We provide a brief synopsis of the unique physical and ecological attributes of sandy beach ecosystems and review the main anthropogenic pressures acting on the world's single largest type of open shoreline. Threats to beaches arise from a range of stressors which span a spectrum of impact scales from localised effects (e.g. trampling) to a truly global reach (e.g. sea-level rise). These pressures act at multiple temporal and spatial scales, translating into ecological impacts that are manifested across several dimensions in time and space so that today almost every beach on every coastline is threatened by human activities. Press disturbances (whatever the impact source involved) are becoming increasingly common, operating on time scales of years to decades. However, long-term data sets that describe either the natural dynamics of beach systems or the human impacts on beaches are scarce and fragmentary. A top priority is to implement long-term field experiments and monitoring programmes that quantify the dynamics of key ecological attributes on sandy beaches. Because of the inertia associated with global climate change and human population growth, no realistic management scenario will alleviate these threats in the short term. The immediate priority is to avoid further development of coastal areas likely to be directly impacted by retreating shorelines. There is also scope for improvement in experimental design to better distinguish natural variability from anthropogenic impacts. Sea-level rise and other effects of global warming are expected to intensify other anthropogenic pressures, and could cause unprecedented ecological impacts. The definition of the relevant scales of analysis, which will vary according to the magnitude of the impact and the organisational level under analysis, and the recognition of a physical–biological coupling at different scales, should be included in approaches to quantify impacts. Zoning strategies and marine reserves, which have not been widely implemented in sandy beaches, could be a key tool for biodiversity conservation and should also facilitate spillover effects into adjacent beach habitats. Setback and zoning strategies need to be enforced through legislation, and all relevant stakeholders should be included in the design, implementation and institutionalisation of these initiatives. New perspectives for rational management of sandy beaches require paradigm shifts, by including not only basic ecosystem principles, but also incentives for effective governance and sharing of management roles between government and local stakeholders.

/pdf/threats-to-sandy-beach-ecosystems-a-review-50zdg3kglj.pdf

Threats to sandy beach ecosystems: A review

Monitoring the saltwater intrusion by time lapse electrical resistivity tomography: The Chioggia test site (Venice Lagoon, Italy)

Heat as a tracer to quantify water flow in near-surface sediments

[1] Two field data sets are used to model near-surface soil temperature profiles in a bare soil. It is shown that the commonly used solutions to the heat flow equations by Van Wijk perform well when applied at deeper soil layers, but result in large errors when applied to near surface layers, where more extreme variations in temperature occur. The reason for this is that these approaches do not consider heat sources or sinks below the surface. This paper proposes a new approach for modeling the surface soil temperature profiles from a single observation depth. This approach consists of two parts: 1) modeling an instantaneous ground flux profile based on net radiation and the ground heat flux at 5 cm depth; and 2) use of this ground heat flux profile to extrapolate a single temperature observation to a complete surface temperature profile. The new model is validated under different field and weather conditions showing low RMS errors of 1–3 K for wet to dry conditions. Finally, the proposed model is tested under limitations in input data that are associated with remote sensing applications. It is shown that these limitations result in only small increases in the overall error. This approach may be useful for satellite-based global energy balance applications. Citation: Holmes, T. R. H., M. Owe, R. A. M. De Jeu, and H. Kooi (2008), Estimating the soil temperature profile from a single depth observation: A simple empirical heatflow solution, Water Resour. Res., 44, W02412, doi:10.1029/2007WR005994.

/pdf/estimating-the-soil-temperature-profile-from-a-single-depth-36ij9xdm5k.pdf

Estimating the soil temperature profile from a single depth observation: A simple empirical heatflow solution

The dual-probe heat-pulse (DPHP) method is useful for measuring soil thermal properties. Measurements are made with a sensor that has two parallel cylindrical probes: one for introducing a pulse of heat into the soil (heater probe) and one for measuring change in temperature (temperature probe). We present a semianalytical solution that accounts for the finite radius and finite heat capacity of the heater and temperature probes. A closedform expression for the Laplace transform of the solution is obtained by considering the probes to be cylindrical perfect conductors. The Laplace-domain solution is inverted numerically. For the case where both probes have the same radius and heat capacity, we show that their finite properties have equal influence on the heat-pulse signal received by the temperature probe. The finite radius of the probes causes the heat-pulse signal to arrive earlier in time. This time shift increases in magnitude as the probe radius increases. The effect of the finite heat capacity of the probes depends on the ratio of the heat capacity of the probes (C 0 ) and the heat capacity of the soil (C). Compared with the case where C 0 /C = 1, the magnitude of the heat-pulse signal decreases (i.e., smaller change in temperature) and the maximum temperature rise occurs later when C 0 /C > 1. When C 0 /C < 1, the magnitude of the signal increases and the maximum temperature rise occurs earlier. The semianalytical solution is appropriate for use in DPHP applications where the ratio of probe radius (a 0 ) and probe spacing (L) satisfies the condition that a 0 /L £ 0.11. Abbreviations: DPHP, dual-probe heat-pulse; ICPC, identical cylindrical perfect conductors. The DPHP method is widely used for measuring soil thermal properties and volumetric water content. Measurements are made with a sensor that consists of two parallel cylindrical probes. The heater probe contains electrical resistance wire used to introduce heat at a constant rate during a finite time interval (typically 8–12 s), and the temperature probe contains a thermistor or thermocouple to measure the change in temperature as a function of time. If the distance between the probes and the rate and duration of heating are known, soil thermal properties (i.e., volumetric heat capacity, thermal conductivity, and thermal diffusivity) can be estimated from the transient temperature response by using an appropriate solution of the heat conduction equation. Volumetric water content can be determined from the volumetric heat capacity if the soil bulk density and the specific heat of the soil solid constituents are known.

/pdf/semianalytical-solution-for-dual-probe-heat-pulse-bo9faz43kw.pdf

Semianalytical Solution for Dual-Probe Heat-Pulse Applications that Accounts for Probe Radius and Heat Capacity

The Buenos Aires (Argentina) and Venice (Italy) coastlands have experienced significant saltwater contamination of the phreatic aquifer, coastal erosion, hydrodynamic changes and relative sea level rise processes due to natural and man-induced factors. These factors expose coastal areas to morpho-hydro-geological hazards, such as soil desertification, frequency and degree of flooding, littoral erosion, and the silting of river mouths and channels. Man-made interventions and actions, such as beach mining, construction of coastal structures and exploitation of aquifers without an adequate knowledge of the hydrology setting and an adequate management program, worsen these natural hazards. Uncontrolled human activity induces environmental damage to the overall coastal plains. The coastal plains play an important role in the social/economic development of the two regions based on land use, such as agriculture, horticulture, breeding, and tourism, as well as industry. Results of investigations on saltwater contamination, sea level rise and morphological changes recently performed in these two coastal areas are presented here.

Coastal processes and environmental hazards: the Buenos Aires (Argentina) and Venetian (Italy) littorals

A model based on an electrical analogy between a soil column and an electrical transmission line was developed to predict temperature and heat flow as functions of depth and time in a sandy soil, taking into account changes in soil thermal conductivity and volumetric heat capacity due to variations in water content. The model was excited alternatively by both measured soil temperature at the 1-cm depth and solar radiation [S r (t)], and solved with available electrical analysis software. The results were compared with field data collected during a 35-d field experiment carried out in the Lido beach, Venice, Italy. A very simple transfer function was identified for using measured S,(t) as the input signal. This transfer function turned out to vary inversely with S r (t). When the model is excited by temperature, and soil water content Corrected every 5 d, the root mean square error (RMSE) for the calculated temperature at the 5-cm depth is less than 1°C. When it is excited by S,(t), the RMSE at the 1-cm depth is less than 2°C. Hourly temperatures at different depths were found to depend strongly on surface phenomena, and to a lesser extent on other factors like soil water content below the top layers.

Predicting Temperature and Heat Flow in a Sandy Soil by Electrical Modeling

Heat diffusing away from a cylindrical heater embedded in soil with volumetric heat capacity ρc and thermal conductivity λ is modeled analogically and solved using available electrical circuit analysis software. Soil is considered to be divided into a series of heater-centered, cylindrical layers of carefully chosen thicknesses whose thermal resistances and capacitances can be represented by a ladder of variable electrical resistances and capacitances that are connected to a current source which represents heat flow. Starting from the basic analogy between heat flow in soil and current flow in an electrical transmission line of given distributed parameters, the modeling circuit was applied to heaters of cylindrical geometry and different sizes. The circuit was modified to account for finite probe-length effects and the thermal characteristics of the heater. Finite probe-length effects were modeled by enlarging the basic cylindrical diffusion layers at both ends. The thermal characteristics of the heater were represented with a ladder of variable electrical resistances and capacitances connected to the current source. The surrounding soil beyond the last cylindrical layer was modeled by a pure resistance through which capacitors finally discharge, thus representing heat diffusing farther into the soil. Model results compare well with the analytical solution for radial conduction of a short-duration heat pulse and with laboratory measurements carried out with sand. The simplicity, advantages, and range of applications of the electrical model are exposed briefly.

An Electrical Model of Heat Flow in Soil

A thermal method for a rapid measurement of groundwater velocity, particularly in aquifers with preferential flow where groundwater velocities over tenths of (m/d) are expected, was studied. Some instruments for measuring groundwater velocity are based on the application of heat. Those consisting of a central heater surrounded by several thermistors seem adequate for the above purpose, but their measuring range lies below 30m∕d (meters per day) and there are few works about their theory. Based on the diffusion-convection-dispersion equation, an electrical model is proposed for representing this type of instruments and a theoretical study is presented in an attempt to extend their measuring range. The model can be excited with any shape of power or temperature signals, allows the signals to be feedbacked for controlling the heater’s excitation, and includes the thermal features of the heater and thermistors. The model was validated through laboratory tests with velocities of up to 100m∕d and extrapolated u...

Numerical and experimental study of a thermal probe for measuring groundwater velocity.

Fil: Guaraglia, Dardo Oscar. Universidad Nacional de la Plata. Facultad de Ingenieria. Departamento de Hidraulica. Area Hidraulica Basica; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata; Argentina

Dardo Oscar Guaraglia

Papers

Coastal processes and environmental hazards: the Buenos Aires (Argentina) and Venetian (Italy) littorals

Predicting Temperature and Heat Flow in a Sandy Soil by Electrical Modeling

An Electrical Model of Heat Flow in Soil

Numerical and experimental study of a thermal probe for measuring groundwater velocity.

Introduction to Modern Instrumentation: For Hydraulics and Environmental Sciences