DOI: 10.5061/dryad.xwdbrv1gq
title: Dataset for: Tracking freshwater browning and coastal water darkening from boreal forests to the Arctic Ocean

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: 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  Data on Secchi disk measurements and salinity were available from 1) The 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    Data for salinity measurements were available from: 1) The 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) Baltic Nest Institute, https://nest.su.se Chlorophyll a concentrations were obtained based on a series of chlorophyll a estimates and measurements over the period 1912 to 2021. Chlorophyll a measurements were drawn from: 1) The 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) Baltic Nest Institute, https://nest.su.se 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&file=gcb14810-sup-0001-Supinfo.pdf  Freshwater discharge into the Norwegian Coastal Water between Skagerrak and the Barents Sea was drawn from The Norwegian Water Resources and Energy Directorate: https://sildre.nve.no/map   Spectral light absorption measurements in 13 western Norwegian lakes are described here https://doi.org/10.1007/s10021-014-9776-2
description: Metadata template[\[1\]](#_ftn1) for datasets of *L&O-Letters*
 articles \** ** **Table 1.** Description of the fields needed to describe
 the creation of your dataset. | **Title of dataset** | *Dataset for
 article "* Tracking freshwater browning and coastal water darkening
 from boreal forests to the Arctic Ocean\*"\* | |
 :---------------------------------------------------- |
 :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | **URL of dataset** | | | **Abstract** | *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.* | | **Keywords** | *TerraCoast, CDOM, coastal darkening, greening, browning, forest cover, light attenuation, freshwater, Baltic Sea, North Sea, Skagerrak, Norwegian Coastal Water* | | **Lead author for the dataset** | *Anders Frugård Opdal* | | **Title and position of lead author** | *Reseracher and Principle investigator* | | **Organization and address of lead author** | *Thormøhlens gate 53B, 5006 Bergen, Norway* | | **Email address of lead author** | ** | | **Additional authors or contributors to the dataset** | *Tom Andersen, Dag O. Hessen, Christian Lindemann, and Dag L. Aksnes* | | **Organization associated with the data** | *University of Bergen, University of Oslo, Wageningen University and Research, ICES, The Norwegian Water Resources and Energy Directorate, (NVE), Norwegian Environment Agency, Baltic Nest Institute, NOAA,* \*the Swedish Meteorological and Hydrological Institute, Marine Scotland, \* | | **Funding** | *Anders Frugård Opdal, TerraCoast, the Research Council of Norway, funding-ID 287490* | | **License** | ***[CC0](https://creativecommons.org/licenses/by/4.0/)*** | | **Geographic location – verbal description** | \*The Baltic Sea, North Sea, Skagerrak, Kattegat, and Norwegian Coastal Waters, as well land areas draining to these. The latter includes whole, or parts of, the following countries: Norway, Sweden, Finland, Estonia, Latvia, Lithuania, Poland, Czechia, Germany, Denmark, Netherlands, Belgium, Luxembourg, France, Switzerland and the UK.  \* | | **Geographic coverage bounding coordinates** | *Latitude: 45 °N – 72 °N* | | **Time frame - Begin date** | *Jan 1st 1900* | | **Time frame - End date** | *Dec 31st 2021* | | **General study design** | *The study is based on re-analyses of previously collected and published data. Links to appropriate data collection descriptions are provided in below Methods description and Table 3. Data provenance.* | | **Methods description** | *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/#](http://www.geo-informatie.nl/fuchs003/)), and the FAO Global Forest Resources Assessment database (/). For Norway, which is not part of the EU, forest cover was drawn from Norway’s national forest inventory available at [https://landsskog.nibio](https://landsskog.nibio/), and described in * | | **Laboratory, field, or other analytical methods** | \* \* | | **Taxonomic species or groups** | \* \* | | **Quality control** | \* \* | | **Additional information** | \* \* | **Table 2.** Data dictionary: description of the variables (i.e., columns) in EACH dataset. You must provide sufficient detail for another user to understand and use the data. If there are 10 variables (i.e., columns) in the dataset, then there should be 10 rows in this table that describe each column. Be sure to include all relevant information for your dataset, including the unique identifiers for your dataset or system, dates, replicate numbers, latitude and longitude of sampling locations, etc. Dataset filename: *Forest.txt* Dataset description: *Decadal estimates of forest cover in whole or parts of countries draining to the Baltic Sea, the North Sea, or the Skagerrak Sea.  This is a 2D matrix with 1 reference column ( col 1) and  1 reference row (row 1)* | **Column name** | **Description** | **Units** | **Code explanation** | **Data format** | **Missing data code** | | :-------------- | :------------------------------------------------------------------------------ | :-------- | :------------------- | :-------------- | :-------------------- | | *Country/year* | Country refer to column 1 | \*\* \*\* | \*\* \*\* | \*\* \*\* | \*\* \*\* | | *Country/year* | *Year refer to the top row and relates to the 2D matrix values in columns 2-14* | \* \* | \*\*\* \*\*\* | \* \* | \* \* | | *Matrix* | *Forest cover* | *km2* |   |   |   | Dataset filename: *Secchi.txt* Dataset description: *Secchi disk depth measurements in the Baltic Sea, Kattegat, Skagerak and North Sea* | **Column name** | **Description** | **Units** | **Code explanation** | **Data format** | **Missing data code** | | :-------------- | :------------------ | :-------- | :------------------- | :-------------- | :-------------------- | | *Year* | *Year* | \* \* | \*\*\* \*\*\* | \* \* | \* \* | | *Month* | *Month in year* |   |   |   |   | | *Day* | *Day of month* |   |   |   |   | | *Lat* | *Latitude* | °N |   |   |   | | *Lon* | *Longitude* | °E |   |   |   | | *Secchi* | *Secchi disk depth* | m |   |   |   |   Dataset filename: *Salinity.txt* Dataset description: S*alinity measurements in the Baltic Sea, Kattegat, Skagerak and North Sea* | **Column name** | **Description** | **Units** | **Code explanation** | **Data format** | **Missing data code** | | :-------------- | :-------------- | :-------- | :------------------- | :-------------- | :-------------------- | | *Year* | *Year* | \* \* | \*\*\* \*\*\* | \* \* | \* \* | | *Month* | *Month in year* |   |   |   |   | | *Day* | *Day of month* |   |   |   |   | | *Lat* | *Latitude* | °N |   |   |   | | *Lon* | *Longitude* | °E |   |   |   | | *Salinity* | *Salinity* | psu |   |   |   |   Dataset filename: *Chlorophyll.txt* Dataset description: *Chlorophyll a concentrations in the Baltic Sea, Kattegat, Skagerak and North Sea* | **Column name** | **Description** | **Units** | **Code explanation** | **Data format** | **Missing data code** | | :-------------- | :---------------------------------------------------------- | :-------- | :--------------------- | :-------------- | :-------------------- | | *Year* | *Year* | \*\* \*\* | \*\* \*\* | \*\* \*\* | \*\* \*\* | | *Month* | *Month in year* | \* \* | \*\*\* \*\*\* | \* \* | \* \* | | *Day* | *Day of month* |   |   |   |   | | *Lat* | *Latitude* | °N |   |   |   | | *Lon* | *Longitude* | °E |   |   |   | | *Chla* | *Chlorophyll a concentration* | mg m-3 |   |   |   | | *Sample* | *Type of method used to obtain chlorophyll a concentration* |   | 1 = direct measurement |   |   |   Dataset filename: *Lakes_light_absorption.txt* Dataset description: *Non-phytoplankton spectral light absorption in 13 lakes in Western Norway. This is a 2D matrix with reference 7 columns (col 1-7) and reference 1 row (row 1).* | **Column name** | **Description** | **Units** | **Code explanation** | **Data format** | **Missing data code** | | :--------------- | :------------------------------------------------------------------------------------------ | :-------- | :------------------- | :-------------- | :-------------------- | | *Lake name* | *Name of lake* | \* \* | \*\*\* \*\*\* | \* \* | \* \* | | Lake ID | Numeric identifier |   |   |   |   | | *Lat* | *Latitude* | °N |   |   |   | | *Lon* | *Longitude* | °E |   |   |   | | *Year* | *Year* |   |   |   |   | | *Month* | *Month in year* |   |   |   |   | | *Day/wavelength* | *Day* |   |   |   |   | | *Day/wavelength* | *Wavelength is denoted in the top row and relates to the 2D matrix values in columns 8-358* | nm |   |   |   | | *Matrix* | *Light absorption* | m-1 |   |   |   |   Dataset filename: *Catchment_discharge.txt* Dataset description: *Water discharge from catchment areas draining to the Norwegian Coastal Waters between Skagerrak and the Barents Sea* | **Column name** | **Description** | **Units** | **Code explanation** | **Data format** | **Missing data code** | | :-------------- | :---------------- | :-------- | :-------------------------------------------------------- | :-------------- | :-------------------- | | *Year* | *Year* | \* \* | \*\*\* \*\*\* | \* \* | \* \* | | *Month* | *Month in year* | \* \* | \* \* | \* \* |   | | *Day* | *Day of month* | \* \* | \* \* | \* \* |   | | *Catchm.* | *Catchment ID* | \* \* | *See Catchment boundary files for geographical locations* | \* \* |   | | *Discharge* | *Water discharge* | *m3 s-1* | \* \* | \* \* |   | Dataset filename: *Catchment_boundaries_Latitude.txt* Dataset description: *Latitudinal boundaries for the catchments* *draining to the Norwegian Coastal Waters between Skagerrak and the Barents Sea. This is a 2D matrix with 1reference column (col 1)* | **Column name** | **Description** | **Units** | **Code explanation** | **Data format** | **Missing data code** | | :------------------- | :-------------------------------- | :-------- | :------------------- | :-------------- | :-------------------- | | *Catchment/Latitude* | *Catchment ID refers to column 1* | \* \* | \*\*\* \*\*\* | \* \* | \* \* | | *Catchment/Latitude* | Latitudes for each catchment | °N |   |   |   | Dataset filename: *Catchment_boundaries_Longitude.txt* Dataset description: *Longitudinal boundaries for the catchments* *draining to the Norwegian Coastal Waters between Skagerrak and the Barents Sea. This is a 2D matrix with 1 reference column (col 1)* | **Column name** | **Description** | **Units** | **Code explanation** | **Data format** | **Missing data code** | | :-------------------- | :------------------------------- | :-------- | :------------------- | :-------------- | :-------------------- | | *Catchment/Longitude* | *Catchment ID refer to column 1* | \* \* | \*\*\* \*\*\* | \* \* | \* \* | | *Catchment/Longitude* | Longitudes for each catchment | °E |   |   |   |   Dataset filename: *Catchments_to_regions.txt* Dataset description: *List of catchments and the region to which they belong* | **Column name** | **Description** | **Units** | **Code explanation** | **Data format** | **Missing data code** | | :-------------- | :-------------- | :-------- | :------------------- | :-------------- | :-------------------- | | *Catchm.* | *Catchment ID* | \* \* | \*\*\* \*\*\* | \* \* | \* \* | | Region | Region ID |   |   |   |   | **Table 3. Data provenance** If you used data derived from other sources, provide the information here so future users know where the data came from. | **Dataset title** | **Dataset DOI or URL** | **Creator (name & email)** | | :----------------------------------------- | :-------------------------------------------------------------------------------- | :--------------------------------------------------- | | *Forest.txt (1900-2010)* | [http://www.geo-informatie.nl/fuchs003/#](http://www.geo-informatie.nl/fuchs003/) | Richard Fuchs | | *Forest.txt (2010-2020)* | . | FAO | | *Forest.txt (Norway)* | | Aksel Granhus | | *Secchi.txt (1903-2021)* | | Hjalte Parner, | | *Secchi.txt (1967-2021)* | | Emma Rova, | | *Secchi.txt (1979-2021)* | | Norwegian Environmental Agency | | *Secchi.txt(1903-1998)* | () | Thorkild Aarup | | *Secchi.txt (1903-1990)* | | Tim P. Boyer. | | *Salinity.txt (1903-2021)* | | Hjalte Parner, | | *Salinity.txt (1903-2021)* | | Emma Rova, | | *Salinity.txt (1979-2021)* | | Norwegian Environmental Agency | | *Salinity.txt (1965-2021)* | | Bo Gustafsson | | *Chlorophyll.txt (1961-2021)* | ) | Hjalte Parner, | | *Chlorophyll.txt (1970-2021)* | | Emma Rova, | | *Chlorophyll.txt (1979-2021)* | | Norwegian Environmental Agency | | *Chlorophyll.txt (1965-2021)* | | Bo Gustafsson | | *Chlorophyll.txt (PCI, 1949-2017)* | | David Johns | | *Chlorophyll.txt (CellCount,  1912, 1946)* | | Anders F. Opdal, | | *Lakes\_light\_absorption.txt* | | Tom Andersen | | *Catchment\_discharge.txt* | | Stein Beldring | | *Catchment\_boundaries\_Latitude.txt* | | The Norwegian Water Resources and Energy Directorate | | *Catchment\_boundaries\_Longitude.txt* | | The Norwegian Water Resources and Energy Directorate | *Scripts/code (software) –* *OPTIONAL* It is recommended that you also provide your scripts along with your data, although it is not required at this time in our journal. | **File name** | **Description** | **Scripting language** | | :----------------------------- | :------------------------------------------------------------ | :--------------------- | | *Particle\_tracking\_code.txt* | *Code used to run the OpenDrift Lagrangian particle tracking* | *Python* | |   |   |   | **Notes and Comments:**                                --- ***[\[1\]](#_ftnref1)** This document liberally borrows from a similar document provided by the Environmental Data Initiative*