32 research outputs found

    The Effect of Wildfire on Soil Mercury Concentrations in Southern California Watersheds

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    Mercury (Hg) stored in vegetation and soils is known to be released to the atmosphere during wildfires, increasing atmospheric stores and altering terrestrial budgets. Increased erosion and transport of sediments is well-documented in burned watersheds, both immediately post-fire and as the watershed recovers; however, understanding post-fire mobilization of soil Hg within burned watersheds remains elusive. The goal of the current study is to better understand the impact of wildfire on soil-bound Hg during the immediate post-fire period as well as during recovery, in order to assess the potential for sediment-driven transport to and within surface waters in burned watersheds. Soils were collected from three southern California watersheds of similar vegetation and soil characteristics that experienced wildfire. Sampling in one of these watersheds was extended for several seasons (1.5 years) in order to investigate temporal changes in soil Hg concentrations. Laboratory analysis included bulk soil total Hg concentrations and total organic carbon of burned and unburned samples. Soils were also fractionated into a subset of grain sizes with analysis of Hg on each fraction. Low Hg concentrations were observed in surface soils immediately post-fire. Accumulation of Hg coincident with moderate vegetative recovery was observed in the burned surface soils 1 year following the fire, and mobilization was also noted during the second winter (rainy) season. Hg concentrations were highest in the fine-grained fraction of unburned soils; however, in the burned soils, the distribution of soil-bound Hg was less influenced by grain size. The accelerated accumulation of Hg observed in the burned soils, along with the elevated risk of erosion, could result in increased delivery of organic- or particulate-bound Hg to surface waters in post-fire systems

    Predicting the Impacts of Urbanization on Basin-scale Runoff and Infiltration in Semi-arid Regions

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    The current study was undertaken to improve the understanding of the long-term impacts of urbanization on hydrologic behavior and water supply in semi-arid regions. The study focuses on the Upper Santa Clara River basin in northern Los Angeles County which is undergoing rapid and extensive development. The Hydrologic Simulation Program- Fortran (HSPF) model is parameterized with land use, soil, and channel characteristics of the study watershed. Model parameters related to hydrologic processes are calibrated at the daily timestep using various spatial configurations of precipitation and parameters. Results indicate that the HSPF performs best with distributed precipitation forcing and parameters (distributed scenario), however the model performs fairly well under all scenarios. The model also shows slightly better performance during wetter seasons and years than during drier periods. Potential urbanization scenarios are generated on the basis of a regional development plan. The calibrated (and validated) model is run under the proposed development scenarios for a ten year period. Results reveal that increasing development increases total annual runoff and wet season flows, while decreases are observed in baseflow and groundwater recharge during both dry and wet seasons. As development increases, medium sized storms increase in both peak flow and overall volume, while low and high flow events (extremes) appear less affected. Urbanization is also shown to decrease recharge and, when considered at the regional-scale, could potentially result in a loss of critical water supply to southern California

    Assessing the effects of climate change on urban watersheds: a review and call for future research

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    Considerable efforts have been made to control and manage hydrology and water quality of watersheds impacted by urban development through construction of stormwater control measures (SCMs). Climate change (CC) could, however, undermine these efforts through intensifying precipitation and hydrologic extremes. Although the impact of CC on water resources has been well-documented, its impact on urban hydrology remains less studied. CC may complicate sustainable urban hydrology, which can cause reduction in SCM efficiency with changes in precipitation pattern (i.e., change in duration, frequency, depth, and intensity). More intense precipitation may result in reduced runoff reduction and treatment efficiency given that SCMs have the finite surface storage volume and surface infiltration capacity. Determining the functionality of various SCMs under future climate projections is important to better understand the impact of CC on urban stormwater and how well these practices can build resiliency into our urban environment. The purpose of this review is to provide the needs and opportunities for future research on quantifying the effect of CC on urban SCMs and characterizing the performance and effectiveness of these systems under existing and projected climate scenarios. A summary of the modeled constituents as well as the stormwater and climate models applied in these studies is provided. We concluded that there are still limitations in exploring the impact of future change in meteorological variables will influence the operation of SCMs in the long-term. Previous studies mostly focused on the impacts of CC on urban runoff quantity and only handful studies have explored water quality impacts from CC such as potential changes in water temperature, metals and pathogens. Assessing pollutant removal efficiency of SCMs such as bioretention, infiltration trenches, dry and wet swales, rooftop disconnections, wet and dry ponds, which are common practices in urban watersheds, also needs more attention. Analysis on the cost of adapting SCMs to CC to maintain the same performance as current climate conditions is also recommended for future research.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

    Improving Spatial Soil Moisture Representation Through Integration of AMSR-E and MODIS Products

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    Increased dry season water yield in burned watersheds in Southern California

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    The current work evaluates the effects of the 2003 Old Fire on semi-arid systems in the San Bernardino Mountains, California. Pre- and post-fire daily streamflow are used to analyze flow regimes in two burned watersheds. The average pre-fire runoff ratios in Devil Canyon and City Creek are 0.14 and 0.26, respectively, and both increase to 0.34 post-fire. Annual flow duration curves are developed for each watershed and the low flow is characterized by a 90% exceedance probability threshold. Post-fire low flow is statistically different from the pre-fire values ( α  = 0.05). In Devil Canyon the annual volume of pre-fire low flow increases on average from 2.6E + 02 to 3.1E + 03 m ^3 (1090% increase) and in City Creek the annual low flow volume increases from 2.3E + 03 to 5.0E + 03 m ^3 (118% increase). Predicting burn system resilience to disturbance (anthropogenic and natural) has significant implications for water sustainability and ultimately may provide an opportunity to utilize extended and increased water yield
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