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This work deals with the impacts of dams on large gravel -bed rivers in terms of altering coarse transport regimes and the relationship with river morphodynamics. Using data collected by a tracer -based monitoring programme carried out in a 4 -km -long study sector of the Parma River (Italy), located downstream from a relatively recently established dam, we applied a virtual velocity approach to estimate the coarse bed material load at four river cross -sections. Monitoring and calculation results provided new insights into the impacts of the dam on streambed material mobility and the sediment regime over the 17 -month calculation period. A longitudinal gradient of effects was observed along the study sector. Sections located closer to the dam are characterized by more evident impacts due to deficits in coarse sediment input from upstream. Sediment mobility here is strongly altered, especially in the highly armoured main channel, and the overall bed material load is extremely low. A partial recovery of sediment dynamics was observed at the sections located further from the dam, where estimates indicate higher sediment yield. The observed longitudinal trend in the coarse sediment transport regime matches the morphology, as the river shifts downstream from a sinuous configuration with alternate bars to a wandering one. The novel insights into alteration of coarse sediment dynamics and the relationship with river morphodynamics are potentially applicable to many other fluvial contexts affected by similar impoundments. © 2019 John Wiley & Sons, Ltd. 相似文献
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YONG Wai-Kuan LIM Phaik-Eem VELLO Vejeysri SIM Kae-Shin ABDUL MAJID Nazia MUSTAFA Emienour Muzalina NIK SULAIMAN Nik Meriam LIEW Kan-Ern CHEN Brenna Jia-Tian PHANG Siew-Moi 《海洋湖沼学报(英文)》2019,(1):186-198
A freshwater green microalgae Chlorella sp., UMACC344 was shown to produce high lipid content and has the potential to be used as feedstock for biofuel production. In this study, photosynthetic effciency, biochemical pro?les and non-targeted metabolic pro?ling were studied to compare between the nitrogen-replete and deplete conditions. Slowed growth, change in photosynthetic pigments and lowered photosynthetic effciency were observed in response to nitrogen deprivation. Biochemical pro?les of the cultures showed an increased level of carbohydrate, lipids and total fatty acids, while the total soluble protein content was lowered. A trend of fatty acid saturation was observed in the nitrogen-deplete culture with an increase in the level of saturated fatty acids especially C16:0 and C18:0, accompanied by a decrease in proportions of monounsaturated and polyunsaturated fatty acids. Fifty-nine metabolites, including amino acids, lipids, phytochemical compounds, vitamins and cofactors were signi?cantly dysregulated and annotated in this study. Pathway mapping analysis revealed a rewiring of metabolic pathways in the cells, particularly purine, carotenoid, nicotinate and nicotinamide, and amino acid metabolisms. Within the treatment period of nitrogen deprivation, the key processes involved were reshu ? ing of nitrogen from proteins and photosynthetic machinery, together with carbon repartitioning in carbohydrates and lipids. 相似文献
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Brenna M. Sweetman Jordan R. Cissell Sandra Rhine Michael K. Steinberg 《The Professional geographer》2019,71(1):123-134
Measuring land-use, land-cover change in biodiverse, tropical countries is critical for conservation management and sustainable planning because it provides quantifiable data regarding broad environmental changes. This project uses Landsat satellite imagery to document vegetation cover change on Ambergris Caye, Belize, from 2000 to 2017. The close proximity of the Belize Barrier Reef Reserve System has made Ambergris Caye the most popular tourist destination and economic hub in Belize. As a result, the region has undergone intense commercial and residential development coupled with rapid population growth over the past two decades. Understanding general trends in landscape dynamics is critical for the natural resource–based tourism industry of Belize to continue to thrive. Unsupervised classification methods and a per pixel postclassification comparison were used with Landsat imagery to estimate loss in vegetation cover and increases in urban and barren land. The results indicate a 10.85 percent decrease in vegetation and a 39 percent increase in urban and barren land during the seventeen-year study period with an annual forest loss rate of 0.67 percent per year using a compound interest rate formula. The results of this analysis represent a baseline study of vegetation change on Ambergris Caye to inform management and conservation efforts. 相似文献
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Susanna E. Honig Brenna Mahoney Jess S. Glanz Brent B. Hughes 《Marine pollution bulletin》2017,114(1):539-546
It is well established that anthropogenic nutrient inputs harm estuarine seagrasses, but the influence of nutrients in rocky intertidal ecosystems is less clear. In this study, we investigated the effect of anthropogenic nutrient loading on Phyllospadix spp., a rocky intertidal seagrass, at local and regional scales. At sites along California, Washington, and Oregon, we demonstrated a significant, negative correlation of urban development and Phyllospadix bed thickness. These results were echoed locally along an urban gradient on the central California coast, where Phyllospadix shoot δ15N was negatively associated with Phyllospadix bed thickness, and experimentally, where nutrient additions in mesocosms reduced Phyllospadix shoot formation and increased epiphytic cover on Phyllospadix shoots. These findings provide evidence that coastal development can threaten rocky intertidal seagrasses through increased epiphytism. Considering that seagrasses provide vital ecosystem services, mitigating eutrophication and other factors associated with development in the rocky intertidal coastal zone should be a management priority. 相似文献
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Yong Wai-Kuan Lim Phaik-Eem Vello Vejeysri Sim Kae-Shin Abdul Majid Nazia Mustafa Emienour Muzalina Nik Sulaiman Nik Meriam Liew Kan-Ern Chen Brenna Jia-Tian Phang Siew-Moi 《中国海洋湖沼学报》2019,37(1):186-198
Journal of Oceanology and Limnology - A freshwater green microalgae Chlorella sp., UMACC344 was shown to produce high lipid content and has the potential to be used as feedstock for biofuel... 相似文献
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Mechanisms driving polymagmatic activity at a monogenetic volcano, Udo, Jeju Island, South Korea 总被引:3,自引:1,他引:2
Marco Brenna Shane J. Cronin Ian E. M. Smith Young Kwan Sohn Karoly Németh 《Contributions to Mineralogy and Petrology》2010,160(6):931-950
High-resolution, stratigraphically ordered samples of the Udo tuff cone and lava shield offshore of Jeju Island, South Korea,
show complex geochemical variation in the basaltic magmas that fed the eruption sequence. The eruption began explosively,
producing phreatomagmatic deposits with relatively evolved alkali magma. The magma became more primitive over the course of
the eruption, but the last magma to be explosively erupted had shifted back to a relatively evolved composition. A separate
sub-alkali magma batch was subsequently effusively erupted to form a lava shield. Absence of weathering and only minor reworking
between the tuff and overlying lava implies that there was no significant time break between the eruptions of the two magma
batches. Modelling of the alkali magma suggests that it was generated from a parent melt in garnet peridotite at c. 3 to 3.5 GPa
and underwent mainly clinopyroxene + olivine ± spinel fractionation at c. 1.5 to 2 GPa. The sub-alkali magma was, by contrast,
generated from a chemically different peridotite with residual garnet at c. 2.5 GPa and evolved through olivine fractionation
at a shallower level compared to its alkali contemporary. The continuous chemostratigraphic trend in the tuff cone, from relatively
evolved to primitive and back to evolved, is interpreted to have resulted from a magma batch having risen through a single
dyke and erupted the batch’s head, core and margins, respectively. The alkali magma acted as a path-opener for the sub-alkali
magma. The occurrence of the two distinct batches suggests that different magmatic systems in the Jeju Island Volcanic Field
have interacted throughout its history. The polymagmatic nature of this monogenetic eruption has important implications for
hazard forecasting and for our understanding of basaltic field volcanism. 相似文献