Spatial Distribution of Shelf- and Slope-Dwelling Fishes Collected by Bottom Longline off Lanzarote and Fuerteventura, Canary Islands

Abstract. A total of 1789 fish belonging to 38 families and 73 species were collected at depths between 18 and 1102 m during 216 bottom longline operations off Lanzarote and Fuerteventura, Canary Islands, between February 1994 and December 1995. For each species the depth distribution is provided. Length-weight and depth-size relationships are reported for three shelf-dwelling species. The bigger-deeper relationship found in two of them contrasts with the bigger-shallower pattern of the deeper living trichiurid Lepidopus caudatus . In November 1997, nine additional bottom longline operations were carried out off eastern Fuerteventura at depths between 805 and 1217 m. In this area, after earlier studies in October 1995, a spawning aggregation of the morid Mora moro was encountered for the second time. The catches of 1997 revealed a strongly male-biased sex ratio. Also, the males showed a significantly lower gonadosomal index than two years earlier. These findings indicate slight interannual variations in reproductive timing and an earlier arrival of male Mora moro at the spawning grounds. Clear variations in the number of fish collected at adjacent sites possibly reflect a preference for distinct microhabitats. Preliminary evidence of local upwelling of cold water above the spawning grounds is provided by satellite imagery.     

Stratigraphy, Chronology, and Paleoenvironmental Reconstruction of the Quaternary Sedimentary Infilling of a Volcanic Tube in Fuerteventura, Canary Islands

La Cueva del Llano is a volcanic tube of Pleistocene age on Fuerteventura Island, in the Canary Islands. Part of it is infilled with sediments of external origin. These deposits are exceptional in stratigraphic complexity and thickness compared with other known tube infillings, and they comprise nine stratigraphic units deposited in five phases. In Phase I, which has not been dated, sedimentation of cinder from a nearby cone occurred. Phase II began ca. 16,830 ± 900 ¹⁴C yr B.P., whereas phase IV dates to 9280 ± 370 ¹⁴C yr B.P. The interpretation of sedimentary features shows that phases III and V correspond to a dry climate, similar to the present one, whereas the climate was much wetter during phases II and IV. This paleoclimatic sequence agrees with those suggested by the study of deposits formed in other sedimentary environments, not only in Fuerteventura but on other islands of the Canary group and the Sud-Maroc region.     

Stream channel erosion in a rapidly urbanizing region of the US–Mexico border: documenting the importance of channel hardpoints with Structure‐from‐Motion photogrammetry

Urbanization can lead to accelerated stream channel erosion, especially in areas experiencing rapid population growth, unregulated urban development on erodible soils, and variable enforcement of environmental regulations. A combination of field surveys and Structure‐from‐Motion (SfM) photogrammetry techniques was used to document spatial patterns in stream channel geometry in a rapidly urbanizing watershed, Los Laureles Canyon (LLCW), in Tijuana, Mexico. Ground‐based SfM photogrammetry was used to map channel dimensions with 1 to 2 cm vertical mean error for four stream reaches (100–300 m long) that were highly variable and difficult to survey with a differential GPS. Regional channel geometry curves for LLCW had statistically larger slopes and intercepts compared with regional curves developed for comparable, undisturbed reference channels. Cross‐sectional areas of channels downstream of hardpoints, such as concrete reaches or culverts, were up to 64 times greater than reference channels, with enlargement persisting, in some cases, up to 230 m downstream. Percentage impervious cover was not a good predictor of channel enlargement. Proximity to upstream hardpoint, and lack of riparian and bank vegetation paired with highly erodible bed and bank materials may account for the instability of the highly enlarged and unstable cross‐sections. Channel erosion due to urbanization accounts for approximately 25–40% of the total sediment budget for the watershed, and channel erosion downstream of hardpoints accounts for one‐third of all channel erosion. Channels downstream of hardpoints should be stabilized to prevent increased inputs of sediment to the Tijuana Estuary and local hazards near the structures, especially in areas with urban settlements near the stream channel. Copyright © 2017 John Wiley & Sons, Ltd.     

Monitoring of landslide displacements using UAS and control methods based on lines

This study describes a new methodology for monitoring landslide displacements using a set of linear elements included in the terrain. These linear elements are digitized using the products obtained from several photogrammetric flights implemented by means of unmanned aircraft systems in several dates. The control of the displacements between dates is carried out using some new metrics and methods based on lines. The results of the control of the lines are used to analyse the general and particular behaviour of the landslide. Using this type of elements allows us to study some singular behaviour of linear elements included in the landslides (e.g. an affected road can react as a block). The methodology has been tested with success using a real case of an active slope with several landslides which was studied on three separate dates. The results have demonstrated the viability of using this methodology for studying the evolution of the landslides and their consequences regarding certain elements included in the terrain.     

In‐Situ Sonication for Enhanced Recovery of Aquifer Microbial Communities

Sampling methods for characterization of microbial communities in aquifers should target both suspended and attached microorganisms (biofilms). We investigated the effectiveness and reproducibility of low‐frequency (200 Hz) sonication pulses on improving extraction efficiency and quality of microorganisms from a petroleum‐contaminated aquifer in Studen (Switzerland). Sonication pulses at different power levels (0.65, 0.9, and 1.1 kW) were applied to three different groundwater monitoring wells. Groundwater samples extracted after each pulse were compared with background groundwater samples for cell and adenosine tri‐phosphate concentration. Turbidity values were obtained to assess the release of sediment fines and associated microorganisms. The bacterial community in extracted groundwater samples was analyzed by terminal‐restriction‐fragment‐length polymorphism and compared with communities obtained from background groundwater samples and from sediment cores. Sonication enhanced the extraction efficiency up to 13‐fold, with most of the biomass being associated with the sediment fines extracted with groundwater. Consecutive pulses at constant power were decreasingly effective, while pulses with higher power yielded the best results both in terms of extraction efficiency and quality. Our results indicate that low‐frequency sonication may be a viable and cost‐effective tool to improve the extraction of microorganisms from aquifers, taking advantage of existing groundwater monitoring wells.     

Tidal exposure or microhabitats: what determines sandy‐beach nematode zonation? a case study of a macrotidal ridge‐and‐runnel sandy beach in Belgium

Lately, across‐shore zonation has been found to be more important in structuring the nematode community of a tropical macrotidal sandy beach than microhabitat heterogeneity. To evaluate whether this zonation pattern applies to a temperate beach, a macrotidal ridge‐and‐runnels sandy beach in the North Sea was studied. We investigated whether a similar zonation occurs in sandbar and runnel microhabitats, and whether the runnels harbour a different community from the subtidal. Our results indicate that nematode communities from runnel and sandbar habitats are significantly different. In addition, horizontal zonation patterns for nematode communities differ between both habitats. Nematode assemblages from sandbars are divided to lower, middle and upper beach while upper and middle runnels cluster together. The subtidal and upper runnels showed dissimilar nematode assemblages, although runnels showed the same dominant species (Daptonema normandicum), which increases its abundance towards the upper runnels. This study illustrates the importance of microhabitat heterogeneity, which resulted in different zonation patterns across the sandy beach examined. The divergent zonation between sandbars and runnels in the macrotidal temperate sandy beach, compared with the pattern observed for a subtropical sandy beach with similar morphodynamics, indicates that generalizations about nematode distribution patterns should be made with caution.     

Copper in the sediment and sea surface microlayer near a fallowed, open-net fish farm

Sediment and sea surface microlayer samples near an open-net salmon farm in Nova Scotia, were analysed for copper. Copper is a constituent of the feed and is an active ingredient of anti-foulants. The salmon farm was placed in fallow after 15years of production. Sampling was pursued over 27months. Elevated copper concentrations in the sediments indicated the farm site as a source. Bubble flotation due to gas-emitting sediments from eutrophication is a likely process for accumulating copper in the sea surface microlayer at enriched concentrations. Elevated and enriched concentrations in the sea surface microlayer over distance from the farm site led, as a result of wind-drift, to an enlarged farm footprint. The levels of copper in both sediments and sea surface microlayer exceeded guidelines for protection of marine life. Over the 27months period, copper levels persisted in the sediments and decreased gradually in the sea surface microlayer.     

Land use and topography as predictors of nutrient levels in a tropical catchment

The influence of landscape on nutrient concentration and yield was analyzed in a tropical catchment, the Guare River in northern Venezuela. Spatial and temporal variation in nitrate, SRP and total P were determined in 15 sites located along the river mainstem and tributaries. Higher nitrate concentrations and yields were reported from upper sites and both decreased in the downstream direction along the river mainstem. These trends appear to be related to more pronounced slopes and larger proportions of agricultural and forest lands in subcatchments located in the upper part of the basin, and dense algal mats in the lower reaches. Nitrate values were higher during periods of high discharge, suggesting that nitrate is primarily transported by shallow subsurface flow. SRP represented between 60 and 80% of total P. Phosphorus concentrations were homogeneous along the river mainstem and showed little seasonal variation, while yields were higher in the upper basin. Multiple regression identified slope, runoff and agriculture as primary predictors of nitrate and phosphorus across the watershed, which suggests that both natural and anthropogenic landscape characteristics have a strong influence on nutrient levels in the Guare catchment.