Particulate organic carbon formation and phosphorus/iron supply ratios along pH and trophic gradients in lakes

在全球范围内，湖泊沉积物储存了大量的碳。沉积物中藻类残留物的存在，如色素、细胞壁等，表明沉积物碳部分来自藻类。 然而，有证据表明，藻类碳很容易被微生物群落矿化，因此似乎必须有一个主要的沉积物碳的非生物来源。在上一个资助周期，在我的实验室的工作表明，酸性流沃茨与人工阳光照射导致形成颗粒有机碳（POC）从溶解的有机碳（DOC）和颗粒铁的形成发挥了重要作用，可能是因为DOC粘附在新形成的颗粒铁的表面。我们推测，这种机制起着重要的作用，在转移DOC沉积物。本提案的第一部分旨在扩大这项工作的范围，在酸性和非酸性沃茨在UVB的情况下，POC的形成检查。在本提案的第二部分，我建议检查之间的关系生产的“不稳定”的铁在新鲜的沃茨和藻类占主导地位的浮游植物群落。良性真核生物物种通常与非常小的蓝藻共存于营养贫乏的寡营养湖泊中，其中生产力通常是由低水平的磷。营养丰富的富营养化沃茨通常以大型蓝藻为主。目前还不清楚有毒的蓝藻是如何取代更良性的真核生物物种的。我开发了一个概念模型，其中不稳定的铁供应率磷酸盐供应率的比例是决定蓝藻的相对丰度的关键。我提出的研究的主要目标是使用一种方法来比较磷酸盐和不稳定铁的供应率，该方法可以在24小时内捕获不稳定铁和磷酸盐，以获得藻类物种组成。这将有助于确定磷/铁供应比例的变化是否会影响藻类群落的组成。

Globally, lake sediments store a very large amount of carbon. The presence of algal remains in sediments such as pigments, cell walls, etc indicates that sediment carbon is partially derived from algae.  However, evidence shows that algal carbon is readily mineralized by the microbial community so it appears that there must be a major non-biological source of sediment carbon. During the last grant cycle, work in my laboratory demonstrated that irradiation of acidic stream waters with artificial sunlight resulted in formation of particulate organic carbon (POC) from dissolved organic carbon (DOC) and that formation of particulate iron played a major role, probably because DOC adheres to the surface of newly formed particulate iron. We hypothesize that this mechanism plays a major role in transferring DOC to sediments. The first part of this proposal seeks to extend this work by examining the extent of POC formation in acidic and non-acidic waters in the absence of UVB.In the second part of this proposal, I propose to examine the relationship between the production of 'labile' iron in freshwaters and the algal species that dominate phytoplankton communities. Benign eukaryotic species typically co-exist with very small cyanobacteria in nutrient-poor oligotrophic lakes where productivity is usually by low levels of phosphorus. Nutrient-rich eutrophic waters are typically dominated by large cyanobacteria. It is not clear how more benign eucaryotic species are displaced by toxic cyanobacteria. I developed a conceptual model in which the ratio of labile iron supply rate to phosphate supply rate is critical in determining the relative abundance of cyanobacteria. The primary goal of my proposed research is to compare supply rates of phosphate and labile iron using a method that captures labile iron and phosphate over a 24 hour period to algal species composition. This will help determine whether variation in the phosphorus/iron supply ratio affects the composition of the algal community.