Use of Sugar Kelp Aquaculture in Long Island Sound and the Bronx River Estuary for Nutrient Extraction

We previously demonstrated the suitability of seaweed aquaculture as a nutrient management tool, using the warm temperate rhodophyte Gracilaria tikvahiae McLachlan. The present follow-up study revealed an even higher nutrient bioextraction capacity in the cold-water species Saccharina latissima at 3 sites—the mouth of the Bronx River Estuary (Bronx, NY; BRE), western Long Island Sound (Fairfield, CT; WLIS) and central Long Island Sound (Branford, CT; CLIS), during winter and spring of the 2012−2013 growing season. These sites differ in temperature (BRE > CLIS > WIS), salinity (BRE < WLIS = CLIS) and nutrients (BRE >> WLIS = CLIS). We estimated that S. latissima could remove up to 180, 67 and 38 kg N ha−1 at BRE, WLIS and CLIS respectively, in a hypothetical kelp farm system with 1.5 m spacing between longlines. In the same hypothetical kelp farm system, the estimated carbon sequestration values are 1350 (BRE), 1800 (WLIS) and 1200 (CLIS) kg C ha−1. The potential monetary values of N sequestration by the sugar kelp are up to $1600 (BRE), $760 (WLIS) and $430 (CLIS) ha−1, if incorporated in the State of Connecticut Nitrogen Credit Trading Program and a carbon-pricing scheme. The potential economic values of C sequestration are up to $30−300 (BRE), $40−400 WLIS), and $24−240 (CLIS) ha−1. These results suggest that seaweed aquaculture is a useful technique for nutrient bioextraction in urbanized coastal waters, such as LIS and BRE. Alternation of the warm- and cold-water species would maximize nutrient bioextraction and augment other ecosystem services, producing economic benefits for the region while helping to manage non-source eutrophication.