The C-biogeochemistry of a Midwestern USA agricultural impoundment in context: Lake Decatur in the intensively managed landscape critical zone observatory

The damming of rivers has created hotspots for organic carbon sequestration and methane production on a global scale as the reservoirs intercept fluvial suspended and dissolved loads. To better understand how the C-biogeochemistry of a reservoir responds to watershed processes and evolves over time, Lake Decatur, located in the Intensively Managed Landscape Critical Zone Observatory (IML-CZO) was studied. Solid phase analyses (% organic C, C/N, δ¹³C, δ¹⁵N) of soils and sediments sampled from stream bank exposures, river suspensions, and the lake bottom were conducted to characterize organic C (OC) sources throughout the sedimentary system. Agriculturally-driven soil erosion rapidly altered lake bathymetry causing an evolution of sedimentary and OC deposition patterns, which in turn shaped where and when methane production occurred. A positive correlation between OC accumulation rate and porewater dissolved inorganic C (DIC) δ¹³C profiles indicates that methane generation is strongly influenced by OC burial rate. The sources of the lake bed particulate organic C (POC) have also evolved over time. Drowned vegetation and/or shoreline inputs were dominant initially in areas adjacent to the original river channel but were rapidly overwhelmed by the deposition of sediments derived from eroded agricultural soils. Eutrophication of the lake followed with the onset of heavy fertilizer application post-1960. This succession of sources is expected to be commonplace for reservoirs greater than?~?50–60 years old in agricultural settings because of the relative timing of tillage and fertilizer practices. The ¹³C/¹²C ratios of methane from Lake Decatur were more depleted in ¹³C than what is commonly expected for freshwater sedimentary environments. The ¹³C-depletion suggests that CO₂-reduction is the dominant methanogenic pathway rather than the anticipated acetate dissimilation process. The isotopic observations reveal that commonly held assumptions about methane production and its C-isotopic signature in freshwater systems are over-simplified and not strictly applicable to this system.     

Arsenite‐induced changes in hepatic protein abundance in cynomolgus monkeys (Macaca fascicularis)

Arsenic is an environmental pollutant, and its liver toxicity has long been recognized. The effect of arsenic on liver protein expression was analyzed using a proteomic approach in monkeys. Monkeys were orally administered sodium arsenite (SA) for 28 days. As shown by 2D‐PAGE in combination with MS, the expression levels of 16 proteins were quantitatively changed in SA‐treated monkey livers compared to control‐treated monkey livers. Specifically, the levels of two proteins, mortalin and tubulin beta chain, were increased, and 14 were decreased, including plastin‐3, cystathionine‐beta‐synthase, selenium‐binding protein 1, annexin A6, alpha‐enolase, phosphoenolpyruvate carboxykinase‐M, erlin‐2, and arginase‐1. In view of their functional roles, differential expression of these proteins may contribute to arsenic‐induced liver toxicity, including cell death and carcinogenesis. Among the 16 identified proteins, four were selected for validation by Western blot and immunohistochemistry. Additional Western blot analyses indicated arsenic‐induced dysregulation of oxidative stress related, genotoxicity‐related, and glucose metabolism related proteins in livers from SA‐treated animals. Many changes in the abundance of toxicity‐related proteins were also demonstrated in SA‐treated human hepatoma cells. These data on the arsenic‐induced regulation of proteins with critical roles may help elucidate the specific mechanisms underlying arsenic‐induced liver toxicity.     

BOOK REVIEW

Biological Control: Pacific Prospects–Supplement 1. D. F. Waterhouse and K. R. Norris. Australian Centre for International Agricultural Research, Monograph No. 12, 1989, vii +, 125 pp. ISBN 0949511 98 6. $49.00.