Biochar to Clean and Green: Will All Forms of Biochar Amendments Improve the Quality and Quantity of Green Roof Runoff? DATE: June 14th, 2013 PROJECT: Senior ESRM Capstone Thesis NAME: Gar-Yun Ho B.S. Environmental Science and Resource Management B.L.A. Landscape Architecture ADVISOR: Prof. Soo-Hyung Kim
PROJECT SUMMARY Extensive green roofs provide environmental, economic, and aesthetic benefits. Yet, studies have shown that the quality of green roof runoff is decreased from higher levels of watersoluble nitrates and phosphorus being leached from fertilizers present in green roof substrate. Biochar, a by-product of the pyrolysis of organic materials thermally decomposed to produce energy, has proven to provide multiple environmental assets: pollution remediation, increased water-holding capacity, and carbon sink capabilities. This project evaluates and compares the impact that two types of biochar have on the quality of runoff leached from green roof soils, as well as water-retention abilities of the amendments. Two different types of 7% (v/v) biochar, added to a green roof soil mix currently used in a permanent installation at the University of Washington, were tested. 5 cm deep green roof trays with and without biochar were planted with common green roof species: Allium cernuum (nodding onion), Festuca glauca (blue fescue), and Anaphalis margaritacea (western pearly everlasting), and unplanted trays with and without biochar were also tested as controls. Runoff was collected and analyzed for nutrient content and electrical conductivity. Amending green roof soils with biochar may be the key to improving storm water runoff quality and potentially mitigating a future source of water pollution. Electrical conductivity was significantly lower for biochar treatments with and without fertilizer (Without Fertilizer, F(2,72) = 13.58, p < 0.05; With Fertilizer, F (2,72) = 8.535, p < 0.05). pH was significantly different for the treatments that received fertilizer (F(2,72) = 3.762, p = 0.028), but was not for the treatments that did not receive fertilizer. The greatest coverage was in the treatment groups with biochar amendments from Biochar Now, CO. The treatment groups with biochar from Carbon Cultures showed minimal amount of growth, with the least amount of growth in the treatment group with fertilizer along with the biochar (Total leaf/shoot: F(5,24) = 7.506, p<0.0002; total root: F(5,24) = 3.349, p<0.020; Shoot/Root Ratio: F(5,24) = 8.432; p<0.0001). Water-holding capacity, plant growth, and nutrient retention are all interrelated in soil and plant interactions. Therefore, although evidence suggests that biochar does have a significant effect, it may be difficult to deduce causal connections between tested attributes and experimental results. Conclusive analysis for results must take into account potential interactions that may be affecting the results of the experiment.
INTRODUCTION About biochar. The production and use of biochar amendments is an age-old practice. Ample evidence has been found for the use of charcoal as soil additives in the Amazon Basin by pre-Columbian natives, as well as other parts of the world â&#x20AC;&#x201C; including Ecuador, Peru, Western Africa, South Africa, Australia, and Asia (Elad et al., 2011). However, the utilization of charcoal as soil amendments declined as charcoal increased in its value as fuel, and other synthetic fertilizers and pesticides were developed. Recently in the 21st century, the awareness of the benefits of biochar is steadily increasing once again, in a time when climate change, sustainability, and renewable energy are becoming issues and topics of increasing importance. Much more research must be performed on biochar, nonetheless, since soil health benefits must still be quantified, and standards for the production and implementation of biochar have still yet to be established. Biochar is a product of pyrolysis, an energy production process that results in three products: syngas, which provides energy for the pyrolysis process, liquid-fuels, and biochar (Kammann, et al., 2011; Lehmann, 2007). Pyrolysis involves the heating of biomass at moderate to high temperatures, ranging from 400°C to 800°C (Meyer et al., 2011), under low-oxygen or completely excluded levels of oxygen. Released from the exothermic processes the biomass undergoes during pyrolysis, heat, gases, and bio-oils are captured as energy products; biochar is the carbon-rich, low-density, solid byproduct of pyrolysis (Lehmann, 2007). Discovered to have a multitude of characteristics that are beneficial for plant growth and allow for carbon sequestration, biochar has also been found to reduce nutrient leaching from soils, and to increase soil fertility by increasing the cation exchange capacity of soils, as well as nutrient adsorbent capacities (Kammann, et al., 2011; Laird, 2008; Lehmann, 2007; Novak, 2009; Sohi et al., 2010). Other benefits include the promotion of mycorrhizal fungi and microbial ecology (Rondon et al., 2007; Sohi et al., 2010; Warnock et al., 2007), and the neutralization of phytotoxic compounds in the soil (Wardle et al., 1998). The addition of biochar to clayey soils helps to lower overall bulk density, and allows for drainage, aeration, and root penetration (Laird, 2008). Subsequently, adding biochar to low-nutrient, sandy soils increases water and nutrient retention (Laird, 2008; Novak, 2009). Finally, biochar is currently one of the most effective adsorbent materials for metals (Regmi et al., 2012).
Applications of biochar amendments to soils have been investigated heavily in agricultural research, due to concerns from scientists, conservationists, and farmers about the degradation of soil and water quality (Laird, 2008). The ability to retain nutrients and adsorb cations is greater for biochar than any other soil organic matter (Sombroek et al., 2003), as a result of greater surface area, greater negative surface charge, and greater charge density (Liang et al., 2006). By increasing the amount of nutrients that are retained in soil through adsorption to minerals and organic matter, more nutrients are made readily available for plants, and can improve growth and yield productivity. Currently, there are a multitude of different techniques and technologies being tested for the production of carbonized organic matter. As each process results in fundamentally different physical and chemical properties in the char, it has become increasingly important to provide further assessment and comprehensive data on the different types of char and production technologies. Recent biochar production technologies include: torrefaction (pyrolysis processes at low temperatures), slow pyrolysis, intermediate pyrolysis, fast pyrolysis, gasification (biomass is partially oxidized in gasification chamber, with temperatures at about 800째C), hydrothermal carbonization (elevated temperatures are applied to biomass in a suspension with water), and flash carbonization (a packed bed of biomass is ignited with a flash fire, along with elevated pressure from above) (Meyer et al., 2011). Solid biochar product yields from gasification and fast pyrolysis processes are lower than the yields of the other processes (Meyer et al., 2011). Pyrolysis feedstock types also have a wide range, since not only agricultural waste residues can be used, but many other organic wastes can also be treated and converted as well (Elad et al., 2011). Some other feedstock types include wood, energy crops, sewage sludge, anaerobic digestate, and municipal wastes (Ronse et al., 2013). This variability allows for increased versatility, flexibility, and less competition for resources (Elad et al., 2011). Unfortunately, this diversity in feedstock, coupled with the numerous types of technology available, makes it difficult for studies to assure and predict product quality; physicochemical properties of biochar, along with their capabilities as soil amendments and carbon sinks may have significant differences (Ronse et al., 2013). Recent studies have begun to delve into the multi-dimensional aspects of biochar production. Evidence has been shown the fixed carbon content in biochar depends on the
intensity of the thermal treatment (Ronse et al., 2013), and yield amount depends on biomass feedstock, heating rate, pyrolysis temperature, and vapor residence time (Han et al., 2013; Ronse et al., 2013). pH and surface area positively correlated with pyrolysis temperatures (Ronse et al., 2013), and chars that have undergone only mild thermal treatment have larger amounts of volatile, more easily biodegradable, carbon compounds (Ronse et al., 2013). â&#x20AC;&#x153;Freshâ&#x20AC;? biochar that has not undergone as intense of a thermal treatment may contain mild toxicity (Ronse et al., 2013). The pH of biochar produced from wood is generally 2 pH units lower than other feedstocks, yet woody biochar allows for the highest potential of surface area and low ash content (Han et al., 2013; Ronse et al. 2013). Background â&#x20AC;&#x201C; Climate Change and Green Roofs. Sustainability is a major issue posed for our current age. The structure and planning of global urban communities must now respond and adapt to a multitude of environmental problems that are due to urbanization trends. These issues include: global climate change, the depletion of non-renewable sources of energy, and the degradation of air and water quality (Evans, 2011). Increased awareness, scientific discoveries and new publications on environmental health issues are currently challenging traditional approaches and attitudes towards urban health and city planning. In response to these environmental issues, scientists, policy-makers, and design professionals are exploring adaptive measures and interventions to address these threats to both agricultural sectors and urban socioecological systems (Evans, 2011) and to promote resilience and sustainable development.
One intervention that is becoming increasingly popular in the built urban environment is the implementation of vegetated green roofs on buildings. Contemporary vegetated green roofs provide many environmental, economic, social, and aesthetic benefits and uses. Some benefits include: improvement of storm water management, conservation of energy, mitigation of urban heat island effects, increased longevity of roofing membranes, reduction of noise and air pollution, provision of habitat and increase of urban biodiversity, space for urban agriculture, sequestration of carbon, and the provision of aesthetically pleasing green spaces for people to work, live, and relax (Getter et al., 2009; Rowe et al., 2011). A building simulation model that was supported by the U.S. Department of Energy showed that green roofs lower the demand for heating and air conditioning use in buildings (Getter et al., 2009). With a model of a generic building with a green roof that is 2000 sq. m., annual energy savings could range from 27.2 to
30.7 GJ of electricity and 9.5 to 38.6 GJ of natural gas, depending on the climate and design of the green roof (Getter et al., 2009). The type of vegetation planted and the amount of resources used varies, depending on the green roof design. Modern green roofs are separated into two categories: intensive or extensive. Intensive green roofs mimic parks and green spaces on the ground level, and typically have substrate depths greater than 15cm (Rowe et al., 2011). Intensive green roofs may contain shrubs and trees, along with groundcover, and exert a high demand on resources, including water and maintenance. Extensive green roofs require minimal maintenance, and have shallower substrate depths. An appropriate substrate composition is essential to reap the full environmental benefits that extensive green roofs could provide. Plant selection is mainly composed of herbaceous perennial or annual groundcover species. Due to building weight restrictions, resource use limitations, and maintenance limitations, extensive green roofs are more common than intensive green roofs. Maintenance, plant mortality, carbon footprint of green roof construction materials, weeding, and irrigation demands are costs that must be taken into account when investigating the benefits of modern green roofs. Objective. The objective of this capstone project was to evaluate nutrient-retention and water-absorption capabilities of biochar, and assess the impact biochar has on the quality of runoff leached from green roof soils. This project also determined whether or not biochar amendments on green roof soils could be effectively used to benefit and enhance plant growth in a green roof environment. Furthermore, the project assessed different levels of fertilizer treatments, to determine if there was an optimal balance between biochar amendments and fertilizer treatment levels for plant growth, water absorption, and nutrient retention. Finally, this study assessed any discrepancies in results between two types of biochar that have undergone different speeds of pyrolysis, are composed of different types woody material, and come from different manufacturers – one from Washington state, and one from Colorado state. Hypothesis and Expected Results. Biochar applications have been tested extensively on agricultural soils, and have shown to reduce nutrient leaching, increase soil fertility, increase water absorption, and enhance plant growth. Treatment groups with biochar amendments were expected to produce similar results and improve the resulting runoff water quality from the “rainfall” events in comparison to treatment groups without the amendments. Plant growth in the
treatment trays with biochar and liquid fertilizer were hypothesized to be the greatest, while plant growth in the treatment trays without biochar and without liquid fertilizer would be the least. Nutrient leaching was expected to be the highest in the treatment groups that received liquid fertilizer, but should also be decreased with biochar amendments. Water absorption and retention should be greatest in the groups treated with biochar and liquid fertilizer. MATERIALS AND METHODS Treatments. Biochar from two different manufacturers (Biochar Now, Loveland, CO; Carbon Cultures, Seattle, WA) will be tested. The biochar product from Biochar Now originates from beetle-kill western pine parent materials (Pinus contorta, Pinus ponderosa, some Pseudotsuga menziesii), which undergo a slow pyrolysis process (resonance time greater than 5 hours, with a reaction temperature greater than 400°C). The biochar from Carbon Cultures comes from slash piles, mainly composed of a mix of hardwood and softwood species common in the Pacific Northwest (Pseudotsuga menzesii, Thuja plicata, Prunus serotina, Pinus spp.), which have been pyrolyzed specifically at slash pile sites with an innovative mobile kilns, with burn durations from 90 minutes to 3 hours. Standard liquid fertilizer (10X Qubit solution, with ammonium nitrate (NH4)NO3) was used for the fertilizer treatments. 5 cm deep planting trays, 25.4cm by 25.4cm, will be filled with a soil mix prepared specifically for green roof environments (Croft-top A, mixed by Specialty Soils from Covington, WA). The soil mix contained (per bag): Ingredients (%/m3): 5.66% Diatomaceous earth (unkilned, natural soil insect control); 9.43% Saskatchewan sphagnum fine peat (air dried); 61.32% Pumice SLO #7; 14.15% KL Pumice; 9.43% Prep L. & G. Compost. Nutrients (kg/m3): 0.125 Sulphate of potash (0-0-50); 0.13 Ammo-phosphate (11-52-0); 0.15 Ferrous sulphate (20% Fe); 0.59 Agricultural gypsum (Calcium Sulphate 90%); 1.25 Apex 22-6-12 (12-month release); 1.79 Dolomite flour (Calcium Carbonate 50% - Magnesium Carbonate 40%). Nutrients (g/m3): 74.59 fritted micronutrients (Fe, Cu, Zn, Mn, B, Mo); 32.08 essential wetting agent & growth stimulant (OMRI approved). pH range: 6.2 – 6.6, EC range: 1.3 – 2.2. Plant materials. Proper plant species selection is essential for the long-term performance of green roofs. Species must be able to withstand harsh environmental conditions. High air temperatures, exposure to wind, extreme temperature and moisture fluctuations in the root zone
due to shallow substrate depths are some of the adversities that plants must face in a green roof environment (Schroll et al., 2011). Due to high solar radiation and exposure, as well as minimal to no irrigation, it is important that chosen species have drought tolerance. As a result of the many external restrictions, suitable plant species are limited to herbaceous species, grasses, drought-tolerant succulents, and mosses. Results from a study conducted in Corvallis, OR, showed that in the Pacific Northwest there was potential for further study on bulbs and rhizomatous forbs, as well as the commonly-used succulents. These plant species could potentially fare well on extensive green roofs in seasonally dry climates, even without supplemental irrigation (Schroll et al., 2011). Future studies for green roof plant selection should explore a mix of different species besides non-native sedums, which might not be the optimal vegetation choice. Research has typically focused on remediation-based ecological services of green roofs, with little focus on the assembly and maintenance of biotic systems and a biodiverse range of species (McGuire et al., 2013). Sedum species are most often chosen for the implementation of extensive green roofs, and are often grown in monocultures and pre-grown mats; Sedums can endure a range of tough conditions, and are hardy plants that can store water and use CAM photosynthesis. However, Sedums might not be the optimal choice when attempting to assemble a biodiverse community of plant species. By choosing native or local plant communities that have evolved to survive in their regional and microclimate regions, green roofs may require less irrigation and maintenance, and also provide ecological services as habitat for regional species (MacIvor et al., 2011). In terms of stormwater remediation, evidence has shown that graminoids are the most successful in capturing rainfall, and are also amongst some of the most successful in surviving drought periods. 4â&#x20AC;? pots of Allium cernuum (nodding onion, a bulbous species), Festuca glauca (blue fescue, a native grass), and Anaphalis margaritacea (western pearly everlasting, a stoloniferous perennial herb that attracts butterflies and fares well in dry conditions) were purchased and shipped from Plants of the Wild (Tekoa, WA), and were planted on 27 February, 2013 at the University of Washington Center for Urban Horticulture (Seattle, WA) into trays filled with the Croft-top-A green roof soil mixture. In total, there were 36 treatment trays, each treatment group
consisting of 5 trays, with 1 un-planted control tray per treatment. (See diagram 1)
Diagram 1. Treatment Groups â&#x20AC;&#x201C; flats were randomized per each treatment session.
Nutrient-absorption and water-retention analysis. Watering events were conducted on treatment groups in intervals of 3 days. Initial water runoff was collected half an hour after the event, and was analyzed for pH, dissolved ions, and electrical conductivity (mms). Initial preplanting water holding capacity of each treatment group will be attained by calculating the volume of each treatment tray, measuring equal volumes of completely dry samples, and then measuring the weight when completely saturated. Weights will be converted to volumes and multiplied by the factor by which the sample volume is increased to calculate the water holding capacity.
Plant health analysis. After the controlled “rainfall” events, total biomass of plants per tray will be taken. Morphological traits will be measured through ImageJ (NH) software, which will assess the “greenness” of each plot. To measure the percent composition of each species, a point-grid method will be used. Statistical methods. Treatment groups will be randomized in placement and arrangement on greenhouse tables. Trays will be randomly moved after each “rainfall” event. Water-retention, nutrient retention, and biomass between all six treatments will be analyzed by ANOVA tests, and the different biochar treatments will be compared and analyzed by t-tests. Online statistical analysis tools were provided by St. John’s University. RESULTS Water Quality. Electrical conductivity was significantly lower for biochar treatments with and without fertilizer (Without Fertilizer, F(2,72) = 13.58, p < 0.05; With Fertilizer, F (2,72) = 8.535, p < 0.05) (See diagram 2). pH was significantly different for the treatments that received fertilizer (F(2,72) = 3.762, p = 0.028), but was not for the treatments that did not receive fertilizer (See diagram 3). Overall, the trend showed that both types of biochar provided similar nutrient adsorption capabilities, in comparison to the treatment groups without biochar amendments. Electrical conductivity in substrate results from the presence of metals (sulfides) in the soil, and is influenced as well by porosity, clay content, and pore saturation. As some of the most toxic inorganic pollutants found in water and soils, heavy metals can be taken up by plants, leach into groundwater, and cause poisonous and harmful effects to humans and non-human species. Evidence has shown that biochar is an effective adsorber of metals (Regmi et al., 2012). Furthermore, activated carbon solids may be one of the most suitable substrates for pollutant adsorption, due to its porous structure (Regni et al., 2012). Biochar has been shown in studies to increase nutrient retention capabilities in soil (Kammann, et al., 2011), and thus reduce the amount of nutrients leaching into runoff water. Soil pH measures the acidity or alkalinity of the substrate. As a result of rainwater runoff that leaches basic ions, soils typically become more
acidic. Biocharâ&#x20AC;&#x2122;s nutrient-retaining capabilities could slow down the acidification of soils.
Diagram 2. Electrical Conductivity comparison between treatment groups
Diagram 3. pH comparison between treatment groups
Plant Growth. The total coverage of plants per treatment group were shown to be significantly different, using the point-grid method (See Figure 1, Figure 2) (F(5,24) = 4.101, p < 0.005). The greatest coverage was in the treatment groups with biochar amendments from
Biochar Now, CO. Total shoot and root biomass weights were also taken and analyzed, along with shoot-root ratios. The treatment groups with biochar from Carbon Cultures showed minimal amount of growth, with the least amount of growth in the treatment group with fertilizer along with the biochar (See diagram 4). (Total leaf/shoot ANOVA: F(5,24) = 7.506, p<0.0002; total root ANOVA: F(5,24) = 3.349, p<0.020; Shoot/Root Ratio ANOVA: F(5,24) = 8.432; p<0.0001) The results for the shoot to root ratio provided an interesting comparison between treatments with and without additional fertilizer, as ratios were closer to 1 with fertilizer, and significantly smaller without the additional fertilizer treatments (See diagram 5). The species coverage between different biochar treatments were not statistically significant (See diagram 6). Upon assessment with the ImageJ software, there was no significant difference between treatment types. However, image processing was complicated, as the software found it difficult to differentiate between substrate and vegetation, and the multitude of colors from shoots and flowers made it even trickier to process.
Figures 1 and 2. Point-grid method of determining coverage of each species, and overall coverage.
Diagram 4 and 5. Total root biomass and root to shoot ratio comparison between all treatment groups.
Diagram 6. Species %coverage between two different biochar types and their fertilizer treatment groups
Water retention. There was a significant difference between the different treatment groups for total water runoff volume (mL) (F(5,144) = 6.351, p < 0.05), with the greatest amount
of water retention from the treatment trays with Biochar #1, with fertilizer (See diagram 7). However, the cause for this difference is unclear, as there are a number of plant, soil, and environment mechanisms and interactions that could be influencing the water retention of the different treatments.
Diagram 7. Water runoff volumes for different treatment groups
DISCUSSION Due to the variability of biochar production technologies and materials, further research and publication of reliable and comprehensive data is needed for proper evaluation on biochar. A literature review (Meyer et al., 2011) on the technological, economical, and climate-related aspects of biochar production technologies carried out an analysis on different published scientific articles on the different available carbonization technologies. What was discovered was that, although there was a significant amount of research done on pyrolysis processes, few studies were performed on gasification, and even less on hydrothermal and flash carbonization technologies (Meyer et al., 2011).
Many aspects of biochar-based remediation of soil must still be researched for increased effectiveness for the utilization of these amendments â&#x20AC;&#x201C; some knowledge including: proper assessment of the various techniques and technologies used to process biochar, the length of time and temperature needed for optimal development of adsorptive properties, further comparison of different feedstock types, and increased precision in estimating the half-life of biochar (Lehmann, 2007). There have been vague suggestions on the extent of biocharâ&#x20AC;&#x2122;s longevity, but further assessment of different biochar types from different feedstocks that decompose at different rates would be valuable in the discussion of climate change mitigation. Another aspect of biochar production that should be further assessed would be cost-estimate studies on the viability of certain methods of biochar production. How might biochar be made more readily accessible for the public sector, especially urban farmers and designers that are seeking to enhance and increase the presence of green infrastructure within the city? Finally, there are some aspects of the experimental design that could have been improved upon. All of the plants were planted in the trays within 1-4 days of receiving the shipment. However, there may be some variability in growth amount, which could affect the amount of water and nutrients absorbed by plants per tray, and skew results. Also, since the plants were not grown from seed and monitored from the start, and were instead bought from a nursery, further variability in plant growth and health could be increased. Also, this experiment was conducted in the green house at the University of Washington Center for Horticulture, and was not tested in an outdoor roof environment. Although conditions were simulated with limited irrigation, many factors of an outdoor environment could affect the actual results of biochar amendments to green roof soils; one issue could include wind and water erosion of biochar particulates. Another issue is the limitation of time. Age is an important factor that is the most commonly overlooked between all green roof evaluations and studies. Most studies typically draw conclusions after one or two years. When studies are lengthened to three or more years, conclusions can be significantly, or even dramatically, different. This capstone project investigates nutrient leaching and water runoff during the implementation phase of green roofs, which is when the most pollution occurs. However, plants are given only 2 months of growing time, when the implementation phase (complete with irrigation, fertilization, and monitoring) of a green roof should span to at least half a year.
In conclusion, biochar is an age-old technology that is once again being utilized and assessed by scientists, farmers, and researchers for its many beneficial properties as a substrate amendment, carbon-storing potential, and tool for environmental restoration. The volumes of evidence available that supports the utilization of biochar for environmental and economical benefits has been overwhelming; efforts should be made to provide precise assessments of biochar production and usage, and to make biochar readily accessible for all scales of implementation. APPENDIX Acknowledgements. I would like to thank my advisor, Professor Soo-Hyung Kim, who patiently helped me throughout the process of this capstone research project. I would also like to thank everyone at the Plant Ecophysiology Lab, especially Drew Zwart, Hyungmin Rho, and Jenny Knoth. Finally, I would like to thank Biochar Now and Carbon Cultures for generously donating samples of biochar for this experiment. Background information. Gar-Yun Ho is currently pursuing a double degree in Environmental Science and Resource Management (BS) and Landscape Architecture (BLA) at the University of Washington â&#x20AC;&#x201C; Seattle. She is particularly interested in urban design, ecological restoration, and environmental horticulture and how ongoing research in these fields informs and interacts with the process and progress of modern landscape design. She is also an undergraduate student researcher at the Plant Ecophysiology Lab, led by Professor Soo-Hyung Kim, PhD and Associate Professor of Plant Science in the School of Environmental and Forest Sciences at the University of Washington. Research in the lab involves the exploration of the way that plants function, respond, and interact with various abiotic and biotic factors in the environment, and focuses on the topics of plant environmental stress physiology, process-based modeling of crop physiology and ecology, and the ecophysiology of crop-microbe interactions. Evaluation and Dissemination. Experimental results were presented, evaluated, and discussed at the Undergraduate Research Symposium. The Symposium is a conference that brings together the research work of undergraduates at the University of Washington, and allows for a university-wide discussion on a diverse range of research topics from all disciplines. In 2012, nearly 1,000 undergraduates participated in the Symposium, which had an attendance of
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