Ice cover and thaw events influence nitrogen partitioning and concentration in two shallow eutrophic lakes

Abstract

The frequency and duration of lake ice cover is rapidly declining in the Northern Hemisphere. Limited research in oligotrophic and mesotrophic lakes suggests that extended periods of ice cover influence nitrogen (N) cycling by promoting nitrate (NO 3 -) accumulation. However, ice cover impacts on N cycling in shallow, high-nutrient, eutrophic lakes remains poorly understood. To understand drivers of under-ice water column N concentrations, we examined concurrent under-ice N concentration, hydrometerological, and physicochemical time series from two shallow eutrophic systems during sustained cold and thaw periods. We compared data from both lakes during a historically cold winter to assess how different lake-watershed physical configurations and algal biomass affected under-ice N cycling. We also used time series data from consecutive winters to assess the influence of a mild versus a historically cold winter on under-ice N cycling in one of the lakes. We found that ice cover promoted NO 3 depletion when sustained cold disconnected lakes from watershed loading, but the amount of depletion varied between lakes and was enhanced during the colder winter. Thaw events increased NO 3 concentrations compared to late winter and altered the concentration and distribution of N species in the water column, but the degree and nature of increased NO 3 varied with thaw severity, the source of meltwater, timing, and lakewatershed morphometry. Our results suggest that winters with shorter ice duration and more thaw events may result in less NO 3 depletion and higher peak NO 3 concentrations in shallow eutrophic lakes, with potential implications for N cycling and phytoplankton ecology.

Seasonal Drivers of Nutrient Concentration in Lake Ecosystems: Evaluating Climate and Ice Phenology Characteristics in a Shallow Eutrophic Lake

“…facilitated by microbial processes (N mineralization and nitri cation) is a predominate N cycling pathway across different ecosystems (Wetzel 2001; Bernhardt et al 2002; Reddy and DeLaune 2008; Schlesinger and Bernhardt 2013). In lake ecosystems that experience cold/freezing conditions, nitri cation can be a major seasonal in uence on N speciation providing an ammonium sink and nitrate source leading to the accumulation of nitrate during ice-on periods (Voytek et al 1999; Pettersson et al 2003; Powers et al 2017; Kincaid et al 2022).Consistent with prior studies(Powers et al 2017;Kincaid et al 2022), DIN accumulation, of which nitrate is a component, was strongly related to the number of days since ice-on and the severity of the winter period (Fig.5). Powers et al (2017) reported nitrate accumulation rates ranging from 0.15 to 2.70 µg N L − 1 d − 1 , indicating a consistent net accumulation of nitrate during the ice-on period.…”

“…Powers et al (2017) reported nitrate accumulation rates ranging from 0.15 to 2.70 µg N L − 1 d − 1 , indicating a consistent net accumulation of nitrate during the ice-on period. Moreover,Kincaid et al (2022) reported reduced rates of -11.2 to -0.42 µg N L − 1 d − 1(Kincaid et al 2022). Based on these two studies it appears that accumulation rates may be depth-dependent and could be in uenced by the occurrence of strati cation and/or turn-over(Dugan 2021).…”

Reduced snow and increased nutrients show enhanced ice‐associated photoautotrophic growth using a modified experimental under‐ice design

“…Nutrients (e.g., availability, ratios) were important in describing winter/spring phytoplankton community structure in a hypereutrophic lake (Hrycik et al 2022). Nitrate was also depleted under the ice in two shallow, eutrophic lakes although it was unclear what led to the declines, and possibly could be attributed to denitrification (Kincaid et al 2022). Lake Itasca is considered a mesotrophic lake and our experimental results add to a body of research that indicates nutrient availability, in addition to light availability and temperature, should be considered when assessing winter photoautotroph dynamics even in lakes that are not considered depleted in nutrients.…”

Analysis of Three Dimethyl Sulfides in Freshwater Lakes Using Headspace Solid-Phase Microextraction-Gas Chromatography with Flame Photometric Detection

“…Recent studies have shown that the DMS concentration in the water column of Yangcheng Lake, a shallow eutrophic lake, is significantly higher than that in deep-water lakes [11]. Therefore, DMSs have become a prevalent olfactory substance in freshwater bodies, including eutrophic lakes, reservoirs, and rivers [12][13][14].…”