Preliminary Analysis of Historical Water Quality in the Tidal Christina River, Delaware

Abstract:

Understanding the impacts of land-use changes on tidal rivers over millennial time scales is critical to better predict the long-term impact of current management practices on estuarine water resources. The Christina River, a tidal river which flows into the Delaware River near Wilmington, Delaware, has been impacted by diverse land-use changes. Following European settlement, the region was largely deforested and converted to agriculture, increasing sediment and nutrient inputs. Later industrialization and urbanization affected the region with the growth of cities and the installation of refineries and factories, all of which further input nutrients as well as other chemicals. To better understand these changes, diatom samples were collected from vibracores taken in the fresh to oligohaline marshes surrounding the tidal portion of the river. Lead-210, cesium-137, and carbon-14 dating were used to date the sediments. Diatoms were analyzed to determine how the communities changed with time, from the present to approximately 1350-1410 years ago, in response to natural and anthropogenic impacts. Preliminary analyses indicate large shifts in the relative abundances in diatom species, as well as changes in the species present. Species richness and diversity indices were affected as well, generally being higher around and before the start of the 20^th century. Additionally, the ratio of centric to pennate diatom species, an indicator of turbidity and phytoplankton productivity, appears to peak early in the 20^th century. Continued research will identify additional trends and use the autecology of the species present in each sample to further analyze environmental changes.