The response of flow duration curves to afforestation

The hydrologic effect of replacing pasture or other short crops with trees is reasonably well understood on a mean annual basis. The impact on flow regime, as described by the annual flow duration curve (FDC) is less certain. A method to assess the impact of plantation establishment on FDCs was developed. The starting point for the analyses was the assumption that rainfall and vegetation age are the principal drivers of evapotranspiration. A key objective was to remove the variability in the rainfall signal, leaving changes in streamflow solely attributable to the evapotranspiration of the plantation. A method was developed to (1) fit a model to the observed annual time series of FDC percentiles; i.e. 10th percentile for each year of record with annual rainfall and plantation age as parameters, (2) replace the annual rainfall variation with the long term mean to obtain climate adjusted FDCs, and (3) quantify changes in FDC percentiles as plantations age. Data from 10 catchments from Australia, South Africa and New Zealand were used. The model was able to represent flow variation for the majority of percentiles at eight of the 10 catchments, particularly for the 10–50th percentiles. The adjusted FDCs revealed variable patterns in flow reductions with two types of responses (groups) being identified. Group 1 catchments show a substantial increase in the number of zero flow days, with low flows being more affected than high flows. Group 2 catchments show a more uniform reduction in flows across all percentiles. The differences may be partly explained by storage characteristics. The modelled flow reductions were in accord with published results of paired catchment experiments. An additional analysis was performed to characterise the impact of afforestation on the number of zero flow days (N_zero) for the catchments in group 1. This model performed particularly well, and when adjusted for climate, indicated a significant increase in N_zero. The zero flow day method could be used to determine change in the occurrence of any given flow in response to afforestation. The methods used in this study proved satisfactory in removing the rainfall variability, and have added useful insight into the hydrologic impacts of plantation establishment. This approach provides a methodology for understanding catchment response to afforestation, where paired catchment data is not available.     

Integration of In Situ Experiments and Numerical Simulations to Reveal the Physicochemical Circumstances of Organic and Inorganic Precipitation at a Thermal Spring

Organic and inorganic precipitates are both characteristic in the active hypogenic karst area of Buda Thermal Karst in Hungary. As an active system, it is a good natural laboratory to study ongoing precipitation processes. Because of anthropogenic influence and the complexity of spring environments, it is challenging to reveal all the governing factors in the process of precipitation. In situ experiments, i.e. artificially controlled natural systems simplify the complexity by adding, excluding or stabilizing influencing parameters during the experiment. CO₂ degassing drives changes in the physicochemical parameters of spring waters from the discharge along their flow path. The rate and spatial extension of these changes depend on local hydrogeological, geological, climatic, topographical etc. factors, affecting precipitation processes. In this study, two one-day-long in situ experiments were executed to examine the physicochemical parameter changes of thermal water in a tunnel. The integration of the results with reactive transport models revealed the physicochemical processes of ingassing and degassing and predicted CaCO₃ precipitation along the flow path. Small-scale roughness of the channel surface seemed to further influence pH and concentration of HCO₃^?. After 6 weeks of thermal water flowing, organic precipitate (biofilm) formed close to the discharge and then, with a sharp change, inorganic precipitate (calcite) dominates a bit further from the discharge. In situ experiments and connected numerical simulations revealed the role of CO₂ degassing and calcite precipitation in the changes of physicochemical parameters, but organic precipitates also have to be considered near the discharge.     

Groundwater flow in the transition zone between freshwater and saltwater: a field-based study and analysis of measurement errors

The quantification of groundwater flow near the freshwater–saltwater transition zone at the coast is difficult because of variable-density effects and tidal dynamics. Head measurements were collected along a transect perpendicular to the shoreline at a site south of the city of Adelaide, South Australia, to determine the transient flow pattern. This paper presents a detailed overview of the measurement procedure, data post-processing methods and uncertainty analysis in order to assess how measurement errors affect the accuracy of the inferred flow patterns. A particular difficulty encountered was that some of the piezometers were leaky, which necessitated regular measurements of the electrical conductivity and temperature of the water inside the wells to correct for density effects. Other difficulties included failure of pressure transducers, data logger clock drift and operator error. The data obtained were sufficiently accurate to show that there is net seaward horizontal flow of freshwater in the top part of the aquifer, and a net landward flow of saltwater in the lower part. The vertical flow direction alternated with the tide, but due to the large uncertainty of the head gradients and density terms, no net flow could be established with any degree of confidence. While the measurement problems were amplified under the prevailing conditions at the site, similar errors can lead to large uncertainties everywhere. The methodology outlined acknowledges the inherent uncertainty involved in measuring groundwater flow. It can also assist to establish the accuracy requirements of the experimental setup.     

Al Huwaysah 010: The most reduced brachinite,so far

Al Huwaysah 010 is an ungrouped achondrite meteorite, recently referred to as a brachinite-like meteorite. This meteorite, showing a fine-grained assemblage of low-Ca pyroxene and opaque phases, is strongly reduced in comparison to other reduced brachinites. The occurrence of some tiny plates of graphite and oldhamite in this meteorite suggests that a partial melt residue has experienced a further reduction process. Olivine, the most abundant phase, is compositionally homogeneous (Fo_83.3) as well as the clinopyroxene (En_45.5Fs_10.8Wo_43.7) and the plagioclase (Ab_69.5). Orthopyroxene (En_85.4Fs_13.9Wo_0.7) also occurs but only in a fine intergrowth. Other accessory phases are Fe metal grains (Ni-free or Cr-bearing Fe-Ni alloy), troilite, chlorapatite, pentlandite (as inclusions in chromite). The sample shows two different closure temperatures: the highest (≈900°C) is determined via the olivine–chromite intercrystalline geothermometer and the lowest temperature (≈520°C) is determined via the pyroxene-based intracrystalline geothermometer. These temperatures may represent, respectively, the closure temperature associated with the formation and a subsequent impact event excavating the sample from the parental body. The visible to near-infrared (VNIR) reflectance spectra of Al Huwaysah 010 exhibit low reflectance, consistent with the presence of darkening components, and weak absorptions indicative of olivine and pyroxene. Comparing the spectral parameters of Al Huwaysah 010 to potential parent bodies characterized by olivine–pyroxene mineralogy, we find that it falls within the field previously attributed to the SIII type asteroids. These results lead us to classify the Al Huwaysah 010 meteorite as the most reduced brachinite, whose VNIR spectral features show strong affinities with those of SIII asteroids.     

Evaluation of the CORDEX-Africa multi-RCM hindcast: systematic model errors

Monthly-mean precipitation, mean (T_AVG), maximum (T_MAX) and minimum (T_MIN) surface air temperatures, and cloudiness from the CORDEX-Africa regional climate model (RCM) hindcast experiment are evaluated for model skill and systematic biases. All RCMs simulate basic climatological features of these variables reasonably, but systematic biases also occur across these models. All RCMs show higher fidelity in simulating precipitation for the west part of Africa than for the east part, and for the tropics than for northern Sahara. Interannual variation in the wet season rainfall is better simulated for the western Sahel than for the Ethiopian Highlands. RCM skill is higher for T_AVG and T_MAX than for T_MIN, and regionally, for the subtropics than for the tropics. RCM skill in simulating cloudiness is generally lower than for precipitation or temperatures. For all variables, multi-model ensemble (ENS) generally outperforms individual models included in ENS. An overarching conclusion in this study is that some model biases vary systematically for regions, variables, and metrics, posing difficulties in defining a single representative index to measure model fidelity, especially for constructing ENS. This is an important concern in climate change impact assessment studies because most assessment models are run for specific regions/sectors with forcing data derived from model outputs. Thus, model evaluation and ENS construction must be performed separately for regions, variables, and metrics as required by specific analysis and/or assessments. Evaluations using multiple reference datasets reveal that cross-examination, quality control, and uncertainty estimates of reference data are crucial in model evaluations.     

Women/chickens vs. men/cattle: Insights on gender–species intersectionality

This paper is conceptually grounded in feminist–posthumanist intersectionality, offering an empirical case study that is geographic in scope, balances discursive and material elements, focuses on gender–species relations, and details dynamics of othering and privileging. It is empirically situated in a case study featuring women and chickens, men and cattle in the southern African nation of Botswana. It considers their symbolic associations with certain social realms, their spatial placements into and within particular locales, and the resulting context-specific dynamics that occur and shape their daily lives and interrelations with one another. Such socio-spatial practices are the means through which men, women, chickens and cattle become privileged and/or othered within dominant gender–species hierarchical arrangements. The paper also explores emerging urban and commercial agriculture spaces in contemporary Botswana, which empower women and chickens through increased access to land and productive activities, and increased visibility, status and value. Such empowerment remains bounded, however, given significant material, discursive and ethical implications of re-positioning within dominant structures.     

Regional soil erosion in response to land use and increased typhoon frequency and intensity,Taiwan

Reservoir sedimentation data and sediment yields from Taiwanese rivers show increased soil erosion in response to both 20th century changes in land use and a more recent increase in typhoon frequency and intensity. Decadal variations of up to 5- to 20-fold in suspended-sediment rating curves demonstrate supply-limited transport and correspond to increased sediment delivery from hillslopes due to changes in land use, regional ground shaking during the Chi-Chi earthquake, and post-2000 changes in typhoon frequency and intensity. While accelerated erosion in central Taiwan after the Chi-Chi earthquake has been documented previously, our results show that periods of increased upland erosion also occurred earlier, in response to 20th century changes in land use. Analyses of rainfall records and typhoon frequency for the period 1900–2009 further point to an island-wide increase in erosion rates corresponding to increased typhoon frequency and intensity after 1990.     

Influence of model conceptualisation on one-dimensional recharge quantification: Uley South,South Australia

Model conceptualisation is a key source of uncertainty in one-dimensional recharge modelling. The effects of different conceptualisations on transient recharge predictions for the semi-arid Uley South Basin, South Australia, were investigated. One-dimensional unsaturated zone modelling was used to quantify the effect of variations of (1) lithological complexity of the unsaturated zone, and (2) representation of preferential flow pathways. The simulations considered ranges of water-table depths, vegetation characteristics, and top soil thicknesses representative for the study area. Complex lithological profiles were more sensitive to the selected vegetation characteristics and water-table depth. Scenarios considering runoff infiltration into, and preferential flow through sinkholes resulted in higher and faster recharge rates. A comparison of modelled and field-based recharge estimates indicated that: (1) the model simulated plausible recharge rates, (2) only the models with preferential flow correctly reproduced the timing of recharge, and (3) preferential flow is probably redistributed in the unsaturated zone rather than passing to the water table directly. Because different but equally plausible conceptual models produce widely varying recharge rates, field-based recharge estimates are essential to constrain the modelling results.     

Geochemical and Environmental Evaluation of Um Shashoba Gold Mine Area,Southeastern Desert,Egypt

A suite of elements(Ag,Au,Ba,Bi,Cd,Co,Cr,Cu,Ga,Hf,Hg,Mn,Mo,Ni,Pb,Rb,Sb,Se, Sr,Te and Zn),total organic carbon(TOC)and pH were analyzed in stream sediment and tailing samples from Um Shashoba area,in order to evaluate Au placer and the sediments being impacted by old mining activities.Analytical results were examined using statistical,graphical and mapping methods.In spite of the results revealing that Au and most of the elements in sediments were in general significantly lower than those in tailing,Au wa...     

The Potential Response of Terrestrial Carbon Storage to Changes in Climate and Atmospheric CO2

We use a georeferenced model of ecosystem carbon dynamics to explore the sensitivity of global terrestrial carbon storage to changes in atmospheric CO₂ and climate. We model changes in ecosystem carbon density, but we do not model shifts in vegetation type. A model of annual NPP is coupled with a model of carbon allocation in vegetation and a model of decomposition and soil carbon dynamics. NPP is a function of climate and atmospheric CO₂ concentration. The CO₂ response is derived from a biochemical model of photosynthesis. With no change in climate, a doubling of atmospheric CO₂ from 280 ppm to 560 ppm enhances equilibrium global NPP by 16.9%; equilibrium global terrestrial ecosystem carbon (TEC) increases by 14.9%. Simulations with no change in atmospheric CO₂ concentration but changes in climate from five atmospheric general circulation models yield increases in global NPP of 10.0–14.8%. The changes in NPP are very nearly balanced by changes in decomposition, and the resulting changes in TEC range from an increase of 1.1% to a decrease of 1.1%. These results are similar to those from analyses using bioclimatic biome models that simulate shifts in ecosystem distribution but do not model changes in carbon density within vegetation types. With changes in both climate and a doubling of atmospheric CO₂, our model generates increases in NPP of 30.2–36.5%. The increases in NPP and litter inputs to the soil more than compensate for any climate stimulation of decomposition and lead to increases in global TEC of 15.4–18.2%.