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461.
In the Atlantic Coastal Plain region of southern Georgia (USA), cotton (Gossypium hirsutum L.) acreage increased threefold in the past decade. To more effectively protect water quality in the region, best management practices are needed that reduce pesticide runoff from fields in cotton production. This study compared runoff of two herbicides, fluometuron [N,N-dimethyl-N'-[3-(trifluoromethyl)-phenyl]-urea] and pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitro-benzenamine], from plots in strip-tillage (ST) and conventional-tillage (CT) management near Tifton, GA. Rainfall simulations were conducted one day after preemergence herbicide applications to 0.0006-ha plots and runoff from 0.15-ha plots due to natural rainfall following preemergence pendimethalin and fluometuron and postemergence fluometuron use was monitored. Pendimethalin runoff was greater under CT than ST due to strong pendimethalin soil sorption and higher erosion and runoff under CT. The highest losses, 1.3% of applied in CT and 0.22% of applied in ST, were observed during rainfall simulations conducted 1 DAT. Fluometuron runoff from natural rainfall was substantially lower from ST than from CT plots but the trend was reversed in rainfall simulations. In all studies, fluometuron runoff was also relatively low (<1% of applied), and on plots under natural rainfall, desmethylfluometuron (DMF) represented about 50% of total fluometuron runoff. Fluometuron's relatively low runoff rate appeared linked to its rapid leaching, and high DMF detection rates in runoff support DMF inclusion in fluometuron risk assessments. Results showed that ST has the potential to reduce runoff of both herbicides, but fluometuron leaching may be a ground water quality concern. 相似文献
462.
Henry H. Sprague Richard Block Jonathan W. Bulkley 《Journal of the American Water Resources Association》1983,19(6):1003-1006
ABSTRACT: The production of videotape as a product of a water resources seminar is an innovative approach to graduate education. The research effort required builds upon the traditional graduate seminar approach. The videotape production requires research effort to be focused into a coherent body of information which may be widely disseminated and effectively communicates information to the public. The use of outside speakers and field trips blends very well into the preparation of a videotape. The requriement to present the many sides of a complex water resource issue in a fair and equitable manner requires maturity and professional capability on the part of the students. The research effort requires the students to meet their professional obligation to present an objective, factual, and accurate statement of the issues studies. 相似文献
463.
Sebastian Theis Jonathan L.W. Ruppert Karling N. Roberts Charles K. Minns Marten Koops Mark S. Poesch 《Conservation biology》2020,34(1):41-53
Land-use change via human development is a major driver of biodiversity loss. To reduce these impacts, billions of dollars are spent on biodiversity offsets. However, studies evaluating offset project effectiveness that examine components such as the overall compliance and function of projects remain rare. We reviewed 577 offsetting projects in freshwater ecosystems that included the metrics project size, type of aquatic system (e.g., wetland and creek), offsetting measure (e.g., enhancement, restoration, and creation), and an assessment of the projects’ compliance and functional success. Project information was obtained from scientific and government databases and gray literature. Despite considerable investment in offsetting projects, crucial problems persisted. Although compliance and function were related to each other, a high level of compliance did not guarantee a high degree of function. However, large projects relative to area had better function than small projects. Function improved when projects targeted productivity or specific ecosystem features and when multiple complementary management targets were in place. Restorative measures were more likely to achieve targets than creating entirely new ecosystems. Altogether the relationships we found highlight specific ecological processes that may help improve offsetting outcomes. 相似文献
464.
Constraints on tree seedling establishment in montane grasslands of the Valles Caldera, New Mexico 总被引:1,自引:0,他引:1
Montane and subalpine grasslands are prominent, but poorly understood, features of the Rocky Mountains. These communities frequently occur below reversed tree lines on valley floors, where nightly cold air accumulation is spatially coupled with fine soil texture. We used field experiments to assess the roles of minimum temperature, soil texture, grass competition, and ungulate browsing on the growth, photosynthetic performance, and survival of transplanted ponderosa pine (Pinus ponderosa) seedlings at 32 sites straddling such reversed tree lines in the Valles Caldera National Preserve (VCNP) of the Jemez Mountains, New Mexico (USA). Seedling growth increased most strongly with increasing nighttime minimum temperatures away from the valley bottoms; seedlings experiencing the coldest temperatures on the caldera floor exhibited stunted needles and often no measurable height growth. Based on the chlorophyll fluorescence ratios PhiPSII and Fv/Fm, we found that low minimum temperatures, low soil moisture, and fine soil texture all contributed to photoinhibition. Neighboring herbs had only minor negative effects on seedlings. We found no effect of ungulates, but golden-mantled ground squirrels (Spermophilus lateralis) caused substantial seedling mortality. Second-year seedling survival was highest on sandy soils, and third-year survival was highest at sites with higher minimum temperatures. We conclude that differential tree seedling establishment driven by low minimum temperatures in the valley bottoms is the primary factor maintaining montane grasslands of the VCNP, although this process probably operated historically in combination with frequent surface fire to set the position of the tree line ecotone. As at alpine tree lines, reversed tree lines bordering montane and subalpine grasslands can represent temperature-sensitive boundaries of the tree life form. 相似文献
465.
Ecotone shift and major droughts during the mid-late Holocene in the central Tibetan Plateau 总被引:1,自引:0,他引:1
A well-dated pollen record from a large lake located on the meadow-steppe ecotone provides a history of ecotone shift in response to monsoonal climate changes over the last 6000 years in the central Tibetan Plateau. The pollen record indicates that the ecotone shifted eastward during 6000-4900, 4400-3900, and 2800-1600 cal. yr BP when steppes occupied this region, whereas it shifted westward during the other intervals when the steppes were replaced by meadows. The quantitative reconstruction of paleoclimate derived from the pollen record shows that monsoon precipitation fluctuated around the present level over the last 6000 years in the central Tibetan Plateau. Three major drought episodes of 5600-4900, 4400-3900, and 2800-2400 cal. yr BP are detected by pollen signals and lake sediments. Comparison of our record with other climatic proxy data from the Tibetan Plateau and other monsoonal regions shows that these episodes are three major centennial-scale monsoon weakening events. 相似文献
466.
Pair bonds can end in two different ways: either death of the partner or divorce, where the frequency of divorce varies enormously
among bird species, from 0% to 100%. To better understand this variation, we created and analyzed the largest dataset so far,
consisting of 158 species and 20 variables that quantify the species’ body size, life history, diet, and other characteristics.
Our results suggest that species with a high divorce rate have a high mortality rate, tend to be ornamented and sexually dichromatic,
live colonially, and form part-time rather than continuous partnerships. Traits quantifying body size or life history are
often nonlinearly related with divorce rate. These nonlinearities might (partly) be caused by nonlinear relationships of the
same traits with mortality rate which is, in turn, linearly related with divorce rate. In contrast to what has been found
previously, mortality rate appears as a key factor for divorce rate in our study. This makes sense, as the likelihood that
a partner survives from one year to the next decreases with increasing mortality rate, diminishing the likely success of a
partner that attempts to locate its previous partner. We also found taxonomic differences in divorce rate. Specifically, Anseriformes
have an exceptionally low divorce rate, which, however, can be explained by the generally important determinants of divorce
rate: They also have a lower mortality rate, lower degree of ornamentation and coloniality, and more continuous partnerships
than members of other orders.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
467.
We used guppies to study repeatability in sperm competitiveness and postcopulatory sexual selection on male ornamentation.
In a block design involving 25 pairs of males, artificial insemination was used to mate each pair (A and B) to four unrelated
females—two that were mated with the combined ejaculates of both males (sperm-competition treatment) and two receiving sperm
from each of the two males individually (single-male treatment). Our analysis revealed significantly repeatable patterns of
paternity across females in the sperm-competition treatment, suggesting that certain males are intrinsically better sperm
competitors than others, irrespective of female identity. Next, we compared mean brood success (number of offspring per brood)
between sperm competition and single-male treatments. We found no significant effect of treatment on female fecundity, suggesting
that the previously reported direct benefits of polyandry in this species may be due to factors such as differential maternal
effects or differences in the number of inseminated sperm between treatments. Our artificial insemination assay was designed
to control both factors. Finally, we determined whether variation in relative paternity was random with respect to male phenotype.
Unlike previous work on Trinidadian populations, we found no significant relationship between male sexual ornamentation and
sperm competitiveness in the focal population. 相似文献
468.
469.
Jessica L. D'Ambrosio Andrew D. Ward Jonathan D. Witter 《Journal of the American Water Resources Association》2015,51(4):910-922
Straight, trapezoidal‐shaped surface drainage channels efficiently drain the soil profile, but their deviations from natural fluvial conditions drive the need for frequent maintenance. Ecological and socioeconomic impacts of drainage ditch maintenance activities can be significant, leading to harmful algal blooms and increased sedimentation. We developed a two‐stage ditch design that is more consistent with fluvial form and process. The approach has potential to enhance ecological services while meeting drainage needs essential for agricultural production. We studied geomorphic change of the inset channel, benches and banks of seven two‐stage ditches in Ohio, Indiana, and Michigan. Three to 10 years after construction, inset channel changes reflected natural adjustments, but not all ditches had reached their quasi‐equilibrium state. Ditches had experienced both degradation and aggradation on the benches at a rate of 0.5‐13 mm/yr. Aggradation on the benches was not likely to threaten tile drain outlets. Localized scour was observed on the banks at some sites, but at all but one site changes were not statistically significant. Except for the removal of woody vegetation, none of the ditches required routine maintenance since construction. Two‐stage ditches can be a stable, viable option for drainage ditch management if designed and installed properly on the landscape. 相似文献
470.
Longwen Chen Michel Ondarts Jonathan Outin Yves Gonthier Evelyne Gonze 《环境科学学报(英文版)》2018,30(12):58-70
Processes based on non-thermal plasma (NTP) for indoor air treatment inevitably lead to the formation of toxic by-products such as ozone (O3) and nitrogen oxides (NOx). Adding a step of heterogeneous catalysis in series with NTP could allow for the decomposition of the by-products. Therefore, different catalysts were developed based on transition metal oxides, such as NiOx, CoOx and MnOx with different weight percentage 1, 5 and 10 wt.%, deposited on a γ-Al2O3 support. The O3 removal efficiency (ORE) and the NOx removal efficiency (NRE) were very encouraging in dry air: about 65% and 80%, respectively, by using 2 g 5 wt.% MnOx/Al2O3 catalyst under the experimental conditions. However, strongly negative effects of relative humidity (RH) on the catalytic decomposition performance were observed. To overcome this limitation, the catalyst surface was modified to make it hydrophobic using a cost-effective chemical grafting method. This treatment consisted in impregnating the 5 wt.% MnOx/Al2O3 catalyst with different trichloro(alkyl)silanes (TCAS). The effects of different linker lengths and amounts of TCAS for the hydrophobicity and the decomposition performance of surface-modified catalysts under humid conditions were investigated. Our results show that the surface-modified catalyst with the shortest linker and 0.25 mmol/gcat of modifying agent represents the best catalytic decomposition performance for O3. Its ORE is 41% at 60% RH, which is twice that of the non-modified catalyst. 相似文献