Wetlands (2014) 34:1097–1108 DOI 10.1007/s13157-014-0569-3
ORIGINAL RESEARCH
Drastic Turnover of Bryophyte Vegetation on Bog Microforms Initiated by Air Pollution in Northeastern Estonia and Bordering Russia Kai Vellak & Jaan Liira & Edgar Karofeld & Olga Galanina & Maria Noskova & Jaanus Paal
Received: 16 January 2014 / Accepted: 5 August 2014 / Published online: 14 August 2014 # Society of Wetland Scientists 2014
Abstract Human influence on bogs, including air pollution, causes changes in vegetation leading to the degradation of an ombrotrophic bog ecosystem into a more uniform transitional mire-like system. We have hypothesized that intensive atmospheric alkaline pollution will cause an increase in water pH and convergence of bryophyte species composition among microforms. We also expected that bog-specific acidophilic species will be replaced by species indigenous to neutral pH habitats. Through GLM and DCA analyses, we found that although natural acidic bogs are more species poor than polluted bogs, the increase in pH can lead to a decrease in bogspecific vegetation. In polluted bogs, the species composition in different bog microforms will become similar; in particular bog-specific Sphagnum mosses will be increasingly replaced by more tolerant brown mosses, particularly in lawns. Keywords Alkaline input . Characteristic species . Microtopography . Raised bogs
Introduction Peatlands cover only 3 % of the world’s land area but their importance as valuable ecosystems for water storage and regulation, carbon accumulation and as a habitat for rare species is significant (Constanza et al. 1997; Wieder and Vitt 2006). The value of multiple ecosystem services by peatlands seems meager compared with the economic profit from K. Vellak (*) : J. Liira : E. Karofeld : J. Paal Institute of Ecology and Earth Sciences, University of Tartu, Lai 40, Tartu 51005, Estonia e-mail:
[email protected] O. Galanina : M. Noskova St Petersburg State University, Vasiljevsky Ostrov, 10 Liniya 33-35, 199178 St. Petersburg, Russia
cropland or forest logging, which may account for the destruction and degradation of peatlands by humans with little attention to the consequences to peatland ecosystems (Mitch and Gosselnick 2000; Lachance and Lavoie 2004). Ombrotrophic raised bogs (EU habitat type codes 7110, 7120) are typical mire ecosystems in northern latitudes, formed mainly by Sphagnum mosses, and characterized by a particular microhabitat (microform) pattern, known as a hummock-lawn-hollow complex (Sjörs 1961; Andrus 1986; Karofeld 1998). The microtopography of bogs determines the contrast in plant community patterns between higher and relatively dry (hummocks) and lower and wetter parts (lawns and hollows) (Kenkel 1988; Vivian-Smith 1997; Nungesser 2003; Bruland and Richardson 2005; Smith et al. 2012). The drainage of bogs has a long history and its destructive effect on bog communities is well documented (e.g. Lachance and Lavoie 2004), whereas the influence of air pollution has become evident and understood much later (e.g. Karofeld 1996; Turetsky and St. Louis 2006). Human intervention has induced degradation of ombrotrophic ecosystems, reflected in increased rates of peat decomposition and mineralization (Sheffer and Carpenter 2003; Krunk et al. 2003; Paal et al. 2010), the disappearance of Sphagnum mosses and the degradation of microtopographic structure (Gignac and Beckett 1986; Adams and Preston 1992). Because of their reliance on atmospheric input of nutrients and water, raised bogs have a low ecological buffering capacity; consequently their response to atmospheric pollution is more pronounced than in many other plant communities (Adams and Preston 1992; Goubet et al. 2006; Tousignant and Pellerin 2010). As the inundation and nutrient transport properties differ among microform units (Courtwright and Findlay 2011), the reaction of bog vegetation to airborne pollution is not uniform, but varies between microtopographic subunits (Weltzin et al. 2001). When the natural microtopography of raised bogs is degraded by altered water and carbon
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accumulation processes (Swanson 2007), the loss of hummocks causes the overall vegetation of the habitat to become more homogeneous (Tomasson et al. 2004; Robroek et al. 2007; Paal et al. 2010). However, the flow of water from hummocks toward lower parts should carry nutrients and pollutants more into lawns providing plants on hummocks some buffering time, while lawns and hollows should show more adverse reactions (Courtwright and Findlay 2011). We chose bryophytes as the target group for this study, because bryophytes, especially Sphagnum mosses, are the edificatory species of bog ecosystems (Sjörs 1961; Andrus 1986; Rydin and Jeglum 2006), and therefore characterization of their response to environmental change is crucial to understand ecological processes in bogs and assess the degradation of their habitat. Due to their specific morphological features– the lack of roots and acquisition of nutrients and water with the whole body surface–bryophytes react more rapidly to environmental changes (Vanderpoorten and Goffinet 2006) than vascular plants, and exhibit rather clear responses to pH and trophicity gradients in mires (Limpens et al. 2003; Gunnarsson and Flodin 2007; Mälson et al. 2008). The objective of our study is to elucidate responses of bryophyte communities and individual species of different microforms in bogs to increases in pH caused by airborne alkaline pollution. Because water flow in hummock-hollow complexes should transport pollutants from higher micro-topographical parts to the lower parts (lawns and hollows), plants in lower microforms should be more affected by airborne pollution than plants on hummocks. We hypothesized that airborne pollution, which increases bog water pH, will decrease bryophyte species richness and that bryophyte diversity in different microforms will converge.
Materials and Methods Though peatlands cover 22.3 % of Estonian territory (Orru 1995), their area has decreased dramatically during the last half century and currently mires in a natural state and with peat deposits thicker than 30 cm cover ca. 5.5 % of Estonia (Paal and Leibak 2011). The main reasons for the decrease in mire area in Estonia are drainage for agriculture or forestry, peat extraction, mining of mineral resources (mainly oil shale) and expansion of urban areas. Since the 1950s mires in northeastern Estonia have also been affected by long-term air pollution emitted from oil shale-based industry. Emissions peaked in the 1980s and early 1990s when 440–470 thousand tons of pollutants were emitted annually (incl. ~207,000 t of SO2, ~179,000 t of oil shale fly ash and ~16,000 t of NOx; Liblik and Rätsep 1994). The air pollution in the region is characterized by its alkalinity (precipitation pH 7.5–9.5) caused by the high Ca content in fly ash emitted from electric power stations (containing CaO 30.5 %, Al2O3 8.8 %, K2O 6.8 %) and a
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cement factory (containing CaO 42.5 %) (Pets et al. 1985; Liblik et al. 2003). The computed long-term average deposition load of calcium in most polluted areas during 1970–1990s exceeded 80 mg m−2 per day, compared to
