Changes in net ecosystem production over the past 40 years in arctic tundra ponds near Barrow, Alaska: Application of historic and modern techniques

Arctic environments have gained interest recently due to their sensitivity to climate change. As warming has created longer growing seasons, extended ice-free periods as well as permafrost thaw, the production in freshwater ecosystems has the potential to be greatly impacted. It is hypothesized that as climate change and warming occurs, increases in primary production will occur and ponds will become carbon sinks. Net ecosystem production (NEP) was determined using phytoplankton and periphyton samples collected weekly during the growing season (June–August) from arctic tundra ponds near Barrow, Alaska. Enrichment with 14C was used to determine both weekly photosynthetic rates and maximum rates of photosynthesis measured at multiple temperatures (8, 14 and 20°C) and light levels. All data collected from these experiments was compared to data collected in the 1970s. Free water metabolism was determined using a YSI logger installed in the pond throughout the growing seasons (2010-2). While there was no significant difference among phytoplankton NEP throughout the growing season in 1970-2 as compared to 2011-12, NEP was slightly higher during the latter half of the season in 2011-2. Photosynthesis – Irradiance (P-I) curves in 2012 did not reach maximum levels of photosynthesis at all temperature for phytoplankton or benthic algae; however, increases in maximum rates of photosynthesis appeared to have occurred. Free water metabolism showed positive net ecosystem production throughout the growing season in 2010-12 indicating the system to be net autotrophic. NEP, measured using both 14C and free water metabolism, increased substantially at a threshold level of chlorophyll that was regularly exceeded in 2008-12, but rarely observed in the 1970s (1.19-1.30 &mgr;g/L). As the growing season continues to increase in length due to climate change, these results suggest that algal primary production in arctic tundra ponds will increase and tundra ponds may become vital carbon sinks in northern latitudes