Sampling Design

The sampling design of the 1994 Pilot Project was based on three design principles. First, the program was bight-wide, covering the continental shelf (operationally defined as the surf zone to 200 meters depth) from Point Conception to the Mexican border. Present monitoring efforts in the Bight are spatially limited; some areas are sampled intensively, but almost no data are collected from large expanses of the system, such as areas north of Point Dume and areas deeper than 100 m. Developing an effective management strategy for the Southern California Bight (as opposed to addressing site specific problems) requires an understanding of the extent and distribution of environmental degradation throughout the bight.

Second, data was collected using a probability-based (randomized) sampling design. The probability-based sampling design will ensure unbiased estimation of condition, which is not possible when sampling sites are pre-selected by the investigator, as in present monitoring efforts in the Bight. The probability based sampling design also allows investigators to calculate confidence intervals around estimates of condition. Confidence intervals provide managers with full knowledge of the strength or weakness of the data upon which their decisions will be based.

Another advantage of the probability-based sampling design is that it allows investigators to estimate the actual area (i.e., number of acres) in the system in which ecological conditions differ from reference areas; the estimation of areal extent of anthropogenic influence on the coastal ecosystem was and is a primary goal of our regional monitoring efforts. This emphasis on estimating areal extent is a departure from traditional approaches to environmental monitoring, which generally estimate the average condition. Estimating the areal extent of degraded ecological condition offers several advantages. First, it provides a more direct assessment of current status. For instance, identifying that the average concentration of dissolved oxygen in the Bight is 6.7 ppm provides less usable information for environmental managers than does identifying what specific percentage of the Bight fails to meet water quality standards. A second advantage of estimating areal extent concerns trend detection. If conditions in the Bight change over time such that some areas improve and others worsen, the average condition might not change. By estimating the areal extent of degradation, we are able to describe these changes.

The third design principle is that the we use a uniform set of indicators and sampling methods throughout the Bight. The probability-based sampling design provides a framework for integrating data into a comprehensive regional assessment, but the validity of such an assessment depends on ensuring that all the data that contribute to it are comparable. To ensure that each participant in the Pilot Project collecting and processing samples produced comparable data, SCCWRP worked with participants to develop and document standard field and laboratory methods and quality assurance protocols. Developing standard methods manuals for regional monitoring in the Southern California Bight not only ensured that all data collected for the SCBPP could be integrated, but also will provided a framework upon which to build further monitoring efforts.

Sampling design details
Map of sample sites
List of indicators measured