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Direct and indirect coupling of primary production and diel nitrate dynamics in a subtropical spring‐fed river
Author(s) -
Heffernan James B.,
Cohen Matthew J.
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.2010.55.2.0677
Subject(s) - diel vertical migration , denitrification , nitrate , environmental science , primary production , autotroph , heterotroph , atmospheric sciences , environmental chemistry , ecology , chemistry , nitrogen , biology , ecosystem , geology , genetics , organic chemistry , bacteria
We used high‐frequency in situ measurements of nitrate (NO 3 − ) and dissolved oxygen (DO) from the springfed Ichetucknee River, Florida, to derive multiple independent estimates of assimilatory nitrogen (N) demand, and to evaluate the short‐term dependence of heterotrophic assimilation and dissimilation (e.g., denitrification) on gross primary productivity (GPP). Autotrophic N assimilation estimates derived from diel DO variability and GPP stoichiometry agreed closely with estimates based on integration of diel variation in NO 3 − concentration, although the correspondence of these metrics depended on the method used to estimate NO 3 − baselines. In addition, day‐to‐day changes in nocturnal NO 3 − concentration maxima were strongly negatively correlated with day‐to‐day changes in GPP. Diel temperature variation in the Ichetucknee River indicated that this pattern could not be explained by hydrologic dispersion, while relationships between N assimilation and O 2 production at hourly intervals indicated minimal physiological lags. The estimated magnitude of heterotrophic assimilation was small, indicating that the relationship between changes in GPP and changes in nocturnal NO 3 − maxima reflects sensitivity of denitrification to variation in exudation of labile organic matter by primary producers. We estimate that ~ 35% of denitrification may be fueled by the previous day’s photosynthesis; this result is consistent with the broader hypothesis that the magnitude of autochthonous production in aquatic systems influences the fate of N via both direct and indirect mechanisms.