The Biota Assessment is divided 

 into two phases. The purpose of 

 Phase I was to establish base con- 

 ditions and develop methodologies 

 with which to identify effects of low 

 flow conditions on biological organ- 

 isms. Phase II, which will begin 

 during the autumn of 1980, will use 

 these methodologies, together with 

 salinity data from the Corps' 

 hydraulic model to make assessments 

 of biological effects during 



a drought comparable to 

 that which occurred dur- 

 ing the mid 1960's, 



a period of increased 

 consumptive water loss 

 due to increases in 

 population and water use 

 in the bay area (as pre- 

 dicted for the year 2020) , 

 and 



a combination of drought 

 and consumptive water 

 loss (i.e. a drought 

 occurring in the year 

 2020). 



The methods developed to analyze 

 these scenarios are explained in 

 the remainder of this paper. 



DEVELOPMENT 

 OF METHODOLOGY 



A given factor at the onset 

 of the Biota Assessment of the 

 Chesapeake Bay Low Flow Project 

 was that it be based on the volu- 

 minous existing research on the 

 Chesapeake Bay. Research con- 

 ducted in the assessment was to be 

 aimed toward synthesis and classi- 

 fication of this information and 

 was to derive theoretical methods 

 to increase its usefulness. No 

 new field research was conducted. 



LITERATURE SEARCH 



The initial tasks included a 

 search and compilation of the litera- 

 ture and establishment of working 

 contact with bay researchers in a 

 wide variety of fields and insti- 

 tutions. The literature search task 

 consisted of a "keyword" computer 

 search of major sources, coupled to a 

 manual search of major journals and 

 the "grey literature," including 

 technical publications of academic 

 institutions and government agencies. 



Establish Baselines 



The methodology developed during 

 Phase I involved a multiple approach 

 to assessing low flow impacts. This 

 multiple approach included (1) set- 

 ting a baseline, (2) selecting study 

 species, and (3) defining tolerances 

 for and interactions between those 

 species. These multiple approaches 

 are discussed in this and the fol- 

 lowing two subsections. 



The word "impact" presupposes a 

 change that can be measured. Such 

 measurement requires establishment of 

 base conditions and delineation of 

 change from that base. For an estu- 

 ary as complex as Chesapeake Bay, 

 knowledge of the state of the system 

 at a given time is severely limited 

 by the difficulty of doing simul- 

 taneous studies. Rather, even 

 research on large projects is 

 typically concentrated in a parti- 

 cular tributary or bay-segment. 

 Therefore, baselines were selected 

 from particular time periods best 

 suited to the data. 



Physical, chemical and bio- 

 logical baseline periods were select- 

 ed in order to set base conditions 

 from which to draw data compilations 

 and to serve as a basis for mapping. 

 The physical baseline focused on sa- 

 linity. The base period selected was 



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