Quantifying uncertainty in coastal salinity regime for biological application using quantile regression

Abstract

Salinity regimes in coastal ecosystems are highly dynamic and driven by complex geomorphic and hydrological processes. Estuarine biota are generally adapted to salinity fluctuation, but are vulnerable to salinity extremes. Characterizing coastal salinity regime for ecological studies therefore requires representing extremes of salinity ranges at time scales relevant to ecology (e.g., daily, monthly, and seasonally). Here, we propose a framework for modeling coastal salinity with these overall goals: (1) quantify uncertainty in salinity associated with important terrestrial and oceanographic drivers, (2) examine time scales of salinity response to river streamflow events, and (3) predict salinity continuously over space at key time scales. Salinity is modeled as quantile surfaces related to river discharge, tidal dynamics, wind, and spatial location, applied to Suwannee Sound estuary, FL, USA, where salinity has been monitored spatially since 1981. Each quantile level is regressed independently, and together they comprise a distribution of salinity uncertainty across space, with upper and lower quantiles describing salinity extremes. Effects of physical drivers on salinity are compared through four base models with various combinations of tide and wind variables, each including spatial coordinates and a single streamflow metric (in cubic meters per second). Multiple time scales of streamflow are considered by taking means across various periods, from 1 to 12 days, and at various lagged intervals prior to salinity sample, totaling 144 streamflow metrics. We found that the Suwannee coastal salinity regime is dynamic at multiple time scales and varies nonlinearly across space from the river effluence outward. Salinity increases nonlinearly with decreasing river flow rates below 200 m 3 /s, most prominently in the lower quantiles of salinity (τ = 0.05-0.25). Wind appears to have a stronger influence on salinity than astronomic tides for this estuary. The regression approach developed here can be applied to any coastal system that has sufficient spatial and temporal monitoring coverage to capture multiple flood and drought events.

Physiologically informed organismal climatologies reveal unexpected spatiotemporal trends in temperature

“…Considerations of fine-scale heterogeneities have begun to trickle through when managing ecosystems, for instance by accounting for spatial variability in three dimensions across estuarine models supporting fisheries stock assessments ( Yurek et al., 2023 ), as well as in conservation, where local environmental conditions change more slowly than surrounding areas and populations of organisms are able to survive despite overall warming trends ( Morelli et al., 2020 ; Salois et al., 2022 ). Associated fine-scale effects manifest both in space ( Sears et al., 2016 ) and time ( Kefford et al., 2022 ), both of which are critical to biologically relevant interpretations.…”

Modeling the effects of large-scale interior headland restoration on tidal hydrodynamics and salinity transport in an open coast, marine-dominant estuary

“…These oysters are sensitive to extreme salinities (<5 and >35 pss), particularly if they are exposed for prolonged periods of time (Marshall et al, 2021a;Marshall et al, 2021b). Oysters can be impacted at both extremes in locations where salinity broadly fluctuates, which may affect feeding rates, respiration and even result in mortality (Yurek et al, 2023). The mean salinity for all scenarios in the frontal and tropical periods remained within the optimal range.…”

“…The mean salinity concentrations were calculated from the CDFs at each station as well as at the GNDPCWQ station on the Mississippi side of the estuary for comparison (Table 1). The CDFs show changes in mean salinity, as well as the extremes (maximum and minimum), which are meaningful in terms of ecosystem health and may not be represented if salinity is generalized as a mean (Yurek et al, 2023).…”

“…For example, salt marshes are governed by tidal inundation, salinity and sediment supply (Alizad et al, 2016, Alizad et al, 2018, Ganju et al, 2019. Ecological processes are moderated by coastal salinity ranges, particularly extreme values of salinity, which can affect the viability of species such as oysters (Yurek et al, 2023).…”

Potential challenges for the restoration of Biscayne Bay (Florida, USA) in the face of climate change effects revealed with predictive models

“…SLR will aggravate the problem (Chang, 2011;Basack et al, 2022) by increasing hydrostatic pressure at the coast and favoring landward saltwater transport. Modeling coastal salinity regimes requires accurate representation of salinity fluctuations across ranges of the underlying physical drivers, as well as spatially across the landscape (Yurek et al, 2023). Robust and comprehensive models that represent coastal processes correctly are required for planning management scenarios.…”