Biogeochemical silica mass balances in Lake Michigan and Lake Superior

Silica budgets for Lake Michigan and Lake Superior differ in several respects. Mass balance calculations for both lakes agree with previous studies in that permanent burial of biogenic silica in sediments may be only about 5% of the biogenic silica produced by diatoms. Because dissolution rates are large, good estimates of permanent burial of diatoms can not be obtained indirectly from the internal cycle of silica (silica uptake by diatoms and subsequent dissolution) but must be obtained from the sediment stratigraphy. The annual net production of biogenic silica in Lake Michigan requires 71% of the winter maximum silica reservoir which must be maintained primarily by internal cycling in this large lake whereas the comparable silica demand in Lake Superior is only 8.3%. The greater silica demand in Lake Michigan is the result of phosphorus enrichment which has increased diatom production. It is hypothesized that steady-state silica dynamics in Lake Michigan were disrupted by increased diatom production between 1955 and 1970 and that a new steady state based on silica-limited diatom production developed after 1970. Mass balance calculations for Lake Michigan show in contrast with previous work that the hypothesized water column silica depletion of 3.0 g · m −3 could have occurred even though 90% or more of the biogenic silica production is recycled.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42471/1/10533_2004_Article_BF02187199.pd

Polychlorinated Biphenyls (PCBs) Atmospheric Concentrations and Deposition in Sub-Alpine Northern Italy

Atmospheric transport and deposition are important processes determining the fate of many persistent organic pollutants (POPs) in the environment. Research has been carried out in the last decades on ambient concentrations and controls of numerous POPs families. Experimental measurements alone (active and passive sampling) or combined with model estimations have been used to study the POPs environmental processing, transport and behavior in specific regions. However, there are many areas for which little or no information on POPs ambient levels is available. Such is the case with Southern-Western Europe, that remains uncovered by the EMEP POPs monitoring network. Moreover, the scarcity of consistent experimental data sets on atmospheric concentrations poses a problem for proper validation of models. Our main objective was to initiate POPs atmospheric measurements (weekly resolution) in order to assess air concentrations and seasonal variations of selected POPs in a sub-alpine location where little information is available on POPs ambient levels. To achieve this goal, a monitoring and research station was set up at the Joint Research Centre EMEP site (Ispra, Italy). We present and discuss a one year data set (2005-2006) on PCB air concentrations (gas and particulate phases). ¿7PCBs monthly averaged concentration varied from 31-76 pg m-3. These values are within the range of those reported for rural, semi-rural or remote areas around the world. Advection of air masses and re-volatilization from local sources seem to play a dominant role as drivers of PCB atmospheric concentrations in the area. The importance of the wet deposition in this region (1 ug m-2 yr-1 ¿7PCBs yearly total wet deposition flux; 650-2400 pg L-1 rainwater concentrations) is emphasizedJRC.DDG.H.5-Rural, water and ecosystem resource

The University of Minnesota aquifer thermal energy storage (ATES) field test facility -- system description, aquifer characterization, and results of short-term test cycles

Phase 1 of the Aquifer Thermal Energy Storage (ATES) Project at the University of Minnesota was to test the feasibility, and model, the ATES concept at temperatures above 100{degrees}C using a confined aquifer for the storage and recovery of hot water. Phase 1 included design, construction, and operation of a 5-MW thermal input/output field test facility (FTF) for four short-term ATES cycles (8 days each of heat injection, storage, and heat recover). Phase 1 was conducted from May 1980 to December 1983. This report describes the FTF, the Franconia-Ironton-Galesville (FIG) aquifer used for the test, and the four short-term ATES cycles. Heat recovery; operational experience; and thermal, chemical, hydrologic, and geologic effects are all included. The FTF consists of monitoring wells and the source and storage well doublet completed in the FIG aquifer with heat exchangers and a fixed-bed precipitator between the wells of the doublet. The FIG aquifer is highly layered and a really anisotropic. The upper Franconia and Ironton-Galesville parts of the aquifer, those parts screened, have hydraulic conductivities of {approximately}0.6 and {approximately}1.0 m/d, respectively. Primary ions in the ambient ground water are calcium and magnesium bicarbonate. Ambient temperature FIG ground water is saturated with respect to calcium/magnesium bicarbonate. Heating the ground water caused most of the dissolved calcium to precipitate out as calcium carbonate in the heat exchanger and precipitator. Silica, calcium, and magnesium were significantly higher in recovered water than in injected water, suggesting dissolution of some constituents of the aquifer during the cycles. Further work on the ground water chemistry is required to understand water-rock interactions

Report to Dr. A. Petersen, Vice President for Research, Dr. A. Hopkins, Vice President for Arts, Sciences, and Engineering, University of Minnesota on Water Water Sciences, Technology, Education and Research

Report presents a strategy to build a coherent community of water scientists