GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 43-8
Presentation Time: 3:35 PM


CHRISTIE, Margaret A.1, CHARLES, Don F.2, MARTIN, Ronald E.1, MCLAUGHLIN Jr., Peter P.3 and PIZZUTO, James E.1, (1)Department of Geological Sciences, University of Delaware, Newark, DE 19716, (2)Patrick Center for Environmental Research, The Academy of Natural Sciences of Drexel University, Philadelphia, PA 19103, (3)Delaware Geological Survey, University of Delaware, Newark, DE 19716,

Tidal rivers represent an environment that is both under-studied and vulnerable to changes caused by human activities. Widespread deforestation, agriculture, urbanization, and industrialization have impacted the tidal Christina River from before European settlement through the present. Cores from three sites along the tidal Christina River were collected and sediments deposited over the past 1000-1400 years were analyzed in order to compare how water quality has changed pre- and post- European settlement. Age-depth relationships were constructed for the cores using a combination of radiocarbon dating, Pb-210, Cs-137, and pollen-based deforestation horizons. The relationship between age and depth was consistent among the cores. Diatoms from the sediments were analyzed using established indices and autecological groupings to better understand trophic level and other changes in water quality. Generally, nutrient concentrations increased concurrently with use of the land for agriculture following European settlement, then increased further in the 1950s following the introduction of industrial fertilizers. Diatom assemblages cluster into groups which correspond to known ecological transitions such as deforestation and increased use of industrial fertilizers. The concentrations of metals in the sediments were analyzed to assess the impacts of urbanization and industrialization. Sediment analyses showed that zinc and other heavy metals increase in concentration following industrialization, peaked in the 1950s, and decreased after environmental legislation restricted the release of pollutants into waterways in the 1970s. Nitrogen and phosphorous concentrations were also measured to provide support for the diatom indices. Together, diatom and chemical analyses enable a detailed reconstruction of water quality changes in a tidal river. Diatom indices help to reconstruct the impact nutrients have had on water quality, which does not necessarily correlate well with sediment nutrient analyses. Chemical analyses of the sediments pinpoint the timing and influence of other activities that can degrade water quality, such as industrialization.
  • GSA_Talk_MChristie2016.pptx (23.5 MB)