1) Quantify nutrients (N,P) and carbon (CO2) uptake and retention in kelp.
2) Determine carrying capacity of natural phototrophic population in affected regions.
3) Estimate potential of bioremediation benefits by seaweed farming.
Industrial kelp facilities will occupy large areas in the sea in both the horizontal and vertical directions, thus impacting ocean currents, wind driven mixing and water column light conditions. During growth, N and, P, and inorganic carbon (CO2) from the water will be taken up by kelp and incorporated into live biomass. Both nutrient concentrations and carbon chemistry (pH levels) of the ambient water masses will be affected, thus natural phototrophic populations (micro- and macroalgae) will compete for the same resources.
The affected region will depend on the size of the farming facility, potentially affecting entire semi-enclosed bays or fjord regions. Also water column light conditions will be altered locally due to physical constructions, light absorption by farmed kelp and by kelp-produced coloured dissolved organic matter (CDOM), i.e. so-called ‘water-darkening’.
Industrial kelp culturing may exceed the carrying capacity of a local ecosystem, i.e. then the resources available become smaller than the demand of the growing population. Such cases will lead to decreasing ecosystem primary production with impacts on the food supply to secondary producers (i.e. zooplankton, larvae, etc.), and ultimately for fish. At the same time, these biogeochemical processes have a potential for eutrophication and CO2 mitigation, as removal of nutrients and CO2 will benefit pelagic ecosystems that are threatened by eutrophication (excess of nutrients) and lowering of pH (high pCO2/ocean acidification).
T3.1. Quantification of nutrient (N, P) and C (CO2) uptake and retention in kelp. Uptake rates for N, P and C will be quantified in growing kelp (Saccharina and Alaria) from farms (SES). Measurements will be taken every 2 to 4 weeks following the production season to account for variation in age, leaf density and natural availability from a cultivation facility (SES). The task will benefit from MACROSEA (RCN 2016-2020) undertaking laboratory growth experiment including nutrient dynamic studies.
T3.2. The effect of kelp farming on the carrying capacity of the coastal waters will be assessed based on existing and new data on water column nutrient and light availability (including transport, mixing and upwelling from deep water) and input from T3.1, aided by simulations using SINMOD (see WP1). The scenarios for small to large scale production facilities (WP1) will be used for the selected geographical regions. Carrying capacity calculated will be based on published methods and the model system allows for two-way coupling between the relevant physical (light, currents) and biochemical (nutrients) variables and the kelp cultures. Thus, reduction of water currents by kelp farms, uptake of nutrients and release of exuded organic matter will be taken into account. Existing time series data from 8 stations through 2 years and 4 stations through one year (Frøya) will strengthen calculations, and new mooring installations (current, mixing depth, temperature, and light) will be sampled continuously during a growth season (Feb – Jun, SES). These data will in addition strengthen the SINMOD model (WP1). Exchange of physical data with ENTICE (RCN 2016-2018) will benefit the task.
T3.3 The potential of bioremediation by kelp farming will be assessed in a similar manner to T3.2 using input from T3.1 and SINMOD. Small to large scale production facilities (WP1) will be evaluated with specific focus on the potential for CO2 mitigation and removal of excess nutrients. Also the potential for reduction of ‘water darkening’ will be evaluated. A 50% funding of an existing post doc (NTNU) will ensure analysis and processing of kelp, mooring and water samples. An existing PhD student (NTNU) will work in synergy with the project. Sampling of kelp and water will be performed by SES (Frøya).
• Paper on kelp carbon and nutrient uptake stoichiometry at future industrial-scaled facilities.
• Paper on carrying capacity of the coastal pelagic ecosystem in light of industrial-scaled kelp production.
• Paper on potential of bioremediation and CO2 mitigation by kelp farming.
• Input data to WP5 for assessment of positive and negative impacts on fjord and coast ecosystem services.