Estimating Forest Ecosystem Evapotranspiration at Multiple Temporal Scales With a Dimension Analysis Approach1

Abstract:  It is critical that evapotranspiration (ET) be quantified accurately so that scientists can evaluate the effects of land management and global change on water availability, streamflow, nutrient and sediment loading, and ecosystem productivity in watersheds. The objective of this study was to derive a new semi‐empirical ET modeled using a dimension analysis method that could be used to estimate forest ET effectively at multiple temporal scales. The model developed describes ET as a function of water availability for evaporation and transpiration, potential ET demand, air humidity, and land surface characteristics. The model was tested with long‐term hydrometeorological data from five research sites with distinct forest hydrology in the United States and China. Averaged simulation error for daily ET was within 0.5 mm/day. The annual ET at each of the five study sites were within 7% of measured values. Results suggest that the model can accurately capture the temporal dynamics of ET in forest ecosystems at daily, monthly, and annual scales. The model is climate‐driven and is sensitive to topography and vegetation characteristics and thus has potential to be used to examine the compounding hydrologic responses to land cover and climate changes at multiple temporal scales.     

Watershed Evapotranspiration Increased due to Changes in Vegetation Composition and Structure Under a Subtropical Climate1

Abstract: Natural forests in southern China have been severely logged due to high human demand for timber, food, and fuels during the past century, but are recovering in the past decade. The objective of this study was to investigate how vegetation cover changes in composition and structure affected the water budgets of a 9.6‐km² Dakeng watershed located in a humid subtropical mountainous region in southern China. We analyzed 27 years (i.e., 1967‐1993) of streamflow and climate data and associated vegetation cover change in the watershed. Land use/land cover census and Normalized Difference of Vegetation Index (NDVI) data derived from remote sensing were used to construct historic land cover change patterns. We found that over the period of record, annual streamflow (Q) and runoff/precipitation ratio did not change significantly, nor did the climatic variables, including air temperature, Hamon’s potential evapotranspiration (ET), pan evaporation, sunshine hours, and radiation. However, annual ET estimated as the differences between P and Q showed a statistically significant increasing trend. Overall, the NDVI of the watershed had a significant increasing trend in the peak spring growing season. This study concluded that watershed ecosystem ET increased as the vegetation cover shifted from low stock forests to shrub and grasslands that had higher ET rates. A conceptual model was developed for the study watershed to describe the vegetation cover‐streamflow relationships during a 50‐year time frame. This paper highlighted the importance of eco‐physiologically based studies in understanding transitory, nonstationary effects of deforestation or forestation on watershed water balances.     

European monitoring for raptors and owls: state of the art and future needs

Sixty-four percent of the 56 raptor and owl species that occur in Europe have an unfavorable conservation status. As well as requiring conservation measures in their own right, raptors and owls function as useful sentinels of wider environmental "health," because they are widespread top predators, relatively easy to monitor, and sensitive to environmental changes at a range of geographical scales. At a time of global acknowledgment of an increasing speed of biodiversity loss, and new, forward-looking and related European Union biodiversity policy, there is an urgent need to improve coordination at a pan-European scale of national initiatives that seek to monitor raptor populations. Here we describe current initiatives that make a contribution to this aim, particularly the current "MEROS" program, the results of a questionnaire survey on the current state of national raptor monitoring across 22 BirdLife Partners in Europe, the challenges faced by any enhanced pan-European monitoring scheme for raptors, and some suggested pathways for efficiently tapping expertise to contribute to such an initiative.     

PUMP-CTD-System for trace metal sampling with a high vertical resolution. A test in the Gotland Basin, Baltic Sea

It is a great challenge to sample seawater across interfaces, for example the halocline or the redoxcline, to investigate trace metal distribution. With the use of 10l sampling bottles mounted to a wire or a CTD-Rosette it is possible to obtain a maximum vertical resolution of 5m. For the detection of small vertical structures in the vertical distribution of trace metals across the redoxcline, the CTD-Bottle-Rosette is not sufficient. Therefore, a PUMP-CTD-System was developed, which enables water sampling with high resolution (1m maximum) along a vertical profile. To investigate the suitability and possible contamination sources of this device two experiments were carried out in the Gotland Basin. The first experiment consisted of two separate profiles. The first profile was obtained with the CTD-Bottle-Rosette and the second with the PUMP-CTD-System. Both were taken from the bottom to the surface water layer. The second experiment was a combined profile obtained from the surface to the bottom with the PUMP-CTD-System attached to the CTD-Bottle-Rosette. Concentrations of dissolved Pb, Cd, Cu, Zn, Fe, Mn, Co and Ni from the "Niskin Bottles" and from the PUMP were measured and compared for each investigation. We demonstrate that it is useful to perform vertical sampling from lower to higher concentrations, e.g. surface to bottom in this environment, and that a longer flushing is required for sampling seawater in the anoxic bottom water. A comparison of the two systems for oxygen and hydrogen sulphide measurements showed an improvement of the precision and the quality of the sampling when using the PUMP. Thus, metal speciation at the oxic-anoxic gradient zone and on a high vertical resolution will be accessible. As concentrations of dissolved Pb, Cd, Cu, Zn, Co, Ni, Fe and Mn in seawater sampled with both devices were in the same range, we conclude that the PUMP-CTD-System is well suited to sample seawater for trace metal analyses.     

Removal and degradation of aromatic compounds from a highly polluted site by coupling soil washing with photocatalysis

The possible application of two environmental remediation technologies - soil washing and photocatalysis - to remove and decompose various aromatic pollutants present in excavated soils of a contaminated industrial site has been investigated. Aqueous solutions containing the non-ionic surfactant Brij 35 were used to extract the contaminants from the soil samples. The photocatalytic treatment of the obtained washing wastes, performed in the presence of TiO(2) suspensions irradiated with simulated sunlight, showed a slow abatement of the toxic compounds due to the relevant concentrations of organics in the waste. A neat improvement of the process performances, obtained by operating in the presence of added potassium peroxydisulfate, suggests a feasible treatment route.     

Leaf accumulation of trace elements and polycyclic aromatic hydrocarbons (PAHs) in Quercus ilex L

Quercus ilex L. leaves were collected four times in one year at six urban sites and one remote area in order to determine trace element and PAH accumulation through concomitant analyses of unwashed and water-washed leaves. Both unwashed and washed leaves showed the highest amounts of trace elements and PAHs in the urban area. Unwashed leaves showed greater differences between urban and remote areas and among the urban sites than washed leaves for trace element and PAH concentrations. Water-washing resulted in a significant (P<0.001) decrease in leaf concentrations of Cr, Cu, Fe, Pb, V and Zn. By contrast, Cd and total PAH concentrations showed no differences between unwashed and washed leaves.     

Wind direction bias in generating wind roses and conducting sector-based air dispersion modeling

Certain widely used wind rose programs and air dispersion models use an overly simple data-transfer algorithm that induces a directional bias in their output products. The purpose of this paper is to provide a revised algorithm that corrects the directional bias that occurs from the aliasing that occurs when the sector widths used to report wind direction data are on the same order of magnitude, but not equal, to the sector widths used in the wind direction summaries. The directional bias issue arises when output products in 16 direction sectors (22.5 degrees each) are produced from wind direction data reported in terms of 36 sectors (10 degrees each). The result directional bias affects the results of simulations of air and surface concentrations using widely applied air dispersion models. Datasets or models with the directional bias discussed here give consistent positive biases (approximately 30%) for cardinal direction sectors (north, south, east, and west) and consistent negative biases for all of the other sectors (around -10%). Data summary and air dispersion programs providing outputs in direction sectors that do not match the observational sectors need to be checked for this bias. A revised data-transfer algorithm is provided that corrects the directional bias that can occur in transferring wind direction data between different sector widths.     

Seasonal Variation of Toxic Benzene Emissions in Petroleum Refinery

Petroleum refineries are largest chemical industries that are responsible for the emission of several pollutants into the atmosphere. Benzene is among the most important air pollutants that are emitted by petroleum refineries, since they are involved in almost every refinery process. Volatile organic compounds (VOCs) are a major group of air pollutants, which play a critical role in atmospheric chemistry. These contribute to toxic oxidants, which are harmful to ecosystem, human health and atmosphere. The variability of pollutants is an important factor in determining human exposure to these chemicals. The ambient air concentrations of benzene were measured in several sites around the Digboi petroleum refinery, near the city of Gowahati in northeast India, during winter and summer 2004. The seasonal and spatial variations of the ambient air concentrations of this benzene were investigated and analyzed. An estimation of the contribution of the refinery to the measured atmospheric levels of benzene was also performed. The ambient air mixing ratios of benzene in a large area outside the refinery was generally low, in ppbv range, much lower than the ambient air quality standards. This article presents the temporal and spatial variation of air pollution in and around petroleum refinery and showed that no health risk due to benzene is present in the areas adjacent to the refinery.     

Impact of continental margins in the Mediterranean Sea: Hints from the surface colour and temperature historical record

The surface colour and temperature fields of the Mediterranean Sea, as appearing in time series, of basin-wide images available in the CZCS (1979–1985) and AVHRR (1982–1991) historical archives, differentiate between basin interior and continental margins affected by coastal patterns, river plumes, and mesoscale features. The original data were processed to apply calibration factors, to correct for atmospheric contamination, and to estimate chlorophyll-like pigment concentration and surface temperature. Composites were derived, as monthly and annual means, using a fixed equal-area projection with a 1-km² pixel grid. Enhanced pigment values and lower temperatures along the northern coastal areas (i.e. the Ligurian, Provençal and Balearic basins, as well as the Adriatic, and Aegean Seas) have been associated with the impact of runoff from continental margins (i.e. both a direct impact due to the sediment load and one induced on the planktonic flora by the associated nutrient load) and with vertical mixing due to the prevailing winds (i.e. the Mistral in the northwest, the Bora in the Adriatic, the Etesians in the Aegean). The pattern of increasing pigments and decreasing temperatures in seen to develop in the monthly images from the coastal zone towards the open sea from summer to winter, and then back from winter to summer. The southern coastal areas show different values, namely lower pigments and higher temperatures (except in areas where the data are altered by signal contamination). It is suggested that differences in geomorphology and meteorology of the basin margins have an impact on both water biogeochemistry and dynamics, influencing the biooptical and thermal properties of the various sub-basins, and of the entire Mediterranean region.