Dynamic behaviours of anoxic saline water in Lake Abashiri, Hokkaido, Japan

Abstract

Lake Abashiri (surface area 32 . 87 km 2 ; maximum depth 16 . 2±16 . 5 m) is consistently strati®ed by the lower anoxic saline layer (salinity 14±20%; dissolved oxygen less than 0 . 1% Sat.). Behaviours of the lower saline water are investigated by continuously and vertically measuring¯ow velocity, salinity and water temperature, and by observing meteorology, river discharge, lake level, sea level and water properties. During the period of ow measurement (June±August 1997), the sea level remained higher than the lake level except for a neap tide of 12±15 June and two large rainfall discharges of the upper Abashiri River of 10±15 August. Consequently, seawater intrusion from the lower Abashiri River occurred almost daily except for these two periods. Longitudinal distributions of salinity, water temperature and turbidity in the lake indicate that a density under¯ow initiated from the seawater intrusion is bifurcated into an inter¯ow and an under¯ow at the halocline. Meanwhile, in a shallow region on the opposite side of the seawater entrance, the halocline becomes unclear with the unstable density structure in the lower layer. This is probably due to the entrainment of saline water by downwelling currents in the lower saline layer, which coincide with wind-driven vertical circulation in the upper layer. Spectral analyses of¯ow velocity (1±6 cm s À1 ), temperature, and salinity in the lower layer, and of wind velocity, revealed that daily cyclic winds or diurnal southward winds with no nocturnal winds induce irrotational water motions in the lower layer with a period of 21 . 3 or 25 . 6 hrs. It was also found that the internal seiche of the ®rst mode is dominant with periods of 6 to 7 hrs during a blowing time of more than 2 days by a one-directional weak wind (maximum speed of 4 m s À1 ) or after a blowing time of more than half a day by a relatively strong wind of more than 5 m s À1 .

Field Observations Reveal How Plunging Mixing and Sediment Resuspension Affect the Pathway of a Dense River Inflow Into a Deep Stratified Lake

“…If no layer of equal density is encountered, the underflow can continue into the deep hypolimnion. This conceptual model is at the basis of numerous models (Akiyama & Stefan, 1984;Ellison and Turner, 1959;Hebbert et al, 1979;Parker et al, 1986;Savage and Brimberg, 1975) and has qualitatively been confirmed by observations in lakes and reservoirs (Chikita, 2000;Fischer and Smith, 1983;Fleenor, 2001;Ford and Johnson, 1983;Giovanoli and Lambert, 1985;Hebbert et al, 1979;Lambert and Giovanoli, 1988;Piton et al, 2022;Soulignac et al, 2021).…”

Ecosystem metabolism dynamics and environmental drivers in Mediterranean confined coastal lagoons

“…These situations typically correspond to days with high temperatures and irradiance. In some systems, anoxia near the surface can result from the upwelling of poorly oxygenated deep waters due to wind influence (Chikita, 2000;Sanford et al, 1990).…”

Characterizing ventilation events in an anoxic coastal basin: Observed dynamics and the role of climatic drivers

“…In particular, the shallower depth where the oxycline now intersects the basin slope around the perimeter of the inner basin will essentially translate to a reduction in the extent of viable habitat for aerobic organisms. In Furnace (Kelly et al 2018 b ) and similar deoxygenated estuaries (e.g., Sanford et al 1990; Chikita 2000), baroclinic waves can dramatically influence dissolved oxygen conditions in nearshore areas. A shallower oxycline following ventilation will therefore mean that upwelling anoxic water could encroach further on communities of nearshore benthic organisms.…”