Quality Assurance Project Plan: Status and Trends Monitoring of Marine Nearshore Mussels in the Puget Lowland Ecoregion for Stormwater Action Monitoring (SAM) 2021-2025

This Quality Assurance Project Plan (QAPP) updates a long-term status and trends monitoring study for toxic contaminants in nearshore habitats of Puget Sound. This program is directed by the Stormwater Action Monitoring (SAM), the regional stormwater monitoring program funded by the Phase I Municipal Stormwater permit and the Western Washington Phase II Municipal Stormwater permittees. SAM and the Washington Department of Fish and Wildlife’s (WDFW) Toxics-Biological Observation System (TBiOS) implement the monitoring program under a long-standing interagency agreement.

This monitoring program in the Puget Lowland Ecoregion is focused on the health of biota in the marine nearshore, and is designed to provide a regional assessment of whether collective stormwater management actions implemented in the region are leading to improved nearshore contaminants levels.

Mussels were selected as the indicator species, or sentinel, to monitor contaminant conditions in the nearshore. As filter feeders, they ingest particles from the water and accumulate contaminants. This allows them to be used as a means to integrate measurable contaminant conditions over time, overcoming many of the difficulties and limitations related to measuring contamination in receiving waters directly.

Beginning in 2021 and onward this study will continue a previous, successful SAM/WDFW mussel monitoring program, using translocated, caged mussels deployed for 3-month periods every-other-year throughout the Puget Lowland nearshore.

The expansion in scale of this program from the Urban Growth Area to the Puget Lowland nearshore required a redesign, to represent the whole nearshore area in the region and to ensure maximizing statistical power to detect trends in a cost-effective way.

This mussel study design employs a random probabilistic sampling scheme, like the previous monitoring in 2016-2020, with some design adjustments to increase statistical power and monitoring efficiency. Beginning in 2020, the core monitoring design has been modified as follows:

• the study area is extended to cover the whole Puget Lowland nearshore from the Urban Growth Area of Puget Sound,
• candidate sampling sites (master points) in the Puget Sound shoreline have been redrawn using updated high-resolution National Hydrography Dataset (NHD) layer,
• the study area is stratified into four different groups (strata) by estimates of impervious surfaces in watersheds to each master point, with sampling sites selected for each stratum,
• sampling will be conducted every other year at selected sites. Thirty-three sites will be selected each sampling year, comprising a combination of new and revisited sites to improve status assessment and trend detection power.
• reference condition sites will be monitored in each sampling event to establish a better comparison of the results from the sampling sites to a ‘least disturbed’ condition.