Under the radar: long-term perspectives on ecological changes in lakes

Abstract

Aquatic ecosystems are constantly changing due to natural and anthropogenic stressors. When dealing with such ‘moving targets’, one of the greatest challenges faced by scientists, managers and policy makers is to use appropriate time scales for environmental assessments. However, most aquatic systems lack monitoring data, and if a programme does exist, rarely have data been collected for more than a few years. Hence, it is often difficult or impossible to determine the nature and timing of ecosystem changes based on these short-term datasets. Furthermore, as environmental assessments are typically performed after a problem is identified, critical data regarding pre-disturbance (or reference) conditions are rarely available. Here, I summarize some recent studies employing lake sediment analyses (i.e. palaeolimnology) that have provided retrospective assessments of ecosystem changes that have been emerging slowly and often innocuously ‘under the radar’. My examples include the identification of legacy effects of acid rain and logging, namely long-term declines in calcium concentrations in softwater lakes, which have led to significant repercussions for ecosystem services. I then show that past trajectories of aerial pollution from the burgeoning oil sands operations of western Canada can be tracked using environmental proxies preserved in dated sediment cores, and how these data can be used to determine the relative contributions of natural versus industrial sources of pollutants. I conclude by reviewing how palaeolimnological analyses have linked climate change with the proliferation of harmful blue-green algal (cyanobacterial) blooms, even without the addition of limiting nutrients. Collectively, these studies show that effective ecosystem management, particularly for incremental environmental stressors, requires temporal sampling windows that are not readily available with standard monitoring, but can be supplemented with high-resolution lake sediment analyses.

Assessing the response of micro-eukaryotic diversity to the Great Acceleration using lake sedimentary DNA

“…Respondent groups include both obligate oxygenic photoautotrophs (in particular Chlorophyceae and Prymnesiophyceae) and mixotrophs (in particular Dinophyceae). Our combined DNA and pigment-based results obtained for 48 lakes are in line with several paleolimnological studies that have reported an increase in primary production throughout the Holocene 10,11 . The ratio and rates of autotrophic and heterotrophic production constitute the basis of the metabolic balance of lake ecosystems in the form of primary productivity and respiration.…”

“…The second part of the twentieth century is unambiguously a time of major and multiple threats that might have disproportionately affected lake biodiversity and associated ecological functions (e.g., nutrient recycling, efficiency of trophic transfer, and quality of fish production) 3 , 8 . Paleolimnological studies have provided evidence supporting the occurrence of states of change in lake ecosystems, for instance the accelerated hypoxia in European lakes after 1900 9 or the increase in autochthonous primary production in lakes (e.g., Lake Superior 10 and see review by Smol 11 ). However, much less is known about the long-term changes of biodiversity.…”

Lakes in the era of global change: moving beyond single‐lake thinking in maintaining biodiversity and ecosystem services

“…Indeed, the majority of ecosystems worldwide, including freshwater ecosystems, are threatened by multiple anthropogenic stressors (Vörösmarty et al ., 2010; McCluney et al ., 2014; Albert et al ., 2020; Birk et al ., 2020). Lakes are no exception, as they are threatened, inter alia , by climate change, land‐use intensification, eutrophication, acidification, water abstraction, water‐level regulation, morphological alteration, and invasive species (Dudgeon et al ., 2006; Smol, 2019). Understanding the resilience and recovery of lakes to environmental change has thus emerged as an important research program from the perspectives of biodiversity conservation and ecosystem services (Angeler & Drakare, 2013; Angeler et al ., 2015).…”

Climate and land-use as the main drivers of recent environmental change in a mid-altitude mountain lake, Romanian Carpathians

“…Anthropogenic activities such as changes in land-use can induce major transformations in lake systems via increased catchment erosion, and its effect on sedimentation rates and nutrient loads leading to eutrophication and ecological shifts affecting lake biota [1][2][3][4][5]. Tracing such environmental dynamics over short timescales and assessing the type and timing of the main drivers of change are needed for a better understanding of the complex cause-effect relationship between environmental responses, anthropogenic activities and natural climate variability, and therefore to improve management strategies [6][7][8].…”