Responses of food web to hypolimnetic aeration in Lake Vesij\xe4rvi

Jukka Ruuhijärvi,Kirsi Kuoppamäki,Mika Vinni,Tommi Malinen,Pasi Ala-Opas

doi:10.1007/s10750-020-04319-6

Jukka Ruuhijärvi, Kirsi Kuoppamäki + Show 3 more

Open Access

https://doi.org/10.1007/s10750-020-04319-6

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Abstract

We studied the responses of a food web, especially fish and zooplankton, to summertime aeration, pumping of oxygen-rich epilimnetic water to the hypolimnion in Lake Vesijärvi, southern Finland. The aim of hypolimnetic aeration was to reduce internal loading of phosphorus from sediment. The population of smelt (Osmerus eperlanus L.), the main planktivore of the pelagial area, collapsed during the two 1st years of aeration due to increased temperature and low oxygen concentrations in the hypolimnion. The population recovered after the 4th year of hypolimnetic aeration, when oxygen conditions were improved. Despite elevated hypolimnetic temperature, smelt reached exceptionally high abundance, which led to a significant reduction in cladoceran body size. The density of perch (Perca fluviatilis L.) increased at first, but then decreased when the proportion of smelt and cyprinids increased. Biomasses of Daphnia decreased probably as a result of the disappearance of dark, low-oxygen deep-water refuge against fish predation and low availability of nutritionally high-quality algae. Occasionally filamentous cyanobacteria, such as turbulence tolerant Planktothrix agardhii (Gomont), were abundant, suggesting deteriorated food resources for zooplankton. The responses of food web were controversial with respect to the aim of the management, which was to prevent the occurrence of harmful algal blooms.

Highlights

Anthropogenic eutrophication of lakes is often manifested as seasonal hypolimnetic oxygen depletion, which may accelerate internal nutrient loading (Schindler, 2006)
Oxygen-rich epilimnetic water can be pumped to deep water layers creating an artificial internal circulation in order to manage eutrophic stratified lakes suffering from hypolimnetic anoxia and internal phosphorous load
The loss of the oxygen-low hypolimnetic refuge can cause a major loss of Daphnia populations and a switch to the dominance of smaller cladocerans indicating increased planktivory by larger populations of juvenile warm-water fish species (Gauthier et al, 2014)

Summary

Introduction

Anthropogenic eutrophication of lakes is often manifested as seasonal hypolimnetic oxygen depletion, which may accelerate internal nutrient loading (Schindler, 2006). Hypolimnetic oxygen depletion can intensify trophic interactions as fish and their zooplanktonic prey become concentrated in layers above hypoxic waters (Vanderploeg et al, 2009) especially if the euphotic zone expands near or well into the anoxic water layer (Vakkilainen & Kairesalo, 2005). In such conditions, large cladocerans may become eliminated by fish (Kitchell & Kitchell, 1980). The artificial circulation technique is suggested to be most applicable in lakes that are not nutrient-limited and where oxygen depletion is a threat to warm-water fish (Cooke et al, 2005)

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