Recipient Organization
CAL POLYTECHNIC STATE UNIV
(N/A)
SAN LUIS OBISPO,CA 93407
Performing Department
Natural Resources Management and Environmental Sciences
Non Technical Summary
Forested watersheds across California provide clean water that supports a broad range of beneficial uses. Following fire in California, state agencies (CDF, CGS), part of the WERT (Watershed Emergency Response Team) perform post-burn analysis on risks of debris flows and flooding (Figure 2). Similarly, the Burned Area Emergency Response (BAER) is a multi-agency post-fire assessment of burn severity that rapidly identifies, and maps fire affects to soils to inventory potential hazards to life and property, as well as natural and cultural resources following fire. The proposed research will focus on new methodologies, as well as calibration and validation data on these post-burn assessments and mapping of soil fire effects. The improvement in post-burn risk assessment and mapping has the potential to save lives and property damage from the burned environment.Wildfires affect soil health and quality, with implications for forest productivity and resilience. Soil health is the evolving paradigm of soil quality that links soil functions and ecosystem services to soils as a dynamic living system. Fire can significantly affect the physical, chemical, and biological properties of soil health. Soil organic carbon (SOC), a key indicator of soil health and critical component of climate change mitigation, is reduced by an average of 27 % post fire. Soil moisture is another key soil health metric that is impacted by fire. Quantifying soil water holding capacity, flow dynamics, and repellency (or hydrophobicity) and their spatial variability in response to fire has implications for infiltration and run-off generation at the watershed scale. Quantifying the effects and spatial variability of fire to soil health and hydrologic properties, as well as the capacity of soils to sequester carbon post-fire, places fire effects to soil at the critical intersection of California's dual crisis of climate change and fire intensity, providing both crisis and opportunity for California's forest and rangeland.We propose a three-year study of the post-fire hydrologic and soil response from the CZU Lightning Complex Fire within Cal Poly's 3200-acre Swanton Pacific Ranch. This will be accomplished through wintertime streamflow and erosion measurements for varied burn severities to gain insight toward risk management for landowners and downstream communities. An assessment of stream water quality response will be performed where physical, biological, and chemical attributes of select streams post fire will provide context to water quality and assist with broader regional interpretations of the risks on aquatic ecology. A diverse set of soil and hydraulic properties will be sampled and analyzed toward the soil health and ecological change in soil following fire. Lab analysis of numerous soil health indicators, including soil moisture retention, permeability, structure, soil organic matter dynamics and fractions, and chemical changes affecting microbial and plant available nutrients will be examined. Advances in predictive mapping of fire effects to soils may provide additional tools to post fire soil burn assessment teams and agencies, with interpretations far beyond categorical burn severity. A spatial model and predictive map of post-fire soil health and hydrologic properties will be created; described in objective 4.The goal of the research is to understand the spatial variability and physical, biological, and chemical responses of soil and water following wildfire to assist California forest and rangeland managers and agencies to better predict the risk and response to wildfire. Given the recent trends towards larger, more severe wildfires in many regions, including California, it is critical that we improve our understanding of the immediate and longer-term effects of wildfire on watershed hydrology and soil health. This knowledge is key to making informed soil and water management decisions. Further, with increased wildfire incidence, California will need more trained professionals to assist in wildfire assessments--training created by funding student research and education.
Animal Health Component
100%
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Goals / Objectives
Goal: Understand the spatial variability of physical, biological, and chemical responses of soil and water following wildfire to assist California forest and rangeland managers and agencies to better predict the risk and response to future wildfires.Objective 1: Quantify post-fire changes to runoff and surface erosionDissemination:Master of Science Thesis (2)Peer-reviewed publications (1-2)Conference presentationsStudent participation and learning in Cal Poly courseworkData sharingObjective 2: Assess stream water quality responses to high severity wildfireDissemination:Master of Science Thesis (1)Peer-reviewed publication (1)Conference presentationStudent participation and learning in Cal Poly courseworkObjective 3: Inventory fire effects on soil health, soil moisture, hydraulic properties, and carbon storage at the watershed scaleDissemination:Master of Science Thesis (2)Peer-reviewed publications (1-2)Conference presentationsStudent participation and learning in Cal Poly courseworkData sharingObjective 4: Prediction of spatial patterns of soil health and hydraulic changes under varying burn severitiesDissemination:Master of Science Thesis (1)Peer-reviewed publications (1)Conference presentationsStudent participation and learning in Cal Poly courseworkData sharing
Project Methods
Objective 1: Quantify post-fire changes to runoff and surface erosionContinuous streamflow, stream depth, and precipitation measurement will occur in varying locations within the Scotts Creek watershed in the Santa Cruz Mountains. Hydrologic measurements will focus on precipitation storm events, particularly in the Little Creek tributary to Scotts Creek (Appendix Figure 2)Pre-fire streamflow and peak flows were measured from 2000-2011 in the Little Creek watershed, tributary to Scotts Creek. The streamflow and peak flows in Little Creek measured during 2010 and 2011 were following the Lockheed Fire (Surfleet et al., 2014) (Appendix Figure 3). The pre-fire and 2 post-fire hydrologic data sets provide a rare and unique opportunity that will enable robust statistical analysis to identify the influence of varied burn severities, past and present, on streamflow during storm events.We will study four hillslopes with similar slopes, with two representative of moderate burn severity and two representative of high burn severity as determined by remote sensing and field surveys. On study hillslopes, we will construct two sediment fences (8 total fences) following established methods (Robichaud and Brown, 2002) to trap eroded sediment from the hillslope plots. All plots will be bounded to the approximate dimensions of 5 m wide along the contour and 15 m downslope (i.e., 75 m2; ~800 ft2). Following major storm events or rainy periods, we will quantify the mass of sediment eroded into each sediment fence. Sediment mass will be quantified by physically removing and weighing the stored sediment in the fences using portable scales by field crews. We will also collect representative sub-samples (0.5 kg), which will be dried in the laboratory at 105°C for 24 hours to allow us to quantify the dry sediment mass. As plot contributing areas will be controlled, we will also quantify sediment yields, the total mass of dry sediment eroded per unit area, which will allow us to scale up the observations (Figure 3). Comparisons will be made to soil erosivity factors and other post-fire erosion estimates to provide context to the erosion rates by burn severity from this study.Objective 2: Assess stream water quality responses to high severity wildfire Bioassessment surveys of macroinvertebrate communities, biological water quality indicators, were collected in select stream segments in Scotts Creek prior to the CZU Lightning Complex Fire (Hardy, 2017). Post-burn bioassessment surveys will be repeated in similar locations, the first post-burn summer season to provide comparisons to pre-burn response and reference streams in the area (California Water Boards, 2020).Physical and chemical measurements conducted in the California Stream Condition Index will be compared to pre-fire stream surveys conducted within the Scotts Creek watershed. These comparisons will allow quantification of a post-fire response to stream physical and chemical conditions.Objective 3: Inventory fire effects on soil health, soil moisture, hydraulic properties, and carbon storage at the watershed scale.Soil samples will be taken at two depths (0-5 cm, and 5-15 cm) at 100 locations. in the post-burn area of Swanton Pacific Ranch, based on a Conditional Latin hypercube sampling (CLHS) and georeferenced. Each sample location will be sampled in year one and year three of the study for comparison over time.Soil health indices to be analyzed include total soil carbon, total nitrogen, soil organic matter fractions, permanganate oxidizable carbon, mineralizable carbon (soil respiration), water stable aggregates, available soil nutrients, and soil pH. Soil sampling locations will be supplemented with field and laboratory measurements of soil texture, soil moisture, hydraulic conductivity, soil water retention, and water repellency. Soil repellency tests will rely on field and laboratory measurement of the water drop penetration time (WDPT) at different soil depths and burn severities. Field infiltration tests will also be conducted along sampling transects across the study site. Ground-based measurement of soil moisture along transects across the study site will be conducted using time-domain reflectometry (TDR) probes and gravimetric laboratory analysis of samples. These measurements will be compared to historical Soil Moisture Active-Passive (SMAP) satellite data over the study area and adjoining watersheds.We will inventory spatiotemporal persistence of water repellency and hydrophobicity in correlation to recovery of microbial activity across the site at land surface and in the shallow subsurface. Water repellency and hydrophobicity tests will be conducted at the field site for a subset of the 100 spatial locations (points) across the watershed at the surface and two shallow subsurface depths. We will evaluate the effect of water repellency on soil moisture retention behavior as well as assess the chemical breakdown, under conditions of increasing soil wetness, of organic compound that induce repellency. Field-scale dependence of water repellency on soil texture will be evaluated. Laboratory batch experiments will be conducted to evaluate susceptibility of water-repellent organic compounds to microbial degradation.Objective 4: Prediction of spatial patterns of soil health and hydraulic changes under varying burn severitiesSoil health indicators and soil hydrologic properties will be combined with remote sensing and machine learning to predict soil properties at various spatial scales. Several machine learning algorithms will be used (random forest, extreme gradient boosting and cubist) to predict fire effects to soil properties across the watershed.We will utilize multiple remotely sensed indexes of burn intensity and severity, terrain attributes from a LiDAR digital elevation model (topographic wetness, slope, aspect, terrain ruggedness, topographic position etc.), and pre-burn remotely sensed vegetation indices as environmental covariables to build predictive spatial models of fire effects to, and recovery of, wildland soil health.30 m pixel predictive maps of fires impact on soil health indices, soil nutrients, and soil carbon storage will be created from data collected in year one and year three of the project. Maps of water repellency and hydrophobicity data will be correlated to fire severity and intensity maps. Mapping of saturated conductivity and water retention properties will further be examined for understanding wildfire effects on soil runoff properties. Together, these maps will allow for watershed scale assessment of the recovery of soil health and soil hydrologic properties on a per pixel basis.Synthesis of objectives: Interpretation of the outcomes of the four post-fire and healthy soil objectives will collectively offer the opportunity to explore the synergy and interpretations of each objectives' response to fire and land management. Changes to runoff and water quality are expected based on soil properties changes affecting soil health and erosion following fire. Soil health is dynamic based on land management, fire, and climate affecting the vegetation enhancement or recovery to land management.