Table 2. (Concluded). 



Parameter 



Higher No change 



Lower 



Source 



Spiller 1975 a 

 Spiller 1975° 

 Spiller 1975 a 

 Spiller 1975 a 

 Spiller 1975 a 



Spiller 1975 

 Spiller 1975 

 Spiller 1975 

 Spiller 1975 

 Spiller 1975 



Spiller 1975 



Spiller 1975 



Spiller 1975 



Spiller 1975 



Spiller 1975 



a Carney (1977) reported similar results for an impounded marsh compared to a marsh with weirs; 

 the vegetation was lower with more hydrologic restriction and the waterfowl density higher only 

 during the winter. 



general there was little difference between weired and unweired marshes, although there was a 

 slight skew in the frequency distribution toward higher (<2 ppt) values behind weirs. Such a small 

 range of differences (Figure 2a) and the consistent 1:1 relationship of salinity in areas with and 

 without weirs (Figure 2b) indicates that the weirs sampled have little impact on marsh salinity. One 

 might also assume that weirs with less impact on water level (slotted weirs, for example) would 

 have even less effect. 



Compared to control marshes, turbidity was slightly lower in weired marshes in three studies, but 

 the same in three other studies. Water dissolved oxygen concentration was unchanged by weirs in 

 two studies. 



Soils 



Weirs had an appreciable impact on soil pH and Eh in the only study that recorded these 

 parameters (Hoar 1975). Soil Eh is an indicator of soil flooding, something which the weir and 

 any flood control device should change. Higher soil flooding (i.e., longer duration or greater 



156 



