Research themes

Our research focuses on understanding how key drivers of change in high-mountain ecosystems - changing climate, changing atmospheric chemistry, and changing land use - cause alterations in the interacting ecosystem processes, from water and nutrient cycles to microbial and ecological dynamics.

By examining these systems across short- and long-term temporal scales, we aim to capture both immediate ecosystem responses and long-term trajectories of change. Working in remote freshwater environments, where direct human influence is minimal, allows us to detect environmental signals that provide clear and sensitive indicators of global change.

At the core of our approach lies the long-term ecological monitoring, serving as an essential framework for detecting, quantifying, and interpreting environmental change. Through this observatory-based approach, we can integrate physical, chemical, and biological information to better understand and predict the functioning of mountain freshwaters under a changing global environment.

Explore the sections below for an overview of LOOP’s major research themes:

Climate change

Using long-term records of air temperature, precipitation, stream temperature, streamflow, snowpack, and lake ice cover we study how high-mountain ecosystems are responding to a changing climate.

We maintain long-term records of air temperature, precipitation, streamflow, groundwater and lake level, stream and lake temperature, and lake ice cover. These in situ measurements are complemented by advanced remote sensing methods and phenological cameras (or phenocams) observations, which together enable detailed monitoring of snow cover and vegetation dynamics across our study catchments. We measure how increasingly frequent and intense extreme weather events—particularly droughts—alter the transfer, cycling and downstream fate of key biogeochemical elements across the landscape continuum (from soils to downstream waters) in high-mountain catchments. We study how reduced snowpack and increased soil freezing during the winter will affect soil and aquatic ecosystem processes across seasons. These records show marked changes in climate, and in the variability of climate over the past decades. The ecosystem response to these changes has been neither simple nor linear, but arises from cumulative responses to climate dynamics operating at multiple time scales.

RyC-Max

Alterations in the biogeochemical cycles of high-mountain watersheds in the context of global change: Implementation of a monitoring plan.

DRYLAND

Drought as an emerging driver of soil carbon and nutrient losses and water quality degradation in high mountain ecosystems.

SERVICO2

Impacts of climate, N and P deposition and land use on water as a driver of the greenhouse gases regulatory ecosystem service in headwater catchments.

Atmospheric chemistry

We study how catchments and inland waters respond to changes in the chemistry of the atmosphere, from declines in air pollution brought about by restrictions on emissions to episodic inputs such as Saharan dust intrusions.

One major component of global environmental change is the alteration of atmospheric fluxes of chemical elements. High-mountain regions act as “cold fingers,” concentrating atmospheric deposition of sulfur, nitrogen, organic micropollutants, trace elements, metals, and metalloids, which has created a long-term legacy of anthropogenic contamination across their catchments and aquatic systems. While some inputs have natural origins, such as dust transported from arid and desert regions across oceans, many are intensified by human activities. Industrial emissions, fossil fuel combustion, intensive agriculture, and biomass burning have greatly increased the atmospheric load of reactive nitrogen, sulfur compounds, trace metals, and organic pollutants. These contaminants are transported over long distances and deposited even in remote mountain catchments, altering the chemical balance of soils, waters, and biota. Moreover, climate-driven changes in temperature, precipitation patterns, and snow dynamics further modulate the deposition and remobilization of these substances, amplifying their ecological and biogeochemical impacts.

We study how lakes and streams respond to changes in the chemistry of the atmosphere, particularly declines in air pollution brought about by federal restrictions on emissions. Before emission restrictions were introduced, Pyrenean landscapes were exposed to acid rain that delivered sulfur and nitrogen compounds to their soils and waters. These acidic inputs depleted calcium and other essential nutrients and increased the mobility of toxic metals such as aluminum. As a result, aquatic acidification caused widespread nutrient imbalances in the area and changes in the pattern of ecological nutrient limitation in lakes. We also study legacy of acid rain on aquatic ecosystem processes like productivity or microbial structure, and we study the interactive effects of recovery from acid rain under the stress of climate change. Finally, we study how dust-induced shifts in the quantity and stoichiometry of dissolved nutrients and pollutants imported to high-mountain watersheds drives lake and stream biogeochemical alterations.

Pyrenees landscapes experienced decades of moderate acid rain, which stripped calcium and other key nutrients from forest soils. We study the legacy of acid rain on forest processes like vegetation growth, and we study the interactive effects of recovery from acid rain under the stressors of climate change. The forests at Hubbard Brook are also affected by increases in carbon dioxide and other greenhouse gases in the atmosphere and by changes in the deposition of nutrients such as nitrogen and calcium.

SERVICO2

Impacts of climate, N and P deposition and land use on water as a driver of the greenhouse gases regulatory ecosystem service in headwater catchments.

RyC-Max

Alterations in the biogeochemical cycles of high-mountain watersheds in the context of global change: Implementation of a monitoring plan.

Palaeolimnology

We use sediment cores retrieved from lakes to unveil long-term changes driven by climate and human influence. These natural archives extend observations beyond instrumental records and provide benchmarks for assessing present-day transformations, from Holocene climate variability to ancient lead pollution.

Sediments cores retrieved from different lakes have allowed us to reconstruct climate and human influence on remote mountain lakes and surrounding ecosystems during the last 15,000 years. Lake sediments archive environmental and ecological information far beyond the lake limits. In the current context of global change, mountain lake sediments contain an invaluable information on postindustrial changes that can be benchmarked against early, pre-disturbance, intervals. The palaeolimnological reconstructions allow us to extend our contemporary observations back in time and offers a reference to assess the importance of present-day changes. Furthermore, sediment archives provide a long-term view of the ecological dynamics that cannot be captured by observational series. As nature never goes the same way twice, the long-term change is more than the sum of the short-term fluctuations. A number of cores retrieved from different lakes have allowed us to reconstruct the winter climate during the Holocene and a lead pollution dated a few millennia back.

WATERSCAPE

The waterscape as a framework for species coexistence: diatoms as model.

Microbial ecology

We use advanced molecular and genomic tools to study how aquatic and sediment microorganisms shape and respond to environmental change in high-mountain aquatic ecosystems.

We study how microorganisms shape and respond to environmental change in high-mountain aquatic ecosystems. These remote lakes, streams, and wetlands host highly specialized microbial communities adapted to extreme and fluctuating conditions of temperature, radiation, and nutrient availability. Despite their microscopic size, these organisms play fundamental roles in nutrient cycling, water purification, and the regulation of ecosystem productivity. Special attention is given to planktonic and benthic communities, including cyanobacteria and other photoautotrophs that drive primary production in these ecosystems. Their interactions with other microorganisms and with higher trophic levels provide essential insights into ecosystem resilience and feedbacks to global change. Through long-term ecological monitoring and comparative analyses, we seek to reveal how microbial life both records and mediates environmental transformations in high-mountain catchments

We use advanced molecular and genomic tools to characterize microbial diversity and track how community composition varies across spatial and temporal gradients. By integrating microbial, chemical, and physical data, we aim to understand the processes that control carbon and nutrient fluxes in oligotrophic environments and how they are affected by climate warming, changing atmospheric inputs, and hydrological variability.

WATERSCAPE

The waterscape as a framework for species coexistence: diatoms as model.

CIANOMONT

Cyanobacterial blooms in high mountain lakes: composition, causes and consequences.

PyriSentinel

Exploring invisible biodiversity in Pyrenean lakes, sentinels of climate change, through high-resolution portable genomics.

Hydro-biogeochemistry

We study how global change alters the cycling and transfer of key biogeochemical elements across the atmosphere–landscape continuum, from precipitation and soils to streams and downstream basins.

We study how global change is reshaping the transport, cycling, and reactivity of key biogeochemical elements—such as carbon, nutrients, and trace elements—across the atmosphere–landscape continuum, from precipitation and soils to headwater streams and downstream basins. In several experimental catchments of the Central Pyrenees, we monitor key biogeochemical and biodiversity variables in atmospheric deposition, lakes, and streams, complemented by detailed measurements and experiments that help unravel the mechanisms driving these ecosystem responses.

We also exploit cutting-edge sensor technologies to capture the rapid and non-linear mechanisms that govern the transfer, cycling and fate of these key biogeochemical elements across the landscape. By deploying high-frequency environmental sensors across spatial gradients in our experimental catchments, we study what events and locations that exert the strongest influence on this modulation and, ultimately, on the fluxes and fate of biogeochemical elements in mountain watersheds.

We use water isotopes (deuterium, tritium, and ¹⁸O) to determine the “age” of water, or mean residence time (MRT)—the average time water spends in a catchment since its deposition as rain or snow. Understanding water age and flow paths provides essential context for interpreting catchment and aquatic biogeochemistry, as hydrological residence time regulates the transport and transformation of nutrients, carbon, and trace elements within mountain ecosystems.

RyC-Max

Alterations in the biogeochemical cycles of high-mountain watersheds in the context of global change: Implementation of a monitoring plan.

DRYLAND

Drought as an emerging driver of soil carbon and nutrient losses and water quality degradation in high mountain ecosystems.

SERVICO2

Impacts of climate, N and P deposition and land use on water as a driver of the greenhouse gases regulatory ecosystem service in headwater catchments.

Regional variability

We study the Pyrenean lake district, which hosts over a thousand high-mountain lakes influenced by diverse bedrock types, climates, and pronounced altitudinal gradients. This diversity shapes lake functioning, and long-term surveys show how climate warming and atmospheric deposition are altering their ecosystems.

The Pyrenees host a remarkable lake district containing just over one thousand high-mountain lakes larger than 0.5 hectares, roughly half of which lie on each side of the range. This natural laboratory encompasses striking geological and climatic diversity: lakes are found on bedrocks of granite, slate, schist, limestone, and volcanic origin, each imparting distinct chemical signatures to the waters. The region also sits at a climatic crossroads—western basins are influenced by the humid Atlantic regime, whereas eastern ones experience stronger Mediterranean conditions.

In addition to this east–west contrast, the lakes are distributed along an altitudinal gradient from about 1,600 to nearly 3,000 meters above sea level, further amplifying variation in temperature, ice cover, and biological productivity. These gradients in lithology, climate, and elevation collectively shape the physical, chemical, and biological characteristics of Pyrenean lakes, producing a mosaic of ecosystem types across the range.

Repeated large-scale surveys, conducted since 1987 at roughly decadal intervals, have provided an unparalleled synoptic view of these ecosystems. They reveal not only the natural spatial variability of lake conditions but also emerging temporal trends linked to climate warming, atmospheric deposition, and other regional-scale environmental drivers.