The catastrophic debris flow that affected Montecito, Calif., in early January, 2018 was the consequence of a rare confluence of severe events. The Thomas Fire have been raging for weeks in Ventura and Santa Barbara counties, and an unusually strong winter storm dumped half an inch of rain in 5 minutes on the newly-charred hills above the suburban enclave. With the tough vegetation that holds the hillsides set up burned up by the fire, a great deal of water, silt, burnt plant matter and rocks roared down the slopes and engulfed the city below, causing massive damage and the death of 23 residents.
Because the community dug itself out from the mud in the aftermath of the disaster, Santa Barbara County’s flood control officials were confronted with a problem: how to proceed with the slurry of silt along with other debris that had flooded creeks, clogged catchments and buried homes. One solution: Go on it to Goleta Beach for disposal, that they did later that month during the period of weeks.
“These were attempting to work alongside OUR MOTHER EARTH to have the debris material dispersed,” recalled Heili Lowman, at that time a graduate student researcher associated with the Santa Barbara Coastal LONGTERM Ecological Research program, beneath the guidance of UC Santa Barbara ecologist John Melack. Wintertime into spring may be the period of probably the most precipitation in your community, she explained, with waves and storms battering the coast and rains filling creeks that come across the sea, that could enhance dispersal of the material offshore.
For Lowman and her colleagueswho could start to see the county’s progress on Goleta Beach from the Marine Science Institute on campusthe situation lent itself to a report exploring what lengths the debris from the emergency disposal would actually travel. Would it not wash up someplace else across the coast or would it not move out in to the open ocean? Would it not accumulate in a marine habitat where it could cause ecological impacts? They conducted a report in collaboration with scientists from the University of Florida and the Universit du Qubec Montral. The outcomes of these study come in the journal Science of the full total Environment.
Tracking terrestrial debris
“The high biodiversity of the Santa Barbara coast is because of the rich and productive mosaic of nearshore marine habitats which includes kelp forests, sandy beaches, surf zones, rocky reefs, surf and eelgrass beds and soft benthos, all closely associated in space,” said UCSB coastal marine ecologist Jenifer Dugan. “Which means that even in a little section of the coast, the impacts of debris disposal may potentially affect multiple marine habitats and their biodiversity. In light of the, increasing our knowledge of the fate of the kind of material and its own disposal is an extremely important part of conserving these marine habitats and their biodiversity once we react to climate change and the probability of future severe events here and elsewhere.”
To obtain a sense of where in fact the detritus from the debris flow had opted after it had been dumped on Goleta Beach, the researchers collected samples from the beach and from Goleta Bay. In addition they sampled the ocean floor in the nearshore zone south of Goleta Slough and along a transect extending westward. To be able to determine if the sediment was from the terrestrial source, like the debris flow, they looked specifically for charcoal and compounds that indicate burned material and terrestrial plant matter. Using samples collected close to the slough, which drains creeks which were not suffering from the Thomas Fire, the scientists could actually compare sediments for an obvious “charcoal signal” that has been the definite sign of the material burned in the fire.
“Fortunately that people did discover that the debris material were largely taken off the beach,” said Lowman, who’s now completing postdoctoral just work at the University of Nevada, Reno. “And we really didn’t pick it up in another intertidal sites that people sampled through time.
“Even though debris material had not been detected in the shallow core samples on Goleta beach, it could have already been buried by the huge amounts of sand that moves from west to east across the beaches of the spot,” Dugan added.
In the nearshore cores, however, the charcoal signal was strong, an indicator that the debris hadn’t traveled very definately not the beach.
“We are able to say with a higher amount of certainty that the charcoal was basically sticking around in the marine sediment,” Lowman said. The nearshore zones in the Santa Barbara Channel may also be home to diverse kelp forest communities that host fish, crustaceans and the casual marine mammal and bird. The debris detected in shallower waters showed a good level of degradation, because of wave action, however, many of the material in deeper waters were somewhat fresher. This is exactly what scientists would expect from organic debris that was not applied by microbes and degraded by the standard downstream travel, but instead transported rapidly from the mountains, then scooped up and placed straight into the ocean.
“Therefore a huge influx of organic matter from the terrestrial environment in to the marine environment occurred in a single big pulse,” Lowman said. “We saw proof fresh terrestrial material at water depths of around 20 meters.”
They didn’t measure the effects this debris could have had on the nearshore marine environment, Lowman added; this study was mainly to see if and what lengths the debris traveled.
“Goleta Bay supports eelgrass beds which are highly sensitive to sedimentation and an enormous community of subtidal benthic infauna,” Dugan said. “A few of the sandy beaches lining the bay are on the list of richest known on the planet and surfgrass beds can thrive in the rocky elements of the shoreline.” The bay historically supported a big kelp forest that stretched from Campus Indicate at night Goleta pier. That kelp forest had a unique growth form that allowed it to flourish on the sandy benthos of the bay, Dugan added.
Given the increasing odds of severe weather eventsthe Thomas Fire was then your largest in California’s history, but has been dwarfed by seven wildfires sinceit might not be the final time burned organic material from the mountains is transported to the ocean. Knowing the impacts these pulses of organic matter have on the nearshore community is essential, based on the researchers.
“This study was to explore set up debris material stuck around, also to motivate additional studies on the impact of the influx of material from the terrestrial environment in to the marine environment,” Lowman said. “Given that we actually understand that it’s here, we have to better study its impacts because it isn’t being dispersed so far as we thought it may be.”
More info: H.E. Lowman et al, Distribution of terrestrial organic material in intertidal and nearshore marine sediment because of debris flow response efforts, Science of THE FULL TOTAL Environment (2022). DOI: doi.org/10.1016/j.scitotenv.2022.156886
Citation: Researchers track movement of charred detritus dispersed from Goleta Beach after 2018 debris flow in California (2022, July 28) retrieved 29 July 2022 from https://phys.org/news/2022-07-track-movement-charred-detritus-dispersed.html
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