Internal phosphorus loading due to sediment anoxia in shallow areas: implications for lake aeration treatments

Olga Tammeorg,Marina Haldna,Gertrud Nürnberg,Jukka Horppila,Juha Niemistö

doi:10.1007/s00027-020-00724-0

Olga Tammeorg, Marina Haldna + Show 3 more

Open Access

https://doi.org/10.1007/s00027-020-00724-0

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Abstract

Shallow lake sediments may be anoxic despite overlying aerated water. In the current study, we aimed to ascertain the contribution of shallow areas to internal phosphorus (P) loading due to sediment anoxia in stratifying lakes. Moreover, we analyzed relationships of the key water quality variables with internal P loading due to sediment anoxia originating solely from stratifying areas (IPobs) and that accounting also for the shallow areas (IPpred) for a set of Finnish lakes, including intentionally aerated and non-aerated lakes. Finally, using a broader set of lakes worldwide, we established a specific combination of lake characteristics that predict sediment P release due to sediment anoxia and linked it to the practices of aeration. Our results showed that shallow lake areas (a difference between IPpred and IPobs) contributed about half of the total P flux due to sediment anoxia. While all of the studied water quality variables related significantly to IPpred, only the concentration of total phosphorus (TP) in the near-bottom water layer related significantly to IPobs. This indicates the key importance of P release of shallow areas for water quality. The concentrations of TP in the surface water layer and chlorophyll a were significantly dependent on IPpred irrespectively of the treatment (aerated lakes or not). P supply from shallow areas may affect aeration effectiveness in stratifying lakes. IPpred was found to be dependent on the specific combination of lake characteristics (including mean and maximum depth, lake and catchment area, external P loading) PC3, driven mainly by external P loading. Hence, external load reduction should be considered as the first priority in lake water quality management. By linking the dependence of IPpred on PC3 to aeration practices, we determined the conditions that promise increased effectiveness of aeration treatments.

Highlights

Lakes act as traps accumulating nutrients at the bottom (Granéli 1999; Søndergaard et al 2003)
Original variables included the lake characteristics that were demonstrated to be of high importance for controlling lake phosphorus dynamics, i.e. maximum depth (Dmax), mean depth (D), lake area (LA), catchment area (CA), external loading of P (IF)
The same approach has been used to describe spatial variability in IPobs (Tammeorg et al 2017). The rationale for this approach is that variations in sediment P release can hardly be explained by any single lake characteristics, as these often correlate to each other

Summary

Introduction

Lakes act as traps accumulating nutrients at the bottom (Granéli 1999; Søndergaard et al 2003). The release of phosphorus (P) from sediments has hindered restoration of lake water quality worldwide by delaying the response to reduced nutrient loading from the catchment (i.e., external loading; Sas 1990; Jeppesen et al 2005). Internal P loading is often regarded to have more influence on algal biomass than external loading, as it is in a more bioavailable form (Nürnberg et al 2013a; Bormans et al 2016) This renders lake sediments the key targets for in-lake measures to reduce phosphorus supply to phytoplankton (Bormans et al 2016; Nürnberg and LaZerte 2016). The transport of P from sediments to the overlying water column is preceded by mobilization processes These processes have been attributed predominantly to the changes in redox conditions.

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