Pelagic food web response to whole lake N fertilization

Deininger, Anne; Faithfull, Carolyn; Karlsson, Jan; Klaus, Marcus; Bergström, Ann‐Kristin

doi:10.1002/lno.10513

Cited by 19 publications

(36 citation statements)

References 80 publications

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“…Annual CO 2 emissions from our lakes were resilient to nutrient additions, despite a clear increase in gross primary production (GPP) following N fertilization (Deininger et al ). Theoretically, two mechanisms could explain our observations.…”

Section: Discussionmentioning

confidence: 91%

Weak response of greenhouse gas emissions to whole lake N enrichment

Klaus

Bergström

Jönsson

et al. 2017

Limnology & Oceanography

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Global warming and land use scenarios suggest increased 21st century nitrogen (N) inputs to aquatic systems. Nitrogen affects in‐lake processing and, potentially, atmospheric exchange of greenhouse gases, probably being most relevant in unproductive systems. Here, we test for the first time the effect of a whole‐lake experimental increase (threefold) in external nitrate loads on the atmospheric exchange of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from N‐limited unproductive boreal lakes. Nitrate enrichment effects were assessed within a paired Before/After‐Control/Impact framework based on 2‐hourly to biweekly surface‐water sampling of dissolved gas concentrations, and monthly whole‐lake inventory surveys, carried out over 4 yrs in six lakes. Nitrate enrichment did not affect gas exchange during summer stratification and whole‐lake gas inventories during summer and winter stratification. This finding specifically emphasizes the modest role of internal carbon fixation for the CO2 dynamics of unproductive boreal lakes. A global synthesis of 52 published studies revealed a wide range of nutrient fertilization effects, both in systems similar to our experimental lakes, and other more productive systems. Effects depended mainly on the spatiotemporal scale of the study and became more pronounced when N enrichment was combined with phosphorous. Conclusively, although short‐term and habitat‐specific effects can occur, changes in N supply have only weak whole‐ecosystem effects on greenhouse gas emissions from unproductive boreal lakes.

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Section: Discussionmentioning

confidence: 91%

Weak response of greenhouse gas emissions to whole lake N enrichment

Klaus

Bergström

Jönsson

et al. 2017

Limnology & Oceanography

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“…Even though brown lakes have phytoplankton species adapted to high‐DOM conditions, the already bacteria‐dominated food web will shift toward even greater bacterial dominance (Faithfull, Mathisen, Wenzel, Bergström, & Vrede, ). Accompanying this increase in bacterial biomass are declines in C:N and C:P ratios of the food for consumers as well as a decrease in food web transfer efficiency (Deininger, Faithfull, Karlsson, Klaus, & Bergstrom, ; Jansson, Karlsson, & Blomqvist, ) (Figure ). Currently, we do not know what threshold in DOM concentration marks this fundamental food web shift from reliance on autotrophic production to reliance on heterotrophic bacterial production supported by terrestrial DOM.…”

Section: Changes In Stoichiometry Affect Food Qualitymentioning

confidence: 99%

Global change‐driven effects on dissolved organic matter composition: Implications for food webs of northern lakes

Creed

Bergström

Trick

et al. 2018

Global Change Biology

270

213

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Northern ecosystems are experiencing some of the most dramatic impacts of global change on Earth. Rising temperatures, hydrological intensification, changes in atmospheric acid deposition and associated acidification recovery, and changes in vegetative cover are resulting in fundamental changes in terrestrial-aquatic biogeochemical linkages. The effects of global change are readily observed in alterations in the supply of dissolved organic matter (DOM)-the messenger between terrestrial and lake ecosystems-with potentially profound effects on the structure and function of lakes. Northern terrestrial ecosystems contain substantial stores of organic matter and filter or funnel DOM, affecting the timing and magnitude of DOM delivery to surface waters. This terrestrial DOM is processed in streams, rivers, and lakes, ultimately shifting its composition, stoichiometry, and bioavailability. Here, we explore the potential consequences of these global change-driven effects for lake food webs at northern latitudes. Notably, we provide evidence that increased allochthonous DOM supply to lakes is overwhelming increased autochthonous DOM supply that potentially results from earlier ice-out and a longer growing season. Furthermore, we assess the potential implications of this shift for the nutritional quality of autotrophs in terms of their stoichiometry, fatty acid composition, toxin production, and methylmercury concentration, and therefore, contaminant transfer through the food web. We conclude that global change in northern regions leads not only to reduced primary productivity but also to nutritionally poorer lake food webs, with discernible consequences for the trophic web to fish and humans.

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“…CO 2 concentrations in the vial headspace were analyzed using a gas chromatographer (Clarus 500; Perkin Elmer) equipped with a methanizer and a flame ionization detector (FID; Deininger et al. ). For N and P, analysis was performed following descriptions elsewhere (Bergström et al.…”

Section: Methodsmentioning

confidence: 99%

“…) using the same protocol outlined in (Deininger et al. ). Volumetric BP was measured using the [ 3 H]‐leucine incorporation method (Karlsson et al.…”

Section: Methodsmentioning

confidence: 99%

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Pelagic food webs of humic lakes show low short‐term response to forest harvesting

Deininger

Jönsson

Karlsson

et al. 2018

Ecological Applications

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Forest harvest in the boreal zone can increase the input of terrestrial materials such as dissolved organic carbon (DOC) and nitrate (NO3−) into nearby aquatic ecosystems, with potential effects on phytoplankton growth through enhanced nutrient (i.e., positive) or reduced light availability (i.e., negative), which may affect ecosystem productivity and consumer resource use. Here, we conducted forest clear‐cutting experiments in the catchments of four small, humic, and nitrogen‐limited unproductive boreal lakes (two controls and two clear‐cut, 18% and 44% of area cut) with one reference and two impact years. Our aim was to assess the effects of forest clear‐cutting on pelagic biomass production and consumer resource use. We found that pelagic biomass production did not change after two years of forest clear‐cutting: Pelagic primary and bacterial production (PP, BP), PP:BP ratio, chl a, and seston carbon (seston C) were unaffected by clear‐cutting; neither did tree harvest affect seston stoichiometry (i.e., N:phosphorus [P], C:P) nor induce changes in zooplankton resource use, biomass, or community composition. In conclusion, our findings suggest that pelagic food webs of humic lakes (DOC > 15 mg/L) might be resilient to a moderate form of forest clear‐cutting, at least two years after tree removal, before mechanical site preparation (e.g., mounding, plowing) and when leaving buffer strips along lakes and incoming streams. Thus, pelagic food web responses to forest clear‐cutting might not be universal, but could depend on factors such as the time scale, share of catchment logged, and the forest practices involved, including the application of buffer strips and site preparation.

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Pelagic food web response to whole lake N fertilization

Cited by 19 publications

References 80 publications

Weak response of greenhouse gas emissions to whole lake N enrichment

Weak response of greenhouse gas emissions to whole lake N enrichment

Global change‐driven effects on dissolved organic matter composition: Implications for food webs of northern lakes

Pelagic food webs of humic lakes show low short‐term response to forest harvesting

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