Discharge, legacy effects and nutrient availability as determinants of temporal patterns in biofilm metabolism and accrual in an arctic river

• Published in: Freshwater Biology
• Main Authors: Kendrick, Michael R., Huryn, Alexander D.
• Other Authors: National Science Foundation, E.O. Wilson Biodiversity Foundation
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2015
• Subjects: Arctic; Alaska
• Online Access: http://dx.doi.org/10.1111/fwb.12659; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Ffwb.12659; https://onlinelibrary.wiley.com/doi/pdf/10.1111/fwb.12659; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/fwb.12659

Summary Significant changes in the timing of thawing and freezing, annual discharge and nutrient supply are anticipated for arctic river ecosystems due to climate warming. Our understanding of the effects of such changes, however, is poor. Since biofilms are both critical to ecosystem processes and subject to control by combinations of freezing dynamics, discharge and nutrient supply, the effects of climate warming on arctic river ecosystems may be substantial. We studied biofilm accrual and metabolism in the Kuparuk River of Alaska with three objectives. First, we assessed biofilm activity during the open‐water season, including the poorly known ‘shoulder seasons’ (periods shortly after the spring thaw and then before autumn freezing). Second, we assessed how discharge and freezing dynamics may affect temporal patterns in biofilm activity. Third, we assessed biofilm response to increases in concentrations predicted as the climate warms. Our study consisted of an upstream reference reach and a downstream treatment reach where H 3 PO 4 was experimentally added for two years (2011–2012; ˜0.3 μ m increase). We used archived reference‐reach data from 1983 to 2014 to assess discharge–chlorophyll relationships. Mean biofilm gross primary production ( GPP ) in the reference reach during 2011 and 2012 was 15.4 ± 2.2 (mean ± S.E.) and 13.4 ± 2.5 mg C m −2 h −1 , respectively, with spring shoulder season values being significantly higher than the summer values that are more routinely measured. An analysis of a 31‐year record from the reference reach revealed that biofilm chlorophyll biomass was significantly ( R 2 = 0.39, P < 0.001) related to the discharge regime of the previous summer. This ‘legacy effect’ is attributable to bedfast ice within the river channel during winter that protects biofilms from scour during the spring thaw. Before–after‐control–impact ( BACI ) analysis showed significant and positive effects on mean biofilm chl‐ a biomass in the treatment reach. This treatment effect was associated with a ...