Spatial and temporal variation of the nekton and hyperbenthos from a temperate European estuary with regulated freshwater inflow

The aquatic macrofauna of the Guadalquivir estuary were sampled (1 mm mesh persiana net) at 5 sampling sites located along the entire (except the tidal freshwater region) estuarine gradient of salinity (outer 50 km). A total of 134 fish and macroinvertebrate species was collected but only 62 were considered common or regularly present in the estuary. Univariate measures of the community structure showed statistically significant differences among sampling sites: species richness, abundance, and biomass decreased in the upstream direction, being positively correlated with the salinity. Temporal differences of these three variables were also statistically significant. While a clear seasonal pattern (minimum densities in winter and maximum in spring-summer) was observed for abundance and biomass, no such pattern existed for the number of species. Mysids was the most dominant group throughout the estuary (96% to 99% of abundance; 49% to 85% of biomass), although fish biomass was also important at the outer estuary (36% to 38%). Multivariate analyses indicated highly significant spatial variation in the macrofaunal communities observed along the salinity gradient. These analyses suggest that the underlying structure was a continuum with more or less overlapping distributions of the species dependent on their ability to tolerate different physicochemical conditions. There were also significant temporal (intermonthly + interannual) variation of the estuarine community; the relative multivariate dispersion indicated that monthly variation was more considerable (relative multivariate dispersion >1) at the outer part of the estuary during the wet year (last 20 km) and was higher in the inner stations during the dry year (32 to 50 km from the river mouth). Since a clear negative exponential relationship was observed between the freshwater input (from a dam located 110 km upstream) and water salinity at all sampling stations, it is concluded that the human freshwater management is probably affecting the studied estuarine communities. While the higher seasonal (long-term) stability of the salinity gradient, due to the human control of the freshwater input, may facilitate the recruitment of marine species juveniles during the meteorologically unstable early-spring, the additional (short-term) salinity fluctuations during the warm period may negatively affect species that complete their lifecycle within the estuary.     

85 Peg A: what age for a low-metallicity solar-like star?

We explore the possible evolutionary status of the primary component of the binary 85 Pegasi, listed as a target for asteroseismic observations by the MOST satellite. In spite of the assessed 'subdwarf' status, and of the accurate distance determination from the Hipparcos data, the uncertainties in the metallicity and age, coupled with the uncertainty in the theoretical models, lead to a range of predictions on the oscillation frequency spectrum. Nevertheless, the determination of the ratio between the small separation in frequency modes, and the large separation as suggested by Roxburgh, provides a very good measure of the star age, quite independent of the metallicity in the assumed uncertainty range. In this range, the constraint on the dynamical mass and the further constraint provided by the assumption that the maximum age is 14 Gyr limits the mass of 85 Peg A to the range from 0.75 to  0.82 M_⊙  . This difference of a few hundredths of a solar mass leads to well detectable differences both in the evolutionary stage (age) and in the asteroseismic properties. We show that the age determination which will be possible through the asteroseismic measurements for this star is independent either of the convection model adopted or the microscopic metal diffusion. The latter conclusion is strengthened by the fact that, although metal diffusion is still described in an approximate way, recent observations suggest that real stars suffer a smaller metal sedimentation compared with the models.     

Tropical salt marsh succession as sea-level indicator during Heinrich events

Centennial–millennial dynamics of tropical salt marsh vegetation are documented in the pollen record from marine core MD03-2622, Cariaco Basin, Venezuela, which spans the glacial period between 63 and 29 ka. Five rapid and abrupt expansions of salt marsh vegetation are linked with North Atlantic Heinrich events (HEs). Within each event, a recurrent pattern – starting with species of Chenopodiaceae, followed by grasses, and subsequently by Cyperaceae species – suggests a successional process that is determined by the close relationship between sea-level and community dynamics. The salt tolerant Chenopodiaceae, at the base of each sequence, indicate hypersaline intertidal environments, which were most likely promoted by extremely dry atmospheric conditions. Rapid sea-level rise characterizes the onset of HE stadials, causing erosion of marsh sediments, and continued recruitment of pioneer species (Chenopodiaceae), which are the only ones capable of tolerating the rapid rate of disturbance. Once, as sea-level drops or as rise decelerates, marsh plants are able to trap and stabilize sediments, favouring the establishment of more competitive species (graminoids). The increment of marsh height as a result of autochthonous sediment accumulation reduces the extent of hypersaline environments, and allows the establishment of mesohaline species. These results add to the scarce knowledge on tropical salt marsh ecosystems, and provide independent paleoclimatic evidence on sea-level changes occurring simultaneously with Antarctica climate variations.     

Using low-density discrete Airborne Laser Scanning data to assess the potential carbon dioxide emission in case of a fire event in a Mediterranean pine forest

The aim of study is to map the carbon dioxide (CO₂) emission of the aboveground tree biomass (AGB) in case of a fire event. The suitability of low point density, discrete, multiple-return, Airborne Laser Scanning (ALS) data and the influence of several characteristics of these data and the study area on the results obtained have been evaluated. A sample of 45 circular plots representative of Pinus halepensis Miller stands were used to fit and validate the model of AGB. The ALS point clouds were processed to obtain the independent variables and a multivariate linear regression analysis between field data and ALS-derived variables allowed estimation of AGB. Then, the influence of several characteristics on the residuals of the model was analyzed. Finally, conversion factors were applied to obtain the CO₂ values. The AGB model presented a R² value of 0.84 with a relative root-mean-square error of 27.35%. This model included ALS variables related to vegetation height variability and to canopy density. Terrain slope, aspect, canopy cover, scan angle and the number of laser returns did not influence AGB estimations at plot level.     

Effect of spatial resolution on regionalization of hydrological model parameters

Lack of availability of historical data series is one of the major hindrances in hydrological modelling. Regionalization of hydrological model parameters is one of the solutions to obtain the parameters for ungauged basins. Recently, lots of methodologies have been developed. They can be categorized as model calibration then fitting regression between model parameters and catchments characteristics, using some kind of transfer function. The aim of this study was to compare different regionalization methods as well as to look how the spatial resolution affects regionalization. In this study, a modified Lipschitz and monotony condition was used for regionalization. To identify the effect of the model resolution, the parameters of a distributed and semi‐distributed version of the Hydrologiska Byråns Vattenbalansavdelning (HBV) model were regionalized. The study was conducted at the upper Neckar catchment of southwest Germany. It has been found that the combination of Lipschitz and monotony condition has performed reasonably. It has been seen that the distributed model structure has outperformed the semi‐distributed model structure. It shows under present data conditions that higher model resolution can describe processes of ungauged basins reasonably. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of the addition of granitic powder to an acidic soil from Galicia (NW Spain) in comparison with lime

The impact of diffuse pollution, agricultural land use and climate change on the long-term response of subsurface–surface water quality is not well understood, but is a prerequisite for evaluation of water management options. The goal of this study is to model geochemical evolution of water chemistry from the infiltration through soil into the unsaturated zone, transport through bedrocks and granular aquifers to a river in order to identify zones of steep concentration gradients and high dynamics under transient flow conditions. A numerical model was constructed comprising a 2-D 1,500 m × 150 m vertical cross-section of typical sedimentary rock formations, a glacio-fluvial quaternary gravel aquifer in the valley and soil layers. The model coupled saturated/un-saturated flow and reactive transport under steady state and transient conditions. Geochemical interactions, include intra-aqueous kinetic reactions of oxygen with dissolved organic matter, as well as kinetics of carbonate dissolution/precipitation. This model section was chosen to provide insight in to the principal processes and time scales affecting water chemistry along different flow paths. The numerical simulator MIN3P was used, a finite volume program for variably saturated subsurface flow and multi-component reactive transport. The results show that subsurface water residence times range from approximately 2 to 2,000 years. Different zones are to be expected with respect to the development of mineral equilibria; namely, purely atmospherically influenced, as well as open and closed system carbonate dissolution. Short-term responses to daily averaged changes in precipitation, however, are only visible to some extent in the shallower and near-river parts of flow system and solute loads. This can most likely be explained by directional changes in flow paths, indicating that equilibrium geochemical condition predominate at the hillslope scale, i.e. water quality depends on transport pathways rather than on kinetic effects. The extent of reducing conditions is controlled by the presence of organic-rich layers (i.e. peat deposits), the dissolution kinetics of aquifer organic matter and the subsequent mixing with oxygenated water by hydrodynamic dispersion.     

Influence of Mussel Culture on the Vertical Export of Phytoplankton Carbon in a Coastal Upwelling Embayment (Ría de Vigo,NW Iberia)

The goal of this paper is to find out whether suspended mussel culture affects the vertical fluxes of biogenic particles in the Ría de Vigo on a seasonal scale. With this aim, vertical fluxes of particulate organic carbon (POC) and the magnitude and composition of vertical export of phytoplankton carbon (Cphyto) collected in sediment traps were examined by comparing data obtained inside a mussel farming area (RaS) with those found at a reference station (ReS) not affected by mussels. Our results indicate that mussel farming has a strong impact on sedimentation fluxes under the rafts, not only increasing POC flux but also altering the magnitude and composition of Cphyto fluxes. Average POC flux at RaS (2564?±?1936 mg m^?2 day^?1) was four times higher than at ReS (731?±?276 mg m^?2 day^?1), and much of this increase was due to biodeposit fluxes (Cbiodep) which accounted for large proportion of POC flux (35–60 %). Indeed, because of this high Cbiodep flux, only a small proportion of the POC flux was due to Cphyto flux (3–12 %). At the same time, we observed an increased sedimentation of phytoplankton cells at RaS that could be explained by a combination of mechanisms: less energetic hydrodynamic conditions under mussel rafts, ballast effect by sinking mussel feces, and diatom aggregates. Moreover, mussel farming also altered the quality of the Cphyto flux by removing part of the predatory pressure of zooplankton and thus matching diatom composition in water column and sediment traps.     

Impact of lightning on organic matter-rich soils: influence of soil grain size and organic matter content on underground fires

A detailed study was carried out on a piece of land that had been struck by lightning during the violent rainstorm that raged over the Island of S?o Miguel (Azores Archipelago) in late October 2006. Temperature and gas measurements (CO₂, CO, H₂S and CH₄) were performed in four study trenches, dug in an area of ∼3 m², where an underground fire had been initiated by the impact with a lightning stroke, followed by the emission of a column of gases and smoke. The soil under study was originally a well-pedogenized about 80 cm thick bed, made of volcanic clayey to silty tephra fallouts and contained 5.5–9.7% of organic matter. The underground fire was monitored for one week and revealed a peak release of 404 ppm CO and 3.4% CO₂ originating from a horizon located about 45 cm under the soil surface. Measurements of temperature, performed one week after the impact, indicated a maximum value of 326°C inside the soil, while 516.5°C were measured on the surface of a lava block interred about 20 cm under the surface. Subsequently, a stratigraphic and sedimentologic study proved the role of the grain-size of the soil and of the organic matter content of the different horizons of the impact area, in determining the ratio between anoxic/oxidised combustion conditions and in the progress of the process itself. It was also noticed that combustion was not total all over in the soil bed and that the process had slightly migrated toward SW during the observation period. The combustion process went on for about ten days, in spite of several other violent rainstorms, until it was artificially extinguished through the excavations made to obtain study trenches. This particular circumstance evidenced the potential natural hazard represented by this kind of atmospheric event, especially in a land where the volcanic nature of the soil may easily mislead inexperienced observers and, consequently, delay proper action.