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Dynamics of stream nitrate sources and flow pathways during stormflows on urban, forest and agricultural watersheds in central Pennsylvania, USA
Author(s) -
Buda Anthony R.,
DeWalle David R.
Publication year - 2009
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/hyp.7423
Subject(s) - baseflow , storm , hydrology (agriculture) , surface runoff , watershed , environmental science , streamflow , surface water , drainage basin , geology , ecology , geography , cartography , geotechnical engineering , machine learning , environmental engineering , computer science , biology , oceanography
Understanding the influence of storm events on nitrate (NO 3 − ) dynamics is important for efficiently managing NO 3 − pollution. In this study, five sites representing a downstream progression of forested uplands underlain by resistant sandstone to karst lowlands with agricultural, urban and mixed land‐use were established in Spring Creek, a 201 km 2 mixed land‐use watershed in central Pennsylvania, USA. At each site, stream water was monitored during six storm events in 2005 to assess changes in stable isotopes of NO 3 − (δ 15 N‐NO 3 − and δ 18 O‐NO 3 − ) and water (δ 18 O‐H 2 O) from baseflow to peakflow. Peakflow fractions of event NO 3 − and event water were then computed using two‐component mixing models to elucidate NO 3 − flow pathway differences among the five sites. For the forested upland site, storm size appeared to affect NO 3 − sources and flow pathways. During small storms (<35 mm rainfall), greater event NO 3 − fractions than event water fractions indicated the prevalence of atmospheric NO 3 − source contributions at peakflow. During larger storms (>35 mm rainfall), event NO 3 − fractions were less than event water fractions at peakflow suggesting that NO 3 − was flushed from stored sources via shallow subsurface flow pathways. For the urbanized site, wash‐off of atmospheric NO 3 − was an important NO 3 − source at peakflow, especially during short‐duration storms where event water contributions indicated the prevalence of overland flow. In the karst lowlands, very low fractions of event water and even lower fractions of event NO 3 − at peakflow suggested the dominance of ground water flow pathways during storms. These ground water flow pathways likely flushed stored NO 3 − sources into the stream, while deep soils in the karst lowlands also may have promoted NO 3 − assimilation. The results of this study illustrated how NO 3 − isotopes and δ 18 O‐H 2 O could be combined to show key differences in water and NO 3 − delivery between forested uplands, karst valleys and fully urbanized watersheds. Copyright © 2009 John Wiley & Sons, Ltd.