High-frequency monitoring of hydrological and biogeochemical fluxes in forested catchments of southern Chile

The variability of rainfall-dependent streamflow at catchment scale modulates many ecosystem processes in wet temperate forests. Runoff in small mountain catchments is characterized by a quick response to rainfall pulses which affects biogeochemical fluxes to all downstream systems. In wet-temperate climates, water erosion is the most important natural factor driving downstream soil and nutrient losses from upland ecosystems. Most hydrochemical studies have focused on water flux measurements at hourly scales, along with weekly or monthly samples for water chemistry. Here, we assessed how water and element flows from broad-leaved, evergreen forested catchments in southwestern South America, are influenced by different successional stages, quantifying runoff, sediment transport and nutrient fluxes during hourly rainfall events of different intensities. Hydrograph comparisons among different successional stages indicated that forested catchments differed in their responses to high intensity rainfall, with greater runoff in areas covered by secondary forests (SF), compared to old-growth forest cover (OG) and dense scrub vegetation (CH). Further, throughfall water was greatly nutrient enriched for all forest types. Suspended sediment loads varied between successional stages. SF catchments exported 455 kg of sediments per ha, followed by OG with 91 kg/ha and CH with 14 kg/ha, corresponding to 11 rainfall events measured from December 2013 to April 2014. Total nitrogen (TN) and phosphorus (TP) concentrations in stream water also varied with rainfall intensity. In seven rainfall events sampled during the study period, CH catchments exported less nutrients (46 kg/ha TN and 7 kg/ha TP) than SF catchments (718 kg/ha TN and 107 kg/ha TP), while OG catchments exported intermediate sediment loads (201 kg/ha TN and 23 kg/ha TP). Further, we found significant effects of successional stage attributes (vegetation structure and soil physical properties) and catchment morphometry on runoff and sediment concentrations, and greater nutrients retention in OG and CH catchments. We conclude that in these southern hemisphere, broad-leaved evergreen temperate forests, hydrological processes are driven by multiple interacting phenomena, including climate, vegetation, soils, topography, and disturbance history.     

Fusion of strings and its consequences at the highest cosmic ray energies

It is shown that the fusion of string is a source of particle production in nucleus-nucleus collisions outside the kinematical limits of nucleon-nucleon collisions. The spectrum of different particles is compared with the high energy data on p-A collisions obtaining a reasonable agreement. Results for A-B collisions at and AGeV are given and possible implications for cosmic rays are examined. Both the enhancement of the cumulative effect and the reduction of multiplicities implied by string fusion should strongly modify the first interactions and the profile of extensive air showers and should be taken into account in their simulation.     

Vegetation changes and sequential flowering after rain in the southern Atacama Desert

We describe the changes in plant cover, species richness, and flowering after rainfall over an entire growing season (September 1989–January 1990) in a southern Atacama Desert site in Chile. One month after the rain, vegetation was dominated by annuals and geophytes which dried out after 19 weeks. Among all species, including shrubs, we found differences of 4–10 weeks in the length and peak of the flowering period. The flowering sequence of the species belonging to the families Brassicaceae, Liliaceae, Onagraceae, and Asteraceae matched closely the sequences described for temperate plant communities, suggesting that this phenological character is phylogenetically determined.     

Terrestrial laser scanning used to determine the geometry of a granite boulder for stability analysis purposes

In this paper we analyze the use of terrestrial laser scanning (TLS) technologies to determine the geometric features of a granite boulder. Accurate determination of these features is a key to performing a reliable stability analysis of the boulder.TLS has been demonstrated to have important advantages over traditional measurement techniques—such as, for example, direct methods based on the use of tapes or indirect methods such as topography or close-range photogrammetry. TLS equipment enables thousands of points to be accurately measured in minutes. In our study TLS-measured points were used to model the surface of a boulder. Geometric parameters were then calculated, namely, centre of gravity, volume of the boulder and dimensions of the boulder contact area with the ground. Taking into account mechanical and environmental factors, these parameters were used to calculate the safety factor of the boulder against toppling and sliding. Our results show that, when seismic activity in the region is taken into consideration, the boulder is borderline stable–unstable.     

Interaction dynamics of avian frugivores and plants in a Chilean Mediterranean shrubland

Studies of plant-frugivore interactions are important for identifying the roles that biotic seed vectors play in seed dispersal, and ultimately plant recruitment. In a subandean shrubland of central Chile, 50% of total flora (14 species) has fleshy fruits dispersed by birds. We examined two aspects of frugivore-plant interaction in this system: the structure of the seed-dispersal network, to predict the effect of hypothetical frugivore species loss for seed dispersal and disperser effectiveness, by analyzing whether birds contribute equally to the removal of seeds from different shrub species. We show that the seed-dispersal network is highly and significantly nested, resulting in a core of interactions among generalist vertebrates and plant species. A reduction in the populations of the three main avian generalists, Turdus falcklandii, Mimus thenca and Elaenia albiceps, would disrupt seed dispersal and natural regeneration for most woody species. Monte Carlo simulations showed that the network was robust to the random loss of frugivorous species but highly sensitive to the loss of generalist species first. Mist-net sampling of birds corroborated that most fruit removal was effected by E. albiceps and T. falcklandii, highlighting the importance of frugivore species identity on seed dispersal for the maintenance of Mediterranean shrublands.     

Concentrated flow erosion as a main source of sediments in Galicia,Spain

Knowledge of soil loss rates by water erosion under given climate, soil, topography, and management conditions is important for establishing soil conservation schemes. In Galicia, a region with Atlantic climatic conditions in Spain, field observations over the last decade indicate that interrill, rill and ephemeral gully erosion may be an important sediment source. The aim of this work was to assess concentrated erosion rates, describe types of rills and ephemeral gullies and determine their origin, evolution and importance as sediment sources. Soil surface state and concentrated flow erosion were surveyed on medium textured soils, developed over basic schists of the Ordenes Complex series (Coruña province, Spain) from 1997 to 2006. Soil surface state was characterized by crust development, tillage features and roughness degree. Soil erosion rate was directly measured in the field. Concentrated flow erosion took place mainly on seedbeds and recently tilled surfaces in late spring and by autumn or early winter. During the study period, erosion rates were highly variable and the following situations could be distinguished: (a) no incision or limited rill incision, i.e. below 2 Mg ha^?1 year^?1; (b) generalized rill and ephemeral gully incision in the class of mean values between 2·5 and 6·25 Mg ha^?1 year^?1, this was the most common erosion pattern; and (c) heavy erosion as observed during an extremely wet winter period, between October 2000 and February 2001, with erosion figures that may be about ten orders of magnitude higher, up to 55–60 Mg ha^?1 year^?1. Therefore, low values of soil losses are dominant, but also large values of rill and ephemeral gully erosion occurred during the study period. Copyright © 2009 John Wiley & Sons, Ltd.     

Assessment of the instability hazard of a granite boulder

This paper aims to assess the instability hazard of a granite boulder. The procedure was first to consider the geological setting and geomorphologic features of the boulder in relation to typical granite landscape forms. Climatic and seismic data were next obtained from different sources, and geomechanical parameters were measured in situ and in the laboratory, with terrestrial laser scanning techniques used to measure shape and volume and to conduct a detailed survey of the boulder. Different analytical approaches were then applied to the calculation of boulder safety factors against sliding and toppling. Since the boulder was considered to be unstable in the worst possible scenario, a particle code approach was used to determine its fall trajectory, calculate the final run out of the block, and assess the risk for houses located at the foot of the slope. Finally, conclusions were drawn regarding the instability hazard, and recommendations were made in regard to definitively stabilizing the granite boulder.