『Abstract
The bioavailability and composition of dissolved organic carbon
(DOC) and nitrogen (DON) were examined in 10 major sub-catchments
of the Swan-Canning estuary, which bisetcts the city of Perth,
in south-western Australia. Catchments contain a mix of forest,
agriculture, and urban-dominated land-use, with the degree of
development increasing near the city center. We incubated water
samples from the 10 sub-catchments for 14 days at 25℃, and measured
changes in DOC and DON and dissolved inorganic nitrogen (DIN).
A greater proportion of DON (4-44％) was decomposed compared to
DOC (1-17％). Both agricultural and urban catchments had high proportions
of bioavailable DOC and DON, but overall DOC and DON losses were
greatest in urban catchments. Using resin isolation techniques,
we found that DOC was concentrated in the hydrophobic (humic)
fraction, whereas DON had both hydrophobic and hydrophilic (non-humic)
fractions. Hydrophobic DOC content was positively related to DOC
decomposition. In contrast, DON decomposition was highly correlated
with hydrophilic DON content and inversely related to the hydrophilic
DOC/DON ratio, indicating a labile fraction of DON from non-humic
sources. Taken together, these relationships suggest that bioavailable
DOC may be supplied in part from terrestrial plant material, but
bioavailable DON is likely to be from highly labile sources, possibly
autochthonous or anthropogenic. Overall, labile DON was greater
than initial DIN concentration at seven of ten sites and was even
dominant in highly developed catchments. This study highlights
the importance of organic N in urbanizing coastal catchments that,
in addition to DIN, may serve as a readily available source of
N for in-stream and estuarine production.
Keywords: Swan-Canning; Estuary; Catchment; Land-use; Decomposition;
Bioavailability; Agriculture; Urban; Humic; Dissolved organic
matter; Dissolved organic carbon; Dissolved organic nitrogen;
Inorganic nitrogen』
Introduction
Study site
Methods
Sample collection
Bioavailability experiment
DOM characterization
Analytical chemistry
Results
Stream chemistry
Bioavailability experiment
DOM composition
DOM bioavailability
Revised DON pools
Discussion
DOM fractions and bioavailability
Ecosystem implications in urbanizing coastal catchments
Acknowledgements
References