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Environmental sciences depend heavily on observational data. Successful studies of ecological processes in lakes require in‐situ data that cover the relevant temporal scales from milliseconds to entire seasons. Temporal and spatial coverage requirements represent a non‐trivial challenge in lake sciences, which have traditionally used sampling campaigns conducted from research vessels or anchored moorings. These come with various logistical tasks and impose constraints on data coverage. An open water platform can overcome many of these limitations by providing continuous access and a wide range of analytical capabilities in direct contact with the lake environment. A consortium of five partner institutions constructed a 10 × 10 m, open‐water, multipurpose platform on Lake Geneva (Switzerland/France) for a broad range of limnological research. The LéXPLORE platform, anchored since February 2019 at a position reaching 110 m depth off the lake's north‐shore, provides workspace for a large number of instruments and up to 16 staff working in parallel on individual or integrated multidisciplinary projects. The safe, dry and protected floating laboratory offers direct access to the lake environment for high‐sensitivity, high‐throughput analyses including those which might advance sensor technology. The platform provides flexible workspace for both high‐resolution measurements and investigations of larger‐scale external forcing. It thus supports multidisciplinary empirical research in limnology, atmospheric sciences, and remote sensing. This article describes the platform and how it will advance aquatic sciences. The large number of projects that have already requested access to the platform demonstrate the efficacy and necessity of the LéXPLORE concept. This article is categorized under: Water and Life > Conservation, Management, and Awareness Water and Life > Methods
LéXPLORE: A floating laboratory on Lake Geneva offering
unique lake research opportunities
Alfred Wüest
| Damien Bouffard
| Jean Guillard
Bastiaan W. Ibelings
| Sébastien Lavanchy
| Marie-Elodie Perga
Natacha Pasche
Limnology Center, ENAC-EPFL,
Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Surface Waters - Research and Management, Kastanienbaum,
Université Savoie Mont Blanc, INRAE, CARRTEL, Thonon-les-Bains, France
Department F.-A. Forel for Environmental and Aquatic Sciences, University of Geneva, Geneva, Switzerland
Institute of Earth Surface Dynamics, Faculty of Geosciences and Environment, University of Lausanne, Lausanne, Switzerland
Alfred Wüest, Surface WatersResearch
and Management, Eawag, Seestrasse
79, CH-6047 Kastanienbaum, Switzerland.
Funding information
Ecole Polytechnique Fédérale de
Lausanne; Schweizerischer Nationalfonds
zur Förderung der Wissenschaftlichen
Forschung, Grant/Award Number:
LéXPLORE no. 206021_157779; Swiss
Federal Office for the Environment;
Université de Savoie Mont Blanc, INRAE,
CARRTEL; Université de Genève;
Université de Lausanne
Edited by: Stuart N. Lane, Editor-in-
Environmental sciences depend heavily on observational data. Successful stud-
ies of ecological processes in lakes require in-situ data that cover the relevant
temporal scales from milliseconds to entire seasons. Temporal and spatial cov-
erage requirements represent a non-trivial challenge in lake sciences, which
have traditionally used sampling campaigns conducted from research vessels
or anchored moorings. These come with various logistical tasks and impose
constraints on data coverage. An open water platform can overcome many of
these limitations by providing continuous access and a wide range of analytical
capabilities in direct contact with the lake environment. A consortium of five
partner institutions constructed a 10 10 m, open-water, multipurpose plat-
form on Lake Geneva (Switzerland/France) for a broad range of limnological
research. The LéXPLORE platform, anchored since February 2019 at a position
reaching 110 m depth off the lake's north-shore, provides workspace for a large
number of instruments and up to 16 staff working in parallel on individual or
integrated multidisciplinary projects. The safe, dry and protected floating labo-
ratory offers direct access to the lake environment for high-sensitivity, high-
throughput analyses including those which might advance sensor technology.
The platform provides flexible workspace for both high-resolution measure-
ments and investigations of larger-scale external forcing. It thus supports mul-
tidisciplinary empirical research in limnology, atmospheric sciences, and
remote sensing. This article describes the platform and how it will advance
aquatic sciences. The large number of projects that have already requested
Received: 30 March 2021 Revised: 10 June 2021 Accepted: 15 June 2021
DOI: 10.1002/wat2.1544
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided
the original work is properly cited.
© 2021 The Authors. WIREs Water published by Wiley Periodicals LLC.
WIREs Water. 2021;e1544. 1of15
access to the platform demonstrate the efficacy and necessity of the LéXPLORE
This article is categorized under:
Water and Life > Conservation, Management, and Awareness
Water and Life > Methods
KEYWORDS, environmental monitoring, freshwater ecosystems, in-situ sensors,
remote sensing
Aquatic systems processes occur over a wide range of time scales, from sub-seconds to decades. These define the fre-
quency, density, and duration requirements of scientific measurements. Historically, collection methods imposed signif-
icant constraints on the coverage and resolution of limnological data. Early and ongoing fieldwork (Forel, 1892)
depended on boats for collecting surface and water column samples. These sampling campaigns faced logistical chal-
lenges and only provided a discrete and often incomplete picture of the lake environment. Development of electronics
and sensors in the late 20
century allowed for sampling by multiparameter profilers and fixed-position moorings.
These, along with Earth observation satellite data gave a more expansive picture of lakes but have uncovered many
new questions about how the systems function.
Autonomous monitoring of aquatic systems has deployed communications and data science advances primarily in
moored buoys and platforms. The freely drifting Argo-floats ocean system (Kerut, 1980) is a classic example of an
autonomous system that continuously transmits open ocean data via satellite links. Improved, off-the-shelf communica-
tions technology allows deployment of automated lake buoys which can perform long-term measurements with
programmed or remotely controlled sensors. Several lake platforms have been deployed (Box 1) in order to collect com-
prehensive datasets (Hamilton et al., 2015). Automated buoys however do not provide space for lab equipment and per-
sonnel. Here we show that an open water platform can overcome these limitations. The vision for LéXPLORE was to
provide (a) space for instrumentation, (b) laboratory-like working conditions, (c) close and continuous proximity to the
lake environment, (d) the possibility to perform in-situ experiments, and (e) a facility for developing and testing new
sensor technology. LéXPLORE will also create novel opportunities for combining advanced in-situ sensors with tradi-
tional lab analyses in an integrated, interdisciplinary research environment.
An open water research platform requires safe surroundings to protect instruments from other lake activities, such
as fishing, transportation, and recreation. Close proximity of the sensors to the platform simplifies instrument opera-
tion, maintenance, and data transfer. The platform itself should provide safe and spacious working conditions including
a shelter, personal facilities, and a motion-dampened workspace. Operating in direct contact with the lake environ-
ment, the platform laboratory is especially useful for using instrument components that are not sealed in watertight
apparatus. The platform size should accommodate a team of researchers (or even multiple teams) and thus supports
interdisciplinary research. A large pontoon mass reduces buffeting and movements to levels suitable for stable atmo-
spheric measurements and optical remote sensing, which require fixed or at least controlled positioning for precise
This publication introduces the LéXPLORE platform (Figure 1) recently installed on Lake Geneva (Switzerland/
France), lists its advantages compared with pre-existing platforms and discusses ongoing and future research that
LéXPLORE can facilitate.
The facilities listed in Box 1 demonstrate the feasibility of an operational field station on Lake Geneva and provided
guidance for development and design. Careful study of these systems evolved into a list of design specifications. These
included (a) stability and ability to withstand a 100-year storm (winds of 140 km/h with 1.5 m significant wave height
2of15 WÜEST ET AL.
and 0.5 m/s water flow), (b) heavy structure to minimize motion, (c) spatial layout allowing adequate equipment
installation and lab bench space necessary for parallel working conditions, (d) a sheltered laboratory for working with
non-weatherproof equipment, preparing samples, conducting IT tasks and providing protection for severe weather and
overnight campaigns, and finally, (e) space for moonpools that directly access the lake surface both inside and outside
the cabin. Site location specifications were (a) a distance far enough offshore to ensure open water conditions,
(b) positioning above depths that represent a substantial part of the hypolimnetic water column, and (c) a location that
addressed concerns of other lake stakeholders. The final location was negotiated with the granting governmental
authorities, professional fishermen, recreational anglers, the public ferry, water police, the local harbor operator, sailing
association, and a local conservation NGO.
The LéXPLORE design emulated existing and past platform designs (Box 1) especially those of the oceano-
graphic Floating Instrument Platform (Fisher & Spiess, 1963) and the WAVES Tower on Lake Ontario (Birch
et al., 1976). The latter installation consists of a bottom-mounted tower at the western end of Lake Ontario. Built in
1975 and powered by a shore-based underwater cable, the tower rests 1.1 km offshore at a local depth of 15 m,
where it can intercept wind fetches of 1300 km. The bi-level design of the tower consists of an 85 m
open grating
upper deck to minimize flow distortion and a lower walkway 3.6 m above the lake surface. The tower allows for
BOX 1 Active platforms on lakes
Instrumented, moored buoys, platforms, and permanent monitoring facilities have been developed and
deployed at various global localities. The following list of five representative examples describes the range of
active stations and how they vary substantially in terms of research objectives and instrumentation. This list is
obviously incomplete.
MÜGGELSEE MONITORING STATION IGB BERLIN: This automated research and monitoring sta-
tion ( has operated since the 1970s on the small, shallow
Müggelsee (Germany). It collects meteorological, physical and biological (plankton) data in real time in order
to investigate the ecological impacts of climate and environmental changes on aquatic communities and biodi-
versity. This station serves both national and international observational programs (Schmidt et al., 2018).
AQUAPROBE EAWAG: This automated lake monitoring station ( on Greifensee
(Switzerland) provides continuous (24 h), high-frequency measurements on phytoplankton and zooplankton at
3 m depth along with environmental monitoring data (multiparameter profiles, weather station, and automated
nutrient sampling). Data streamed in real-time are used to investigate plankton biodiversity and dynamics.
Plankton monitoring consists of scanning flow cytometry ( and observations by the newly
developed Aquascope, an underwater high-resolution, dual-magnification imaging microscope (Orenstein
et al., 2020; Pomati et al., 2011).
ERKEN LABORATORY UPPSALA UNIVERSITY: This program has a long history of monitoring physi-
cal, chemical and biological conditions on Lake Erken and more recently, on Lake Mälaren and surrounding
rivers. Monitoring has been performed manually since 1940 and with automated high-frequency sensor tech-
nology since 1988. The present Erken Monitoring Program ( measures physi-
cal and chemical variables, plankton composition, greenhouse gas fluxes and both inflow and outflow water
quality (Pettersson, 2012). The station is part of the Swedish Infrastructure for Ecosystem Sciences, which mon-
itors diverse habitats and climatic zones to ensure long-term data coverage (
LAKE GEORGE SMART SENSOR NETWORK: While not a singular platform, this project consists of a
network of 12 weather stations, 4 vertical profilers, 12 tributary stations, and several current profilers (https:// As a collaboration between Rensselaer Polytechnic Institute, IBM Research,
and the FUND for Lake George (The United States), the network monitors water flows and water quality in
order to understand human impacts and identify mitigation strategies (Gilbert, 2018).
GREAT LAKES OBSERVING SYSTEM: This project covers the entire Great Lakes System of North Amer-
ica. The network continuously monitors biological, chemical, physical, and meteorological parameters using a
large number of anchored observational buoys (; Data is freely available to
scientists, water managers, government and the public via an on-line data portal (Read et al., 2010).
high-quality wave and wind measurements that capture directional fetch-limited frequency spectra of wind-
generated waves (Donelan et al., 1985).
Five companies participated in design and construction of LéXPLORE. The main tasks consisted of hull construc-
tion, anchorage of the platform and the installation of the protective perimeter. The platform was built on a nearby
dock and anchored after its completion on 19
February 2019 at 570 m off the north shore at a local depth of 110 m.
Financial resources were provided by the five LéXPLORE partner institutions, (a) the Swiss Federal Institute of Tech-
nology, Lausanne (EPFL;, (b) the Swiss Federal Institute of Aquatic Science
and Technology (, (c) the University of Geneva (, (d) the University of
Lausanne (, and (e) CARRTEL INRAE-USMB ( Box 2
summarizes LéXPLORE's technical specifications.
Besides the physical platform on the lake, data management is a crucial component of LéXPLORE (Box 3). There
are two types of data: (a) monitoring data (core dataset), which are freely available for download at www.datalakes- and (b) project-specific data curated by project leaders. The monitoring data include continuous meteorologi-
cal parameters and currents, as well as temperature, oxygen and photosynthetic-active-radiation (PAR) and multi-
parameter profiles (Appendix S1; Ongoing projects use project-specific
equipment and instrumentation, some of which are listed in the Appendix S1. We encourage research teams to make
all data publicly available when projects end, although final decisions and responsibility for data access lie with project
leaders and funding agencies. Since the beginning of operations (February 2019), 30 projects have applied to use
LéXPLORE, which are listed in Appendix S2. In addition to being technically and scientifically feasible, all projects
must comply with LéXPLORE operational and safety policies (
The research partnership established between the five institutions supporting LéXPLORE enables a broad range of
future research projects. Relative to existing platforms, LéXPLORE stands out in terms of its instrumentation and
(j) (i)
(h) (f) (k)
(i)(e) (b)
(g) (c)
(b) (h)
FIGURE 1 Side view of LéXPLORE from the south with the town of Pully in the background. The image shows the sheltered laboratory
and exterior meteorological instruments (a), solar panels (b), on roof and towards south, two A-frames (c), the outdoor moonpool (d) with
electrical winch (e), support frame for lifting loads (f ), and the structure maintaining a thermistor chain (g). Blue anchor winches with
cables for positioning rest at all four corners (h) and are mounted with navigation lights (i). The two doors access the toilet (k) and the
laboratory (l). Battery banks and diesel-generator rest inside the pontoon-hull. The yellow buoys delineate the safety perimeter (j) for
instrument protection. Reprinted with permission from Florian Bentlee, Stuttgart, Germany
4of15 WÜEST ET AL.
accessible workspace. The types of measurements possible on the platform can support interdisciplinary project teams
working in parallel on the same question while using different techniques. Below, we describe research efforts, which
require interdisciplinary collaboration and long-term high frequency observations that allow investigating ecological
phenomena under varying forcing conditions and different scales.
3.1 |Connecting physical and biogeochemical mechanisms of the carbon cycle
A grand challenge facing aquatic biogeochemistry lies in resolving how specific physical, chemical, and biological pro-
cesses of the carbon cycle act at different temporal and spatial scales (Eglinton, 2015). Many driving mechanisms of the
lacustrine carbon cycle occur at time scales much shorter than those addressed by traditional field sampling and labora-
tory analysis. The analytical limitations of high-frequency measurements have long restrained and even confounded
understanding of carbon cycle dynamics in aquatic ecosystems (Hanson et al., 2006; Klaus et al., 2019).
The LéXPLORE platform offers high-frequency automated sensors for different parameters relevant to the aquatic
carbon cycle, including pCO
,UVvisible absorbance and fluorescence, pH, conductivity, and oxygen
BOX 2 LéXPLORE platform technical features
The LéXPLORE platform (Figure 1) consists of a 10 10 m steel pontoon with a vertical dimension of 1.5 m
and a minimum of 1 m freeboard above the water surface. The light and maximum displacements are 35 and
47 metric tons, respectively, with a maximum permitted load of 5 tons including 16 staff. The multichambered
pontoon hull consists of eight individual compartments, which are connected at their tops for wiring, however
their large volumes guarantee that in case of leakage, only one compartment would be flooded. This eliminates
risk of foundering. The four edges of the platform include marine winches (Figure 1) connected to 3-ton heavy
Delta Flipper anchors installed at horizontal distances of 170200 m from the platform. Simulations showed
that this mooring design would hold the pontoon in place within 4 m horizontal dislocation at maximal-
expected wind speeds of 140 km/h (Vuyk, 2019).
Electricity is generated on the platform by (a) 45 m
of photovoltaic (PV) panels (nominal capacity 8.5 kW)
and (b) a back-up soundproof diesel generator (30 kVA). During the first 2 years, the PV panels provided 97%
of the electricity (in total 10.8 MWh). The electrical generator supports specific applications and can help bridge
multiple sun-free days in deep winter. Figure 1 shows the station's 28 PV panels along its southern edifice and
the laboratory roof. The weather-proofed system was installed by certified professionals and meets country-
specify safety standards.
The deck hosts the indoor laboratory, two A-frames, a loading dock with a hand-wheel crane (Figure 1) and
an outdoor moonpool (1.5 1.5 m, Figure 2(b)) equipped with an electrical KC crane for profiling, water sam-
pling or other deep-water assays. The deck also includes a water closet with a toilet and sink (Figure 1). The
inner compartments of the pontoons hold a battery bank (2000 Ah @ 48 V), the back-up electrical generator, a
1000 L diesel supply tank and a 1000 L blackwater tank. The sheltered laboratory (5.9 4.5 2.3 m; Figures 1
and 2) includes a heating unit, a fume hood, a small workshop, cabinetry, shelves, a moonpool (1.5 1.5 m,
Figure 2(d)) equipped with an electrical winch and water pumps for variable-depth water intake and several
bunk beds. A control cabinet contains several computers, controllers and dataloggers for platform operation
and safety checks. These include a pontoon motion monitoring and video camera system. Computers perform
data acquisition from instruments as well as 4G data transmission to remote servers (Box 3).
Water for the toilet and cleaning sink is pumped directly from the lake. Purified water used in analytical
procedures needs to be transported to the platform.
A15,000 m
safety perimeter (Figure 1) surrounds the platform and protects instruments from drifting
fishing nets and boats. The perimeter consists of nine illuminable buoys installed 70 m from the platform and
anchored by 2-ton bottom weights. Fifty-meter long cables hang between buoys to form a protective curtain
that shields scientific equipment. The perimeter allows for undisturbed in-situ measurements and thus forms a
critical component of the platform.
(Watras et al., 2015). These carbon cycle parameters are typically under-sampled over seasonal time scales and during
episodic events (Natchimuthu et al., 2017). Studies of lake carbon processes have also primarily focused on surface
layers where greenhouse gas exchange with the atmosphere occurs. Greater depth-resolved sampling and sensor
options available through LéXPLORE allow for higher resolution monitoring of relevant parameters and active bound-
aries (Perolo et al., 2021). In addition to measuring CO
-related parameters in a mooring array, LéXPLORE instruments
can also detect CH
peaks within the oxic water column (Günthel et al., 2019).
As a station equipped with a broad range of instruments (Box 2; Appendix S1), LéXPLORE will help build a more
integrated understanding especially of physical mechanisms and biogeochemical processes related to the carbon cycle.
Critical questions concerning the role of wind forcing and deep-water upwelling events can be addressed by these
approaches (Natchimuthu et al., 2017). Compared with automated buoys (Box 1), LéXPLORE expands both analytical
scope and data precision by providing a dry working environment for deploying critically sensitive sensors. These
include a UVVis spectrometer for high-frequency dissolved organic matter optical characterization (S::CAN Spec-
trolyzer; Müller et al., 2014) and infrastructure like water-pumps and automated samplers for sequential chemical ana-
lyses (e.g., alkalinity, isotopic compositions, and nutrient concentrations at low levels). The floating laboratory
facilitates ongoing maintenance and calibration of sensors and immediate conditioning, preparation, and analysis of
samples that would otherwise risk alteration during transport or long sampling campaigns.
3.2 |Gas exchange dynamics in response to complex forcing
Dissolved gases are important components of all surface water processes. They figure prominently in biogeochemical
cycles and overall ecosystem function in lakes. Surface waters interact with the atmosphere by exchange of gases such
as oxygen or greenhouse gases, CO
, and N
O (Beaulieu et al., 2019; Cole et al., 2007). Advances in understanding
of the role that lakes play in the global CH
balance has concentrated research activity in limnology. Gas fluxes are
driven by gradients of partial pressures and turbulence at the airwater interface. Newer sensors can measure gas par-
tial pressures at a higher resolution such that gas transfer velocities have become critical sources of the remaining
The LéXPLORE platform allows direct and continuous measurements of gas exchange using multiple tech-
niques applied under varying environmental conditions. Accurate estimation of piston velocity is a primary
goal for establishing reliable semi-empirical parameterizations (Klaus & Vachon, 2020). Various processes
BOX 3 DATALAKESA data management platform for lakes
The LéXPLORE platform with its various monitoring and scientific instruments generates vast quantities of
data. Efficient access to and utilization of LéXPLORE data requires dedicated curation. The web-based open
access data platform Datalakes ( is designed for these needs.
Datalakes serves as a sensor-to-frontend platform for data on any Swiss lake. The software performs contin-
uous acquisition, storage, curation, indexing, patching, visualization, and extraction of lake-related environ-
mental data and products. Datalakes offers a modern, user-friendly online interface with easy-to-use
visualization and extraction functions. The platform also seeks to maximize reproducibility and data integrity.
Access does not require registration and provides raw data (labeled as Level 0) up to commonly used products
integrating information from multiple sensors. As an example, the interface categorizes surface net heat flux
( as Level 2 data.
Both the web portal and GIT repository offer access to processing scripts with the intention that the scien-
tific community will adapt, update, and optimize them. To avoid ill-defined reproducibility, changes in
processing scripts and methods, Datalakes tracks workflow and performs version control using a Renku plat-
form ( Finally, Datalakes is not confined to LéXPLORE data but rather combines
different sources of information. This promotes data visualization and extraction of one-dimensional and three-
dimensional hydrodynamic models using remote sensing data from Meteolakes (; Gaudard
et al., 2019; Baracchini et al., 2020). This GIS-based visualization portal facilitates integration of different data
layers generated by remote sensors, in-situ instruments and hydrodynamic models.
6of15 WÜEST ET AL.
contribute to uncertainties in piston velocities including (a) lateral and temporal variability of wind forcing,
(b) interactions of wind-induced and cooling-induced turbulence, and (c) fluctuations in surface wave-affected
gas transfer (Deike & Melville, 2018; Reichl & Deike, 2020). In addition, the scale of vertical and temporal varia-
tions in gas concentrations in the upper few tens of centimeters of the water column (Watson et al., 2020) and
sub-daily variation in near-surface stratification and gas transfer velocity from intermittent wind, waves, and
heat fluxes can obscure detection of forces driving gas transfer. These dynamics demonstrate that both concen-
tration gradients (driving force) and turbulence levels (transfer velocity) vary considerably over short time
scales of less than a day. Gas fluxes represent the instantaneous product of these processes and thus vary on the
same time scales.
LéXPLORE allows long-term, continuous operation of automated forced-diffusion chambers that measure CO
fluxes at the airwater interface (Perolo et al., 2021; Risk et al., 2011). A CO
eddy-covariance system mounted on the
laboratory roof (Erkkilä et al., 2018; Eugster et al., 2003) can provide flux measurements integrated over larger spatial
scales. These direct observations can further constrain turbulence-based models for gas exchange velocities. Surface
layer turbulence can be quantified with upward-facing High-Resolution Acoustic Doppler Current Profilers, rising
Microstructure Profilers or autonomous profiling Wirewalkers (Rainville & Pinkel, 2001; Figure 2(c)) and (potentially)
water-side eddy-covariance measurements (Berg & Pace, 2017). In summary, the LéXPLORE platform offers the neces-
sary infrastructure (Appendix S1) for evaluating gas fluxes over short time scales and a broad range of forcing condi-
tions and lake dynamics.
3.3 |Resolving surface microlayer dynamics from a stable platform
The airwater interface is the first direct and visible contact, when approaching lakes. In spite of its seeming accessibil-
ity, the size and variation of the airwater interface poses major experimental challenges in lake sciences (Soloviev &
FIGURE 2 LéXPLORE elements (from top left to bottom right): (a) outdoor work area, (b) outdoor moonpool with electric crane (left)
and pump system (right), (c) Wirewalker deployment using an A-frame, (d) partially covered indoor moonpool, and (e) office work area
Lukas, 2013). Surface layers feature distinct dynamic structures down to microscopic scales (<100 μm). These in turn
determine physical and biogeochemical processes for the near-surface and beyond (Cunliffe et al., 2013). Electromag-
netic radiative transfer notwithstanding, molecular bottlenecks of diffusive and viscose boundaries, themselves
governed by adjacent turbulent atmospheric and water layers, determine airwater exchange. Under conditions of
strong winds, breaking waves contribute additional turbulent kinetic energy and thereby enhance this exchange
(Terray et al., 1996).
An illustrative example of the influence of small-scale features is the up to 0.5C temperature differential that can
develop between the thermal sublayer skin and underlying bulk water, which becomes particularly pronounced under
weak wind (Wilson et al., 2013; Irani Rahaghi et al., 2019). This difference exceeds the detection limits of high-
resolution satellite radiometers currently used to monitor lakes. Temperature data for inland waters should thus
include skin-to-bulk differences (Minnett et al., 2011; Riffler et al., 2015). Establishing relations between the skin and
bulk properties or more generally, between the surface microlayer and the turbulent layer beneath, represents a major
challenge in limnology. LéXPLORE provides an observational solution for characterizing differences between near-
surface boundary layers (Section 3.2). Specifically, LéXPLORE allows continuous sensing by closely-spaced thermistor
arrays and highly resolved acoustic Doppler current profiles together with upward fine-structure temperature profiling
and automatized water-sampling. These in-situ observations can be complemented by downward-facing airside radiom-
eters and meteorological instruments (Appendix S1), which together enable quantification of dynamics in near-surface
layers under variable conditions.
The surface boundary layer also hosts unique biogeochemical processes including the formation of biofilms. These
process terrestrial particles (such as pollen in spring) and autochthonous lacustrine organic matter. Surface biofilms
modify the physico-chemical characteristics of the airwater exchange for instance by greater heat absorption, which
increases the skin-to-bulk temperature gradient (Soloviev & Lukas, 2013) or greater viscosity, which increases lake sur-
face tension (Cunliffe et al., 2011). Biofilm organic matter may influence the absorption of ultraviolet radiation and also
by extension, water column penetration of biologically harmful radiation. LéXPLORE provides a unique facility that
help scientists investigate biogeochemical and physical interactions that characterize this directly accessible yet difficult
to analyze surface microlayer.
3.4 |Seasonal apparent and inherent optical properties for remote sensing applications
Accurate interpretation of satellite-based Earth observation imagery depends on fiducial ground reference measure-
ments of Apparent and Inherent Optical Properties (AOPs and IOPs). Calibration and validation of atmospheric correc-
tions and the resulting water-leaving reflectances require standardized measurements of AOPs and specifically of
downwelling irradiance (Ruddick et al., 2019a) and water-leaving radiance (Ruddick et al., 2019b). In practical terms,
such measurements are acquired at several marine sites, most notably by the AERONET-OC network (Zibordi
et al., 2010), BOUSSOLE (Antoine et al., 2008), and MOBY (Franz et al., 2007). The availability of equivalent calibration
data for lakes remains scarce despite efforts by the Committee on Earth Observation Satellite's Radiometric Calibration
Network (RadCalNet) or the WATERHYPERNET to establish comparable measurement data for inland waters
(Vansteenwegen et al., 2019). Measurements from a stationary-oriented platform like LéXPLORE offer advantages over
those collected from a moving boat. IOPs help to rigorously tie AOPs to biophysical parameters such as phytoplankton
concentrations, particles and colored dissolved organic matter. Lab analyses and in-situ measurements can also con-
strain bulk spectral absorption as well as beam transmission and attenuation (Riddick et al., 2015).
LéXPLORE operation in open water settings allows deployment of the automated Thetis profiler (Minaudo
et al., 2021) adjacent to the platform (Figure 3). This profiler acquires bulk IOP measurements at high frequencies and
high vertical resolution (Appendix S1). The tool can capture relatively poorly understood diel and vertical variations in
IOPs that influence a wide variety of aquatic processes including primary production (Figure 3), whiting, grazing, and
intrusion of riverine suspended particles (Minaudo et al., 2021). Using these novel measurements as inputs to radiative
transfer models will yield simulated AOP results showing water-leaving or top-of-atmosphere reflectance. These outputs
can be compared with spectroradiometer measurements acquired in-situ by Thetis, with those acquired by LéXPLORE
surface instruments, or with satellite observations. Dual closure of water-leaving reflectance obtained from measured
and simulated AOP based on measured IOP improves accuracy and reduces uncertainties associated with ground mea-
surements typically used for vicarious calibration (Werdell et al., 2018). LéXPLORE thus provides fiducial reference
measurements for the calibration and validation of atmospheric correction methods.
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3.5 |High-frequency plankton monitoring under environmental change
Populations and individuals face trade-offs in ecosystems. Species may perform well at certain functions but find them-
selves at a disadvantage regarding others. Species within a community are shaped not just by the environment but also
by both disadvantage and advantage matrices of other organisms (Cadier et al., 2019; Ehrlich et al., 2017; Litchman &
Klausmeier, 2008). Predictions of ecological consequences depend on complex webs of interaction but trade-offs in
these webs remain difficult to quantify, especially in aquatic communities that resist experimental interventions
(Ehrlich et al., 2020). The high-frequency in-situ monitoring capabilities of LéXPLORE can address some of these limi-
tations. Together with Pomati et al. (2011), we are developing a combined CytoBuoy flowcytometry and AquaScope
image analyzer to automate phytoplankton and zooplankton monitoring (Box 1). Combined with novel machine-
learning techniques for automated data analysis, these tools can monitor species abundances and environmental condi-
tions over short time scales. Observations can inform studies on environmental interdependence and growth cycles
(Thomas et al., 2018). These new approaches can also enable process-based forecasts on how lake communities respond
to environmental changes on time-scales from weeks to decades.
FIGURE 3 Thetis profiler measurements at LéXPLORE: Thetis deployment with various sensors inside the cylindrical black-meshed
rack (a) and Thetis rising and breaching the surface with its antenna installed above the bright-yellow buoyancy body (b). The antenna
operates via FreeWave radio technology. The three panels show examples of vertical temperature (c), oxygen (d), and chlorophyll-a (e) data
series collected by Thetis in the upper 50 m of the water column near LéXPLORE at a resolution of 3.0 h. Black-dashed and white lines,
respectively, indicate the thermocline and euphotic depths. Thetis can also acquire electrical conductivity, hyperspectral absorption and
attenuation, backscattering and fluorescence at discrete wavelengths, PAR and hyperspectral up-welling and down-welling radiations
(Appendix S1). These exemplary profiles show a warming period in April 2020 interrupted by 2 days of wind-driven mixing/upwelling (black
arrow in c) and subsequent chlorophyll-a and oxygen accumulation in the epilimnion. Reprinted with permission from Minaudo
et al. (2021)
Environmental dependencies in trophic interactions also pose significant challenges for traditional lake monitoring.
Abiotic factors can impose nonlinear effects on the physiology and growth of individual species (Thomas et al., 2017;
Uszko et al., 2017) which in turn influence the growth of interacting species, especially predators (DeLong &
Lyon, 2020). Complex feedbacks can arise from multiple species occupying different trophic levels and interacting
within the environment (Luhring et al., 2018). Evaluating interacting environmental dependencies is critical for under-
standing and predicting how ongoing warming and oligotrophication will affect lake ecosystem function. Current facto-
rial lab experiments are investigating how species respond to changes in multiple environmental dimensions. These are
coupled to model simulations that predict how effects propagate to higher trophic levels. High-frequency observations
from LéXPLORE will help validate model predictions through monitoring of multiple interacting trophic levels. Obser-
vations during extreme meteorological events can provide important constraints on model predictions of how perturba-
tions and temperaturefood relationships will shape the future Lake Geneva ecosystem. Continuous monitoring using
LéXPLORE is critical in capturing data from rare and multidimensional ecosystem events.
3.6 |Long-term studies of fish population dynamics
LéXPLORE offers unique opportunities to research fish population dynamics and species diversity. Both local
and global fisheries studies require information on population dynamics, recruitment, and food web interactions
(Cheung et al., 2009). The platform facilitates sampling and analysis of individuals for traits, maturity, parasitism, and
genetics. These investigations also require high quality environmental background data (Olmos et al., 2020).
LéXPLORE data (Box 3; Appendix S1) and collaborative frameworks can thus support classic ongoing or novel fisheries
In addition to shifts in plankton communities, trophic networks (Section 3.5) and biogeochemical processes
(Section 3.1), reoligotrophication of Lake Geneva has helped restore iconic threatened species such as whitefish (Cor-
egonus sp.; Lynch et al., 2015; Straile et al., 2007) and Arctic charr (Salvelinus alpinus; Caudron et al., 2014). However,
these species now face additional threats from increasing temperatures, modified riverine flows and changing wind pat-
terns during critical development phases (Kelly et al., 2020; Mari et al., 2021; Nõges et al., 2018). Core datasets (Box 3;
Appendix S1) and plankton studies (Section 3.5) from LéXPLORE will support investigations on the temporal coupling
between the emergence of fish larvae and the phenology of plankton, or the risk of so-called matchmismatch phenom-
ena (Cushing, 1990). This synchronism plays a key role in fish recruitment and therefore the size of the fishery. Recruit-
ment depends strongly on short-term weather phenomena such as sudden and pronounced upwelling events
(Baracchini et al., 2020). For example, spring storms can lower the surface temperature by more than 10C in less than
24 h. This can kill perch larvae (Perca fluviatilis) which lack the ability to take refuge in warmer zones. High-frequency
water column data will help constrain key parameters and impacts of these events. Toxic algal blooms (Platt
et al., 2003), microplastics (Parker et al., 2021), and new organic pollutants (Corsolini et al., 2005) all impact fish com-
munities as well. In addition to addressing these, the LéXPLORE platform can provide samples for genomic studies
such as analysis of e-DNA samples (Sales et al., 2021) from different depths or remote hydroacoustic surveys using
broadband sounders (Benoit-Bird & Waluk, 2020; Appendix S1). These datasets can help natural resource specialists
and scientists manage fish communities and invasive species by assaying larval emergence phenology or species diver-
sity, distribution in the water column, and schooling behavior as a function of biotic or abiotic dynamics.
3.7 |Addressing complex questions by integrated, multidisciplinary approaches
LéXPLORE offers the opportunity for several teams to work simultaneously on different or joint projects. Compared
with existing platforms, LéXPLORE stands out in terms of its functionality and flexibility as a workspace which can
serve a broad range of complementary measurement applications and research questions. The question of what regu-
lates primary productionone of the first projects initiated on LéXPLOREis such an example of a prescient, systems-
level science question requiring integrated, multidisciplinary approaches. Primary production depends on both vertical
distribution and vertical flux of nutrients and algal communities, as well as on carbon cycling and light regimes. As
documented by the first LéXPLORE publications, teams working simultaneously and using diverse approaches can
build effective lines of evidence to address these questions (Fern
andez Castro et al., 2021; Minaudo et al., 2021; Perolo
et al., 2021).
10 of 15 WÜEST ET AL.
Given the inherently variable nature of aquatic systems, effective scientific investigations require long-term observa-
tions at high vertical and temporal resolution. To address these needs and overcome limitations imposed by tradi-
tional monitoring by boat, mooring, and automated buoys (Box 1), a consortium of five partner institutions
constructed a multipurpose platform for performing a broad range of scientific observations on Lake Geneva. The
LéXPLORE platform provides a workspace for a large number of instruments and up to 16 staff working in parallel
or on different projects (Box 2). The dry, protected laboratory offers direct access to the lake environment for high-
sensitivity, high-throughput measurements including development of novel sensor technology. In addition, the float-
ities for the public.
The LéXPLORE platform represents unprecedented analytical access to a large, dynamic lake environment
experiencing reoligotrophication under conditions of a changing climate. LéXPLORE combines complex instrumenta-
tion and lake environment access. The station offers diverse analytical opportunities from lake in-situ microscopy of
plankton communities to long-term, multiparameter measurement of local atmospheric dynamics. Since anchoring
of the platform in February 2019, 30 projects (Appendix S2) have made use of LéXPLORE. Initial research projects indi-
cate that LéXPLORE is an effective facility for making major scientific contributions. The greatest effect of LéXPLORE
is its community-building role, as field-based scientists meet and exchange, and thereby stimulate interdisciplinary
studies. We encourage lake researchers to consider how such an equivalent platform might serve their research and also
welcome any inquiries from scientists interested in using LéXPLORE.
We appreciate the contributions by Mridul K. Thomas (U of Geneva), Bieito Fern
andez Castro (U of Southampton),
Daniel Odermatt (Eawag) and especially by Camille Minaudo (EPFL) for providing Figure 3. The build-up of the
scientific-technical instrumentation would have not been possible without the work of Aurélien Ballu, Guillaume
Cunillera, Christian Dinkel, Roxane Fillion, Michael Plüss, Philippe Quétin, James Runnalls, and Viet Tran-Khac. The
technical team received support by Hannah Chmiel, Fabio dos Santos Correia, Nicolas Escoffier, and Pascal Perolo.
The EPFL teams of the technical platform PLTE of ENAC and of the DSPS provided guidance in technical and safety
matters. Finally, a big thank to Andreas Kindlimann (Naval Architecture GmbH) for the design and realization of
LéXPLORE, and to Barbara Tirone for her amazing assistance during the construction phase.
The EPFL Limnology Center financed the development and supervision of the LéXPLORE platform. Four partner insti-
tutions, EPFL, Eawag, the University of Geneva and the University of Lausanne funded construction and installation of
LéXPLORE. These partners and CARRTEL (INRAE-USMB) support the station's ongoing operation. The Swiss Federal
Office for the Environment contributed project funding. Additional funds for instrumentation were made available by
the SNF/EPFL and SNF/UniGE R'Equip Program (Grant LéXPLORE no. 206021_157779), ENAC Calls for Equipment
and the Limnology Center. The EPFL Limnology Center and Ferring International SA support the position of the senior
author, who serves as the LéXPLORE project manager.
The authors have declared no conflicts of interest for this article.
Alfred Wüest: Conceptualization; funding acquisition; project administration; resources; writing-original draft;
writing-review & editing. Damien Bouffard: Conceptualization; funding acquisition; project administration; software;
writing-original draft; writing-review & editing. Jean Guillard: Conceptualization; funding acquisition; project admin-
istration; resources; writing-original draft; writing-review & editing. Bastiaan Ibelings: Conceptualization; funding
acquisition; project administration; resources; writing-original draft; writing-review & editing. Sebastien Lavanchy:
Investigation; project administration; resources. Marie-Elodie Perga: Conceptualization; funding acquisition; project
administration; resources; writing-original draft; writing-review & editing. Natacha Pasche: Conceptualization;
funding acquisition; project administration; resources; supervision; writing-original draft; writing-review & editing.
WÜEST ET AL.11 of 15
All data related to LéXPLORE is freely available at:
Alfred Wüest
Damien Bouffard
Jean Guillard
Bastiaan W. Ibelings
Sébastien Lavanchy
Marie-Elodie Perga
Natacha Pasche
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Additional supporting information may be found online in the Supporting Information section at the end of this article.
How to cite this article: Wüest, A., Bouffard, D., Guillard, J., Ibelings, B. W., Lavanchy, S., Perga, M.-E., &
Pasche, N. (2021). LéXPLORE: A floating laboratory on Lake Geneva offering unique lake research opportunities.
Wiley Interdisciplinary Reviews: Water, e1544.
WÜEST ET AL.15 of 15
... The platform size should accommodate a team of researchers (or even multiple teams) and thus supportsinterdisciplinary research. A large pontoon mass reduces buffeting and movements to levels suitable for stable atmo-spheric measurements and optical remote sensing, which require fixed or at least controlled positioning for preciseobservations. (Boo et al., 2018;Figueroa-Lara et al., 2019;Nair et al., 2018;Wüest et al., 2021). The obtained result shows that increasing stretch of mooring line could reduce motions of the platform, while increase the mooring line tension. ...
... Therefore, the mooring buoy is also equipped with a lamp that has solar panels as a backup energy source to keep it lit at night. (Ghafari & Dardel, 2018;Lat et al., 2022;Wüest et al., 2021). The works to install buoys + ballast at sea for the lifting sinkers (concrete block weights) will be done using the floating method using a mini pontoon. ...
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Analysis of the buoyancy of this platform for use in mid-ocean land survey operations where this platform is loaded with the weight of the tools and workers on the platform. The purpose of this research is to describe the buoyancy of the mooring buoys. The research was conducted by calculating the capacity and weight of each material used and the buoyancy of the buoy to be used as a platform for land surveys in mid-ocean, the ability of seawater to shift the size of the pontoon to be used as a platform and calculate the load on the pontoon itself to obtain the buoyancy value of the pontoon. The ability of the strapping between the pontoon and the anchor was calculated to anticipate unstable pontoon motion and must have a stress capability that exceeds the stress experienced when the pontoon is hit by a wave. The tension in the chain is greatest force is assumed, namely the force of the ballast. When the earthworks pontoon capacity is used as mooring buoy by estimating the total weight of the earthworks pontoon capacity, it is still in a semi-floating condition, although under certain conditions it will drop to as much as 95% of the estimated buoyancy pressure capacity of the mourning buoy.
... However, phytoplankton biomass seemed to unexpectedly remain stable or slightly increase in the past two decades [21]. In 2018, the research platform LéXPLORE was installed in Lake Geneva to better understand biological, chemical and physical processes and how these are interrelated [22]. The platform is located 570 meters off the northern shore and towards the south-east of Lausanne, moored at 110 m depth (Fig. 1). ...
... The platform is located 570 meters off the northern shore and towards the south-east of Lausanne, moored at 110 m depth (Fig. 1). The platform houses state-of-the-art instruments to continuously and simultaneously measure various physical and biological water and environmental parameters [22]. ...
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Quantum yield of fluorescence ( ϕ F ) is key to interpret remote measurements of sun-induced fluorescence (SIF), and whether the SIF signal is governed by photochemical quenching (PQ) or non-photochemical quenching (NPQ). Disentangling PQ from NPQ allows using SIF estimates in various applications in aquatic optics. However, obtaining ϕ F is challenging due to its high temporal and physiological variability, and the combined measurements needed to enclose all relevant optical paths. In inland waters, this type of data is scarce and information on diurnal and seasonal ϕ F dynamics are almost unknown. Using an autonomous hyperspectral Thetis profiler in Lake Geneva, we demonstrate how to estimate ϕ F using an ensemble of in-situ measurements acquired between 2018 to 2021. We use vertical and temporal changes in retrieved ϕ F to determine NPQ and PQ conditions. We observed NPQ in 36% of the total daytime profiles used in the ϕ F analysis. While downwelling irradiance is a significant contributor to ϕ F , its role cannot be easily interpreted. Other factors such as phytoplankton photoregulation and assemblages also likely play significant roles in quenching mechanisms. We conclude that an adapted approach exploiting in-situ data is suitable to determine diurnal and seasonal NPQ occurrence, and helps develop future remote sensing algorithms.
... 00 , Dissanayake et al., 2019). In Lake Geneva, the three ropes (100 m long) were installed in the perimeter of the research platform LéXPLORE (N: 46°30 0 0.82 00 , E: 6°39 0 39.01 00 , Wüest et al., 2021). The experiment was deployed asynchronously due to limited access to the materials and to the lakes: in Lake Constance we installed the ropes in December 2019 and in Lake Geneva in June 2020 (instead of March due to first months of the Covid-19 pandemic). ...
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Quagga and zebra mussels (Dreissena bugensis and D. polymorpha) are spreading across lakes in Europe and North America. In particular, quagga mussels colonize lakes to great depths (>200 m). To better understand the colonization pattern of quagga mussels in deep lakes, we studied the settlement of quagga mussels along a depth gradient on colonization plates at multiple depths (1-140 m) in the pelagic zone of two recently invaded perialpine lakes, Lake Constance and Lake Geneva. We measured coloniza-tion rates every three months over one year on colonization plates deployed in both lakes at defined depths. We also assessed long-term population dynamics from abundance and size distribution using repeated photogrammetry of colonization plates. Highest colonization rates and largest mussel sizes occurred above 8 m depth, and almost no zebra mussels were found. Colonization rates decreased to almost zero below 30 m. Colonization rates on plates were associated with variation in environmental conditions as well as veliger densities in the plankton across season and depth. Temperature was the most important environmental parameter that influenced colonization. Our results will help to better understand the seasonal colonization patterns of invasive quagga mussels in deep lakes.
... Even this being the case, the monitoring challenge is to provide sufficient temporal and spatial coverage. While these simpler, cell-based methods are broadly applicable in many parts of the world, progress is also being made using automated, high-frequency monitoring of lakes and oceans, even for phytoplankton (Marcé et al., 2016;Wüest et al., 2021), that allows data to be acquired and reported in real time. Likewise, algorithm development using the latest generation of satellites like Sentinel-2 is promising HAB detection with wide spatial coverage (Sòria-Perpinyà et al., 2020). ...
... Including standardized, systematic monitoring of phytoplankton and other water quality parameters in winter would provide a more holistic understanding of phytoplankton communities and lake ecology as a whole. Automated lake monitoring strategies, which include instruments for the high frequency, automated quantification of phytoplankton (using underwater microscopes or flow cytometers on lake platforms like LéXPLORE) allow one way forward to obtain continuous data on lake phytoplankton across all seasons (Marcé et al. 2016;Wüest et al. 2021;Merz et al. 2021). Furthermore, experimental mesocosm studies will help to mechanistically understand the effects of environmental drivers and variability for cyanobacterial bloom formation, including the winter season, and support ways of mitigation by testing nature-based solutions (Gerhard et al. 2022). ...
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Cyanobacterial blooms have substantial direct and indirect negative impacts on freshwater ecosystems including releasing toxins, blocking light needed by other organisms, and depleting oxygen. There is growing concern over the potential for climate change to promote cyanobacterial blooms, as the positive effects of increasing lake surface temperature on cyanobacterial growth are well documented in the literature; however, there is increasing evidence that cyanobacterial blooms are also being initiated and persisting in relatively cold‐water temperatures (< 15°C), including ice‐covered conditions. In this work, we provide evidence of freshwater cold‐water cyanobacterial blooms, review abiotic drivers and physiological adaptations leading to these blooms, offer a typology of these lesser‐studied cold‐water cyanobacterial blooms, and discuss their occurrence under changing climate conditions.
... The lake is stratified from April to September with a thermocline deepening from 3 to 30 m. Calcite precipitation occurs throughout during the stratification period (Müller et al. 2016;Escoffier et al. 2023). Two study sites (Fig. S1a-c), the LéXPLORE platform (110-m depth; Wüest et al. 2021) and the Buchillon mast (4-m depth), representative of the pelagic and littoral environments, were investigated over the years 2019 and 2020. ...
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In alkaline freshwater systems, the apparent absence of carbon limitation to gross primary production (GPP) at low CO2 concentrations suggests that bicarbonates can support GPP. However, the contribution of bicarbonates to GPP has never been quantified in lakes along the seasons. To detect the origin of the inorganic carbon maintaining GPP, we analyze the daily stoichiometric ratios of CO2–O2 and alkalinity–O2 in a deep hardwater lake. Results show that aquatic primary production withdraws bicarbonate from the alkalinity pool for two‐thirds of the year. Alkalinity rather than CO2 is the dominant inorganic carbon source for GPP throughout the stratified period in both the littoral and pelagic environments. This study sheds light on the neglected role of alkalinity in the freshwater carbon cycle throughout an annual cycle.
... the information gathered using traditional methods, but they are usually very expensive and strongly oriented to scientific experimental research [20,21]. On Lake Geneva, a floating laboratory is installed, hosting more than 30 scientific projects with the aim of measuring and modelling key physical and biogeochemical processes at high frequency [22]. Data management and integration is the second key issue that this paper would like to focus on. ...
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In some sectors of the water resources management, the digital revolution process is slowed by some blocking factors such as costs, lack of digital expertise, resistance to change, etc. In addition, in the era of Big Data, many are the sources of information available in this field, but they are often not fully integrated. The adoption of different proprietary solutions to sense, collect and manage data is one of the main problems that hampers the availability of a fully integrated system. In this context, the aim of the project is to verify if a fully open, cost-effective and replicable digital ecosystem for lake monitoring can fill this gap and help the digitalization process using cloud based technology and an Automatic High-Frequency Monitoring System (AHFM) built using open hardware and software components. Once developed, the system is tested and validated in a real case scenario by integrating the historical databases and by checking the performance of the AHFM system. The solution applied the edge computing paradigm in order to move some computational work from server to the edge and fully exploiting the potential offered by low power consuming devices.
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The complex interactions from anthropogenic activities, climate change, sedimentation and the input of wastewater has significantly affected the aquatic environment and entire ecosystem. Over the years, the researchers have investigated water monitoring approaches in terms of traditional monitoring or even integrated systems to handle such an environmental assessment and predictions based on warning systems. However, research into the selection and optimisation of water monitoring systems by the combination of parallel approach in terms of sampling techniques, process analysis and results is limited. The research objectives of the present study are to evaluate the existing water monitoring systems based on the latest approach and then provide insights into factors affecting sensor implementation at sampling locations. Here we summarize the advancement and trends of various water monitoring systems as well as the suitability of sensor placement in the area by reviewing more than 300 papers published between 2011 and 2022. The research highlights the urgency of an integrative approach with regard to water monitoring systems including water quality model and water quantity model. A framework is proposed to incorporate all water monitoring approaches, sampling techniques, and predictive models to provide comprehensive information about environmental assessment. It was observed that the urgency of model-based approaches as verification and fusion of data assemble has the ability to improve the performances of the systems. Furthermore, integrated systems with the inclusion of a separate modeling approach through integrated - semi-mechanistic models, data science and artificial intelligence are recommended in the future. Overall, this study provides guidelines for achieving standardized water management by implementing integrated water monitoring systems.
In hardwater lakes, calcite precipitation is an important yet poorly understood process in the lacustrine carbon cycle, in which catchment-derived alkalinity (Alk) is both transformed and translocated. While the physico-chemical conditions supporting the supersaturation of water with respect to calcite are theoretically well described, the magnitude and conditions underlying calcite precipitation at fine temporal and spatial scales are poorly constrained. In this study, we used high frequency, depth-resolved (0-30 m) data collected over 18 months (June 2019 - November 2020) in the deeper basin of Lake Geneva to describe the dynamics of calcite precipitation fluxes at a fine temporal resolution (day to season) and to scale them to carbon fixation by primary production. Calcite precipitation occurred during the warm stratified periods when surface water CO2 concentrations were below atmospheric equilibrium. Seasonally, the extent of Alk loss due to calcite precipitation (i.e., [30-42] g C m-2) depended upon the level of Alk in surface waters. Moreover, interannual variability in seasonal calcite precipitation depended on the duration of stratification, which determined the volume of the water layer susceptible to calcite precipitation. At finer timescales, calcite precipitation was characterized by marked daily variability with dynamics strongly related to that of planktonic autotrophic metabolism. Increasing daily calcite precipitation rates (i.e., maximum values 9 mmol C m-3 d-1) coincided with increasing net ecosystem production (NEP) during periods of enhanced water column stability. In these conditions, calcite precipitation could remove as much inorganic carbon from the productive layers as NEP. This study provides mechanistic insights into the conditions driving pelagic calcite precipitation, and quantifies its essential contribution to the coupling of organic and inorganic carbon cycling in lakes.
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We present a Bayesian inference for a three-dimensional hydrodynamic model of Lake Geneva with stochastic weather forcing and high-frequency observational datasets. This is achieved by coupling a Bayesian inference package, SPUX, with a hydrodynamics package, MITgcm, into a single framework, SPUX-MITgcm. To mitigate uncertainty in the atmospheric forcing, we use a smoothed particle Markov chain Monte Carlo method, where the intermediate model state posteriors are resampled in accordance with their respective observational likelihoods. To improve the uncertainty quantification in the particle filter, we develop a bi-directional long short-term memory (BiLSTM) neural network to estimate lake skin temperature from a history of hydrodynamic bulk temperature predictions and atmospheric data. This study analyzes the benefit and costs of such a state-of-the-art computationally expensive calibration and assimilation method for lakes.
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The gas transfer velocity (k) is a major source of uncertainty when assessing the magnitude of lake gas exchange with the atmosphere. For the diversity of existing empirical and process-based k models, the transfer velocity increases with the level of turbulence near the air–water interface. However, predictions for k can vary by a factor of 2 among different models. Near-surface turbulence results from the action of wind shear, surface waves, and buoyancy-driven convection. Wind shear has long been identified as a key driver, but recent lake studies have shifted the focus towards the role of convection, particularly in small lakes. In large lakes, wind fetch can, however, be long enough to generate surface waves and contribute to enhance gas transfer, as widely recognised in oceanographic studies. Here, field values for gas transfer velocity were computed in a large hard-water lake, Lake Geneva, from CO2 fluxes measured with an automated (forced diffusion) flux chamber and CO2 partial pressure measured with high-frequency sensors. k estimates were compared to a set of reference limnological and oceanic k models. Our analysis reveals that accounting for surface waves generated during windy events significantly improves the accuracy of k estimates in this large lake. The improved k model is then used to compute k over a 1-year time period. Results show that episodic extreme events with surface waves (6 % occurrence, significant wave height > 0.4 m) can generate more than 20 % of annual cumulative k and more than 25 % of annual net CO2 fluxes in Lake Geneva. We conclude that for lakes whose fetch can exceed 15 km, k models need to integrate the effect of surface waves.
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Water inherent optical properties (IOPs) contain integrative information on the optical constituents of surface waters. In lakes, IOP measurements have not been traditionally collected. This study describes how high-frequency IOP profiles can be used to document short-term physical and biogeochemical processes that ultimately influence the long-term trajectory of lake ecosystems. Between October 2018 and May 2020, we collected 1373 high-resolution hyperspectral IOP profiles in the uppermost 50 m of the large mesotrophic Lake Geneva (Switzerland-France), using an autonomous profiler. A data set of this size and content does not exist for any other lake. Results showed seasonal variations in the IOPs, following the expected dynamic of phytoplankton. We found systematic diel patterns in the IOPs. Phases of these diel cycles were consistent year-round, and amplitudes correlated to the diurnal variations of dissolved oxygen, clarifying the link between IOPs and phytoplankton metabolism. Diel amplitudes were largest in spring and summer under low wind condition. Wind-driven changes in thermal stratification impacted the dynamic of the IOPs, illustrating the potential of high-frequency profiles of water optical properties to increase our understanding of carbon cycling in lake ecosystems.
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The gas transfer velocity (k) is a major source of uncertainty when assessing the magnitude of lake gas exchange with the atmosphere. For the diversity of existing empirical and process-based k models, the transfer velocity increases with the level of turbulence near the air-water interface. However, predictions for k can vary by a factor of 2 among different models. Near-surface turbulence results from the action of wind shear, surface waves and buoyancy-driven convection. Wind shear has long been identified as a key driver, while recent lake studies have shifted the focus towards the role of convection, particularly in small lakes. In large lakes, wind fetch can however be long enough to generate surface waves and contribute to enhance gas transfer, as widely recognised in oceanographic studies. Here, field values for gas transfer velocity were computed in a large hardwater lake, Lake Geneva, from CO2 fluxes measured with an automated (forced diffusion) flux chamber and CO2 partial pressure measured with high frequency sensors. k estimates were compared to a set of reference limnological and oceanic k models. Our analysis reveals that accounting for surface waves generated during windy events significantly improves the accuracy of k estimates in this large lake. The improved k model is then used to compute k over a one-year time-period. Results show that episodic extreme events with surface waves (6 % occurrence, significant wave height > 0.4 m) can generate more than 20 % of annual cumulative k and more than 25 % of annual net CO2 fluxes in Lake Geneva. We conclude that for lakes whose fetch can exceed 15 km, k-models need to integrate the effect of surface waves.
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The rates of gross primary production (GPP), ecosystem respiration (R) and net ecosystem production (NEP) provide quantitative information about the cycling of carbon and energy in aquatic ecosystems. In lakes, metabolic rates are often diagnosed from diel oxygen fluctuations recorded with high-resolution sondes. This requires that the imprint of ecosystem metabolism can be separated from that of physical processes. Here, we quantified the vertical and temporal variability of the metabolic rates of a deep, large, mesotrophic lake (Lake Geneva, Switzerland-France) by using a 6-months record (April – October 2019) of high-frequency, depth-resolved (0–30 m) dissolved oxygen measurements. Two new alternative methods (in the time and frequency domain) were used to filter low-frequency basin-scale internal motions from the oxygen signal. Both methods proved successful and yielded consistent metabolic estimates showing net autotrophy (NEP = GPP- R = 55 mmol m−2 d−1 ) over the sampling period and depth interval, with GPP (235 mmol m−2 d−1 ) exceed- ing R (180 mmol m−2 d −1 ). They also revealed significant temporal variability, with at least two short-lived blooms occurring during calm periods, and a vertical partitioning of metabolism, with stronger diel cycles and positive NEP in the upper ∼10 m and negative NEP below, where the diel oxygen signal was dominated by internal motions. The proposed methods expand the range of applicability of the diel oxygen technique to large lakes hosting energetic, low-frequency internal motions, offering new possibilities for unveiling the rich spatio-temporal metabolism dynamics in these systems
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Microplastics (MPs) are small, plastic particles of various shapes, sizes and polymers. Although well studied in marine systems, their roles and importance in freshwater environments remain uncertain. Nevertheless, the restricted ranges and variable traits of freshwater fishes result in their communities being important receptors and strong bioindicators of MP pollution. Here, the current knowledge on MPs in freshwater fishes is synthesized, along with the development of recommendations for future research and sample processing. MPs are commonly ingested and passively taken up by numerous freshwater fishes, with ingestion patterns often related to individual traits (e.g. body size, trophic level) and environmental factors (e.g. local urbanization, habitat features). Controlled MP exposure studies highlight various effects on fish physiology, biochemistry and behaviour that are often complex, unpredictable, species‐specific and nonlinear in respect of dose–response relationships. Egestion is typically rapid and effective, although particles of a particular shape and/or size may remain, or translocate across the intestinal wall to other organs via the blood. Regarding future studies, there is a need to understand the interactions of MP pollution with other anthropogenic stressors (e.g. warming, eutrophication), with a concomitant requirement to increase the complexity of studies to enable impact assessment at population, community and ecosystem levels, and to determine whether there are consequences for processes, such as parasite transmission, where MPs could vector parasites or increase infection susceptibility. This knowledge will determine the extent to which MP pollution can be considered a major anthropogenic stressor of freshwaters in this era of global environmental change.
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The large data sets provided by in situ optical microscopes are allowing us to answer longstanding questions about the dynamics of planktonic ecosystems. To deal with the influx of information, while facilitating ecological insights, the design of these instruments increasingly must consider the data: storage standards, human annotation, and automated classification. In that context, we detail the design of the Scripps Plankton Camera (SPC) system, an in situ microscopic imaging system. Broadly speaking, the SPC consists of three units: (1) an underwater, free‐space, dark‐field imaging microscope; (2) a server‐based management system for data storage and analysis; and (3) a web‐based user interface for real‐time data browsing and annotation. Combined, these components facilitate observations and insights into the diverse planktonic ecosystem. Here, we detail the basic design of the SPC and briefly present several preliminary, machine‐learning‐enabled studies illustrating its utility and efficacy.
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As the global climate warms, the fate of lacustrine fish is of huge concern, especially given their sensitivity as ectotherms to changes in water temperature. The Arctic charr (Salvelinus alpinus L.) is a salmonid with a Holarctic distribution, with peripheral populations persisting at temperate latitudes, where it is found only in sufficiently cold, deep lakes. Thus, warmer temperatures in these habitats particularly during early life stages could have catastrophic consequences on population dynamics. Here, we combined lake temperature observations, a 1-D hydrodynamic model, and a multi-decadal climate reanalysis to show coherence in warming winter water temperatures in four European charr lakes near the southernmost limit of the species’ distribution. Current maximum and mean winter temperatures are on average ~ 1 °C warmer compared to early the 1980s, and temperatures of 8.5 °C, adverse for high charr egg survival, have frequently been exceeded in recent winters. Simulations of winter lake temperatures toward century-end showed that these warming trends will continue, with further increases of 3–4 °C projected. An additional 324 total accumulated degree-days during winter is projected on average across lakes, which could impair egg quality and viability. We suggest that the perpetuating winter warming trends shown here will imperil the future status of these lakes as charr refugia and generally do not augur well for the fate of coldwater-adapted lake fish in a warming climate.
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The ocean is a sink for~25% of the atmospheric CO 2 emitted by human activities, an amount in excess of 2 petagrams of carbon per year (PgC yr −1). Time-resolved estimates of global ocean-atmosphere CO 2 flux provide an important constraint on the global carbon budget. However, previous estimates of this flux, derived from surface ocean CO 2 concentrations, have not corrected the data for temperature gradients between the surface and sampling at a few meters depth, or for the effect of the cool ocean surface skin. Here we calculate a time history of ocean-atmosphere CO 2 fluxes from 1992 to 2018, corrected for these effects. These increase the calculated net flux into the oceans by 0.8-0.9 PgC yr −1 , at times doubling uncorrected values. We estimate uncertainties using multiple interpolation methods, finding convergent results for fluxes globally after 2000, or over the Northern Hemisphere throughout the period. Our corrections reconcile surface uptake with independent estimates of the increase in ocean CO 2 inventory, and suggest most ocean models underestimate uptake.
The combination of global warming and local stressors can have dramatic consequences on freshwater biota. Sediment deposition is an important pressure that can affect benthic species and benthic ontogenetic stages (eggs and larvae) habitat quality. However, knowledge on the effects of sediment in a warming context is lacking. We used a common garden approach to examine the effects of combined exposure to elevated temperature and deposited sediment on early life history traits in offspring of four wild arctic charr (Salvelinus alpinus) populations, originating from geographically isolated lakes at the Southern edge of the species range. We report interactive effects of temperature and sediment, with higher temperature exacerbating the negative effects of sediments on the duration of the incubation period and on the body size-yolk expenditure trade-off during development. Our results highlight that reevaluating the impacts of sediment on organisms under the lens of global warming and at the scale of several wild populations is needed to improve our understanding of how vulnerable species can respond to environmental changes.
The biodiverse Neotropical ecoregion remains insufficiently assessed, poorly managed, and threatened by unregulated human activities. Novel, rapid and cost-effective DNA-based approaches are valuable to improve understanding of the biological communities and for biomonitoring in remote areas. Here, we evaluate the potential of environmental DNA (eDNA) metabarcoding for assessing the structure and distribution of fish communities by analysing water and sediment from 11 locations along the Jequitinhonha River catchment (Brazil). Each site was sampled twice, before and after a major rain event in a five-week period and fish diversity was estimated using high-throughput sequencing of 12S rRNA amplicons. In total, 252 Molecular Operational Taxonomic Units (MOTUs) and 34 fish species were recovered, including endemic, introduced, and previously unrecorded species for this basin. Spatio-temporal variation of eDNA from fish assemblages was observed and species richness was nearly twice as high before the major rain event compared to afterwards. Yet, peaks of diversity were primarily associated with only four of the locations. No correlation between β-diversity and longitudinal distance or presence of dams was detected, but low species richness observed at sites located near dams might that these anthropogenic barriers may have an impact on local fish diversity. Unexpectedly high α-diversity levels recorded at the river mouth suggest that these sections should be further evaluated as putative “eDNA reservoirs” for rapid monitoring. By uncovering spatio-temporal changes, unrecorded biodiversity components, and putative anthropogenic impacts on fish assemblages, we further strengthen the potential of eDNA metabarcoding as a biomonitoring tool, especially in regions often neglected or difficult to access.