Anthropogenic Pressures and Climate Change in Black Lake: Novel Insights from California's Dune Lake System

Keywords: Paleoenvironmental Change, Paleofire, Freshwater Wetlands
Abstract Type: Poster Abstract

Abstract

Black Lake, located within California's Callender Dunes, has been molded by millennia of climatic change and anthropogenic activity. The dune system contains several freshwater lakes, hydrologically connected to each other. These rare wetlands have harbored several threatened and endangered species, which suggests long-term persistence of these delicate aquatic ecosystems. Recently, urban expansion, agricultural groundwater extraction, and drought have put these rare ecosystems at risk. Of these lakes, the only lake known to be perennially wet during this historical period is Black Lake. To examine Black Lake's paleoenvironmental history, two lake sediment cores were collected in collaboration with the U.S. Fish and Wildlife Service, 3.96m and 6.98m respectively. These records span the past 3300 years. Paleoenvironmental proxies indicate dynamic shifts in paleohydrology, organic matter deposition, and fire history throughout the late Holocene. There is a discernible decline in fire frequency in the upper 60 centimeters, potentially tied to European fire suppression practices. Pre-settlement fire regimes likely corresponded to indigenous land use practices, with elevated fire activity that plummeted after European settlement. Notable peaks in sand deposition and magnetic susceptibility in the top two meters of both cores reflect high-energy depositional events, presumably aeolian in origin. Nonetheless, the persistence of Cirsium loncholepis (La Graciosa thistle) indicates that Black Lake has remained a wetland throughout the Holocene. This novel study provides a detailed record of environmental transformations at Black Lake, in an effort to disentangle natural and anthropogenic causes of environmental change, while providing crucial information for preserving California's dwindling natural dune wetlands.