Impact of extreme coastal events on a brackish lake on the Burin Peninsula, Newfoundland, Canada.

The impacts of extreme coastal events (ECEs), such as marine inundations or extreme wind events, on lake ecosystems vary widely from minimal to catastrophic. Accurately predicting the response of a specific system remains challenging due to a limited understanding of the attributes that drive the resilience of lakes. In an attempt to better understand the possible impacts of ECEs on shallow brackish lakes, we employed a paleolimnological approach to reconstruct the responses of Broad Pond to four ECEs identifiable from clear sedimentary markers and dated to ca. 1740, 1790, 1862, and 1993 CE. We aimed to evaluate the overall impacts of ECEs on Broad Pond and their specific effects on various hydrobiont groups. We reinvestigated a previously studied sediment core covering the last ca. 400 years by examining terrestrial and aquatic pollen, spores and non-pollen palynomorphs, cladocerans, and chironomids. Additionally, available diatom data were reexamined. Overall, Broad Pond exhibited resilient responses to ECEs, as indicated by mostly limited compositional turnovers in our proxy records. Statistically significant relationships between species composition and ECEs were observed only for diatoms. The only prolonged change identified is the spread of previously near-absent chironomids in the aftermath of a slight lake refreshment likely associated with the ca. 1740 CE event. This event was also followed by a short-lived (ca. 15 years) five-fold increase in the abundance of Scenedesmus that could have been triggered by the effects of the ECE on nutrient availability. The impact of the remaining three ECEs was discernible only in the diatom record, consistently showing a decline in two calcifobic and oligotrophic species, Achnanthidium petersenii and Platessa oblongella, also evident for the ca. 1740 CE event. The relatively minor ecosystem alteration induced by ECEs in Broad Pond lacks a single explanation and requires consideration of multiple site- and event-specific factors.

The decline of tufa deposition in an alkaline fen ecosystem in East-Central Europe and its impact on biotic assemblages: Insights from monitoring and paleoecological data.

Protection and restoration of the CaCO3 depositing alkaline fens require an in-depth understanding of these unique and declining ecosystems. The present study investigates the development of the formerly heavy tufa depositing alkaline fen in East-Central Europe after CaCO3 precipitation markedly declined ca. 5400 cal yr BP. By combining palaeoecological and monitoring data, we aim to identify the limiting factors for tufa deposition and to recognise the vegetation and mollusc response to the change. Investigation of the current fen ecosystem included a botanical and malacological inventory and a monthly monitoring of the physicochemical properties of the groundwater emerging at the fen. It was also tested whether CaCO3 precipitates there. Transformations of the fen ecosystem since the mid-Holocene tufa decline were recognized by applying plant macrofossil and malacological analyses supplemented with organic matter and CaCO3 contents and the radiocarbon chronologies of the sediment cores. Although macroscopic tufa is currently not observed at the fen surface, the monitoring study revealed the microscopic calcite crystals at the glass slides during the spring and summer. A combination of cooling, gradual depletion of the Ca2+ pool, acidification of soils, and water table fluctuations was likely responsible for limiting tufa deposition in the mid-Holocene and maintaining this state during the late Holocene. Share of the calciphilous species' macrofossils (e.g. moss Tomentypnum nitens) declined following the sedimentary CaCO3 drop, whereas the contribution of species associated with high nutrient levels raised (e.g. Juncus articulatus). Inspection of the contemporary vegetation of the fen revealed that only Carex paniculata is associated with the calcium-rich substrate. The response of molluscs to the decline in tufa deposition remains unclear as mollusc shells did not preserve in CaCO3-depleted sediments, except for the youngest deposits. The present-day malacofauna consists of 21 species, including two rare and protected calciphilous species, namely Vertigo angustior and V. geyeri.