Effects of wave-powered water pump upwelling on kelp mariculture: a case study for Gulf of Maine

In kelp aquaculture, higher nitrate concentration increases productivity, and water temperatures within a favorable range promote kelp survival. In specific oceanic regions these environmental conditions can be produced by artificial upwelling. This work explores whether wave-powered artificial upwelling can modify local environmental conditions to enhance kelp mariculture productivity. A coupled physical-biogeochemical modeling feasibility study was developed using multiyear empirical oceanographic data of temperature, nitrate concentrations, and wave conditions at an ocean case study site in the Gulf of Maine. The study is limited in its approach where mixing conditions are assumed to be ideal, and horizontal advection is assumed to be negligible (or periodic within a much larger kelp farm). The model estimates that wave-powered upwelling can decrease the water temperature by an average of 1.0 ± 0.15 °C from June through October, and increase nitrate concentration by an average of 0.1−1.1 µmol L−1 from June through September depending on parameter uncertainties within a simplified model kelp farm. Additional analysis of farm-scale boundary conditions suggests that the spatial distribution and degree of mixing upwelled water strongly influences the extent of nitrate increase and cooling within kelp farms. The environmental changes in the example kelp farm due to wave-powered upwelling are then applied to a validated kelp growth model with empirical surface current magnitudes and irradiance data, producing an estimate of 0.9−0.0+1.1 DMT ha−1 yr−1 (or approximately 9.5%−10%+1.6%) of additional kelp grown. The kelp growth model assumes that nitrate is the only limiting nutrient in kelp growth, and has some other limitations. This framework facilitates further investigation of wave-powered upwelling as a scalable ocean-based strategy for sustainable kelp aquaculture. Combined, these findings suggest that wave-powered artificial upwelling may enhance kelp productivity under nutrient-limited and seasonally warm conditions in temperate marine ecosystems.