Hydrobiologica, Springer International Publishing | May 30, 2018...
Summary
Macroinvertebrate community taxonomic and trait structure showed consistent differences between riffles and pools across 12 headwater streams in the Sierra Nevada (California) even...
Macroinvertebrate community taxonomic and trait structure showed consistent differences between riffles and pools across 12 headwater streams in the Sierra Nevada (California) even as flows varied from wet to dry years and between seasons. Densities of Ephemeroptera, Plecoptera, Trichoptera, Elmidae, Orthocladiinae and Diamesinae midges, and mites were greater in riffles, whereas Tanypodinae, Chironominae, Sialis, and Pisidium were more abundant in pools. Pools had higher densities but estimated biomass was greater in riffles. Collector-gatherer and micropredator abundances were greater in pools whereas grazers, collector-filterers, and macropredators were more abundant in riffles. Stonefly shredders were most abundant in riffles but some caddis shredders were more abundant in pools. Trait state patterns were related to food resource and physical habitat differences between riffles and pools. Of the distinct pool–riffle differences we found among taxa, only about half conformed to expectations from the literature. Pool and riffle assemblages were most dissimilar at intermediate discharge and converged at low and high flows when one or the other habitat dominated. Bioassessment sampling will need to account for these flow-related differences. Benthic invertebrate communities in these mountain streams clearly differ between pools and riffles, but the relative extent of habitats and biological similarity shift with flow regime.
Central Valley Regional Water Quality Control Board | November 14, 2005...
Summary
Bioassessment has shown significant promise as an effective tool for ambient water quality management in many regions of California. However, the scale and...
Bioassessment has shown significant promise as an effective tool for ambient water quality management in many regions of California. However, the scale and intensity of landscape and water transport alteration in the Central Valley pose substantial challenges to implementing bioassessment to its full potential in the region. Bioassessment programs usually are established around a careful characterization of regional reference conditions, which can be defined as the condition of waterbodies that are least impaired by human activities.
The reference condition defines a benchmark against which to infer biological impairment and to set expectations for biotic condition. Although there are several techniques available for determining reference condition, by far the most commonly applied is the use of reference sites, which are used to establish the range of natural variability in biotic condition.
We investigated the potential for identifying reference sites for segments of sloughs and creeks of the Sacramento Valley at elevations less than 85 meters. We describe here the results of a pilot study designed to adapt an existing reference site selection methodology for use in the Central Valley. Potential reference sloughs and creeks were selected on the basis of a suite of visual assessments of riparian and instream condition and qualitative GIS-based land use data.
Analysis of the benthic macroinvertebrate (BMI) assemblages collected from 30 targeted reference sites (23 creeks and 7 sloughs) was focused on addressing two main questions: 1) should creeks and sloughs be considered unique waterbody classes for the purposes of bioassessment?, 2) what is the potential for reference site based bioassessment in valley waterbodies? We addressed these questions with the BMI data using a combination of direct metric comparisons and NMS ordination. To improve our ability to interpret patterns at our 30 sites, we included two additional datasets of BMI data recently collected from nearby waterbodies.
We drew three general conclusions from this study: 1) the adaptation of reference site selection to Central Valley streams was effective; we were able to find sites in the valley to use as reference and there is enough diversity in the BMI assemblages at these reference sites to use them to detect impairment, 2) although creeks and sloughs may need to be treated as separate classes of waterbodies for bioassessment-based regulation, there is evidence to suggest that the differences are not clear-cut and the question needs further investigation, 3) BMI assemblages in valley floor reference sites are clearly different from those in foothill reference sites.
We discuss the potential for reference site based determination of reference conditions and summarize the current state of the science for defining reference condition in regions without adequate reference sites. We also list a set of recommendations that the Central Valley Regional Water Quality Control Board should consider while constructing a defensible framework for bioassessment in the Central Valley.
