Dynamics of stream nitrate sources and flow pathways during stormflows on urban, forest and agricultural watersheds in central Pennsylvania, USA

Autor: David R. DeWalle, Anthony R. Buda
Rok vydání: 2009
Předmět:
Zdroj: Hydrological Processes. 23:3292-3305
ISSN: 1099-1085
0885-6087
DOI: 10.1002/hyp.7423
Popis: 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 N0 3 - flow pathway differences among the five sites. For the forested upland site, storm size appeared to affect N0 3 - sources and flow pathways. During small storms ( 35 mm rainfall), event NO 3 - fractions were less than event water fractions at peakflow suggesting that N0 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 N0 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 N0 3 - assimilation. The results of this study illustrated how N0 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.
Databáze: OpenAIRE
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