Autogenic and allogenic factors affecting development of a floating Sphagnum-dominated peat mat in a karst pond basin

Abstract

Lateral expansion of floating vegetation mats over the surface of aquatic ecosystems (terrestrialization) is one of the ways of peatland development. This process was commonly studied in kettle-hole lakes, whereas karst ponds have received less attention. We used a suite of palaeoecological analyses at Karstovoe mire (Mordovia, Russia) to reconstruct the formation of a floating Sphagnum-dominated peat mat over the karst pond. The results show that the floating peat mat had covered the central part of the pond by ca. AD 1600. Remains of Scirpus sp. and Calamagrostis sp. in the basal layers indicate that these plants might form a framework on which Sphagnum mosses and sedges were established. The terrestrialization could be triggered by the ‘Medieval Warm Period’ (AD 950–1250) as droughts reduce water levels and allow the pioneering plants to colonize exposed bottom sediments on the margins of lakes. Later, the development of the mire was mainly driven by autogenic factors that could be explained by the relatively stable hydrological regime in freely floating or poorly attached vegetation mats. In the mid 19th century, the surface wetness of the mire started to decline that can be related to both increased human activity associated with fires and to a greater thickness of the mat so that autogenic and allogenic effects were difficult to disentangle. In less than a century after that, the fen transformed to a pioneer raised mire. Our results show complex and context-dependent effect of autogenic and allogenic factors on the development of floating peat mats.

Peatland Development, Vegetation History, Climate Change and Human Activity in the Valdai Uplands (Central European Russia) during the Holocene: A Multi-Proxy Palaeoecological Study

“…In 1350 AD, i.e., approximately in 700 years, the ecosystem shifted to a drier peatland covered by Sphagnum fuscum. The transitions between these periods were relatively rapid (i.e., decades), supporting the idea for the non-linear, step-like behavior of peatland ecosystems at this stage [7]. Testate amoeba and diatom assemblages were characterized by greater roles of xerophilic taxa (Figures 8 and 9), especially in the final stage of peatland development when reconstructed water table depths were minimal (Figure 4).…”

“…From 100 AD, Sphagnum angustifolium and Scheuchzeria palustris appeared along with brown mosses (Figure 6), indicating the formation of a relatively dense floating vegetation mat with areas of ombrotrophication and subsequent acidification. Moreover, the presence of Carex sp., Cyperaceae rootlets and other herbs rootlets, as typical pioneering mat-forming plants, may indicate a classical lateral (centripetal) encroachment of original vegetation mats from the margins of the lake [1,7]. The C:N ratio fluctuated around 30 during the entire stage ( Figure 3) due to a sharp decrease in nitrogen input that indicates the onset of oligotrophication.…”

“…The subsequent succession from fen to bog is the result of local peat accumulation that gradually lifts the surface of the peatland above the influence of the groundwater [4]. While hydroserial succession is a very widespread and common phenomenon, its main driving forces and mechanisms remain debated due to numerous regional patterns related to unique combinations of allogenic (e.g., climate, edaphic conditions and fire) and autogenic (e.g., peat accumulation rate and acidification) factors [4,5,7].…”

“…Palaeoenvironmental reconstructions from across Eurasia show that changes in ecosystems and environment during the Holocene were characterized by high spatial variability [22,23]. Although Russia contains one of the largest areas of peatland in the world [24], there were remarkably few peat-based palaeoecological studies using proxies other than pollen [7,[25][26][27]. In particular, raised bogs in the East European Plain are affected by the continental climate conditions in contrast with better studied Atlantic or Baltic raised bogs of Northern, Western and Eastern Europe [28][29][30][31].…”

A multi-proxy reconstruction of peatland development and regional vegetation changes in subarctic NE Fennoscandia (the Republic of Karelia, Russia) during the Holocene

“…It is assumed that more highly decomposed peat will produce a darker coloured alkali extract resulting in reduced light transmission (Blackford and Chambers, 1993). Such multiproxy reconstructions, which include pollen, plant macrofossils, testate amoebae, peat humification analyses and macro-charcoal, have been successfully applied to reconstruct environmental changes, peatland development and vegetation dynamics in other parts of Russia (Novenko et al, 2015(Novenko et al, , 2016(Novenko et al, , 2018Payne et al, 2016;Tsyganov et al, 2019).…”