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The Influence of Environmental Factors on Solar Radiation-Enhanced Dissolution of Particulate Organic Matter from Estuarine Suspended Sediments

Qiyuan Liu and Christopher G. Shank
The University of Texas at Austin, Marine Science Institute, Port Aransas, Texas

Irradiation of particulate organic matter (POM) by sunlight in aquatic systems can lead to substantial changes in the chemical makeup of POM including releasing organic moieties to the dissolved phase (DOM). We studied the solar radiation-enhanced release of dissolved organic carbon (DOC), chromophoric DOM (CDOM) and total dissolved nitrogen (TDN) from sedimentary POM sampled from different types of estuarine systems. The results in all experiments indicated that photodissolution of POM can result in the production of important quantities of DOC, CDOM and TDN (up to ~30% increment of natural abundances); the organic content of sediment particles plays an important role in controlling the amount of DOC, CDOM and TDN production. The addition of photochemical mediator (nitrate and iron) did not have large effect on the reaction extent, but water chemistry and sediment dry-wet cycle may be strong controlling parameters for photochemical processes in sediment suspensions. Irradiation experiments using wet and dry sediments demonstrated that suspensions of dried sediments and artificial seawater produced three-fold more DOC, slightly more CDOM, and twice as much of TDN than the suspension of wet (raw) sediments. However, similar experiments using organic-rich marsh water instead of artificial seawater generate opposite results: wet sediment suspensions produced more DOC, CDOM and TDN than dry-rewetted sediment suspensions. Our results indicated that sedimentary POM may serve as an important DOC, CDOM and TDN source for shallow coastal systems; the photochemical reaction extents are influenced by environmental factors such as water chemistry, sediment type and sediment dry-wet cycles.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013