Water-column responses

The prediction of the size and permeability of the aquifer is usually difficult, since there is typically little data collected in the water column exploration and appraisal wells are usually targeted at locating oil. Hence the prediction of aquifer response often remains a major uncertainty during reservoir development planning. In order to see the reaction of an aquifer, it is necessary to produce from the oil column, and measure the response in terms of reservoir pressure and fluid contact movement use is made of the material balance technique to determine the contribution to pressure support made by the aquifer. Typically 5% of the STOMP must be produced to measure the response this may take a number of years. 

Comparison with other Studies. How do the results of our investigation compare with similar studies Our results corroborate the data provided in a similar study of the effect of UV-B on primary productivity in the southeastern Pacific Ocean (35). In the latter study, it was noted that enhanced UV-B radiation caused significant decreases in the productivity of surface and deep samples. Compared to ambient, primary productivity decreased with increasing doses of UV-B. In another study in which in situ experiments using natural Antarctic phytoplankton populations, it was noted that incident solar radiation significantly depressed photosynthetic rates in the upper 10-15 meters of the water column (36). It was also found that the spectral region between 305 and 350 nm was responsible for approximately 75 percent of the overall inhibitory effect. 

Figure 7. GPC analysis of (A) 312-nm Dow latex sample SE Dupont silica columns—(a) response at 254-nm wavelength (full scale 0.5 A) (b) response at 340-nm wavelength (full scale 0.02 A) (B) 220-nm Dow latex sample E-Linear Watefs silica columns—response at 254-nm wavelength (full scale 0.5 A) (C) 98-nm Polysciences latex sample E-Linear WatePs silica columns—response at 254-nm wavelength (full scale 0.5 A) (D) 183-nm Polysciences latex sample E-Linear Water s silica columns—response at 254-nm wavelength (full scale 0.5 A)...

Induction did not occur under our exposure conditions in fish exposed to water saturated with a variety of pure hydrocarbons. The compounds studied are commonly found in other pollutants besides petroleum. It is reasonable to speculate that enzyme induction may not be a common response of fish in the environment to various pollutant hydrocarbons which may be available in the water column for short periods. 

One other measurement technique that has been used to measure Kl over a shorter time period, and is thus more responsive to changes in wind velocity, is the controlled flux technique (Haupecker et al., 1995). This technique uses radiated energy that is turned into heat within a few microns under the water surface as a proxy tracer. The rate at which this heat diffuses into the water column is related to the liquid film coefficient for heat, and, through the Prandtl-Schmidt number analogy, for mass as well. One problem is that a theory for heat/mass transfer is required, and Danckwert s surface renewal theory may not apply to the low Prandtl numbers of heat transfer (Atmane et al., 2004). The controlled flux technique is close to being viable for short-period field measurements of the liquid film coefficient. 

We have now developed the necessary tool to continue our analysis of the PCBs in Lake Superior. Remember that we have asked the question how fast the PCB concentration in the lake would respond to a change of the PCB input. We found that the water column alone has a typical response time of about 3 years and then speculated whether the PCBs in the sediments would significantly alter this time. 

You are responsible for the PCB monitoring program in the lake. Despite the fact that all external PCB inputs have been stopped, you still find significant PCB concentrations in the water column. A detailed survey of the sediments shows that in the top 10 cm of the sediment layer the mean concentration, Cssc, of 2,2 ,3,4,5,5 ,6-heptachlorobiphenyl (PCB 185) is 4.0 nmol kg 1. 

When calculating the characteristic coefficient, ku, kn, k2[, k22, of Box 23.3 you will find that the response velocity of the sediment reservoir is much smaller than that of the open water column. In order to predict the decrease of both concentrations, Cssc and C°p, you can assume a quasi-steady state between the two concentrations in which the system is controlled by the decrease of the slowly reacting sediment reservoir. 

Terrestrial Detritus. Variability in ecosystem response to fertilization may be attributed in part to the interaction of aquatic and terrestrial ecosystems. In contrast to the many aquatic ecosystems in which higher trophic levels are fueled almost entirely by organic matter originating in the water column, other systems are driven by inputs of particulate and dissolved organic matter from land. The importance of this land-water interaction in regulating system metabolism has been obvious to stream ecologists for some... 

Detenbeck (37) and Detenbeck and Brezonik (38, 39) examined the effect of pH on phosphorus sorption for LRL sediments. Their results suggested that the flux of inorganic P from sediments could be diminished by as much as 90% if the pH of sediments decreased from 6.0 to 4.5. However, there was no observed treatment effect for TP and an apparent increase in SRP summer averages at pH 4.7 (Figure 4). Therefore, chemical sorption-desorption processes probably do not control phosphorus levels in LRL. The direction of response at lower pH implies that the balance between biotic uptake, deposition to sediments, and release from organic detritus by decomposition most likely controls SRP levels in the water column. 

Residence Times. Phosphorus residence times with respect to major depositional processes (see Tables II and IV) are summarized in Table VI. In comparison, the total-P residence time based on external loading is about 4.5 years. Residence times were calculated for a mean water-column depth of 85 m, and steady state was assumed. Although transport of P to the sediment surface by the combination of diatoms, calcite, and terrigenous material is relatively rapid, the low burial efficiency results in a relatively long residence time for total P (about 5 years). In comparison, the residence time for Pb is about 0.6 years (20). Thus, the response time for P changes with respect to loading should be on the order of 5-15 years. 

We determined the net formation rates in discrete samples at several depths in the water column, with and without filtration, using waters from several lakes. We also investigated the decay processes, in the dark, for whole lake waters, lake waters filtered through varying mesh size filters, and in pure bacterial cultures. These results added to our understanding of the processes responsible for the observed distribution of H202. Our current research activities (18) are reviewed and synthesized in this chapter. 

The distribution of Hg within seepage lakes is a net result of the processes that control Hg transport between the atmosphere, water column, seston, sediments, and groundwater. This discussion focuses on the processes that control the exchange of Hg between the sediments and lake water. We first present data on spatial and temporal concentrations in the water column, sediments, pore water, and groundwater. These data set the context for a subsequent discussion of the chemical and physical processes responsible for the transport of mercury across the sediment-water interface and are necessary for assessing transport rates. 

Processes and mechanisms responsible for recycling at the sediment-water interface cannot be explained by a single process, but are most likely a combination of many biogeochemical processes. Although pore-water HgT concentrations were higher than in lake waters, direct release of pore waters below about 2 cm could not totally account for the observed buildup in the hypolimnion of Little Rock Lake. Remineralization of recently deposited biogenic particulate matter and release of particle-bound Hg from this source most likely accounted for the observed water-column buildup. 

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