced an increasing trend over the last 20 years. It is very likely that rain fade and outage experience a similar trend. This paper presents a globally applicable method to estimate these trends, based on the widely accepted Salonen-Poiares Baptista model. The input data are parameters easily extracted from numerical weather prediction reanalysis data. The method is verified using rain gauge data from the UK, and the predicted trend slopes of 0.01% exceeded rain rate are presented on a global grid