Floodplain hydrology of the Mekong Delta,Vietnam

The Mekong Delta is one of the largest and most intensively used estuaries in the world. Each year it witnesses widespread flooding which is both the basis of the livelihood for more than 17 million people but also the major hazard. Therefore, a thorough understanding of the hydrologic and hydraulic features is urgently required for various planning purposes. While the general causes and characteristics of the annual floods are understood, the inundation dynamics in the floodplains in Vietnam which are highly controlled by dikes and other control structures have not been investigated in depth. Especially, quantitative analyses are lacking, mainly due to scarce data about the inundation processes in the floodplains. Therefore, a comprehensive monitoring scheme for channel and floodplain inundation was established in a study area in the Plain of Reeds in the northeastern part of the Vietnamese Delta. This in situ data collection was complemented by a series of high‐resolution inundation maps derived from the TerraSAR‐X satellite for the flood seasons 2008 and 2009. Hence, the inundation dynamics in the channels and floodplains, and the interaction between channels and floodplains, could be quantified for the first time. The study identifies the strong human interference which is governed by flood protection levels, cropping patterns and communal water management. In addition, we examine the tidal influence on the inundation in various parts of the Delta, since it is expected that climate change‐induced sea level rise will increase the tidal contribution to floodplain inundation. Copyright © 2011 John Wiley & Sons, Ltd.     

Models of natural and human dynamics in forest landscapes: Cross-site and cross-cultural synthesis

We synthesize the study of coupled natural and human systems across sites and cultures through a process of simplification and abstraction based on multiple dimensions of human-nature connectedness: satisfaction of basic needs, psycho-cultural connectedness and regulation of use of natural resources. We thus provide both a place-based and general understanding of value-driven anthropogenic environmental change and response. Two questions guide this research: what are the crucial stakeholder values that drive land use decisions and thus land cover change? And how can knowledge of these values be used to make decisions and policies that sustain both the human and natural systems in a place? To explore these questions we build simulation models of four study sites, two in the State of Texas, United States, and two in Venezuela. All include protected areas, though they differ in the specifics of vegetation and land use. In the Texas sites, relatively affluent individuals are legally converting forests to residential, commercial, and industrial uses, while in Venezuela landless settlers are extra-legally converting forests for purposes of subsistence agriculture. Contemporary modeling techniques now facilitate simulations of stakeholder and ecosystem dynamics revealing emergent patterns. Such coupled human and natural systems are currently recognized as a form of biocomplexity. Our modeling framework is flexible enough to allow adaptation to each of the study sites, capturing the essential features of the respective natural and anthropogenic land use changes and stakeholder reactions. The interactions between human stakeholders are simulated using multi-agent models that act on forest landscape models, and receive feedback of the effects of these actions on ecological habitats and hydrological response. The multi-agent models employ a formal logic-based method for the Venezuelan sites and a decision analysis approach using multi-attribute utility functions for the Texas sites, differing more in style and emphasis than in substance. Our natural-systems models are generic and can be tailored according to site-specific conditions. Similar models of tree growth and patch transitions are used for all the study sites and the differing responses to environmental variables are specified for each local species and terrain conditions.     

Revisit the calibration errors on experimental slant total electron content (TEC) determined with GPS

The calibration errors on experimental slant total electron content (TEC) determined with global positioning system (GPS) observations is revisited. Instead of the analysis of the calibration errors on the carrier phase leveled to code ionospheric observable, we focus on the accuracy analysis of the undifferenced ambiguity-fixed carrier phase ionospheric observable determined from a global distribution of permanent receivers. The results achieved are: (1) using data from an entire month within the last solar cycle maximum, the undifferenced ambiguity-fixed carrier phase ionospheric observable is found to be over one order of magnitude more accurate than the carrier phase leveled to code ionospheric observable and the raw code ionospheric observable. The observation error of the undifferenced ambiguity-fixed carrier phase ionospheric observable ranges from 0.05 to 0.11 total electron content unit (TECU) while that of the carrier phase leveled to code and the raw code ionospheric observable is from 0.65 to 1.65 and 3.14 to 7.48 TECU, respectively. (2) The time-varying receiver differential code bias (DCB), which presents clear day boundary discontinuity and intra-day variability pattern, contributes the most part of the observation error. This contribution is assessed by the short-term stability of the between-receiver DCB, which ranges from 0.06 to 0.17 TECU in a single day. (3) The remaining part of the observation errors presents a sidereal time cycle pattern, indicating the effects of the multipath. Further, the magnitude of the remaining part implies that the code multipath effects are much reduced. (4) The intra-day variation of the between-receiver DCB of the collocated stations suggests that estimating DCBs as a daily constant can have a mis-modeling error of at least several tenths of 1 TECU.     

Taxonomic revision of Cylindroporella ? lusitanica Ramalho, 1970: In search for the origins of the Family Dasycladaceae

A study of new material of Cylindroporella ? lusitanica Ramalho, 1970, from the Upper Jurassic (Oxfordian) strata of Portugal identified features not observed previously. This includes the pattern of its laterals, including the gametophores. The algal body plan is unique and justifies the taxonomic reassessment of this species and the introduction of Barattoloporellopsis n. gen. Furthermore this species is most likely a primitive Dasycladaceae, a “missing link” between the modern ones (starting from the Cretaceous times) and their Jurassic ancestors.     

Screening model for volatile pollutants in dual porosity soils

This paper develops mass fraction models for transport and fate of agricultural pollutants in structured two-region soils. Mass fraction index models, based on a semi-infinite domain solution, are derived that describe leaching at depth, vapor losses through soil surface, absorption, and degradation in the dynamic- and stagnant-water soil regions. The models predict that leaching is the result of the combined effect of the upward vapor-phase transport relative to downward advection, residence time relative to half-life, dispersion, and lateral diffusive mass transfer. Simulations show that leached fraction of volatile compounds does not always decrease monotonically with increased residence time relative to the pollutant half-life, as a result of complex interactions among the different physical and biochemical processes. The results show that leaching, volatilization, and degradation losses can be affected significantly by lateral diffusive mass transfer into immobile-water regions and advection relative to dispersion (i.e. Peclet number) in the mobile-water regions. It is shown that solute diffusion into the immobile phase and subsequent biochemical decay reduces leaching and vapor losses through soil surface. Potential use of the modified leaching index for the screening of selected pesticides is illustrated for different soil textures and infiltration rates. The analysis may be useful to the management of pesticides and the design of landfills.     

Methods for estimating the velocities of the Brazil Current in the pre-salt reservoir area off southeast Brazil (23∘ S–26∘ S)

The Brazil Current (BC) is likely the least observed and investigated subtropical western boundary current in the world. This study proposes a simple and systematic methodology to estimate quasi-synoptic cross-sectional speeds of the BC within the Santos Basin (23^° S–26^° S) based on the dynamic method using several combinations of data: Conductivity, temperature, and depth (CTD), temperature profiles, CTD and vessel-mounted Acoustic Doppler Current Profiler (VMADCP), and temperature profiles and VMADCP. All of the geostrophic estimates agree well with lowered Acoustic Doppler Current Profiler (LADCP) velocity observations and yield volume transports of -5.56 ±1.31 and 2.50 ±1.01 Sv for the BC and the Intermediate Western Boundary Current (IWBC), respectively. The LADCP data revealed that the BC flows southwestward and is ～100 km wide, 500 m deep, and has a volume transport of approximately -5.75 ±1.53 Sv and a maximum speed of 0.59 m s^?1. Underneath the BC, the IWBC flows northeastward and has a vertical extent of approximately 1,300 m, a width of ～60 km, a maximum velocity of ～0.22 m s?¹, and a volume transport of 4.11 ± 2.01 Sv. Our analysis indicates that in the absence of the observed velocities, the isopycnal (σ ₀) of 26.82 kg m^?3 (～500 dbar) is an adequate level of no motion for use in geostrophic calculations. Additionally, a simple linear relationship between the temperature and the specific volume anomaly can be used for a reliable first estimate of the BC-IWBC system in temperature-only transects.     

Polar motion for an elastic Earth model with a homogeneous liquid core using a canonical theory

The rotational motion for an elastic Earth model with a homogeneous liquid core has been obtained using Hamilton's equations. From the canonical equations for the precessional and nutational motions in an inertial frame, the corresponding equations in an Earth fixed frame are deduced. The linearized equations obtained for polar motion and liquid core motion are equivalent to the Sasao-Okubo-Saito equations.     

On the cumulant expansion up scaling of ground water contaminant transport equation with nonequilibrium sorption

The laboratory-scale ground water transport equation with nonequilibrium sorption reaction subjected to unsteady, nondivergence-free, and nonstationary velocity fields is up-scaled to the field-scale by using the ensemble-averaged equations obtained from the cumulant expansion ensemble-averaging method. It is found that existing ensemble-averaged equations obtained with the help of the cumulant expansion method for the system of linear partial differential equations are not second-order exact. Although the cumulant expansion methodology is designed for noncommuting operators, it is found that there are still commudativity requirements that need to be satisfied by the functions and constants exist in the coefficient matrix of the system of ordinary/partial differential equations. A reversibility requirement, which covers the commudativity requirements, is also proposed when applying the cumulant expansion method to a system of partial differential equations/a partial differential equation. The significance of the new velocity correction obtained in this study due to the applied second-order exact cumulant expansion is investigated on a numerical example with a linear trend in the distribution coefficient. It is found that the effect of the new velocity correction can be significant enough to affect the maximum concentration values and the plume center of mass in the case of a trending distribution coefficient in a physically heterogeneous environment.     

EVA: GPS-based extended velocity and acceleration determination

In this work, a new GPS carrier phase-based velocity and acceleration determination method is presented that extends the effective range of previous techniques. The method is named ‘EVA’, and may find applications in fields such as airborne gravimetry when rough terrain or water bodies make difficult or impractical to set up nearby GPS reference receivers. The EVA method is similar to methods such as Kennedy (Precise acceleration determination from carrier phase measurements. In: Proceedings of the 15th international technical meeting of the satellite division of the Institute of Navigation. ION GPS 2002, Portland pp 962–972, 2002b) since it uses L1 carrier phase observables for velocity and acceleration determination. However, it introduces a wide network of stations and it is independent of precise clock information because it estimates satellite clock drifts and drift rates ‘on-the-fly’, requiring only orbit data of sufficient quality. Moreover, with EVA the solution rate is only limited by data rate, and not by the available precise satellite clocks data rate. The results obtained are more robust for long baselines than the results obtained with the reference Kennedy method. An advantage of being independent of precise clock information is that, beside IGS Final products, also the Rapid, Ultra-Rapid (observed) and Ultra-Rapid (predicted) products may be used. Moreover, the EVA technique may also use the undifferenced ionosphere-free carrier phase combination (LC), overcoming baseline limitations in cases where ionosphere gradients may be an issue and very low biases are required. During the development of this work, some problems were found in the velocity estimation process of the Kennedy method. The sources of the problems were identified, and an improved version of the Kennedy method was used for this research work. An experiment was performed using a light aircraft flying over the Pyrenees, showing that both EVA and the improved Kennedy methods are able to cope with the dynamics of mountainous flight. A RTK-derived solution was also generated, and when comparing the three methods to a known zero-velocity reference the results yielded similar performance. The EVA and the improved-Kennedy methods outperformed the RTK solutions, and the EVA method provided the best results in this experiment. Finally, both the improved version of the Kennedy method and the EVA method were applied to a network in equatorial South America with baselines of more than 1,770 km, and during local noon. Under this tough scenario, the EVA method showed a clear advantage for all components of velocity and acceleration, yielding better and more robust results.     

Water balance in the playa-lakes of an arid environment,Monegros, NE Spain

The playa-lakes of the Monegros desert in north-east Spain are saline wetlands in an arid environment, a rare phenomenon in Europe. These extremely valuable habitats are threatened by changes associated with agricultural expansion and incorporation of new irrigated areas. An understanding of the present hydrologic regime will enable changes to be identified, particularly those brought about by flooding and pollution caused by irrigation surplus. This study sets out to show the results of applying a daily water balance in three selected playa-lakes. The balance was in two parts and consisted of: (1) the average balance for all the endorheic basin using the BALAN_11 program, and (2) the water balance in some playa-lakes, applying discharge flows obtained from the previous balance. The resulting volumes of water were converted to water depths and contrasted with reference volumes taken from field and Landsat images. The model was calibrated by applying various hypotheses of function which enabled the results to be adjusted. The proposed balance is an acceptable reproduction of field water measurements during this period, and underlines the consistency of the conceptual model. The methodology used is appropriate for understanding the playa-lakes function and for monitoring them for conservation purposes.