How charred detritus dispersed from Goleta Beach following the 2018 debris flow in Montecito, California:

The catastrophic debris flow that hit Montecito, California in early January 2018 was the result of a rare confluence of serious events. The Thomas Fire had been raging for weeks in Ventura and Santa Barbara counties, and an unusually strong winter storm dumped half an inch of rain in five minutes on the newly charred hills above the panhandle of suburb. With the harsh vegetation holding the hillsides in a scorched position, tons of water, silt, scorched plant matter and rocks rolled down the slopes and engulfed the community below, causing massive damage and the death of 23 inhabitants.

As the community dug itself into the mud following From the disaster, Santa Barbara County flood officials faced a major problem: what to do with the silt mud and other debris that had flooded streams, clogged catchments and buried homes. .. A solution: take it to Goleta Seaside for disposal, which they did later that month over the course of several weeks.

“They were trying to work alongside Mother Character to disperse the debris,” recalls Heili Lowman, then a graduate student affiliated with the Santa Barb Coast Long-Term Ecological Research Program. ara, edited by UC Santa Barbara ecologist John Melack. Winter through spring is the wettest time in the region, she explained, with waves and storms that hit the coast and rains that fill the streams that flow into the sea, which could improve the dispersion of materials at the big.

For Lowman and his colleagues – who have able to see the county’s progress on Goleta Beach from the on-campus Institute of Marine Science – the problem lent itself to a study exploring the distance traveled by debris from the emergency disposal. Will it run aground elsewhere along the coast or will it move out to sea? Would it accumulate in a marine habitat where it could have ecological impacts? They conducted a study in collaboration with scientists from the University of Florida and the University of Quebec in Montreal, and supported by the Coastal Fund and the Countrywide Science Foundation (by means of the SBC LTER). The results of their study are published in the journal Science of the Total Surroundings.

Earth Debris Tracking

“The high biodiversity of the Santa Barbara coast is due to the rich and effective mosaic of coastal marine habitats which includes kelp forests, sandy beaches, surf areas, rocky reefs, surf beds and seagrass and soft benthos, all closely associated in space.” said UCSB coastal marine ecologist Jenifer Dugan. “This means that even in a small area of ​​the coast, the impacts of debris removal could potentially affect several marine habitats and their biodiversity. In light of this, increasing our understanding of the fate of this type of material and its disposal is an important step in conserving these marine habitats and their biodiversity as we respond to climate change and the likelihood of future severe events here and elsewhere.

To get an idea of ​​where the debris flow detritus had gone after it was dumped on Goleta Beach, researchers took samples from the beach and bay of Goleta. They also sampled the seafloor in the littoral zone south of Goleta Slough and along a transect extending west. In order to determine if the sediments came from a terrestrial source, such as the debris flow, they looked specifically for charcoal and compounds indicative of burnt material and terrestrial plant matter. Using samples taken near the swamp, which drains streams that were unaffected by the Thomas Fire, scientists were able to compare the sediments for a clear “charcoal signal” that was the definite sign of material burned in the fire.

“The good news is that we found that the debris appeared to have been largely removed from the beach,” Lowman said , who is currently completing postdoctoral work at the University of Nevada, Reno. “And we really haven’t detected it in the other intertidal sites we’ve sampled over time.

“Although the debris was not detected in the shallow core samples on Goleta beach, it may have been buried by the large amounts of sand that moving west to east along the region’s beaches,” Dugan added. the debris had not traveled very far from the beach.

“We can say with a high degree of certainty that the charcoal remained essentially in the marine sediments”, Lowman said. The coastal areas of the Santa Barbara Channel are also home to various kelp forest communities that support fish, crustaceans, and occasionally marine mammals and birds. The debris detected in the shallower waters showed a fair amount of degradation, thanks to wave action, but some of the material in the deeper waters was a bit cooler. That’s what scientists would expect from organic debris that hadn’t been attacked by microbes and degraded by the standard downstream trip, but rather transported quickly from the mountains, then picked up and placed directly into the ocean.

“This implies that a huge influx of organic matter from the terrestrial environment to the marine environment occurred in one large pulse,” Lowman said. “We saw evidence of fresh terrestrial material at water depths of approximately 20 meters.”

They did not assess the effects this debris might have had on the coastal marine environment, Lowman added that study was primarily to see if and how far the debris traveled.

“Goleta Bay is home to eelgrass beds very sensitive to sedimentation and an abundant community of subtidal benthic infauna,” Dugan said. “Some of the sandy beaches lining the bay are some of the richest known in the world and surf grass beds can thrive in the rocky parts of the coastline.” The bay historically supported a large kelp forest that stretched from Campus Point to beyond Goleta Pier. This kelp forest had an unusual growth form that allowed it to thrive on the bay’s sandy benthos, Dugan added.

Given the increasing likelihood of Severe weather events – the Thomas Fire was then the most pivotal in California history, but has been eclipsed by seven wildfires since – this may not be the last time that organic material burned from the mountains are transported to the ocean. Knowing the impacts of these pulses of organic matter on the coastal community is important, according to the researchers.

“This study aimed to determine whether the debris was stuck or not, and to motivate further studies on the impact of this influx of materials from the terrestrial environment to the marine environment,” Lowman said. “Now that we actually know it’s there, we need to better study its motor impacts since it’s not dispersed as far as we thought.”

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