Effect of eutrophication and humification on nutrient cycles and transfer efficiency of matter in freshwater food webs

Maciej Karpowicz,Jolanta Ejsmont-Karabin,Magdalena Grabowska,Piotr Zieliński,Irina Feniova,Joanna Kozłowska

doi:10.1007/s10750-020-04271-5

Abstract

We evaluated how eutrophication and humification impacted nutrient cycles and the efficiency of carbon transfer in the planktonic food webs of 12 lakes in north-eastern Poland that differed in trophic state. Our results indicated that the effectiveness of carbon transfer between phytoplankton and zooplankton varied from 0.0005% to 0.14%, which is much lower than the theoretical 10%. The highest efficiency of carbon transfer occurred in the mesotrophic lakes due to the higher hypolimnetic zooplankton production, while the lowest efficiency was observed in the dystrophic lakes and in one eutrophic lake that was dominated by cyanobacteria. Inedible algae (e.g. Gonyostomum semen) and cyanobacteria appeared to be the main factors reducing the efficiency of the transfer of matter in pelagic food webs. The results of our study showed that plankton communities are a key component of the nutrient cycle in freshwater food webs. Phytoplankton were a very effective nitrogen sink, and in the mesotrophic lakes, up to 99% of the total nitrogen was sequestrated in phytoplankton. As a result, there was a depletion of inorganic nitrogen in the upper water layer. Furthermore, zooplankton were an important phosphorus sink, thus significantly influencing the nutrient cycles.

Highlights

Plankton communities are a key component in the ecosystems of freshwater lakes
Our results indicated that the effectiveness of carbon transfer between phytoplankton and zooplankton varied from 0.0005% to 0.14%, which is much lower than the theoretical 10%
The lowest efficiency was noted in dystrophic lakes, where only 0.001% of organic carbon production of phytoplankton was incorporated into new biomass of zooplankton

Summary

Introduction

Plankton communities are a key component in the ecosystems of freshwater lakes. Most algae cannot use atmospheric nitrogen directly but, instead, acquire chemically reactive forms of this element, such as nitrate (NO3-) or ammonium (NH4?). Algae use reactive forms of phosphorus (PO43-). Phytoplankton are an important link in the transformation of nutrients from inorganic to organic forms, reducing the amount of reactive nutrient forms. The uptake of oxidized and reduced forms of nutrients can be separated in time and space due to their association with different phytoplankton groups (Yu et al, 2018). Changes in phytoplankton taxonomic structure and growth rates can affect their nutrient demand and uptake and, as such, can influence their carbon: nutrient stoichiometry (Sterner & Elser, 2002). The nutrient cycles can depend on phytoplankton community structures

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