EXPERIMENTAL INVESTIGATION OF TRACE ELEMENT RELEASE FROM IRON RICH LAKE SEDIMENTS DURING DISSIMILATORY IRON-REDUCTION

Iron (hydr)oxides are ubiquitous components of surficial materials and are often the dominant redox buffering solid phases in soils and sediments (Heron et al. 1994, Schwertmann and Cornell, 1996). As a result, the geochemical behavior of these minerals has a profound influence on the global biogeochemical cycling of trace elements, including heavy metals and arsenic (As), in addition to nutrients such as, sulfur (S), carbon (C), nitrogen (N), and phosphorus (P) (Perret et al. 2000, Benner et al. 2002, Stipp et al. 2002). Understanding the behavior of trace elements and nutrients during biological and abiotic processes that affect iron (Fe) mineral phase transformations is paramount for predicting their distribution, mobility, and bioavailability in the environment. In this study we investigate trace metal and nutrient mobility in tropical lake sediments as a function of dissimilatory iron reduction (DIR). In contrast to mid-latitude lakes where Fe (hydr)oxides constitute only a small fraction of the total sediment, tropical lake sediments have been known to comprise up to 40-60 wt. % Fe-oxides. Under suboxic and nonsulphidogenic conditions it is likely that DIR plays a prominent role in early diagenesis of these Fe-rich sediments and therefore, may exert control on the fate and distribution of many trace elements in this environment (e.g., Crowe et al. 2004). This study presents evidence from batch laboratory experiments that the rates of DIR of lake sediments and goethite are very similar and that the release of several trace elements and the macronutrient phosphorus during this process may enable sustained reduction in carbon rich anaerobic lake sediments.