Maria Myrstener

Maria Myrstener, PhD

Email: maria.myrstener@slu.se

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Research Summary

The main focus of my research is nutrient dynamics in running waters in the Boreal and Arctic. It means that I integrate ecology, physical geography, hydrology and chemistry. I am interested in drivers of productivity and biogeochemical interactions between primary producers and their environment. In my PhD project I try to answer questions about fundamental aquatic ecological processes such as drivers of productivity and use of resources, in a landscape under rapid change due to climate warming. More specifically, I study how nutrients and carbon are utilized and cycled within arctic and boreal freshwaters and how it effects productivity changes over the course of the year.

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Project Summary

Ecosystem Dynamics in Arctic Streams

In my PhD project I answered questions about basic ecological processes such as drivers of productivity and use of resources in freshwaters, in a landscape under rapid change due to climate warming. I believe running waters warrant more research attention because they are biogeochemical hotspots within the landscape and they effect on cycling of elements, species diversity and also keep many social services. In my project I want to learn what limits growth in arctic freshwaters and how nutrients are utilized and cycled within those ecosystems. I am also curios about learning how different seasons are connected to each other through resources, species and physical drivers. For example, how much the growing season productivity relies on legacy from previous winter?

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Collaborators

Ryan Sponseller, Umeå University
Reiner Giesler, Umeå University
Ann-Kristin Bergström, Umeå University
Ryan M. Burrows, Griffith University, Brisbane, Australia
Steven A. Thomas, University of Nebraska–Lincoln, Nebraska, United States
Lluís Gomez Gener, École Polytechnique Fédérale de Lausanne, Switzerland

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Photos From the Field

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 Maria Myrstener's Publications

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  2023 (1)

Contrasting impacts of warming and browning on periphyton. Callisto Puts, I.; Ask, J.; Myrstener, M.; and Bergström, A. Limnology and Oceanography Letters, 8(4): 628–638. 2023. Publisher: John Wiley & Sons
Paper   doi   link   bibtex   abstract  

@article{callisto_puts_contrasting_2023,
	title = {Contrasting impacts of warming and browning on periphyton},
	volume = {8},
	url = {https://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-205740},
	doi = {10.1002/lol2.10317},
	abstract = {We tested interactive effects of warming (+2°C) and browning on periphyton accrual and pigment composition when grown on a synthetic substrate (plastic strips) in the euphotic zone of 16 experiment ...},
	language = {eng},
	number = {4},
	urldate = {2024-03-26},
	journal = {Limnology and Oceanography Letters},
	author = {Callisto Puts, Isolde and Ask, Jenny and Myrstener, Maria and Bergström, Ann-Kristin},
	year = {2023},
	note = {Publisher: John Wiley \& Sons},
	pages = {628--638},
}

We tested interactive effects of warming (+2°C) and browning on periphyton accrual and pigment composition when grown on a synthetic substrate (plastic strips) in the euphotic zone of 16 experiment ...

  2022 (1)

Resolving the Drivers of Algal Nutrient Limitation from Boreal to Arctic Lakes and Streams. Myrstener, M.; Fork, M. L.; Bergström, A.; Puts, I.; Hauptmann, D.; Isles, P. D. F.; Burrows, R. M.; and Sponseller, R. A. Ecosystems (New York. Print), 25: 1682–1699. 2022. Publisher: Springer-Verlag New York
Paper   doi   link   bibtex   abstract  

@article{myrstener_resolving_2022,
	title = {Resolving the {Drivers} of {Algal} {Nutrient} {Limitation} from {Boreal} to {Arctic} {Lakes} and {Streams}},
	volume = {25},
	url = {https://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-194276},
	doi = {10.1007/s10021-022-00759-4},
	abstract = {Nutrient inputs to northern freshwaters are changing, potentially altering aquatic ecosystem functioning through effects on primary producers. Yet, while primary producer growth is sensitive to nut ...},
	language = {eng},
	urldate = {2024-03-26},
	journal = {Ecosystems (New York. Print)},
	author = {Myrstener, Maria and Fork, Megan L. and Bergström, Ann-Kristin and Puts, Isolde and Hauptmann, Demian and Isles, Peter D. F. and Burrows, Ryan M. and Sponseller, Ryan A.},
	year = {2022},
	note = {Publisher: Springer-Verlag New York},
	pages = {1682--1699},
}

Nutrient inputs to northern freshwaters are changing, potentially altering aquatic ecosystem functioning through effects on primary producers. Yet, while primary producer growth is sensitive to nut ...

  2021 (2)

Nutrients influence seasonal metabolic patterns and total productivity of Arctic streams. Myrstener, M.; Gómez-Gener, L.; Rocher-Ros, G.; Giesler, R.; and Sponseller, R. A. Limnology and Oceanography, 66(S1): S182–S196. 2021. _eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/lno.11614
Paper   doi   link   bibtex   abstract  

@article{myrstener_nutrients_2021,
	title = {Nutrients influence seasonal metabolic patterns and total productivity of {Arctic} streams},
	volume = {66},
	copyright = {© 2020 The Authors. Limnology and Oceanography published by Wiley Periodicals LLC on behalf of Association for the Sciences of Limnology and Oceanography.},
	issn = {1939-5590},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/lno.11614},
	doi = {10.1002/lno.11614},
	abstract = {The seasonality of gross primary production (GPP) in streams is driven by multiple physical and chemical factors, yet incident light is often thought to be most important. In Arctic tundra streams, however, light is available in saturating amounts throughout the summer, but sharp declines in nutrient supply during the terrestrial growing season may constrain aquatic productivity. Given the opposing seasonality of these drivers, we hypothesized that “shoulder seasons”—spring and autumn—represent critical time windows when light and nutrients align to optimize rates of stream productivity in the Arctic. To test this, we measured annual patterns of GPP and biofilm accumulation in eight streams in Arctic Sweden. We found that the aquatic growing season length differed by 4 months across streams and was determined largely by the timing of ice-off in spring. During the growing season, temporal variability in GPP for nitrogen (N) poor streams was correlated with inorganic N concentration, while in more N-rich streams GPP was instead linked to changes in phosphorus and light. Annual GPP varied ninefold among streams and was enhanced by N availability, the length of ice-free period, and low flood frequency. Finally, network scale estimates of GPP highlight the overall significance of the shoulder seasons, which accounted for 48\% of annual productivity. We suggest that the timing of ice off and nutrient supply from land interact to regulate the annual metabolic regimes of nutrient poor, Arctic streams, leading to unexpected peaks in productivity that are offset from the terrestrial growing season.},
	language = {en},
	number = {S1},
	urldate = {2024-03-26},
	journal = {Limnology and Oceanography},
	author = {Myrstener, Maria and Gómez-Gener, Lluís and Rocher-Ros, Gerard and Giesler, Reiner and Sponseller, Ryan A.},
	year = {2021},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/lno.11614},
	keywords = {\#nosource},
	pages = {S182--S196},
}

The seasonality of gross primary production (GPP) in streams is driven by multiple physical and chemical factors, yet incident light is often thought to be most important. In Arctic tundra streams, however, light is available in saturating amounts throughout the summer, but sharp declines in nutrient supply during the terrestrial growing season may constrain aquatic productivity. Given the opposing seasonality of these drivers, we hypothesized that “shoulder seasons”—spring and autumn—represent critical time windows when light and nutrients align to optimize rates of stream productivity in the Arctic. To test this, we measured annual patterns of GPP and biofilm accumulation in eight streams in Arctic Sweden. We found that the aquatic growing season length differed by 4 months across streams and was determined largely by the timing of ice-off in spring. During the growing season, temporal variability in GPP for nitrogen (N) poor streams was correlated with inorganic N concentration, while in more N-rich streams GPP was instead linked to changes in phosphorus and light. Annual GPP varied ninefold among streams and was enhanced by N availability, the length of ice-free period, and low flood frequency. Finally, network scale estimates of GPP highlight the overall significance of the shoulder seasons, which accounted for 48% of annual productivity. We suggest that the timing of ice off and nutrient supply from land interact to regulate the annual metabolic regimes of nutrient poor, Arctic streams, leading to unexpected peaks in productivity that are offset from the terrestrial growing season.

Nitrogen supply and physical disturbance shapes Arctic stream nitrogen uptake through effects on metabolic activity. Myrstener, M.; Thomas, S. A.; Giesler, R.; and Sponseller, R. A. Freshwater Biology, 66(8): 1502–1514. August 2021. Publisher: John Wiley & Sons, Ltd
Paper   doi   link   bibtex   abstract  

@article{myrstener_nitrogen_2021,
	title = {Nitrogen supply and physical disturbance shapes {Arctic} stream nitrogen uptake through effects on metabolic activity},
	volume = {66},
	issn = {0046-5070},
	url = {https://doi.org/10.1111/fwb.13734},
	doi = {10.1111/fwb.13734},
	abstract = {Abstract Climate change in the Arctic is altering the delivery of nutrients from terrestrial to aquatic ecosystems. The impact of these changes on downstream lakes and rivers is influenced by the capacity of small streams to retain such inputs. Given the potential for nutrient limitation in oligotrophic Arctic streams, biotic demand should be high, unless harsh environmental conditions maintain low biomass standing stocks that limit nutrient uptake capacity. We assessed the drivers of nutrient uptake in two contrasting headwater environments in Arctic Sweden: one stream draining upland tundra and the other draining an alluvial valley with birch forest. At both sites, we measured nitrate (NO3?) uptake biweekly using short-term slug releases and estimated rates of gross primary production (GPP) and ecosystem respiration from continuous dissolved oxygen measurements. Catchment characteristics were associated with distinct stream chemical and biological properties. For example, the tundra stream maintained relatively low NO3? concentrations (average: 46 µg N/L) and rates of GPP (0.2 g O2 m?2 day?1). By comparison, the birch forest stream was more NO3? rich (88 µg N/L) and productive (GPP: 1.7 g O2 m?2 day?1). These differences corresponded to greater areal NO3? uptake rate and increased NO3? use efficiency (as uptake velocity) in the birch forest stream (max 192 µg N m?2 min?1 and 96 mm/hr) compared to its tundra counterpart (max 52 µg N m?2 min?1 and 49 mm/hr) during 2017. Further, different sets of environmental drivers predicted temporal patterns of nutrient uptake at these sites: abiotic factors (e.g. NO3? concentration and discharge) were associated with changes in uptake in the tundra stream, while metabolic activity was more important in the birch forest stream. Between sites, variation in uptake metrics suggests that the ability to retain pulses of nutrients is linked to nutrient supply regimes controlled at larger spatial and temporal scales and habitat properties that promote biomass accrual and thus biotic demand. Overall, constraints on biotic potential imposed by the habitat template determined the capacity of these high latitude streams to respond to future changes in nutrient inputs arising from climate warming or human land use. ?},
	number = {8},
	urldate = {2023-07-22},
	journal = {Freshwater Biology},
	author = {Myrstener, Maria and Thomas, Steven A. and Giesler, Reiner and Sponseller, Ryan A.},
	month = aug,
	year = {2021},
	note = {Publisher: John Wiley \& Sons, Ltd},
	keywords = {Arctic, catchment, metabolism, nutrient uptake, tundra},
	pages = {1502--1514},
}

Abstract Climate change in the Arctic is altering the delivery of nutrients from terrestrial to aquatic ecosystems. The impact of these changes on downstream lakes and rivers is influenced by the capacity of small streams to retain such inputs. Given the potential for nutrient limitation in oligotrophic Arctic streams, biotic demand should be high, unless harsh environmental conditions maintain low biomass standing stocks that limit nutrient uptake capacity. We assessed the drivers of nutrient uptake in two contrasting headwater environments in Arctic Sweden: one stream draining upland tundra and the other draining an alluvial valley with birch forest. At both sites, we measured nitrate (NO3?) uptake biweekly using short-term slug releases and estimated rates of gross primary production (GPP) and ecosystem respiration from continuous dissolved oxygen measurements. Catchment characteristics were associated with distinct stream chemical and biological properties. For example, the tundra stream maintained relatively low NO3? concentrations (average: 46 µg N/L) and rates of GPP (0.2 g O2 m?2 day?1). By comparison, the birch forest stream was more NO3? rich (88 µg N/L) and productive (GPP: 1.7 g O2 m?2 day?1). These differences corresponded to greater areal NO3? uptake rate and increased NO3? use efficiency (as uptake velocity) in the birch forest stream (max 192 µg N m?2 min?1 and 96 mm/hr) compared to its tundra counterpart (max 52 µg N m?2 min?1 and 49 mm/hr) during 2017. Further, different sets of environmental drivers predicted temporal patterns of nutrient uptake at these sites: abiotic factors (e.g. NO3? concentration and discharge) were associated with changes in uptake in the tundra stream, while metabolic activity was more important in the birch forest stream. Between sites, variation in uptake metrics suggests that the ability to retain pulses of nutrients is linked to nutrient supply regimes controlled at larger spatial and temporal scales and habitat properties that promote biomass accrual and thus biotic demand. Overall, constraints on biotic potential imposed by the habitat template determined the capacity of these high latitude streams to respond to future changes in nutrient inputs arising from climate warming or human land use. ?

  2020 (2)

Stream metabolism controls diel patterns and evasion of CO $_{\textrm{2}}$ in Arctic streams. Rocher‐Ros, G.; Sponseller, R. A.; Bergström, A.; Myrstener, M.; and Giesler, R. Global Change Biology, 26(3): 1400–1413. March 2020.
Paper   doi   link   bibtex   abstract  

@article{rocherros_stream_2020,
	title = {Stream metabolism controls diel patterns and evasion of {CO} $_{\textrm{2}}$ in {Arctic} streams},
	volume = {26},
	issn = {1354-1013, 1365-2486},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.14895},
	doi = {10.1111/gcb.14895},
	abstract = {Streams play an important role in the global carbon (C) cycle, accounting for a large portion of CO2 evaded from inland waters despite their small areal coverage. However, the relative importance of different terrestrial and aquatic processes driving CO2 production and evasion from streams remains poorly understood. In this study, we measured O2 and CO2 continuously in streams draining tundra-dominated catchments in northern Sweden, during the summers of 2015 and 2016. From this, we estimated daily metabolic rates and CO2 evasion simultaneously and thus provide insight into the role of stream metabolism as a driver of C dynamics in Arctic streams. Our results show that aquatic biological processes regulate CO2 concentrations and evasion at multiple timescales. Photosynthesis caused CO2 concentrations to decrease by as much as 900 ppm during the day, with the magnitude of this diel variation being strongest at the low-turbulence streams. Diel patterns in CO2 concentrations in turn influenced evasion, with up to 45\% higher rates at night. Throughout the summer, CO2 evasion was sustained by aquatic ecosystem respiration, which was one order of magnitude higher than gross primary production. Furthermore, in most cases, the contribution of stream respiration exceeded CO2 evasion, suggesting that some stream reaches serve as net sources of CO2, thus creating longitudinal heterogeneity in C production and loss within this stream network. Overall, our results provide the first link between stream metabolism and CO2 evasion in the Arctic and demonstrate that stream metabolic processes are key drivers of the transformation and fate of terrestrial organic matter exported from these landscapes.},
	language = {en},
	number = {3},
	urldate = {2020-03-19},
	journal = {Global Change Biology},
	author = {Rocher‐Ros, Gerard and Sponseller, Ryan A. and Bergström, Ann‐Kristin and Myrstener, Maria and Giesler, Reiner},
	month = mar,
	year = {2020},
	keywords = {\#nosource},
	pages = {1400--1413},
}

Streams play an important role in the global carbon (C) cycle, accounting for a large portion of CO2 evaded from inland waters despite their small areal coverage. However, the relative importance of different terrestrial and aquatic processes driving CO2 production and evasion from streams remains poorly understood. In this study, we measured O2 and CO2 continuously in streams draining tundra-dominated catchments in northern Sweden, during the summers of 2015 and 2016. From this, we estimated daily metabolic rates and CO2 evasion simultaneously and thus provide insight into the role of stream metabolism as a driver of C dynamics in Arctic streams. Our results show that aquatic biological processes regulate CO2 concentrations and evasion at multiple timescales. Photosynthesis caused CO2 concentrations to decrease by as much as 900 ppm during the day, with the magnitude of this diel variation being strongest at the low-turbulence streams. Diel patterns in CO2 concentrations in turn influenced evasion, with up to 45% higher rates at night. Throughout the summer, CO2 evasion was sustained by aquatic ecosystem respiration, which was one order of magnitude higher than gross primary production. Furthermore, in most cases, the contribution of stream respiration exceeded CO2 evasion, suggesting that some stream reaches serve as net sources of CO2, thus creating longitudinal heterogeneity in C production and loss within this stream network. Overall, our results provide the first link between stream metabolism and CO2 evasion in the Arctic and demonstrate that stream metabolic processes are key drivers of the transformation and fate of terrestrial organic matter exported from these landscapes.

The role of nutrients for stream ecosystem function in Arctic landscapes : drivers of productivity under environmental change. Myrstener, M. Ph.D. Thesis, Umeå University, Umeå, Sweden, 2020. Publisher: Umeå universitet
Paper   link   bibtex   abstract  

@phdthesis{myrstener_role_2020,
	address = {Umeå, Sweden},
	type = {Doctoral {Thesis}},
	title = {The role of nutrients for stream ecosystem function in {Arctic} landscapes : drivers of productivity under environmental change},
	shorttitle = {The role of nutrients for stream ecosystem function in {Arctic} landscapes},
	url = {http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-177439},
	abstract = {Arctic and sub-Arctic freshwaters are currently experiencing substantial ecosystem changes due to the effects of global warming. Global warming effects on these freshwaters include increasing water ...},
	language = {eng},
	urldate = {2021-01-18},
	school = {Umeå University},
	author = {Myrstener, Maria},
	collaborator = {Sponseller, Ryan A. and Giesler, Reiner and Bergström, Ann-Kristin},
	year = {2020},
	note = {Publisher: Umeå universitet},
	keywords = {\#nosource},
}

Arctic and sub-Arctic freshwaters are currently experiencing substantial ecosystem changes due to the effects of global warming. Global warming effects on these freshwaters include increasing water ...

  2018 (1)

Persistent nitrogen limitation of stream biofilm communities along climate gradients in the Arctic. Myrstener, M.; Rocher-Ros, G.; Burrows, R. M.; Bergström, A.; Giesler, R.; and Sponseller, R. A. Global Change Biology, 24(8): 3680–3691. 2018. _eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1111/gcb.14117
Paper   doi   link   bibtex   abstract  

@article{myrstener_persistent_2018,
	title = {Persistent nitrogen limitation of stream biofilm communities along climate gradients in the {Arctic}},
	volume = {24},
	copyright = {© 2018 John Wiley \& Sons Ltd},
	issn = {1365-2486},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.14117},
	doi = {10.1111/gcb.14117},
	abstract = {Climate change is rapidly reshaping Arctic landscapes through shifts in vegetation cover and productivity, soil resource mobilization, and hydrological regimes. The implications of these changes for stream ecosystems and food webs is unclear and will depend largely on microbial biofilm responses to concurrent shifts in temperature, light, and resource supply from land. To study those responses, we used nutrient diffusing substrates to manipulate resource supply to biofilm communities along regional gradients in stream temperature, riparian shading, and dissolved organic carbon (DOC) loading in Arctic Sweden. We found strong nitrogen (N) limitation across this gradient for gross primary production, community respiration and chlorophyll-a accumulation. For unamended biofilms, activity and biomass accrual were not closely related to any single physical or chemical driver across this region. However, the magnitude of biofilm response to N addition was: in tundra streams, biofilm response was constrained by thermal regimes, whereas variation in light availability regulated this response in birch and coniferous forest streams. Furthermore, heterotrophic responses to experimental N addition increased across the region with greater stream water concentrations of DOC relative to inorganic N. Thus, future shifts in resource supply to these ecosystems are likely to interact with other concurrent environmental changes to regulate stream productivity. Indeed, our results suggest that in the absence of increased nutrient inputs, Arctic streams will be less sensitive to future changes in other habitat variables such as temperature and DOC loading.},
	language = {en},
	number = {8},
	urldate = {2024-03-27},
	journal = {Global Change Biology},
	author = {Myrstener, Maria and Rocher-Ros, Gerard and Burrows, Ryan M. and Bergström, Ann-Kristin and Giesler, Reiner and Sponseller, Ryan A.},
	year = {2018},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1111/gcb.14117},
	keywords = {\#nosource, Arctic, Bioassay, Biofilm, Climate Change, Co-limitation, Nitrogen limitation, Nutrient addition, Stream productivity, bioassay, biofilm, climate change, colimitation, nitrogen limitation, nutrient addition, stream productivity},
	pages = {3680--3691},
}

Climate change is rapidly reshaping Arctic landscapes through shifts in vegetation cover and productivity, soil resource mobilization, and hydrological regimes. The implications of these changes for stream ecosystems and food webs is unclear and will depend largely on microbial biofilm responses to concurrent shifts in temperature, light, and resource supply from land. To study those responses, we used nutrient diffusing substrates to manipulate resource supply to biofilm communities along regional gradients in stream temperature, riparian shading, and dissolved organic carbon (DOC) loading in Arctic Sweden. We found strong nitrogen (N) limitation across this gradient for gross primary production, community respiration and chlorophyll-a accumulation. For unamended biofilms, activity and biomass accrual were not closely related to any single physical or chemical driver across this region. However, the magnitude of biofilm response to N addition was: in tundra streams, biofilm response was constrained by thermal regimes, whereas variation in light availability regulated this response in birch and coniferous forest streams. Furthermore, heterotrophic responses to experimental N addition increased across the region with greater stream water concentrations of DOC relative to inorganic N. Thus, future shifts in resource supply to these ecosystems are likely to interact with other concurrent environmental changes to regulate stream productivity. Indeed, our results suggest that in the absence of increased nutrient inputs, Arctic streams will be less sensitive to future changes in other habitat variables such as temperature and DOC loading.

  2016 (1)

The effects of temperature and resource availability on denitrification and relative N2O production in boreal lake sediments. Myrstener, M.; Jonsson, A.; and Bergström, A. Journal of Environmental Sciences, 47: 82–90. September 2016. 00000
Paper   doi   link   bibtex   abstract  

@article{myrstener_effects_2016,
	title = {The effects of temperature and resource availability on denitrification and relative {N2O} production in boreal lake sediments},
	volume = {47},
	issn = {1001-0742},
	url = {https://www.sciencedirect.com/science/article/pii/S1001074216300328},
	doi = {10.1016/j.jes.2016.03.003},
	abstract = {Anthropogenic environmental stressors (like atmospheric deposition, land use change, and climate warming) are predicted to increase inorganic nitrogen and organic carbon loading to northern boreal lakes, with potential consequences for denitrification in lakes. However, our ability to predict effects of these changes is currently limited as northern boreal lakes have been largely neglected in denitrification studies. The aim of this study was therefore to assess how maximum potential denitrification and N2O production rates, and the relationship between the two (relative N2O production), is controlled by availability of nitrate (NO3−), carbon (C), phosphorus (P), and temperature. Experiments were performed using the acetylene inhibition technique on sediments from a small, nutrient poor boreal lake in northern Sweden in 2014. Maximum potential denitrification and N2O production rates at 4°C were reached already at NO3− additions of 106–120 μg NO3−–N/L, and remained unchanged with higher NO3 amendments. Higher incubation temperatures increased maximum potential denitrification and N2O production rates, and Q10 was somewhat higher for N2O production (1.77) than for denitrification (1.69). The relative N2O production ranged between 13\% and 64\%, and was not related to NO3− concentration, but the ratio increased when incubations were amended with C and P (from a median of 16\% to 27\%). Combined, our results suggests that unproductive northern boreal lakes currently have low potential for denitrification but are susceptible to small changes in NO3 loading especially if these are accompanied by enhanced C and P availability, likely promoting higher N2O production relative to N2.},
	urldate = {2017-02-08},
	journal = {Journal of Environmental Sciences},
	author = {Myrstener, Maria and Jonsson, Anders and Bergström, Ann-Kristin},
	month = sep,
	year = {2016},
	note = {00000},
	keywords = {\#nosource, Acetylene, DOC, NO3, Nitrous oxide ratio, Sediment, carbon},
	pages = {82--90},
}

Anthropogenic environmental stressors (like atmospheric deposition, land use change, and climate warming) are predicted to increase inorganic nitrogen and organic carbon loading to northern boreal lakes, with potential consequences for denitrification in lakes. However, our ability to predict effects of these changes is currently limited as northern boreal lakes have been largely neglected in denitrification studies. The aim of this study was therefore to assess how maximum potential denitrification and N2O production rates, and the relationship between the two (relative N2O production), is controlled by availability of nitrate (NO3−), carbon (C), phosphorus (P), and temperature. Experiments were performed using the acetylene inhibition technique on sediments from a small, nutrient poor boreal lake in northern Sweden in 2014. Maximum potential denitrification and N2O production rates at 4°C were reached already at NO3− additions of 106–120 μg NO3−–N/L, and remained unchanged with higher NO3 amendments. Higher incubation temperatures increased maximum potential denitrification and N2O production rates, and Q10 was somewhat higher for N2O production (1.77) than for denitrification (1.69). The relative N2O production ranged between 13% and 64%, and was not related to NO3− concentration, but the ratio increased when incubations were amended with C and P (from a median of 16% to 27%). Combined, our results suggests that unproductive northern boreal lakes currently have low potential for denitrification but are susceptible to small changes in NO3 loading especially if these are accompanied by enhanced C and P availability, likely promoting higher N2O production relative to N2.