Terrain trapped airflows and precipitation variability during an atmospheric river event

We examine thermodynamic and kinematic structures of terrain trapped airflows (TTAs) during an atmospheric river (AR) event impacting Northern California 10–11 March 2016 using Alpha Jet Atmospheric eXperiment (AJAX) aircraft data, in situ observations, and Weather and Research Forecasting (WRF) Model simulations. TTAs are identified by locally intensified low-level winds flowing parallel to the coastal ranges and having maxima over the near-coastal waters. Multiple mechanisms can produce TTAs, including terrain blocking and gap flows. The changes in winds can significantly alter the distribution, timing, and intensity of precipitation. We show here how different mechanisms producing TTAs evolve during this event and influence local precipitation variations. Three different periods are identified from the time-varying wind fields. During period 1 (P1), a TTA develops during synoptic-scale onshore flow that backs to southerly flow near the coast. This TTA occurs when the Froude number (Fr) is less than 1, suggesting low-level terrain blocking is the primary mechanism. During period 2 (P2), a Petaluma offshore gap flow develops, with flows turning parallel to the coast offshore and with Fr \u3e 1. Periods P1 and P2 are associated with slightly more coastal than mountain precipitation. In period 3 (P3), the gap flow initiated during P2 merges with a pre-cold-frontal low-level jet (LLJ) and enhanced precipitation shifts to higher mountain regions. Dynamical mixing also becomes more important as the TTA becomes confluent with the approaching LLJ. The different mechanisms producing TTAs and their effects on precipitation pose challenges to observational and modeling systems needed to improve forecasts and early warnings of AR events

Structure of the AlgKX modification and secretion complex required for alginate production and biofilm attachment in Pseudomonas aeruginosa

Synthase-dependent secretion systems are a conserved mechanism for producing exopolysaccharides in Gram-negative bacteria. Although widely studied, it is not well understood how these systems are organized to coordinate polymer biosynthesis, modification, and export across both membranes and the peptidoglycan. To investigate how synthase-dependent secretion systems produce polymer at a molecular level, we determined the crystal structure of the AlgK-AlgX (AlgKX) complex involved in Pseudomonas aeruginosa alginate exopolysaccharide acetylation and export. We demonstrate that AlgKX directly binds alginate oligosaccharides and that formation of the complex is vital for polymer production and biofilm attachment. Finally, we propose a structural model for the AlgEKX outer membrane modification and secretion complex. Together, our study provides insight into how alginate biosynthesis proteins coordinate production of a key exopolysaccharide involved in establishing persistent Pseudomonas lung infections.Bio-organic Synthesi

Knowledge discovery from models of soil properties developed through data mining

We modelled the distribution of soil properties across the agricultural zone on the Australian continent using data mining and knowledge discovery from databases (DM&KDD) tools. Piecewise linear tree models were built choosing from 19 climate variables, digital elevation model (DEM) and derived terrain attributes, four Landsat multi-spectral scanner (MSS) bands, land use and lithology maps as predictors of topsoil and subsoil pH, organic C, % clay, and total N and P. The actual geographic location of the sampled soil data points was not used as a predictor. Classification trees were used to estimate topsoil and subsoil horizon thickness and texture class using similar predictors. That maps could be made using the decision tree models attests to the occurrence of knowledge discovery from the soil point databases used as training data. The decision tree models were evaluated and interpreted in a spatial context by: (1) tabulation of variables selected by the tree models; (2) mapping of the extent over which individual predictors were used and their thresholds; and (3) mapping of the extent over which combinations of predictors were used. The evaluation and interpretation process indicates that the models are consistent with general principles of soil genesis and that detailed investigation of the models¿ structure in a spatial context may have other uses in biogeographical studies and geo-ecological process modelling

Use of soil survey information to assess regional salinization risk using geographical information systems

Previous experience in southern and western Australia has shown that tree clearing alters the water balance in a landscape, leading to increased deep drainage and consequent rises in phreatic water tables. Assessment of the risk of regional salinization involves integration of hydrology, hydrogeology, soil and land management issues. An example of the use of soil survey data, integrated with water resources and digital elevation data in a GIS, to estimate the risk of salinization after tree clearing is illustrated for the upper Burdekin river basin in the wet/dry tropics of North Queensland. Soft map unit descriptions include information on soil-landform relations, parent material, soil thickness, depth to bedrock and dominant and subdominant soil types. Such information can be used to qualitatively estimate permeability and drainage classes (high, medium, or low) and to determine likely recharge and discharge areas in the landscape. Analysis of the spatial association between surveyed electrical conductivity measurements and estimated recharge and discharge areas was used to cross-check this qualitative classification. The distributions of saline soils and shallow water tables are used to assess the salinity hazard of the region. Where % total soluble salts (TSS) are >0.25% and water table 0.25%, recharge areas should not be cleared

Linked fluvial and aeolian processes fertilize Australian bioregions

The pattern of 137Cs-derived net (1950s–1990) soil redistribution over Australia, together with back-trajectory modeling of major dust storms, shows extensive areas of contemporary aeolian deposition. While the Cobar Peneplain and Gawler bioregions are the largest, the Wet Tropics is also a locus of deposition, consistent with the theory that dust is a source of nutrients for tropical rainforests growing on ancient weathered soils. Here we describe a new dust transport pathway over northeastern Australia and substantiate the link between fluvial and aeolian processes, and biogeochemical cycling between Australia’s arid interior and its coastal forest

Tree clearing and dryland salinity hazard in the Upper Burdekin Catchment of North Queensland

This paper provides experimental data on the effect of tree clearing, introduction of perennial Stylosanthes based pastures, and the use of native grasses on the water balance of a red earth soil in the Upper Burdekin Catchment near Charters Towers. The water balance simulation models SWIM and PERFECT are used to extend the results and estimate deep drainage for this and other soils in this tropical environment. The analysis illustrates that the soil/climate interaction in the wet/dry tropics has a similarity with the winter-dominant rainfall zone where vegetation change can substantially increase deep drainage beyond the root-zone. Salt distribution in the soil/landscapes of the Upper Burdekin suggests that there is a salinity hazard, should a significant shift in the water balance occur as a result of tree clearing. Therefore, in the Upper Burdekin Catchment of North Queensland, indiscriminate tree clearing is a hazardous form of land management and should only proceed after the risks of dryland salinity have been evaluated and shown to be negligible

Climate and geochemistry as drivers of eucalypt diversification in Australia

Eucalypts cover most of Australia. Here, we investigate the relative contribution of climate and geochemistry to the distribution and diversity of eucalypts. Using geostatistics, we estimate major element concentrations, pH, and electrical conductivity at sites where eucalypts have been recorded. We compare the median predicted geochemistry and reported substrate for individual species that appear associated with extreme conditions; this provides a partial evaluation of the predictions. We generate a site-by-species matrix by aggregating observations to the centroids of 100-km-wide grid cells, calculate diversity indices, and use numerical ecology methods (ordination, variation partitioning) to investigate the ecology of eucalypts and their response to climatic and geochemical gradients. We find that β-diversity coincides with variations in climatic and geochemical patterns. Climate and geochemistry together account for less than half of the variation in eucalypt species assemblages across Australia but for greater than 80% in areas of high species richness. Climate is more important than geochemistry in explaining eucalypts species distribution and change in assemblages across Australia as a whole but there are correlations between the two sets of environmental variables. Many individual eucalypt species and entire taxonomic sections (Aromatica, Longistylus of subgenus Eucalyptus, Dumaria, and Liberivalvae of subgenus Symphyomyrtus) have distributions affected strongly by geochemistry. We conclude that eucalypt diversity is driven by steep geochemical gradients that have arisen as climate patterns have fluctuated over Australia over the Cenozoic, generally aridifying since the Miocene. The diversification of eucalypts across Australia is thus an excellent example of co-evolution of landscapes and biota in space and time and challenges accepted notions of macroecology