Disentangling natural and anthropogenic drivers of changes in a shallow lake using palaeolimnology and historical archives

Abstract

Shallow lakes are susceptible to catastrophic regime shifts characterised by the presence or absence or macrophytes. However, the long-term controls on macrophyte succession in shallow lakes are incompletely understood. To investigate this, we analysed multiple sediment proxies in Lake Rotcze (Eastern Poland), a small, shallow and densely macrophyte-covered lake to (1) reconstruct the 'reference conditions' (sensu WFD) and development of the lake in recent centuries, (2) compare historical evidence with the sedimentary record, and (3) identify the natural and anthropogenic drivers of macrophyte succession. Before the twentieth century, conditions in the lake may be referred to as 'reference conditions'. Subsequently forest clearance in the catchment resulted in lower water transparency, but concurrent catchment drainage lowered water levels and increased macrophyte development. Since 1950 elevated nutrient supply and climatically driven increases in water levels led to the deterioration of water transparency and partial macrophyte withdrawal. At the end of the twentieth century lake-level drawdown led to low phytoplankton biomass and clear water creating a novel ecosystem where macrophytes invade the whole lake. These patterns suggest that both natural and anthropogenically induced water level fluctuations have been critical drivers of macrophyte development.

Towards a more precisely defined macrophyte-dominated regime: the recent history of a shallow lake in Eastern Poland

“…Thus our hypothesis that the current macrophyte-dominated state of the lake has been a persistent feature over the recent centuries cannot be rejected. This seems to be typical of lakes in a landscape generally unaffected by human activity (Moss, 1998a;Scheffer, 1998;Little & Smol, 2000;Davidson et al, 2005;Salgado et al, 2010, Kowalewski et al, 2016.…”

An over 200-Year Environmental Change Record from the Highly Impacted Small, Hardwater Lake Pniówno (Chełm Hills)

“…Given the above, the macrophyte development despite the high cultural eutrophication, might have resulted from alleviation of human activity, as well as the improvement of light conditions resulted from declined water level. The subsequent factor was found to be decisive for the development of macrophytes in Lake Rotcze in the second half of the 20 th century (Kowalewski et al 2016).…”

“…Data on changes of ecological status of Łęczna-Włodawa Lakes covering periods longer than a few decades are scarce. So far only few lakes: Kleszczów (Kornijów et al 2016), Rotcze (Kowalewski et al 2016) and Głębokie Uścimowskie (Kowalewski et al 2013) have been comprehensively studied by applying paleolimnological methods. Although for all these lakes the development of macrophytes were very important phenomena, the results clearly point to the considerable differences in the trajectories of their changes within the last 200 years, as well as the important role of local factors in the process, especially with regard to transformation of their catchment.…”

Oxygen stable isotope composition of carbonate encrustations of two modern, widely distributed, morphologically different charophyte species

“…Therefore, analysis of plant macrofossils is commonly applied in paleolimnological reconstructions (Hannon & Gaillard, 1997;Bešta et al, 2009;Gałka & Apolinarska, 2014;Kowalewski et al, 2016).…”