Overview: We
are
investigating the controls on nitrogen (N) cycling throughout the
Ipswich River watershed in northeastern Massachusetts. The
Ipswich
River watershed landuse is a mix of urban, agrictultural, and reference
types. To understand how aquatic networks control N exports, we
require knowledge of what controls N reactivity across the entire range
of river sizes that comprise the river network. Much research has been
devoted to quantifying N cycle processes in small headwater streams,
with a recent emphasis on denitrification. It remains unknown whether
the controls in
small streams apply to larger river reaches. In particular, the role of
the hyporheic zone is potentially critical, yet scaling rules
describing changes in transient storage zone/hyporheic
characteristics and associated N cycle processes have yet to be
determined.Specific Objectives:
1) Characterize the major interactions involving surface water hydraulics, hyporheic flow and nitrate concentrations in regulating rates of aquatic denitrification and nitrate retention across stream orders;
2) Determine how the spatial distribution of denitrification and nitrate retention interacts with the distribution of nitrate inputs to define river network control of N exports to the coastal zone.
Location: Our field sites are within the Ipswich River watershed in Massachusetts (www.mass.gov).
