Collaborative Research: Mass Transfer Due to Oscillatory Flow Over Coral Reefs

新的生产、有机碳循环和珊瑚礁系统的营养吸收之间的关系尚不清楚。实验表明，珊瑚礁群落对营养物质的吸收受到质量传递的限制，或者受到营养物质被物理输送到珊瑚礁自养生物活性表面的速率的限制。已经建立了一套简单的传质关系来预测溶解无机营养物的吸收。这些关系是在10-20米长的水槽和稳定、非振荡流动条件下进行的实验中得出的。Drs。Atkinson和Monismith认为，这些传质方程不适用于理解自然珊瑚礁环境中浅水珊瑚礁群落的营养吸收，在自然珊瑚礁环境中，波浪驱动的水运动主导着周围的流场。他们从理论和经验两方面论证了振荡流动对传质的增强作用。他们强调，没有关于波浪和自然粗糙表面的传质研究，这是研究底栖生态系统所特有的问题。该项目有三个总体目标：1)了解波浪如何影响自然粗糙表面的传质率；2)确定波浪如何影响适应波浪驱动的水流环境的珊瑚礁群落的营养吸收；3)实际证明海浪提高了天然珊瑚礁群落对营养物质的就地吸收率。为了实现这些目标，这些科学家提出了一套由两个实验室研究和一个实地研究组成的环环相扣的研究方案。其中第一项是关于珊瑚群落在稳定和振荡水流条件下的营养吸收的实验室实验，将在椰子岛的hib实验室进行。第二部分，将在斯坦福大学环境流体力学实验室对珊瑚的应力和质量传递进行详细的流体力学研究。最后，为了测试实验室结果的应用，将进行一系列现场实验，以确定在波浪驱动的水流条件下，天然珊瑚礁群落的营养吸收率是否与入射波能正相关，并确定这些速率是否与根据实验室实验得出的传质相关性估计的底部剪切应力相一致。这些实验的结果将为我们确定珊瑚礁群落营养吸收速率的空间变异性提供定量基础，并促进对珊瑚礁群落典型的动态物理环境如何定义其代谢的理解。

The relationship between new production, organic carbon cycling, and nutrientuptake into coral reef systems is not well understood. Nutrient uptake into experimentalcoral reef communities has been shown to be mass-transfer limited, or limited by the rate at which nutrients can be physically delivered to the active surfaces of reef autotrophs. A set of simple, mass transfer relationships have been developed to predict uptake of dissolved inorganic nutrients. These relationships were derived from experiments which were conducted in 10-20 m long flumes and under steady, non-oscillatory flow conditions. Drs. Atkinson and Monismith reason that these mass transfer equations are inappropriate for understanding nutrient uptake by shallow-water reef communities in natural reef environments, where wave-drive water motion dominates the surrounding flow field. They have argued with both theoretical and empirical evidence that there should be some enhancement of mass transfer due to oscillatory flow. They emphasize that there are no mass transfer studies with both waves and naturally rough surfaces and that this is a problem unique to the study of benthic ecosystems. The project has three general goals: 1) To understand how waves influence rates of mass transfer to naturally roughsurfaces; 2) To determine how waves influence nutrient uptake into reef communitiesadapted to wave-driven flow environments; 3) To actually demonstrate that waves enhance in situ rates of nutrient uptakeby natural reef communities.To achieve these goals, these scientists propose an interlocking set of two lab studies and one field study. The first of these, a laboratory experiment on nutrient uptake by a coral community under both steady and oscillating flow conditions, will be conducted at the HIMB lab on Coconut Island. The second, a detailed study of the fluid mechanics ofstress and mass transfer over corals will be carried out at the Environmental FluidMechanics Laboratory at Stanford. Finally, to test the application of the lab results, aseries of field experiments will be carried out to determine whether rates of nutrientuptake by natural reef communities under wave-driven flow conditions are positivelycorrelated with incident wave energy, and, to determine whether these rates scale withestimates of bottom shear stress according to mass transfer correlations derived fromlaboratory experiments. Results of these experiments will give us the quantitative basis to determine thespatial variability in rates of nutrient uptake into reef communities, and to promote anunderstanding of how the dynamic physical environment typical of reef communitiesmay be defining their metabolism.