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Tracing Nitrate-Nitrogen Sources and Modifications in a Stream Impacted by Various Land Uses, South Portugal
Yevenes, M.A.; Soetaert, K.; Mannaerts, C.M. (2016). Tracing Nitrate-Nitrogen Sources and Modifications in a Stream Impacted by Various Land Uses, South Portugal. Water 8(9): 385. dx.doi.org/10.3390/w8090385
In: Water. MDPI AG: Basel. ISSN 2073-4441, more
Peer reviewed article  

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Author keywords
    nitrate-nitrogen; stable isotopes; streams; reactive transport model

Authors  Top 
  • Yevenes, M.A.
  • Soetaert, K., more
  • Mannaerts, C.M.

Abstract
    The identification of nitrate-nitrogen (NO3–N) origin is important in the control of surfaceand ground water quality. These are the main sources of available drinking water. Stable isotopes(15N and 18O) for NO3–N and along with a 1-D reactive transport model were used to study the originand processes that lead to nitrogen transformation and loss in a major stream that flows into a reservoirwithin an intensively cultivated catchment area (352 km2) in Alentejo-Portugal. Seasonal watersamples (October–November 2008, March 2009 and September 2009) of stream surface water, wellsand sediment pore water were collected. The results showed consistently increasing isotope valuesand decreasing NO3–N concentrations downstream. During winter (wet period, November 2008 andMarch 2009) slightly higher NO3–N concentrations were found in comparison to early fall (dry period:October 2008) and summer (dry period: September 2009). Isotopic composition of 15N and 18O valuesin surface water samples from the stream and wells indicated that the dominant NO3–N sources werederived mainly from the soil and fertilizers. There was also significant nitrification in surface water atthe head of the stream. Sediment pore waters showed high NO3–N values near the sediment-waterinterface (reaching 25 mg?N?L?1) and NO3–N concentrations sharply decreasing with sedimentdepth, suggesting significant NO3–N consumption. Denitrification was also detected using the 15Nsignature in upstream waters, but not downstream where very low NO3–N levels were measured.In the stream, the calculated isotopic enrichment factor for NO3–N was ?2.9‰for 15N and ?1.78 for18O, this indicates that denitrification accounts for 7.8% to 48% of nitrate removal.

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