From the end of a boardwalk that juts into Oakland’s Arrowhead Marsh, it can be hard to appreciate the fragility of this ecosystem. At low tide, native cordgrass and pickleweed brim with life, rustling, snapping and popping as they dry under the morning sun. California clapper rails dig their long beaks into the mudflats in search of small crustaceans. Above, bright white kestrels dart, periodically diving into the water and emerging with small, shining baitfish. Birdsong crescendos, sage fills the air and wildflowers accent backdrops of green and brown. A few blocks away, just upstream on Elmhurst Creek, a wholly different scene unfolds. Behind tall chain-link fences and concrete walls, dozens of cars in various states of disrepair line a large recycling lot. Pick-n-Pull, a subsidiary of the global Radius Recycling company, collects junk cars and invites customers to dismantle them for parts. The process results in an accumulation of heavy metals, oil, …