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Spatial scale and the aggregation of stream macroinvertebrates associated with leaf packs (1998)

Murphy, John F. ; Giller, Paul S. ; Horan, Margaret A.

Oxford, UK : Blackwell Science Ltd, UK

Freshwater biology 39 (1998), S. 0

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ISSN: 1365-2427

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: 1. An experimental field study examined the aggregation of stream macroinvertebrates associated with leaf packs over different spatial scales (several metres–km) (extent), at different patch sizes (grain) and temporal scales (2 and 4 weeks).2. Standardized leaf packs were constructed and set in eighteen blocks of nine equally spaced packs in glide areas over a 2 km stretch of a wooded stream. The distribution of macroinvertebrates colonizing the artificial leaf packs was investigated to examine the extent of both intraspecific and interspecific aggregation across leaf packs.3. All major colonizing taxa were intraspecifically aggregated across the leaf packs. Aggregation decreased with increasing patch size (grain) (from pack to block), and also decreased with decreasing spatial extent (from 2 km stretch to within-block scale) with patch size held constant. Interspecific associations among all major taxa were not common on most occasions at the short temporal scale, although the proportion of significant associations tended to increase somewhat over time and with spatial scale, but did not exceed 42% of all possible associations. The vast majority of significant associations were positive rather than negative.4. The influence of heterogeneity in a number of environmental variables measured for each leaf pack (accumulated detritus and sediment, leaf mass, flow and depth) on the distribution of invertebrates was considered, but this could only partially explain the variation in macroinvertebrate abundance across leaf packs.5. The roles of intrinsic aggregation and stochastic processes were examined as alternative explanations for the distribution patterns observed. It is apparent from this study that intrinsic aggregation, in concert with resource partitioning, influences the community structure of stream macroinvertebrates associated with leaf packs. These findings may also have implications for the distribution of taxa in the benthos as a whole.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2427.1998.00284.x

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Making RMP hazard assessment meaningful (1998)

Murphy, John F. ; Zimmermann, Keith A.

New York, NY [u.a.] : Wiley-Blackwell

Process Safety Progress 17 (1998), S. 238-242

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ISSN: 1066-8527

Keywords: Chemistry ; Chemical Engineering

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology

Notes: The Brazoria County Petrochemical Council, 13 companies that are working together to enhance relations between industry and the community, united in a joint effort at complying with the EPA's Risk Management Program. One of the significant issues the group had to address was the need to develop meaningful hazard assessment for presentation to the public. The EPA's “Table Look-Up Approach” found in the Offsite Consequence Analysis Guidance document is certainly a good tool; however, the built-in conservatism results in over-estimates of potential hazard areas. Much more meaningful results are shown to be obtained using one of the hazard release models.The value of using a credible scenario with realistic meteorological data is demonstrated through the consistently smaller areas predicted by the PHAST Model for planning purposes. Realistic scenarios/failure modes and realistic model parameters are important so that the risk to the public is not overstated. Proprietary models such as PHAST are invaluable in providing more meaningful consequences for planning purposes.

Additional Material: 2 Tab.