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Results for “Journal of North American Benthological Society”

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58 records · Page 4Linked to original sources
USGS2002

Sampling effort affects multivariate comparisons of stream assemblages

Multivariate analyses are used widely for determining patterns of assemblage structure, inferring species–environment relationships and assessing human impacts on ecosystems. The estimation of ecological patterns often depends on sampling effort, so the degree to which sampling effort affects the outcome of multivariate analyses is a concern. We examined the effect of sampling effort on site and group separation, which was measured using a mean similarity method. Two similarity measures, the Jaccard Coefficient and Bray–Curtis Index were investigated with 1 benthic macroinvertebrate and 2 fish data sets. Site separation was significantly improved with increased sampling effort because the similarity between replicate samples of a site increased more rapidly than between sites. Similarly, the faster increase in similarity between sites of the same group than between sites of different groups caused clearer separation between groups. The strength of site and group separation completely stabilized only when the mean similarity between replicates reached 1. These results are applicable to commonly used multivariate techniques such as cluster analysis and ordination because these multivariate techniques start with a similarity matrix. Completely stable outcomes of multivariate analyses are not feasible. Instead, we suggest 2 criteria for estimating the stability of multivariate analyses of assemblage data: 1) mean within-site similarity across all sites compared, indicating sample representativeness, and 2) the SD of within-site similarity across sites, measuring sample comparability.

Journal of the North American Benthological Societ↗
USGS1999

Behavioral responses to disturbance in freshwater mussels with implications for conservation and management

Knowledge about the ability of freshwater unionid mussels to recover from physical disturbance is important to their conservation and management. Threatened species may be disturbed by relocation to refugia as a conservation measure, and some species are disturbed by size- and species-selective harvesting of shells for use in the production of cultured pearls. The activity of freshwater unionid mussels generally decreases with water temperature, but intra- and interspecific differences in the frequency and distribution of recovery behaviors following disturbances at specific water temperatures have not been previously quantified. We observed righting, moving, and burrowing behavior of 4 mussel species, Amblema plicata plicata, Potamilus alatus, Fusconaia flava, and Lampsilis cardium, at 3 water temperatures (7, 14, and 21°C). The temporal frequency (intensity) and times-to-1st-event of behaviors were analyzed using proportional hazards models. Righting events and consecutive movements occurred at different intensities among temperatures and species. For righting, intensity increased by 8%/°C within the range of 7-21°C. Subsequent movements increased in intensity by 10%/°C. Amblema plicata was the slowest to respond, and had an intensity of turning upright only 27% of that for P. alatus. The intensities of movements for A. plicata and F. flava were 16% of those for P. alatus. Lampsilis cardium righted themselves most quickly, and had an intensity of righting 124% of that for P. alatus. The distribution of the 3 behaviors among treatment groups at 1 wk was analyzed with a proportional odds model. The distribution of righting, moving, and burrowing 1 wk after disturbance was described entirely by high-order interactions in our proportional odds model. Therefore, that model revealed little interpretable pattern in the endpoint data and it was less sensitive than our analysis of time-to-event data for measuring the effects of disturbance. We attributed the difference in sensitivity between the 2 models to the greater information content of time-until-event data. For similar studies of occurrences of key events, times to events should be recorded and interpreted whenever feasible and consistent with study objectives. Our results suggest that water temperature has an important effect on the outcome of mussel conservation projects and commercial harvesting activities. Our modeling approach, applied to other species, could help guide decisions about which species can safely be disturbed and the optimal seasonal timing of those disturbances.

Journal of the North American Benthological Societ↗
USGS1999

Evaluating adequacy of the representative stream reach used in invertebrate monitoring programs

Selection of a representative stream reach is implicitly or explicitly recommended in many biomonitoring protocols using benthic invertebrates. We evaluated the adequacy of sampling a single stream reach selected on the basis of its appearance. We 1st demonstrated the precision of our within-reach sampling. Then we sampled 3 or 4 reaches (each ∼20× mean width) within an 8-16 km segment on each of 8 streams in 3 ecoregions and calculated 4 common metrics: 1) total taxa; 2) Ephemeroptera, Plecoptera, and Trichoptera taxa; 3) biotic index; and 4) Shannon's diversity index. In only 6% of possible cases was the coefficient of variation for any of the metrics reduced >10% by sampling additional reaches. Sampling a 2nd reach on a stream improved the ability to detect impairment by an average of only 9.3%. Sampling a 3rd reach on a stream additionally improved ability to detect impairment by only 4.5%. We concluded that a single well-chosen reach, if adequately sampled, can be representative of an entire stream segment, and sampling additional reaches within a segment may not be cost effective.

Journal of the North American Benthological Societ↗
USGS2006

Variability and regulation of denitrification in an Upper Mississippi River backwater

Sediments in the backwaters of the Upper Mississippi River (UMR) are highly organic and provide an optimal environment for N removal. We monitored an 8.6-ha UMR backwater site near La Crosse, Wisconsin, for nearly 3 y to assess temporal variability, seasonal trends, and the factors regulating denitrification. We measured rates of unamended denitrification (DEN) and denitrification enzyme activity (DEA) rates at ambient temperature and DEA at 30 degrees C (DEA30). Seasonal mean (+/- 1 SE) DEN rates ranged from 0.041 +/- 0.015 to 0.47 +/- 0.23 mu g N cm(-2) h(-1)and were highest in winter and lowest in autumn. Seasonal rates of DEA exhibited a different pattern with the highest rates in summer (25.6 +/- 3.4 mu g N cm(-2) h(-1)) and the lowest rates in winter (10.6 +/- 2.1 mu g N cm(-2) h(-1)). The overall mean DEA30 rate was 31.0 +/- 1.9 mu g N cm(-2) h(-1) but showed no significant seasonal pattern. Short-term (weekly) and seasonal variability exhibited by rates of DEN and DEA were best explained by water-column NO3- concentration and temperature, respectively. No environmental variables explained a significant amount of variability in DEA30. Our results suggest that nutrient (i.e., NO3-) availability and temperature are both regulators of denitrification, with NO3- concentration being the most important limiting factor in this system. The high DEN rates during winter were in response to elevated NO3- concentrations resulting from a chain reaction beginning with algal blooms creating oxic conditions that stimulated nitrification. Increasing hydrological connectivity in large rivers as a river management tool to reduce N flux to downstream areas may be beneficial.

Journal of the North American Benthological Societ↗