Nitrogen oxides in the firn air at Summit, Greenland

Measurements of NOx within the snowpack at Summit, Greenland were carried out from June 2008 to July 2010, using a novel system to sample firn air with minimal disruption of the snowpack. These long-term measurements were motivated by the need of improving the representation of air-snow interactions in global models. Results indicated that the NOx budget within the snowpack was on the order of 550 pptv as maximum, and was constituted primarily for NO2. NOx production was observed within the first 50 cm of the snowpack during the sunlight season between February and August. Presence of NOx at larger depths was attributed to high speed wind and vertical transport processes. Production of NO correlated with the seasonal incoming radiation profile, while NO2 maximum was observed in April. These measurements constitute the larger data set of NOx within the firn and will improve the representation of processes driving snow photochemistry at Summit.

Relationship between instream habitat characteristics, emergent insects, and riparian bird communities

Streams and riparian areas can be intricately connected via physical and biotic interactions that influence habitat conditions and supply resource subsidies between these ecosystems. Streambed characteristics such as the size of substrate particles influence the composition and the abundance of emergent aquatic insects, which can be an important resource for riparian breeding birds. We predict fine sediment abundance in small headwater streams directly affects the composition and number of emergent insects while it may indirectly affect riparian bird assemblages. Streams with abundant fine sediments that embed larger substrates should have lower emergence of large insects such as phemeroptera, Plecoptera and Trichoptera. Streams with lower emergent insect abundance are predicted to support fewer breeding birds and may lack certain bird species that specialize on aquatic insects. This study examined relationships between streambed characteristics, and emergent insects (composition, abundance and biomass), and riparian breeding birds (abundance and richness) along headwater streams of the Otter River Watershed. The stream bed habitats of seven stream reaches were characterized using longitudinal surveys. Malaise traps were deployed to sample emergent aquatic insects. Riparian breeding birds were surveyed using fixed-radius point-counts. Streams differed within a wide range of fine sediment abundances. Total emergent aquatic insect abundance increased as coverage by instream substrates increased in diameter, while bird community was unresponsive to insect or stream features. Knowledge of stream and riparian relationships is important for understanding of food webs in these ecosystems, and it is useful for riparian forest conservation and improving land-use management to reduce sediment pollution in these systems.