Nutrient dynamics in water and sediment of Mediterranean ponds across a wide hydroperiod gradient     

María Sahuquillo  Maria Rosa Miracle  Sara María Morata  Eduardo Vicente 《Limnologica》2012,42(4):282-290

In Mediterranean ponds, summer drought enhances seasonality whose intensity varies along topographic and climatic gradients. The alternation of wet and dry periods in rain dependent ponds affects their biogeochemistry and differentiates them from ponds fed by more stable water sources, such as groundwater springs. Superimposed onto this, land use is also a very strong factor of variability. In this study we compared nutrients and organic matter concentrations, in water and in sediment, among different types of Mediterranean ponds based on the source of water, hydroperiod and land use. Forty-three ponds were sampled in Eastern Spain corresponding to five pond types: (1) permanent spring ponds in lowlands, (2) permanent spring ponds in mountains, (3) semi-permanent rain ponds, (4) temporary rain ponds with long hydroperiod and (5) temporary rain ponds with short hydroperiod.The results of this study indicate relevant differences among these pond types. The temporary rain ponds with short hydroperiod are characterized by high turbidity due to suspension of sediment particles rich in phosphorous adsorbed onto them (argillotrophic aquatic systems). They are used for watering domestic sheep that enhance sediment suspension by trampling. Total phosphorous (TP) concentrations in the water are high (like those of hypertrophic lakes), but planktonic chlorophyll a is very low and not correlated with TP, because of the low P-bioavailavility in the water. At the other extreme, we have permanent ponds in lowlands fed by groundwater springs. They are heavily loaded with nitrates due to the surrounding intensive agriculture. In these and other permanent/semipermanent ponds chlorophyll is highly correlated with TP. Sediment characteristics provide a good indication of the hydroperiod, since desiccation has important effects on biogeochemical transformations. A threshold of 5% organic matter (OM) in the sediment separates temporary ponds with a short hydroperiod from those with a long hydroperiod, and a threshold of 8% separates the later from the semi-permanent and permanent ponds. Besides OM reduction, important loss of N occurs during desiccation through mineralization, ammonia volatization and the sequential nitrification/denitrification pathway. On the other hand, the increase of organic P mineralization in dry sediments does not represent a loss of P from the system, since o-P remains adsorbed or bound onto the soil. This leads to a low TN/TP ratio in sediments in temporary ponds with short hydroperiod. These characteristics have to be taken into account when establishing pond typologies and ecological thresholds to assess water quality in these unique aquatic habitats.  相似文献   

Implications of Arctic industrial growth and strategies to mitigate future vessel and fishing gear impacts on bowhead whales     

Randall ReevesCheryl Rosa  J.Craig GeorgeGay Sheffield  Michael Moore 《Marine Policy》2012,36(2):454-462

The objective of this paper was to investigate and illustrate how insights gained from experience managing human activities in order to protect North Atlantic right whales (Eubalaena glacialis) along the heavily industrialized east coast of North America might be applied in the Arctic, where bowhead whales (Balaena mysticetus) face some of the same risks as right whales. The reduced extent and thickness of sea ice and the resultant longer open-water season have major, complex implications for the Arctic marine ecosystem. Increased maritime ship traffic and commercial fishing in the Arctic are bound to affect bowheads and Native (indigenous) hunting communities who depend on whales for subsistence and cultural identity. Bowheads and right whales were greatly depleted by commercial whaling in the 19th and early 20th centuries. While the Western Arctic bowhead population has been recovering steadily in recent decades, North Atlantic right whales remain highly endangered because of persistent lethal and sublethal vessel strikes and frequent entanglement in commercial fishing gear. Entanglement can be transitory or persistent, with debilitation lasting for months before the animal finally succumbs. Vessel strike and fishing gear trauma has been documented in bowheads, but at a much lower rate than in right whales. Initiatives intended to mitigate the impacts of ship traffic on North Atlantic right whales have included speed limits and routing changes. Those meant to reduce the incidence and severity of entanglements include the modification of gear design and gear deployment practices. Management measures need to be considered in advance in the Arctic in order to minimize the risks to bowhead whales as shipping and industrial fishing expand in the Arctic with ice retreat.  相似文献   

Constructed wetlands increase the taxonomic and functional diversity of a degraded floodplain   总被引：1，自引：0，他引：1  

Cecilia Español  Belinda Gallardo  Francisco A. Comín  M. Rosa Pino 《Aquatic Sciences - Research Across Boundaries》2015,77(1):27-44

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A test for directional-linear independence,with applications to wildfire orientation and size     

Eduardo García-Portugués  Ana M. G. Barros  Rosa M. Crujeiras  Wenceslao González-Manteiga  José Pereira 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(5):1261-1275

A nonparametric test for assessing the independence between a directional random variable (circular or spherical, as particular cases) and a linear one is proposed in this paper. The statistic is based on the squared distance between nonparametric kernel density estimates and its calibration is done by a permutation approach. The size and power characteristics of various variants of the test are investigated and compared with those for classical correlation-based tests of independence in an extensive simulation study. Finally, the best-performing variant of the new test is applied in the analysis of the relation between the orientation and size of Portuguese wildfires.  相似文献   

Goodness-of-fit tests for the spatial spectral density   总被引：1，自引：1，他引：0  

Rosa M. Crujeiras  Rubén Fernández-Casal  Wenceslao González-Manteiga 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(1):67-79

Detection and modeling the spatial correlation is an important issue in spatial data analysis. We extend in this work two different goodness-of-fit testing techniques for the spatial spectral density. The first approach is based on a smoothed version of the ratio between the periodogram and a parametric estimator of the spectral density. The second one is a generalized likelihood ratio test statistic, based on the log-periodogram representation as the response variable in a regression model. As a particular case, we provide tests for independence. Asymptotic normal distribution of both statistics is obtained, under the null hypothesis. For the application in practice, a resampling procedure for calibrating these tests is also given. The performance of the method is checked by a simulation study. Application to real data is also provided.  相似文献   

Determination of confined phreatic aquifer anisotropy     

Fallico C  Mazzuca R  Troisi S 《Ground water》2002,40(5):475-480

The determination of anisotropy in a phreatic aquifer by means of a pumping test can be carried out, under given conditions, with common analysis methods. This paper develops and applies an amended method based on a technique proposed by Boulton (1970). This new method enables a quick, simple determination of vertical hydraulic conductivity, given drawdown data from a pumping well and at least one observation well, that is applicable to confined phreatic aquifers.  相似文献   

Enhancement of ionizing radiation during a solar flare     

O. K. Garriott  A. V. Da Rosa  M. J. Davis  L. S. Wagner  G. D. Thome 《Solar physics》1969,8(1):226-239

Measurements of electron concentrations in the ionosphere, between 100 and 250 km altitude, were used to compute the increase in solar ionizing radiation during two flares on 21 and 23 May 1967. Since the altitude of maximum absorption of the solar energy (approximately unit optical depth) depends on the wavelength of the radiation, it is possible to estimate separately the energy enhancement in different portions of the spectrum. An ionizing energy flux increase of nearly 5 erg cm^–2 sec^–1 was observed on 21 May, while on the 23rd, the increase was over 7 erg cm^–2 sec^–1. In both flares, most of the absolute increase occurred in the 20–205 Å region of the spectrum, although the relative increase was much larger at the shorter wavelengths.  相似文献   

PCBs,DDTs and other chlorinated hydrocarbons in marine organisms from the Mediterranean coast of Israel     

Rosa Ravid  Josepha Ben-Yosef  Hava Hornung 《Marine pollution bulletin》1985,16(1):35-38

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Structural and thermodynamic properties of water related defects in α-quartz     

A. L. Rosa  A. A. El-Barbary  M. I. Heggie  P. R. Briddon 《Physics and Chemistry of Minerals》2005,32(5-6):323-331

We have investigated the atomic geometries and thermodynamic properties of water related defects in α-quartz using first-principles calculation. We confirm that the (OH)₄ group is thermodynamically most stable and aggregates to form platelets in the form of microcracks with hydrolysed surfaces. We also examine other forms of defects which can be accessible out of equilibrium at high temperature. Finally, we discuss the consequences of our results for the hydrolytic weakening of α-quartz.  相似文献   

Fault–valve action and vein development during strike–slip faulting: An example from the Ribeira Shear Zone, Southeastern Brazil     

Frederico Meira Faleiros  Ginaldo Ademar da Cruz Campanha  Rosa Maria da Silveira Bello  Kazuo Fuzikawa 《Tectonophysics》2007,438(1-4):1-32

Fluid inclusion microthermometry and structural data are presented for quartz vein systems of a major dextral transcurrent shear zone of Neoproterozoic–Cambrian age in the Ribeira River Valley area, southeastern Brazil. Geometric and microstructural constraints indicate that foliation–parallel and extensional veins were formed during dextral strike–slip faulting. Both vein systems are formed essentially by quartz and lesser contents of sulfides and carbonates, and were crystallized in the presence of CO₂–CH₄ and H₂O–CO₂–CH₄–NaCl immiscible fluids following unmixing from a homogeneous parental fluid. Contrasting fluid entrapment conditions indicate that the two vein systems were formed in different structural levels. Foliation–parallel veins were precipitated beneath the seismogenic zone under pressure fluctuating from moderately sublithostatic to moderately subhydrostatic values (319–397 °C and 47–215 MPa), which is compatible with predicted fluid pressure cycle curves derived from fault–valve action. Growth of extensional veins occurred in shallower structural levels, under pressure fluctuating from near hydrostatic to moderately subhydrostatic values (207–218 °C and 18–74 MPa), which indicate that precipitation occurred within the near surface hydrostatically pressured seismogenic zone. Fluid immiscibility and precipitation of quartz in foliation–parallel veins resulted from fluid pressure drop immediately after earthquake rupture. Fluid immiscibility following a local pressure drop during extensional veining occurred in pre-seismic stages in response to the development of fracture porosity in the dilatant zone. Late stages of fluid circulation within the fault zone are represented dominantly by low to high salinity (0.2 to 44 wt.% equivalent NaCl) H₂O–NaCl–CaCl₂ fluid inclusions trapped in healed fractures mainly in foliation–parallel veins, which also exhibit subordinate H₂O–NaCl–CaCl₂, CO₂–(CH₄) and H₂O–CO₂–(CH₄)–NaCl fluid inclusions trapped under subsolvus conditions in single healed microcracks. Recurrent circulation of aqueous–carbonic fluids and aqueous fluids of highly contrasting salinities during veining and post-veining stages suggests that fluids of different reservoirs were pumped to the ruptured fault zone during faulting episodes. A fluid evolution trending toward CH₄ depletion for CO₂–CH₄–bearing fluids and salinity depletion and dilution (approximation of the system H₂O–NaCl) for aqueous–saline fluids occurred concomitantly with decrease in temperature and pressure related to fluid entrapment in progressively shallower structural levels reflecting the shear zone exhumation history.  相似文献