General Background:
- Small, headwater streams have been associated with substantial denitrification and nitrogen uptake.
- Previous studies have shown that streams vary markedly in their ability to cycle nitrogen, yet streams that have high removal rates may be important nitrogen sinks across the landscape.
- Intermittent streams, which flow continuously for extended periods in the spring and fall, can also be important elements of stream networks in certain physiographic and climate conditions, but the extent, structure and function of these intermittent streams are poorly understood.
- We hypothesize that intermittent streams bordered by forested riparian vegetation have long retention times, shallow depths and interaction with labile C, creating conditions favorable for substantial N removal.
Our Approach:
- Examined six forested intermittent streams located in glacial till deposits of southern New England.
- Estimated the hydroperiod (the extent of time with continuous flow) using an array of temperature sensing ibuttons within the channel.
- Used slug tests with bromide and nitrate-N to characterize N removal, flow rates and stream velocity of each stream.
- Characterized the structural elements (e.g., pools, riffles, runs) within each reach.
- Denitrification enzyme activity (DEA) of sediments in debris dams, pools, and runs was measured in the autumn of 2011.
Preliminary Results:
We found evidence of water in the stream channel on 80 to 95% of the days from winter to mid-summer of 2010. Flow rates ranged from 0.3 to 16.7 L/sec across all seasons. We observed N removal capacities ranging from 0 to 5.5 kg N per month over a 100 m reach of stream, with each site displaying elevated N removal capacity in at least one slug test. Pools were found to be hotspots of N removal with the highest DEA (mean = 1299 mg kg-1 h-1). Since pool volumes were only 2 to 11 % of the total reach volume, hyporheic flow is likely to be important in increasing residence time and processing N.
Take-Home Message:
To maintain the N removal potential of intermittent streams, preserving the woody structure of the riparian area will be critical as these ecosystems are built on woody structure - debris dam formation for pool establishment and root networks that create opportunities for hyporheic exchange.
Related posters:
Talk will be presented at the 2012 AWRA Summer Specialty Conference, June 2012.
Two page project summary for EPSCoR (pdf)
Undergraduate poster at URI Coastal Fellows' event 2011 (pdf): Progress as of Nov 2011
Undergraduate poster at URI Coastal Fellows' event 2010 (pdf): Progress os of Nov 2010 (placed 2nd in poster competition)
