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ANNUAL CYCLE AND INTERANNUAL VARIABILITY OF ECOSYSTEM METABOLISM IN A TEMPERATE CLIMATE EMBAYMENT
Author(s) -
Smith S. V.,
Hollibaugh J. T.
Publication year - 1997
Publication title -
ecological monographs
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.254
H-Index - 156
eISSN - 1557-7015
pISSN - 0012-9615
DOI - 10.1890/0012-9615(1997)067[0509:acaivo]2.0.co;2
Subject(s) - dissolved organic carbon , alkalinity , environmental science , bay , nutrient , organic matter , environmental chemistry , carbon cycle , temperate climate , estuary , redfield ratio , colored dissolved organic matter , ecosystem , phosphorus , chemistry , oceanography , ecology , phytoplankton , geology , biology , organic chemistry
We have studied the net and gross metabolism of Tomales Bay, a temperate climate estuary in northern California. Tomales Bay has proved to be heterotrophic, implying that the bay oxidizes a subsidy of organic carbon from outside the system, in excess of inorganic nutrients supplied to it from outside and in addition to material cycling within it. Net organic oxidation releases dissolved inorganic nutrients, and the system exports these dissolved inorganic products. Dissolved inorganic phosphorus is exported to the ocean via mixing and constitutes the most direct record of net ecosystem production (NEP). Excess dissolved inorganic nitrogen is lost to denitrification. Excess dissolved inorganic carbon largely results in alkalinity elevation and hydrographic export of alkalinity due to sulfate reduction. The negative NEP of this system results in little release of CO 2 to the atmosphere, because of this alkalinity elevation. A major purpose of the study was to ascertain the relative importance of various sources of organic material supplied to the system from outside its boundaries and undergoing net reactions within it. In order to address the question, we used stoichiometrically linked whole‐system budgets of carbon, nitrogen, and phosphorus. The difference between dissolved inorganic phosphorus (DIP) fluxes to and from the bay is a measure of net internal sources or sinks of DIP and is used as a quantitative index of NEP, with the assumption that the C:P ratio of organic matter is constant (∼106:1). The system is thus defined in terms of water column dissolved material composition; this definition includes time, as well as space. Net changes in the standing stocks of dissolved materials can originate from (spatial) transport to or from the system or from internal (temporal) transformations between the dissolved and particulate materials (i.e., changes in organic storage). Over the 8‐yr study, the system respired 12 mmol·m −2 ·d −1 more organic C than the internal system primary production of ∼100 mmol·m −2 ·d −1 . The system is thus heterotrophic by ∼10%, with substantial seasonality in the extent of heterotrophy. By deconvoluting the time series of NEP into a seasonal cycle and interannual variation, we infer that terrestrial and marine sources each account for about half of the carbon required to support negative NEP in this system, but with quite different turnover time scales. Temporal response of NEP to terrigenous input appears to be extremely modulated, so that there is no obvious immediate (same year) response to extreme interannual variation in terrigenous organic loading. In contrast, NEP responds both interannually and seasonally to marine organic inputs. We interpret the differences in response to loading of terrestrial vs. marine organic matter as reflecting differences in the reactivity of these carbon reservoirs.