475 



Prom: 



Gross Physical and Biolog-ical Effects of Overboard Spoil Dispos-al 

 in Upper Chesapeake Bav 



Fish and Wildlife Service, Maryland Department of Natural 

 Resources, Maryland Board of Public Works and other 

 agencies concerned with optimal management of estuariiie 

 areas, 



^ These papers also make a major contribution to under- 

 standing of an important esiuarine area which is becoming 

 subject to growing and s<miciiine5 conihcting demands and 



.uses. It is highly probable that the results will serve many 

 uses in the solution of important practical and fundamental 

 questioni 

 The publications and reports are listed in the Appendix. 



Effects of Dredging and Spoil Disposal in 1966 



The following summaries of effects draw freely from 

 data and conclusions ia subsequent detailed final reports 

 by Biggs, Flemer, Pfitzenmeyer, Good^yn, Dovel and 

 Ritchie. Supporting evidence and discussion appear in those 

 reports. Suggestions of guidelines for dredging projects 

 and of certain recommendations have involved all of the 

 !icientists of llie program. 



1. Fine sediments from the channel were released in shoal 

 water over similar sediments, as a semi-liquid mixture, 



2. Turbidity Increased over an area of 1.5-1.9 square 

 miles (4-5 square kilometers) around the disposal site 

 (Fig. S-3). Ov er most of the area, the sus pended sedi- 

 ment load was within the range of natural variatio n 

 obser\'ed, but at a dilTerent season from observed nat- 

 ural maxima (see Biggs). 



Fig. S.3. The area liudlecJ during the 1966 hydrauUc dredging from 

 tKe DREDGED AREA and pipe-Mne disposal Into the DISPOSAL 

 AREA. "A" illustrdtei the spredd of water-horns sediments ob- 



3. Suspended sediments (In the top of 10 feet of wa(cr) 



cnrrled in a tide-related plu 



distance of about 3.1 miles (5000 meters), and vJr- 

 lually disappeared within two hours, when pumping 



ceased (see Biggs). 



4. Total phosphate and nitrogen were Increased in the 

 immediate vicinity of the discharge by factors of about 

 50 and 1000, respectively,* over ambient levels (see 

 Biggs), but limited field experiments did not show 

 any de tectable ellects on photosynthesis hy phytoplank - 

 Ma (see Flemer). 



5. The spoil material deposited on (he botioni covered ro 

 at least 1 foot (.3 meter) an area at least 5 times as 

 large as that of the defined disposal site (see B.igg.4 

 and Fig. S-3).' 



6. Approximately- 12% of the deposited sediment dis- 

 appeared from the spoil "pile" in l.'iO days after de- 

 position (see Biggs). 



7. No gross effect of dredging or spoil disposal was nh- 



served 



phytoplanklon primary productivity, zoo- 



plankton, fish e^^f, and hirvne. or fish (see Flemer, 

 Goodwyn, Dovel and Ritchie). 



8. There was a reduction of about 70% '" tlic average 

 number of bendilc individuals per square yard and 

 of about 65% in the bcnthic blomass in die spoil dis- 

 posal area, accompanied by a marked reduction in the 

 number of species present. After one and a half years, 

 numerical abundance, blomass, and .species diversity 

 had recovered to approximately the pre-disposal levels. 

 Individual species varied greatly in susceptibility to 

 damage and in recovery patterns (see Pfitzenmeyer). 



9. At the site of dredging in die channel, an erratic 

 series of species fluctuations occurred. After one year, 

 the channel had about the same number of individuals 

 as during the pre-dredging period, but not as many 

 species were present (see Pfitzenmeyer). 



Guidelines for Dredging and Spoil Disposal 



The environment of tlils project must be considered in 

 appl ying the res ults to oilier dredging and disposal sites. 

 T^his is the variable low salinity area of a large estuary. A 

 sediment trap is in effect, natural turbidities are often high, 

 and wind and wave effects on sediments are considerable. 

 The sediments involved do not, so far as we know, contain 

 any highly toxic metals, oils, or other deleterious materials. 

 TTie sediments of tiie channel and the disposal area are 

 bodi of fine grain size, similar to the sediments of many 

 upper esiuarine areas. W herever compa rable cnndiilons 

 exist, the f ollowing gultle li ncs are probably useful. 



1. In esiuarine areas like llie Upper Chesapeake, whlcii 

 Is of liigh value as a fish nursery and siii>ports popula- 

 tions of plankton, benthic animals and useful fish, pro- 

 posed large-scale environmental .modifications sliould 

 he thoroughly analyzed, with special concern ti> avoid 

 or rigorously minimize damage to atiuatlc resources. 



2. Disposal of fine sediments on flat bottom areas from 

 hydraulic pumping will affect a wide area because of 

 the spread of seml-llqnid spod and movement of sedi- 

 ment after original deposition (see Biggs). Since the 



(4) 



(5) 



