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Nikolaos P. Nikolaidis Aristomenis P. Karageorgis Vasilios Kapsimalis Paraskevi Drakopoulou Nikolaos Skoulikidis Horst Behrendt Zlatko Levkov 《Ecological modelling》2009
The estimation of nutrient fluxes, the determination of spatial and temporal response and the understanding of biogeochemical changes in the past, present and future in the Axios River catchment, in Greece, as well as the impacts to the coastal zone of Thermaikos Gulf were accomplished by the use of harmonized watershed and coastal zone models. The mathematical model MONERIS was the watershed management model that was used to model the export loads of nutrients in Axios River. MONERIS was developed to estimate the nutrient inputs into river basins by point sources and various diffuse pathways. Watershed hydrologic and water quality data were collected and synthesized to develop input data sets for the simulation of Axios River catchment. The model was modified to better assess organic nitrogen export loads in Mediterranean watersheds. The results showed the importance of agricultural and livestock activities, concerning their nutrients emissions in the River. MONERIS was integrated with the coastal zone model WASP 6.0 to assess the impacts of the nutrient loads to the eutrophication status of the coastal zone. Several management scenarios were assessed. Management scenarios included measures for reduction in the emissions from the fertilizer plant of Veles, removal of phosphorous from the detergents in FYROM, treatment of urban wastes to EU Standards, reduction in N-fertilizer input, reduction in erosion and the green scenario that represented the maximum reduction scenario of all the measures together. The model simulations indicated that the coastal zone of Axios mouth will be eutrophic for nitrate (2.69–3.34 μM) and phosphate (0.2–0.68 μM) and upper mesotrophic for chlorophyll-a (0.74–1.45 μg/l) for the scenarios tested. The results suggest that the impact of the management scenarios will be largely negligible (no change in trophic status) for the Thermaikos Gulf sector nearby the Axios River due to additional sources such as the loads from Thessaloniki's waste water treatment plant which appear to affect the region to a greater extent. The integration of watershed and coastal zone models can be used to assess management scenarios in order to illustrate the significance of various land use practices to the eutrophication of the Gulf. 相似文献
147.
Methods that are more cost-effective and objective are needed to detect important vegetation change within acceptable error
rates. The objective of this research was to compare visual estimation to three new methods for determining vegetation cover
in the sagebrush steppe. Fourteen management units at the US Sheep Experiment Station were identified for study. In each unit,
20 data collection points were selected for measuring plant cover using visual estimation, laser-point frame (LPF), 2 m above-ground-level
(AGL) digital imagery, and 100-m AGL digital imagery. In 11 of 14 management units, determinations of vegetation cover differed
(P < 0.05). However, when combined, overall determinations of vegetation cover did not differ. Standard deviation, corrected
sums of squares, coefficient of variation, and standard error for the 100 m AGL method were half as large as for the LPF and
less than the 2-m AGL and visual estimate. For the purpose of measuring plant cover, all three new methods are as good as
or better than visual estimation for speed, standard deviation, and cost. The acquisition of a permanent image of a location
is an important advantage of the 2 and 100 m AGL methods because vegetation can be reanalyzed using improved software or to
answer different questions, and changes in vegetation over time can be more accurately determined. The reduction in cost per
sample, the increased speed of sampling, and the smaller standard deviation associated with the 100-m AGL digital imagery
are compelling arguments for adopting this vegetation sampling method. 相似文献
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Geochemical processes leading to either mobilization or retention of radionuclides in an aquifer system are significantly influenced by their interaction with rock, sediment and colloid surfaces. Therefore, a sound safety assessment of nuclear waste disposal requires the elucidation and quantification of those processes. State-of-the-art analytical techniques as e.g. laser- and X-ray spectroscopy are increasingly applied to study solid–liquid interface reactions to obtain molecular level speciation insight.We have studied the sorption of trivalent lanthanides and actinides onto aluminium oxides, hydroxides and purified clay minerals by the time-resolved laser fluorescence spectroscopy and X-ray-absorption spectroscopy. Chemical constitution and structure of surface bound actinides are proposed based on spectroscopic information. Open questions still remain with regard to the exact nature of mineral surface ligands and the mineral/water interface. Similarities of spectroscopic data obtained for M(III) sorbed onto γ-alumina, and clay minerals suggest the formation of very comparable inner-sphere surface complexes such as S–O–An(III)(OH)x(2 − x)(H2O)5 − x at pH > 5. Those speciation data are found consistent with those predicted by surface complexation modelling. The applicability of data obtained for pure mineral phases to actinide sorption onto heterogeneously composed natural clay rock is examined by experiments and by geochemical modelling. Good agreement of experiment and model calculations is found for U(VI) and trivalent actinide/lanthanide sorption to natural clay rock. The agreement of spectroscopy, geochemical modelling and batch experiments with natural rock samples and purified minerals increases the reliability in model predictions.The assessment of colloid borne actinide migration observed in various laboratory and field studies calls for detailed information on actinide–colloid interaction. Kinetic stabilization of colloid bound actinides can be due to inclusion into inorganic colloid matrix or by macromolecular rearrangement in case of organic, humic/fulvic like colloids. Only a combination of spectroscopy, microscopy and classical batch sorption experiments can help to elucidate the actinide–colloid interaction mechanisms and thus contribute to the assessment of colloids for radionuclide migration. 相似文献
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Pawel Wasowicz Alexander N. Sennikov Kristine B. Westergaard Katie Spellman Matthew Carlson Lynn J. Gillespie Jeffery M. Saarela Steven S. Seefeldt Bruce Bennett Christian Bay Stefanie Ickert-Bond Henry Vre 《Ambio》2020,49(3):693-703
We present a comprehensive list of non-native vascular plants known from the Arctic, explore their geographic distribution, analyze the extent of naturalization and invasion among 23 subregions of the Arctic, and examine pathways of introductions. The presence of 341 non-native taxa in the Arctic was confirmed, of which 188 are naturalized in at least one of the 23 regions. A small number of taxa (11) are considered invasive; these plants are known from just three regions. In several Arctic regions there are no naturalized non-native taxa recorded and the majority of Arctic regions have a low number of naturalized taxa. Analyses of the non-native vascular plant flora identified two main biogeographic clusters within the Arctic: American and Asiatic. Among all pathways, seed contamination and transport by vehicles have contributed the most to non-native plant introduction in the Arctic. 相似文献
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