Winter weather and lake‐watershed physical configuration drive phosphorus, iron, and manganese dynamics in water and sediment of ice‐covered lakes

Abstract

While decreasing occurrence and duration of lake ice cover is well-documented, biogeochemical dynamics in frozen lakes remain poorly understood. Here, we interpret winter physical and biogeochemical time series from eutrophic Missisquoi Bay (MB) and hyper-eutrophic Shelburne Pond (SP) to describe variable drivers of under ice biogeochemistry in systems of fundamentally different lake-watershed physical configurations (lake area, lake : watershed area). The continuous cold of the 2015 winter drove the MB sediment-water interface to the most severe and persistent suboxic state ever documented at this site, promoting the depletion of redoxsensitive phases in sediments, and an expanding zone of bottom water enriched in reactive species of Mn, Fe, and P. In this context, lake sediment and water column inventories of reactive chemical species were sensitive to the severity and persistence of subfreezing temperatures. During thaws, event provenance and severity impact lake thermal structure and mixing, water column enrichment in P and Fe, and thaw capability to suppress redox front position and internal chemical loading. Nearly identical winter weather manifest differently in nearby SP, where the small surface and watershed areas promoted a warmer, less stratified water column and active phytoplankton populations, impacting biogeochemical dynamics. In SP, Fe and P behavior under ice were decoupled due to active biological cycling, and thaw impacts were different in distribution and composition due to SP's physical structure and related antecedent conditions. We find that under ice biogeochemistry is highly dynamic in both time and space and sensitive to a variety of drivers impacted by climate change.

The unique methodological challenges of winter limnology

“…Moreover, the links between ice‐cover dynamics, microbial ecology, and physical processes below ice have important implications for redox potential at the sediment–water boundary. Changes in redox have repercussions for under‐ice internal loading of nutrients from the sediments (North et al ; Joung et al ; Orihel et al ) and for the amount and type of greenhouse gases (GHGs; e.g., carbon dioxide [CO 2 ] and methane [CH 4 ]) emitted from lakes at ice melt (Denfeld et al ). Therefore, biogeochemical processes that occur during the winter have the potential to affect spring and summer conditions (Bertilsson et al ).…”

Freezing degree‐day thresholds and Lake ice‐out dates: Understanding the role of El Niño conditions

“…Resulting seasonal temperatures can disrupt the lake phenology and linked processes, species dynamics and succession, and nutrient loading and mixing characteristics. For instance, for temperate and arctic North American lakes, winter climate variability has directly or indirectly been shown to affect ice cover phenology and extent (e.g., Bai et al, ; Beyene and Jain, ), water temperatures (e.g., Austin and Colman, ), onset of stratification period (e.g., Winder and Schindler, ), seasonal plankton composition, abundance and succession (e.g., Goldman et al, ; Hampton et al, ), fish population (e.g., Farmer et al, ) and seasonal geo‐chemical dynamics (e.g., Joung et al, ; Powers et al, ). In a changing climate, successful conservation and restoration of lake ecosystems can benefit from climate‐based risk framework presented here, thus affording pinpointed estimates of trends and transitions in lake variables.…”

Under-ice mesocosms reveal the primacy of light but the importance of zooplankton in winter phytoplankton dynamics

“…Manipulation of zooplankton biomass may also alter nutrient levels through excretion (Corner and Newell 1967, Oliver et al 2015). Other sources of nutrient inputs that are important in the open-water season, including phosphorus release from sediment (Penn et al 2000, Søndergaard et al 2003), may also be a significant source of phosphorus under ice if oxygen is limited (Joung et al 2017). We expected that nutrient concentrations would respond to changes in plankton communities but not to the extent that they affected phytoplankton growth (Sommer et al 2012).…”