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21.
Thomas J. Myers Sherman Swanson 《Journal of the American Water Resources Association》1992,28(4):743-754
ABSTRACT: Many natural and anthropogenic factors contribute to the stability or erodibility of stream channels. Although a stream rating procedure used by more than 60 percent of the U.S. National Forests provides an estimate of overall stability, it does not identify the cause of instability or indicate corrective management. To better sort natural from livestock influences, stream stability rating indicator variables were related to stream types and levels of ungulate bank damage in a large data base for streams in northern Nevada. Stability and the range in stability varied naturally with stream type. Ungulate bank damage had different effects on different stream types and on different parts of their cross-sections. Vegetation is more important for stability on certain stream types than on other types. Streams with noncohesive sand and gravel banks are most sensitive to livestock grazing. Range managers should consider the stream type when setting local standards, writing management objectives, or determining riparian grazing strategies. 相似文献
22.
A generalized approach for producing,quantifying, and validating citizen science data from wildlife images 总被引:1,自引:0,他引:1
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Alexandra Swanson Margaret Kosmala Chris Lintott Craig Packer 《Conservation biology》2016,30(3):520-531
Citizen science has the potential to expand the scope and scale of research in ecology and conservation, but many professional researchers remain skeptical of data produced by nonexperts. We devised an approach for producing accurate, reliable data from untrained, nonexpert volunteers. On the citizen science website www.snapshotserengeti.org , more than 28,000 volunteers classified 1.51 million images taken in a large‐scale camera‐trap survey in Serengeti National Park, Tanzania. Each image was circulated to, on average, 27 volunteers, and their classifications were aggregated using a simple plurality algorithm. We validated the aggregated answers against a data set of 3829 images verified by experts and calculated 3 certainty metrics—level of agreement among classifications (evenness), fraction of classifications supporting the aggregated answer (fraction support), and fraction of classifiers who reported “nothing here” for an image that was ultimately classified as containing an animal (fraction blank)—to measure confidence that an aggregated answer was correct. Overall, aggregated volunteer answers agreed with the expert‐verified data on 98% of images, but accuracy differed by species commonness such that rare species had higher rates of false positives and false negatives. Easily calculated analysis of variance and post‐hoc Tukey tests indicated that the certainty metrics were significant indicators of whether each image was correctly classified or classifiable. Thus, the certainty metrics can be used to identify images for expert review. Bootstrapping analyses further indicated that 90% of images were correctly classified with just 5 volunteers per image. Species classifications based on the plurality vote of multiple citizen scientists can provide a reliable foundation for large‐scale monitoring of African wildlife. 相似文献
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Huntington S. Swanson Charles S. Beightler Don T. Phillips 《Journal of the American Water Resources Association》1971,7(4):708-716
ABSTRACT .The problem analyzed in this paper is how to allocate optimally the available surface water in a river system among those who compete for its use, while acknowledging explicitly that for coastal states the ecology of bays and estuaries must be numbered among the competitors. The objective is to maximize the benefit resulting from water use while satisfying a set of constraints on flow. Benefit is assumed to be a function of the amount of water used and the time period in which the water is used. A mathematical model of this problem is shown to fit the format of the minimum cost circulation network flow problem. The Out-of-Kilter algorithm of D. R. Fulkerson is proposed as a solution technique. Sensitivity analysis on the input data is described as a means of determining the minimum economic benefit required to justify the allocation of a given volume of water needed to sustain the ecology of an estuary. 相似文献
25.
C. L. Swanson R. L. Shogren G. F. Fanta S. H. Imam 《Journal of Polymers and the Environment》1993,1(2):155-166
Recent starch-plastic research at the National Center for Agricultural Utilization Research is reviewed and related worldwide efforts are noted. Properties of starch that influence its formulation and performance in plastics are discussed. Methods are given for preparation of starch-poly(methyl acrylate) graft copolymer, starch-poly(ethylene-co-acrylic acid), and starch-poly(ethylene-co-acrylic acid)-polyethylene plastics. Their physical properties are discussed, as is degradability by enzymes or amylolytic organisms from soil, ponds, and streams.The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned. 相似文献
26.
Robert H. Swanson 《Journal of the American Water Resources Association》1998,34(4):755-763
ABSTRACT: Forest hydrology should be a mature science with routine use of hydrological procedures to evaluate the effect of past, current and proposed harvesting practices on water resources. It is not. However, water users are pressuring forest managers to exercise their role in managing forested watersheds for water supply. Most forest managers are poorly equipped to carry out this role. Forestry schools need to ensure that their graduates, whether employed in forest management positions or as specialists in watershed management, understand that all forestry operations may affect instream or downstream water users. Specialists in forest hydrology should be fully aware of the following: (1) climate and watershed characteristics influence streamflow in separate ways; (2) forestry practices produce changes in water yield and quality, and that only these changes need to be evaluated to estimate their effects; (3) watershed storage is a critical factor in evaluating the effects of harvesting on streamflow; and (4) the effect of harvest on one watershed cannot be extrapolated to another without consideration of the processes affected. Research is needed to assist watershed managers in applying models to watersheds for which climate and streamflow data are insufficient. Research is also needed to incorporate climate, streamflow and other data for hydrological models into geographic information systems. Joint research projects are needed to develop physical relationships between stream channel characteristics of importance to fisheries biologists and streamflow characteristics affected by forest harvest. 相似文献
27.
Endogenous swimming rhythms of blue crab, Callinectes sapidus , megalopae: effects of offshore and estuarine cues 总被引:1,自引:0,他引:1
Larvae of the blue crab Callinectes sapidus Rathbun develop on the continental shelf. The postlarval stage (megalopa) occurs near the surface and is transported shoreward
by wind-driven surface currents. It then uses selective tidal stream transport for migration up an estuary. Endogenous swimming
rhythms were measured under constant dark conditions in the laboratory in megalopae collected from the Newport River Estuary
(North Carolina), the Delaware Bay, and offshore from the Newport River Estuary. Megalopae from all areas had a similar circadian
activity rhythm, in which they swam during the time of the day phase in the field and were inactive at night. This rhythm
predicts the presence of a reverse, diel, vertical-migration pattern offshore which would contribute to the location of megalopae
near the surface during the day. The rhythm lacks obvious ecological significance in estuaries because it does not contribute
to selective tidal stream transport and would increase vulnerability to visual predators during the day. Attempts to entrain
a circatidal rhythm in swimming by cyclic and step changes in salinity were unsuccessful, as the circadian rhythm persisted.
The rhythm also continued in the presence of the eelgrass Zostera marina, which is a site of settlement and metamorphosis in the field. Thus, megalopae enter estuaries with a solar day rhythm in
activity. This rhythm, however, is not expressed, because light inhibits swimming during the day upon exposure to estuarine
water. Since this light inhibition is removed in offshore waters, the rhythm would be expressed if, after entering an estuary,
megalopae were transported back to offshore areas.
Received: 19 December 1995 / Accepted: 2 August 1996 相似文献
28.
29.
Symbiotic Aiptasia pulchella and freshly isolated zooxanthellae were incubated in NaH14CO3 and NH4Cl for 1 to 240 min, and samples were analysed by reverse-phase high-performance liquid chromatography (HPLC) and an online
radiochemical detector. NH4
+ was first assimilated into 14C-glutamate and 14C-glutamine in the zooxanthellae residing in A. pulchella. The specific activities (dpm nmol−1) of 14C-glutamate and 14C-glutamine in vivo, were far greater in the zooxanthellae than in the host tissue, indicating that NH4
+ was principally incorporated into the glutamate and glutamine pools of the zooxanthellae. 14C-α-ketoglutarate was taken up from the medium by intact A. pulchella and assimilated into a small amount of 14C-glutamate in the host tissue, but no 14C-glutamine was detected in the host fraction. The 14C-glutamate that was synthesized was most likely produced from transamination reactions as opposed to the direct assimilation
of NH4
+. The free amino acid composition of the host tissue and zooxanthellae of A. pulchella was also measured. The results presented here demonstrate that NH4
+ was initially assimilated by the zooxanthellae of A. pulchella.
Received: 3 February 1997 / Accepted: 24 October 1997 相似文献
30.