Post-fire management effects on sediment (dis)connectivity in Mediterranean forest ecosystems: Channel and catchment response     

Javier González-Romero  Manuel López-Vicente  Elena Gómez-Sánchez  Esther Peña-Molina  Pablo Galletero  Pedro Plaza-Alvarez  Daniel Moya  Jorge De las Heras  Manuel Esteban Lucas-Borja 《地球表面变化过程与地形》2021,46(13):2710-2727

Forest fires and post-fire practices influence sediment connectivity (SC). In this study, we use the ‘aggregated index of connectivity’ (AIC) to assess SC in five Mediterranean catchments (198–1090 ha) affected by a wildfire in 2012 in south-eastern Spain. Two temporal scenarios were considered, immediately after the fire and before post-fire management, and 2 years after the fire including all practices (hillslope barriers, check-dams, afforestation, salvage logging and skid trails). One LiDAR (light detection and ranging)-derived digital elevation model (DEM, 2 m × 2 m resolution) was generated, per scenario. The five catchment outlets were established as the computation target (AIC_OUT), and structural and functional SC were calculated. Index outputs were normalized to make the results of the non-nested catchments comparable (AIC_N-OUT). The output analysis includes the SC distribution along the catchments and at local scale (929 sub-catchments, 677 in the burned area), the hillslope and channel measures' effect on SC, and a sedimentological analysis using observed area-specific sediment yield (SSY) at 10 new (built after post-fire practices) concrete check-dams located in the catchments (SSY = 1.94 Mg ha⁻¹ yr⁻¹; σ = 1.22). The catchments with more circular shapes and steeper slopes were those with higher AIC_N-OUT. The structural SC maps – removing the rainfall erosivity influence – allowed evaluating the actual role played by the post-fire practices that reduced SC ( $\overline{x}$= − 1.19%; σ = 0.41); while functional SC was linked to the actual change of SC ( $\overline{x}$= + 5.32%; σ = 0.62). Hillslope treatments resulted in significant changes on AIC_N-OUT at sub-catchment scale with certain disconnectivity. A good and positive correlation was found between the SSY and the changes of AIC_N-OUT. However, the coarse DEM resolution explained the lack of effect of the rock check-dams – located on the secondary channels – on AIC_N-OUT. AIC_N-OUT proved to be a useful tool for decision making in post-fire restoration, but an optimal input data is still necessary to refine calculations.  相似文献   

Chronic food limitation of egg production in populations of copepods of the genusAcartia in the San Francisco estuary     

Wim J. Kimmerer  Nissa Ferm  Mary Helen Nicolini  Carolina Peñalva 《Estuaries and Coasts》2005,28(4):541-550

Egg production of planktonic copepods, is commonly measured as a proxy for secondary production in population dynamics studies and for quantifying food limitation. Although limitation of copepod egg production by food quantity or quality is common in natural waters, it appears less common or severe in estuaries where food concentrations are often high. San Francisco Estuary, California, has unusually low concentrations of chlorophyll compared to other estuaries. We measured egg production rates of three species ofAcartia, with dominate the zooplankton biomass at salinity above 15 psu, on 36 occasions during 1999–2002. Egg production was determined by incubating up to 40 freshly collected individual copepods for 24 h in 140 ml of ambient water. Egg production was less than 10 eggs female⁻¹ d⁻¹ most of the year, but as high as 52 eggs female⁻¹ d⁻¹ during month-long spring phytoplankton blooms. Egg production was a saturating function of total chlorophyll concentration with a mean of 30 eggs female⁻¹ d⁻¹ above a chlorophyll concentration of 12±6 mg chl m⁻³. We take chlorophyll to be a proxy for total food ofAcartia, known to feed on microzooplankton as well as phytoplankton. These findings, together with long-term records of chlorophyll, concentration and earlier studies of abundance of nauplius larvae in the estuary, imply chronic food limitation ofAcartia species, with sufficient food for maximum egg production <10% of the time over the last 25 yr. These results may show the most extreme example of food limitation of copepod reproduction in any temperate estuary. They further support the idea that estuaries may provide suitable habitat forAcartia species by virtue of other factors than high food concentration.  相似文献   

Quasigeoids for the Territory of the Czech Republic     

Kostelecký  J.  Kostelecký  J.  Pešek  I.  Šimek  J.  Švábenský  O.  Weigel  J.  Zeman  A. 《Studia Geophysica et Geodaetica》2004,48(3):503-518

Several quasigeoid models for the Czech Republic have been developed for different purposes since mid-seventies using different data sources: gravimetric, astronomical and GPS/levelling observations, as well as data gained from the territories of neighbouring countries. Two of the recent solutions, namely the VUGTK96 quasigeoid obtained from heterogeneous data and gravimetric quasigeoid CR2000 are described and compared. Accuracies of the models were estimated with the help of accuracy characteristics resulting from the processing, by comparison with GPS/levelling results available for most of the territory, and, finally, tested on a special GPS/levelling profile across the steepest slope of the quasigeoid surface in the south-eastern part of the territory. It is shown that the CR2000 gravimetric quasigeoid is suitable for transformation of ellipsoidal GPS heights to the gravity related heights with an accuracy of 3 cm.  相似文献   

Simultaneous determination of Earth orientation parameters and station coordinates from combination of results of different observation techniques     

I. Pešek  J. Kostelecký 《Studia Geophysica et Geodaetica》2006,50(4):537-548

Described is a method for non-regular combination of different techniques, where the normal equations matrix cannot be restored, to obtain a representative set of Earth orientation parameters and station coordinates. The method is based on combining station position vectors transformed to the celestial reference frame, where they are functions of both the EOP and the station coordinates. Three types of constraints are applied to stabilize the system, separate celestial pole offset from polar motion and, to tie the EOP between individual epochs. VLBI, GPS, SLR and Doris data as collected for the ‘IERS SINEX Combination Campaign’ was used to check the method. After combination, dispersion of station coordinates decreased from 0.040 to 0.031 m. The effect of the combination on EOP is of the order of 0.2 mas and it can be seen in Figs. 3 and 4 as a difference of the final and a priori values.  相似文献   

On the dynamics of rocking motion of single rigid‐block structures     

F. Peña  F. Prieto  P. B. Lourenço  A. Campos Costa  J. V. Lemos 《地震工程与结构动力学》2007,36(15):2383-2399

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Evaluating and modelling the hydrological and erosive behaviour of an olive orchard microcatchment under no‐tillage with bare soil in Spain     

E. V. Taguas  J. L. Ayuso  A. Peña  Y. Yuan  R. Pérez 《地球表面变化过程与地形》2009,34(5):738-751

Despite the high risk of erosion in olive orchards located in mountainous areas in Spain, little research has been carried out to account for the complexity and interaction of the natural processes of runoff and soil erosion on the catchment scale or small catchment scale. In this study, a microcatchment of 6·7 ha in a mountainous area under no‐tillage farming with bare soil was set up to record runoff and sediment. Soil erosion and runoff patterns were monitored over a two‐year period. Totally, 22 events were observed. The data were analysed, and then used to calibrate the AnnAGNPS model, which allowed us to complete the data period and describe the hydrological and erosive behaviour on a monthly and annual basis. A high variability in catchment responses was observed, due to differences in the storms and to the effect of the surface soil moisture content. Maximum intensities of 10 and 30 min determined the final runoff values while the total sediment loads were dependent on the rainfall depth. The impact of management on the reduction of porosity can explain the relationship between runoff and intensity in the microcatchment. However, the impact of the spatial scale meant that the transport of sediment required substantial rainfall depths to ensure a continuous flow from the hillslopes. The results of the calibration (E >0·60 and r >0·75) on the event and monthly scale confirmed the applicability of AnnAGNPS to predict runoff and erosion in the microcatchment. The predicted average runoff coefficient was 3·3% for the study period and the total average sediment loads, 1·3 Mg/ha/yr. Despite these low values, the model simulation showed that much larger runoff coefficients and soil losses can be expected for periods with several consecutive years in which the annual rainfall depth was over 500 mm. The use of cover is recommended to prevent the high levels of erosion associated with these conditions. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Bioturbation and erosion rates along the soil-hillslope conveyor belt,part 2: Quantification using an analytical solution of the diffusion–advection equation     

Andrea Román-Sánchez  Ana Laguna  Tony Reimann  Juan Vicente Giráldez  Adolfo Peña  Tom Vanwalleghem 《地球表面变化过程与地形》2019,44(10):2066-2080

Particles on soil-mantled hillslopes are subject to downslope transport by erosion processes and vertical mixing by bioturbation. Both are key processes for understanding landscape evolution and soil formation, and affect the functioning of the critical zone. We show here how the depth–age information, derived from feldspar-based single grain post-infrared infrared stimulated luminescence (pIRIR), can be used to simultaneously quantify erosion and bioturbation processes along a hillslope. In this study, we propose, for the first time, an analytical solution for the diffusion–advection equation to calculate the diffusivity constant and erosion–deposition rates. We have fitted this model to age–depth data derived from 15 soil samples from four soil profiles along a catena located under natural grassland in the Santa Clotilde Critical Zone Observatory, in the south of Spain. A global sensitivity analysis was used to assess the relative importance of each model parameter in the output. Finally, the posterior probability density functions were calculated to evaluate the uncertainty in the model parameter estimates. The results show that the diffusivity constant at the surface varies from 11.4 to 81.9 mm² a^-1 for the hilltop and hill-base profile, respectively, and between 7.4 and 64.8 mm² a^-1 at 50 cm depth. The uncertainty in the estimation of the erosion–deposition rates was found to be too high to make a reliable estimate, probably because erosion–deposition processes are much slower than bioturbation processes in this environment. This is confirmed by a global sensitivity analysis that shows how the most important parameters controlling the age–depth structure in this environment are the diffusivity constant and regolith depth. Finally, we have found a good agreement between the soil reworking rates proposed by earlier studies, considering only particle age and depth, and the estimated diffusivity constants. The soil reworking rates are effective rates, corrected for the proportion of particles actually participating in the process. © 2019 John Wiley & Sons, Ltd.  相似文献   

Forward stratigraphic modelling of sediment pathways and depocentres in salt‐influenced passive‐margin basins: Lower Cretaceous,central Scotian Basin     

Christopher Sangster  David J. W. Piper  Nicolas Hawie  Georgia Pe‐Piper  Francky Saint‐Ange 《Basin Research》2019,31(4):728-753

Source‐to‐sink studies and numerical modelling software are increasingly used to better understand sedimentary basins, and to predict sediment distributions. However, predictive modelling remains problematic in basins dominated by salt tectonics. The Lower Cretaceous delta system of the Scotian Basin is well suited for source‐to‐sink studies and provides an opportunity to apply this approach to a region experiencing active salt tectonism. This study uses forward stratigraphic modelling software and statistical analysis software to produce predictive stratigraphic models of the central Scotian Basin, test their sensitivity to different input parameters, assess proposed provenance pathways, and determine the distribution of sand and factors that control sedimentation in the basin. Models have been calibrated against reference wells and seismic surfaces, and implement a multidisciplinary approach to define simulation parameters. Simulation results show that previously proposed provenance pathways for the Early Cretaceous can be used to generate predictive stratigraphic models, which simulate the overall sediment distribution for the central Scotian Basin. Modelling confirms that the shaly nature of the Naskapi Member is the result of tectonic diversion of the Sable and Banquereau rivers and suggests additional episodic diversion during the deposition of the Cree Member. Sand is dominantly trapped on the shelf in all units, with transport into the basin along salt corridors and as a result of turbidity current flows occurring in the Upper Missisauga Formation and Cree Member. This led to sand accumulation in minibasins with a large deposit seawards of the Tantallon M‐41 well. Sand also appears to bypass the basin via salt corridors which lead to the down‐slope edge of the study area. Sensitivity analysis suggests that the grain size of source sediments to the system is the controlling factor of sand distribution. The methodology applied to this basin has applications to other regions complicated by salt tectonics, and where sediment distribution and transport from source‐to‐sink remain unclear.  相似文献   

The Mesolithic–Neolithic transition in southern Iberia     

Miguel Cortés Sánchez  Francisco J. Jiménez Espejo  María D. Simón Vallejo  Juan F. Gibaja Bao  António Faustino Carvalho  Francisca Martinez-Ruiz  Marta Rodrigo Gamiz  José-Abel Flores  Adina Paytan  José A. López Sáez  Leonor Peña-Chocarro  José S. Carrión  Arturo Morales Muñiz  Eufrasia Roselló Izquierdo  José A. Riquelme Cantal  Rebecca M. Dean  Emília Salgueiro  Rafael M. Martínez Sánchez  Nuno F. Bicho 《Quaternary Research》2012,77(2):221-234

New data and a review of historiographic information from Neolithic sites of the Malaga and Algarve coasts (southern Iberian Peninsula) and from the Maghreb (North Africa) reveal the existence of a Neolithic settlement at least from 7.5 cal ka BP. The agricultural and pastoralist food producing economy of that population rapidly replaced the coastal economies of the Mesolithic populations. The timing of this population and economic turnover coincided with major changes in the continental and marine ecosystems, including upwelling intensity, sea-level changes and increased aridity in the Sahara and along the Iberian coast. These changes likely impacted the subsistence strategies of the Mesolithic populations along the Iberian seascapes and resulted in abandonments manifested as sedimentary hiatuses in some areas during the Mesolithic–Neolithic transition. The rapid expansion and area of dispersal of the early Neolithic traits suggest the use of marine technology. Different evidences for a Maghrebian origin for the first colonists have been summarized. The recognition of an early North-African Neolithic influence in Southern Iberia and the Maghreb is vital for understanding the appearance and development of the Neolithic in Western Europe. Our review suggests links between climate change, resource allocation, and population turnover.  相似文献   

Major moisture sources for Western and Southern India and their role on synoptic‐scale rainfall events     

Paulina Ordóñez  Pedro Ribera  David Gallego  Cristina Peña‐Ortiz 《水文研究》2012,26(25):3886-3895

Although the identification of the moisture sources of a region is of prominent importance to characterize precipitation, the origin and amount of moisture towards the Indian Subcontinent and its relationship with the occurrence of precipitation are still not completely understood. In this article, the origin of the atmospheric water arriving to the Western and Southern India during a period of 5 years (1 January 2000–31 December 2004) is investigated by using a Lagrangian diagnosis method. This methodology computes budgets of evaporation minus precipitation by calculating changes in the specific humidity of thousands of air particles aimed to the study area following the observed winds. During the summer monsoon, the main supply of moisture is the Somali Jet, which crosses the equator by the West Indian Ocean. The recycling process is the main water vapour source in winter. Two additional moisture sources located over northwestern India and the Bay of Bengal are identified. A 30% increase in the moisture flux from the Indian Ocean has been related to the occurrence of strong precipitation in the area, and at the end of the monsoon, the recycling became a significant contribution to the last part of the wet season of Western and Southern India. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献