High-resolution paleolimnology opens new management perspectives for lakes adaptation to climate warming

Abstract

Varved lake sediments provide opportunities for high-resolution paleolimnological investigations that may extend monitoring surveys in order to target priority management actions under climate warming. This paper provides the synthesis of an international research program relying on >150 years-long, varved records for three managed perialpine lakes in Europe (Lakes Geneva, Annecy, and Bourget). The dynamics of the dominant, local human pressures, as well as the ecological responses in the pelagic, benthic, and littoral habitats were reconstructed using classical and newly developed paleo-proxies. Statistical modeling achieved the hierarchization of the drivers of their ecological trajectories. All three lakes underwent different levels of eutrophication in the first half of the XXth century, followed by re-oligotrophication. Climate warming came along with a 2 • C increase in air temperature over the last century, to which lakes were unequally thermally vulnerable. Unsurprisingly, phosphorous concentration has been the dominant ecological driver over the last century. Yet, other human-influenced, local environmental drivers (fisheries management practices, river regulations) have also significantly inflected ecological trajectories. Climate change has been impacting all habitats at rates that, in some cases, exceeded those of local factors. The amplitude and ecological responses to similar climate change varied between lakes, but, at least for pelagic habitats, rather depended on the intensity of local human pressures than on the thermal effect of climate change. Deep habitats yet showed higher sensitivity to climate change but substantial influence of river flows. As a consequence, adapted local management strategies, fully integrating nutrient inputs, fisheries management, and hydrological regulations, may enable mitigating the deleterious consequences of ongoing climate change on these ecosystems.

Effects of long term nutrient and climate variability on subfossil Cladocera in a deep, subalpine lake (Lake Garda, northern Italy)

“…Disentangling the effects of these two stressors is further complicated by the fact that organisms generally react to combinations of different environmental drivers in their multidimensional ecological niches (Salmaso 2002). In addition, timing of climate warming in the Alpine region largerly coincided with the onset of nutrient enrichment (Perga et al 2015).…”

“…Sediment records spanning over both the pre-and post-human disturbance periods can partially overcome this difficulty (Lotter et al 1997;Kamenik et al 2007). However, only multi-proxy approaches can exploit the ability of different biological proxies to track different aspects of the overall lake ecological response to overlapped stressors, such as nutrient levels and climate (Perga et al 2015).…”

“…Several studies on subfossil Cladocera have been conducted in Alpine lakes, including both mountain lakes (Lotter et al 1997;Bigler et al 2006;Kamenik et al 2007;Nevalainen et al 2011) and peri-alpine deep lakes such as Lakes Constance (Hofmann 1998), Geneva, Bourget, Annecy (Alric et al 2013;Perga et al 2015) and Zurich (Boucherle and Züllig 1983). However, of the large and deep lakes south of the Alps, which together account for over 80% of Italy's surface freshwater, only Lake Maggiore has been analyzed for subfossil Cladocera (Manca et al 2007).…”

Solar and atmospheric forcing on mountain lakes

“…Lake ecological states and services are compromised by multiple local human activities they host, and by the complex effects of climate change (Perga et al, 2015). Lakes are effective sentinels for climate change because they are sensitive to climatic variability, respond rapidly to change, and integrate information about changes in the catchment (Adrian et al, 2009).…”

Urban point sources of nutrients were the leading cause for the historical spread of hypoxia across European lakes

“…Depending on the multitudinous local differences in catchment and lake morphology, river transport capacity, climate, geology, and regional trajectories in socioeconomic development, the responses of lakes to surrounding land changes can differ greatly in intensity, modalities, and kinetics (9)(10)(11)(12). Multiple sites need to be investigated to quantify a regional trend, as well as to evaluate local to regional heterogeneities.…”