How the city’s sewer system might affect eelgrass

Carmen Jaramillo
Posted 1/22/20

If the City of Port Townsend changes course on plans for a new sewer drain at North Beach, it may be due, in part, to concerns about eelgrass, an aquatic plant beachcombers take for granted but scientists worry about.

This item is available in full to subscribers.

Please log in to continue

Log in

How the city’s sewer system might affect eelgrass


If the City of Port Townsend changes course on plans for a new sewer drain at North Beach, it may be due, in part, to concerns about eelgrass, an aquatic plant beachcombers take for granted but scientists worry about.

Though the City Council voted in November to approve a plan for a new wastewater discharge pipe, or outfall, at North Beach, the City Council also agreed to reconvene and consider other options in the new year before construction begins.

The main concern of members of the public who spoke against the outfall was their hope for less environmental impact by switching the facility to a different type of treatment, a move which they believed, while potentially expensive, would save money in the long run.

The science is clear; nutrient overloading, be it from outfalls or storm water run off into the Puget Sound has an effect on marine life and indirectly on eelgrass beds, which provide important marine habitat.

Eelgrass is recognized as an important part of the marine ecosystem and its abundance is used as a way to measure the health of the ocean by the Puget Sound Partnership, a consortium of environmental advocacy and governmental groups dedicated to the protection and restoration of the Sound. It is used as a vital sign because of its sensitivity to changes in ocean acidification, temperature and pollution.

Eelgrass grows in the shallow waters of the sound and it serves as a food source, nursery and shelter for many species like herring, crab, waterfowl and salmonids. It also filters sediments and nutrients, improving water clarity and protecting shorelines from erosion.

Dr. Ron Thom, Staff Scientist Emeritus at the Pacific Northwest National Laboratory’s Marine Sciences Laboratory in Sequim, has worked with eelgrass and outfalls for his entire career as a marine biologist. He said nutrients from outfalls and storm water runoff can directly affect eelgrass in several ways. All outfalls in the Puget Sound affect the overall health of the ecosystem, but specific eelgrass beds and their relationship to an individual outfall is different and harder to measure.

In general, he said, how much one outfall affects a bed of eelgrass is a function of the distance of the discharge point from the bed, the depth of the outfall and the water currents. Wastewater, or effluent, from outfalls will affect eelgrass less if it is sufficiently diluted by mixing in the water. That will prevent any additional suspended sediment from muddying the water, preventing light from reaching eelgrass, changing the temperature of the water, or overloading nutrients into a specific area.

If nutrients from sewage, like nitrate and phosphate, are not well-diluted and become abundant around eelgrass, it can create an algal bloom which harms the plant.

The physical disturbances during construction of outfalls can also affect eelgrass beds.

The proposed Port Townsend outfall construction would necessitate digging a forty-foot trench through an existing eelgrass bed off North Beach. In order to mitigate the effect of construction, a survey team would harvest the eelgrass from the construction path and maintain it in holding tanks until construction was completed and then replant it on top of where the outfall is under the seabed.

The same method was used in 2009 for the construction of an outfall in King County. Thom worked on the King County project with a team from the Marine Sciences Lab and said monitoring on that eelgrass since construction has shown it is doing okay. However, this method of replanting eelgrass does not always work, he said, and sometimes the cause for the failure is unknown.

The City of Port Townsend, like all other Washington State cities and townships, adopted a “no net loss” policy for marine resources in 2012 when it passed its Shoreline Master Program, required by the state Shoreline Management Act.

City Manager John Mauro said from his understanding, the city will need the new outfall regardless of any changes to the wastewater plant.

The northbeach facility is, however, continually recognized by the Department of Ecology as one of the most well run facilities in the state in terms of its commitment to water quality and proper operation of the plant.

It’s up to the citizens to decide what kind of investment they want to make, but he does not think people want to see their utility bills, which have already been a point of contention, “skyrocket” in order to build another facility while the outfall is already funded.

In the coming months, the City Council will meet for a workshop on the issue, to discuss the many facets including environmental impacts and investigate alternative options to the outfall.


No comments on this story | Please log in to comment by clicking here
Please log in or register to add your comment