determine whether the source of contamination is in the city. Such 

 information is essential to determine the magnitude and likely 

 cause of the problem. Accordingly, the acquisition of these data 

 probably would be given a high priority. New data could be collected 

 at a series of sampling stations located at increasing distances from 

 the city and the area of high concentrations. 



Use of New Sampling Stations 

 To Fill Spatial Data Gaps 



Pollutant Concentration 



High 



Low 



New Stations 



Sampling New Stations Yields Following Results 



Upstream source with 

 little dilution in estuary, 

 or strong source in all 

 areas (e.g., atmosphere 

 or runoff). 



Source Is city 



Source is city but 

 pollutant is degraded, 

 diluted, or sedimented 

 by the time it reaches 

 estuary. 



Figure 3.8 New sampling to fill in missing spatial data can yield 



important information about the source and extent of a 

 problem. 



Insufficient evidence about a suspected cause-effect relationship 

 can lead to a pressing need to obtain missing data. Again, the 

 relationship between declining aquatic vegetation and increased 

 nitrogen concentration provides an illustration. This relationship 

 could be due to the stimulative effect of the nutrient nitrogen on 

 phytoplankton populations and the resulting decrease in light 

 penetration through the water column. The relationship could be 

 confirmed experimentally by exposing the aquatic vegetation to 

 varying light intensities. Such an experiment would show the 

 relationship between light reduction and mortality of the vegetation 

 (Figure 3.9). 



34 



