Unit 6.1: Biogeochemical Modeling Framework - Biogeochemical Cycling - Inputs, Transformations, and Outputs

Introduction

In this unit, you will learn about the dynamic movement of nutrients among and within ecosystems primarily through the reading and discussion of scientific literature. Short introductory materials are provided to introduce you to some of the general concepts and processes in the study of biogeochemistry. Additionally, in this unit, you will:

• read and interpret scientific literature
• examine how scientific hypotheses are developed and tested
• describe how biogeochemical processes are linked over space and time by studying biogeochemical processes at multiple spatial and temporal scales and exploring the role of organisms in nutrient transformations

Unit 6.1: Biogeochemical Cycling - Inputs, Transformations, and Outputs

Part 1 - Biogeochemistry and Allochthonous Inputs

Pre-class

• You and your group-mates are to read, answer questions, and be prepared to report on the paper indicated by your instructor. These papers explore allochthonous inputs. Please make your reports about 10 minutes long.

• Gioda, A. et al. 2013. Chemical constituents in clouds and rainwater in the Puerto Rican rainforest: potential sources and seasonal drivers. Atmospheric Environment. 68:208-220. Gioda_etal_Reading_Questions (Microsoft Word 2007 (.docx) 13kB Dec25 16)
• McDowell, W.H. 1998. Internal nutrient fluxes in a Puerto Rican rainforest. Journal of Tropical Ecology. 14: 521-536. McDowell_Reading_Questions (Microsoft Word 2007 (.docx) 13kB Dec25 16)
• McDowell, W.H. and S.G. Fisher. 1976. Autumnal processing of dissolved organic matter in a small woodland stream ecosystem. Ecology. 57: 561-569. McDowell_Fisher_Reading_Questions (Microsoft Word 2007 (.docx) 13kB Dec25 16)

Biogeochemistry Background

• We will review some biogeochemistry slides before beginning an in-depth discussion. These PowerPoint slides are intended to serve as a very general introduction to the four main biogeochemical cycles, to emphasize the multiple compartments that elements cycle through, and the significant role that microorganisms such as bacteria and fungi serve in these cycles.

Discuss Allochthonous Input Papers

• Each group will report on the paper they read prior to class. The papers highlight how nutrients are introduced into ecosystems, and the concept of allochthony (from outside the system) is used to demonstrate how biogeochemistry requires an integrated approach over space and time and includes components of scale. This includes wind borne inputs from the Sahara Desert and marine ecosystems to neo-tropical rain forests, the role of Pacific salmon in delivering marine-derived nitrogen to terrestrial forests and stream ecosystems, and the influence of riparian leaf litter in stream ecosystems.

Homework

• You and your group-mates are to read, answer questions, and be prepared to report on the paper indicated by your instructor. These papers explore the role of organisms in biogeochemistry. Please make your reports about 10 minutes long.
• Bump, J.K. et al. 2009. Wolves modulate soil nutrient heterogeneity and foliar nitrogen by configuring the distribution of ungulate carcasses. Ecology. 90: 3159-3167.Bump etal. Reading Questions (Microsoft Word 2007 (.docx) 15kB Dec25 16)
• Helfield, J.M. and R.J. Naiman. 2001. Effects of salmon-derived nitrogen on riparian forest growth and implications for stream productivity. Ecology. 82:2403-2409. Helfield_Naiman_Reading_Questions (Microsoft Word 2007 (.docx) 15kB Dec25 16)

Part 2 - Role of Organisms in Biogeochemistry

In-class

Discuss Organisms in Biogeochemistry Papers

• Each group will report on the paper they read prior to class. The papers examine the role of organisms in transforming nutrients within ecosystems by considering how the presence of a top-predator (wolves) influences nitrogen dynamics across the landscape and how marine derived nutrients can be delivered to forests via salmon.

Carbon and Nitrogen Isotope Activity Introduction

• Isotopic-based techniques are becoming an increasingly powerful and popular tool in biogeochemical research. Two data and excel-based activities are provided here to provide experience in interpreting isotopic data and creating and interpreting graphs. The first activity includes ¹²C and ¹³C data to look at the effects of precipitation and drought on two different species of trees. The second activity uses ¹⁵N data based on Marks et al. (2009) to study the effects of invasive fish species on the structure of aquatic food webs.

Homework

• You and your group-mates are to read, answer questions, and be prepared to report on the paper indicated by your instructor. These papers explore the role of organisms in biogeochemistry. Please make your reports about 10 minutes long.
• Vitousek, P.M. and W. A. Rainers. 1975. Ecosystem succession and nutrient retention: a hypothesis. Bioscience. 25: 376-381
• Tilman D. et al. 1996. Productivity and sustainability influenced by biodiversity in grassland ecosystems. Nature. 379: 718-720.
• Hungate et al. 2003. Nitrogen and climate change. Science. 302: 1512.
• Mulholland et al. 2008. Stream denitrification across biomes and its response to anthropogenic nitrate loading. Nature. 452: 202-205.

• Finish the Carbon and Nitrogen Isotope Activity that was introduced in class.
• Carbon isotope data (Excel 2007 (.xlsx) 10kB Dec25 16)
• Nitrogen isotope data (Excel 2007 (.xlsx) 9kB Dec25 16)

Part 3 - Ecological Theory, Biodiversity and Grand Challenges in Biogeochemistry

In-class

Discuss Ecological Theory, Biodiversity, and Grand Challenge Papers

• Each group will report on the paper they read prior to class. The papers explore the effect of forest age and the effect of biological diversity on nutrient retention. Ecosystem stability is also explored using examples from two Long Term Ecological Research (LTER) sites: Hubbard Brook Experimental Forest (New Hampshire) and Cedar Creek (Minnesota). The Vitousek and Rainers (1975) paper on forest age/succession and nutrient uptake also provides a nice example of classic scientific literature in which the impact is still felt nearly 40 years later. The last set of papers are examples from the scientific literature demonstrating how biogeochemical theory can be useful in creating solutions for humanity's Grand Challenges. Examples include the role of nitrogen in global climate change and how excess nutrients may be removed from ecosystems.

Review/discuss carbon and nitrogen isotope activity.

• We will discuss the results of the carbon and nitrogen isotope activity that was started in class and you finished prior to coming to class. Special attention will be focused on the assigned questions.

Additional Resources

• Weiss, S.B. 1999. Cows, cars, and checkerspot butterflies: nitrogen deposition and management of nutrient-poor grasslands for a threatened species. Conservation Biology. 13: 1476-1486
• McClain, M.E. et al. 2003. Biogeochemical hot spots and hot moments at the interface of terrestrial and aquatic ecosystems. Ecosystems. 6: 301-312.
• Zak, D.R. et al. 2006: A Molecular Dawn for Biogeochemistry. Trends in Ecology and Evolution. 21: 288-295.
• Swap, R. et al. 1992. Saharan dust in the Amazon Basin. Tellus. 44B: 133-149.
• Lavery, T.J. et al. 2010. Iron defecation by sperm whales stimulates carbon export in the Southern Ocean. Proceedings of the Royal Society B: Biological Sciences. 277: 3527-3531.