and the diluting effects of the Columbia River discharge may substantially 



reduce estuarine salinities. In light of this, Kistritz (1978) suggests 



that the term "salt marsh" may often be inappropriate in describing tidal 

 marshes of the Pacific Northwest. 



Mixed diurnal tidal fluctuations result in abrupt changes of immersion 

 and exposure times at about 2.7 meters or mean higher high water (MHHW) , 

 where mean lower low water (MLLW) is the zero datum. Below MHHW a distinc- 

 tive salt marsh vegetation characterized by pickleweed (Salioomia virginioa) 

 commonly known as "low marsh," extends down to about mean lower high water 

 (MLHW) . Above MHHW, a "high marsh," characterized by tufted hair grass 

 [peschampsia oaespitosd) , grades into terrestrial vegetation at about 

 extreme high water (EHW) . Jefferson (1974) lists six vegetation types for 

 Oregon saline-brackish intertidal marshes: (a) low sand marsh, (b) low 

 silt marsh, (c) sedge marsh, (d) immature high marsh, (e) mature high 

 marsh, and (f) bulrush and sedge marsh. One to seven vegetative communities 

 may occur within each vegetation type. These communities and marshes form 

 complex and somewhat variable relations with each other and with tidal 

 level which Jefferson treats as successional. Three successional patterns 

 occur, depending on substrate (sand versus silt) and freshwater influence. 

 Lyngbye's sedge {Cavex tyngbyei) is intermediate in all three patterns, 

 widely distributed, and considered by Jefferson to typify Oregon salt 

 marshes. 



Low marshes typically advance through coalescing colonies of seaside 

 arrowgrass {Tvigloohin maviti-ma) or rhizomous mats of pickleweed. The 

 lower edges of the marsh are also commonly lined with three-square bulrush 

 (^Sairpus ameriaanus) . Transitions from low to high marsh may be gradual 

 or abrupt across an eroded bank. Tidal flat to high marsh eroded banks 

 may be 1 meter high. Extensive diking, landfills, and other man-induced 

 effects have significantly changed the marshlands. Jefferson (1974) 

 states that undiked old, high marsh is nearly nonexistent in Oregon. 



2 . Siletz and Netarts Bays . 



Siletz Bay, a spit-protected estuary of about 4.8 square kilometers, 

 is located on the central Oregon coast (Fig. 1). The bay receives runoff 

 from the Siletz River and two creeks. The average winter and summer 

 Siletz River discharge is 45 and 6 cubic meters per second, respectively. 

 Logging has caused extensive sedimentation, and diking, roadbuilding, and 

 filling projects have restricted flushing, causing tidelands to increase; 

 therefore, the marshes are expanding. Salinity varies widely according to 

 discharge and tide stage. During winter freshets, the salinity of surface 

 waters is often less than 5 parts per thousand where the Siletz River 

 enters the bay; summer surface salinities exceed 20 parts per thousand 

 (Rauw, 1975) . Temperatures generally vary from 7° to 15° Celsius (Rauw, 

 1975), but may exceed 18° Celsius in some habitats (Table 1). 



Netarts Bay, a shallow, bar-built estuary of about 10.4 square 

 kilometers, is located on the north-central Oregon coast (Fig. 1). The 

 bay has a very small watershed, which drains through 13 small creeks, and 

 is therefore usually completely mixed and marine-dominated. Salinities 

 usually exceed 25 parts per thousand. Bay temperatures generally reflect 

 ocean temperatures (about 8° to 15° Celsius); however, temperatures greater 



