Exchange Flow and Material Transport Along the Salinity Gradient of a Long Estuary

Abstract

Characteristics of the transport and fate of the waterborne materials (e.g., pollutants, sediments, organisms, and nutrients) between an estuary and the adjacent coastal ocean depend significantly on the strength of estuarine exchange flow (

Vertical Transport Timescale of Surface‐Produced Particulate Material in the Chesapeake Bay

“…The resuspension ratio increases and the high value expands to the whole bay (mostly confined below the pycnocline; Figures 11f) as the settling velocity increases to 10 m/day since the resuspended high-sinking material is less prone to be transported outside but more likely to be kept inside the bay. The distribution of high resuspension ratio can reach to the surface over the Rappahannock Shoal (37.2°-37.5°N), consistent with the localized vigorous vertical exchange (Xiong et al, 2021a).…”

“…It is also noted that the location of the maximum net deposition age shifts downstream and the along‐channel gradients in the net deposition age decrease with the increased settling velocity (Figure 10). For example, the maximum VDA for w s = 0 m/day is around 38.5°–39°N and the peak net deposition age moved toward 37.5°–38°N for the fastest‐sinking material ( w s = 10 m/day) as the downward transport is less controlled by the water column stratification but more by the settling velocity and likely the strong water reflux and the vigorous vertical water exchange associated with the shoaling of the deep channel (Xiong et al., 2021a). A non‐dimensional coefficient ( R = 1−net deposition age/in‐suspension age) was estimated to specify the resuspension ratio in the water column (Figures 11d–11f).…”

“…The amount of consumption and transformation of OM in an estuary increases with the residence time. For example, the long residence time (∼180 days; Du & Shen, 2016) associated with the bathymetry‐induced strong water reflux (Xiong et al., 2021a) can result in high retention of nutrients and OM in the middle reach of the Chesapeake Bay (CB), promoting high rates of internal Autoc‐OM production (Fennel & Testa, 2019) and respiration (Du & Shen, 2015; Kemp et al., 1992), and further developing the recurring summertime hypoxia and anoxia in the deep central basin (Murphy et al., 2011). Accumulating evidence suggests the connection between the deposition of springtime OM to sediments and the summertime oxygen depletion in the bottom of CB (Cerco, 2000; Malone et al., 1988; Zheng & DiGiacomo, 2020), yet the specific transport time for the surface‐produced OM from the spring phytoplankton blooms to reach the bottom has not been quantified.…”

“…The OM that fuels the oxygen consumption may originate from the watershed, that is, allochthonous source, such as vascular plant detritus, soil leaching and erosion, and agriculture runoff, or from the settled phytoplankton production within the system, that is, autochthonous source (Autoc-OM), such as senescent cells, zooplankton fecal pellets, and marine aggregates (Rabalais et al, 2010).The amount of consumption and transformation of OM in an estuary increases with the residence time. For example, the long residence time (∼180 days; Du & Shen, 2016) associated with the bathymetry-induced strong water reflux (Xiong et al, 2021a) can result in high retention of nutrients and OM in the middle reach of the Chesapeake Bay (CB), promoting high rates of internal Autoc-OM production (Fennel & Testa, 2019) and respiration…”

“…The amount of consumption and transformation of OM in an estuary increases with the residence time. For example, the long residence time (∼180 days; Du & Shen, 2016) associated with the bathymetry-induced strong water reflux (Xiong et al, 2021a) can result in high retention of nutrients and OM in the middle reach of the Chesapeake Bay (CB), promoting high rates of internal Autoc-OM production (Fennel & Testa, 2019) and respiration…”