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Papanicolaou G 《Science (New York, N.Y.)》1915,41(1054):401-404
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Properly calibrated, single storm event, model simulations can be valuable quantitative tools for evaluating the effectiveness of grassed waterways (GWWs) and identifying a threshold length for an effective GWW. Current specifications for GWW lengths in Iowa are lacking. The key objective of this study is to employ the well-established Water Erosion Prediction Project model (WEPP) for determining an effective (or threshold) GWW length for reducing runoff and sediment yields under a wide range of hydrologic and management conditions in an agricultural Iowa watershed, namely Clear Creek, IA. The advantage of this physically based, distributed-parameter model is its ability to replicate processes at the hillslope scale where GWW performance is mostly evaluated. Overall, 84 WEPP runs were performed for assessing (i) the effect that GWW length has on reducing runoff and sediment yields within a representative test hillslope, and (ii) the effect of the gradient of the drainage area on GWW efficiency. Results show that the GWW efficiency for all GWW lengths is governed by hydrology, expressed as Qpeak. The results suggest that the threshold length for an effective GWW is 500 m for the hydrologic conditions in this study and for a representative drainage area of approximately 27 ha. For all storm events, a threshold drainage area gradient of approximately 3% was found above which the GWW efficiency was independent of topographic steepness. The results demonstrate similar trends to other studies although the relative increases in reduction in runoff and sediment delivery differ between sites and are very much dictated by Qpeak and hydrologic soil group. The effectiveness of models to evaluate GWW efficiency for nearly saturated conditions and shallow flows is discussed. 相似文献
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Papanicolaou GN 《Science (New York, N.Y.)》1942,95(2469):438-439
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Christopher G. Wilson A. N. Thanos Papanicolaou Kevin D. Denn 《Journal of Soils and Sediments》2012,12(6):966-981
Purpose
This study was developed to improve understanding of the temporal variability of sediment delivery in a representative, intensively agricultural, headwater system of the U.S. Midwest by identifying the primary sediment source (i.e., uplands or channel banks) to the fine suspended sediment loads of three consecutive runoff events (with the third event being a flash flood) using naturally occurring radionuclides.Materials and methods
Suspended sediment concentrations (C s) from discrete and continuous sampling techniques agreed well despite differences in operating principles. The total sediment flux (Q s) during each event was quantified over a 24-h period from the initiation of the rainfall using the following: (1) measured C s and flow discharges (Q w); (2) individual Q w?CQ s relationships for each event (herein called individual event relationships); and (3) a cumulative Q w?CQ s rating curve. The radionuclide tracers, beryllium-7 (7Be) and excess lead-210 (210Pbxs), were used with a simple two end-member mixing model to differentiate eroded upland surface soils and channel-derived sediments in the suspended loads of each event.Results and discussion
Total load estimates from the measurement-based values and individual event relationships were similar, within 10?%, because they accounted for an observed non-linearity between C s and Q w (i.e., a clockwise hysteresis) during the events. The sediment rating curve assumed a linear relationship between C s and Q w and under-estimated the loads of the first two events while over-estimating the load of the flood event. The radionuclide partitioning quantified the proportion of eroded upland soils at 67?% for the first event, which was attributed to a ??first flush?? of readily available material from past events. For the subsequent and flood-event loads, 34?% and 21?% were respectively derived from the uplands, because less material was readily available for mobilization. Proportions are based on integrated samples for each event and are consistent with individual samples where available. During the flood event, stream bank mass failure was observed and bank erosion estimates from multiple methods compared favorably with the load results.Conclusions
The radionuclide analysis showed decreasing proportions of eroded upland soils in the loads of the three successive events that was supported by observed clockwise hysteresis from source material exhaustion. Decreasing slopes observed in successive hysteresis plots for the events suggested that less material was readily available for mobilization following the first event flushing. The results of this study can assist watershed planners in identifying erosion-prone areas and determining optimal management strategies for sediment control. 相似文献6.
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Due to evolving molecular and informatics technologies, modern genome sequencing projects have more different characteristics than what most biologists have become accustomed to during the capillary-based sequencing era. In this paper, we explore the characteristics that made past insect genome projects successful and place them in the context of next-generation sequencing. By taking into account the intricacies of whitefly biology and the community, we present a roadmap for whitefly-omics, which focuses on the formation of an international consortium, deployment of informatic platforms and realistic generation of reference sequence data. 相似文献
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Composition and seasonal variation of the essential oil from leaves and peel of a Cretan lemon variety. 总被引：1，自引：0，他引：1
Stavroula A Vekiari Eftihios E Protopapadakis Parthena Papadopoulou Dimitrios Papanicolaou Christina Panou Manolis Vamvakias 《Journal of agricultural and food chemistry》2002,50(1):147-153
The essential oil of leaves and peel from the Cretan variety Zambetakis (Citrus limon) was obtained by steam distillation with a Clevenger apparatus. The essential oil was subjected to GC-MS analysis, and 35 substances were identified. The main component in both essential oils was limonene. beta-Pinene, myrcene, neral, geranial, neryl acetate, geranyl acetate, and beta-caryophyllene have been identified in the leaf oil. The peel oil contained gamma-terpinene, beta-pinene, myrcene, neral, and geranial. The quantification of volatile substances was based on the internal standard method, using octyl acetate as internal standard, and expressed in milligrams per kilogram of the essential oil. The high contents of neral and geranial were indicative of the high quality of both essential oils. The aroma profile and quantitative variations among the essential oil components were measured at six different time intervals over a period of greater than one year. Differences between the components of lemon leaves and peel were observed. 相似文献