Land use in coastal watersheds is widely agreed to influence sediment composition and delivery to estuarine environments. Changing estuarine sedimentation rates due to watershed anthropogenic activities have the potential to degrade water quality, yet the ecological dimensions of long-term changes in land use are difficult to reconstruct from historical records alone. In particular, the rates and extents of past land use and cover change remain largely unknown. To address the lack of context for modern and historical water quality regimes we examine how an estuarine sedimentary record preserves land cover change across the Euro-american settlement horizon in the South Slough of Coos Bay Estuary. To establish temporal variations in sediment accumulation rates, we modeled age-depth relationships using PB210 and radiocarbon chronology. In addition, we analyzed fossil pollen as a proxy of vegetation change due to anthropogenic activity by grouping disturbance adapted taxa. We compared this record with road development and local timber harvest from aerial photography surveys and records of timber harvest in Coos County.
Results/Conclusions
We determined average deposition varied between 0.15 and 0.45 g/cm2-yr based on two ~80 cm sediment cores spanning the last 330 years. Disturbance regime inferred from fossil pollen suggests intermediate levels prior to Euro-American settlement followed by a period of widspread recovery before timber harvests began to climb in the middle of last century. The sedimentation rate corroborates this finding, suggesting upland disturbance and sedimentation are fundamentally linked. The highest sustained sedimentation rates over the record have occurred over the past 50 years coiciding with timber extraction and extensive wetland restoration activities. Climate and weather explain little of this variability, indicating that land use is likely the key factor governing variations in sediment accumulation. These results refine previous work reconstructing water quality in the estuary, suggesting land-use has synergistic effects with climate on estuarine water quality. Furthermore, these long-term ecological dynamics provide key baseline information for water managers and restoration projects seeking to understanding estuarine conditions which supported pre-Euro-American ecologies.