Tree rings record 100 years of hydrologic change within a wetland

Abstract

One of the primary responsibilities of the Water Resources Division of the United States Geological Survey is to monitor the amount and quality of waters in our rivers, lakes, and wetlands. Hydrologists can evaluate these important resources in the present day, but how can they determine what conditions were like in past decades or even centuries? Moreover, are conditions part of a natural cycle or caused primarily by human activities? It is sometimes possible to answer these questions by examining the annual growth rings of trees. Each ring can be assigned an exact year of formation, and yearly differences in ring widths can be used to compare past and present conditions on a flood plain, along a river, or within a wetland. Thus, tree rings provide information that otherwise might be difficult or even impossible to obtain. Hydrology and tree growth were investigated within a small wetland in the Tully Valley of central New York, about 20 miles south of Syracuse. In late 1994 it was noted that some wetland trees were dying, and local residents reported that flow of a small stream draining the wetland seemingly increased and became more brackish since the mid to late 1980s. The wetland is about 3 miles north of an extensive salt mining operation known to have degraded local water quality, but no effects of mining had been confirmed previously near the wetland. The oldest wetland trees started to grow before the onset of mining in 1889, and thus tree-ring studies were undertaken not only to investi-gate recent hydrologic change within the wetland, but also to search for evidence of any other changes during the last 100 years.