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1.
The relationship between soil geochemistry and die back of montane forests in Sri Lanka: a case study 总被引：1，自引：1，他引：0
P. N. Ranasinghe C. B. Dissanayake D. V. N. Samarasinghe R. Galappatti 《Environmental Geology》2007,51(6):1077-1088
Tropical montane forests of Sri Lanka form a unique ecosystem with more than 50% of endemic plant species. It has been noted
that trees, belonging to different size and age classes of these forest, have been dying due to a yet unknown factor. This
phenomenon was first observed in the Horton Plains National Park, which is a high plateau, composed of tropical montane forests.
Later dying of forests were observed at several areas including Hakgala montane forest.
Physical parameters trace nutrients as well as toxic element concentrations in soils, were studied in order to identify the
possible geochemical factors behind the forest die back. Systematic soil sampling was carried out covering the entire Horton
Plains National Park and random samples were collected from Hakgala montane forest. Samples were analyzed for available Fe,
Mn, Zn, Cu, Ni, Cd, Al and Pb using standard colorimetric and atomic absorption spectrometric procedures. Physical parameters
such as pH, moisture content, and conductivity of the samples were also measured.
Among extractable micro-nutrients Cu and Zn, and Ni show no deficiency or excess levels. However, the recorded available high
concentrations of Fe, Mn and Al can be toxic to certain montane plant species. Acidic moist soil of the area may enhance the
toxic effects of these elements. Possible source of these elements should be the underground lithology of the area.
According to the results obtained, there is a relationship between forest die back and high Pb concentrations. The same phenomenon
was also observed in the Hakgala forest. The distribution pattern of Pb in the Horton Plains coincides well with the die back
distribution pattern. The observed Pb values at Horton Plains and Hakgala are almost similar to values observed at Pannipitiya
and Dombagaskanda locations, which are located close to main roads carrying heavy traffic. It is quite possible therefore,
that Pb toxicity may be a significant factor behind the forest die back even though other factors should not be completely
ruled out at this juncture. Strong monsoon winds, bringing Pb from the polluted southwestern part of the country, can be the
most possible source of soil Pb. Further studies however are indeed necessary to confirm the conclusion. 相似文献
2.
The quantity of coastline retreat resulting from storm erosion is one of the most important phenomena that needs to be accurately quantified to facilitate effective coastal management strategies. Historically, the volume of storm erosion (and coastline retreat) accommodated for coastal planning decisions has been directly linked to the storm (usually defined by considering wave height and duration only) with a certain pre-defined return period, known as a Synthetic Design Storm (SDS) (e.g. 1 in 100 year storm). The SDS method of estimating storm erosion volumes for coastal planning thus assumes that, for example, the 1 in 100 year storm event also results in a 1 in 100 year erosion event. This communication discusses the physical reality of this assumption and demonstrates the improved performance of a new method, based on Joint Probability Distributions (JPD) for estimating storm erosion volumes proposed by Callaghan et al. [Callaghan, D.P., Nielsen, P., Short, A.D. and Ranasinghe, R., 2008. Statistical simulation of wave climate and extreme beach erosion. Coastal Engineering, 55(5): 375–390] using one of the world's longest beach profile surveys from Sydney, Australia. 相似文献
3.
Subtidal nearshore sandbars may exhibit cyclic net offshore migration during their multi‐annual lifetime along many sandy coasts. Although this type of behavior can extend continuously for several kilometers, alongshore variations in cross‐shore bar position and bar amplitude are commonly observed. Alongshore variability is greatest when bars display km‐scale disruptions, indicative of a distinct alongshore phase shift in the bar cycle. An outer bar is then attached to an inner bar, forming a phenomenon known as a bar switch. Here, we investigate such large‐scale alongshore variability using a process‐based numerical profile model and observations at 24 transects along a 6 km section of the barred beach at Noordwijk, The Netherlands. When alongshore variability is limited, the model predicts that the bars migrate offshore at approximately the same rate (i.e. the bars remain in phase). Only under specific bar configurations with high wave‐energy levels is an increase in the alongshore variability predicted. This suggests that cross‐shore processes may trigger a switch in the case of specific antecedent morphological configurations combined with storm conditions. It is expected that three‐dimensional (3D) flow patterns augment the alongshore variability in such instances. In contrast to the observed bar behaviour, predicted bar morphologies on either side of a switch remain in different phases, even though the bars are occasionally located at a similar cross‐shore position. In short, the 1D model is not able to remove a bar switch. This data‐model mismatch suggests that 3D flow patterns are key to the dissipation of bar switches. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
4.
Ana Vila-Concejo Michael G. Hughes Andrew D. Short Roshanka Ranasinghe 《Ocean Dynamics》2010,60(2):285-298
Estuarine shorelines are often classified as low-energy coasts and are, therefore, expected to undergo little variation. Port
Stephens (SE Australia) is a ria-like drowned river valley microtidal estuary located on a wave-dominated coast. The outer
part of the estuary is tide-dominated and has a large shallow flood-tide delta, which is also affected by waves. The northern
(predominantly low-energy) shoreline of outer Port Stephens is a continuous stretch of sand comprising areas of high mobility
and areas of relative stability terminating in a western extending sand spit. This paper investigates the effects of periodic
high-energy conditions during which waves penetrate into the estuary by analysing two types of storms, low to moderate (more
frequent type) storms and severe to extreme (low frequency) storms. It is established that low to moderate storms cause generalised
erosion over the northern shoreline. On the contrary, severe to extreme storms, while causing erosion on parts of the beach,
can transport new sediment across the flood-tide delta and deposit it to build a mobile shore attached sandwave. Long-term
(decadal) trends identified in the study area are in agreement with short- and medium-term results. Moving into the estuary
are four complementary zones of sediment transport which include: (1) sandwave formation and westward migration; (2) a relatively
stable area between the sandwave and an erosion zone; (3) an erosion zone undergoing shoreline retreat and finally (4) a depositional
terminus causing westward extension of the sand spit. 相似文献
5.
Tidal velocity asymmetry at inlets influences sediment transport pathways and the morphological evolution of estuaries/lagoons connected to these inlets. Generation of overtides is generally seen as the main cause of tidal velocity asymmetry. Whilst majority of studies examining tidal velocity asymmetry have concentrated on inlets located in semi-diurnal tidal regimes, here, attention is focused on the processes responsible for causing tidal velocity asymmetry at inlets located in diurnal tidal regimes. Using field data collected from three West Australian inlets, it is shown that tidal velocity asymmetry in this type of system is caused by the oceanic tidal conditions. It is also shown that in these systems, the occurrence of flood/ebb dominance can be determined using oceanic tidal elevations, which are more readily available than inlet current data. In contrast to semi-diurnal systems the flood/ebb dominance in diurnal systems varies throughout the year depending on the phase angle relationship between the significant oceanic tidal constituents. The net sediment transport in to/out of these systems, which determines the morphological evolution of the systems, is shown to be governed more by the degree of tidal velocity asymmetry rather than the number of occurrences or duration of flood/ebb-dominant periods. 相似文献
6.
Recent developments in extreme values modelling have been used to develop a framework for determining the coastal erosion hazard on sandy coastlines. This framework quantitatively reproduced the extreme beach erosion volumes obtained from field measurements at Narrabeen Beach, Australia. This encouraging finding was achieved using Kriebel and Dean's [Kriebel, D.L. and Dean, R.G., 1993. Convolution method for time-dependent beach profile response. Journal of Waterway, Port, Coastal and Ocean Engineering, 119(2): 204–226.] simple beach erosion and accretion model. The method includes allowances for joint probability between all basic erosion variates including; wave height, period and direction, event duration, tidal anomalies and event spacing. A new formulation for the dependency between wave height and period has been developed. It includes the physical wave steepness limitation. Event grouping, where significantly more erosion can occur from two closely spaced storms is handled by temporally simulating the synthetic wave climate and the resulting beach erosion and accretion. 相似文献
7.
Priyantha Jinadasa Sinhalage Uday Pathirana Gayan Ranasinghe Pradeep Nalak Centurioni Lu Hormann Verena 《海洋学报(英文版)》2020,39(3):103-112
Monsoon driven water mass exchange between the Bay of Bengal(Bo B) and Arabian Sea(AS) is the common experience. However, it is not yet firmly confirmed that the exchange pathway is either passing through southern tip of Sri Lanka or Palk Strait. Local circulation patterns impact the pathways followed by the East Indian Coastal Currents(EICC) that drive exchange, thereby modulating mixing and water mass transformation in the Bay of Bengal around Sri Lanka. In this study, observations from surface drifters were incorporated with the satellite derived data to understand the monsoonal impact on circulation patterns in the Indian Ocean. This was the first multi-national scientific effort which was conducted in the Bo B and AS during 2013 to 2015 to understand the monsoonal impact on circulation patterns in the complex region. The results indicated that seasonally reversing monsoonal currents of southern Sri Lanka, traced by the wintertime freshwater export pathways of the EICC. The deflection of monsoon currents running along the east coast of Sri Lanka by forming cyclonic and anti-cyclonic eddies, which influence the mixing and stirring associated with these flows. Results further indicate the low salinity cold water flows from the Bo B to AS along the western boundary of the Bo B during northeast monsoon. In the same way, reverses the phenomena during southwest monsoon, transporting high salinity warm water from AS to the Bo B. This maintain the bay status which occurred due to freshwater influx from large rivers and high saline water from AS. However, no evidences were observed for the exchange through Palk Strait during the study.Also, there are some mis-matches in in-situ and remotely sensed measurements which imply the necessity of systematic observation system for the complex region as an alternative approach. 相似文献
8.
Submerged breakwaters (SBWs) are becoming a popular option for coastal protection, mainly due to their low aesthetic impact on the natural environment. However, SBWs have rarely been employed for coastal protection in the past and therefore, their efficacy remains largely unknown. The main objective of the present study was to investigate the structural and environmental conditions that govern the mode of shoreline response (i.e shoreline erosion vs shoreline accretion) to SBWs. The relative importance of the key structural and environmental parameters governing the response mode to a single shore parallel SBW is investigated through a combination of theoretical analysis and numerical modelling. Using physical considerations, a theoretical response-function model is derived under several simplifying assumptions including parallel depth contours, linear wave theory, shore normal waves, and no wave–current interaction. Numerical modelling is undertaken with the Mike21 model suite to simulate the depth averaged velocity fields (without morphological updating) due to waves acting on a single shore-parallel SBW located on a schematised beach with parallel depth contours. In total 92 coupled wave–current simulations were undertaken. The results indicate that the mode of shoreline response to the SBW can be expressed in terms of the two non-dimensional parameters hB/H0 and (sB/hB)3/2(LB/hB)2(A3/hB)1/2 (variables defined in the text). 相似文献
9.
Field and laboratory studies on the geology and mineralogy of gem sediments and associated rocks reveal that gem minerals occur both in garnetiferous gneisses and granulites. It has been observed that PT conditions characteristic of granulite facies had favoured the formation of gem minerals such as topaz, corundum, beryl, spinel, tourmaline and zircon.
Resume Les travaux sur le terrain ainsi qu'au laboratoire portant sur les sédiments et les roches associes aux pierres precieuses montrent que les minéraux précieux se trouvent dans les gneiss à grenat et les granulites. Il a été observé que les conditions de pression et de température qui caractérisent le faciès des granulites ont favorise la formation des minéraux precieux tels que des topazes, corindons, béryls, spinelles, tourmalines et zircons.相似文献
10.
Simon Rozalyn A. Ranasinghe Purnika Damindi Barazanji Nawroz Jungeström Malin Bergman Xu Jie Bednarska Olga Serrander Lena Engström Maria Bazylinski Dennis A. Keita Åsa V. Walter Susanna 《中国海洋湖沼学报》2021,39(6):2044-2052
Journal of Oceanology and Limnology - Magnetotactic bacteria (MTB), ubiquitous in soil and fresh and saltwater sources have been identified in the microbiome of humans and many animals. MTB... 相似文献