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Transport‐based method for estimating in‐stream nitrogen uptake at ambient concentration from nutrient addition experiments
Author(s) -
Claessens Luc,
Tague Christina L.
Publication year - 2009
Publication title -
limnology and oceanography: methods
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.898
H-Index - 72
ISSN - 1541-5856
DOI - 10.4319/lom.2009.7.811
Subject(s) - nutrient , saturation (graph theory) , nitrogen , chemistry , soil science , biological system , nitrate , environmental science , streams , hydrology (agriculture) , mathematics , analytical chemistry (journal) , environmental chemistry , computer science , computer network , geotechnical engineering , organic chemistry , combinatorics , biology , engineering
Nutrient addition experiments are commonly used for reach‐scale quantification of in‐stream nitrogen uptake. Traditional, short‐term nutrient addition experiments are subject to nutrient saturation effects, which influence the measured uptake rates, and are not transport based, which limits their ability to distinguish between channel and hyporheic processes. We developed a transport‐based nutrient addition approach adapted to account for the effect of nutrient saturation. We incorporated the Michaelis‐Menten saturation‐limited uptake function into the One‐dimensional Transport with Inflow and Storage (OTIS) solute transport model and specifically designed the field experiments for this modified version of the model (called OTIS‐MM). Cross‐method evaluations were performed for estimates of NH 4 + and NO 3 − uptake lengths ( S w ). For NH 4 + , OTIS‐MM and sequential, multiple‐level traditional experiments produced almost identical S w values (124 versus 122 m), and the slopes of the regression lines relating S w to added concentration were similar (4% difference). For NO 3 − , the methods produced similar S w values (872 versus 909 m), but the slopes of the regression lines relating S w to added concentration were different (23% difference). We complemented the cross‐method evaluations with sensitivity analyses for both NH 4 + and NO 3 − , which confirmed that the estimates of the OTIS‐MM uptake parameters were robust. Our field‐modeling approach can easily be designed to cover multiple, sequential reaches in one single addition; hence, it allows for increased spatial coverage.