Aspects of the cycle of inorganic nitrogen compounds in the tropical rain forest of the Ivory Coast     

Jean Servant  Robert Delmas  Jacques Rancher  Marcel Rodriguez 《Journal of Atmospheric Chemistry》1984,1(4):391-401

A partial balance of mineral N is given for the basins of two coastal rivers in a forest zone in the Ivory Coast. The dry and wet depositions on the basin surfaces is given for particulate matter (NO₃ ^–, NH₄ ⁺). The quantity of mineral N washed away in the rivers is evaluated. The losses from leaching of the soils by rainwater are about 0.33 to 1.0% of the atmospheric depositions for NH₄ ⁺–N and 2.2 to 5.8% for NO₃ ^––N. The yearly atmospheric input of N compounds to the ecosystem, about 1.4 g N m^–2 y^–1, is at least 14% of mineral N formed in the soils and is therefore quite significant.  相似文献   

Spatial organization of decadal and bidecadal rainfall fluctuations in southern North America and southern South America     

Omar Abel Lucero  Norma C. Rodriguez 《Atmospheric Research》2001,57(4)

The spatial organization of decadal and bidecadal components (fluctuations) of annual rainfall is identified in this research for two regions: (1) southern South America, and (2) southern North America (conterminous USA, southeastern Canada and northern and central Mexico). Findings indicate that these decadal and bidecadal components have highly coherent wave-like spatial organization. Two types of organization of decadal and bidecadal components of annual rainfall were identified: a train of propagating fluctuations and quasi-standing fluctuations. For decadal components, such patterns alternate in time. A widespread change in the spatial organization of decadal component of annual rainfall took place simultaneously in both continents in 1932. The bidecadal component is organized as standing fluctuations in southern North America and as travelling fluctuations in southern South America, The spatial pattern of decadal fluctuations of annual rainfall has 12- and 13-year cycles, and the spatial pattern of bidecadal fluctuations has predominantly 21- and 22-year cycles.  相似文献   

A methodology to estimate renewal time scales in estuaries: the Tagus Estuary case   总被引：2，自引：0，他引：2  

Frank?BraunschweigEmail author  Flávio?Martins  Paulo?Chambel  Ramiro?Neves 《Ocean Dynamics》2003,53(3):137-145

High-resolution hydrodynamic models are a common tool to simulate water dynamics in estuaries. Results from these models are, however, difficult to interpret without the aid of additional parameters to integrate the information. In this paper a methodology to understand the transport patterns in the Tagus Estuary is proposed. It is based on the computation of two renewal time scales: residence time and integrated water fraction. This last parameter is used to build a dependency matrix that gives the integrated influence of each region of the estuary at a selected point. The parameters are computed using a Lagrangian transport model coupled to the hydrodynamic model. Results show that Tagus Estuary has two different types of regions: the central part of the estuary, with low renewal efficiency, and three regions with higher renewal efficiency. Renewal mechanisms are, however, different for each region as shown by the dependency matrix. Comparison of renewal time scales with results from a water-quality model revealed that residence time is not a limiting parameter for primary production in the Tagus Estuary.Responsible Editor: Hans Burchard  相似文献   

Nutrient dynamics in Mediterranean temporary streams: A case study in Pardiela catchment (Degebe River, Portugal)   总被引：1，自引：0，他引：1  

Ana Isabel Lilleb  Manuela Morais  Pedro Guilherme  Rita Fonseca  Antnio Serafim  Ramiro Neves 《Limnologica》2007,37(4):337-348

Most of the streams in the Mediterranean region are temporary, following predictable seasonal of flooding and drying, with a transition from lotic conditions to shallow lentic conditions. The goal of our study was to assess the nitrogen and phosphorus dynamics in channel-bed processes of temporary streams between floods. Results show that, during winter, temperatures ranged between 9.5 and 11.2 °C and oxygen concentration ranged from 8.0 to 9.5 mg L⁻¹, whereas, during summer, temperatures varied between 21.2 and 26.8 °C and oxygen between 1.2 and 5.3 mg L⁻¹, with oxygen depletion in the pools during the night. The nitrate concentrations were far more abundant during winter (February), while ammonium concentration increased after stream fragmentation into pools (especially in July when oxygen depletion conditions favoured ammonification). Results on sediment profiles showed that the most active sediment layers for NH₄-N are the top 2–3 cm, corresponding to the sediment depositional sites of the stream. Phosphate concentrations had larger variability, yet concentrations decreased from winter to spring and increased again in summer, when the shallow water pools were formed. Sediment profiles at the sediment depositional sites showed that PO₄-P was more dynamic in the first 6 cm.

In Mediterranean temporary streams, nutrient dynamics vary seasonally, as the system transits from lotic conditions to shallow lentic conditions, evidencing the regeneration of nutrients from organic and inorganic matter during the flow cessation period.  相似文献   

European retirees on the Costa del Sol: a cross-national comparison     

Rodriguez V  Fernandez-mayoralas G  Rojo F 《International journal of population geography : IJPG》1998,4(2):183-200

"This paper studies northern European retired immigrants, using data generated by a questionnaire survey of 300 respondents and in-depth interviews with 20 people in 13 municipalities. Reasons for moving to Spain, the advantages and disadvantages reported of living there, and the perceived impacts on the local region were analysed, paying particular attention to cross-national differences between British, German, Benelux and Nordic retirees. The results show that sociodemographic and economic features of the settlers tend to be quite similar, whilst reasons for moving, stated advantages and disadvantages, and consequences and impacts exhibit some cross-national differentiation."  相似文献   

The impact of land use change and check‐dams on catchment sediment yield     

Carolina Boix‐Fayos  Joris de Vente  María Martínez‐Mena  Gonzalo G. Barberá  Víctor Castillo 《水文研究》2008,22(25):4922-4935

Extensive land use changes have occurred in many areas of SE Spain as a result of reforestation and the abandonment of agricultural activities. Parallel to this the Spanish Administration spends large funds on hydrological control works to reduce erosion and sediment transport. However, it remains untested how these large land use changes affect the erosion processes at the catchment scale and if the hydrological control works efficiently reduce sediment export. A combination of field work, mapping and modelling was used to test the influence of land use scenarios with and without sediment control structures (check‐dams) on sediment yield at the catchment scale. The study catchment is located in SE Spain and suffered important land use changes, increasing the forest cover 3‐fold and decreasing the agricultural land 2·5‐fold from 1956 to 1997. In addition 58 check‐dams were constructed in the catchment in the 1970s accompanying reforestation works. The erosion model WATEM‐SEDEM was applied using six land use scenarios: land use in 1956, 1981 and 1997, each with and without check‐dams. Calibration of the model provided a model efficiency of 0·84 for absolute sediment yield. Model application showed that in a scenario without check dams, the land use changes between 1956 and 1997 caused a progressive decrease in sediment yield of 54%. In a scenario without land use changes but with check‐dams, about 77% of the sediment yield was retained behind the dams. Check‐dams can be efficient sediment control measures, but with a short‐lived effect. They have important side‐effects, such as inducing channel erosion downstream. While also having side‐effects, land use changes can have important long‐term effects on sediment yield. The application of either land use changes (i.e. reforestation) or check‐dams to control sediment yield depends on the objective of the management and the specific environmental conditions of each area. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Spatial and temporal variations in aboveground and belowground biomass of Spartina maritima (small cordgrass) in created and natural marshes     

Jesús M. Castillo  Pablo Leira-Doce  Alfredo E. Rubio-Casal  Enrique Figueroa 《Estuarine, Coastal and Shelf Science》2008,78(4):819-826

Spartina species are commonly used for salt marsh manipulative projects, where aboveground and belowground biomasses are functional traits that play important roles, showing high spatial and temporal variations. This work analyses variations in AGB and BGB of Spartina maritima and abiotic environmental parameters along a chronosequence of six marshes created from 1997 to 2003 with disparate sediment dynamics, and adjacent natural marshes and unvegetated tidal flats. S. maritima behaved as an autogenic engineer, as its colonization of bare sediments yielded abiotic environmental changes: specifically, bed level rise accompanied by higher oxygenation and salinity. These modifications of the environment were site-specific, depending mainly on sedimentary dynamics. At the same time, abiotic environmental changes determined biomass production rates of S. maritima that were higher in more-accreting marshes; however, AGB was kept constant from early in its development (2 years). The increase in BGB with elevation seemed to be related to the inhibition of subsurface tissue development in anoxic sediments. Biomass accumulation and production varied markedly, depending on the spatial scale, indicating the relevance of the plot size chosen for the analysis of biomass of cordgrasses. Our results show that managers of salt marshes should consider sedimentary dynamics carefully when setting realistic expectations for success criteria of created and restored wetlands.  相似文献   

A reach‐scale biogeochemical model for temporary rivers     

Ourania Tzoraki  Nikolaos P. Nikolaidis  Anna Rosa Trancoso  Frank Braunschweig  Ramiro Neves 《水文研究》2009,23(2):272-283

The RS‐tempQ Model ( r each– s cale t emporary flow biogeochemical model) is a conceptual model that can describe the hydrologic, sediment transport and biogeochemical processes of temporary rivers at the reach scale. The model takes into account the expansion–contraction of the inundated area of the river. It simulates the sediment transport and the nutrient fluxes that are transferred to the coastal area due to the first flash flood and during extreme rain events. The RS‐tempQ Model simulates the in‐stream processes during the wet and dry cycles as the river corridor expands and contracts. The model was used to assess and quantify the hydrologic and geochemical processes occurring in a temporary river reach (Krathis River) in Greece. Since the conventional gauging techniques cannot measure the flow in rivers that are split into small braided streams, discharge measurements could not be obtained in order to calibrate and verify the model. Other field measurements such as infiltration losses and sediment accumulation were used for model calibration. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Linking Remote-Sensing and <Emphasis Type="Italic">In Situ</Emphasis> Observations of Coronal Mass Ejections Using STEREO     

L. Rodriguez  M. Mierla  A. N. Zhukov  M. West  E. Kilpua 《Solar physics》2011,270(2):561-573

The twin STEREO spacecraft have been observing the Sun since 2006. Even though STEREO has only been active during solar minimum conditions so far, an important number of coronal mass ejections (CMEs) and their interplanetary counterparts (ICMEs) have been observed. Many of the ICMEs can be linked back to the corresponding CMEs on the Sun through the combination of remote-sensing and in situ observations. This paper aims to answer the question whether a CME observed by a coronagraph will be detected in situ by a spacecraft in a specific location in the heliosphere. We use a flux-rope-like model fit to the STEREO SECCHI/COR2 data to obtain the direction of CME propagation and its geometrical configuration in three dimensions. Based on model parameters, we then calculate their angular widths and determine whether they should have been detected by STEREO-A, STEREO-B, Wind or ACE. We compare the results with corresponding in situ observations of ICMEs. We find that predictions of ICME detections on the base of COR2 data generally match well the actual in situ observations.  相似文献   

Low dispersive modeling of Rayleigh waves on partly staggered grids     

O. Rojas  B. Otero  J. E. Castillo  S. M. Day 《Computational Geosciences》2014,18(1):29-43

In elastic media, finite-difference (FD) implementations of free-surface (FS) boundary conditions on partly staggered grid (PSG) use the highly dispersive vacuum formulation (VPSG). The FS boundary is embedded into a “vacuum” grid layer (null Lame’s constants and negligible density values) where the discretized equations of motion allow computing surface displacements. We place a new set of compound (stress-displacement) nodes along a planar FS and use unilateral mimetic FD discretization of the zero-traction conditions for displacement computation (MPSG). At interior nodes, MPSG reduces to standard VPSG methods and applies fourth-order centered FD along cell diagonals for staggered differentiation combined with nodal second-order FD in time. We perform a dispersion analysis of these methods on a Lamb’s problem and estimate dispersion curves from the phase difference of windowed numerical Rayleigh pulses at two FS receivers. For a given grid sampling criterion (e.g., six or ten nodes per reference S wavelength λ ^S), MPSG dispersion errors are only a quarter of the VPSG method. We also quantify root-mean-square (RMS) misfits of numerical time series relative to analytical waveforms. MPSG RMS misfits barely exceed 10 % when nine nodes sample the minimum S wavelength $\lambda _{\text {MIN}}^{\mathrm {S}}$ in transit (along distances $\sim $ 145 $\lambda _{\text {MIN}}^{\mathrm {S}}$ ). In same tests, VPSG RMS misfits exceed 70 %. We additionally compare MPSG to a consistently fourth-order mimetic method designed on a standard staggered grid. The latter equates the former’s dispersion errors on grids twice denser and shows higher RMS precision only on grids with six or less nodes per $\lambda _{\text {MIN}}^{\mathrm {S}}$ .  相似文献