Lake restoration influences nutritional quality of algae and consequently Daphnia biomass

Abstract

Food quality is one of the key factors influencing zooplankton population dynamics. Eutrophication drives phytoplankton communities toward the dominance of cyanobacteria, which means a decrease in the availability of sterols and long-chain polyunsaturated fatty acids (EPA and DHA). The effects of different restoration measures on the nutritional quality of the phytoplankton community and subsequent impacts on zooplankton biomass have rarely been considered. We analyzed the nutritional quality of phytoplankton in the eutrophic Lake Vesijärvi in southern Finland over a 37-year period, and studied the impacts of two restoration measures, biomanipulation and hypolimnetic aeration, on the abundance of high-quality phytoplankton. We found that biomanipulation had a positive impact on the abundance of taxa synthesizing sterols, EPA, and DHA and, concurrently, on the biomass of the keystone species Daphnia. In contrast, hypolimnetic aeration did not result in such a beneficial outcome, manifested as a decrease in the abundance of Daphnia and frequent phytoplankton blooms dominated by cyanobacteria suggesting reduction in the nutritional quality of food for Daphnia. Our analysis shows that the determination of the nutritional value of algae and the contribution of essential fatty acids and sterols is an effective method to evaluate the success of various restoration measures.

Preface: Restoration of eutrophic lakes: current practices and future challenges

“…In such cases, hypolimnetic aeration may contribute to large reductions in sediment P release (e.g., up to 90%, Walker et al, 1989). However, many studies have questioned the efficacy of aeration itself, including several in this Special Issue (e.g., Chorus et al, 2020;Niemistö et al, 2020;Ruuhijärvi et al, 2020;Taipale et al, 2020). For example, destabilization of the thermocline and increased bottom water temperatures can lead to increased sediment P release and/or transport to surface waters.…”

“…One article presents a review of existing worldwide examples of hypolimnetic withdrawal, as well as a feasibility study for its new application in Lake Borsjön, Sweden (Nürnberg, 2020). The remaining studies assess the influence of various restoration measures, including aeration and biomanipulation, on food webs and biogeochemical cycles in two heavily human-impacted Finnish Lakes, Vesijärvi and Tuusulanjärvi (Niemistö et al, 2020;Rask et al, 2020;Ruuhijärvi et al, 2020;Taipale et al, 2020).…”

“…They provide evidence that although the approach lowers internal P loading, it is not likely to result in a shift of the lake's overall trophic status towards better water quality. Taipale et al (2020) studied the response of food quality in phytoplankton and subsequent changes to the zooplankton community to both the hypolimnetic oxygenation program, and earlier biomanipulation measures, in Lake Vesijärvi. They point out that food quality of phytoplankton can be a complimentary method for evaluating restoration success.…”

Planktonic Invertebrates in the Assessment of Long-Term Change in Water Quality of the Sorbulak Wastewater Disposal System (Kazakhstan)

“…The reaction of Daphnia to toxins of blue-green algae is species-specific [76]. Experimental and field studies have shown that Daphnia thrives in the presence of green algae, cryptophytes, chrysophytes, or diatoms [77][78][79].…”

Synergistic interaction among reservoirs along a cascade system and their response to the ongoing anthropogenic and climatic pressures: evidence from deterministic hydrodynamic-biogeochemical modelling

“…Hypolimnetic aeration can be achieved by adding oxygen to bottom waters using mechanical agitation, direct injection of pure oxygen, and direct injection of air (Bormans et al, 2016) to promote oxic conditions at the sediment-water interface aiming at suppressing the sediment release. Previous studies reported that the hypolimnetic aeration promoted sufficient DO at the bottom, but no effect on P reduction and phytoplankton biomass was achieved, suggesting that aeration induced the mineralisation of organic matter and the phosphorus recycling (Niemistö et al, 2016;Taipale et al, 2020). Similarly, the simulated scenario of hypolimentic aeration did not affect TP and chl-a concentrations within the reservoir, despite the increase of DO concentration at the bottom layers.…”