DOI: 10.5061/dryad.vx0k6djvs
title: Landscape determinants of lake benthic and pelagic primary production

description: Global change affects gross primary production (GPP) in benthic and
 pelagic habitats of northern lakes by influencing catchment
 characteristics and lake water biogeochemistry. However, how changes in
 key environmental drivers manifest and impact total (i.e., benthic +
 pelagic) GPP and the partitioning of total GPP between habitats, here
 represented by the benthic share (autotrophic structuring) is unclear.
 This dataset presentes compiled data on summer gross primary productivity
 (GPP) in benthic and pelagic habitats sampled in situ between 2005-2017,
 together with water chemistry, from 26 shallow lakes (maximum 3.7-15.8 m
 deep) from three different sites in northern Sweden, located in the Arctic
 (Norrbotten), subarctic (Jämtland) and boreal (Västerbotten) biomes. The
 three study regions have variable elevation gradients and vegetation
 cover. The study lakes cover a wide range of DOC (1.5-16.3 mg·L-1) and
 accompanied water physico-chemistry. Using this dataset, we investigate
 how catchment properties (air temperature, land cover, hydrology) affect
 lake physico-chemistry and patterns of total GPP and autotrophic
 structuring. We find that total GPP was mostly light limited, due to high
 dissolved organic carbon (DOC) concentrations originating from catchment
 soils with coniferous vegetation and wetlands, which is further promoted
 by high catchment runoff. In contrast, autotrophic structuring related
 mostly to the relative size of the benthic habitat, and was potentially
 modified by CO2 fertilization. Across Arctic and subarctic sites, DIC and
 CO2 were unrelated to DOC, indicating that external inputs of inorganic
 carbon can influence lake productivity patterns independent of terrestrial
 DOC supply. By comparison, DOC and CO2 were correlated across boreal
 lakes, suggesting that DOC mineralization acts as an important CO2 source
 for these sites. Our results underline that GPP as a resource is regulated
 by landscape properties, and is sensitive to large-scale global changes
 (warming, hydrological intensification, recovery of acidification) that
 promote changes in catchment characteristics and aquatic
 physico-chemistry. Our findings aid in predicting global change impacts on
 autotrophic structuring, and thus community structure and resource use of
 aquatic consumers in general. Given the similarities of global changes
 across the Northern hemisphere, our findings are likely relevant for
 northern lakes globally. 
description: Database accompanying arcticle "Landscape determinants of
 pelagic and benthic primary production in northern lakes" with
 pelagic and benthic GPP<sub>z</sub> rates, and
 GPP<sub>lake-average</sub> with physico-chemical data for each
 lake.  <strong>Sampling, lake water
 physico-chemistry and bathymetry</strong> Water
 chemistry, PAR and temperature were measured on the same dates as GPP
 measurements. PAR and temperature were measured from the surface to the
 bottom with 1m depth intervals at the deepest part of the lake, with
 additional measurements at 0.25m and 0.5m using a handheld probe. Light
 attenuation coefficients (Kd) of the lake water were calculated as the
 absolute slope of natural logarithmically transformed photosynthetically
 active radiation (PAR) against depth. The sum of incoming PAR over the day
 was retrieved from stations we installed next to the lake. We used the
 water temperature measured at 0.2m depth (Twater) as proxy for lake
 epilimnion temperatures. Average air temperatures one month before
 sampling (Tair) were retrieved from weather stations (extracted from
 https://www.smhi.se) situated closest (within a range of 60km) to the
 sampling sites, and we included a temperature decrease of 0.57°C per 100m
 elevation difference between station and sampling site (sensu Karlsson et
 al., 2005 and references therein). Water samples for measuring pH,
 dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), total
 nitrogen (TN) and phosphorus (TP) were taken at 1m depth (epilimnion), or
 in nine cases from composite water samples (unstratified lakes). pH was
 measured directly after sampling and CO<sub>2</sub>
 concentrations in the lake water were calculated from DIC, pH and
 temperature . In brief, DOC was filtered through a 0.45µm filter (Sarstedt
 Filtropur), acidified with HCl to an end concentration of 12 mM, and
 stored in a refrigerator before analyzed. TN and TP (unfiltered) samples
 were kept frozen until analysis. The DIC concentration was calculated from
 the headspace CO<sub>2</sub> concentration in closed vials
 containing acidified lake water according to Åberg et al. (2007), and were
 analyzed as soon as possible. More details and specific lab operating
 procedures afterwards can be found in Appendix S1 accompanying the
 msnuscript. Detailed lake bathymetry was acquired through integrated GPS
 and echo-sounding depth measurements, from which we calculated lake
 average depth (z<sub>avg</sub>), lake volumes and areas (as a
 whole, or in different sections), as well as the relative areal size of
 the littoral benthic habitat
 (%A<sub>littoral</sub>).
 <strong>Gross primary production
 (GPP)</strong> GPP was measured between 21 June
 and 28 July in variable years between 2005-2017 in situ in the benthic and
 pelagic on the same date. Benthic GPP was measured using the Dome-method
 (subarctic) or the DIC-method (Arctic and boreal). For the DIC-method,
 intact sediment cores with overlaying water were collected in incubation
 tubes using a gravity corer on three or five depths, and incubated for
 about 24h at the depth of collection. GPP rates at the discrete depths
 were measured by tracking changes in DIC concentrations between the onset
 and end of the incubation period in sealed off dark (respiration (R)) or
 transparent (R+GPP) tubes. In the Dome-method, three transparent domes
 equipped with a miniDOT oxygen logger were gently placed on the sediment
 at a different depth each, and O<sub>2</sub> metabolism of the
 separated sediment area was measured for 24 hours. Benthic GPP rates at
 the three discrete depths were derived from net ecosystem production (NEP)
 using the R-package Lake Metabolizer (Winslow et al., 2016) and by
 assuming that GPP equals NEP plus R (by assuming R is oxygen loss during
 dark period; 24h metabolism). Pelagic GPP was measured at the surface,
 0.25m, 0.5m and at following 1m depth intervals, where the deepest
 measurement depended on the lake depth and water turbidity. Measurements
 were done by incubating transparent glass bottles in situ filled with
 water from the sampling depth, with additional incubations in dark bottles
 at the most shallow and deepest measurements, for about four hours around
 noon using a <sup>14</sup>C isotopic tracer. The GPP values
 measured for 4 hours midday at varying depths were converted to daily
 values by relating the midday measurements to the ratio of incident PAR
 during incubation time in relation to the daily PAR (24h). We used
 averages for duplicate or triplicate measurements of pelagic and benthic
 rates. An average lake GPP (mg
 C·m<sup>-2</sup>·day<sup>-1</sup>) was calculated
 for the benthic (benthic GPP<sub>lake-average</sub>) and
 pelagic (pelagic GPP<sub>lake-average</sub>) habitat. Benthic
 and pelagic GPP daily rates at discrete depths were upscaled to a lake
 average per m<sup>2</sup> (benthic- and pelagic
 GPPlake-average; mg
 C·m<sup>-2</sup>·day<sup>-1</sup>) by integrating
 the GPP rates over the corresponding lake surface (benthic) or lake volume
 (pelagic) per depth interval, and relating the sum to the total lake area.
 The total average GPP of the lake (total GPPlake-average) is expressed as
 the sum of benthic and pelagic GPPlake-average (mg
 C·m<sup>-2</sup>·day<sup>-1</sup>), and
 autotrophic structuring is expressed as the relative amount (%) of GPP
 that takes place in the benthic habitat.