A Targeted Approach to Delineating the Source(s) and Optical Properties of CDOM

有色溶解性有机物的来源和光学性质的有针对性的描述方法在所有天然沃茨中，溶解性有机物（DOM）的有色组分都不同程度地吸收光。这种物质被称为有色或发色溶解有机物（CDOM），在确定天然沃茨的颜色方面起着至关重要的作用，并影响渗透到水体中的紫外线和可见光的量。由于CDOM强烈吸收紫外线，它可以保护水生生物免受有害辐射的影响，而其在可见光中的吸收可以减少光合作用的光量，从而可能影响水生生态系统。CDOM对光的吸收也引发了一系列光化学反应，这些反应产生的活性氧可以转化CDOM和其他化合物，并影响水生生物对必需微量金属的可用性。尽管它在水化学中的重要性已经确立，但引起光吸收和发射并产生光化学反应的化合物和结构仍然知之甚少。这项工作将使用一系列实验室测试，以确定CDOM中影响其光学和光化学特性的化学基团，以及这些基团如何随来源而变化。（和他们可以提供的信息）包括：1）硼氢化钠还原对光学吸收和发射性质的影响（酮/醛对光学性质的贡献）; 2）在硼氢化物还原之前和之后光谱吸收和发射的pH依赖性（确定羧酸和酚的贡献以及这些基团与酮/醛之间可能的电子相互作用）; 3）缺氧还原连二亚硫酸盐对光学性质的影响（醌类的含量及其对光学性质的影响）; 4）来自不同来源的CDOM的光学性质的分子尺寸依赖性;区域以及硼氢化物还原和pH值如何影响这一点。这项工作将侧重于腐殖物质的实验室研究，以及在过去的野外工作中从不同的海洋和淡水站点获得的CDOM存档样本，但通过与美国宇航局的一个项目互补合作，从切萨皮克湾收集的样本将得到补充，该项目旨在通过直接采样和光学遥感检查贝类床的水质。以及马里兰州的乔治王子郡公立学校的肯穆尔中学的天才学生。该项目的计划包括向中学的学生和教师进行与该项目目标相关的演示/演示，然后访问感兴趣的，选择一组学生到PI的实验室，在那里他们将被允许看到和操作本项目中使用的一些科学仪器，并参与额外的手-该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

A Targeted Approach to Delineating the Source(s) and Optical Properties of Chromophoric Dissolved Organic MatterThe colored components of dissolved organic matter (DOM) absorb light to varying degrees in all natural waters. This material, known as colored or chromophoric dissolved organic matter (CDOM), plays an essential role in determining the color of natural waters and influences the amount of ultraviolet and visible light that penetrates into water bodies. Because CDOM absorbs strongly in the ultraviolet, it can protect aquatic organisms from damaging radiation, whereas its absorption in the visible can reduce the amount of light available for photosynthesis, thus potentially affecting aquatic ecosystems. The absorption of light by CDOM also initiates a series of photochemical reactions, which produce reactive oxygen species that can transform CDOM and other compounds, and affect the availability of essential trace metals to aquatic organisms. Despite its established importance in aquatic chemistry, the compounds and structures that give rise to light absorption and emission and produce the photochemical reactions are still poorly understood. This work will use a series of laboratory tests to identify chemical groups within the CDOM that influence its optical and photochemical properties and how these vary with source.These tests (and the information they can provide) include: 1) the effect of sodium borohydride reduction on the optical absorption and emission properties (contribution of ketones/aldehydes to optical properties); 2) pH dependence of the spectral absorption and emission before and after borohydride reduction (identify contributions of carboxylic acids and phenols and possible electronic interactions between these groups and ketones/aldehydes); 3) the effect of anoxic dithionite reduction on the optical properties (content and impact of quinones to optical properties); 4) molecular size dependence of the optical properties of CDOM from differing sources/locales and how this may be affected by borohydride reduction and pH. This work will focus on laboratory studies of humic substances and of archived samples of CDOM acquired in past field work from diverse oceanic and freshwaters sites, but will be augmented by samples collected from the Chesapeake Bay through a complementary collaboration with a NASA project that aims to examine water quality in shellfish beds through direct sampling and optical remote sensing.This proposal will further support plans to initiate a program for talented and gifted students at Kenmoor Middle School in the Prince George’s County Public Schools in Maryland. Plans for this program include presentations/demonstrations to the students and faculty at the middle school that are related to the goals of this project, followed by a visit of an interested, select group of students to the PI’s laboratory where they will be allowed to see and operate some of the scientific instruments employed in this project and be involved in additional hands-on demonstrations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.