Liming induces changes in the macrophyte vegetation of Norwegian softwater lakes by mitigating carbon limitation: results from a field experiment

Abstract

AbstractQuestionDoes liming mitigate carbon limitation to the original submerged vegetation of Norwegian softwater lakes?LocationDybingsvatn (Dalane region, Southern Norway).MethodsEight plots (1 m2) were permanently marked in the deeper part (1.5 m) of the littoral zone of Dybingsvatn in 1994. Half of the plots were limed four times with dolocal (1 kg m−2) in the period 1994–1998. Pore water, surface water chemistry and the occurrence of new plant species were monitored until 2008. In 2008, the composition and cover of the vegetation were estimated and the dominant isoetid plant species were harvested for determination of additional plant characteristics.ResultsLiming lowered the redox potential of the sediment and led to higher concentrations of dissolved inorganic carbon, Ca2+, Mg2+, Fe2+ and Mn2+ in the sediment pore water. Submerged macrophytes that could in some way profit from the higher carbon dioxide concentrations developing in the pore water (e.g. Juncus bulbosus, Sparganium angustifolium and Callitriche hamulata) expanded or colonized the limed plots at different time‐points. Four years of liming did not affect the cover and composition of the original isoetid vegetation, but led to development of taller and heavier plants with higher molar carbon to nitrogen ratios in the shoots, indicating a higher availability and uptake of carbon dioxide from the sediment.ConclusionsLiming leads to a higher availability of carbon dioxide in the sediment, partly owing to dissolution of carbonates, and partly by inducing anaerobic decomposition of organic matter and the consequent reduction of iron (IIII) hydroxides in the iron‐rich sediment (in‐lake alkalinity generation). All observed changes in the vegetation indicate that liming leads to mitigation of carbon dioxide limitation in Norwegian softwater lakes. Liming may be beneficial for fish populations by reducing concentrations of labile aluminium, but it does not preserve the characteristic chemical sediment properties and original vegetation of softwater lakes. We wish to point out that liming may, in the worst case, lead to an alternative stable lake state with anaerobic sediments as relatively highly productive isoetid plant species have a risk of uprooting.