The value of paleolimnology in reconstructing and managing ecosystem vulnerability: a systematic map

Examining climate variability and ecosystem responses of the past can help describe an ecosystem’s capacity for change. Decisions about conservation, restoration, and often remediation, cannot be effective unless a clear understanding of the cause of the issue exists (Vos et al. 2000). Environmental monitoring aims to measure certain variables over time and space, and can be recognized as a tool for early warning and control (Vos et al. 2000). As such, monitoring informs policy makers with the necessary information for designing and implementing effective environmental policy (Lovett et al. 2007), as well as for managing vulnerability and the conditions that cause it (Luers 2005). Here lies an inherent problem, understanding the context of vulnerability and elucidating the factors that make a system susceptible is essential for a decision-makers ability to prepare and adapt to change (Ford and Smit 2004). However, “vulnerability” is not easily quantifiable and is used in a variety of contexts, such as describing conditions in social, economic, or environmental settings.

Vulnerability can be discussed on multiple scales, for example, the fragility of urban water infrastructures facing the impacts of climate change addresses social (those that rely on the infrastructures), economic (potential costs due to damages), and environmental (detrimental impacts to the resource) vulnerabilities (Dong et al. 2020). Thus, vulnerability as a measure can only be considered as a result of a complex set of factors, each requiring multiple parameters to define and quantify (Aven 2010). As a core concept, vulnerability has been defined as the potential for loss (Adger 2006), but the determination of vulnerability in a system contains components of risk and resilience (Aven 2010) as well as exposure, sensitivity, and the capacity to adapt to changes (Ford et al. 2007). While these descriptions are applied to general discussion of vulnerability, they are especially relevant in the context of ecosystems (Weißhuhn et al. 2018).

Defining the state of an ecosystem can partly be done through the lens of monitoring ecological integrity, which evaluates the extent that an ecosystem has comparable diversity and function of other similar local natural ecosystems, and an ability to maintain and support these ecological processes (Karr and Dudley 1981). Ecological integrity demonstrates self-organization of an ecosystem and can include elements of biotic structures and changes in energy, hydrological, and chemical budgets (Müller et al. 2009). The concept of integrity inherently implies an adaptive capacity to support and maintain the balance and trajectory of the system (Karr 1996), and understanding factors that contribute to ecological integrity, such as responses and resilience to change, can help determine the system’s ability to adapt to change or to disturbance (Luers 2005). In an ecological context, adaptation refers to a process or action that allows the ecosystem to adjust or cope with stress (Smit and Wandel 2006), and adaptive capacity is considered the extent of an ecosystem’s functional ability to be able to respond and reduce risk (Ford and Smit 2004). Being capable of adapting can greatly affect resilience to external pressures, such as anthropogenic stressors that could lead to collapse (Perga et al. 2015), making this an important factor in determining ecosystem vulnerability.

Vulnerability assessments help to identify the ecosystem components facing the biggest threat and the extent of that exposure (Luers 2005) and are generally not a one-size-fits-all approach. Though vulnerability assessments are historically most applied to a social context, ecological vulnerability assessments, which categorize risk, have gained more traction in recent decades (De Lange et al. 2010). The determination of risk can vary based on the scope of assessments for ecological vulnerability. For example, in the case of chemical contamination, data on the toxicity of chemicals released to the environment can provide a “yes” or “no” answer to whether risk exists for a general non-site-specific assessment; whereas a site-specific assessment requires characterization of a system’s specific biological and ecological properties (such as structure or sensitivity) for more precise quantification of risk (De Lange et al. 2010). However, these assessments are rarely spatially explicit (Lee et al. 2018) and often require more baseline information for an in-depth understanding of site-specific vulnerability. To improve understanding of specific ecosystems, long-term historical data can offer a well-rounded representation of the environment and demonstrate its natural history, providing target conditions and offering insight into potential effective management practices (Smol 1992). However, many ecosystems are missing long-term data; therefore, they are missing historical context on how the ecosystem has functioned and experienced changes (Smol 1992).

Regular monitoring usually does not occur over a long enough time period to provide reference (predisturbance) conditions (Norberg et al. 2008), meaning that an external method is often required to collect missing long-term monitoring data. When predisturbance data are missing (which is often the case), paleolimnology can fill this gap (Walker et al. 1991). Paleolimnology is a science that joins the study of lacustrine sediments with the historic and prehistoric ecological context (Smol 1992), offering a range of quantitative data over a calibrated time scale that is otherwise difficult to collect (Walker 2001). The collection of aquatic, terrestrial, and atmospheric deposition in lakes preserves the context of surrounding environment in deposited sediments over time (Williamson et al. 2009), meaning lakes can act as indices for climate variability (Saulnier-Talbot 2016). This is particularly true for closed lakes, which have defined boundaries that control the flow of inputs and outputs (Fergusson and Bangerter 2015). These boundaries allow lakes to preserve proxy records, making lake dynamics such as water level and chemistry highly responsive to climatic changes (Sullivan and Charles 1994; Walker 2001). Lakes are also especially vulnerable to climate change because of the limited capacity for species to relocate due to habitat fragmentation, water density dependence on ambient temperature, and high exposure to human activity (Woodward et al. 2010), making them good sites for analyzing impacts. Using this recording of long-term trends preserved in lakes quantifies past ecosystem changes—a valuable insight for projecting future scenarios (Fordham et al. 2020).

To gain a comprehensive understanding of the value of paleolimnological practices in assessing vulnerability in ecosystems, it is prudent to understand the extent and reach of current research. Here, we conduct a literature search using a systematic mapping approach to analyze the extent of peer-reviewed articles where paleolimnology has been applied in relation to vulnerability as well as review the value of paleolimnological practices in vulnerability assessment. This will help to highlight how paleolimnology can be used to reconstruct ecosystem vulnerability and inform decision-makers. By identifying examples of the use of paleolimnology in monitoring, management, and restoration in the literature, we argue that paleolimnological practice has a rightful place in analyzing vulnerability and ecological integrity. Paleolimnology provides an important comprehensive perspective on ecosystem change and what work needs to be done, so that management needs can be fulfilled.

To understand the extent of paleolimnological methods used in vulnerability assessments, a systematic map protocol was used to identify, select, and synthesize articles using replicable methods (Supplementary Material 1). Using the ROSES format (Haddaway et al. 2017), the trends in the extent and range of published literature was mapped in broad topic areas to identify gaps in research and clarify the types of approaches that paleolimnological methods are using within a larger context of vulnerability and ecological integrity. Our review included three steps: (i) identifying the broad research realm of paleolimnology and vulnerability assessment through a key word search, (ii) systematically identifying and selecting key research articles that captured the themes identified, and (iii) extracting and summarizing the results to identify key knowledge gaps. For this study, the aim was to include as many relevant articles as possible in our initial key word search to be able to gather a broad scope of studies in the field of paleolimnology including content related to the desired topics.

A total of 52 unique peer-reviewed primary research articles were found (Table 1). Among all search criteria, 25 articles were selected from Web of Science (4 unique), 28 from Scopus (7 unique), and 21 from PubMed (20 unique). One article overlapped all three databases, and 20 articles overlapped Web of Science and Scopus. Some articles also resulted in more than one combination of key words and were identified in more than one Boolean search process (e.g., counted as results for Pal*eolimnolog AND vulnerability AND monitor* as well as Pal*eolimnolog* AND vulnerability AND manag*) but were only counted once in the total of unique papers. The 5 most popular key words used throughout the 52 articles were “paleolimnology”, “lakes”, “diatoms”, “climate change”, and “Holocene” (Fig. 1). Forty-four of the 52 articles, just over 84%, were published in the last decade (between 2011 and 2020).

The terms adaptation and capacity are both discussed when defining the concept of vulnerability, and are often used to describe its magnitude in interchangeable ways (Adger 2006; Plummer et al. 2012). Capacity can define the ability of an ecosystem to cope with or adapt to circumstances that make it vulnerable (Füssel and Klein 2006), and absence of the capacity to adapt in an ecosystem can also lead to vulnerability, making adaptation vital to achieve ecosystem recovery whether that is natural or managed (Adger 2006). In our systematic mapping process, adaptation was found to be used much more frequently than capacity. All of the articles identified in our search that contained a discussion of the concept of adaptation referenced it in the context of disturbance(s) or climate change (Table 2). This is intuitive as methods in paleolimnology are often used to analyze environmental change and (or) environmental disturbance (Burge et al. 2017). Only 18 articles considered either adaptation or capacity in a vulnerability context. Although the low number of papers published that consider these could be due to a variation in key words, it is more likely that these contexts are only recently being investigated with approaches that use paleolimnology. There is a significant increase in papers that use the terms “paleolimnology” and “vulnerability” after 2010, and the majority of the studies took place in either North America or Europe. We can infer that the use of paleolimnology in the context of discussions of vulnerability is an emerging field, with over 30% of articles in this search having been published in the last 3 years (2018 to July 2020). The terms used for this literature search offered insight into some of the different ways paleolimnology can be applied to assess vulnerability. Here, we discuss the role of paleolimnology in vulnerability assessment as well as four subtopics (ecological integrity, reference conditions and ecosystem monitoring, establishing management goals, and creating targets for ecosystem restoration) that display the validity of paleolimnological application. To keep discussion concise and to avoid repetition, only select articles from the review are integrated.

Paleolimnological methods can be a useful tool for reconstructing environmental vulnerability. Our systematic mapping process established that 84% of articles included were published in the last decade, and just over 30% of articles in this search were published in the last 3 years at the time of our search. This seems to indicate that including paleolimnology in the discussion of vulnerability is an emerging topic, and it is proven in the literature to have a valid role in the reconstruction of ecosystem vulnerability because of its capacity to broaden the scope of long-term monitoring, as well as its potential for helping establish management and restoration goals.

The multi-faceted science is an integral priming step for establishing reference conditions so that decision-makers can move forward with management plans and conservation goals. However, Gillson and Marchant (2014) showed that paleolimnological tools and data lack a transparency and are not always applicable or user-friendly for stakeholders or policy-makers, preventing it from being used more commonly in conservation sciences. Even when considering conservation or restoration practices, it is not stable or realistic to plan to prevent disturbance from occurring in a dynamic system. Therefore, full understanding of a system requires integrating available facets of information in a multi-scalar perspective such as historical ecology, long-term monitoring, etc., in combination with paleolimnology (Gillson and Marchant 2014). Steps to manage vulnerability need to be well informed, and paleolimnology should be applied often in studies due to the range of perspective it can offer. Full knowledge of the ecosystem gained through paleolimnology can be a key factor in establishing management, but it can only be effective if it is implemented successfully and maintained over time (Frissell and Bayles 1996).

Ecosystem monitoring can also be improved by conceptualizing environmental change that has occurred over time as well as creating benchmarks that help with implementing ecosystem management and restoration efforts. Paleolimnology can define susceptibility and thresholds for change and, as a result, its vulnerability. Understanding the insight that paleolimnology can provide for ecosystem vulnerability can promote its value and place in ecosystem decision-making. Based on our research and the literature we have reviewed, we believe that paleolimnological practice has a rightful place in analyzing vulnerability and ecological integrity.

This project was funded by the Fathom Fund of the Marine Environmental Observation Prediction and Response Network (MEOPAR), and by direct donations by the public through projectDAL (Dalhousie University). We would like to thank Sonia Wesche for discussions on the context of vulnerability in environmental assessment. We thank the editor and reviewers for their comments that improved the format and delivery of this manuscript.