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21.
To which extent do wildfires affect runoff production, soil erosion and sediment transport in upland catchments? This transient effect is investigated here by combining data of long term precipitation, sediment yield and wildfire records with a fine resolution spatially distributed modeling approach to flow generation and surface erosion. The model accounts for changes in the structure and properties of soil and vegetation cover by combining the tube-flux approach to topographic watershed partition with a parsimonious parametrization of hydrologic processes. This model is used to predict hydrologic and sediment fluxes for nine small catchments in Saint Gabriel mountains of southern California under control (pre-fire) and altered (post-fire) conditions. Simulation runs using a 45 years record of hourly precipitation show the passage of fire to significantly modify catchment response to storms with a major effect on erosion and flood flows. The probability of occurrence of major floods in the post-fire season is shown to increase up to an order of magnitude under same precipitation conditions. Also, the expected anomaly of sediment yield can increase dramatically the desertification hazard in upland wildfire prone areas. One should further consider the role of firefloods produced by the combined occurrence of wildfires and storms as a fundamental source of non-stationarity in the assessment of hydrologic hazard. 相似文献
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In the framework of the linear baroclinic instability problem for planetary geostrophic flows, bounds on the related complex eigenvalues are deduced. The main feature of this result is the independence of these bounds from the latitude and the density stratification, so that it generalizes the results of previous work on the subject. 相似文献
24.
Akash Anandraj Renzo Perissinotto Christian Nozais Derek Stretch 《Estuarine, Coastal and Shelf Science》2008,79(4):599-606
Mouth breaching is a recurrent event in temporarily open/closed estuaries (TOCEs). Such disturbances result in flushing and sediment scouring, reducing the microalgal biomass stock. The depletion of these microalgae may have negative repercussions in the form of depleted stocks of commercial fish, game fish, crustaceans and mollusks. The aim of this investigation was therefore: (1) to monitor the recovery of microalgal biomass and production following a breaching event; and (2) to determine the key environmental parameters influencing primary production during the open and recovery phases. Phytoplankton and benthic microalgal production was measured (14C-uptake method) successively during the closed, open and recovery phases of the Mdloti TOCE (South Africa). Upon breaching, 94–99% of microalgal biomass was washed out to sea through flushing and sediment scouring. A temporary recovery of phytoplankton and benthic microalgal biomass was observed during the open phase, but this was not sustained because of continual flushing and scouring of the sediment. During the re-closure (recovery phase), microalgal biomass immediately increased, reaching pre-breaching levels 35–40 days following the breaching event. In contrast to biomass, autochthonous pelagic primary production reached a maximum level (341 mg C m−2 h−1) during the open phase. Pelagic primary production normalized to biomass (PB) significantly increased during the open phase. This is attributed to a favorable combination of optimum light conditions, high influx of macronutrients and high water temperatures (33 °C). Similarly, benthic primary production normalized to biomass (PB) peaked during the open phase (35 mg C mg chl-a−1 h−1). Multivariate analysis showed that major variations in primary production were mainly controlled by temperature, dissolved inorganic nitrogen (DIN) to phosphorus (DIP) molar ratios (water-column and pore-water) and light extinction (Kd), all of which were regulated by the state of the mouth. 相似文献
25.
The St. Lucia estuarine lake on the north coast of KwaZulu-Natal, South Africa, is one of the largest estuarine systems in Africa and of unique importance for the adjacent marine and terrestrial ecosystems. The area regularly experiences periods of drought, resulting in hypersaline conditions in its shallow lakes and the closure of the estuarine mouth. This study aimed to assess the primary production rates of phytoplankton and microphytobenthos throughout an annual cycle of this drought phase. Primary production rates were assessed at representative sites, namely the Mouth, Narrows, South and North Lakes from June 2006 to May 2007. Because of the drought, the salinity gradient from the mouth to the head of the estuary was reversed by comparison to estuarine systems with a steady freshwater inflow and regular marine exchange. In March 2007, during the study, the mouth opened as a result of rough seas, and the marine influence broke the existing reversed gradient, producing a marine salinity throughout the system. Microphytobenthic primary productivity varied between 0 and 34 mg C m−2 h−1 and showed strong correlations with salinity, DIN:DIP ratios and irradiance. Benthic productivity was high across the system after breaching of the mouth. Pelagic primary productivity (between 0 and 180 mg C m−2 h−1), showed a correlation with temperature and irradiance and was highest across the system in February 2007 when the mouth was still closed. There was no significant correlation between production rates and biomass (chl-a) in either the benthic or pelagic habitats. The negative correlation between DIN:DIP ratio and benthic primary productivity indicated that phosphorus was the limiting nutrient. This study shows that salinity, along with seasonally dependent parameters such as temperature and irradiance, correlates with the rate of microalgal production. Hence, in these shallow lakes, the largest primary productivity can occur in either the pelagic or benthic subsystems, depending on prevailing conditions at the time. 相似文献
26.
Renzo Richiardone Elena Giampiccolo Silvia Ferrarese Massimiliano Manfrin 《Boundary-Layer Meteorology》2008,128(2):277-302
We describe the coordinate transformations that can be used to convert the velocity components measured by a set of sonic
anemometers with time-dependent tilt fluctuations into a single, time-independent coordinate system. By applying the planar
fit method (PFM) to each anemometer dataset, it is possible, for planar flows, to locate the flow plane at each measurement
point and compare its orientation with the topography. Installation on a ship is also considered. An application of this method
to intercomparison data has led to the detection of an instrument error due to a misalignment between the assembly of the
sonic transducers and the anemometer pedestal. If this error occurs, pedestal levelling does not guarantee that measurements
are unbiased. A correction method is proposed and the results of two experiments are shown. Flow planarity at different levels
and flow distortion caused by the mast are highlighted. The influence of the error on the evaluation of the Reynolds stresses
using PFM or the double rotation method and the triple rotation method is discussed and the tilt corrected stresses calculated
using the three methods compared. 相似文献
27.
Ian A. Navarrete Kiyoshi Tsutsuki Victor B. Asio Renzo Kondo 《Environmental Geology》2009,58(6):1257-1268
This study was conducted to evaluate the physical, chemical, and mineralogical characteristics of rain forest soils derived
from late Quaternary basaltic rocks in Leyte, Philippines. Four sites along a catena were selected at an elevation of 75–112 m
above sea level with an average annual rainfall of 3,000 mm and an average temperature of 28°C. Results indicate that the
soils are deep, clayey, and reddish in color, which is indicative of the advanced stage of soil development. They also posses
excellent physical condition (friable and highly porous) although they are plastic and sticky when wet as is usual for clayey
soils. In terms of chemical characteristics, the soils are acidic with low CEC values and generally low in organic matter
and nutrient contents. The clay mineralogy of the soils is dominated by halloysite and kaolinite with minor amounts of goethite
and hematite, and they also have generally high dithionite-extractable Fe contents confirming the advanced stage of their
development. The soils in the more stable slope positions (PL-1, PL-2, and PL-4) have generally similar characteristics and
appeared more developed than the one in the less stable position (PL-3). The most important pedogenic processes that formed
the soils appear to be weathering, loss of bases and acidification, desilification, ferrugination, clay formation and translocation,
and structure formation. The nature of the parent rock and climatic conditions prevailing in the area as well as slope position
appear to have dominant effects on the development of the soils. 相似文献
28.
The statistical distribution of the daily Snow Water Equivalent (SWE) is investigated for a network of gauging stations in the Alpine part of Lombardia region, in the central Italian Alps. An event based data analysis is carried out using a 14 year long data set dating back to 1989. SWE is estimated when the new snow depth is greater than 6 cm. The SWE sample average in time is shown to be related to physiographic attributes of the gauging area, thus not being homogeneous in space. The values of SWE scaled by their average, or index value, instead show well approximated homogeneity of the second order moment, or coefficient of variation, in space. This suggests the use of a regional approach for frequency estimation of SWE. The frequency of occurrence of the normalized values of SWE is evaluated and tentatively accommodated by four probability distributions, often adopted in statistical modeling of hydrological variables. The Lognormal distribution shows the best performance. Single site distribution fitting is then carried out using the regional distribution, providing satisfactory results. 相似文献
29.
Ｓｅｎｓｉｔｉｖｉｔｙ Ｓｔｕｄｙ ｏｆ Ｎｏｎｌｏｃａｌ Ｔｕｒｂｕｌｅｎｃｅ ＣｌｏｓｕｒｅＳｃｈｅｍｅ ｉｎ Ｌｏｃａｌ ＣｉｒｃｕｌａｔｉｏｎＣｈｅｎＭｉｎｇａｎｄＨｏｎｅＺｈｏｎｇｘｉａｎｇ（ＩｎｓｔｉｔｕｔｅｏｆＡｔｍｏｓｐｈｅｒｉｃＰｈ... 相似文献
30.
Vincenzo Minganti Renzo Capelli Giuliana Drava Rodolfo De Pellegrini Giorgio Brunialti Paolo Giordani Paolo Modenesi 《Journal of Atmospheric Chemistry》2003,45(3):219-229
The concentrations of Cd, Cu, Mn, Ni, Pb, V, and Zn were measured in four different species of lichens (Parmelia caperata, P. pastillifera, P. saxatilis, P. sulcata) sampled in North-West Italy, in order to obtain maps showing metal distribution and the degree of deviation from background (natural) conditions. Significant differences among the species were found for Zn, Mn, Pb and V, suggesting that the combined use of mixed species in biomonitoring surveys can affect the interpretation of results. Results obtained for Parmelia caperata samples have been compared with background (natural) levels, and maps showing the distribution of each metal expressed as deviation from background levels have been obtained. Overall such maps show a medium to high alteration degree in the study area. 相似文献