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Designing profitable algal biofuel ponds: Ecological applications to _____________________________________________________________a global problem Jakob Nalley – ESP 801 White Paper March 11, 2014 ___ Abstract As global development continues to increase at unprecedented rates, the demand for fossil fuel energy sources has increased exponentially. This rapid rate of consumption has led to a number of environmental issues (i.e. habitat destruction, climate change), while analysts have projected that fossil fuel resources will be depleted within one hundred years. This large demand of a finite resource and the accompanying environmental impacts has generated a large interest in developing alternative, more environmentally sustainable energy sources. One extremely promising alternative fuel source is producing “bio-­‐diesel” fuel from algae. But, there are a number of limitations to mass-­‐producing algal derived diesel that must be addressed for this technology to reach an industrial scale. Here we will focus on the research being conducted to achieve the highest possible fuel yields through optimizing the cultivation techniques. These algal systems, just like large agricultural operations (corn, soy, etc.) will be extremely vulnerable to weather conditions, invasion by “weeds,” and viruses/bacteria. This paper focuses on how ecologists are applying some basic knowledge of community and ecosystem interactions to achieve large energy yields from these algal systems while reducing the negative impacts on the environment. Introduction The era of inexpensive fossil fuels is coming to a rapid end as global demand for energy is ever increasing. If this rate of consumption continues to grow at a conservative level of 3% annually, a recent report projects that fossil fuel resources will be completely depleted within the next 60-­‐100 years, depending on how successful new energy reserve exploration is (Stephens et al., 2010). In addition to these resources being finite and rapidly being depleted, the environmental impacts of their combustion is beginning to be realized. Habitat destruction for mining and extraction has dramatic impacts on wildlife populations and the quality of other natural resources (water, air, etc.). The growing evidence for human-­‐caused climate change is also a direct result from combusting these fossil fuel sources releasing an unprecedented amount of carbon dioxide (CO2) into the atmosphere. This increased level of CO2, a strong greenhouse gas, is leading to increased global temperatures, rising sea levels, and more frequent and violent storms. These findings demand that society begins to invest and develop alternative energy resources. For these renewable resources to be realized, they must be produced at an industrial scale to meet the increasing demand, be produced efficiently to maintain low energy costs for the consumers, not take land from the global food system, and most importantly be environmentally sustainable. There have been a number of biologically derived energy sources explored over the past few decades, such as corn-­‐based ethanol, soybean biodiesel, cellulosic ethanol derived from any plant material, and palm oil. Most of the these biofuel options have been hampered from reaching an industrial scale due to large land requirements, large energy inputs, and low energy yields (Mata et al., 2007). One of the most promising biofuel resources currently being investigated is biodiesel made from algae. Microalgae, or microscopic algae, holds a huge potential for biofuel production due to its rapid reproduction rate, low nutrient requirements, high energy content, and low land requirement for industrial scale production. Algae also sequester large amounts of CO2 throughout their short life, resulting in a “carbon neutral” life cycle for this fuel source, meaning the CO2 they take in during their life is equal to the CO2 produced when the biodiesel is combusted (Chisti 2007). This highly promising biofuel source has not been realized though due to a number of limitations. The cultivation of such large quantities of algae to meet the demand has proved problematic while the harvesting and extraction of the fuel is extremely energy intensive (NRC, 2012). There are countless species of microalgae, and each species has a different level of lipid content. Lipids are the feedstock that can be extracted from the algal cells to be converted into diesel fuel. Some algae can be made of 80% lipids, while some can be only 10% by volume. But algae face a trade-­‐off where they can either produce lipids to store energy for later use (similar to bears “fattening” for hibernation), or they can asexually reproduce. So species that produce high lipid content per cell, do not divide rapidly, resulting in low overall fuel production. Algae that rapidly reproduce generate a large amount of algae that has little lipid content, again resulting in a low overall fuel content. A large research effort is investigating how these species can be genetically manipulated to ultimately produce lipids AND continues to reproduce. My research bypasses this genetic component, and investigates how we can combine different algal species together in the same system to produce large amounts of lipids (precursor to diesel fuel) through the application of basic knowledge we have gleaned from studying natural systems. Application of Ecological Principles to Optimize Yields To help minimize costs for mass-­‐producing algae, cultivating algae in large outdoor ponds will be required. These ponds can span many acres with a depth of around thirty centimeters and a single paddlewheel would gently circulate the water throughout the “raceway” pond, aptly named due to their shape (Figure 1). Although these systems are relatively inexpensive to build, the main drawback of this approach is the pond will be open to the surrounding natural environment. These ponds will be experiencing fluctuating temperatures and light levels (daily, seasonally), invasion of “weed” algal species that are undesired, algal crop loss due to predation from zooplankton, pond-­‐wide pathogen infections, and competition between algae for nutrients like nitrogen and phosphorus. With these pond conditions in mind, it seems logical to address these issues like a farmer would: apply our knowledge of natural systems to manage these algal ponds to ultimately achieve optimal yields. This can be accomplished through a single, simple approach: promoting species diversity. Figure 1: Design of an outdoor, open algal pond. Top View: Paddlewheel gently circulates the water through the raceway. Profile View: Depth of the pond is very shallow, 30 centimeters, to allow for light to penetrate through the entire algal culture. Photo Credit: hplusmagazine.com A large body of work has investigated the role biodiversity plays in ecosystem functioning and dynamics. Here we will define biodiversity as the number of species present in the system, where 1 species would be the lowest measure of diversity. This work has produced a number of core ecological theories that have a number of highly beneficial applications to topics like restoration efforts and biofuel production. To summarize the core findings: Higher levels of species diversity leads to: •
Higher productivity (Naeem et al., 1994) •
Reduced success of establishment of invading species (Farigone and Tilman, 2005) •
Higher stability and reduced vulnerability to environmental stress (i.e. drought) (Tilman and Downing, 1994) •
More efficient use of resources (Striebel et al., 2009) These fundamental findings can be explained through an understanding of a species “niche,” or the set of resources and range of environmental conditions a species can live under. For example, each algal species has a different range of temperatures that it thrives under, different levels of nitrogen and phosphorus it requires, different light levels to properly photosynthesize. These differences lead to algal species with different niches. In Figure 2, the axes could represent any resource (ie nitrogen concentrations) or environmental factor (ie temperature) within a given environment. The circles each represent a single species range of conditions under which it can survive, or its niche. As you increase the number of species present in the environment, the amount of empty niche space (black color) decreases. Meaning that in a given environment, if more species are present more niche space will be filled, resulting in higher overall productivity compared to an environment with lower species diversity (less occupied niche space). With environmental conditions always changing through time, more occupied niche space results in an overall community has species that thrive under all temperatures resulting in less susceptibility to these environmental fluctuations. And finally with more niche space filled, invading species do not have any available niche space to take advantage of, leading to low invasion success. With these ecological principles in mind, let us work through a thought experiment to investigate how promoting algal species richness in these outdoor ponds can be beneficial. Let us investigate the two potential approaches: growing a single algal species (“monoculture”), or growing a community of algal species together (“polyculture” or “mixture”). If a single species of algae were to be grown in an outdoor pond, unwanted algal species, or “weeds,” and algal predators called zooplankton, borne by the wind or stuck to waterfowl that land in the ponds, would quickly invade the pond. These “weeds” will begin competing for vital nutrients with the wanted algal species, potentially pushing the fuel species to extinction. The zooplankton will also begin preying on the algae in the pond, including the fuel species, decreasing the overall fuel production of the pond (Smith et al., 2010). Pathogens, such as fungi and/or bacteria, will also quickly invade through these “duck butt introductions” when birds land in the pond. These pathogens could quickly infect the entire population of algae and within a 48-­‐hour period kill the entire fuel crop (Shurin et al., 2013). The local environmental conditions will also influence the desired algal species within the pond, and as light levels and temperatures fluctuate throughout the day and seasonally, these conditions may become too intense for the algal species to handle, ultimately leading to the species demise. Overall, producing biodiesel from a single species of algae in an outdoor, open pond system appears to be rife with limitations and problems. Next, let us move to a more “community level approach” with an outdoor pond containing a mixture of algal species (>10 species of algae). A duck lands in the pond carrying a number of “weedy” algal species and zooplankton. The assembled mixture of desired algae in the pond will occupy a higher level of available niche space greatly limiting the ability of “weed” species to establish. The zooplankton will devour the fuel crop regardless of the level of diversity, so to combat predation, small fish that eat zooplankton can be added to the pond to tamp down zooplankton populations, effectively making predation non-­‐existent (Smith et al., 2010). Just like in humans where certain individuals are immune to certain pathogens, if a pathogen infection were to spread through a diverse algal pond, certain species may be susceptible while other may not be. Fungicides can also be applied to the systems if a particular virulent strain were to infect the ponds. This “community level approach” would maintain large quantities of WANTED algal species within the pond throughout environmental fluctuations, ultimately leading to consistent, high levels of energy yields. Through promoting biodiversity of primary producers, studies have shown that plants biomass increases compared to systems with lower biodiversity. With algal biofuel production though biomass AND lipid production are essential for these ponds to have large energy yields. To date only a few studies have investigated how biodiversity impacts lipid production. A terrific study by Stockenreiter et al. (2012) investigated how biodiversity impacted both algal biomass and lipid production (Figure 3). Not only did the researchers find that more biologically diverse systems yielded higher than expected biomass, they also produced higher levels of lipids, or energy content, compared to less diverse systems. This provides evidence that promoting species diversity within these systems is largely beneficial, and we are building on this to begin investigate how changing environmental conditions would impact algal biofuel production. How we are applying this knowledge (Past and future research questions) Our research draws on this vast body of ecological research to address an overarching question of, “Can we use ecological principles to produce large quantities of algal biofuels in outdoor, open ponds?” Underneath this umbrella question, we are addressing smaller questions that can ultimately be combined to address the larger questions. 1.) How does fluctuating light levels influence the growth and lipid production of individual algal species and a mixture of species? 2.) Can traits of algal species help us assemble a highly productive algal community under fluctuating temperatures? 3.) Which algal species are better invaders/competitors in highly biodiverse systems? And why? Some Concluding Thoughts Biofuel technologies are still hindered by a number of limitations, but I remain optimistic that with a growing societal need and interest these technologies will continue to develop and overcome these issues. Through the application of growing understanding of natural systems, I believe that algal-­‐based biofuels can be a reality in the future. Our research is focusing on how we can begin to “piece together” a species-­‐rich community of algae that can be tailored to the environmental conditions and resource levels that are present to ultimately produce high levels of diesel feedstock to help meet the ever increasing demand for energy in the developing global economy. References: Chisti Y (2007) Biodiesel from microalgae. Biotechnol Adv 25:294–306. Fargione, Joseph E., and David Tilman. "Diversity Decreases Invasion via Both Sampling and Complementarity Effects." Ecology Letters (2005): 604-­‐11 Mata TM, Martins A a., Caetano NS. Microalgae for biodiesel production and other applications: A review. Renew Sustain Energy Rev (2010) 14:217–232. Naeem, Shahid, Lindsey J. Thompson, Sharon P. Lawler, and Richard M. Woodfin. "Declining Biodiversity Can Alter the Performance of Ecosystems." Nature National Resource Council. Sustainable Development of Algal Biofuels in the United States. 2010 Shurin JB, Abbott RL, Deal MS, Kwan GT et al. Industrial-­‐strength ecology: trade-­‐offs and opportunities in algal biofuel production. Ecol Lett, (2013) 16:1393-­‐1404 Smith VH, Sturm BSM, deNoyelles FJ and Billings SA. The ecology of algal biodiesel production. Trends Ecol Evol, (2010) 25:301-­‐309. Stephens E, Ross IL, Mussgnug JH, et al., Future prospects of microalgal biofuel production systems. Trends Plant Sci. (2010) 15:554–64. Striebel, Maren, Stephan Behl, and Herwig Stibor. "The Coupling of Biodiversity and Productivity in Phytoplankton Communities: Consequences for Biomass Stoichiometry." Ecology 90.8 (2009): 2025-­‐031 Stockenreiter M, Graber A-­‐K, Haupt F and Stibor H. The effect of species diversity on _____lipid production by micro-­‐algal communities. J Appl Phycol, (2012) 24:45-­‐54 Tilman, David, and John A. Downing. "Biodiversity and Stability in Grasslands." Nature (1994) 376:363-­‐65. Print. Tilman, David. “Ecological Consequences of Changes in Biodiversity: A Search for General Principles .” Ecology (1999) 80:1455-­‐74