Environmental factors controlling the spatiotemporal distribution of microbial communities in a coastal, sandy aquifer system (Doñana, southwest Spain)

Currently, aquifers are considered to be ecosystems that interchange materials and energy with other systems located in their surroundings. The aquifer system of Doñana (southwest Spain) has been studied over recent decades from a hydrogeological point of view, although nothing is known about its biological or ecological aspects. In order to describe the general characteristics of its microbial communities, bacterial abundance, cell biomass, bacterial biomass and microbial activities of functional groups were investigated by sampling, over a 2-year period, 13 wells located in the vicinity of four very productive shallow lakes in the most superficial part of this coastal, sandy aquifer system. Multivariate analysis of variance (MANOVA) indicated differences in abundance and biomass variables among sampling locations, seasons and sampling locations × seasons. Principal component analysis showed that temperature and dissolved oxygen appeared to be the most important factors controlling the temporal variability of microbial communities. Hydrological connectivity between surface water and groundwater was important in the control of the spatiotemporal distribution of microbial communities. Due to this hydrological connection, the aquifer system and the wetlands constitute a unique entity, a unique ecosystem, called the “hydroecosystem”, where microbial communities could play a central ecological role.     

Pyroclast textural variation as an indicator of eruption column steadiness in andesitic Plinian eruptions at Mt. Ruapehu

Hudson is one of the most active volcanoes in the Southern Andes—it had one of the largest eruptions of the 20th century in 1991 (VEI?=?5) and smaller eruptions in 1971 (VEI?=?3), maybe 1973, and 2011 (VEI of 1-2). We use satellite-based interferometric synthetic aperture radar (InSAR) and thermal imagery to characterize the activity of Hudson between 2004 and 2011 and during the 2011 eruption. InSAR data show that the volcano inflated between 2004 and 2010 with a maximum change rate of between 2 and 3 cm/yr—about half of the deformation rate observed during a previous deformation episode from 1993–1999. Inversion for an inflating point source suggests magma accumulation beneath the SW part of the caldera at an average depth of 10 km. This inferred source is deeper than both the sources estimated for the magma chamber of the 1991 eruption (from petrology) and for the 1993–1999 deformation event. Also, the deformation from 2004–2010 is centered at a slightly different location and has a smaller volume change than that between 1993–1999—further indicating that there is either a large magma reservoir or several separate ones. While the deformation center is a few km from the eruption location near the caldera rim, the two are possibly linked since the predicted static Coloumb stress changes due to the inferred inflation source would encourage unclamping on potential faults in the caldera rim. We also analize nighttime satellite thermal images from MODIS and ASTER. While MODIS did not show any unambiguous evidence for hot spots, ASTER thermal imagery show that at least four months before the eruption there were locations with temperatures 7–8ºK above background. Lahars observed by helicopter overflights on 4 March 2011 and October 2011 suggest that the hotspots may have been caused by lakes or subglacial melting. There is no InSAR data available for the months immediately preceding the eruption, but the ASTER thermal imagery results may indicate an increase in geothermal activity that could have been used to forecast the eruption.     

Reproductive synchrony in a diverse Acropora assemblage,Vamizi Island,Mozambique

Multi‐specific synchronous spawning has never been documented for East Africa, but coral spawn‐slicks are observed annually around Vamizi Island, Northern Mozambique. We monitored gamete development in Acropora species from July 2012 to October 2013 and from August to September 2014 to describe patterns of reproductive seasonality and synchrony within and amongst species of Acropora. Gamete maturation was highly synchronized within and amongst Acropora species and culminated in multi‐specific spawning events lasting 1–3 nights in each year of the study, in late August or September. In 2013 and 2014, 50% or more of the colonies of over 50% of the species sampled prior to the spawning events had mature gametes. In all years, 91–99% colonies sampled after the spawning events had no visible gametes. The percentage of colonies with mature gametes was up to 100% for some species. In other species, the absence of mature gametes throughout the study period indicates that they might not spawn in certain years. The analysis of a 8‐year record of observations of spawn‐slicks showed that spawning generally occurred once a year for a few consecutive days between September and December, during periods of rising sea surface temperature and low wind speed and rainfall. This study is the first to quantitatively document coral reproduction in Mozambique and multi‐specific synchronous spawning off the coast of Africa. These findings contrast with the asynchronous breeding reported for Kenyan reefs and support the absence of breakdown in coral reproductive synchrony towards low latitudes.     

Effects of Paracentrotus lividus (Lamark, 1816) harvesting on benthic assemblages. An experimental approach

The effect of harvesting on the diversity and structure of benthic assemblages is nowadays a relevant component of fishery management. Invertebrate harvesting is increasing worldwide and sea urchins are one of the main invertebrate target species. However, current knowledge about the effects of sea urchin harvesting on benthic assemblages is still poor. The aim of this study is to evaluate the influence of Paracentrotus lividus (Lamark, 1816) harvesting on tide pool assemblages from intertidal rocky shores. To achieve this objective, a field removal experiment was done for 10 months. Results of univariate and multivariate analyses showed that P. lividus harvesting had a significant effect on the number of taxa and structure of the benthic assemblage. Assemblages from pools where P. lividus were removed showed significant differences against controls; namely, where P. lividus were eliminated, pools showed higher number of taxa than control pools. This result contrasts with previous studies assessing effects of invertebrate harvesting that generally have found a biodiversity reduction in the exploited habitat. Despite this apparently positive effect of P. lividus harvesting, we should be cautious because effects of P. lividus harvesting on higher trophic levels or during long periods of time remain unexplored.     

Modeling speleothem δC variability in a central Sierra Nevada cave using C and Sr/Sr

Carbon isotopes in speleothems can vary in response to a number of complex processes active in cave systems that are both directly and indirectly related to climate. Progressing downward from the soil zone overlying the cave, these processes include soil respiration, fluid-rock interaction in the host limestone, degassing of CO₂ and precipitation of calcite upflow from the speleothem drip site, and calcite precipitation at the drip site. Here we develop a new approach to independently constrain the roles of water-rock interaction and soil processes in controlling stalagmite δ¹³C. This approach uses the dead carbon proportion (dcp) estimated from coupled ¹⁴C and ²³⁰Th/U measurements, in conjunction with Sr isotope analyses on stalagmite calcite from a central Sierra Nevada foothills cave in California, a region characterized by a highly seasonal Mediterranean-type climate, to determine the roles of water-rock interaction and soil processes in determining stalagmite δ¹³C. Increases in stalagmite dcp between 16.5 and 8.8 ka are coincident with decreased δ¹³C, indicating a varying yet substantial contribution from the soil organic matter (SOM) reservoir, likely due to significantly increased average age of SOM in the soil veneer above the cave during wet climatic intervals.We use geochemical and isotope mixing models to estimate the host-carbonate contribution throughout the δ¹³C time series and determine the degree of degassing and calcite precipitation that occurred prior to precipitation of stalagmite calcite. The degree of degassing and prior calcite precipitation we calculate varies systematically with other climate indicators, with less degassing and prior calcite precipitation occurring during wetter climatic intervals and more during drier intervals. Modeled δ¹³C values and degassing calculations suggest that some degree of prior calcite precipitation is necessary at all time intervals to explain measured stalagmite δ¹³C values, even during relatively wet intervals. These results illustrate the importance of constraining degassing and prior calcite precipitation in the interpretation of speleothem δ¹³C records, particularly those from caves that formed in seasonal semi-arid to arid environments.     

Factors controlling present-day tufa dynamics in the Monasterio de Piedra Natural Park (Iberian Range, Spain): depositional environmental settings, sedimentation rates and hydrochemistry

The tufa record and hydrochemical characteristics of the River Piedra in the Monasterio de Piedra Natural Park (NE Spain) were studied for 6 years. The mean discharge of this river was 1.22 m³/s. The water was supersaturated with calcium carbonate. The HCO₃ ⁻, Ca²⁺ and TDIC concentrations decreased along the 0.5-km-long studied stretch, whereas the calcite SI showed no systematic downstream or seasonal variation over the same stretch. Several sedimentary subenvironments exist in which four broad types of tufa facies form: (1) Dense laminated tufa (stromatolites), (2) Dense to porous, massive tufa, (3) Porous, coarsely laminated tufa with bryophytes and algae, and (4) Dense, hard, laminated deposits in caves. The half-yearly period thickness and weight of sediment accumulated on 14 tablets installed in several subenvironments showed that the deposition rate was greater in fast flowing river areas and in stepped waterfalls, and lower in slow flowing or standing river areas and in spray and splash areas. Mechanical CO₂ outgassing is the main factor controlling calcite precipitation on the river bed and in waterfalls, but this process does not explain the seasonal changes in depositional rates. The deposition rates showed a half-yearly period pattern recorded in all fluvial subenvironments persistent over time (5.26 mm, 0.86 g/cm² in warm periods; 2.26 mm, 0.13 g/cm² in cool periods). Mass balance calculations showed higher calcite mass values in warm (21.58 mg/L) than in cool (13.68 mg/L) periods. This biannual variation is mainly attributed to the seasonal differences in temperature that caused changes in inorganic calcite precipitation rate and in biomass and the correlative photosynthetic activity. Tufa sedimentation was therefore controlled by both physicochemical and biological processes. The results of this study may help test depositional rates and their environmental controls and thus assess the climatic and hydrological significance of ancient tufas in semi-arid conditions, in particular in the Quaternary.     

Windblown desert sands in coeval shallow marine deposits: a key for the recognition of coastal ergs in the mid‐Cretaceous Iberian Basin,Spain

Grain size and SEM analyses suggest the presence of Cretaceous windblown desert sands in coeval shallow marine environments. Size distributions and microtexture data allowed us to infer a climate change to more arid conditions in the Iberian Basin during the mid‐Cretaceous. The grain size of the sands in the late Aptian to early Cenomanian shallow‐marine deposits in the western sub‐basins of the Maestrazgo Basin (Teruel, Spain) is almost exclusively in the range between 1.5 and 3 Φ (0.35–0.125 mm), reflecting a prolonged or at least recurrent preselection of aeolian sands. The palaeolatitude of 25°N showed a change from a warm humid climate during the Lower Cretaceous to an arid desert climate in the eastern sector of Iberia during the late Aptian–early Cenomanian. Winds supplied abundant desert sand to the estuarine and deltaic sedimentary environments where it was worked up in sandy sub‐ and intertidal facies with a striking absence of mud in cross‐bedded sets which otherwise clearly reflect the influence of a semi‐diurnal tidal system.     

A comparison between the Linear Regression Model with autocorrelated errors and the Partial Adjustment Model

In this paper we consider a Linear Regression Model with a design matrix that fits the periodic structure of a time series. As a consequence, the residuals are very often autocorrelated. The main problem is that residual autocorrelation does not necessarily entail error autocorrelation. To analyse the effects of selecting different formulations to accommodate the autocorrelation in the residuals, we consider two seemingly different ways to deal with this problem: the Linear Regression Model with the error terms following an Autoregressive Stationary Process and the Partial Adjustment Model. We study the equivalence between the two formulations. We go over the problem of estimating the parameters and, especially, of making inferences in this framework. After parameter estimation, we analyse the adequacy of the models. We demonstrate that the issue of selecting the most appropriate model to capture the autocorrelation in the residuals is, in this context, a kind of an artefact since the main results concerning the fitted values and forecasting features are the same. These modelling procedures are applied to the Portuguese coastal upwelling data and we compare the estimated models.     

Effects of temporal variation of the seaweed Caulerpa prolifera cover on the associated crustacean community

The aim of this study was to establish the effect of temporal variation of the alga Caulerpa prolifera cover on the composition and stability of the associated crustacean community. Forty‐five crustacean species were found, amphipods and tanaidaceans being the most abundant groups. The stations were grouped mainly based on the gradient of algal cover, independently of location or sampling period (MDS analyses). Considering separately epifaunal and infaunal species, the epifauna occurred mainly at high cover (HC) and medium–low cover (MLC) stations, while the infauna occurred at MLC and unvegetated (UV) stations. Infaunal species were predominant in all stations and sampling periods, and the abundance and numbers of epifaunal species showed a clear dependence of algal cover. To quantify the loss of biodiversity due to the plant cover variations, we applied the average and variation in taxonomic distinctness (Δ⁺ and Λ⁺, respectively). The HC stations, especially those with fewer algal cover variations along the study period, showed few fluctuations of Δ⁺,and Λ⁺ was usually located near mean; however, UV stations tended to fall in the area where the statistical power of the test is reduced and showed more oscillations of Λ⁺. The ability of these indices to test the fauna composition in function of the alga presence is discussed.