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1.
《Limnologica》2020
The removal of native forest affects stream characteristics, processes, and organisms at the local scale. We compared the structure of fish assemblages between microbasins impacted by deforestation and those in pristine condition in the Amazonian Machado River basin, Brazil. Fish were collected with seine and dip nets along an 80-m stretch of 28 streams. At each site, we recorded physical, chemical, and land-water ecotone variables. We collected 6,586 specimens of 109 species, being 39 and 18 of them exclusively of forested and deforested streams, respectively. Non-significant differences were found for abundance and species richness between forested and deforested streams. A total of four main trophic groups were identified. Carnivores were more abundant in forested streams, whereas herbivores, omnivores and detritivores species were the most abundant in deforested streams. The deforested streams showed higher abundance and richness of algae and periphyton consumers, while forested streams presented higher abundance and richness of invertebrate consumers. Forested streams presented longer foodchains, higher occurrence and abundance of species that have more specialized habits and are intolerant to degraded environments, whereas generalist and tolerant species predominated in deforested streams. We conclude that species composition in Amazonian streams predictably responds to the degree of forest cover. 相似文献
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Rafael C. Carvalho David M. Kennedy Yakufu Niyazi Chloe Leach Teresa M. Konlechner Daniel Ierodiaconou 《地球表面变化过程与地形》2020,45(11):2540-2555
Historical aerial photographs are an invaluable tool in shoreline mapping and change detection in coastal landscapes. We evaluate the extent to which structure-from-motion (SfM) photogrammetric methods can be applied to quantify volumetric changes along sandy beaches, using archival imagery. We demonstrate the application of SfM-derived digital surface models (DSMs) at East Beach and Lady Bay in southwest Victoria, Australia, using photographic datasets taken in 1969, 1977 and 1986, and compare them to LiDAR-derived DSMs acquired at both sites in 2007. The SfM approaches resulted in two entire and two partial suitable DSMs out of six datasets. Good-quality DSMs were spatially continuous with a good spread of ground control points (GCPs) near the beach at Lady Bay, whereas unsuitable DSMs were mostly restricted by poor distribution and number of GCPs in spatially segmented areas of East Beach, due to limited overlapping of images, possible poor quality of GCPs and also the propagation of errors in the derived point clouds. A volume of approximately 223 000 ± 72 000 m3 was deposited at Lady Bay between 1969 and 2007, despite minimal erosion observed near the breakwater. The partially suitable dataset of East Beach indicated that beach erosion of at least 39 m3 m−1 occurred immediately to the east of the seawall after 1977. We also discuss the drawbacks and strengths of SfM approaches as a benchmark of historical erosion assessments along sandy beaches. © 2020 John Wiley & Sons, Ltd. 相似文献
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The simultaneous transfer of pore fluid and vapour was studied in the unsaturated shallow subsurface of a Plio-Pleistocene marine mudstone badland slope in southwestern Taiwan during the dry season using field monitoring data and numerical simulations. Data from field monitoring show mass-basis water contents of ~0.05 to ~0.10 that decrease towards the unsaturated ground surface and were invariant during the middle part of the dry season, except for daily fluctuations. In addition, the observed daily fluctuations in water content correlate with fluctuations in bedrock temperature, especially at depths of 2.5–5.0 cm. Periodic increases in water content occurred most notably during the day, when the bedrock temperature showed the greatest increase. Water contents then decreased to the previous state as bedrock temperature decreased during the night. Calculated vapour fluxes within the mudstone during the day increased up to 6 × 10−6–1 × 10−5 kg m−2 s−1, deriving a 0.01–0.02 increase in mass-basis water content at 2.5 cm depth for a 12-h period. This agrees with field monitoring data, suggesting that increases in water content occurred due to vapour intrusions into the bedrock. Pore water electrical conductivity (EC) showed periodic variations due to vapour intrusion, and gradually increased between the ground surface and depths of 2.5–5.0 cm. In contrast, pore water EC gradually decreased between 15 and 40 cm depth. Calculated water fluxes at depths of 2.5–40.0 cm varied from −4 × 10−6 to −2 × 10−9 kg m−2 s−1. These fluxes generated an increase in solute concentrations at the ground surface, with negative values of water flux indicating an upwards movement of water towards the surface. We show that the increase in solute content due to solute transfer from depth is highly dependent on variations in water flux with depth. © 2020 John Wiley & Sons, Ltd. 相似文献
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Base flows are important for tropical regions with pronounced dry seasons, which are facing increasing water demands. Base flow generation, however, is one of the most challenging hydrological processes to characterize in the tropics. In many years during the May–December wet season in the Panama Canal Watershed (PCW), base flows in rivers abruptly increase. This increase persists until the start of the December–April dry season. Understanding this unusual base flow jump (BFJ) behaviour is critical to improve water provisioning in the seasonal tropics, especially during droughts and extended dry seasons. This study developed an integrated approach combining piecewise regression on cumulative average base flow and sensitivity analysis to calculate the timing and magnitude of BFJ. Rainfall, forest cover, mean land surface slope, catchment area, and estimated subsurface storage were tested as predictors for the occurrence and magnitude of the BFJs in seven subcatchments of the PCW. Sensitivity analysis on correlated predictors allowed ranking of predictor contributions due to isolated and cross-correlation effects. Correlations between observed BFJs and BFJs predicted by watershed and rainfall-related predictors were 0.92 and 0.65 for BFJ timing and magnitude, respectively. Forest cover was the second most significant predictor after cumulative rainfall for jump magnitude, owing to larger subsurface storage and groundwater recharge in forests than pastures. Catchments in the mountainous eastern PCW always generated larger jumps due to their higher rainfall and greater forest cover than the western PCW catchments. The cross-correlations between predictors contributed to more than 50% of the jump variances. The results demonstrate the importance of rainfall gradient and catchment characteristics in affecting the sudden and sustained BFJs, which can help inform land management decisions intended to enhance water supplies in the tropics. This study underscores the need for more research to further understand the hydrological processes involved in the BFJ phenomenon, including better BFJ models and field characterizations, to help improve tropical ecosystem services under a changing environment. 相似文献
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Time series of hydrogen and oxygen stable isotope ratios (δ2H and δ18O) in rivers can be used to quantify groundwater contributions to streamflow, and timescales of catchment storage. However, these isotope hydrology techniques rely on distinct spatial or temporal patterns of δ2H and δ18O within the hydrologic cycle. In New Zealand, lack of understanding of spatial and temporal patterns of δ2H and δ18O of river water hinders development of regional and national-scale hydrological models. We measured δ2H and δ18O monthly, together with river flow rates at 58 locations across New Zealand over a two-year period. Results show: (a) general patterns of decreasing δ2H and δ18O with increasing latitude were altered by New Zealand's major mountain ranges; δ2H and δ18O were distinctly lower in rivers fed from higher elevation catchments, and in eastern rain-shadow areas of both islands; (b) river water δ2H and δ18O values were partly controlled by local catchment characteristics (catchment slope, PET, catchment elevation, and upstream lake area) that influence evaporation processes; (c) regional differences in evaporation caused the slope of the river water line (i.e., the relationship between δ2H and δ18O in river water) for the (warmer) North Island to be lower than that of the (cooler, mountain-dominated) South Island; (d) δ2H seasonal offsets (i.e., the difference between seasonal peak and mean values) for individual sites ranged from 0.50‰ to 5.07‰. Peak values of δ18O and δ2H were in late summer, but values peaked 1 month later at the South Island sites, likely due to greater snow-melt contributions to streamflow. Strong spatial differences in river water δ2H and δ18O caused by orographic rainfall effects and evaporation may inform studies of water mixing across landscapes. Generally distinct seasonal isotope cycles, despite the large catchment sizes of rivers studied, are encouraging for transit time analysis applications. 相似文献
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利用完备经验模态分解方法(CEEMD)对我国沿海地区6个GNSS基准站(2010—2018)的高程时序数据进行了处理分析。结果表明:CEEMD在高程时间序列分析中具有一定的优越性,可准确分解出各GNSS站高程时序中存在的周、月、季节、年等变化周期项,其中周年运动是主要贡献项,各站高程时间序列的短周期变化与潮汐变化周期具有密切关联性;沿海GNSS站的地面沉降既具有区域的一致性,又存在区域间差异性,其中D区DBJO、DZJJ站呈现先下降后上升的趋势,N区NZUH、NWZU站呈下降趋势,B区的BZMW呈上升趋势,而同海区的BLHT站则呈显著的下降趋势。 相似文献
10.
面向数字孪生城市的智能化全息测绘 总被引:2,自引:0,他引:2
以大数据、物联网、人工智能、虚拟现实、云计算、智能驾驶等新技术为代表的信息化浪潮席卷全球,数字世界与物理世界正形成两大平行发展、相互作用的体系,数字孪生技术应运而生。随着物联网技术(IOT)的发展,数字孪生的理念被引入到智慧城市建设中来,深刻影响着城市规划、建设与治理。笔者所在单位面向数字孪生城市和自然资源统一监管对测绘地理信息的新需求,在全国开创性地开展了面向数字孪生城市的智能化全息测绘试点工作。本文结合上海市智能化全息测绘试点工作,从数字孪生城市、数字孪生城市对地理信息的新需求、智能化全息测绘关键技术及测绘成果等方面展开了论述,重点介绍了智能化全息测绘的技术体系和产品体系,以及在社会各领域的应用成果。 相似文献