The Coming and Going of a Marl Lake: Multi-Indicator Palaeolimnology Reveals Abrupt Ecological Change and Alternative Views of Reference Conditions
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ORIGINAL RESEARCH published: 12 August 2015 doi: 10.3389/fevo.2015.00082 The coming and going of a marl lake: multi-indicator palaeolimnology reveals abrupt ecological change and alternative views of reference conditions Emma Wiik 1, 2*, Helen Bennion 1, Carl D. Sayer 1, Thomas A. Davidson 3, 4, Stewart J. Clarke 5, Suzanne McGowan 6, 7, Stephen Prentice 8, Gavin L. Simpson 9 and Laura Stone 1 1 Department of Geography, Environmental Change Research Centre, University College London, London, UK, 2 Department of Biology, University of Regina, Regina, SK, Canada, 3 Lake Group, Department of Bioscience, Aarhus University, Silkeborg, Denmark, 4 Section for Ecoinformatics and Biodiversity, Department of Bioscience, Aarhus University, Aarhus, Denmark, 5 The National Trust, Bury St. Edmunds, UK, 6 School of Geography, University of Nottingham, Nottingham, UK, 7 School of Geography, University of Nottingham Malaysia Campus, Semenyih, Malaysia, 8 School of Geography, Archaeology and Palaeoecology, Queen’s University Belfast, Belfast, UK, 9 Institute of Environmental Change and Society, University of Regina, Regina, SK, Canada Edited by: Isabelle Larocque-Tobler, Eutrophication is the most pressing threat to highly calcareous (marl) lakes in Europe. The L.A.K.E.S. Institute, Switzerland Despite their unique chemistry and biology, comprehensive studies into their unimpacted Reviewed by: conditions and eutrophication responses are underrepresented in conservation literature. Mariusz Lamentowicz, Adam Mickiewicz University in A multi-indicator palaeolimnological study spanning ca. 1260–2009 was undertaken at Poznan, Poland Cunswick Tarn (UK), a small, presently eutrophic marl lake, in order to capture centennial Krystyna Magdalena Saunders, timescales of impact. Specific aims were to (1) establish temporal patterns of change University of Bern, Switzerland (gradual/abrupt) across biological groups, thereby testing theories of resistance of marl *Correspondence: Emma Wiik, lake benthic communities to enrichment, and (2) compare the core record of reference Department of Biology, University of condition with prevailing descriptions of high ecological status. Analyses of sediment Regina, Laboratory Building, 3737 Wascana Parkway, Regina, SK calcium (Ca), phosphorus (P), pigments, diatoms, testate amoebae, cladocerans, and S4S0A2, Canada macrofossils, revealed three abrupt changes in ecosystem structure. The first (1900s), [email protected] with biomass increases in charophytes and other benthic nutrient-poor indicators, Specialty section: supported ideas of resistance to eutrophication in Chara lakes. The second transition This article was submitted to (1930s), from charophyte to angiosperm dominance, occurred alongside reductions in Paleoecology, macrophyte cover, increases in eutrophic indicators, and a breakdown in marling, in a section of the journal Frontiers in Ecology and Evolution support of ideas of threshold responses to enrichment. Core P increased consistently Received: 01 May 2015 into the 1990s when rapid transitions into pelagic shallow lake ecology occurred and Accepted: 07 July 2015 Cunswick Tarn became biologically unidentifiable as a marl lake. The moderate total P at Published: 12 August 2015 which these changes occurred suggests high sensitivity of marl lakes to eutrophication. Citation: Wiik E, Bennion H, Sayer CD, Further, the early record challenges ideas of correlation between ecological condition, Davidson TA, Clarke SJ, McGowan S, charophyte biomass and sediment Ca. Instead, low benthic production, macrophyte Prentice S, Simpson GL and Stone L cover, and Ca sedimentation, was inferred. Management measures must focus on (2015) The coming and going of a marl lake: multi-indicator palaeolimnology reducing external nutrient and sediment loads at early stages of impact in order to reveals abrupt ecological change and preserve marl lakes. alternative views of reference conditions. Front. Ecol. Evol. 3:82. Keywords: marl lake, chara, palaeolimnology, eutrophication, lake management, ecological quality, cladocera, doi: 10.3389/fevo.2015.00082 macrofossils Frontiers in Ecology and Evolution | www.frontiersin.org 1 August 2015 | Volume 3 | Article 82 Wiik et al. Eutrophication: marl lake ecosystem change Introduction marl lakes have widely been held resistant to eutrophication (Wiik et al., 2013). However, the immobilization of P may Globally, freshwater habitats are among the most be restricted temporally (e.g., dissociation in winter) and anthropogenically impacted (Geist, 2011). Increasing spatially (e.g., dissociation in hypolimnion/sediment) (Wiik population density along with technological advances in et al., 2013), and P may be recycled in the sediment via food production have increased hydrological modification, uptake by macrophytes. Therefore, substantial changes in the landscape homogenization, as well as nutrient loading and benthos may occur despite low limnetic P. Indeed, even minor sediment losses from terrestrial to aquatic habitats especially increases in limnetic nutrient availability have been linked over the twentieth century (Stoate et al., 2001; Geist, 2011). The to substantial changes in macrophyte communities (Krause effects on freshwater ecosystems include eutrophication (Hasler, and King, 1994; Free et al., 2007) and extirpations of key 1947; Ulén et al., 2007), reductions in biodiversity (Baastrup- biodiversity species at a European scale (Stewart, 2001; Blaženèicˇ Spohr et al., 2013), and diminished recreational value (Pretty et al., 2006). In lakes, moderately clear water combined et al., 2003; Priskin, 2008). The widespread alteration of fresh with dense aquatic flora is frequently considered near-pristine waters especially in lowland areas where population densities are conditions, yet may not reflect truly unimpacted ecology. highest, has likely changed how freshwater habitats are perceived This may be especially true for marl lakes should further following increasingly few incidences of human encounters empirical support for sensitivity of their benthic communities with truly natural habitats. Therefore, cultural perceptions of arise. what constitutes natural, undisturbed conditions, may have Cunswick Tarn in northern England, despite being listed as become biased (i.e., shifting baseline syndrome) (Papworth et al., a marl lake (Pentecost, 2009), currently contains no marl lake 2009). In turn, where records of pre-disturbance conditions indicator species, does not undergo visible marl precipitation are lacking, restoration can often be misguided when based on in the summer months, and has brown and turbid rather increasingly old and scattered anecdotal evidence (Tibby et al., than clear blue-green, water color. It would not, therefore, 2008). be biologically categorized as a marl lake (Wiik et al., 2014) In terms of freshwater biology, it is desirable to characterize and has been classed as a (naturally) eutrophic water body lake ecosystems prior to significant human impact, a in legal documentation for Sites of Special Scientific Interest prerequisite for drafting international legislation and guidelines (SSSI) (SD 49/2). Sufficient historical records do not currently on environmental protection and restoration (European exist to characterize the unimpacted “reference status” ecology Commission, 2000; Lake, 2001). Science and legislation, in (European Commission, 2000) of the site. In order to elaborate turn, need to shape the decisions and actions of monitoring on concepts of marl lake ecology and -reference status, a agencies, site managers, and owners of private land, in order multi-indicator palaeolimnological approach was undertaken to have a tangible positive impact on the environment. with specific aims to (1) establish the centennial-scale temporal It is difficult to ascertain pre-impact conditions without patterns of change (gradual/abrupt) across biological groups, historical information, yet in Europe especially, human impact thereby testing theories of resistance of marl lake benthic extends beyond the beginning of the Industrial Revolution to communities to enrichment, (2) test whether ecological change Medieval, Roman, and prehistoric times, for which ecological was limited to one or two biological groups or whether literature is scarce. Consequently, knowledge of the natural it was apparent at an ecosystem level (physical–chemical state of the environment requires additional methods such function; multiple biological groups at all observed trophic levels; as palaeolimnology (Brenner et al., 1993; Bennion et al., synchronicity across responses), and (3) compare the core record 2011). Palaeolimnological methods for tracking changes in evidence of reference condition with prevailing descriptions of ecological structure and function in response to multiple high ecological status for marl lakes. drivers such as eutrophication (Sayer et al., 2010; Davidson Given the steep shelving of the margins of Cunswick Tarn, and and Jeppesen, 2013; Bennion et al., 2015), climate (Last and the sensitivity of charophytes to light penetration through the Smol, 2001; Leng et al., 2006), hydrology, and chemistry water column (Middelboe and Markager, 1997), eutrophication (Smol et al., 2001) have developed substantially over the effects were expected to be reflected by noticeable and relatively previous decades, allowing for increasingly confident ecosystem rapid changes in the charophyte community (as abundance of reconstructions. fossil charophyte oospores; Zhao et al., 2006). These changes In the UK, most