Historical changes in the macrophyte community of a Norwegian softwater lake

Abstract

Changes in macrophyte communities have occurred over the past decades in many oligotrophic softwater lakes with low carbon availability. Slowgrowing isoetid species have been replaced by fastergrowing elodeid species. Commonly, these changes are explained by anthropogenic nutrient enrichment or acidification of the lake water. Here we present a multi-proxy study in which we analysed plant macrofossils, pollen and spores, as well as sedimentological data from several cores taken from a SW Norwegian softwater lake. Our results indicate that the elodeid macrophyte Callitriche hamulata first appeared in this lake in the 1970s. Proliferation of C. hamulata occurred in the 1990s, replacing the hitherto dominant submerged Isoe¨tes macrophyte vegetation. Independent lines of evidence, such as diatom-inferred TP and pH reconstructions, showed no change during the past 200 years, therefore ruling out both acidification and phosphorus enrichment of the lake as possible causes for the observed change in the macrophyte community. Alternatively, expansion of Callitriche at the expense of Isoe¨tes may have been related to increased aquatic carbon availability, although nitrogen enrichment may also have been important.

Harnessing the potential of the multi‐indicator palaeoecological approach: an assessment of the nature and causes of ecological change in a eutrophic shallow lake

“…The identifiable remains of a range of biological groups, representing all aspects of the food web, are preserved in sediment cores, including inter alia: diatoms (Battarbee et al, 2001), macrophytes (Odgaard & Rasmussen, 2001;Davidson et al, 2005;Sayer et al, 2010a;Spierenburg et al, 2010), cladocerans (Jeppesen et al, 2001;Guilizzoni et al, 2006), Mollusca (Walker et al, 1993;Ayres et al, 2008), chironomids (Brodersen et al, 2001;Langdon et al, 2010) and fish (Davidson et al, 2003;Sayer et al, 2006), among an array of other invertebrate groups which are less frequently employed. Numerous palaeoecological studies have examined one or more of these fossil groups to assess ecological response to eutrophication (e.g.…”

Global historical trends and drivers of submerged aquatic vegetation quantities in lakes

“…In the English Broad lakes, increases in temperature and the number of sunny days were related to higher SAV coverage (Phillips et al, 2015), while in a Spanish karst lake (Lagunillo del Tejo), positive NAO phase where associated with drought and drying up of the outer ring of SAV (López‐Blanco et al, 2012). Finally, the effect of browning seemed to depend on initial trophic state and was positive in an oligotrophic lake through increasing nutrient inputs associated with colored dissolved organic matter or negative in cases where there was an increased loss of light (Ejankowski & Lenard, 2015; Spierenburg et al, 2010).…”