Hydrological behaviour of a small catchment in the dehesa landuse system (Extremadura, SW Spain)

Investigations of the hydrological processes operating in a small experimental catchment representative of the dehesa ecosystem were carried out. The dehesa constitutes a system of agro-silvo-pastoral landuse, which is characterized by a Mediterranean, semi-arid climate. The study includes an analysis of the relationships between rainfall, soil water content and discharge, as well as the establishment of the annual water budget. The results demonstrate a complex hydrological response. The relationships between the factors involved and the operating processes are difficult to explain because of the decisive role played by the valley bottoms. These areas typically possess a sediment fill, and contrast with the shallow soils developed on the hillslopes. Genesis and quantity of runoff (Hortonian or saturation) measured at the outlet depend on the antecedent moisture conditions of the valley bottoms because of their water-retention capacity. Annual runoff coefficients are similar to those reported from other semi-arid areas. The analysis of the annual water budget shows that rainfall is positively related with both actual evapotranspiration and discharge.     

Discriminating sources of PCB contamination in fish on the coastal shelf off San Diego, California (USA)

Management of coastal ecosystems necessitates the evaluation of pollutant loading based on adequate source discrimination. Monitoring of sediments and fish on the shelf off San Diego has shown that some areas on the shelf are contaminated with polychlorinated biphenyls (PCBs). Here, we present an analysis of PCB contamination in fish on the shelf off San Diego designed to discriminate possible sources. The analysis was complicated by the variability of species available for analysis across the shelf, variable affinities of PCBs among species, and non-detects in the data. We utilized survival regression analysis to account for these complications. We also examined spatial patterns of PCBs in bay and offshore sediments and reviewed more than 20 years of influent and effluent data for local wastewater treatment facilities. We conclude that most PCB contamination in shelf sediments and fish is due to the ongoing practice of dumping contaminated sediments dredged from San Diego Bay.     

Water level control on coastal landform distribution and associated processes in a highly fluctuating shallow lake (Gallocanta Lake,NE Spain)

Shallow lakes in semi-arid environments are very sensitive to hydrological alterations associated with climate change. Their shorelines and geometry can change according to water level fluctuations. Gallocanta Lake (NE Spain) is a typical example of such lacustrine conditions because it is exposed to strong winds parallel to its elongation axis and is located in a semi-arid Mediterranean environment. In this work, a high-resolution digital elevation model (DEM) of the area is used to compare the distribution of coastal forms (beaches, barrier islands, deltas, lagoons, etc.) with the frequency at which different water levels are attained. As a result, a clear relationship is obtained between presently active forms and the water levels most frequently reached in the lake. It is deduced that, once formed, the surrounding coastal plains related to these coastal forms control the permanence of water around a given height interval, favouring the development of these morphologies, in a positive feedback mechanism only broken by subsequent climate warming and lake water lowering. The hydrodynamic conditions responsible for activating the coastal forms have been analysed by applying a mathematical model of wind-driven currents in the lake that predicts the present erosional/progradational trends associated with them. The combination of the different results obtained was used to generate a synthetic map of active coastal processes and trends along the lake shore during high water episodes, with two versions according to the two dominant wind scenarios in the region. The distribution of erosion/sedimentation trends along the lake shores has helped to propose the existence of longitudinal littoral cells, each one recording different shoreline trend (retreat, progradation, and stability), depending on the prevailing wind scenario. This synthetic scheme can be useful for predicting the eco-morphological trends of the lake shore and adapting the present management practices in this protected area accordingly.     

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.     

Dispersion of naturally occurring ions in groundwater from various rock types in a portion of the San Pedro river basin, Arizona

The groundwater in an alluvial basin in southern Arizona was analyzed for concentrations of Ca⁺⁺, Mg⁺⁺, Na⁺, and Cl⁻, ions.

The variety of rock types in the area, plus the undisturbed state of the groundwater basin, make comparative rock mineralization-groundwater ionization interpretations possible. Ionic dispersion in groundwater eminating from source areas composed of differing rock types is plotted as isogram maps. These isolated areas of differing mineral composition each exhibit a unique ionic contribution to groundwater. The ion concentrations in groundwater were then used as naturally occurring tracers to determine source areas of recharge and to delineate subsurface barriers to the normal basin flow net. Ion dispersion plots reveal the carbonates of the Dragoon Mountains to be a major contributor of Ca⁺⁺ and Mg⁺⁺ to the deep alluvial portion of the basin. Cl⁻ dispersion patterns show the granitic intrusives of the Tombstone Hills produce a barrier effect in the normal flow pattern of the basin as well as being a contributor of Cl⁻ to groundwater.     

Multi-source water pollution in a highly anthropized wetland system associated with the estuary of Huelva (SW Spain)

Major ions, nutrients, trace elements and pesticides distribution were studied in a coastal wetland heavily impacted by human development in Spain. Past land use has altered the local hydrodynamics leading to the partitioning of the ecosystem into a tideland subject to marine influence, and an artificial freshwater reservoir created by stream impoundment. The tideland stretch is flooded twice a day with a heavy metal plume that emerges from the mine-polluted estuary of Huelva and propagates landward depicting the same dispersal trend of major seawater ions. Additionally, the tidal channel receives acid discharges from industrial point sources that contribute to metal enhancement. The impounded area and stream tributaries are affected by agrochemicals runoff (nitrate, phosphate, pendimethalin, simazine, diuron and therbuthylazine) from surrounding agricultural lands. The tidal regime plays a crucial role in the transport and dispersion of pollutants, except in the artificial reservoir where freshwater exhibits a seasonal mineralization pattern.     

Stability analysis of a slope subject to real accelerograms by finite elements. Application to San Pedro cliff at the Alhambra in Granada

The dynamic stability analysis of slopes is often conducted by the traditional method of slices, using pseudo-static calculations. However, the response of a geotechnical structure subjected to seismic loads can be studied through a dynamic finite element analysis, which can be considered one of the most complete available tools, as information about the stress distribution and the deformations can be obtained. The dynamic analysis of the stability of San Pedro cliff at the Alhambra in Granada is studied in this paper. The results have been compared with pseudo-static calculations worked out with the method of slices. Real accelerograms have been selected for the dynamic tests. Thorough in situ and laboratory tests have been conducted in order to properly characterize the cliff. The soil constitutive model is also explained in this paper. Finally, the influence of the sources of energy dissipation has been studied through the material damping, the integration scheme and the boundary conditions.     

Bioaccumulation of polychlorinated biphenyls in mullet fish in a former ship dismantling harbour, a contaminated estuary, and nearby coastal fish farms

This study investigated the bioaccumulation of polychlorinated biphenyls (PCBs) toward mullet fish (Liza macrolepis) living in former PCB contaminated areas, the Ann-Ping harbour and the Er-Jen estuary, and fish farms located near the above two areas in 2003. The PCB body burdens of collected fish samples are proportional to the contamination level of their locations with the following rank order (greatest to least) from the Er-Jen estuary, the Ann-Ping harbour to the fish farms. Concentration of PCBs of the estuarine mullet has been approximately decreased to one-half of the peak concentration of the 1990s. Although the concentration of PCBs in farmed fish inhabiting near the two contaminated areas was greater than the average of those of fish from local fish markets in Taiwan, no particularly great contamination level was observed in their bodies. Using the less chlorinated PCB fraction (triCB + tetraCB)/total PCBs as the indicator of the origins of PCBs, fish near former contaminated areas had greater body burdens of the more chlorinated PCB congeners, while the farmed fish exhibited a PCB pattern more like that known to originate from air–water exchange with less chlorinated PCBs predominating. Although the PCB contamination has been stopped for a decade, the residual contaminants, supposedly existing in soil and sediments, still contribute to the body burden of fish residing in the estuary and the harbour.     

Evaluation of heavy metals and arsenic speciation discharged by the industrial activity on the Tinto-Odiel estuary, SW Spain

This study reports the annual amount of heavy metals discharged by industrial activity into the estuary of the Ría of Huelva (SW Spain). The findings showed that the discharged metals found in highest amounts were Fe (11 t y⁻¹), Zn (3.4 t y⁻¹) and Mo (0.88 t y⁻¹). There were other metals with high pollutant charge, such as Ti (232 kg y⁻¹), As (228 kg y⁻¹), Ni (195 kg y⁻¹), Pb (100 kg y⁻¹), Cr (39 kg y⁻¹) and Cd (33 kg y⁻¹). These results were compared with pollutants transported via the Tinto and Odiel rivers from abandoned mining activities in the Iberian Pyrite Belt (IPB), and it was deduced that the amounts spilled exclusively by industries were less than 1% in relation to the total discharge. Hence, the treatment of residues from the IPB should be the priority goal to improve water quality in the estuary.     

On the dynamics of low latitude,wide and shallow coastal system: numerical simulations of the Upper Gulf of Thailand

A high-resolution (～1 km horizontal grid and 21 vertical layers) numerical model based on the Princeton Ocean Model (POM) has been used to study the 3D dynamics of the Upper Gulf of Thailand (UGOT). While influenced by tides and rivers like other estuarine systems, the UGOT is unique because it is wide (～100 km?×?100 km), it is shallow (average depth of only ～15 m), it is located in low latitudes (～12.5°N–13.5°N), and it is influenced by the seasonal monsoon. Sensitivity studies were thus conducted to evaluate the impact that surface heat fluxes, monsoonal winds, river runoffs, and the low latitude may have on the dynamics; the latter has been evaluated by modifying the Coriolis parameter and comparing simulations representing low and mid latitudes. The circulation in the UGOT changes seasonally from counter-clockwise during the northeast monsoon (dry season) to clockwise during the southwest monsoon (wet season). River discharges generate coastal jets, whereas river plumes tend to be more symmetric near the river mouth and remain closer to the coast in low latitudes, compared with mid-latitude simulations. River plumes are also dispersed along the coast in different directions during different stages of the monsoonal winds. The model results are compared favorably with a simple wind-driven analytical estuarine model. Comparisons between an El Niño year (1998) and a La Niña year (2000) suggest that water temperatures, warmer by as much as 2 °C in 1998 relative to 2000, are largely driven by decrease cloudiness during the El Niño year. The developed model of the UGOT could be used in the future to address various environmental problems affecting the region.     

Seasonal contribution of living phytoplankton carbon to vertical fluxes in a coastal upwelling system (Ría de Vigo, NW Spain)

The aim of this study is to explore the contribution of living phytoplankton carbon to vertical fluxes in a coastal upwelling system as a key piece to understand the coupling between primary production in the photic layer and the transfer mechanisms of the organic material from the photic zone. Between April 2004 and January 2005, five campaigns were carried out in the Ría de Vigo (NW Iberian Peninsula) covering the most representative oceanographic conditions for this region. Measurements of particulate organic carbon (POC), chlorophyll-a (chl a), phaeopigments (phaeo), and identification of phytoplankton species were performed on the water column samples and on the organic material collected in sediment traps.The POC fluxes measured by the sediment traps presented no seasonal variation along the studied period ranging around a mean annual value of 1085±365 mg m⁻² d⁻¹, in the upper range of the previously reported values for other coastal systems. The fact that higher POC fluxes were registered during autumn and winter, when primary production rates were at their minimum levels points to a dominant contribution of organic carbon from resuspended sediments on the trap collected material. On the contrary, fluxes of living phytoplankton carbon (C_phyto) and chl a clearly presented a seasonal trend with maximum values during summer upwelling (546 mg m⁻² d⁻¹ and 22 mg chl a m⁻² d⁻¹, respectively) and minimum values during winter (22 mg m⁻² d⁻¹ and 0.1 mg chl a m⁻² d⁻¹, respectively). The contribution of C_phyto to the vertical flux of POC ranged between 2% and 49% in response to the pelagic phytoplankton community structure. Higher values of C_phyto fluxes were registered under upwelling conditions which favour the dominance of large chain-forming diatoms (Asterionellopsis glacialis and Detonula pumila) that were rapidly transferred to the sediments. By contrast, C_phyto fluxes decreased during the summer stratification associated with a pelagic phytoplankton community dominated by single-cell diatoms and flagellates. Minimal C_phyto fluxes were observed during the winter mixing conditions, when the presence of the benthic specie Paralia sulcata in the water column also points toward strong sediment resuspension.     

The optical and molecular signatures of DOM under the eutrophication status in a shallow,semi-enclosed coastal bay in southeast China

We applied stable carbon isotopes, ultraviolet-visible absorption(UV-Vis), fluorescence excitation-emission matrices spectroscopy(EEMs), and Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR-MS) to investigate the chemical composition and sources of the dissolved organic matter(DOM) in both the water column and pore water in Xiangshan Bay, a representative semi-enclosed and eutrophic bay in Zhejiang Province, China. One protein-like fluorescent component(C1) and two humic-like fluorescent components(C2 and C3) were identified by PARAFAC modeling. The concentration of dissolved organic carbon(DOC), the relative intensities of C2, C3, and black carbon-like compounds are all negatively correlated with salinity, indicating that there is a dilution effect of terrestrial signals by seawater in Xiangshan Bay. The differences in light penetration ability of Xiangshan Bay cause different degrees of photo-degradation, which may play an important role in the transformation of organic matter in Xiangshan Bay. The weak correlation between the C1 fluorescent component and salinity indicates that autochthonous sources cannot dominate the protein-like FDOM in the Xiangshan Bay drainage area. Multiple sources(such as anthropogenic inputs and release of pore water) also affect the distribution of the protein-like fluorescent component under eutrophication conditions. The relative proportion of the protein-like fluorescent component in Xiangshan Bay is on a medium level in China and anthropogenic inputs may be a significant source of DOM in coastal bays.     

Analysis of landslide frequencies and characteristics in a natural system,coastal British Columbia

Two hundred and one debris slides and debris ?ows were analyzed in a 286 km² study area on the west coast of Vancouver Island, British Columbia, Canada. The study area remains essentially untouched by humans and therefore affords a natural setting in which to examine slope processes. Landslides were identi?ed and characterized on aerial photographs from 1:15 000 to 1:31 680, and were then mapped and transferred to a GIS for analysis. Based on detailed landslide surveys, we propose a new method to accurately determine volume of landslides of this type by measured total area. Results indicate average denudation rates of 56 m³ y^?1 km^?2, and higher natural rates of failure than analogous regions in coastal British Columbia. In contrast, the landslide rates are substantially less than those from forested watersheds. Landslide distribution is spatially clustered in air photograph epochs, and we propose intense storm cells within regional events as the causal mechanism. Further, failures occurred preferentially over the West Coast Crystalline Complex (by 1·4 times), a metamorphic assemblage of gabbros, schists and amphibolites, but 1·5 times less often over the Island Plutonic Suite, a granitic intrusive formation. The former result represents a new ?nding, while the latter corroborates ?ndings of previous authors. We examined magnitude–frequency relationships of the data set and present for the ?rst time a strong argument that the rollover effect is not merely an artefact, but is instead a consequence of the physical characteristics of the landslides themselves. We subsequently analyzed magnitude–frequency relationships from two other complete data sets from coastal British Columbia and produced a family of curves corroborating this result. Copyright © 2004 John Wiley & Sons, Ltd.     

Stable isotopes of helium, nitrogen and carbon in a coastal submarine hydrothermal system

Geothermal gases from submarine and subaerial hot springs in Ensenada, Baja California Norte, Mexico, were sampled for determination of gas chemistry and helium, nitrogen and stable carbon isotope composition. The submarine hot spring gas is primarily nitrogen (56.1% by volume) and methane (43.5% by volume), whereas nearby subaerial hot spring gases are predominantly nitrogen (95–99% by volume). The N₂/Ar ratios and σ ¹⁵N values of the subaerial hot spring gas indicate that it is atmospheric air, depleted in oxygen and enriched in helium. The submarine hot spring gas is most probably derived from marine sediments of Cretaceous age rich in organic matter. CH₄ is a major component of the gas mixture (σ ¹³C = −44.05%₀), with only minor amounts of CO₂ (σ¹³C= −10.46%₀). The σ¹⁵N of N₂ is + 0.2%₀ with a very high N₂/Ar ratio of 160. The calculated isotopic equilibra tion temperature for CH₄---CO₂ carbon exchange at depth in the Punta Banda submarine geothermal field is approximately 200°C in agreement with other geothermometry estimates. The ³He/⁴He ratios of the hot spring gases range from 0.3 to 0.6 times the atmospheric ratio, indicating that helium is predominantly derived from the radioactive decay of U and Th within the continental crust. Thus, not all submarine hydrothermal systems are effective vehicles for mantle degassing of primordial helium.     

Integration and influence of paleoseismic and geologic data for the seismic hazard evaluation in the Catalan coastal ranges, Spain

In this study, the influence of paleoseismic and geologic data in the seismic hazard estimation for the Catalan coastal ranges is analysed. We computed the probabilistic seismic hazard using area seismic sources with a Poissonian assumption for the earthquake occurrence. For the computations, a previously published attenuation relationship based on European strong motion data was applied. The resulting hazard estimates show similarities to the previous assessments in the region. These results were then used as a reference for comparison with other new models. In order to analyse the influence of the paleoseismic data three different models were tested. Since the number of faults that are investigated in detail are few, the same area sources that were used in the Poissonian assumption were kept in all three new models. In addition, the new paleoseismic data with faults expressed as line sources were used. In this case, a cyclic earthquake occurrence was assumed. The three models were based on the paleoseismic data with different assumptions on the time elapsed since last event. The time elapsed was set to 0, 10 and 85% of the recurrence interval in each model. The results are presented as maps showing the difference between the three models and the reference model with the Poissonian assumption. The results are given in horizontal peak ground acceleration contour maps for different return periods, also taking into account large return periods as high as 25,000 years. This is done to demonstrate the effect of large recurrence intervals found for some of the active faults. In general, we observe that for short return periods (<1000 years), the Poissonian assumption of earthquake occurrence is probably sufficient and provides a robust estimate of the hazard. However, for longer return periods (>5000 years) the effects of the paleoseismic data become increasingly significant. In order to estimate the true seismic hazard potential of this apparently low seismicity area, long-term behaviour of the possible active faults in the region needs to be investigated systematically.     

Effects of particulate matter released by a fish farm (Eilat,Red Sea) on survival and growth of Stylophora pistillata coral nubbins

This field study aims to determine whether increased levels of organically enriched particulate matter released by net pen fish farms (Eilat, Red Sea) would affect the growth of nubbins taken from the branching coral Stylophora pistillata. We followed the survival and growth of 1322 nubbins pruned from five colonies that were transplanted at a depth of 6 m in the vicinity of the fish cages and in a reference site, in front of the Interuniversity Institute (IUI). Nubbins were attached on U-shaped PVC plates in three orientations (up, vertical and down positions). After 50 days, survival was high in both localities and no difference was recorded between the spatial orientations. At the fish farm, however, burial of the nubbin's lateral growths and partial coverage of nubbins by settled particulate matter resulted in significant reduction of the lateral growth rates of nubbins settled in the up position as compared to the reference site. On the other hand, faster growth rates were recorded in the vertical set of nubbins at the fish farm when compared with the IUI site. These results strengthen the conclusion that physical effects, rather than nutrient enrichment, may constitute the main cause of stress for minute coral fragments (resembling coral recruits) growing near the vicinity of a fish farm.     

Distribution of heavy metals in marine bivalves, fish and coastal sediments in the Gulf and Gulf of Oman

An assessment of marine contamination due to heavy metals was made in the Gulf and Gulf of Oman based on marine biota (fish and various bivalves) and coastal sediment collected in Bahrain, Oman, Qatar, and the United Arab Emirates (UAE) during 2000-2001. Sediment metal loadings were generally not remarkable, although hot spots were noted in Bahrain (Cu, Hg, Pb, Zn) and on the east coast of the UAE (As, Co, Cr, Ni). Concentrations of As and Hg were typically low in sediments and the total Hg levels in top predator fish commonly consumed in the region were < 0.5 microg g(-1) and posed no threat to public health. Very high Cd concentrations (up to 195 microg g(-1)) in the liver of some fish from southern Oman may result from food-chain bioaccumulation of elevated Cd levels brought into the productive surface waters by upwelling in the region. Very high As concentrations (up to 156 microg g(-1)) were measured in certain bivalve species from the region. Although not certain, the As is probably derived from natural origins rather than anthropogenic contamination.     

Mixing of event and pre‐event water in a shallow Entisol in sloping farmland based on isotopic and hydrometric measurements,SW China

Water percolation and flow processes in subsurface geologic media play an important role in determining the water source for plants and the transport of contaminants or nutrients, which is essential for water resource management and the development of measures for pollution mitigation. During June 2013, the dynamics of the rainwater, soil water, subsurface flows and groundwater in a shallow Entisol on sloping farmland were monitored using a hydrometric and isotopic approach. The results showed that effective mixing of rainwater and soil water occurred in hours. The rebound phenomenon of δD profiles in soils showed that most isotope‐depleted rainwater largely bypassed the soil matrix when the water saturation in the soil was high. Preferential‐flow, which was the dominant water movement pattern in the vadose zone, occurred through the whole soil profile, and infrequent piston‐flow was mainly found at 20–40 cm in depth. The interflow in the soil layer, composed of 75.2% rainwater, was only generated when the soil profile had been saturated. Underflow in the fractured mudrock was the dominant flow type in this hillslope, and outflow was dominated by base flow (groundwater flow) with a mean contribution of 76.7%. The generation mechanism of underflow was groundwater ridging, which was superimposed upon preferential‐flow composed mainly of rainwater. The quick mixing process of rainwater and soil water and the rapid movement of the mixture through preferential channels in the study soil, which shows a typical bimodal pore size distribution, can explain the prompt release of pre‐event water in subsurface flow. Water sources of subsurface flows at peak discharge could be affected by the antecedent soil water content, rain characteristics and antecedent groundwater levels. Copyright © 2016 John Wiley & Sons, Ltd.