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L. J. Tilley

Publications and source records attributed to L. J. Tilley.

6 recordsLinked to original sources
USGS1991

Mesh-size effects on drift sample composition as determined with a triple net sampler

Nested nets of three different mesh apertures were used to study mesh-size effects on drift collected in a small mountain stream. The innermost, middle, and outermost nets had, respectively, 425 ??m, 209 ??m and 106 ??m openings, a design that reduced clogging while partitioning collections into three size groups. The open area of mesh in each net, from largest to smallest mesh opening, was 3.7, 5.7 and 8.0 times the area of the net mouth. Volumes of filtered water were determined with a flowmeter. The results are expressed as (1) drift retained by each net, (2) drift that would have been collected by a single net of given mesh size, and (3) the percentage of total drift (the sum of the catches from all three nets) that passed through the 425 ??m and 209 ??m nets. During a two day period in August 1986, Chironomidae larvae were dominant numerically in all 209 ??m and 106 ??m samples and midday 425 ??m samples. Large drifters (Ephemerellidae) occurred only in 425 ??m or 209 ??m nets, but the general pattern was an increase in abundance and number of taxa with decreasing mesh size. Relatively more individuals occurred in the larger mesh nets at night than during the day. The two larger mesh sizes retained 70% of the total sediment/detritus in the drift collections, and this decreased the rate of clogging of the 106 ??m net. If an objective of a sampling program is to compare drift density or drift rate between areas or sampling dates, the same mesh size should be used for all sample collection and processing. The mesh aperture used for drift collection should retain all species and life stages of significance in a study. The nested net design enables an investigator to test the adequacy of drift samples. ?? 1991 Kluwer Academic Publishers.

Hydrobiologia↗
USGS1989

Diel drift of Chironomidae larvae in a pristine Idaho mountain stream

Simultaneous hourly net collections in a meadow and canyon reach of a mountain stream determined diel and spatial abundances of drifting Chironomidae larvae. Sixty-one taxa were identified to the lowest practical level, 52 in the meadow and 41 in the canyon. Orthocladiinae was the most abundant subfamily with 32 taxa and a 24 h mean density of 294 individuals 100 m-3 (meadow) and 26 taxa and a mean of 648 individuals 100 m-3 (canyon). Chironominae was the second most abundant subfamily. Nonchironomid invertebrates at both sites and total Chironomidae larvae (meadow) were predominantly night-drifting. Parakiefferiella and Psectrocladius were day-drifting (meadow) whereas 8 other chironomid taxa (meadow) and 2 taxa (canyon) were night-drifting. All others were aperiodic or too rare to test periodicity, Stempellinella cf brevis Edwards exhibited catastrophic drift in the canyon only. The different drift patterns between sites is attributed to greater loss of streambed habitat in the canyon compared to the meadow as streamflow decreased. Consequent crowding of chironomid larvae in the canyon caused catastrophic drift or interfered with drift periodicty. This study adds to knowledge of Chironomidae drift and shows influences on drift of hydrologic and geomorphic conditions. ?? 1989 Kluwer Academic Publishers.

Hydrobiologia↗
USGS1977

Benthic invertebrates in an arctic mountain stream, Brooks Range, Alaska

A 1-day, late-summer reconnaissance of the Dietrich River, Alaska, determined species composition and diversity of benthic invertebrates and examined the correlation between stream order and invertebrate distribution. Benthic invertebrates were collected by dip net, drift net, and 10-rock collections, and results were combined for each station. Forty-nine taxa were identified from 5 stations representing stream orders 1 through 5. Aquatic insects comprised 88 percent of all taxa and 97 percent of all individuals from the Dietrich River. Diptera, especially Chironomidae, was the most abundant, followed by Plecoptera. Diamesinae was abundant at the headwaters, decreasing downstream; Orthocladiinae exhibited the reverse distribution pattern. Diversity of collections generally increased downstream. The station collections were compared using coefficients of similarity, cluster analysis, and taxonomy. Collections from adjacent stations were most similar and similarity decreased with increasing distance. The fauna was tentatively divided into zones with characteristic communities: a Diamesinae-Simuliidae fauna in zone I (stream order 1), zone II, a region of transition (orders 2-4), and an Orthocladiinae-Plecoptera-Ephemeroptera fauna in zone III (order 5). The fauna compares closely with that of other arctic streams. Although not conclusive, the benthic invertebrate results are consistent with the hypothesis that stream order is related to lotic biological communities.

Alaska↗
USGS1976

Evaluation of three collecting methods for a reconnaissance of stream benthic invertebrates

A 1-day reconnaissance of the Dietrich River, Alaska, included collection of benthic invertebrates. Three methods were used at each of five stations to increase sampling effectiveness and to evaluate each method. Chironomidae and Plecoptera comprised 91 percent of all individuals and 47 percent of all taxa in the combined faunal list. At each station, the most abundant organisms were taken by all methods but the less abundant ones by only one or two methods. The dip net collected the highest percentage of taxa, and the second highest percentage of individuals. The 10-rock method collected the highest percentage of individuals but was relatively ineffective for taxa. The drift net collected the fewest individuals, but the percentage of taxa was relatively high. Of the 27 unique taxa (those taxa collected by only one of the methods), 15 were collected by dip net, 8 by drift net, and 4 by the 10-rock method. The methods differed in their effectiveness with regard to collecting the most abundant taxonomic groups. Although the dip net was most effective for collecting taxa, more thorough scrubbing of substrates to remove clinging organisms probably would improve the technique.

Alaska↗
USGS1972

Measurement of salt-wedge excursion distance in the Duwamish River Estuary, Seattle, Washington, by means of the dissolved-oxygen gradient

The Duwamish River estuary has been the object of a series of comprehensive studies undertaken to predict the effects of the changing character of waste-water inputs on the water quality of the estuary. This report discusses the fresh- and salt-water relations of the estuary. The distance that the salt-water wedge in the estuary moves upstream and downstream with the tide is measured by a method that utilizes the persistence of the longitudinal gradient of dissolved oxygen in the salt water of the wedges. The method, though unorthodox, can serve as an independent check on any other measurements of tidal-excursion distance. Typical values obtained were a 1-kilometer excursion for a 1.3-meter tide range and a 3-kilometer excursion for a 3-meter tide range. This method of tracing the water movement seems to work because of two unusual aspects of the Duwamish River estuary: (1) the channel configuration is simple and well-suited to synoptic measurement and (2) the physical properties of the entering salt water are nearly constant.

Water Supply Paper↗