Tracking freshwater browning and coastal water darkening from boreal forests to the Arctic Ocean
Creators: name: Opdal, Anders Frugård
name: Andersen, Tom
name: Hessen, Dag Olav
name: Lindemann, Christian
name: Aksnes, Dag L.
Publisher: name: Zenodo
Year: 2023
Subjects: CDOM
coastal darkening
greening
browning
Forest cover
light attenuation
freshwater
Baltic Sea
Skagerrak
Norwegian Coastal Water

description: The forest cover of Northern Europe has been steadily expanding during the last 120 years. More terrestrial vegetation and carbon fixation leads to more export to surface waters. This may cause freshwater browning, as more degraded plant-litter ends up as chromophoric (coloured) dissolved organic matter. Although most freshwater ultimately drains to coastal waters, the link between freshwater browning and coastal water darkening is poorly understood. Here, we explore this relationship through a combination of centennial records of forest and coastal water clarity, contemporary optical measurements in lakes and coastal waters, as well as an ocean drift model. We suggest a link between forest cover in Northern Europe and coastal water clarity in the Baltic, Kattegat and Skagerrak Sea and show how brown coloured freshwater from Northern European catchments can dictate coastal water clarity across thousands of kilometres, from the Baltic lakes to the Barents Sea.
description: Funding provided by: Norges Forskningsråd<br>Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100005416<br>Award Number: 287490
description: <em>The forest cover data was retrieved from the Historic Land Dynamics Assessment (HILDA) database provided by the Department of Geoinformation Science and Remote Sensing, Wageningen University, Netherlands (http://www.geo-informatie.nl/fuchs003/#), and the FAO Global Forest Resources Assessment database (https://fra-data.fao.org/WO/fra2020/home/). For Norway, which is not part of the EU, forest cover was drawn from Norway's national forest inventory available at https://landsskog.nibio, and described in https://doi.org/10.1186/s40663-020-00261-0 </em> <em> </em> <em>Data on Secchi disk measurements and salinity were available from</em> 1) The <em>International Council for the Exploration of the Sea, https://data.ices.dk; 2) Swedish Meteorological and Hydrological Institute, https://www.smhi.se/data; 3) Norwegian Environment Agency, https://vannmiljo.miljodirektoratet.no; 4) Secchi disk archive www.ices.dk/data/ (Aarup 2002); 5) World Ocean Database, https://www.ncei.noaa.gov/products/world-ocean-database </em> <em> </em> <em>Data for salinity measurements weere available from:</em> 1) The <em>International Council for the Exploration of the Sea, https://data.ices.dk; 2) Swedish Meteorological and Hydrological Institute, https://www.smhi.se/data; 3) Norwegian Environment Agency, https://vannmiljo.miljodirektoratet.no; 4)</em> Baltic Nest Institute, https://nest.su.se <em> </em> <em>Chlorophyll a concentrations were obtained based on a series of chlorophyll a estimates and measurements over the period 1912 to 2021. </em> <em>Chlorophyll a measurements were drawn from: </em> 1) The <em>International Council for the Exploration of the Sea, https://data.ices.dk; 2) Swedish Meteorological and Hydrological Institute, https://www.smhi.se/data; 3) Norwegian Environment Agency, https://vannmiljo.miljodirektoratet.no; 4)</em> Baltic Nest Institute, https://nest.su.se <em> </em> <em>Chlorophyll a estimates were based on two additional sources 1) phytoplankton colour indices (PCI) sampled by continuous plankton recorders and converted to chlorophyll a concentrations, and 2) chlorophyll a concentrations derived from individual cell counts in 1948 and 1912. Detailed methods are found here: https://onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1111%2Fgcb.14810&amp;file=gcb14810-sup-0001-Supinfo.pdf </em> <em> </em> <em>Freshwater discharge into the Norwegian Coastal Water between Skagerrak and the Barents Sea was drawn from The Norwegian Water Resources and Energy Directorate:</em> <em>https://sildre.nve.no/map </em> <em> </em> <em>Spectral light absorption measurements in 13 western Norwegian lakes are described here </em>https://doi.org/10.1007/s10021-014-9776-2