Data Science
In addition to laboratory and field measurements used to answer novel questions in ecology, Maya often uses data science techniques that include meta-analysis, systematic reviews, sociological surveys, computer models and spatial analyses to synthesize large bodies of work or scale up localized findings to regional, national or global levels. Data science allows for the compilation of data to develop theory and build more robust conclusions as well as facilitates interdisciplinary connections between biogeochemistry, ecology, food, and global change in order to build a path towards sustainable future.
Abstracts
Deep Soil Nitrogen.
Previous estimates of deep soil reservoirs of biologically available nitrogen have been limited to that of desert soils, however recent evidence suggests that these pools are far more ubiquitous across biomes and therefore may be an unaccounted for source in global nitrogen budgets. We surveyed the literature and found 92 instances of deep soil (2-86 m) inorganic nitrogen measurements, most of which were reported as nitrate, across a variety of biomes. From these studies, we collect metadata such as soil texture, depth and type; N deposition and fertilization rates; land use history; and precipitation and mean annual temperature. We use statistical and process-based approaches to evaluate major controls on soil nitrogen accumulation in the form of nitrate, use a spatial modeling approach to project other areas where deep soil nitrogen may accumulate. We found that deep soil nitrogen pools ranged from 5.24-3,702 kg N/ha, with a mean of 522 kg N/ha. Deep soil nitrogen was significantly higher beneath grasslands and shrublands compared to other vegetation types (p=0.0005). In croplands, deep soil nitrogen increased significantly with fertilization rate (p = 0.04). When soil orders were reported, deep soil nitrogen pools were typically found in oxisols and ultisols. Deep soil nitrogen was negatively correlated with mean annual temperature (p=0.001) and precipitation (p=0.03). As a rough approximation, if we apply our mean soil nitrogen inventory value to just highly weathered, and typically deep, oxisols (8% of soils) and ultisols (7% of soils), we get an estimate of 3,993 Tg, which increases the total soil nitrogen pool (9,500 Tg) by 30% globally. While we found evidence that nitrogen deposition, historical nitrogen fixation, and fertilizer inputs contribute to this pool, the source and fate of deep soil nitrogen likely varies by region. We examine the possible influence of nitrogen deposition, rock derived nitrogen, fertilization, denitrification, soil exchange capacity, leaching and land use on this understudied pool of nitrogen.
Smog Emitting Soils.
Nitrogen oxides (NOx=NO+NO2) are a primary component of air pollution – a leading cause of premature death in humans and biodiversity declines worldwide. Although regulatory policies in California have successfully limited transportation sources of NOx pollution, several of the US’s worst-air quality districts remain in rural regions of the state. Site based findings suggest that NOx emissions from California’s agricultural soils could contribute to air quality issues; however, a statewide estimate is hitherto lacking. We show that agricultural soils are a dominant source of NOxpollution in California, with especially high soil NOx emissions from the state’s Central Valley region. We base our conclusion on two independent approaches: 1) a bottom-up spatial model of soil NOx emissions; and 2) top-down airborne observations of atmospheric NOx concentrations over the San Joaquin Valley. These approaches point to a large, overlooked NOx source from cropland soil, which is estimated to increase the NOx budget by20-51%. These estimates are consistent with past studies of point-scale measurements of NOx emissions from the soil. Our results highlight opportunities to limit NOx emissions from agriculture by investing in management practices that will bring co-benefits to the economy, ecosystems, and human health in rural areas of California.
A Census of Denitrification Research.
Denitrification plays a critical role in regulating ecosystem nutrient availability and anthropogenic reactive nitrogen (N) production. Its importance has inspired an increasing number of studies, yet it remains the most poorly constrained term in terrestrial ecosystem N budgets. We censused the peer-reviewed soil denitrification literature (1975–2015) to identify opportunities for future studies to advance our understanding despite the inherent challenges in studying the process. We found that only one-third of studies reported estimates of both nitrous oxide (N2O) and dinitrogen (N2) production fluxes, often the dominant end products of denitrification, while the majority of studies reported only net N2O fluxes or denitrification potential. Of the 236 studies that measured complete denitrification to N2, 49% used the acetylene inhibition method, 84% were conducted in the laboratory, 81% were performed on surface soils (0–20 cm depth), 75% were located in North America and Europe, and 78% performed treatment manipulations, mostly of N, carbon, or water. To improve understanding of soil denitrification, we recommend broadening access to technologies for new methodologies to measure soil N2 production rates, conducting more studies in the tropics and on subsoils, performing standardized experiments on unmanipulated soils, and using more precise terminology to refer to measured process rates (e.g., net N2O flux or denitrification potential). To overcome the greater challenges in studying soil denitrification, we envision coordinated research efforts based on standard reporting of metadata for all soil denitrification studies, standard protocols for studies contributing to a Global Denitrification Research Network, and a global consortium of denitrification researchers to facilitate sharing ideas, resources, and to provide mentorship for researchers new to the field.