In situ, high-resolution time series of dissolved phosphate in Green Bay, Lake Michigan

Zorn, Michael E.; Waples, James T.; Valenta, Tracy J.; Kennedy, John; Klump, J. Val

doi:10.1016/j.jglr.2018.07.008

Cited by 7 publications

(8 citation statements)

References 10 publications

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“…There are previously reported rates and trends published for re‐aerated sediment P release. Zorn et al (2018) reports average release rates of 20.74 ± 23.3 mg m −2 d −1 following eight re‐aeration events observed in Green Bay using in situ instrumentation. There was no distinct trend in the eight reported release rates relative to each other, attributed to different sets of properties driving water replacement and P release.…”

Section: Resultsmentioning

confidence: 99%

“…Pinpointing these conditions is especially important in Lake Erie, where hypoxia and anoxia exhibit dramatic inter‐annual variability (Zhou et al, 2013), and advection or upwelling can disrupt stratification and hypolimnion anoxia, causing abrupt changes in the redox condition at the sediment–water interface (Ruberg et al, 2008). Detailed continuous monitoring in Green Bay, Lake Michigan by Zorn et al (2018) showed that turnover events and subsequent re‐stratification had mixed effects on hypolimnion phosphorus concentration and DO consumption during organic matter remineralization, but the effects on P flux were not fully characterized. Our study mimics re‐stratification events in experimental cores in order to observe and replicate the conditions and rates of P release in response to short‐term disruptions of the hypolimnion at a fine scale.…”

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confidence: 99%

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Accelerated sediment phosphorus release in Lake Erie's central basin during seasonal anoxia

Anderson

Johengen

Miller

et al. 2021

Limnology & Oceanography

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Eutrophication remains a serious threat to Lake Erie and has accelerated over past decades due to human activity in the watershed. Internal phosphorus (P) loading from lake sediment contributes to eutrophication, but our understanding of this process in Lake Erie is more uncertain than for its riverine P inputs. Past study has focused on incubating sediment cores in oxic or anoxic conditions, meaning we know little about sediment flux during state transitions. We used 56 controlled sediment core incubation experiments to quantify rates and onset of P release in Lake Erie's central basin as a function of depositional environment, season (spring, summer, and fall), temperature, and dissolved oxygen (DO) concentration. P flux under oxic or hypoxic (> 0 to ≤ 2 mg L−1 DO) conditions was slow (0.31–0.50 mg m−2 d−1) compared to anoxic P flux (5.19–30.7 mg m−2 d−1). The transition between slow and fast flux occurred within 24 h of anoxia (0 mg L−1 DO). Oxic or anoxic P flux was generally similar across seasons and incubation temperatures (8°C and 14°C). In 14°C incubated cores anoxic P flux onset was earliest in fall, when sediments had already been exposed to anoxic conditions in the lake. Re‐oxygenation of experimental cores that temporarily developed anoxia reversed the direction of P flux, but P release resumed at similar rates once the water returned to anoxia. Understanding the effects of hypolimnion oxygen conditions on internal P loading allows us to better constrain nutrients sources and implications for P budget management.

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Accelerated sediment phosphorus release in Lake Erie's central basin during seasonal anoxia

Anderson

Johengen

Miller

et al. 2021

Limnology & Oceanography

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“…Recent advancements in in situ phosphorus analyzers have presented novel sensing techniques and analytical protocols for characterizing P flux at the sediment–water interface . For example, Zorn demonstrated the ability of these analyzers to quantify hypolimnetic P concentration increases between stratification turnover events in Green Bay of Lake Michigan and related these patterns with observed hypolimnetic dissolved oxygen consumption. The study presented here builds upon these previous approaches by using continuous in situ monitoring to measure the rates and timing of sediment phosphorus flux at two study sites in Lake Erie’s central basin.…”

Section: Introductionmentioning

confidence: 99%

Continuous In Situ Nutrient Analyzers Pinpoint the Onset and Rate of Internal P Loading under Anoxia in Lake Erie’s Central Basin

et al. 2021

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Lake Erie's central basin experiences seasonal anoxia, contributing to internal sediment phosphorus (P) loading and exacerbating eutrophication. The precise conditions required for internal loading are poorly understood. This study constrains the timing and rates of internal P loading using continuous in situ temperature, dissolved oxygen (DO), and soluble reactive P (SRP) observations from two sites. SRP concentrations remained low during normoxia (>2 mg of DO L −1 ) and hypoxia (0−2 mg of DO L −1 ) but increased abruptly after anoxia for 12−42 h. SRP flux rate estimations varied, likely due to advection and hypolimnion thickness variation, but could still be reasonably quantified. Flux rates and standard errors during anoxia averaged 25.67 ± 5.5 mg m −2 day −1 at the shallower site and 11.42 ± 2.6 mg m −2 day −1 at the deeper site. At the shallower site, the anoxic hypolimnion was displaced with normoxic water, causing cessation of P flux until anoxia returned, and higher flux rates resumed immediately (89.1 ± 8.6 mg m −2 day −1 ), suggesting rapid, redox-controlled P desorption from surface sediments. On the basis of our rate and onset findings, the expected anoxic area and duration in the basin could yield an annual internal SRP load comparable to the annual central basin TP tributary load of 10000−11000 metric tonnes.

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“…The study was conducted between July and September in 2014 and 2015. The timing of the field study coincided with the time of year during which bottom water hypoxia is observed (Hamidi et al 2015, Zorn et al 2018, allowing us to investigate the drivers of hypoxia as it occurred.…”

Section: Study Sitementioning

confidence: 99%

Seiche- and storm-driven benthic oxygen uptake in a eutrophic freshwater bay determined with aquatic eddy covariance

et al. 2021

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Oxygen depletion in bottom waters of lakes and coastal regions is expanding worldwide. To examine the causes of hypoxia, we quantified the drivers of benthic oxygen uptake in Green Bay, Lake Michigan, USA, using 2 techniques, aquatic eddy covariance and sediment core incubation. We investigated benthic oxygen uptake along a gradient in C deposition, including shallow water near the riverine source of eutrophication and deeper waters of lower Green Bay where high net sediment deposition occurs. Time-averaged eddy covariance oxygen uptake was high near the source of eutrophication (11.5 mmol m 22 d 21 ) and at the shallower of the high deposition sites (9.8 mmol m 22 d 21 ). The eddy covariance technique revealed a decrease in benthic oxygen uptake with depth at the high deposition sites. These patterns were consistent with benthic uptake being driven by the deposition of autochthonous production. Additionally, eddy covariance revealed a nearly proportional relationship between benthic oxygen uptake and current velocity at all sites. Specifically, because of the lake seiche, water velocity typically varied 3Â at a site and caused a 3Â variation in benthic oxygen uptake. A summer storm also doubled bottom-water velocities and caused a further doubling of uptake to 28 mmol m 22 d 21 . This high sensitivity of benthic oxygen uptake to seiche-driven water velocities indicates that redox conditions in surficial cohesive sediments are highly dynamic.

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In situ, high-resolution time series of dissolved phosphate in Green Bay, Lake Michigan

Cited by 7 publications

References 10 publications

Accelerated sediment phosphorus release in Lake Erie's central basin during seasonal anoxia

Accelerated sediment phosphorus release in Lake Erie's central basin during seasonal anoxia

Continuous In Situ Nutrient Analyzers Pinpoint the Onset and Rate of Internal P Loading under Anoxia in Lake Erie’s Central Basin

Seiche- and storm-driven benthic oxygen uptake in a eutrophic freshwater bay determined with aquatic eddy covariance

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