Cost-Benefit Analysis of Macroalgal Harvesting for Nitrogen Abatement

Abstract

This project explored seaweed (macroalgae) harvesting as a means to remove nitrogen from eutrophic estuaries and compared the costs of suction harvesting to other nutrient abatement approaches. Elevated nutrients in estuaries can trigger macroalgal blooms, which can suffocate and kill marine organisms. Harvesting macroalgae removes nitrogen from estuaries and can improve the health of aquatic ecosystems. Macroalgal biomass and nitrogen surface water data were collected to try to identify an optimal macroalgal harvest window. A macroalgal harvesting pilot study was conducted to determine the costs of suction harvesting and how much macroalgae and thus nitrogen could be harvested on a dollars/kg basis. The costs for nitrogen abatement measures, such as reducing fertilizer use or wastewater treatment upgrades, range from $1 to $16,000/kg of nitrogen removed. This study found the cost for removing nitrogen using suction macroalgal harvesting to range from $62 to $3,271/kg, depending on macroalgae condition and wages. The costs per kg of nitrogen removed for macroalgal harvesting were on the higher end of the range of interventions. However, this approach has a low point of entry cost of roughly $1000 compared to some interventions that require millions of dollars of investment. In addition, there is potential to improve the efficiency of harvesting and lower costs through refinement of harvesting methods. Macroalgae harvesting is unlikely to remove enough nitrogen to resolve nitrogen- loading problems in eutrophic estuaries. However, it presents a useful option for communities to reach their water quality goals in conjunction with other measures and may provide some benthic habitat benefits in the short to medium term.