Lecture 1 Study Guide: Introduction to Biogeochemistry Brahney 2017 Introduction to Biogeochemistry Learning outcomes Gain an appreciation for the scope and power of biogeochemistry Understand the merits and limitations of observational, experimental, and modeling studies Understand system science terminology Be able to create systems diagrams and conduct basic systems analyses Understand the concept of ecological stoichiometry and how it applies to system science Readings Jacobson et al. Chapter 1 Videos Daisyworld: https://youtu.be/sCxIqgZA7ag What is Biogeochemistry? Biogeochemistry (BGC) is in a broad sense the study of elemental cycles through abiotic and biotic systems. In practice biogeochemists use geochemistry as a tool to quantify interactions amongst ‘geospheres’, trace the movement of key nutrients or pollutants through the environment, quantify aspects of ecosystem function, determine anthropogenic impacts on the environment, develop tools for remediation. Biogeochemisty is broad in scope with respect to both spatial (sub-micron (µm) to astronomical units (AU)) and temporal scales (seconds to billions of years). Many different elemental cycles (C, N, P, etc) are influenced by processes that occur at different rates and can therefore be considered at different time-scales. For example, at small spatial scales the carbon cycle is influenced by microbial production of enzymes that break down organic matter. At large temporal scales the carbon cycle in influenced by the rate of weathering and volcanic outgassing. How are biogeochemical processes studied? Biogeochemists use one or a combination of scientific studies to address specific questions. These are ‘Observational’, ‘Experimental’, and ‘Modeling’ studies. Each method has strengths and limitations and best practice typically involves combining one or more of the approaches. Observational There is only one planet earth so we cannot run repeated experiments at the planetary scales nor can we go back in time to sample a lake or atmosphere. For many research questions, the best we can do is use observational studies to make inferences about how the system is functioning. We use what is called ‘inductive reasoning’ or logic, to determine the most probable mechanism given the available data. Lecture 1 Study Guide: Introduction to Biogeochemistry Brahney 2017 An example - Early in Earth’s history rocks were formed that cannot be formed today. For example, bandedironstone formations required extremely large amounts of reduced iron to accumulate within the oceans. The presence of oxygen on the surface of today’s Earth causes iron to oxidize. - Based on this geochemical knowledge, we can determine (with a high probability) that the early Earth atmosphere did not contain oxygen. Experimental Experiments are the foundation of many scientific disciplines and play a strong role in biogeochemistry. Experiments allow researchers to manipulate a system in a controlled way using repeated trials so that cause and effect, and variability of the effect, can be determined. A classic example is the nutrient amendment studies conducted at the Experimental Lakes Area by Dr. David Schindler (Schindler 1974 “ Eutrophication and Recovery in Experimental Lakes Project”) . At the time, effluent was leading to the large scale fouling of waterways, e.g. drinking water was contaminated by toxic algal blooms, and sport fisheries were closed due to massive fish kills. It was not known which limiting nutrient was responsible for increased blooms, C, N, or P. Dr. Schindler conducted an experiment where he separated a lake into two basins, on one side he added C and N, and on the other side he added C,N, P. Only the side with P added produced algal blooms, demonstrating that phosphorus was the limiting nutrient leading to algal blooms. This blog sums up the strengths: http://evidenceanderror.blogspot.com/2012/05/phosphorous-detergent-and-canadas.html A limitation of experimental studies in the environmental sciences is that it can be difficult to extrapolate results beyond the bounds of the experiment. With respect to P limitation in lakes, this is often true – but not always true (See Lewis and Wurtsbaugh 2008 “Control of Lacustrine Phytoplankton by Nutrients: Erosion of the Phosphorus Paradigm) Modeling Modeling is an approach frequently used because some aspects of BGC systems are fundamentally not measureable. E.g. How do you measure in real time the rate of subduction and carbon loss to the lithosphere? So many processes that are global in nature are modeled. We can also model what might happen in a river, a lake, or across a given region. Advantages to modeling - Provides an overview of what may be happening in a system - Can identify knowledge gaps, provide a hypothesis to test using an experiment - Helps to estimate the relative magnitudes of anthropogenic and natural fluxes - Stimulates q’s such as where is the material coming form, where is it going Lecture 1 Study Guide: Introduction to Biogeochemistry Brahney 2017 Disadvantages to modelling - Superficial – does not fully describe what the mechanisms Gives false impression of certainly - cycle must mathematically add up Based on averages of not easily measured components. Three fundamental concepts in Biogeochemistry - System science Stoichiometry Thermodynamics System Science - Definitions Reservoir: An amount of material defined by certain physical, chemical, or biological characteristics. Typically as mass, or moles. Examples are O2 in the atmosphere, Carbon in the soils, water in the atmosphere Flux: the amount of material transferred from one reservoir to another per unit time. (mass per time) or we may consider ‘flux density’ mass per unit area per unit time. Examples are evaporation of water from the ocean to the atmosphere. Rate of phosphorus deposition to lake sediments, rate of denitrification – conversion of one form to another Source: Flux into a reservoir Sink: Flux out of a reservoir Budget: overall balance sheet. Turnover time: the ratio of the content to the sum of sinks or sources ( Reservoir/Flux). E.g Time it will take to empty the reservoir in absence of sources or average time spent by individual molecules or atoms in the reservoir Cycle: A system consisting of two or more connected reservoirs. Where a large part of the material is transferred through the system in a cyclic fashion. Steady state: - if sources and sinks balance and do not change with time. Open System: A system that exchanges matter with the environment Closed System: A system that is isolated from the environment. Positive Feedback Loop: When the product of a reaction enhances the propensity for the reaction to occur. E.g. it amplifies or enhances the effects and tends to move a system away from the equilibrium state. Negative Feedback Loop: Negative feedbacks will buffer changes to hold a system in equilibrium or steady state. Steady State vs Equilibrium: A system that is in steady state means that it is not changing over time because inputs equal outputs. The maintenance of that state requires continual work. If the processes Lecture 1 Study Guide: Introduction to Biogeochemistry Brahney 2017 that maintain the system cease, the conditions would change. In contrast, equilibrium refers a nonchanging state where no energy is required to maintain the condition over time.
