Megafire affects stream sediment flux and dissolved organic matter reactivity, but land use dominates nutrient dynamics in semiarid watersheds

Climate change is causing larger wildfires and more extreme precipitation events in many regions. As these ecological disturbances increasingly coincide, they alter lateral fluxes of sediment, organic matter, and nutrients. Here, we report the stream chemistry response of watersheds in a semiarid re...

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Bibliographic Details
Published in:PloS one 2021-09, Vol.16 (9), p.e0257733
Main Authors: Crandall, Trevor, Jones, Erin, Greenhalgh, Mitchell, Frei, Rebecca J, Griffin, Natasha, Severe, Emilee, Maxwell, Jordan, Patch, Leika, St Clair, S Isaac, Bratsman, Sam, Merritt, Marina, Norris, Adam J, Carling, Gregory T, Hansen, Neil, St Clair, Samuel B, Abbott, Benjamin W
Format: Article
Language:English
Subjects:
Agricultural land
Agriculture
Anthropogenic factors
Biodegradability
Biodegradation
Carbon - analysis
Causes of
Chemistry
Climate change
Climatic changes
Creeks & streams
Dissolved organic carbon
Dissolved organic matter
Earth Sciences
Ecology and Environmental Sciences
Ecosystem
Ecosystem disturbance
Ecosystems
Environmental aspects
Environmental Monitoring - methods
Extreme weather
Fluctuations
Groundwater
Groundwater recharge
Human influences
Humans
Hydrology
Influence
Isotopes
Land use
Nitrogen - analysis
Nutrient concentrations
Nutrient dynamics
Nutrient sources
Nutrient status
Nutrients
Optical properties
Organic carbon
People and places
Physical Sciences
Precipitation
Rain
Rainfall
Rainfall increase
River ecology
River networks
Rivers - chemistry
Sediments
Semi arid areas
Semiarid climates
Semiarid lands
Semiarid zones
Social Sciences
Storms
Stormwater
Surface water
Suspended sediments
Urban agriculture
Urban Renewal
Utah
Vegetation
Water analysis
Water sampling
Watersheds
Wildfires
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Summary:Climate change is causing larger wildfires and more extreme precipitation events in many regions. As these ecological disturbances increasingly coincide, they alter lateral fluxes of sediment, organic matter, and nutrients. Here, we report the stream chemistry response of watersheds in a semiarid region of Utah (USA) that were affected by a megafire followed by an extreme precipitation event in October 2018. We analyzed daily to hourly water samples at 10 stream locations from before the storm event until three weeks after its conclusion for suspended sediment, solute and nutrient concentrations, water isotopes, and dissolved organic matter concentration, optical properties, and reactivity. The megafire caused a ~2,000-fold increase in sediment flux and a ~6,000-fold increase in particulate carbon and nitrogen flux over the course of the storm. Unexpectedly, dissolved organic carbon (DOC) concentration was 2.1-fold higher in burned watersheds, despite the decreased organic matter from the fire. DOC from burned watersheds was 1.3-fold more biodegradable and 2.0-fold more photodegradable than in unburned watersheds based on 28-day dark and light incubations. Regardless of burn status, nutrient concentrations were higher in watersheds with greater urban and agricultural land use. Likewise, human land use had a greater effect than megafire on apparent hydrological residence time, with rapid stormwater signals in urban and agricultural areas but a gradual stormwater pulse in areas without direct human influence. These findings highlight how megafires and intense rainfall increase short-term particulate flux and alter organic matter concentration and characteristics. However, in contrast with previous research, which has largely focused on burned-unburned comparisons in pristine watersheds, we found that direct human influence exerted a primary control on nutrient status. Reducing anthropogenic nutrient sources could therefore increase socioecological resilience of surface water networks to changing wildfire regimes.
ISSN:1932-6203
1932-6203
DOI:10.1371/journal.pone.0257733