Centennial-scale changes to the aquatic vegetation structure of a shallow eutrophic lake and implications for restoration

Abstract

1. We investigate long-term (>200 years) changes to the composition and spatial structure of macrophyte communities in a shallow, eutrophic lake (Barton Broad, eastern England) and consider the implications for lake restoration. 2. Historical macrophyte data were assembled from a variety of sources: existing plant databases, museum herbaria, journal articles, old photographs and eyewitness accounts. Additionally, two types of sediment core sample were analysed for plant macro-remains and pollen; bulk basal samples from multiple core sites analysed to provide information on ‘pre-disturbance' macrophyte communities and two whole cores analysed to determine historical change. 3. Prior to the late 1800s, macrophyte communities were diverse and included a multilayered mosaic of short-stature submerged taxa and taller submerged and floating-leaved species. With the progression of eutrophication after around 1900, the former community was displaced by the latter. Diversity was maintained, however, since an encroaching Schoenoplectus-nymphaeid swamp generated extensive patches of low-energy habitat affording refugia for several macrophytes otherwise unable to withstand the hydraulic forces associated with open water conditions. When this swamp vegetation disappeared in the 1950s, many of the ‘dependent' aquatic macrophytes also declined leaving behind a sparse, species-poor community (as today) resilient to both eutrophication and turbulent open waters. 4. The combination of historical and palaeolimnological data sources offers considerable benefits for reconstructing past changes to the aquatic vegetation of lakes and for setting restoration goals. In this respect, our study suggests that successful restoration might often be better judged by reinstatement of the characteristic structure of plant communities than the fine detail of species lists; when nutrients are low and the structure is right, the right species will follow

Sedimentary macrofossil records reveal ecological change in English lakes: implications for conservation

“…Changes in a lake's aquatic vegetation can be determined from historical botanical data yet, with a few exceptions (Sand-Jensen 1997;Davidson et al 2005;Madgwick et al 2011;Dudley et al 2012), such records rarely exist for time periods (decades to centuries) sufficient to assess human impacts. An alternative, or indeed complementary, tool for assessing long term changes in vegetation is the palaeoecological record.…”

“…Notwithstanding the taphonomic issues associated with the plant-macrofossil relationship arising from the varying reproductive strategies and dispersal capabilities of plants, several comparative studies of macrofossil records with botanical records have shown plant macrofossils to reliably record shifts in the dominant aquatic vegetation of shallow lakes (Davidson et al 2005;Salgado et al 2010;Clarke et al 2014;Levi et al 2014). Plant macrofossils have been variously employed to investigate long-term successional changes in the submerged vegetation of lakes (Bradshaw et al 2005;Rasmussen and Anderson 2005), responses to recent eutrophication (McGowan et al 2005;Salgado et al 2010;Sayer et al 2010a;Madgwick et al 2011) and top-down impacts of fish (Sayer et al 2016), and to inform on lake conservation status and the need for appropriate management (Sayer et al 2012;Wiik et al 2014).…”

How effective are plant macrofossils as a proxy for macrophyte presence? The case of Najas flexilis in Scotland

“…Several studies have shown that plant remains from different species have different distributions within lake basins (Davidson et al 2005;Zhao et al 2006;Salgado et al 2010;Madgwick et al 2011). Clarke et al (2014) recommend that cores therefore be taken close enough to the shore of a lake to pick up as many remains as possible, but not so close that the sediment profile is disturbed.…”

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

“…Monitoring data from such periods are usually scarce or non-existent, with some exceptions (Egertson et al, 2004;Hargeby et al, 2007;Sand-Jensen et al, 2008;Hilt et al, 2013;Hobbs et al, 2014). In situation without reliable long-term monitoring data, studies into historical ecosystem state can be supported by paleolimnological analyses (Battarbee et al, 2005;Sayer et al, 2010a;Madgwick et al, 2011;Kowalewski et al, 2013Kowalewski et al, , 2015. This particularly concerns shallow lakes distinguished by abundant development of macrophytes accompanied by a rich invertebrate fauna, and providing conditions favourable for the deposition of macrofossils (Rawcliffe et al, 2010).…”