William J. Gerth

Effect of sampling different habitat types in regional macroinvertebrate bioassessment surveys

Abstract One of the dilemmas in designing any large-scale macroinvertebrate bioassessment is deciding where to sample within streams. Streams contain a wide variety of habitats with varying macroinvertebrate assemblages, yet consistency in sampling protocol is needed to interpret results across sites in a region. The Environmental Monitoring and Assessment Program (EMAP) conducted large regional probability surveys in the mid-Atlantic (1993–1998) and the western US (2000–2001). In these surveys, 2 macroinvertebrate sample types were collected at each site: pool and riffle in the mid-Atlantic region, and reachwide and riffle in the western US. We analyzed data from sites where both types of samples had been collected (206 mid-Atlantic and 293 western US sites) to examine the effects of sample type on typical metric and multivariate analyses done in bioassessments. Sample types differed in terms of taxon richness measures and assemblage composition, and differences were more pronounced between mid-Atlantic riffle and pool samples than between western US reachwide and riffle samples. Nonetheless, sample-type differences did not obscure the overall pattern in ordination analyses, nor did they influence detection of important environmental gradients. In addition, bioassessments based on Ephemeroptera, Plecoptera, and Trichoptera taxon richness showed that regional assessments differed little with sample type. Our analyses indicate that typical bioassessment methods are relatively robust with respect to sample type in regional surveys. Reachwide sampling could be used with little risk to the quality of assessments in surveys covering large geographic areas where a single targeted habitat may not occur at all sites. Reachwide sampling is also easy to apply consistently at most sites and requires approximately the same effort and cost as single-habitat sampling.

Fish Use of Intermittent Watercourses Draining Agricultural Lands in the Upper Willamette River Valley, Oregon

Historically, the upper Willamette River valley in western Oregon was characterized by seasonal floods and large expansions of its stream network. During the past century, human activities have altered or eliminated many intermittent stream and floodplain habitats in the valley. As a result, the remaining intermittent streams and ditches, referred to as watercourses, may still provide habitat that is critical for native fish. Our objectives were to determine (1) fish presence, (2) the spatial gradients of fish distribution (including species identity, native versus nonnative status, and numbers), (3) fish use of the intermittent streams as spawning and nursery habitats, and (4) the main factors that influence the numbers of fish and fish species. In the winter and spring of 2002-2003, we examined the distributions of fish species in five subbasins within the Willamette River valley. The sampling sites were in intermittent watercourses that drained grass seed- producing fields. We collected water samples and sampled fish from December to May with minnow traps and an electrofishing unit and collected data on the standard fish habitat variables at all sites in spring. Thirteen fish species were found and only three of them were exotic. The presence of recently hatched and juvenile fish shows that intermittent watercourses offer conditions suitable for spawning and juvenile rearing. The two watershed-scale variables with the most influence on fish species richness were the percentage of the watershed covered by forest and the distance to perennial water, the first of which had a direct relationship to species diversity and the second an inverse relationship. In turn, fish abundance had a negative, albeit modest, relationship with the distance to perennial water. Among local-scale variables, water velocity and conductivity were inversely related to species richness and fish numbers. Our results highlight the relevance of intermittent agricultural watercourses for native fish species in the Willamette River valley and call for the promotion of agricultural conservation practices that benefit farmers while maintaining aquatic biodiversity in floodplain habitats.

Introduction of the exotic tick Hyalomma truncatum on a human with travel to Ethiopia: A case report

An Oregon resident returned from a photography trip to Ethiopia with a male Hyalomma truncatum tick attached to the skin on his lower back. The tick was identified morphologically and deposited in the U.S. National Tick Collection housed at Georgia Southern University, Statesboro, Georgia. The public health importance of Hyalomma species of ticks and diagnostic dilemmas with identifying exotic ticks imported into the U.S. are discussed.

Diversity of Large-Bodied Macroinvertebrates in Ponds Created on the Debris-Avalanche Deposit Following the 1980 Eruption of Mount St. Helens

The numerous ponds formed in the weeks following the 1980 eruption of Mount St. Helens provided a unique opportunity to investigate macroinvertebrate communities in young (23- to 25-year-old) fishless ponds following a large natural disturbance. Over a 3-year period, Large-bodied macroinvertebrates were sampled from 97 ponds with a range of hydroperiods and biophysical characteristics. Macroinvertebrate communities from these ponds were spatially and temporally variable in spite of their close geographical proximity, shared regional species pool, and similar creation history. We identified 110 taxa, many of which were observed at only one pond or in only one year. Community differences appeared to be influenced more by pond size and riparian tree development rather than by hydroperiod alone, and stochastic colonization events were likely an important factor determining community composition.