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Temporal and spatial variability in the cycling of nitrogen within a constructed wetland: A whole‐system stable‐isotope‐addition experiment
Author(s) -
Erler Dirk V.,
Eyre Bradley D.,
Davison Leigh
Publication year - 2010
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2010.55.3.1172
Subject(s) - nitrification , eutrophication , wetland , macrophyte , environmental chemistry , denitrification , effluent , cycling , hydrology (agriculture) , nitrogen , environmental science , stable isotope ratio , nutrient , constructed wetland , chemistry , ecology , environmental engineering , geology , biology , history , physics , geotechnical engineering , organic chemistry , archaeology , quantum mechanics
Constructed wetlands attenuate effluent nutrients, are hydrodynamically well defined, and are a useful proxy for the study of nitrogen (N) transformation in eutrophic natural systems. A whole‐system stable‐isotope addition was undertaken to describe the N cycling within a constructed wetland. Addition of 15 NH 4 + and particulate organic 15 N (PO 15 N) and a conservative tracer (Li + ) revealed that, initially, sedimentation of PO 15 N and assimilatory uptake of 15 NH 4 + near the wetland inlet removed most of the added 15 N. Denitrification of NO 3 ‐ dominated inorganic N dynamics and was higher upstream than downstream owing to the greater availability of NO 3 − upstream. More NHz 4 was mineralized upstream where PON settlement was highest, and settled PON started being mineralized within 14 d. Nitrification was insignificant upstream but was an important process in the downstream region of the wetland in spite of low oxygen concentration. In the medium term (2–8 weeks), the PO 15 N initially removed to the sediments continued to be mineralized, releasing 15 NH 4 + back to the water column. Remineralized 15 N spiraled through sediment and then macrophyte pools. A dry‐out period resulted in a minor washout of N during the subsequent inundation. After 157 d, 30.8% ± 7.3% of the added 15 N was still in sediments, 7.4% ± 3.8% was in plants, 40.8% ± 8.3% had been lost most likely as 15 N 2 , and the remainder had been released in the wetland outlet water. Internal recycling retards the flow of N through wetlands, and short‐term retention leads to eventual enhanced removal through denitrification.