Optical properties of DOM and their relationships with dissolved trace metals in shallow lakes of southern Ontario, Canada
Abstract
Recent advances in optical characterization of dissolved organic matter (DOM) have improved our ability to study the chemical composition and biogeochemical processing of this important carbon pool in aquatic systems. We examined the relationships between optical properties of DOM and dissolved trace metal concentrations (free and organic bound fractions) in 9 of the Kawartha Lakes of southern Ontario using samples collected monthly between March and August of 2010. We found that the β:α ratio (an index of recently produced to degraded DOM), a spectral slope ratio (SR) and a humification index (HIX) of DOM varied among the Kawartha Lakes and between seasons, likely reflecting the watershed characteristics of the contributing tributaries, the productivity of the lake, and seasonal processing from light and/or microbes. Total dissolved iron (Fe) concentrations averaged 1.25 µM in Precambrian Shield-influenced sites and 0.85 nM in sites receiving agricultural and urban run-off. Copper (Cu) and molybdenum (Mo) concentrations showed no significant difference between Shield and non-Shield influenced-sites. Dissolved organic carbon (DOC) concentrations averaged 3.6 to 8.9 mg L-1, with the highest values in two wetland-influenced sites. Similar spatial patterns as dissolved Fe concentrations were observed in β:α, SR, and HIX. Moreover, total dissolved Fe concentrations negatively correlated with β:α and SR but positively with HIX, indicating a gradient of increased Fe concentrations with increased levels of degraded and humic-like DOM. Organic bound Fe fractions represented as much as 70% of the total dissolved Fe pool in sites characterized by highly aromatic, terrestrial-like DOM (HIX > 0.9), and decreased with increasing microbial influence. These results suggest that the quality of the DOM pool, in addition to the concentration of DOC, can be a significant controller of Fe mobility and bioavailability in aquatic systems.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.B32C..07M
- Keywords:
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- 0428 BIOGEOSCIENCES / Carbon cycling;
- 0461 BIOGEOSCIENCES / Metals;
- 0489 BIOGEOSCIENCES / Trace element cycling