This overall project is divided into four major themes, each comprised of multiple subtasks that are described below.
Quantification of Seaweed Biomass Fates
In this theme we focus on the design, implementation, and validation of the delivery of seaweed biomass from the farm area to deep water sequestration sites and the fates of the released carbon during biomass decomposition. Specifically, we will design and implement four biomass packaging procedures, design and validate methods to assess decomposition and sinking rate as a function of packaging and the environment, and determine the product partitioning of the biomass carbon into particulates and dissolved organic/inorganic forms.
Quantification of Seaweed Dissolved Organic Matter Fates
Growing and harvested seaweed can release large amounts of dissolved organic carbon (DOC) into the water column and a fraction of this DOC may be recalcitrant to degradation, enhancing carbon sequestration. In this theme we develop and validate methods to assess DOC release rate as a function of the physiological state of the seaweed, environmental conditions, and packaging procedure. Additionally, we measure the composition of the seaweed-derived DOC to gain insights on bioreactivity throughout the growth, harvest, and sequestration cycle. Finally, we experimentally determine the decomposition rate of the released seaweed DOC across a range of environmental parameters, including temperature, dissolved oxygen, nutrients, and microbial community.
Modeling the Environmental Impacts of Seaweed CDR
In this theme we use regional ocean modeling to assess the production and sequestration potential, alterations of the physical environment, and biogeochemical impacts of large scale seaweed farming in two sub-regions. In each sub-region domain (1. Southern California Bight, 2. TBD) we explore nine farm scenarios consisting of three multi-farm orientations and three sinking procedures. We couple a seaweed growth model with ROMS-BEC to simulate the production and the conveyance of the harvested biomass to depth using parameters gleaned from the Seaweed Biomass and Seaweed Dissolved Organic Matter themes. The ROMS-BEC model allows us to examine the environmental impacts of seaweed biomass production, including nutrient removal, shading, alternations to mixing, and changes in phytoplankton production and carbon export. We will also model the biogeochemical impacts at the sequestration site, including alterations of pH, dissolved oxygen, and metabolic oxygen stress on higher organisms.
Marine Spatial Planning
In this theme we use marine spatial planning to assess the best locations for seaweed farm production and sequestration activities. We first develop a spatial layer of existing ocean uses to avoid conflicts with fishing, shipping, industry, military, and marine sanctuaries. We then incorporate model outputs from the Environmental Impacts of Seaweed CDR theme combined with multi-decadal time series of remotely sensed data to assess the mean state and spatiotemporal variability of kelp production. Additionally, we will use model outputs to determine the distance of seaweed farms to durable sequestration areas. Finally, we combine these data to perform a spatial tradeoff analysis to optimize farm production, environmental stability, and distance to durable sequestration areas while minimizing environmental impacts and conflicts with existing ocean uses.