Carbon Content of Coastal Lake Sediments from Whidbey Island, Washington State

Variations in the type and amount of carbon in coastal lake sediments represent changes in marine influence, human activities, or other environmental factors through time. The carbon stored in lake sediments is less well studied than that from other environments, such as peatlands and saltmarshes. However, existing studies suggest lakes store large amounts of carbon and are important carbon sinks. In this study we measured the organic and inorganic carbon content of sediments from sediment cores taken from Oliver Lake and West Beach Lake, which are located on Whidbey Island in Washington State. While these lakes are both coastal, West Beach is located at sea level and has more marine influence, and therefore higher inorganic carbon content throughout the core, than Oliver Lake which is located at the top of a cliff. In the cores studied, the carbon density of sediments ranged from 0.02 to 0.08 gC cm-3, with an average of ~0.05 gC cm-3. The cores indicate a general decline in organic carbon in the uppermost 10-20 cm, which we hypothesize to represent human activities that have introduced inorganic matter to the environment over the past ~20 years. We compare the distribution of carbon density values from our study to those from other published studies and show that the lake sediments measured have a higher average carbon density than those published for other coastal sediments in the area; however, additional data are needed to determine how representative these results are.