Collaborative Research: Macrofaunal community effects on benthic exchange fluxes

海底在浅水生态系统的元素循环中起着至关重要的作用。尽管沿海底栖动物已经得到了较好的研究，但动物在改变关键生态系统服务（如养分循环）中的定量作用仍然很少受到限制。这在很大程度上源于难以将在地块（mm - m）尺度上观察到的生物地球化学动力学扩展到更大的沿海生态系统框架。在这个合作项目中，乔治亚大学和马里兰大学的研究人员？切萨皮克生物实验室将量化在受控条件下的小尺度动物活动及其生态相互作用的动态，并将这些数据纳入沉积物生物地球化学的新型建模方法。具体而言，他们将开展一系列实验研究，以确定在复杂的三维区域中洞穴的空间排列在多大程度上改变了沉积物的生物地球化学，2)测量物种相互作用对沉积物生物地球化学的影响和反馈，以及3)利用这些发现为本质上异质性的沿海海底采样提供指导。实验室实验将利用人工洞穴和真实生物的沉积物微观世界进行。在单独的实验中发现了无处不在的凤头沙蚕和五彩沙蚕。将测量几种成岩和生态上重要的溶质的沉积物和上覆水之间的通量。洞穴模拟实验将为洞穴灌溉和空间定向对沉积物-海水交换的影响提供详细的经验信息。这些信息将用于参数化三维反应输运模型。包含两种大型动物物种以均匀和聚集的空间安排分布的不同组合的微观世界将用于确定物种相互作用对洞穴几何形状和灌溉的影响，以及对溶质通量的影响。实验数据将阐明动物对空间接近的响应以及物种间和物种内的相互作用。观测数据与模型模拟的比较将用于评估大型动物相互作用对沉积物生物地球化学的影响。最后，对不同密度和空间分布的大型动物及其相互作用进行反应性输运模型模拟。通过将海底划分为可获得模型通量估计值的小块，可以估计通过沉积物-水界面的聚集通量。这一方法将用于评价各种可能的取样策略，并确定有限数量的通量测量能在多大程度上近似底栖动物对沿海生物地球化学循环的贡献。就更广泛的影响而言，这项研究预计将提供一个框架，将在沿海沉积物中进行的单个通量测量换算为更大规模的质量通量。这些发现将扩大我们对沿海海洋营养动态的理解，并通过为通量数据的解释和测量活动的设计提供背景，使一般实验界受益。一名研究生将接受实验和数值方法学方面的培训。此外，为CBL游客中心开发有关沉积物生物地球化学和底栖动物的宣传材料和展览，每年将使大约3500名游客了解海洋环境的鲜为人知的方面。

The seafloor plays a critical role in the elemental cycling within shallow water ecosystems. Although the coastal benthos has been relatively well studied, the quantitative role of infauna in modifying critical ecosystem services such as nutrient cycling remains still poorly constrained. This stems largely from difficulties in scaling biogeochemical dynamics observed at the plot (mm - m) scale to the larger framework of coastal ecosystems. In this collaborative project, researchers at the University of Georgia and the University of Maryland?s Chesapeake Biological Laboratory will quantify small-scale dynamics of infaunal activities and their ecological interactions under controlled conditions and incorporate these data into a novel modeling approach of sediment biogeochemistry. Specifically, they will carry out a series of experimental studies to 1) determine to what extent spatial arrangement of burrows in a complex 3-dimensional domain alters sediment biogeochemistry, 2) measure species-interaction effects and feedbacks on sediment biogeochemistry, and 3) use these findings to provide guidance on sampling the intrinsically heterogeneous coastal seafloor. Laboratory experiments will be developed using sediment microcosms with artificial burrows and real organisms ? the ubiquitous Arenicola cristata and Nereis diversicolor - in separate experiments. Fluxes between the sediment and the overlying water of several diagenetically and ecologically important solutes will be measured. Burrow mimic experiments will provide detailed empirical information on burrow irrigation and spatial orientation effects on sediment-seawater exchange. This information will be used to parameterize a three-dimensional reactive transport model. Microcosms containing different combinations of the two macrofaunal species distributed in even and clustered spatial arrangements will be used to determine species interaction effects on burrow geometry and irrigation, and consequences for solute fluxes. The experimental data will elucidate the response of infauna to spatial proximity as well as the interaction across and within species. Comparison of observational data to model simulations will be used to assess the impact of macrofaunal interactions on sediment biogeochemistry. Finally, reactive transport model simulations will be performed for scenarios differing in densities and spatial arrangement of macrofauna, as well as their interactions. Aggregate fluxes across the sediment water interface will be estimated by dividing the seafloor up into tiles for which model flux estimates can be obtained. This approach will be used to evaluate various possible sampling strategies, and determine how well a limited number of flux measurements can approximate the contribution of benthic infauna to coastal biogeochemical cycles. In terms of broader impacts, this study is expected to provide a framework for scaling individual flux measurements taken in coastal sediments to larger scale mass fluxes. The findings will broaden our understanding of nutrient dynamics in the coastal ocean and benefit the general experimental community by providing context for the interpretation of flux data and design of measurement campaigns. One graduate student will be trained in experimental and numerical methodology. In addition, development of outreach materials and exhibits about sediment biogeochemistry and benthic infauna for the CBL visitor center will expose roughly 3500 visitors per year to lesser known aspects of the marine environment.