Benoît is an aquatic ecologist with two research areas: (i) biodiversity and ecosystem functions primarily through the lens of river metabolism (photosynthesis and respiration) integrated with food webs (nodes connectivity, trophic transfer efficiencies), nutrient cycling (C, N, P), hydrology and hydraulics (advection-dispersion); (ii) species distribution models to run climate and nutrient scenarios on the distribution of aquatic plants in North West Europe. Work is underway to generalise the models through the use of species traits in a phylogenetic context.

Benoît joined the freshwater ecology team at Bad Saarow to further investigate river metabolism and food web in the project MetaBoxWeb led by Janine Rüegg (https://www.b-tu.de/en/fg-gewaesseroekologie/team/staff/rueegg-janine) and Mario Brauns (https://www.ufz.de/index.php?en=39960), funded by the German Research Foundation (DFG).

Benoît led and participated in national and international research projects with fieldwork in Britain, Iceland, Kamchatka, Norway mostly funded by the Scottish Government's Rural and Environment Science and Analytical Services (RESAS), UK Natural Environment Research Council (NERC), Norwegian Research Council (NRC), and the European Union (EU).

River metabolism. The basic principle of using changes in dissolved oxygen between night and day to estimate photosynthesis and respiration is very simple, but can be surprisingly difficult to apply in real life situations. Thus, it is important to continue testing and developing novel open channel methods with dissolved oxygen sensors to infer photosynthesis and respiration of whole river reach, with associated uncertainties. Notable contributions from my work include dealing with spatial heterogeneity in natural channels using two (or multiple) stations (Demars et al 2011 Freshwater Biology), linking hydrology to metabolism with advection dispersion models (Pathak & Demars 2023 Journal of Geophysical Research: Biogeosciences), and inferring metabolism under total dissolved gas supersaturation downstream of hydropower plants (Demars & Dörsch 2023 Water Research).

Working with large natural ecosystems brings difficulties to test hypotheses and theories.  The use of robust survey designs can allow to make stronger inferences, e.g. (i) replicated comparative surveys to test the role of stream temperature on the metabolic balance (biotic CO2 emissions) of streams in Iceland and Kamchatka (Demars et al 2016 Nature Geoscience), (ii) before and after control impact (BACI) designs to test the role of waste water treatment plants effluent (Stutter et al 2010 Science of the Total Environment), and (iii) the role of dissolved organic carbon on ecosystem processes (nutrient cycling, metabolism and food web) in Scotland (Demars et al 2020 Ecological Monographs, Demars et al 2021 Ecosystems). 

Over the past decade, metabolism has been scaled from a few days to year-round estimates (e.g. Demars 2019 Limnology & Oceanography, Demars et al 2024 Science of the Total Environment), and from river reach to river basins. The sub-arctic is currently undergoing large landscape changes recovering from historical events under ongoing climatic changes. River carbon loss from CO2 emissions and dissolved organic carbon (DOC) fluxes are of the same order of magnitude as C sink on land, and thus play a fundamental role in our understanding of the global C cycle. Heterotrophic respiration, derived from stream metabolism, was used to quantify the proportion of land DOC respired in the river network under varying hydrological conditions, in the 16,000 km² River Tana in northern Norway, elucidating further C cycling at the interfaces of land – water – atmosphere (Demars et al in preparation). 

Food web. Whole stream metabolism approach and metabolic theory allowed to test predictions on trophic transfer efficiencies in stream food webs along a temperature gradient in Iceland (O’Gorman et al 2016 Global Change Biology). Flow food webs, the quantification of carbon and energy flows through the food web, and the use of C stable isotope ratios (including compound specific fatty acids) were able to unravel a novel microbial loop in streams where a substantial proportion of the CO₂ respired by bacteria contributes greatly to algae photosynthesis in the biofilm (Demars et al 2020 Ecological Monographs, Demars et al 2021 Ecosystems). Thus, the green and brown webs were found to be more tangled than previously thought. The approach was used to test the fate of C through the food web during browning events (river becoming more coloured following rainfall). Those experiments are critical to better understand the effect of climate change on carbon cycling and biodiversity. The extent towards which stream metabolism metrics could make predictions in food web properties remains to be further investigated.

Peer review papers

Stutter M., Jackson-Blake L., McGovern M-, D'Andrilli J., Junker J.R., Dörsch P., Watson H., Karlsen S.R. & Demars B.O.L. (2025) Riparian soils inform dissolved organic matter delivery in a Norwegian subarctic river. European Journal of Soil Science, 76, e70185.

Demars B.O.L., Schneider S.C., Thiemer K., Dörsch P., Pulg U., Stranzl S.F., Velle G. & Pathak D. (2024) Light and temperature controls of aquatic plant photosynthesis downstream of a hydropower plant and the effect of plant removal. Science of the Total Environment, 912, 169201.

Demars B.O.L. & Dörsch P. (2023) Estimation of ecosystem respiration and photosynthesis in supersaturated stream water downstream of a hydropower plant. Water Research, 247, 120842.

Pathak D. & Demars B.O.L. (2023) Metabolism modelling in rivers with unsteady flow conditions and transient storage zones. Journal of Geophysical Research: Biogeosciences, 128, e2022JG007245.

Mjelde M., Thrane J.-E., Demars B.O.L. (2023) High aquatic macrophyte diversity in Norwegian lakes north of the arctic circle. Freshwater Biology, 68, 509–522. 

Eriksen, T. E., Jacobsen D., Demars B.O.L., Brittain J.E., Søli G., and Friberg N. (2022) Effects of pollution-induced changes in oxygen conditions scaling up from individuals to ecosystems in a tropical river network. Science of the Total Environment, 814, 151958.

Thiemer K., Schneider S.C. & Demars B.O.L. (2021) Mechanical removal of macrophytes in freshwater ecosystems: implications for ecosystem structure and function. Science of the Total Environment, doi.org/10.1016/j.scitotenv.2021.146671

Demars B.O.L., Kemp J.L., Marteau B., Friberg N. & Thornton B. (2021) Stream macroinvertebrates and carbon cycling in tangled food webs. Ecosystems, doi.org/10.1007/s10021-021-00626-8

Moe T.F., Hessen D.O. & Demars B.O.L. (2021) Juncus bulbosus tissue nutrient concentrations and stoichiometry in oligotrophic ecosystems: variability with seasons, growth forms, organs and habitats. Plants, 10, 441

Clokie M.R.J., Blasdel B., Demars B.O.L. & Sicheritz-Pontén T. (2020) Rethinking phage ecology by rooting it within an established plant framework. Phage, 1, 121-136.

Demars B.O.L., Friberg N. & Thornton B. (2020) Pulse of dissolved organic matter alters reciprocal carbon subsidies between autotrophs and bacteria in stream food webs. Ecological Monographs, 90, e01399

Anglès d’Auriac M.B., Strand D.A., Mjelde M., Demars B.O.L. & Thaulow J. (2019) Detection of an invasive aquatic plant in natural water bodies using environmental DNA. PLOS One, 14, e0219700. 

Moe T.F., Hessen D.O. & Demars B.O.L. (2019) Functional biogeography: stoichiometry and thresholds for interpreting nutrient limitation in aquatic plants. Science of the Total Environment, 677, 447-455. 

Demars B.O.L. (2019) Hydrological pulses and burning of dissolved organic carbon by stream respiration. Limnology & Oceanography, 64, 406–421. 

Demars B.O.L., Gíslason G.M., Ólafsson J.S., Manson J.R., Friberg N., Hood J.M., Thompson J.J.D., Freitag T.E. (2016) Impact of warming on CO2 emissions from streams countered by aquatic photosynthesis. Nature Geoscience, 9, 758-761.

O’Gorman E.J., Ólafsson Ó.P., Demars B.O.L., Friberg N., Guðbergsson G., Hannesdóttir E.R., Jackson M.C., Johansson L.S., McLaughlin Ó.B., Ólafsson J.S., Woodward G., Gíslason G.M. (2016) Temperature effects on fish production across a natural thermal gradient. Global Change Biology, 22, 3206-3220.

Demars B.O.L., Thompson J., Manson J.R. (2015) Stream metabolism and the open diel oxygen method: principles, practice and perspectives. Limnology & Oceanography: Methods, 13, 356-374. 

Kosten S., Demars B.O.L., Moss B. (2014) Distinguishing autotrophic and heterotrophic respiration based on diel oxygen change curves: revisiting Dr. Faustus. Freshwater Biology, 59, 649-651.

Demars B.O.L., Wiegleb G., Harper D.M., Bröring U., Brux H., Herr W. (2014) Aquatic plant dynamics in lowland river networks: connectivity, management and climate change. Water, 6, 868-911. 

Demars B.O.L. & Manson J.R. (2013) Temperature dependence of stream aeration coefficients and the effect of water turbulence: a critical review. Water Research, 47, 1-15. 

Demars B.O.L. (2013) Uncertainties in biotic indicators and a corrigendum to Ponader et al. (2007): implications for biomonitoring. Ecological Indicators, 27, 44-47. 

Demars B.O.L., Potts J.M., Trémolières M., Thiébaut G, Gougelin N., Nordmann V. (2012) Aquatic macrophyte indices: not the Holy Grail! Freshwater Biology, 57: 1745–1759. 

Perkins D.M., Yvon-Durocher G., Demars B.O.L., Reiss J., Pichler D.E., Friberg N., Trimmer M. & Woodward G. (2012) Consistent temperature dependence of respiration across ecosystems contrasting in thermal history. Global Change Biology, 18, 1300–1311.

O’Gorman E.J., Pichler D.E., Adams G., Benstead J.P., Cohen H., Craig N., Cross W.F., Demars B.O.L., Friberg N., Gíslason G.M., Gudmundsdóttir R., Hawczak A., Hood J.M., Hudson L.N., Johansson L., Johansson M., Junker J.R., Laurila A., Manson J.R., Mavromati E., Nelson S., Ólafsson J.S., Perkins D.M., Petchey O., Plebani M., Reuman D.C., Rall B.C., Stewart R., Thompson M. & Woodward G. (2012) Impacts of warming on the structure and functioning of aquatic communities: individual- to ecosystem-level responses. Advances in Ecological Research, 47, 81-176.

Demars B.O.L., Kemp J.L., Friberg N., Usseglio-Polatera P. & Harper D.M. (2012) Linking biotopes to invertebrates in rivers: biological traits, taxonomic composition and diversity. Ecological Indicators, 23, 301–311. 

Bergfur J., Demars B.O.L., Stutter M.I., Langan S.J. & Friberg N. (2012) The Tarland catchment initiative and its effect on stream water quality and macroinvertebrate indices. Journal of Environmental Quality, 41, 314–321.

Demars B.O.L., Manson J.R., Ólafsson J.S., Gíslason G.M. & Friberg N. (2011) Stream hydraulics and temperature determine the metabolism of geothermal Icelandic streams. Knowledge and Management of Aquatic Ecosystems, 402, 05.

Demars B.O.L., Manson J.R., Ólafsson J.S., Gíslason G.M., Gudmundsdóttir R., Woodward G., Reiss J., Pichler D.E., Rasmussen J.J., Friberg N. (2011) Temperature and the metabolic balance of streams. Freshwater Biology, 56, 1106-1121.

Stutter M.I., Demars B.O.L. & Langan S.J. (2010) River phosphorus cycling: separating biotic and abiotic uptake during short-term changes in sewage effluent loading. Water Research, 44, 4425-4436.

Demars B.O.L. & Trémolières M. (2009) Aquatic macrophytes as bioindicators of carbon dioxide in groundwater fed rivers. Science of the Total Environment, 407, 4752-4763.

Demars B.O.L. & Edwards A.C. (2009) Distribution of aquatic macrophytes in contrasting river systems: a critique of compositional-based assessment of water quality. Science of the Total Environment, 407, 975-990.

Demars B.O.L. & Edwards A.C. (2008) Tissue nutrient concentrations in aquatic macrophytes: comparison across biophysical zones, surface water habitats and plant life forms. Chemistry & Ecology, 24: 413-422.

Demars B.O.L. (2008) Whole-stream phosphorus cycling: testing methods to assess the effect of saturation of sorption capacity on nutrient uptake length measurements. Water Research, 42, 2507-2516.

Demars B.O.L. & Thiébaut G. (2008) Distribution of aquatic macrophytes in the Northern Vosges rivers: implications for biomonitoring and conservation. Aquatic Conservation: Marine and Freshwater Ecosystems, 18, 619-632.

Stutter M.I., Langan S.J. & Demars B.O.L. (2007) River sediments provide a link between catchment pressures and ecological status in a mixed land use Scottish river system. Water Research, 41, 2803-2815.

Demars B.O.L. & Edwards A.C. (2007) Tissue nutrient content in freshwater aquatic macrophytes: high inter-taxa differences and low phenotypic response to nutrient supply Freshwater Biology, 52, 2073-2086.

Demars B.O.L. & Edwards A.C. (2007) A seasonal survey of surface water habitats within the River Spey basin, Scotland: major nutrient properties. Aquatic Conservation: Marine and Freshwater Ecosystems, 17, 565-583.

Demars B.O.L. & Harper D.M. (2005) Water column and sediment phosphorus in a calcareous lowland river and their differential response to point source control measures. Water, Air and Soil Pollution, 167, 273-293.

Demars B.O.L., Harper D.M., Pitt J. & Slaughter R. (2005) Impact of phosphorus control measures on in-river phosphorus retention associated with point source pollution. Hydrology and Earth Systems Sciences, 9, 43-55.

Demars B.O.L. & Harper D.M. (2005) Distribution of aquatic vascular plants in lowland rivers: separating the effects of local environmental conditions, longitudinal connectivity and river basin isolation. Freshwater Biology, 50, 418-437.

Demars B.O.L. & Gornall R.J. (2003) Identification of British Callitriche L. species by means of isozymes. Watsonia, 24, 389-399.

Demars B.O.L. & Harper D.M (2002) Phosphorus in a lowland calcareous river basin: a multiscale approach to understanding human impacts. International Journal of Ecohydrology & Hydrobiology, 2, 149-164.

Willby N.J., Abernethy V.J. & Demars B.O.L. (2000) An attribute-based classification of European hydrophytes and its relationship to habitat utilisation. Freshwater Biology, 43, 43-74.

Demars B.O.L. & Harper D.M. (1998) The aquatic macrophytes of an English lowland river system: assessing response to nutrient enrichment. Hydrobiologia, 384, 75-88.

Preprints and R scripts

Demars, B.O.L. (2024) European freshwater macroinvertebrate richness and abundance: alternative analyses and new findings. bioRxiv, https://doi.org/10.1101/2024.1108.1113.607735

Code availability: R script and data in public repository Github

https://github.com/benoit-demars73/Haase_2023

Solheim, A.L., Demars, B.O.L., Mjelde, M., Moe, J., Marmol-Guijarro, A., Mentzel, S., Thrane, J.-E., Rasmussen, J. and Dillinger, B. (2024) D5.3 Past-to-present EBV integrated datasets and status indicators using Water Framework Directive data streams for selected freshwater ecosystem types in the Habitats Directive. ARPHA Preprints 5, e128109. https://doi.org/10.3897/arphapreprints.e128109 

Code availability: R script and data in public repository Github benoit-demars73/EuropaBon (github.com)

Datasets

Demars B.O.L., Kemp, J.L., Friberg, N., Usseglio-Polatera, P., Harper, D.M., (2012). Macroinvertebrate abundance and proportion of trait categories in river biotopes across England and Wales. PANGAEA dataset #777728, https://doi.pangaea.de/10.1594/PANGAEA.777728 

Demars B.O.L. (2019): High frequency data for estimation of whole stream metabolism, 2007-2008, Glensaugh, Scotland. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.909277 

Stutter M., Jackson-Blake L., Lilly A., McGovern M., D'Andrilli J., Junker J., Dörsch P., Watson H., DemarsB.O.L. (2025). Soil description and nutrient chemistry data from the subarctic River Tana catchment (Finmark, Norway) collected as part of the project QUANTOM. Figshare, Dataset,  https://doi.org/10.6084/m9.figshare.28696835.v1 

Book chapters

Manson J.R., Wallis S.G., Demars, B.O.L., Mick J.D., Gíslason G.M., Ólafsson J.S., Friberg N. (2016) A comparison of three solute transport models using mountain stream tracer experiments. In: Hydrodynamic and Mass Transport at Freshwater Aquatic Interfaces; GeoPlanet: Earth and Planetary Sciences; Rowiński P.M., Marion A. (eds), Springer International Publishing, Switzerland, pp 77-90.

Gray C., Bista I., Creer S., Demars B.O.L., Falciani F., Monteith D.T., Sun X., Woodward G. (2015) Freshwater conservation and biomonitoring of structure and function: genes to ecosystems. In: Aquatic functional biodiversity: an ecological and evolutionary perspective, Belgrano A., Woodward G., Jacob U. (eds), Elsevier, Amsterdam, pp 241-271.

Wallis S.G., Manson J.R., Demars B.O.L. (2014) On the re-aeration coefficient in channels of complex shape. In: 7th International Conference on Fluvial Hydraulics: River Flow 2014, Ecole Polytechnique Fédérale de Lausanne, Switzerland; Schleiss A.J., De Cesare G., Franca M.J., Pfister M. (eds), CRC Press, London, pp 259-264.

Wallis S.G., Osuch M., Manson J.R., Romanowicz R., Demars B.O.L. (2013) On the estimation of solute transport parameters for rivers. Paper presented at 32nd International School of Hydraulics, Lochow, Poland, May 2012. Experimental and Computational Solutions of Hydraulic Problems, Rowinski P.M. (ed), Springer, pp 415-425.

Manson J.R., Demars B.O.L. & Wallis S.G. (2011) Integrated experimental and computational hydraulic science in a unique natural laboratory. In: Rowinski P. (ed.), Experimental methods in hydraulic research. Springer book series, Geoplanet: Earth and Planetary Sciences, Vol. 1, pp 123-131.

Zalewski, M., Harper D.M., Demars B.O.L., Jolánkai G., Crosa G., Janauer G.A. & Pacini N. (2008) Linking biological and physical processes at the river basin scale: the origins, scientific background and scope of ecohydrology. In: Harper D.M., Zalewski M. & Pacini N. (Eds) Ecohydrology: processes, models and case studies. CAB International, Wallingford, pp 1-17.