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

Abstract

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.

Anoxia begets anoxia: A positive feedback to the deoxygenation of temperate lakes

“…Our results reinforce previous research affirming that AF (the duration and spatial extent of anoxia) may be strongly positively correlated with hypolimnetic TP concentrations (Figures 4 and 5; e.g., North et al, 2014;Nürnberg et al, 2019). A threshold relationship between DO and TP is well supported by previous research across sediment core incubations, in situ sediment chamber measurements, and mass-balance whole ecosystem analyses (e.g., Anderson et al, 2021;Einsele, 1936;Mortimer, 1942;Orihel et al, 2017). Here, our threshold value of 1.8 mg/L DO, averaged throughout the entire hypolimnion, likely reflects DO conditions of ~0 mg/L near the sediment-water interface (which inherently is challenging to quantify empirically), resulting in enhanced TP loading (Nürnberg, 2019).…”

Vallisneria spiralis Promotes P and Fe Retention via Radial Oxygen Loss in Contaminated Sediments

“…However, such action can produce little evidence of decreasing rates of primary production due to internal recycling [7,8]. Indeed, the accumulation of organic matter in the benthic compartment may fuel mechanisms of nutrient recycling that more than compensate for the reduction of external loads and maintain for decades algal blooms and large photosynthetic rates [9]. The reduction of internal nutrient recycling is, therefore, another important action to contrast eutrophication [10].…”