Numerical simulation of dissolved aquaculture waste transport based on water circulation around shellfish and salmon far
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ORIGINAL ARTICLE
Numerical simulation of dissolved aquaculture waste transport based on water circulation around shellfish and salmon farm sites in Onagawa Bay, Northeast Japan Jinxin Zhou1 · Daisuke Kitazawa2 · Takero Yoshida2 · Toyonobu Fujii3 · Junbo Zhang4 · Shuchuang Dong2 · Qiao Li2 Received: 18 May 2020 / Accepted: 14 September 2020 © The Japan Society of Naval Architects and Ocean Engineers (JASNAOE) 2020
Abstract The Marine Environmental Committee (MEC) ocean model was applied to Onagawa Bay to examine the bay-scale water circulation and to evaluate the current configuration of aquaculture facilities that were devastated by the 2011 Tohoku earthquake. In this study, the drag forces of aquaculture facilities and the blocking effects of both stocked fish and shellfish were integrated to MEC ocean model. The model was validated with long-term observations regarding tide level, flow velocity, and water quality. In summer, the remote water discharge from the Kitakami river significantly affected the density-driven currents at the surface in Onagawa Bay, whereas, in winter, wind stresses by the prevailing monsoon altered the tidal level fluctuations as well as influenced the surface water circulation. The model also revealed the drag forces of the aquaculture facilities exerted a limited influence on the bay-scale water circulation. The dispersal of dissolved aquaculture waste was further studied by a tracer method. The degree of waste accumulation was geographically different in Onagawa Bay, and a reallocation of the aquaculture facilities between the southern bay and the western coast area may mitigate the accumulation of aquaculture waste. Overall, a further ecosystem study on material circulation is required to incorporate the effects of interactive processes between farmed species and sediments below and/or the water column around aquaculture facilities. Keywords MEC ocean model · Bay-scale water circulation · Aquaculture effects · Multiple nesting grids
1 Introduction Onagawa Bay in Miyagi Prefecture is located on the Pacific coast of northern Japan (Fig. 1). Aquaculture is a very symbolic industry and its related industries are the main source of commerce in the Onagawa area [1]. However, a megaquake shook the bay on March 11, 2011, and a subsequent tsunami destroyed nearly the entire Onagawa area, including * Jinxin Zhou [email protected]‑tokyo.ac.jp 1
Graduate School of Engineering, The University of Tokyo, 5‑1‑5 Kashiwanoha, Kashiwa, Chiba 2778574, Japan
2
Institute of Industrial Science, The University of Tokyo, Kashiwa, Chiba, Japan
3
Tohoku Ecosystem-Associated Marine Sciences, Graduate School of Agricultural Science, Tohoku University, Sendai, Japan
4
College of Marine Sciences, Shanghai Ocean University, Shanghai, China
the aquaculture facilities in the bay. There were over 1200 long-lines and approximate 120 fish cages prior to the earthquake, all of which were carried away by the tsunami [2]. Aquaculture redevelopment has therefore become a focus of policymaking and scientif
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