Department of Earth and Environment, Boston University, Boston, Massachusetts 02215, United States.
Department of Marine Sciences, University of Georgia, Athens, Georgia 30605, United States.
Environ Sci Technol. 2020 Nov 3;54(21):14096-14106. doi: 10.1021/acs.est.0c03605. Epub 2020 Oct 23.
The photobleaching of chromophoric dissolved organic matter (CDOM) is considered an important loss process for CDOM absorption in sunlit natural waters, where it can regulate the biota's exposure to sunlight, surface solar heating, and dissolved organic matter dynamics. Despite its importance, this sink remains poorly quantified, primarily because of the difficulty of determining photobleaching apparent quantum yields (AQYs) that capture the dual spectral dependency of this process and are applicable to polychromatic sunlight. Here, we present a simple method to determine a CDOM photobleaching AQY matrix (AQY-M) for natural water samples that does not require any a priori assumptions about the spectral dependency of photobleaching. It combines controlled irradiation experiments, a partial least-square regression, and an optimization procedure to produce AQY-Ms that are spectrally coherent and optimized for modeling accurate photobleaching rates in natural waters. Water temperature and the solar exposure history of CDOM had a major influence on the magnitude and spectral characteristics of the AQY-M. These factors should be considered when determining the AQY-M of samples and provide constraints when modeling photobleaching rates in natural waters. We expect that this effective method will provide future studies with a robust means to characterize and understand the variability of AQY-M in natural waters.
色氨酸溶解有机质（CDOM）的光漂白被认为是阳光照射下自然水体中 CDOM 吸收的一个重要损失过程，它可以调节生物对阳光、表面太阳加热和溶解有机质动态的暴露。尽管它很重要，但这个汇仍然被严重低估，主要是因为很难确定光漂白表观量子产率（AQY），这些 AQY 可以捕捉到这个过程的双重光谱依赖性，并且适用于多色阳光。在这里，我们提出了一种简单的方法来确定自然水样的 CDOM 光漂白 AQY 矩阵（AQY-M），该方法不需要对光漂白的光谱依赖性做出任何先验假设。它结合了受控辐照实验、偏最小二乘回归和优化程序，以产生光谱上一致的 AQY-M，这些 AQY-M 经过优化，可用于准确模拟自然水中的光漂白速率。水温和 CDOM 的太阳暴露历史对 AQY-M 的大小和光谱特征有很大影响。在确定样品的 AQY-M 时应考虑这些因素，并为在自然水中模拟光漂白速率提供约束。我们期望这种有效的方法将为未来的研究提供一种可靠的手段来描述和理解自然水中 AQY-M 的可变性。
