科研之友
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摘要
1. 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. 2. 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 PO43- concentrations predicted as the climate warms. 3. Our study consisted of an upstream reference reach and a downstream treatment reach where H3PO4 was experimentally added for two years (2011-2012; 0.3m increase). We used archived reference-reach data from 1983 to 2014 to assess discharge-chlorophyll relationships. 4. Mean biofilm gross primary production (GPP) in the reference reach during 2011 and 2012 was 15.42.2 (mean +/- S.E.) and 13.4 +/- 2.5mg Cm(-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 PO43- effects on mean biofilm chl-a biomass in the treatment reach. This treatment effect was associated with a parallel increase in GPP. 5. High biofilm activity in the Kuparuk River during the shoulder seasons indicates its potential significance to the energetics of arctic river ecosystems, particularly in the context of climate change. The related legacy effect' probably underlies the scope for rapid recovery of biofilm activity during the spring. Finally, increases in PO43- at concentrations predicted as the climate warms are likely to result in increases in summer biofilm biomass and metabolism. Further studies of biofilm processes during the shoulder seasons, and how these are affected by shifts in discharge, freezing dynamics and nutrient supply, are required for a comprehensive understanding of the effects of climate warming on arctic river ecosystems.
- 出版日期2015-11
