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

在全球范围内，湖泊沉积物储存了非常大量的碳。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源于藻类。然而，有证据表明，藻类碳很容易被微生物群落矿化，因此看来沉积物碳一定有一个主要的非生物来源。在上一个赠款周期中，我的实验室的工作表明，人工太阳光照射酸性溪流水会导致溶解有机碳(DOC)形成颗粒有机碳(POC)，颗粒铁的形成起主要作用，可能是因为DOC附着在新形成的颗粒铁的表面。我们推测，这一机制在将DOC转移到沉积物中起着主要作用。这项建议的第一部分试图通过研究在没有紫外线的情况下酸性和非酸性水域中POC的形成程度来扩展这项工作。在这项建议的第二部分，我建议研究淡水中不稳定铁的产生与主导浮游植物群落的藻类物种之间的关系。良性的真核生物物种通常与非常小的蓝藻共存于营养不良的贫营养湖泊，那里的生产力通常是通过低水平的磷来实现的。营养丰富的富营养化水域通常以大型蓝藻为主。目前还不清楚更良性的真核物种是如何被有毒的蓝藻取代的。我开发了一个概念模型，在该模型中，不稳定的铁供应速率与磷供应速率的比率在确定蓝藻的相对丰度时至关重要。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活性铁的供应速度，这种方法可以捕捉24小时内藻类物种组成的不稳定铁和磷酸盐。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.