Stormwater Action Monitoring 2015/16 Mussel Monitoring Survey: Final Report

Toxic contaminants enter the Puget Sound from a variety of pathways including non-point sources such as stormwater runoff, groundwater releases, and air deposition, and point sources like marinas, industrial and sewage treatment plant outfalls, and combined sewer overflows. However, stormwater is considered one of the biggest contributors to water pollution in the urban areas of Washington State because it is ongoing and damages habitat, degrades aquatic environments, and can have serious impacts on the health of the Puget Sound. Monitoring pollutants and their effects on the marine biota of Puget Sound is critical to inform best management practices and remediation efforts in this large and diverse estuary. In the winter of 2015/16 the Washington Department of Fish and Wildlife (WDFW), with the help of citizen science volunteers, other agencies, tribes, and non-governmental organizations, conducted the first of a series of biennial, nearshore mussel monitoring efforts under the new Stormwater Action Monitoring (SAM) program. SAM is a new collaborative stormwater program funded by municipal stormwater permit holders. This monitoring survey for SAM was intended to characterize the spatial extent of tissue contamination in nearshore biota residing inside the urban growth areas (UGAs) of Puget Sound, using mussels as the primary indicator organism. Future biennial SAM surveys will continue to track mussel tissue contamination in the Puget Sound nearshore to answer the question: "Is the health of biota in the urban nearshore improving, deteriorating, or remaining the same related to stormwater management?"

In this study we used native mussels (Mytilus trossulus) as indicators of the degree of contamination of nearshore habitats. We transplanted relatively uncontaminated mussels from a local aquaculture source to over 70 locations along the Puget Sound shoreline, covering a broad range of upland land-use types from rural to highly urban. At the end of the study we measured the concentration of several major contaminant classes in mussels: polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs, or flame retardants), chlorinated pesticides (including dichlorodiphenyltrichloroethane compounds, or DDTs) and six metals (lead, copper, zinc, mercury, arsenic, cadmium). We also determined the mortality and condition of mussels at the end of the exposure period.

Overall, the mussel survey was a success. We recovered mussels from 90% of the sites and survival was over 78%. The most abundant organic contaminants measured were PAHs, PCBs, PBDEs, and DDTs. PAHs and PCBs were detected in mussels from every site, and the concentrations were significantly higher in Puget Sound's most urbanized areas, as measured both by municipal land-use classification (i.e., cities and unincorporated-UGAs) and by the percent of impervious surface in upland watersheds adjacent to the nearshore (Table 3). Although lower in overall concentration, PBDEs and DDTs followed a similar pattern. In addition, most of these organic contaminants were elevated in areas near marinas and ferry terminals. The other organic contaminants were detected in mussels at only a few study sites and at low levels. Five of the six metals (lead was the exception) were found in mussels from all the study sites, though their concentrations were relatively low. Though zinc and lead were the only two metals that were significantly related to land-use in our testing, our power to detect differences in most of the metals (mercury, arsenic, cadmium, copper and lead) was often low.

These findings suggest toxic contaminants are entering the nearshore food web of the greater Puget Sound, especially along shorelines adjacent to highly urbanized areas. Based on the results of this survey and a number of power analyses, WDFW recommends the following:

1. To identify the major sources of contamination into the greater Puget Sound, and to better understand temporal trends and mechanisms, we recommend a) long-term nearshore mussel monitoring, and b) incorporation of our findings with other SAM monitoring studies.
   
2. In order to improve our ability to identify patterns and track changes in nearshore contamination SAM should relocate some of the mussel sites to better cover of the full spectrum of urbanization in Puget Sound. To accomplish this, SAM could introduce substrata into the GRTS model used to assign sites, utilizing mean impervious surface in nearshore watersheds to delineate the substrata. Depending on the number of substrata (three to four), between five to 10 sites would be required per substratum (20-40 sites total) to give sufficient power to detect changes in nearshore contamination in the future.
   
3. Once the new sites are selected, all of the mussel sites should become permanent SAM nearshore sites (i.e., index sites) to be revisited and resampled in future surveys for time trend analyses.
   
4. Considering the low power to detect differences in some of the metals during this first round of monitoring, SAM should commission a literature review of the efficacy of using mussels to detect changes in different types of metals and either drop or retain them from the list as appropriate.
   
5. Given recent evidence of contaminants of emerging concern (CECs) in Puget Sound fish (Peck et al., 2011, Johnson et al., 2008; Fiest et al., 2011), we recommend adding some CECs to the list of contaminants analyzed. We further recommend seeking guidance from PSEMP's Toxics Workgroup on which stormwater-related CECs are relevant to the Puget Sound and measurable via current methods.

The success of this large-scale, field-intensive monitoring study was due in large part to lessons learned from a separate WDFW pilot study using caged mussels (37TLanksbury et al., 201437T), expertise gained from the National Status and Trends' 37TMussel Watch Program37T, and the hundreds of hours of help from many citizen science volunteers. We recommend WDFW be retained to continue the SAM Mussel Monitoring program, and that volunteers continue to be utilized for this monitoring. In addition, partner groups sponsored a number of additional sites (25) to this study, including many locations outside the UGA, where SAM had no sites. These sponsors brought a benefit to SAM Mussel Monitoring by allowing for additional comparisons between UGAs and non-UGAs in this first survey.