DOI: 10.5061/dryad.1zcrjdg2w
title: Data from: The key role of nitrogen in boosting algal growth in Arctic rivers

description: Increasing nutrient loads are impairing water quality and the ecological
 status of aquatic ecosystems globally, but their effects on Arctic
 freshwaters remain less studied. Nutrients in Arctic freshwaters are
 increasing due to expanding anthropogenic land use and climate change
 induced alterations in nutrient leaching and transport. Also, increased
 occurrences of non-native semelparous Pacific pink salmon (Oncorhynchus
 gorbuscha) in the northern European rivers can enhance nutrient
 availability. These additional nutrients may be readily available for
 aquatic primary producers in often inherently (ultra-)oligotrophic Arctic
 freshwaters. We used an experimental field set-up with nutrient diffusing
 substrates to study temporal and spatial differences in the response of
 primary producers to increased phosphorus (P) and nitrogen (N) levels in
 Arctic rivers. Additional NO3-N enhanced algal growth (chlorophyll-a
 (Chl-a) amount) of epilithic biofilm. PO4-P alone had no effect,
 indicating N as the primary limiting factor for algal growth. This was
 particularly evident in autumn, while early summer showed evidence for
 secondary P limitation. The response to nutrient additions was mostly
 dictated by the background availability of inorganic N. Our results
 suggest that Arctic rivers are highly sensitive to nutrient additions,
 especially N. Thus, any increase in nutrients can boost algal growth,
 causing cascading effects throughout Arctic
 ecosystems.     
description: The study was conducted within the Teno River catchment in
 northern Finland. In total, 18 spatially independent study sites were
 selected from the catchment area based on their location and size (1st,
 3rd and 5-6th order). We used Nutrient Diffusing Substrates (NDS) to test
 the reactivity of epilithic algal communities to additional nutrients and,
 consequently, to identify the resources limiting algal productivity. The
 experiment was conducted in 2022 and replicated at the same study sites
 twice: June-July and August-September. NDS were prepared following the
 instructions by Tank et al. (2006; Methods in Stream Ecology. Elsevier,
 pp. 213-238) with minor adjustments. Sets of NDS cups (each treatment
 replicated four times) were incubated in the rivers for 23 – 26 and 25 –
 29 days in early summer (13.6.-13.7.2022) and autumn (15.8.-16.9.2022),
 respectively. After each incubation period tiles were removed from the NDS
 cups and stored in a dark cold box until freezing to -20°C within the same
 day. To obtain chl-a from the tiles we used acetone extraction following
 closely the protocol presented in Steinman et al. (2017; Methods in Stream
 Ecology. Elsevier, pp. 223–241). Extraction was done separately for each
 tile resulting in four replicates per treatment per site and per
 time. 
description: # Data from: The key role of nitrogen in boosting algal growth in Arctic
 rivers
 [https://cdnsciencepub.com/doi/full/10.1139/as-2024-0074](https://u4974989.ct.sendgrid.net/ls/click?upn=u001.ADulCZCq7orTe-2BMo0jHv-2B91GmmGVFCA18qfFXmjM0Hfuk-2F-2Ba7RmpjBezrGOEYG8Xd9l-2FKUaJCxzMZBG50RQAxg-3D-3DA3bL_RdMqDRA62AVQYCz3mJJTdVuKH8tac7IsTH-2F3c7bu0AXQH-2Bt48x-2FJbpJFgDTpO5CnO9ZZL8Ln-2BTcD-2FtlWS7aD3FDzqpMd8ocmJyup8PLK-2ByylTt6htTbJKVJEW-2FgWwIIiB68pY9-2FSVHSr2nwupEK-2FKm6CxISuNv3bwx6m0b8I-2FLK41750C7SgQY5nAljtoDrzJ3k4HWhMH3IjbAnlaUdvDqIOkxo-2B-2BYpvGLnGyD-2FvHyXrfWj0nGoBbtc1XPXIOzTp6jNlNxv96eLyJ-2BjGBce2gbRgFDQxtBpCSbQlzp16vDQ-3D) ## Description of the data and file structure Use of nutrient diffusing substrates to study the reactivity of epilithic algae to additional nutrients across a network of various-sized Arctic rivers at the two extremes of a growing season: early summer and autumn. ### Files and variables #### File: NDS\_data\_Huttunen\_et\_al\_rev2.xlsx **Description:** The xlsx-file includes four sheets i) the measured (non-transformed) Chl-a values as total amounts and as daily values; ii) location of the study sites; iii) incubation periods; and iv) environmental data.   ##### Sheet 1 (Chl-a values) * Includes the values for the response variables. Chl-a values are given for each replicate (block) separately.  * Sample = sample code including information for site, treatment and block * Treatment = C (control), N (nitrogen), P (phosphorus), NP (nitrogen & phosphorus) * Season =  indicates the season (Early summer vs. Autumn) * Area = defines the geographic area, from each area we sampled one small, one intermediate and one large river * Site = defines the study river * Size = defines the size of the study river based on Strahler stream order (1 = small, 3 = intermediate, 5-6 = large) * Block = defines the within-site replicates (4 for each treatment / site / season)  * chl_a_total = total amount of Chl-a (μg/cm2) in a sample  * chl_a_per_day  = daily amount of Chl-a (μg/cm2/day) in a sample, i.e., total Chl-a divided by the number of incubation days ##### Sheet 2 (Location) * Gives information on the location of the study sites * River_name = full name of the study river * Area (see above) * Site (see above) * Size (see above) * N = latitude (ETRS TM35)   * E = longitude (ETRS TM35)   ##### Sheet 3 (Incubation days) * Gives information on the timing and duration of the study * Site (see above) * Season (see above) * Start_date = the date of commencement of the treatments (dd.m.yyyy) * End_date = the date of closing the treatments (dd.m.yyyy) * Number_of_full_days = the number of full days for the incubation (used to calculate chl_a_per_day on Sheet 1) ##### Sheet 4 (Environmental data) * Gives information on the explanatory / descriptive variables * River_name (see above) * Size (see above) * Site (see above) * Catchment_area_km2 = size of the catchment area (km^2)  * Urban_and_agricultural_areas_% = cover of urban and agricultural area within the catchment area (%) * Simpsons_substrate_diversity = the value for Simpson's substrate diversity used to describe the heterogeneity of the substrate (range 0-1; high values indicate high heterogeneity) * Bryophyte_cover_% = average percentage cover of stream bryophytes (%) * Stream_velocity_ms = average stream velocity measured as meters per second (m/s) * Scrapers_% = percentage of invertebrates defined as scrapers regarding their feeding habits (%) * Collector_gatherers_%  = percentage of invertebrates defined as collector-gatherers regarding their feeding habits (%) * Water_temperature_C_summer = average water temperature (°C) during the early summer sampling period * Water_temperature_C_autumn = average water temperature (°C) during the autumn sampling period * Light_intensity_lux_summer = average light intensity (lux) during the early summer sampling period * Light_intensity_lux_autumn = average light intensity (lux) during the early summer sampling period * pH_summer = pH value in the water chemistry analysis for the early summer samples  * pH_autumn =  pH value in the water chemistry analysis for the autumn samples * PO4_ugL_summer = PO4 (phosphate, ug/L) value in the water chemistry analysis for the early summer samples * PO4_ugL_autumn = PO4 (phosphate, ug/L) value in the water chemistry analysis for the autumn samples * DIN_ugL_summer = DIN (dissolved inorganic nitrogen, i.e. NO2+ NO3+NH4, ug/L) value in the water chemistry analysis for the early summer samples * DIN_ugL_autumn = DIN (dissolved inorganic nitrogen, i.e. NO2+ NO3+NH4, ug/L) value in the water chemistry analysis for the autumn samples ## Code/software saved as an Excel file with four separate sheets: i) chl-a data; ii) location of the study sites; iii) incubation periods; and iv) environmental data ## Access information Data was derived from the following source: Collected from the field by the authors