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

有的放矢地描绘有色溶解有机物的来源(S)和光学性质溶解有机物(DOM)的有色成分在所有自然水域中都有不同程度的吸光作用。这种物质被称为有色或有色溶解有机物(CDOM)，在确定自然水域的颜色方面发挥着至关重要的作用，并影响穿透水体的紫外线和可见光的量。由于CDOM对紫外线的吸收能力很强，可以保护水生生物免受有害辐射的伤害，而它在可见光下的吸收会减少可用于光合作用的光量，从而潜在地影响水生生态系统。CDOM对光的吸收还会引发一系列的光化学反应，产生能转化CDOM和其他化合物的活性氧物种，并影响必需的痕量金属对水生生物的有效性。尽管它在水生化学中具有公认的重要性，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。这项工作将利用一系列实验室测试来确定CDOM中影响其光学和光化学性质的化学基团以及这些化学基团如何随来源而变化。这些测试(以及它们可以提供的信息)包括：1)硼氢化钠还原对光吸收和发射性质的影响(酮/醛对光学性质的贡献)；2)硼氢化钠还原前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)缺氧二亚硫酸盐还原对光学性质的影响(含量和对光学性质的影响)；4)不同来源/地点的CDOM的光学性质与分子大小的关系以及硼氢化物还原和pH对其的影响。这项工作将侧重于对腐殖质和CDOM存档样本的实验室研究，这些样本是在过去的实地工作中从不同的海洋和淡水地点获得的，但将通过与NASA的一个旨在通过直接采样和光学遥感检查贝类床层水质的补充合作，从切萨皮克湾收集样本来扩大研究。这项提议将进一步支持马里兰州乔治王子县公立学校肯穆尔中学为有才华和有天赋的学生发起的计划。该项目的计划包括向中学的学生和教职员工进行与该项目目标相关的演示/演示，然后由感兴趣的选定的学生小组访问PI的实验室，在那里他们将被允许观看和操作该项目中使用的一些科学仪器，并参与额外的动手演示。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.