Seasonal Patterns of Mixing and Arsenic Distribution in a Shallow Urban Lake

Abstract

Arsenic, a carcinogenic contaminant, has accumulated in the bottom sediments of lakes around the world due to a range of anthropogenic activities, such as mining, smelting, and the application of arsenic-containing pesticides (Gawel et al., 2014;Rice et al., 2002;Smedley & Kinniburgh, 2002). When arsenic is mobilized from sediments into overlying lake water, it can be taken up by primary producers (Barrett et al., 2018;Caumette et al., 2011) and move up the aquatic food web, including into organisms consumed by humans (Hull et al., 2021;Rahman et al., 2012). Both physical and biogeochemical lake processes control arsenic mobilization, transport, and concentration in lake water and thus control ecosystem and human exposure to arsenic. Recent findings show that conditions within shallow lakes, as opposed to deep lakes, facilitate rapid cycling of arsenic between the sediment and overlying lake water (Barrett et al., 2019), and enhance spatial overlap between oxygen-requiring biota and mobilized arsenic (Barrett et al., 2018;Hull et al., 2021).According to lake mixing classifications, most shallow lakes are polymictic, meaning they circulate perennially and only stratify for short periods (Hutchinson & Löffler, 1956;Lewis Jr., 1983). Based on this reasoning, the

A review on arsenic in the environment: contamination, mobility, sources, and exposure

“…128–130 In well-oxygenated water and sediments, nearly all arsenic is present in the arsenate form. 131–134 The MMA and DMA (dimethyl arsenic acid) are also present in some water. 15,28,135–137…”

“…[128][129][130] In welloxygenated water and sediments, nearly all arsenic is present in the arsenate form. [131][132][133][134] The MMA and DMA (dimethyl arsenic acid) are also present in some water. 15,28, [135][136][137] The solubility and mobility of As in the environment increase with increasing alkalinity and salinity.…”

Short‐Term Arsenic Cycling in a Shallow, Polymictic Lake

“…To characterize stratification within the water column, we calculated density profiles (IOC et al., 2010) and buoyancy frequency (N 2 ) profiles, as described in Fung et al. (2022). The theoretical period of a first mode internal wave was calculated using the following equation: $$$t=\frac{2L}{\sqrt{g\frac{{\Delta }\rho }{{\rho }_{0}}\frac{h(H-h)}{H}}}$$$ where L is the fetch, g is gravity, Δ ρ is the density difference between the epilimnion and hypolimnion, ρ 0 is the epilimnion density, H is the lake depth, and h is the epilimnion depth (Fischer, 1979).…”

“…De-spiked data were used to calculate hourly vertical turbulent intensities, w′) 2 , at each sample bin, where w′ is the vertical velocity residual, w′ = w w, and w and w are the instantaneous vertical velocities and the 10-min burst-average vertical velocities, respectively. To characterize stratification within the water column, we calculated density profiles (IOC et al, 2010) and buoyancy frequency (N 2 ) profiles, as described in Fung et al (2022). The theoretical period of a first mode internal wave was calculated using the following equation:…”

“…Once in dissolved form, lake depth, stratification, and frequency of lake mixing control the concentration and distribution of As in the lake water column (Fung et al., 2022). Various factors, including temperature and mixing frequency, control seasonal trends in As concentrations in lake water (Fung et al., 2022; Martin & Pedersen, 2002; Palmer et al., 2019); however, less is known about the short term dynamics of As in freshwater systems.…”