Find in Library

We present absorption properties of colored dissolved organic matter (CDOM) sampled in six different water bodies along extreme altitudinal, latitudinal, and trophic state gradients. Three sites are in Norway: the mesotrophic Lysefjord (LF), Samnangerfjord (SF), and R&#248;st Coastal Water (RCW); two sites are in China: the oligotrophic Lake Namtso (LN) and the eutrophic Bohai Sea (BS); and one site is in Uganda: the eutrophic Lake Victoria (LV). The site locations ranged from equatorial to subarctic regions, and they included water types from oligotrophic to eutrophic and altitudes from 0 m to 4700 m. The mean CDOM absorption coefficients at 440 nm [<inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>a</mi> <mi>CDOM</mi> </msub> <mrow> <mo>(</mo> <mn>440</mn> <mo>)</mo> </mrow> </mrow> </semantics> </math> </inline-formula>] and 320 nm [<inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>a</mi> <mi>CDOM</mi> </msub> <mrow> <mo>(</mo> <mn>320</mn> <mo>)</mo> </mrow> </mrow> </semantics> </math> </inline-formula>] varied in the ranges 0.063&#8722;0.35 m<inline-formula> <math display="inline"> <semantics> <msup> <mrow></mrow> <mrow> <mo>&#8722;</mo> <mn>1</mn> </mrow> </msup> </semantics> </math> </inline-formula> and 0.34&#8722;2.28 m<inline-formula> <math display="inline"> <semantics> <msup> <mrow></mrow> <mrow> <mo>&#8722;</mo> <mn>1</mn> </mrow> </msup> </semantics> </math> </inline-formula>, respectively, with highest values in LV, Uganda and the lowest in the high-altitude LN, Tibet. The mean spectral slopes <inline-formula> <math display="inline"> <semantics> <msub> <mi>S</mi> <mrow> <mn>280</mn> <mo>&#8722;</mo> <mn>500</mn> </mrow> </msub> </semantics> </math> </inline-formula> and <inline-formula> <math display="inline"> <semantics> <msub> <mi>S</mi> <mrow> <mn>350</mn> <mo>&#8722;</mo> <mn>500</mn> </mrow> </msub> </semantics> </math> </inline-formula> were found to vary in the ranges of 0.017&#8722;0.032 nm<inline-formula> <math display="inline"> <semantics> <msup> <mrow></mrow> <mrow> <mo>&#8722;</mo> <mn>1</mn> </mrow> </msup> </semantics> </math> </inline-formula> and 0.013&#8722;0.015 nm<inline-formula> <math display="inline"> <semantics> <msup> <mrow></mrow> <mrow> <mo>&#8722;</mo> <mn>1</mn> </mrow> </msup> </semantics> </math> </inline-formula>, respectively. The highest mean value for <inline-formula> <math display="inline"> <semantics> <msub> <mi>S</mi> <mrow> <mn>280</mn> <mo>&#8722;</mo> <mn>500</mn> </mrow> </msub> </semantics> </math> </inline-formula> as well as the lowest mean value for <inline-formula> <math display="inline"> <semantics> <msub> <mi>S</mi> <mrow> <mn>350</mn> <mo>&#8722;</mo> <mn>500</mn> </mrow> </msub> </semantics> </math> </inline-formula> were found in LN. Scatter plots of <inline-formula> <math display="inline"> <semantics> <msub> <mi>S</mi> <mrow> <mn>280</mn> <mo>&#8722;</mo> <mn>500</mn> </mrow> </msub> </semantics> </math> </inline-formula> versus <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>a</mi> <mi>CDOM</mi> </msub> <mrow> <mo>(</mo> <mn>440</mn> <mo>)</mo> </mrow> </mrow> </semantics> </math> </inline-formula> and <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>a</mi> <mi>CDOM</mi> </msub> <mrow> <mo>(</mo> <mn>320</mn> <mo>)</mo> </mrow> </mrow> </semantics> </math> </inline-formula> values ranges revealed a close connection between RCW, LF, and SF on one side, and BS and LV on the other side. CDOM seems to originate from terrestrial sources in LF, SF, BS, and LV, while RCW is characterized by autochthonous-oceanic CDOM, and LN by autochthonous CDOM. Photobleaching of CDOM is prominent in LN, demonstrated by absorption towards lower wavelengths in the UV spectrum. We conclude that high altitudes, implying high levels of UV radiation and oligotrophic water conditions are most important for making a significant change in CDOM absorption properties.