Disaggregating soil erosion processes within an evolving experimental landscape

Soil‐mantled landscapes subjected to rainfall, runoff events, and downstream base level adjustments will erode and evolve in time and space. Yet the precise mechanisms for soil erosion also will vary, and such variations may not be adequately captured by soil erosion prediction technology. This study sought to monitor erosion processes within an experimental landscape filled with packed homogenous soil, which was exogenically forced by rainfall and base level adjustments, and to define the temporal and spatial variation of the erosion regimes. Close‐range photogrammetry and terrain analysis were employed as the primary methods to discriminate these erosion regimes. Results show that (1) four distinct erosion regimes can be identified (raindrop impact, sheet flow, rill, and gully), and these regimes conformed to an expected trajectory of landscape evolution; (2) as the landscape evolved, the erosion regimes varied in areal coverage and in relative contribution to total sediment efflux measured at the outlet of the catchment; and (3) the sheet flow and rill erosion regimes dominated the contributions to total soil loss. Disaggregating the soil erosion processes greatly facilitated identifying and mapping each regime in time and space. Such information has important implications for improving soil erosion prediction technology, for assessing landscape degradation by soil erosion, for mapping regions vulnerable to future erosion, and for mitigating soil losses and managing soil resources. Copyright © 2017 John Wiley & Sons, Ltd.     

Distribution and abundance patterns of flatfishes in the Sado estuary, Portugal

The flatfish community of the Sado estuary was studied based on beam trawl catches in six sampling areas. Temperature and salinity were recorded during surveys and sediment composition was determined at each sampling area. A total of 12 species were identified (1 Bothidae, 1 Pleuronectidae, and 10 Soleidae).Dicologoglossa hexophthalma (Bennett 1831),Microchirus ocellatus (Linnaeus 1758), andSynaptura lusitanica (Capello 1868) were new records to this estuarine system.Monochirus hispidus Rafinesque, 1814, was the most abundant species (about 80% of the total individuals caught). Community structure reflected both spatial and temporal patterns. A longitudinal abundance pattern was noticed with some species much more abundant in outer estuarine areas, namelyM. hispidus, Arnoglossus laterna (Walbaum 1792), andBuglossidium luteum (Risso 1810), while others, such asSolea solea (Linnaeus 1758) andSolea senegalensis Kaup, 1858, presented the highest densities in inner areas. Besides temperature and salinity gradients, species distribution was also influenced by sediment composition. Seasonal variation was mainly determined by the different periods of juvenile peak abundance according to the species which emphasize the role of the estuary as a nursery ground for several flatfish species.     

Contrasts in genetic structure and historical demography of marine and riverine populations of Atherina at similar geographical scales

In this paper, we compare the genetic structure and the historical demography of two populations of the sand smelt Atherina boyeri from the rivers Tagus and Mondego (Portugal) with two groups of samples of the closely related marine Atherina presbyter collected on the shore at comparable latitudes. A. presbyter is a pelagic marine inshore fish, while A. boyeri is typically found in coastal lagoons, estuaries and freshwaters bodies. Analysis of mtDNA control region sequences showed that the marine A. presbyter did not display signs of genetic differentiation between sites some hundreds of kilometers apart. On the contrary, A. boyeri showed clear differences between populations. The populations of A. boyeri showed a much lower genetic diversity and younger coalescence times when compared with A. presbyter. We suggest that these differences reflect the interplay between differences in ecology between the two species and the historical impact of the glaciations. While A. presbyter likely moved to the south evading the cold periods, A. boyeri probably went extinct and its populations in Western Europe are recent recolonizations from western Mediterranean refugia.     

Elemental and Single Particle Aerosol Characterisation at a Background Station in Kazakhstan

Aerosol sampling in Kazakhstan was performed at a remote astronomical observatory in the Tien Shan mountain region. The background character of the site was considered by comparing the elemental concentrations, obtained by Energy Dispersive X-Ray Fluorescence (EDXRF), with those reported for other remote stations. On the basis of the variability of the elemental concentrations and the source of origin, the elements could be classified into two main groups. These findings, complemented with enrichment factor calculations revealed the first group of elements to be originating mainly from local sources, and the second group to be related to long-range transport of anthropogenic aerosol. Automated individual particle analysis by electron probe X-ray microanalysis (EPXMA) and subsequent cluster analysis resulted in the identification of 12 distinct aerosol particle types. Relative particle type abundances were converted to absolute abundances by estimating the particle number concentrations for the detected particles, exploring the seasonal particle variation. Based on the absolute abundances, a strong seasonal pattern was found for Si-Al-Fe-, Si-, Ca-S-Si-, Ca-Si-, Fe-Si- and Ti-Si-rich particles. These particle types can mainly be attributed to the local soil source. For most of the remaining particle types, a completely different seasonal trend was found, which can be related to anthropogenic emissions. Their abundance in winter can be related to long-range transport of anthropogenic aerosols. As a result, these data can be representative for the Tien Shan site and may be useful to climate modellers and environmentalists.     

The effects of sample scheduling and sample numbers on estimates of the annual fluxes of suspended sediment in fluvial systems

Since the 1970s, there has been both continuing and growing interest in developing accurate estimates of the annual fluvial transport (fluxes and loads) of suspended sediment and sediment‐associated chemical constituents. This study provides an evaluation of the effects of manual sample numbers (from 4 to 12 year^?1) and sample scheduling (random‐based, calendar‐based and hydrology‐based) on the precision, bias and accuracy of annual suspended sediment flux estimates. The evaluation is based on data from selected US Geological Survey daily suspended sediment stations in the USA and covers basins ranging in area from just over 900 km² to nearly 2 million km² and annual suspended sediment fluxes ranging from about 4 Kt year^?1 to about 200 Mt year^?1. The results appear to indicate that there is a scale effect for random‐based and calendar‐based sampling schemes, with larger sample numbers required as basin size decreases. All the sampling schemes evaluated display some level of positive (overestimates) or negative (underestimates) bias. The study further indicates that hydrology‐based sampling schemes are likely to generate the most accurate annual suspended sediment flux estimates with the fewest number of samples, regardless of basin size. This type of scheme seems most appropriate when the determination of suspended sediment concentrations, sediment‐associated chemical concentrations, annual suspended sediment and annual suspended sediment‐associated chemical fluxes only represent a few of the parameters of interest in multidisciplinary, multiparameter monitoring programmes. The results are just as applicable to the calibration of autosamplers/suspended sediment surrogates currently used to measure/estimate suspended sediment concentrations and ultimately, annual suspended sediment fluxes, because manual samples are required to adjust the sample data/measurements generated by these techniques so that they provide depth‐integrated and cross‐sectionally representative data. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.