The influence of Holocene forest dynamics on the chironomid fauna of a boreal lake (Flocktjärn, northeast Sweden)

Abstract

There is a notable lack of palaeoecological records, particularly quantitative palaeoenvironmental reconstructions, for northeast Sweden. Here I use a lake sediment record from lake Flocktjärn to reconstruct Holocene terrestrial vegetation change and lake ecosystem dynamics, and to study the relationship between these components of the environment. After a period in which the vegetation around the lake is characterized by boreal forest, thermophilous arboreal taxa such as Ulmus establish in the Flocktjärn area from 6000 cal. a BP onward. Picea becomes abundant from 2930 cal. a BP onward, in line with results from other records from the region. The chironomid fauna of the lake shows high turnover before 7700 cal. a BP, after which an assemblage dominated by taxa indicative of shallow, warm and relatively nutrient rich conditions establishes. A transition to chironomid taxa that are indicative of slightly lower temperatures and lower nutrient levels occurs at 5260 cal. a BP. A chironomid‐inferred mean July air temperature record shows unreliable inferences for the record pre‐dating 7700 cal. a BP, a Holocene Thermal Maximum with temperatures around 14 °C between 7700–5260 cal. a BP, and temperatures around 12.5 °C between 5260 cal. a BP and the present. A numerical comparison between upland vegetation change and chironomid faunal dynamics for the first time shows that either vegetation change directly impacted on the chironomid fauna of the lake, or alternatively an external factor impacted on both the terrestrial and the aquatic ecosystem, resulting in concurrent changes in both parts of the ecosystem. This novel evidence of ecosystem connectivity is of vital importance to landscape management, as ongoing climate and land use change is likely to lead to increased pressure on lake ecosystems.

Responses of a shallow temperate lake ecosystem to major late-Holocene terrestrial vegetation shifts

“…Such a result of the pRDA confirms the association of our proxy records with vegetation type between the MTVSs. Overall, our findings are consistent with the results of several other studies reporting the substantial influence of terrestrial vegetation dynamics on lake ecosystems over long temporal scales (Engels, 2021; Mariani et al, 2018; Puusepp and Kangur, 2010). The MTVS effects on Lake Spore were variable and could have included impacts on lake productivity, chemistry, and water levels (Figure 6).…”

“…Overall, an insight that emerges from the available paleolimnological records is that major vegetation turnover is usually concurrent with noticeable lake ecosystem changes, including alterations in trophic state, acidity, or water levels (e.g. Beck et al, 2018; Engels, 2021; Mariani et al, 2018; Neil and Gajewski, 2018; Puusepp and Kangur, 2010). These changes to lake environment can be attributed to multiple drivers.…”

“…The impact of major vegetation turnover on lake ecosystems is likely to be recorded even in single proxy paleolimnological studies (Engels, 2021; Puusepp and Kangur, 2010). However, comprehensive reconstructions of lake ecosystem responses to terrestrial vegetation shifts require the adaptation of a multiproxy approach (Beck et al, 2018) due to various ecosystem components differing in terms of their vulnerability to disturbance, and only a record that involves stacking of several proxies can provide ecosystem-wide inferences (Davies et al, 2018).…”

Paleoreconstruction of natural conditions as the basis for the rational use of natural resource management on the territory of the Neva Lowland

“…The time and reasons for the formation of the Neva -whether it was the result of a revolutionary restructuring of the river network or a gradual transformation of a narrow sea channel into a river -are debated. It should be noted that macroregional characteristics obtained in different parts of the Baltic Sea and similar conditions in North America [15][16][17][18][19][20][21][22][23], as well as the methods of general physical geography and geomorphology developed in recent decades [24], are still poorly involved in this discussion. The doctrine of rhythms in nature by A.V.…”