Characterizing the effects of turbulence on sediment oxygen and sediment nitrate demand using flow-through reactors

Onondaga Lake has received the municipal effluent and industrial waste from the city of Syracuse for more than a century. Historically, 75 metric tons of mercury were discharged to the lake by chlor-alkali facilities. These legacy deposits of mercury now exist primarily in the lake sediments. Under anoxic conditions, methylmercury is produced in the sediments and can be released to the overlying water. Natural sedimentation processes are continuously burying the mercury deeper into the sediments. Eventually, the mercury will be buried to a depth where it no longer has an impact on the overlying water. In the interim, electron acceptor amendment systems can be installed to retard these chemical releases while the lake naturally recovers. Electron acceptor amendment systems are designed to meet the sediment oxygen demand in the sediment and maintain manageable hypolimnion oxygen concentrations. Historically, designs of these systems have been under designed resulting in failure. This stems from a mischaracterization of the sediment oxygen demand. Turbulence at the sediment water interface has been shown to impact sediment oxygen demand. The turbulence introduced by the electron amendment system can thus increase the sediment oxygen demand, resulting in system failure if turbulence is not factored into the design. Sediment cores were gathered and operated to steady state under several well characterized turbulence conditions. The relationship between sediment oxygen/nitrate demand and turbulence was then quantified and plotted. A maximum demand was exhibited at or above a fluid velocity of 2.0 mm•s-1. Below this velocity, demand decreased rapidly with fluid velocity as zero velocity was approached. Similar relationships were displayed by both oxygen and nitrate cores.

Early season ozone uptake is important for determining ozone tolerance in two trembling aspen clones

There is substantial genetic variability in response to ozone amongst and within tree species. Aspen is a highly variable species with a wide range of responses to ozone. Aspen response to elevated O3 levels is being investigated at the Aspen FACE site near Rhinelander, WI where five aspen clones of varying O3 tolerance have been fumigated with elevated O3 over the past decade. In this study, we examined the physiological differences in two of the aspen clones that differed significantly in their O3 tolerance with 8L being tolerant and 42E being sensitive. Throughout the 2007 and 2008 growing seasons we periodically estimated instantaneous photosynthetic rates, ACi responses and light response curves. The results of our study suggest that aspen clone 8L’s tolerance is due in part to decreased stomatal conductance early in the season, which lowered ozone uptake. Later during the season O3 uptake was comparable for the two clones. Our results also suggest the response of Vcmax, TPU, Rd, Gm, light compensation point and quantum flux to elevated O3 did not differ significantly between the two clones. Ozone uptake is important for ozone tolerance in clone 8L early in the season but cannot explain late season tolerance. Photosynthetic parameters for the two clones were similar, so clone 8L’s ozone tolerance is not due to a more efficient photosynthetic system.