The paleoecological record of human disturbance in wetlands of the Lake Tahoe Basin

Increased human activities since discovery of gold in northern California have changed the structure and function of many ecosystems. To reconstruct the changes in watershed environmental conditions, sediment cores were collected from three montane marshes in northern Sierra Nevada, CA. Pollen analysis was conducted, and water content, bulk density, ash, carbon, nitrogen, phosphorus, major cations, and lead concentrations of sediments were determined. Cores were dated by the 210Pb method. Pollen analyses showed changes in plant communities in this region due to severe logging in the late-1800s and moderate logging in the 1900s. The local changes were more clearly recorded in small marsh pollen profiles than regional changes. The water milfoil (Myriophyllum spicatum L.) introduction into Tahoe Basin was inferred from the pollen record and ²¹⁰Pb dating. Road construction and maintenance activities were recorded in physical and chemical characteristics, such as increases in sodium, calcium, and magnesium concentrations. Pollen and physical and chemical records also documented the time line of the expansion of dry meadow, and the decrease of pine forest in one of the watersheds. This study showed that sediments in small marshes were especially useful to reconstruct local disturbance by human activities.