May 24 2017

4:00 pm 158 HH

Randal Orton

Geology matters: An unusually severe example of Al-Karajis Principles in Malibu Creek, California Geology matters: An unusually severe example of Al-Karajis Principles in Malibu Creek, California


20th Annual Biology Research Symposium

Malibu Creek is the largest coastal stream in the Santa Monica Mountains National Recreation Area (SMMNRA), California, supporting both state and federally designated endangered fishes in both its lower reaches and estuary (Malibu Lagoon). Yet it also has unusually poor mineral water quality, with sulfate, magnesium and phosphate levels exceeding those found in alkaline streams downstream of mountain top coal mining in Pennsylvania, Virginia, and Kentucky.

We traced the creeks high salt levels (SC between 1,200 - 3,800 S/cm) to large upstream deposits of the Miocene marine Monterey / Modelo Formation and other marine sedimentary rock in Malibu Creeks northern headwaters. Both the amount and composition of the creeks salt is unusual in relation to other SMMNRA streams and most other US streams, with elevated levels of sulfate, bicarbonate, chloride, magnesium, calcium phosphate and nitrogen consistent with the levels of these elements in Monterey Formation rock and their leaching rates under controlled tests. Moving from mineral water quality to Malibu Creeks biology, we show that the Monterey Formations impact extends across three trophic levels, with the species composition and abundance of benthic algae (diatoms, macroalgae), aquatic macroinvertebrates and native fish dominated by brackish water high sulfate tolerant species. High indoor radon risk in the watershed also coincides with mapped surface exposures of the Monterey Modelo Fm., probably due to its relatively high uranium content. The Monterey Formation is widespread in California, and our findings suggest that its impact on water quality and aquatic life may occur in other locations as well. In the Malibu Creek watershed, for example, these impacts went unnoticed for 40 years, despite historical well records of very poor groundwater quality in the creeks northern headwaters and intensive water quality testing by multiple agencies.











































































































































































































































































































































































































































































































































































































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