Historical data sets for most estuaries differ in terms of factors like 

 temporal and spatial coverage, kinds of measurements, and level 

 of detail. Tfierefore, the analytical metfiods used for chiarac- 

 terization generally include various quantitative and qualitative 

 tecfiniques. Nevertheless, the goal is to integrate a wealth of 

 diverse information into a unified description of the past, present, 

 and probable future conditions in each estuary (without, of course, 

 exceeding inherent data limitations). 



As historical data are being analyzed during estuary characteriza- 

 tion, various gaps in the historical data base are uncovered. Some 

 of these data gaps substantially influence data analysis and there- 

 fore must be addressed. It is not feasible to address every missing 

 link in the historical data base. Scientists must therefore rank this 

 missing information to determine its importance to accurate 

 analysis and interpretation. Once they have determined which 

 information is required, they can overcome the deficiency by re- 

 evaluating existing data or by collecting new information. 



There may be significant gaps in data on temporal trends. Although 

 a decline in landings of a species of fish may have been docu- 

 mented between 1950 and 1980, for instance, similar information 

 may not have been summarized since 1980 (Figure 3.7). Without 

 these data, it would be difficult to estimate whether landings con- 

 tinued to decline after 1980. This would be especially true if the 

 number of landings remained relatively constant between 1970 

 and 1 980. To determine whether the problem still exists, scientists 

 would have to identify and collect additional existing information on 

 landings from 1 980 to the present. If a source of information cannot 

 be identified, the estuary program may have to undertake its own 

 sampling program to determine current conditions and any trends. 



Historical Data Gaps 



05 



C 



T3 



C 

 CO 



_i 



New sampling 

 conducted during 

 estuary program 

 may show 

 continuation or 

 reversal of 

 trend 



1950 



Figure 3.7 



1960 



1970 

 Year 



1980 



1990 



Missing information on the trend of parameters through 

 time can be supplied by newly funded synthesis of 

 previously collected data or new sampling. 



Data for spatial patterns may also be incomplete. The presence of 

 high concentrations of copper in bottom sediments downstream 

 from a city again provides an illustration (Figure 3.8). Assume that 

 information on concentrations upstream from the city and down- 

 stream from the area of high concentrations is not available. Without 

 it, scientists cannot characterize the spatial extent of contamination or 



Consideration of 

 Incomplete Data 



33 



