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AQUATIC METABOLISM AND ECOSYSTEM HEALTH ASSESSMENT USING DISSOLVED O 2 STABLE ISOTOPE DIEL CURVES
Author(s) -
Venkiteswaran Jason J.,
Schiff Sherry L.,
Wassenaar Leonard I.
Publication year - 2008
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/07-0491.1
Subject(s) - diel vertical migration , saturation (graph theory) , chemistry , environmental chemistry , respiration , ecology , botany , biology , mathematics , combinatorics
Dissolved O 2 concentration and δ 18 O‐O 2 diel curves can be combined to assess aquatic photosynthesis, respiration, and metabolic balance, and to disentangle some of the confounding factors associated with interpretation of traditional O 2 concentration curves. A dynamic model is used to illustrate how six key environmental and biological parameters interact to affect diel O 2 saturation and δ 18 O‐O 2 curves, thereby providing a fundamental framework for the use of δ 18 O‐O 2 in ecosystem productivity studies. δ 18 O‐O 2 provides information unavailable from concentration alone because δ 18 O‐O 2 and saturation curves are not symmetrical and can be used to constrain gas exchange and isotopic fractionation by eliminating many common assumptions. Changes in key parameters affect diel O 2 saturation and δ 18 O‐O 2 curves as follows: (1) an increase in primary production and respiration rates increases the diel range of O 2 saturation and δ 18 O‐O 2 and decreases the mean δ 18 O‐O 2 value; (2) a decrease in the primary production to respiration ratio ( P : R ) decreases the level of O 2 saturation and increases the δ 18 O‐O 2 values; (3) an increase in the gas exchange rate decreases the diel range of O 2 saturation and δ 18 O‐O 2 values and moves the mean O 2 saturation and δ 18 O‐O 2 values toward atmospheric equilibrium; (4) a decrease in strength of the respiratory isotopic fractionation (α R closer to 1) has no effect on O 2 saturation and decreases the δ 18 O‐O 2 values; (5) an increase in the δ 18 O of water has no effect on O 2 saturation and increases the minimum (daytime) δ 18 O‐O 2 value; and (6) an increase in temperature reduces O 2 solubility and thus increases the diel range of O 2 saturation and δ 18 O‐O 2 values. Understanding the interplay between these key parameters makes it easier to decipher the controls on O 2 and δ 18 O‐O 2 , compare aquatic ecosystems, and make quantitative estimates of ecosystem metabolism. The photosynthesis to respiration to gas exchange ratio ( P : R : G ) is better than the P : R ratio at describing and assessing the vulnerability of aquatic ecosystems under various environmental stressors by providing better constrained estimates of ecosystem metabolism and gas exchange.