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Helton receives EPA STAR grant |
Ashley Helton, an Institute of Ecology Ph.D. student at the University of Georgia and student affiliate of Eco-metrics, Inc., has received a STAR Fellowship from the U.S. Environmental Protection Agency to support her doctoral research. This
prestigious award provides 3 years of salary support for Ashley
as well as discretionary research funds. Ashley's research will
investigate how hydrology interacts with the biological transformation of
nitrogen within streams to determine the fate and transport of excess
nitrogen in river networks.
According to the Environmental Protection Agency, excess nutrients (predominantly nitrogen and
phosphorous) are number 5 on the list of the 100 leading causes of
water quality impairment
in the United States. Recently,
other research has focused on biological utilization (“biological
uptake”) of nitrogen (N) as a mechanism that removes N from streams and
reduces N
export to receiving water bodies such as coastal ecosystems. This
riverine N removal is substantial: e.g., 50% removal of incoming N from
small streams (Peterson et al. 2001); 20% removal of total watershed N
(Van Breemen et al. 2002); 37-67% incoming N removed during transport
(Seitzinger et al. 2002). Thus, streams play an important role
in retaining and removing nutrients from the landscape.
Although recent research has focused on development and application of
techniques for determining biotic uptake rates, the ultimate fate
of this assimilated N is poorly documented. Some N is undoubtedly
removed from streams permanently via denitrification, but much of the
assimilated N may be stored temporarily and re-released to the
water column at a later time, such as during flood events.
Similarly, physical processes such as hyporheic exchange (the
bidirectional exchange of ground and surface water) also influence N
transport via physical storage of N and by facilitating biological
uptake. Thus, in order to predict and understand downstream
transport of N within stream networks, we must understand interactions
between the hydrologic dynamics, physiochemical conditions, and
biological processes that determine how N is removed from, stored
within, and re-released into streams.
The goal of Ashley's research is to
advance the understanding of in-stream N dynamics by
investigating: 1) how physical storage within the a stream’s hyporheic
(shallow groundwater) zone influences N transport rates though streams
networks and facilitates
biological uptake of N within stream networks; and 2) how the
biogeochemical context of N uptake influences the amount of N that is
stored within the stream vs. the amount of N permanently removed from
the stream via denitrification.
Ashley's findings should improve scientists' ability to understand how
N in streams is stored within, removed from, or ultimately released
downstream by river networks.
Literature Cited
- Peterson, B. J., W.M. Wollheim, P.J. Mulholland, J.R. Webster, J.L.
Meyer, J.L. Tank, E. Marti, W.B. Bowden, H.M. Valett, A.E. Hershey,
W.H. McDowell, W.K. Dodds, S.K. Hamilton, S. Gregory, and D.D. Morrall
(2001). Control of Nitrogen Export from Watersheds by Headwater
Streams. Science 292: 86-90.
- Seitzinger, S. P., R.V. Styles, E.W. Boyer, R.B. Alexander, G.
Billen, R.W. Howarth, B. Mayer and N. Van Breemen (2002). Nitrogen
retention in rivers: model development and application to
watersheds in the northeastern U.S.A. Biogeochemistry 57/58: 199-237.
- Van Breemen, N., E.W. Boyer, C.L. Goodale, N.A. Jaworski, K.
Paustian, S.P. Seitzinger, K. Lajtha, B. Mayer, D. Van Dam, R.W.
Howarth, K.J. Nadelhoffer, M. Eve, and G. Billen (2002). Where did all
the nitrogen go? Fate of nitrogen inputs to large watersheds in the
northeastern U.S.A. Biogeochemistry 57/58: 267-293.
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