Diatoms and Other Siliceous Indicators Track the Ontogeny of a Bofedal (Wetland) Ecosystem in the Peruvian Andes
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Botany Diatoms and other siliceous indicators track the ontogeny of a bofedal (wetland) ecosystem in the Peruvian Andes Journal: Botany Manuscript ID cjb-2020-0196.R1 Manuscript Type: Article Date Submitted by the 20-Feb-2021 Author: Complete List of Authors: King, Connor; Queen’s University, Department of Biology Michelutti, Neal; Queen’s University, Department of Biology Meyer-Jacob, Carsten; Queen’s University, Department of Biology Bindler, Richard; Umeå University, Department of Ecology and EnvironmentalDraft Sciences Tapia, Pedro; INAIGEM Grooms, Christopher; Queen’s University, Department of Biology Smol, John; Queen's University Tropical Andes, Cushion bogs, High-altitude peat, Distichia muscoides, Keyword: Cordillera Vilcanota Is the invited manuscript for consideration in a Special Not applicable (regular submission) Issue? : © The Author(s) or their Institution(s) Page 1 of 37 Botany 1 Diatoms and other siliceous indicators track the ontogeny of a bofedal (wetland) ecosystem in the Peruvian Andes Connor King1, Neal Michelutti1*, Carsten Meyer-Jacob1, Richard Bindler2, Pedro Tapia3, Christopher Grooms1, John P. Smol1 1Paleoecological Environment Assessment and Research Laboratory (PEARL), Department of Biology, 116 Barrie Street, Queen’s University, Kingston, ON K7L 3N6, Canada 2Department of Ecology and Environmental Sciences, Umeå University, 901 87 Umeå, Sweden (email: [email protected]) 3INAIGEM – Dirección de Investigación en Ecosistemas de Montañas, Huaraz, Peru e-mail: [email protected] Draft *Corresponding Author: email: [email protected]; phone: 613.533.6159; fax: 613.533.6617 © The Author(s) or their Institution(s) Botany Page 2 of 37 2 Abstract Recent warming in the Andes is affecting the region’s water resources including glaciers and lakes, which supply water to tens of millions of people downstream. High altitude wetlands, known locally as bofedales, are an understudied Andean ecosystem despite their key role in carbon sequestration, maintaining biodiversity, and regulating water flow. Here, we analyze subfossil diatom assemblages and other siliceous bioindicators preserved in a peat core collected from a bofedal in Peru’s Cordillera Vilcanota. Basal radiocarbon ages show the bofedal likely formed during a wet period of the Little Ice Age (1520-1680 CE), as inferred from nearby ice core data. The subfossil diatom record is marked by several dynamic assemblage shifts documenting a hydrosere succession from an open-water system to mature peatland. The diatoms appear to be responding largely to changes in hydrology that occur within the natural development of the bofedal, but also to pH and possibly nutrient enrichment from grazing animals. The rapid peat accretion recorded post-1950 at this site is consistent with recent peat growth ratesDraft elsewhere in the Andes. Given the many threats to Peruvian bofedales including climate change, overgrazing, peat extraction, and mining, these baseline data will be critical to assessing future change in these important ecosystems. Key Words: Tropical Andes, Cushion bogs, High-altitude peat, Distichia muscoides, Cordillera Vilcanota, X-ray fluorescence spectroscopy, Climate change Introduction Temperature increases in the tropical Andes are occurring at a rate nearly double the global average (Vuille et al. 2003) and are already resulting in marked environmental changes, including rapidly receding glaciers (Salzmann et al. 2013; Thompson et al. 2013), changes to agricultural practices (Halloy et al. 2005), and shifts in species ranges (Seimon et al. 2007; Schmidt et al. 2008). Anthropogenic climate change will have unpredictable effects on Andean ecosystems, particularly on plant communities whose habitat is restricted to the highest elevations and therefore may be under threat of mountaintop extirpation. Andean wetlands, regionally known as bofedales (singular bofedal), are of particular concern because many exist at the altitudinal and hydrological limits for plant life (Squeo 2006). Bofedales often form downstream from glaciers where topographical and hydrological conditions favour water pooling. This vegetation provides rich forage in an © The Author(s) or their Institution(s) Page 3 of 37 Botany 3 otherwise barren environment, supporting a variety of camelids, avifauna, and larger predators. For millennia, indigenous communities have been directly dependent upon bofedales to graze their livestock including llamas, alpacas and now cows, which remain the basis of the local economy. In addition, bofedales provide various ecological services that promote biodiversity and act as water buffers preventing floods and increasing base flow during the dry season (Maldonado Fonkén, 2015). In Peru, the societal and ecological importance of bofedales has been recognized via their identification as “fragile ecosystems” under Peruvian General Environmental Law (Law No. 28611, Article 99; Maldonado Fonkén 2010) and they are considered areas for conservation or protection under Peruvian Ecological-Economic Zoning Regulations (DS Nº 087-2004-PCM, Article 9, PCM 2004). However, effective management of bofedales will require a greater understanding of their relationship with climate, specifically how they respond to rising temperatures, altered precipitation regimes and dwindling glacial runoff. In addition, Andean bofedales are increasingly threatened by overgrazing, peat cutting, mining and drainage (Benavidez 2014; MaldonadoDraft Fonkén 2015; Sánchez et al. 2017). A common characteristic of bofedales is the underlying presence of peat, which accumulates when production of the vegetation exceeds decomposition. Peatlands are dynamic ecosystems and undergo a series of successional changes, known as hydroseres, driven largely by changes in hydrology and vegetation. A common hydroseral succession is the transition from an open water-to-fen-to-bog environment, although variability exits along this trajectory (Charman 2002). Peatlands are useful natural archives because the organic material that accumulates over time contains physical, chemical, and biological indicators that reflect changing environmental conditions over long-term timescales (Engel et al. 2014; Hribljan et al. 2015; van Bellen et al 2016). Paleoecological studies of peat deposits play an important role in conservation research (McCarroll et al. 2016) as they inform about the development of the peatland itself, as well as past climate and other environmental changes (Gaiser and Rühland 2010; Carballeira and Pontevedra-Pombal 2020). For example, diatom algae (Bacillariophyceae) preserved in peat deposits have been used throughout the world to track changes in hydrology, water chemistry, landscape disturbances, and climate variability (Rühland et al. 2000; Hargan et al. 2015). Diatom studies in Andean wetlands have typically focused on floristic descriptions (Maidana and Seeligmann, 2006; Seeligmann et al. 2008) with a few studies assessing seasonal and spatial patterns (Salazar-Torres and Huszar 2012). Here, we analyze fossil © The Author(s) or their Institution(s) Botany Page 4 of 37 4 diatom assemblages preserved in a bofedal peat core from the Cordillera Vilcanota in southeastern Peru (Fig. 1). Although peat cores have been used to reconstruct long-term environmental change elsewhere in the Andes (Skrzypek et al. 2011; Engel et al. 2014; Hribljan et al. 2015; Benfield et al. 2021), few have focused on paleoecology. In addition to diatoms, we also document the relative abundances of other siliceous microfossils, namely chrysophycean stomatocysts (Duff et al. 1995; Wilkinson et al. 2001), disassociated plates of testate amoeba (Douglas and Smol 1987; 1988), and phytoliths (Piperno 2001). Chrysophytes, although traditionally viewed as being planktonic algae common in oligotrophic waters, are also known to be periphytic and often associated with mosses in shallow waterbodies (Douglas and Smol 1995). As such, they may respond sensitively to changes in vegetation and moisture levels expected with peatland succession. Testate amoebae are often the most common protists living in peat habitats (Heal 1962), and in past studies have been shown to closely track bog development (van Bellen et al. 2016; Zhang et al. 2020). Phytoliths are siliceous deposits that form in plant tissue and because they are released upon death and decompositionDraft (Piperno 2006), their abundances may be related to levels of peat decomposition; but other factors such as fire and aerial transport can also alter their concentrations in peat cores (Mullholland and Rapp 1992; Rühland et al. 2000). Collectively, these siliceous microfossils may provide valuable paleoecological evidence, independent of diatoms, on peatland changes over time. To characterize the peat core stratigraphy and help interpret shifts in the biological communities, we also measured the loss-on-ignition (LOI) to estimate organic content, as well as a suite of major and trace elements using X-ray fluorescence spectroscopy (XRF), which can provide information on, for example, changes in peat decomposition or redox conditions (Biester et al. 2004; López et al. 2006). We demonstrate that diatoms and other siliceous indicators sensitively track successional changes in the study of this bofedal since its inception, providing some perspective on how future climate changes may affect bofedales throughout the Andes. This research provides novel data on long-term changes of a bofedal from Peru’s Cordillera Vilcanota. Together with paleoenvironmental records from nearby ice cores