Research Areas > Bioassessment > Evaluation of Assessment Indicators and Sampling Methods in Low-Gradient Streams

Project: Evaluation of Assessment Indicators and Sampling Methods in Low-Gradient Streams

Background and Objectives

Low-gradient streams (i.e., slope <1%) are a common feature of Southern California’s landscape. These streams experience numerous environmental impacts and intensive modification. However, most bioassessment tools, such as macroinvertebrate sampling methods and indices of biological health (like the Southern California Index of Biotic Integrity, IBI) were initially developed in high-gradient streams, which are typically richer in species and microhabitat diversity. Thus, the applicability of these tools in low-gradient streams is unknown.

Status

This project was completed in 2008.

Methods

Benthic macroinvertebrates were collected from 21 low-gradient sites using three sampling methods. These sites ranged from moderately to severely disturbed. At several sites, samples were collected in triplicate. Metrics and the IBI were calculated for each sample and compared in order to determine if each sampling method provided similar information and had equivalent power to detect differences in biological condition using multivariate and univariate analyses.

Findings

One sampling method (the multi-habitat sampling method) usually undersampled organisms, particularly at sites with shifting sandy substrate. In some samples, fewer than a dozen individuals were collected – far below the requisite 500 organisms needed for calculation of the IBI. In general, though, the samples of adequate size contained very similar communities, and differences in IBI scores were small.