The Harmful Algal Bloom (HAB) in the Ross Island lagoon (RIL) has been occurring with increasing frequency, and has led to the recent listing of the lagoon as impaired. The RIL HAB is unique due to its occurrence in river, and solutions to the HAB are complicated by environmental, regulatory, and logistical constraints. OSU faculty and students have been supporting stakeholders in identifying potential solutions for addressing the HAB, including hosting a design charrette, synthesizing current knowledge about the system, and developing hydraulic models of proposed solutions to examine their feasibility and effectiveness. Students evaluated a wide range of potential solutions, ranging from hydraulic modifications to microbial solutions (e.g. floculents, aeration, nanobubbles, ultrasonic pontoons, barley straw floats).

Details on the findings and recommendations are provided here. High-level findings include:

1) Hydraulic solutions may be effective, but a hydraulic model that represents vertical variations is needed to more fully understand the impacts of hydraulic solutions on stratification. It is not clear if the hydraulic solutions can produce enough mixing to fully suppress the bloom, or what mixing depth is actually needed to suppress the bloom. While hydraulic solutions may not fully mix the epilimnion, they should help suppress the bloom. In addition, advection of algae cells out of the lagoon may further suppress the HAB, though the benefit of flushing cells is difficult to predict.

2) From the perspective of hydraulic drivers, the momentum from the river drives mixing through the winter. The tides drive mixing during the summer low flows. Thus, solutions that take advantage of both will be most effective, and most expensive.

3) There are some promising non-hydraulic solutions. However, these are all generally short-term solution that would need regular application and have their own uncertainties with respect to effectiveness.

4) Existing management actions and data limitations may be further exacerbating the HAB and are limiting the range of solutions at Ross Island.

Project Introduction

Ross Island HAB Design Charrette`

Synthesis of Ross Island history, regulations, and science

Hydraulic models and alternatives analysis