Stochastic characterization of the onset of and recovery from hypoxia in Tokyo Bay, Japan: Derived distribution analysis based on “strong wind” events

Abstract

[1] This paper uses derived distribution analysis to explore the process controls of the onset of and recovery from hypoxic conditions in Tokyo Bay, Japan. A conceptual, lumped model of dissolved oxygen (DO) dynamics in Tokyo Bay is proposed and, through comparison with a three-dimensional simulation model, is verified to have sufficient accuracy for the prediction of the onset of and recovery from hypoxia. This conceptual DO model was implemented in continuous simulation mode, with 14 years of wind data and data on streamflow entering the Tokyo Bay, and was used to identify and quantify the various process controls of the onset of and recovery from hypoxia. The underlying process controls were identified to be streamflow discharge, as well as duration and strength of both northeast "positive" winds and southwest "negative" winds. The analysis helped to isolate, in particular, the potential for rapid and strong recovery from hypoxia due to "strong negative winds", (i.e., negative winds that exceed a wind speed threshold of 10 m s −1) and the critical roles of the duration of these strong winds and the antecedent DO concentration on the strength of DO recovery. Motivated by these results, derived distribution analysis is adopted to predict the strength of DO recovery during periods of strong winds, using a simplified model of DO recovery, focused on isolated strong winds, that explicitly captures the effects of both wind duration and antecedent DO concentration.Citation: Nakayama, K., M. Sivapalan, C. Sato, and K. Furukawa (2010), Stochastic characterization of the onset of and recovery from hypoxia in Tokyo Bay, Japan: Derived distribution analysis based on "strong wind" events, Water Resour. Res., 46, W12532,

Horizontal and residual circulations driven by wind stress curl in Tokyo Bay

“…Wind fields around Tokyo Bay were estimated using nine land‐based meteorological observation stations of the Automated Meteorological Data Acquisition System (AMeDAS System), since topography around the bay induces shear and curl in the wind field. Since the observed wind speed at a height of 10 m over Tokyo Bay has been found to be about twice that measured at a height of 10 m on land [ Nakayama et al ., ; Satoh et al ., ], we doubled the wind speeds observed by the AMeDAS system and then interpolated the wind vectors using an exponential weighting function. To validate this technique for estimating the wind fields, we compared the observed wind vectors at a station to the wind vectors interpolated without using the data from the station.…”

Projection of “strong wind” events related to recovery from hypoxia in Tokyo Bay, Japan

“…(2012) and Nakayama et al . (), hypoxia tends to occur more often if the duration of strong wind events is less than 20 h. In other words, the future water quality of Tokyo Bay largely depends on wind climatology in a globally changing environment. However, it should be noted that the criteria for strong negative winds may change along with other meteorological and hydrological conditions around Tokyo Bay.…”

“…Positive winds were revealed to enhance exchange of sea water between the inner bay and the ocean, whereas negative winds tended to suppress exchange with the ocean and thus contribute to the onset of hypoxia. However, strong negative winds above a threshold of 10 m s −1 (‘strong wind’ events) were revealed to play the greatest role in rapid and strong recovery from hypoxia due to the mixing of the inner bay water with ocean water (Sato et al ., ; Nakayama et al ., ). Although such strong negative wind events are rare, their ecological impact may be disproportionately large in terms of determining the influence of hypoxia on aquatic organisms.…”

“…Nakayama et al . () demonstrated that southwesterly winds (hereafter called negative winds), northeasterly winds (hereafter called positive winds) and river discharge are the most important factors influencing DO concentrations in Tokyo Bay. Positive winds were revealed to enhance exchange of sea water between the inner bay and the ocean, whereas negative winds tended to suppress exchange with the ocean and thus contribute to the onset of hypoxia.…”

Adaptive management in Kushiro Wetland in the context of salt wedge intrusion due to sea level rise

“…Also, climaterelated issues have been revealed to have significant implications for coastal and natural resource management (NOAA, 2006;Nakayama et al, 2010). Solomon et al (2007) and Dutta et al (2005) found that climate change increases the occurrence of natural disasters, such as storm surges or flood events, leading to environmental damage, which can in turn increase the impact of natural disasters (Belfiore, 2003;Hirabayashi and Kanae, 2009;Kwak et al, 2012;Ma et al, 2010;Walsh, 2004;Watson, 2008).…”