2,426 research outputs found
Constraining Holocene hydrological changes in the CarpathianâBalkan region using speleothem δ18O and pollen-based temperature reconstructions
Here we present a speleothem isotope record (POM2) from AscunsÄ Cave (Romania) that provides new data on past climate changes in the CarpathianâBalkan region from 8.2 ka until the present. This paper describes an approach to constrain the effect of temperature changes on calcite δ18O values in stalagmite POM2 over the course of the middle Holocene (6â4 ka), and across the 8.2 and 3.2 ka rapid climate change events. Independent pollen temperature reconstructions are used to this purpose. The approach combines the temperature-dependent isotope fractionation of rain water during condensation and fractionation resulting from calcite precipitation at the given cave temperature. The only prior assumptions are that pollen-derived average annual temperature reflects average cave temperature, and that pollen-derived coldest and warmest month temperatures reflect the range of condensation temperatures of rain above the cave site. This approach constrains a range of values between which speleothem δ18O changes should be found if controlled only by surface temperature variations at the cave site. Deviations of the change in δ18Ocspel values from the calculated temperature-constrained range of change are interpreted towards large-scale variability of climateâhydrology.
Following this approach, we show that an additional âź0.6â° enrichment of δ18Oc in the POM2 stalagmite was caused by changing hydrological patterns in SW Romania across the middle Holocene, most likely comprising local evaporation from the soil and an increase in Mediterranean moisture δ18O. Further, by extending the calculations to other speleothem records from around the entire Mediterranean basin, it appears that all eastern Mediterranean speleothems recorded a similar isotopic enrichment due to changing hydrology, whereas all changes recorded in speleothems from the western Mediterranean are fully explained by temperature variation alone. This highlights a different hydrological evolution between the two sides of the Mediterranean.
Our results also demonstrate that during the 8.2 ka event, POM2 stable isotope data essentially fit the temperature-constrained isotopic variability. In the case of the 3.2 ka event, an additional climate-related hydrological factor is more evident. This implies a different rainfall pattern in the Southern Carpathian region during this event at the end of the Bronze Age
Pesticide Use Changes in New York Vegetables: 1978 to 1998
Pesticide use patterns in 1978 and 1998 were compared for 15 vegetable crops grown in New York State. Insecticide use decreased in almost all vegetables over this period, with an overall decline of 65%. Total herbicide use declined 24%, while fungicide use increased 76%. Within crops, potatoes and onions received more than 60% of all pesticide use on vegetables. Large declines in pesticide use occurred in some crops and usually were associated with the substitution of low use-rate for high use-rate insecticides or herbicides. Strategies for future reductions in pesticide use are discussed
Larval Performance in Relation to Labile Oviposition Preference of Crocidolomia pavonana [F.] (Lepidoptera: Pyralidae) Among Phenological Stages of Cabbage
Crocidolomia pavonana (=binotalis) [F.] demonstrates oviposition peaks in the field that we believe to be correlated with host plant phenology. In previous two-choice laboratory experiments, we found the highest relative proportion of oviposition on cabbage to correspond either to plant growth stages ≈7–8 wk or ≈9–11 wk old, depending on the alternate host plant with which it was presented. In cabbage-only trials, leaves from 7- to 8-wk-old plants were preferred. Inconsistency in preference led to the question of whether oviposition on either cabbage growth stage would confer adaptive advantages in offspring performance. We simulated oviposition on four phenological stages of cabbage in two ways. In a study of complete immature development, growth rate, pupal weight, and survivorship were measured. We also compared food utilization efficiency during the fourth larval instar by analyzing growth rate, efficiency of biomass accumulation, and frass production by analysis of covariance (ANCOVA). For both experiments, cabbage plants of defined phenological stages were designated at the time of oviposition, and larvae were fed from these as plants continued to grow throughout larval development. Our data indicate adaptive advantages in larval growth rate and food conversion efficiency to oviposition on cabbage at ≈7–8 wk from planting. Oviposition on later cabbage growth stages resulted in comparatively poor larval performance. Possible explanations for C. pavonana oviposition behavior in light of these results are discusse
Effects of Host Plant Phenology on Oviposition Preference of Crocidolomia pavonana (Lepidoptera: Pyralidae)
Field studies have demonstrated mixed success in trap cropping to manage Crocidolomia pavonana (=binotalis) [F.], a major pest of cruciferous crops in Asia. A possible explanation for this is an influence of host plant phenology on oviposition preference. We tested this in simultaneous two-choice oviposition bioassays under laboratory conditions. In cylindrical cardboard experimental arenas, with 5-cm2 leaf windows, individual C. pavonana females were offered eight sequential phenological stages of cabbage (Brassica oleracea L., Capitata group, cultivar Gloria) with a constant stage of preflowering Indian mustard (Brassica juncea, variety rugosa, cultivar Green Wave). Results showed a significant effect of cabbage developmental stage on oviposition preference. We continued with two-choice bioassays, using whole leaves, in screen cage experimental arenas. Females were offered the three most preferred phenological stages of cabbage and differing stages of four potential trap crop alternatives: preflowering Indian mustard; preflowering Chinese cabbage (B. rapa L., variety pekinensis [Lour.] Olsson); preflowering, flowering, and "with siliqueâ sawi manis (B. rapa, variety parachinensis [Bailey] Tsen and Lee); and preflowering and flowering sayur pahit (B. rapa, variety parachinensis [Bailey] Tsen and Lee). Results indicated that the phenological stages of both plants had a significant effect on relative oviposition preference. However, patterns of preference changed in the context of the different plant species combinations. In addition, implicit hierarchical preference order was frequently contradicted. These results have implications for the improvement of trap cropping strategies to manage C. pavonana and for the potential success of biological control of Plutella xylostella [L.], where these pests occur in comple
Symmetry and Electronic Structure of Noble Metal Nanoparticles and the Role of Relativity
High resolution photoelectron spectra of cold mass selected Cu_n-, Ag_n- and
Au_n- with n =53-58 have been measured at a photon energy of 6.42 eV. The
observed electron density of states is not the expected simple electron shell
structure, but seems to be strongly influenced by electron-lattice
interactions. Only Cu55- and Ag55- exhibit highly degenerate states. This is a
direct consequence of their icosahedral symmetry, as is confirmed by density
functional theory calculations. Neighboring sizes exhibit perturbed electronic
structures, as they are formed by removal or addition of atoms to the
icosahedron and therefore have lower symmetries. Gold clusters in the same size
range show completely different spectra with almost no degeneracy, which
indicates that they have structures of much lower symmetry. This behaviour is
related to strong relativistic bonding effects in gold, as demonstrated by ab
initio calculations for Au55-.Comment: 10 pages, 3 figure
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