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Counting at low concentrations: the statistical challenges of verifying ballast water discharge standards
Citation:
FRAZIER, M. R., A. W. Miller, H. LEE, II, AND D. REUSSER. Counting at low concentrations: the statistical challenges of verifying ballast water discharge standards. ECOLOGICAL APPLICATIONS. Ecological Society of America, Ithaca, NY, 23(2):339-351, (2013).
Impact/Purpose:
Scientists from WED, USGS, and the Smithsonian collaboratively describe some of the challenges of sampling ballast discharge for validating ballast treatment systems or for monitoring the compliance of individual ships. This information will help regulators adopt sampling protocols that are protective, efficient, and fair for enforcing concentration-based ballast discharge standards. Ballast water discharge is one of the primary vectors of nonindigenous species (NIS) into coastal aquatic environments. In response, several state, federal, and international organizations have proposed very stringent standards for the concentration of organisms that can be present in ballast discharge, ranging from “zero detectable organisms” to 10 organisms/m3. However, stringent discharge standards promote a false sense of security unless they are paired with adequate sampling protocols. Based on statistical sampling models it will be very difficult to process sufficient volumes of ballast discharge for compliance monitoring of individual ships, and therefore, enforcement of discharge standards may be best achieved through land or ship-based verification of ballast water treatment systems.
Description:
Discharge from the ballast tanks of ships is one of the primary vectors of nonindigenous species in marine environments. To mitigate this environmental and economic threat, the U.S. Coast Guard and the U.S. Environmental Protection Agency will regulate the concentration of living organisms that may be discharged from ballast tanks of ships operating in U.S. waters. The standards proposed by various agencies have ranged from “zero detectable organisms” to 10 organisms/m3 of ballast discharge. If standard sampling methods are used, verifying whether ballast discharge complies with these stringent standards will be challenging due to the inherent stochasticity of sampling. Furthermore, at low concentrations, very large volumes of water must be sampled to find enough organisms to accurately estimate concentration. Despite these challenges, adequate sampling protocols are a critical aspect of establishing standards because they define the actual risk level associated with a standard. For example, a standard that appears very stringent may be effectively lax if it is paired with an inadequate sampling protocol. We describe the statistical issues associated with sampling at low concentrations to help inform the development of protocols that ensure discharge standards are adequately implemented and to help regulators understand the uncertainties of sampling.
