11:00 AM - 11:15 AM
[AOS15-08] Analysis of macroalgae ecosystems’ impacts on carbon and major nutrient concentrations in shallow coastal areas
Keywords:Shallow coastal areas, High-resolution numerical model, Carbon cycle, Nitrogen and phosphorous concentrations
Blue carbon (BC) projects and initiatives have become an attractive “trend topic” worldwide in the past years because they can be used for carbon dioxide removal (CDR). These activities involve the reforestation of coastal areas with seagrass and macroalgae to promote carbon sequestration. Additionally, these practices help in the restoration and ecosystem functioning of coastal areas, enhancing the recovery of biodiversity and promoting economic activities like fishery and seaweed cultivation for human consumption. Japan has a long history of intensive macroalgae cultivation along its coasts driven by dietary habits however, the environmental importance and implications of this practice in the carbon cycle and carbon sequestration is a difficult task that involves an interdisciplinary approach.
The present work summarizes some of our findings when applying the new high-resolution numerical model we developed for coastal shallow areas. This model uses the NPZD (Nutrient, Phytoplankton, Zooplankton, and Detritus) Model as a base, and considers the complex benthic ecosystems that are representative of shallow coastal areas in Japan. We selected Kanazawa Bay, a small bay located the south of Yokohama City, because its geographic (influence of a small river system, average depth, etc.) and socioeconomic characteristics (intensive konbu and wakame cultivation, fishery, etc.) can be considered representative of Japanese shallow coastal areas.
To evaluate the effect of macroalgae cultivation and seagrass meadows in Kanazawa Bay on the concentrations of dissolved organic matter (DOM), particulate organic matter (POM), dissolved inorganic nitrogen (DIN), and dissolved nitrogen-phosphorous ratio (N-P ratio), we proposed 4 different study cases with different combinations of macroalgae. The study cases were selected as follows: a) actual conditions that include seagrass meadows, wild and cultivated macroalgae; b) exclusion of macroalgae intensive cultivation; c) exclusion of seagrass meadows and wild macroalgae (only intensive cultivation); d) exclusion of seagrass meadows (only wild and cultivated macroalgae). These selected variables were followed for 12 months in three different points with different vegetation and water circulation characteristics for all the cases, and the results were analyzed and compared.
We found that in Kanazawa Bay, the variations are seasonal and are affected by the combination of submerged coastal vegetation (seagrass and macroalgae types), which directly impacts the types of ecosystems in the area. As shown in many Japanese coastal areas, phosphorous seems to be the limiting nutrient for biomass productivity in the study region. The nutrient variations are also seasonal and differ differently depending not only on the vegetation but also on the water circulation patterns at the chosen observation points.
We could successfully estimate the response to different combinations of submerged vegetation in Kanazawa Bay with our model, and determine concentration patterns on the variables directly related to the carbon cycle and the biomass productivity of shallow coastal ecosystems. Additionally, our findings reinforce the necessity of good assessment tools for designing and promoting BC initiatives and increasing their effectiveness while avoiding undesirable effects in shallow coastal waters, particularly those that affect socioeconomic activities in target areas.
The present work summarizes some of our findings when applying the new high-resolution numerical model we developed for coastal shallow areas. This model uses the NPZD (Nutrient, Phytoplankton, Zooplankton, and Detritus) Model as a base, and considers the complex benthic ecosystems that are representative of shallow coastal areas in Japan. We selected Kanazawa Bay, a small bay located the south of Yokohama City, because its geographic (influence of a small river system, average depth, etc.) and socioeconomic characteristics (intensive konbu and wakame cultivation, fishery, etc.) can be considered representative of Japanese shallow coastal areas.
To evaluate the effect of macroalgae cultivation and seagrass meadows in Kanazawa Bay on the concentrations of dissolved organic matter (DOM), particulate organic matter (POM), dissolved inorganic nitrogen (DIN), and dissolved nitrogen-phosphorous ratio (N-P ratio), we proposed 4 different study cases with different combinations of macroalgae. The study cases were selected as follows: a) actual conditions that include seagrass meadows, wild and cultivated macroalgae; b) exclusion of macroalgae intensive cultivation; c) exclusion of seagrass meadows and wild macroalgae (only intensive cultivation); d) exclusion of seagrass meadows (only wild and cultivated macroalgae). These selected variables were followed for 12 months in three different points with different vegetation and water circulation characteristics for all the cases, and the results were analyzed and compared.
We found that in Kanazawa Bay, the variations are seasonal and are affected by the combination of submerged coastal vegetation (seagrass and macroalgae types), which directly impacts the types of ecosystems in the area. As shown in many Japanese coastal areas, phosphorous seems to be the limiting nutrient for biomass productivity in the study region. The nutrient variations are also seasonal and differ differently depending not only on the vegetation but also on the water circulation patterns at the chosen observation points.
We could successfully estimate the response to different combinations of submerged vegetation in Kanazawa Bay with our model, and determine concentration patterns on the variables directly related to the carbon cycle and the biomass productivity of shallow coastal ecosystems. Additionally, our findings reinforce the necessity of good assessment tools for designing and promoting BC initiatives and increasing their effectiveness while avoiding undesirable effects in shallow coastal waters, particularly those that affect socioeconomic activities in target areas.