A nitrogen budget model with a user-friendly interface, to assess water renewal rates and nitrogen limitation in commercial seaweed farms

Key factors affecting the economic sustainability of any aquaculture industry and in particular the seaweed industry are its ecological interactions and impacts. Understanding these issues requires an extended production analysis and simulation, given the natural variability and dynamics of external factors that affect those interdependencies. As such, making sense of production data is required for suitable planning and resource optimization in a seaweed farm. The present work calculates the required water renewal rates for seaweed flow-through production units, using a novel simple user-friendly nitrogen budget model. The user interface is straightforward and the model parameter inputs and outputs are minimal, whereby the target users are commercial seaweed farmers. The model was parameterized for production kinetics of Ulva spp. based on an extensive literature survey, and was evaluated with published data on seaweed-growing experiments. Results for the estimated number of volume renewals per day are in agreement with the experimental data. The outputs indicate that this application can be used to estimate the envelope, i.e. average lower and upper ranges for water renewal rates for a given production in a given site. This model and corresponding parameterization for Ulva spp. are available to be used by farmers, managers and researchers in the form of a spreadsheet file (available as Supplementary Material). The conceptual model and application presented herein represent the basis for future developments to incrementally increase complexity, regarding additional seaweed species and production settings (in recirculating and integrated multitrophic aquaculture systems) by farmers and planners.