SA012
Macroinvertebrate species list of the Andrews Experimental Forest, 1992/1993

PRINCIPAL INVESTIGATOR:

Judith L. Li

ORIGINATOR:

Stanley V. Gregory

OTHER RESEARCHER:

Alan Herlihy, William J. Gerth, J. Boone Kauffman

DATA SET CONTACT PERSON:

Donald L. Henshaw

METADATA CREATION DATE:

20 Oct 1995

MOST RECENT METADATA REVIEW DATE:

4 Mar 2013

KEYWORDS:

Insects, Long-Term Ecological Research (LTER), Populations, Spatial variability, Streams, Trophic structure, Populations

METHODS:

Experimental Design - SA012:

Description:

The diversity and environmental sensitivity of lotic invertebrates make them useful indicators of stream conditions; consequently macroinvertebrates have become increasingly popular in regional comparisons of streams (Hilsehoff 1988; Kerans and Kerr 1994; Rosenberg and Resh 1993). However, spatial and temporal variability in abundance and diversity among individual collections (at the reach scale) can make detection of differences among streams difficult (Norris and Georges 1993) necessitating some level of replication or physical compositing of samples. A dilemma we often face is how to determine the adequate number of samples. One approach has been to adjust the number of replicates to yield the desired level of precision (Elliott, 1977; Resh 1979); a criterion of ñ40% mean total abundances has been suggested as a practical goal (Resh and McElravy 1993; Pinder el al 1987). Another approach has been to evaluate the stability of the mean with increasing sampling effort (Elliott, 1977). These methods are limited by relying heavily on numerical abundance, with little regard for other assemblage attributes.

Our approach for assessing sampling adequacy was to consider a number of broadly representative metrics, and to identify appropriate levels of sampling effort to achieve stable values of these assemblage measures, somewhat analogous to one method suggested in Elliott (1977). Biomonitoring programs often use descriptors (often called metrics) designed to represent three basic assemblage characteristics: numerical abundance (total numbers of individuals), measures of diversity (taxa richness, diversity indices, and measures of evenness or dominance), and proportional abundances (proportions of total numbers including groups or taxa of special interest such as taxonomic order, dominant taxa, functional feeding groups or pollution-tolerant taxa). Some of these measures overlap, particularly those based on proportions that are all dependent on the same denominator, e.g. total abundance. We chose five metrics that represent different aspects of assemblage components: total abundance, taxa richness, Shannon diversity, proportional relative abundance of Ephemeroptera, Trichoptera and Plecoptera (EPT), and percent dominance of the most dominant taxon.

In this article, we focus on the adequacy of field macroinvertebrate sampling to discern differences among stream reaches within ecoregions. We greatly oversampled each stream reach, examining the incremental changes in metric values resulting from increases in sampling effort within each stream reach. This intense, hierarchical sampling design allowed us to quantitatively compare the relative magnitudes of macroinvertebrate assemblage metric variances across the range of spatial scales from within-habitat (eg. within a riffle) up to within-region (ie, comparing ecoregions).

Field Methods - SA012:

Description: Site Selection :

We collected macroinvertebrates intensively from 16 streams distributed over two western Oregon ecoregions: the Willamette Valley and the Cascade Mountains (Fig. 1). In the Willamette Valley, agriculture and urbanization have influenced low gradient, fine substrate streams for over a century, while logging and human settlement have altered the higher gradient, coarse bedded Cascade streams over a similar time period. Our study streams, a probability sample from the considerable diversity of wadeable streams in the region, include low gradient, meandering streams, agricultural ditches, and cobble-bedded mountain cascades. Dominant substrates in the sample streams range from silt to boulders, and riparian vegetation includes old-growth conifers, deciduous trees (alder, ash or maple), grasses and herbs, or agricultural stubble. Nutrient concentrations, clarity, and water temperature vary markedly among these streams. Our results are probably representative of a wide variety of stream types.

The sample stream segments were chosen in two steps. The first step involved dropping an acetate sheet dotted with an inked set of rectangular grid points over the 100,000 scale topographic maps for each ecoregion. Stream segments were defined as the length of stream between "blue line" confluences or between a confluence and the headward extent of the blue line. The stream segment "hit" by following the topographic fall line down from the grid point was selected as a potential field sampling segment. This resulted in a set of about 200 Cascade and Valley stream segments. In the second step, these segments were assigned to either the small or large size class (by stream order) and randomized within each of the four ecoregion/size class strata. The first four wadeable streams on the list in each stratum to which we were allowed site access were selected for field sampling. The exact sampling location on each stream segment was chosen using a random number table. In addition to the 16 randomly selected streams, two hand-picked stream sites (Lookout and Mack Creeks) in the H.J. Andrews Experimental Forest/Cascade Mt. Long-term Ecological Research area were also sampled to allow comparison to the large available database at these sites. Mack Creek is a small first order stream, Lookout Creek is a fairly large third order stream. Due to logistical constraints, macroinvertebrates were not sampled in two of the randomly selected streams (one valley and one cascade). Thus, in this study, 16 streams (9 Cascade and 7 Valley) were sampled for macroinvertebrate assemblages.

Field Sampling and Counting:

Macroinvertebrate field sampling took place in late September, 1992. From the random start point on each stream, 14 study transects (cross-sections) were marked off upstream at 10 m intervals in small streams, and 25 m intervals in large streams. Three, one ft² Surber samples, one on the right side, center and left were taken within each transect (Fig. 2). At least 7 transects of fast water habitat (riffles, rapids or cascades) and 7 transects of slow-water habitat (pools or glides) were sampled on each stream. If 7 of each habitat were not encountered after 14 transects, the crew continued upstream sampling at the same transect intervals in only the under-represented habitat until 7 were sampled. As a result, total number of transects varied from 14 to 20 per stream. Each macroinvertebrate sample was filtered through a 500 micro-meter soil sieve at stream side. Samples were placed in whirlbags and preserved in 70% ethanol. Stream habitat at each Surber sample location was qualitatively classified as either a pool, glide, riffle, rapid, or cascade.

Invertebrate samples were sorted and counted in the laboratory. At least 100 organisms, or all organisms, whichever count was achieved first, were enumerated for all samples. In 378 of the 449 samples, the entire sample was counted. If organisms were extremely dense or organic debris made enumeration very difficult the original sample was subsampled using a 0.5 m subsampler grid (Caton et al 1991). If subsampling was necessary, final counts were calculated by multiplying the observed count by the inverse of the proportion counted. Insect taxa,with the exception of Chironomidae, were identified to genus; Chironomidae were identified to tribe. Molluscs, Branchiopoda, and Copepoda were identified to family. Other invertebrate groups were identified to order. These taxa groupings were used in calculating metrics including taxa richness, and non-insectan taxa. For 3 Valley and 3 Cascade streams, all 3 samples from each transect were enumerated (Table 1). For the remaining streams (4 valley and 6 mountain), only 1 sample per transect was enumerated; the left, center, or right sample was picked at random for the first transect and then alternated in a left, center, right order over the remaining transects.

SUPPLEMENTAL INFORMATION:

This Andrews Forest data is excerpted from the EPA emap study published in : (in press 1995)

Quantifying Stream Macroinvertebrate Assemblages: The Relative Influence of Sample Size and Spatial Distribution, Judith Li, Alan Herlihy, William Gerth, Philip Kaufmann, and Stanley Gregory, Department of Fisheries and Wildlife, Nash Hall, Oregon State University, Phil Larsen, U.S. EPA National Health and Environmental Effects Research Laboratory, Western Ecology Division, 200 SW 35th St., Corvallis, OR 97333.

Almost all assemblages were characterized by a log series abundance distribution . The number of new taxa added with increasing sample effort increased rapidly with the first 4-8 surber samples (500-1000 individuals counted), then increased more gradually. The number of new taxa added never reached zero even after counting more than 50 surber samples. Thus any measure of stream taxa richness is highly dependent on sampling effort. However, 6-9 samples captured a reasonable approximation of assemblage structure. Bootstrap analysis suggested between 65-87% of total taxa richness were described with nine samples. Stability in proportional measure values depend on the degree of dominance by one taxon, and generally stabilize between 5-10 samples in moderately diverse assemblages. A spatial analysis of variance showed differences between streams for all 5 metrics, indicating that within stream variability was not so large as to prevent detecting among stream differences. Within a stream, there was more variability among transects than within transects; this was also true for fast or slow water habitats analyzed separately. Overall, we caution against the use of protocols that sample less than 6 samples for assessing macroinvertebrate assemblages because of the excessive variability among small sample sizes and loss in assemblage structure information. We recommend a protocol of 6-9 samples spread out longitudinally along the sample stream.

SITE DESCRIPTION:

The study was restricted to wadeable streams and four strata were used for site selection; two ecoregion classes (Cascade Mountains and Willamette Valley) and two size classes (small/large). Streams were chosen randomly from the Willamette Valley and the west slope of the Cascade Mountains from 1:100,000 scale USGS topographic maps (Figure 1). Wadeable streams were defined as third order (Strahler) and smaller on the 100,000 scale maps. First order streams were classified as small streams and second/third order streams were considered large. The ecoregion boundaries were taken from the Omernik and Gallant (1986) ecoregion map. Only streams between 44oN and 45oN (roughly between the cities of Salem and Eugene) were considered for sampling.

GENERAL TAXONOMIC COVERAGE:

Ephemeroptera, Plecoptera, and Trichoptera

TAXONOMIC SYSTEM:

None

GEOGRAPHIC EXTENT:

Mack Creek and Lookout Creek, Central Western Cascades of Oregon

MEASUREMENT FREQUENCY:

annual

PROGRESS DESCRIPTION:

Study collection is completed and no new collection is planned

UPDATE FREQUENCY DESCRIPTION:

Data is updated as needed

CURRENTNESS REFERENCE:

"Ground condition" is the range of dates during which the site was visited and data collected.