Freshwater environments in New Zealand provide a range of ecosystem services and contain important biodiversity. Managing these environments effectively requires a comprehensive inventory of the resource and cost-effective tools for regular monitoring. The complex and extensive margins of natural water bodies make them difficult to sample comprehensively. Problems thus occur with extrapolating point-specific sampling to accurately represent the diversity of vegetation in large freshwater bodies. Mapping freshwater vegetation using satellite remote sensing can overcome problems associated with access, scale and distribution, but it requires high-resolution images that have appropriate spectral characteristics. This paper provides an overview of the optical satellite data characteristics required for mapping riparian, submerged and emergent vegetation associated with freshwater environments in New Zealand. 相似文献
The hemipelagic mudrocks of the Nankai accretionary prism, Japan, contain hydrothermal deposits associated with a relict spreading center in the Shikoku Basin. Initial work on core samples from Ocean Drilling Program site 808 found several samples with elevated concentrations of calcium, magnesium, iron and manganese, at depths of between 1060 and 1111 m below sea floor. However, the origin of these sediments was uncertain, due to a lack of data. There was no recorded evidence of whether these elevated concentrations were present throughout this interval of core, or if they were present as discrete layers with the background hemipelagic mudrocks in between. In the present study the core was resampled, and the sediments with anomalous chemical compositions were found to be present in discrete layers. This fact, along with a detailed interpretation of their geochemistry, has allowed them to be identified as hydrothermal sediments, associated with the relict spreading center in the Shikoku Basin. The lower (older) two layers display a chemical composition typical of umbers, while the upper (younger) two layers are metalliferous mudrocks typical of deposits found further from the spreading center. 相似文献
Groundwater samples from boreholes and springs in the unconfined Chalk aquifer of Cambridgeshire were analysed for N2O and other N species on a monthly basis between March 1995 and February 1996. Land use in the study area is devoted to intensive arable farming supported by the application of N-based fertilisers. All groundwater samples were strongly oversaturated with N2O, with concentrations ranging from 13 to 320 times the saturation concentration with respect to air-equilibrated water.A very good positive correlation between N2O and NO3 concentrations was obtained (r2=0.80), but no relationship was established between N2O and NO2 or NH4 concentrations. Concentrations of N2O and NO3 increased continuously in the direction of groundwater flow, with molar net gain ratios of NO3 to N2O varying between 204 and 410. These ratios are within the range reported in previous studies of nitrification. Corresponding dissolved O2 levels in groundwater samples were moderately undersaturated, further indicating that the main source of N2O in Chalk groundwater in Cambridgeshire is probably nitrification. No consumption of N2O seems to take place within the unconfined aquifer with degassing to the atmosphere apparently being the sole mechanism for N2O removal from groundwater.An estimated N2O flux of around 0.05 kg N2O ha−1 a−1 from the sampled groundwater discharge points to the atmosphere was calculated for the study area. This figure is likely to be much higher, since it does not account for diffuse N2O emissions from groundwater seepage areas or any degassing from the unconfined aquifer through the unsaturated zone. Both these processes will contribute substantially to the total aerial flux, thus suggesting that groundwater may be a significant contributor to the global N2O budget. 相似文献
The morphology of coastal sequences provides fundamental observations to unravel past sea level (SL) variations. For that purpose, converting morphometric observations into a SL datum requires understanding their morphogenesis. The long-lasting sequence of coral reef terraces (CRTs) at Cape Laundi (Sumba Island, Indonesia) could serve as a benchmark. Yet, it epitomizes a pitfall that challenges the ultimate goal: the overall chronology of its development remains poorly constrained. The polycyclic nature of the terraces, involving marine erosion and reoccupation of old coral colonies by more recent ones hinders any clear assignment of Marine Isotope Stages (MIS) to specific terraces, in particular the reference datum corresponding to the last Interglacial maximum (i.e., MIS 5e). Thus, to overcome these obstacles, we numerically model the genesis of the sequence, testing a range of eustatic SL (ESL) reconstructions and uplift rates, as well as exploring the parameter space to address reef growth, erosion and sedimentation. A total of 625 model runs allowed us to improve the morpho-chronological constraints of the coastal sequence and, more particularly, to explain the morphogenesis of the several CRTs associated with MIS 5e. Our results suggest that the lowermost main terrace was first constructed during the marine transgression of MIS 5e and was later reshaped during the marine regression of MIS 5e, as well as during the MIS 5c and MIS 5a highstands. Finally, we discuss the general morphology of the sequence and the implications it may have on SL reconstructions. At Cape Laundi, as elsewhere, we emphasize the necessity of addressing the development of CRT sequences with a dynamic approach, that is, considering that a CRT is a landform built continuously throughout the history of SL oscillations, and not simply during a singular SL maximum. 相似文献
Drill sites in the southern Bay of Bengal at 3°N 91°E (International Ocean Discovery Program Expedition 362) have sampled for the first time a complete section of the Nicobar Fan and below to the oceanic crust. This generally overlooked part of the Bengal–Nicobar Fan System may provide new insights into uplift and denudation rates of the Himalayas and Tibetan Plateau. The Nicobar Fan comprises sediment gravity-flow deposits, mostly turbidites, that alternate with hemipelagite drapes and pelagite intervals of varying thicknesses. The decimetre-thick to metre-thick oldest pre-fan sediments (limestones/chalks) dated at 69 Ma are overlain by volcanic material and slowly accumulated pelagites (0.5 g cm−2 kyr−1). At Expedition 362 Site U1480, terrigenous input began in the early Miocene at ca 22.5 Ma as muds, overlain by very thin-bedded and thin-bedded muddy turbidites at ca 19.5 Ma. From 9.5 Ma, sand content and sediment supply sharply increase (from 1–5 to 10–50 g cm−2 kyr−1). Despite the abundant normal faulting in the Nicobar Fan compared with the Bengal Fan, it offers a better-preserved and more homogeneous sedimentary record with fewer unconformities. The persistent connection between the two fans ceased at 0.28 Ma when the Nicobar Fan became inactive. The Nicobar Fan is a major sink for Himalaya-derived material. This study presents integrated results of International Ocean Discovery Program Expedition 362 with older Deep Sea Drilling Project/Ocean Drilling Program/International Ocean Discovery Program sites that show that the Bengal–Nicobar Fan System experienced successive large-scale avulsion processes that switched sediment supply between the Bengal Fan (middle Miocene and late Pleistocene) and the Nicobar Fan (late Miocene to early Pleistocene). A quantitative analysis of the submarine channels of the Nicobar Fan is also presented, including their stratigraphic frequency, showing that channel size/area and abundance peaked at ca 2 to 3 Ma, but with a distinct low at 3 to 7 Ma: the intervening stratigraphic [sub]unit was a time of reduced sediment accumulation rates. 相似文献
‘Community geography’ is a growing sub-field that leverages academic resources to facilitate spatial research in partnership with local communities. The Mapping Prejudice Project and the CREATE Initiative, two interdisciplinary projects at the University of Minnesota, demonstrate some of the opportunities and challenges associated with practicing community geography. Mapping Prejudice is leveraging community crowdsourcing to build the first comprehensive spatial database of racially restrictive housing covenants in the United States. CREATE is co-developing research on critical problems at the intersection of environment and equity through collaboration with community partners. These two projects incorporate a methodological commitment to place-based and historically grounded research that seeks to make knowledge in—and in relation to—a specific place. Incorporating earlier feminist and critical GIS theory, these projects have adopted an iterative research model that places under-resourced communities at the forefront of the research process. Their work produces a fluid, responsive, and co-creative approach that has the capacity to legitimate its knowledge claims through responsiveness to community needs and collective experience.
We present the first sulfur and oxygen isotopic data for tephra from the catastrophic 1883 eruption of Krakatau. Sulfur isotopic ratios in unaltered Krakatau tephra erupted August 26–27, 1883 are markedly enriched in 34S relative to mantle sulfur. High δ34S values of +6.3 to +16.4‰ can best be explained by open-system or multi-stage degassing of SO2 from the oxidized rhyodacitic and gray dacitic magmas with 34S enrichment of SO2−4 remaining in the melt. Lower whole-rock δ34S values of +2.6‰ and +4.0‰ in two oxidized gray dacitic samples indicate more primitive subarc mantle sulfur in the 1883 magma chamber. Initial δ34S of the rhyodacitic magma was probably in the +1.5‰ to +4.0‰ range and similar to δ34S values measured in arc volcanic rocks from the Mariana Arc. 相似文献
We assessed short-term ecological and potential human health effects of wastewater treatment plant (WTP) effluent by measuring δ15N‰ and microbial concentrations in oysters and suspended particulate matter (SPM). We also tested male-specific bacteriophage (MSB) as an alternative to fecal coliforms, to assess potential influence of wastewater contamination on shellfish. WTP effluent did not affect oyster growth or survival, but SPM and oysters acquired wastewater-specific δ15N‰. δ15N values were depleted near the WTP, typical of low-level processed wastewater. Fecal coliform and MSB concentrations were higher in samples taken closest to the WTP, and MSB values were significantly correlated with δ15N‰ in oyster tissues. Overall, oysters demonstrated relatively rapid integration and accumulation of wastewater-specific δ15N‰ and indicator microorganisms compared to water samples. These data suggest oysters were superior sentinels compared to water, and MSB was a more reliable indicator of wastewater influence on shellfish than fecal coliforms. 相似文献