1920] Allen: Plankton of the San Joaquin River 11 



RIVER CONDITIONS NEAR STOCKTON 



Relation of Stockton to Tidewater 



In this connection it is doubtless worth while to reconsider the 

 points already mentioned which have most obvious relation to Stock- 

 ton conditions. First, we may emphasize the fact of the low gradient. 

 Since the steamer landing at Stockton is only sixteen feet above sea 

 level the water level must be only about eight feet above sea level for 

 a considerable part of each year. Stockton is about one hundred 

 miles from the Golden Gate, so the gradient to the sea is only about 

 0.08 foot to the mile. This must account in large measure for the 

 range of the tide, which sometimes shows a difference of something 

 over three feet between high and low water in Stockton Channel. 



River Gradient Above Stockton 



In the other direction, we find a rise to one hundred and seventy- 

 five feet above sea level at the mouth of Kings River, probably about 

 two hundred miles above Stockton. Assuming this distance as an 

 approximation, we find the gradient above Stockton to average a little 

 more than 0.8 foot to the mile. As might be expected from such a 

 low gradient, there is a great deal of swamp land throughout the 

 distance. Formerly there was annual flooding of this low area during 

 the wet season, with a good deal of deposit of silt and stirring up of 

 organic matter, much of which came from the death of plants and 

 animals in the preceding dry season. The definite limitation and 

 constant alternation of dry and wet seasons, together with the prox- 

 imity of the mountains, must have had a very marked influence on 

 plankton production in the low lands under such conditions. 



OPPORTUNITIES FOR PLANKTON DEVELOPMENT 



Recently more and more of these low lands have been reclaimed 

 and protected by levees. The run-off is thus materially hastened in 

 flood season and there is much less opportunity for plankton devel- 

 opment than Kofoid has found for the Illinois River. There is also the 

 further consideration that most cases in which impounding of the 

 water occurs, show rapid evaporation after river subsidence, with 

 great destruction of organisms before they have opportunity to get 

 into the river channel. Unfortunately, definite information as to 

 areas still open and details of their seasonal history are not available. 



