Watershed Alnus cover alters N:P stoichiometry and intensifies P limitation in subarctic streams

Denise A. Devotta, Jennifer M. Fraterrigo, Patrick B. Walsh, Stacey Lowe, Daniel K. Sewell, Daniel E. Schindler, Feng Sheng Hu

Research output: Contribution to journalArticlepeer-review


In many watersheds, nitrogen (N)-fixing alder (Alnus spp.) provides key nutrient subsidies to terrestrial and aquatic ecosystems. The importance of these subsidies may increase as alder cover expands under climate warming at high latitudes. We assessed how landscape features and meteorological conditions affect aquatic N and phosphorus (P) availability and stoichiometry in 26 streams across natural gradients of alder cover in southwestern Alaska over the spring and summer, covering 4 years. Analyses of resin lysimeter samples from select watersheds showed that annually, soils under alder leached almost three times more N, and two times more P than under non-alder vegetation. Stream NO3 concentrations displayed a non-linear relationship with alder cover; NO3 was low where alder cover was < 30%, but increased markedly where alder cover was > 30%. Watershed elevation was inversely related to alder cover, stream NO3 concentrations, and stream NO3 yields. Dissolved and particulate stream P were unrelated to alder cover, watershed elevation or discharge, highlighting decoupling of controls on P between terrestrial and aquatic ecosystems. Snowmelt-associated nutrient pulses and hydrology likely resulted in greater stream N and P in the spring, compared to the summer. However, weather parameters only impacted stream N via their interaction with alder. Stream DIN:TP increased with alder cover and decreased with elevation, suggesting that alder intensified P-limitation. Hence, aquatic P-limitation may become increasingly pronounced as climate-induced alder expansion continues. These results demonstrate that the elevational gradient in watershed alder cover determined spatial patterns in stream N availability and nutrient limitation.

Original languageEnglish (US)
Pages (from-to)155-176
Number of pages22
Issue number2
StatePublished - Apr 2021


  • Alaska
  • Alder
  • Nitrate
  • Phosphorus
  • Streams
  • Watershed biogeochemistry

ASJC Scopus subject areas

  • Environmental Chemistry
  • Water Science and Technology
  • Earth-Surface Processes


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