Relationship of trophic and chemical conditions to photobleaching of dissolved organic matter in lake ecosystems

Citation
I. Reche et al., Relationship of trophic and chemical conditions to photobleaching of dissolved organic matter in lake ecosystems, BIOGEOCHEMI, 44(3), 1999, pp. 259-280
Citations number
55
Categorie Soggetti
Environment/Ecology
Journal title
BIOGEOCHEMISTRY
ISSN journal
01682563 → ACNP
Volume
44
Issue
3
Year of publication
1999
Pages
259 - 280
Database
ISI
SICI code
0168-2563(199903)44:3<259:ROTACC>2.0.ZU;2-9
Abstract
Dissolved organic matter (DOM) is a major light-absorbing substance, respon sible for much of the color in water bodies. When sunlight energy is absorb ed by DOM, some color can be lost by the process of photobleaching. We meas ured rates of DOM photobleaching in thirty lakes that varied greatly in col or, trophic status and ionic composition. Loss of color (measured as absorb ance at 440 nm and expressed as absorption coefficients) was a first order function of sunlight dose, and rates were nearly identical for 0.2 mu m- an d GF/F-filtered samples suggesting that the process was predominantly abiot ic. Photobleaching rates were rapid (color loss of 1-19% d(-1)) and varied about seven-fold among lakes. Our method underestimated the actual rate by 15-20% based on comparisons between the glass bottles we used in the survey and quartz containers. The large variation in photobleaching rates was exa mined in relation to lake trophy and chemical conditions. The best predicto r of this variability was acid-neutralizing capacity (ANC) (r(2) = 0.94; p < 0.001) such that photobleaching was most rapid in the most alkaline lakes . The relationship between ANC and photobleaching suggests that differences in ionic conditions among lakes may influence the solubility and configura tion of humic and fulvic acids and hence their susceptibility to photobleac hing.