Water and soil fertility 



Water fertility . --It is generally recog- 

 nized that fertility of surface water is primarily 

 dependent upon fertility of the watershed from 

 which it drains. A major share of the 47 per- 

 cent of Minnesota land classed as good to ex- 

 cellent for general agricultural production 

 (Engene and Pond 2^) lies in the upper Missis- 

 sippi River drainage. It includes much of the 

 Clarion -Webster soil association which is 

 unsurpassed by any other In the State for com 

 production (McMiller, 31^) . It might then be 

 expected that the water which drains from this 

 region would also be fertile. Water analyses V 

 were nin on samples collected in area B and 

 vicinity on October 3, 1955 and July 24, 1956 

 and in the main channel at La Crosse, Wiscon- 

 sin on September 10, 1956 (Table 32). Concen- 

 trations of total phosphorus in and near area B 

 ranged from 0.091 to 0.114 ppm and those of 

 total nitrogen from 0.69 to 1 .43 ppm. The 

 average phosphorus -nitrogen ratios in water 

 samples collected October 3, 1955 and July 24, 

 1956 were 1:8.2 and 1:10.9, respectively. 

 Total alkalinity ranged from 100.0 to 115.0 

 ppm among the combined samples from area B 

 and vicinity . 



Moyle ( 33) reported that total alkalinity 

 and total phosphorus appear to be the most 

 valuable indices of lake productivity in Minne- 

 sota waters. Lakes with a total alkalinity of 

 91 ppm or more were classed as high in both 

 fish and plant productivity. Those with a total 

 phosphorus content (unfiltered samples) of 0.051 

 to 0.10 and 0.11 to 0.20 were rated good and 

 very good, respectively, in terms of phosphorus 

 fertility. Moyle found the average fish yields 

 from hard water ponds with total phosphorus 

 exceeding 0.05 ppm to be highest when total 

 nitrogen ranged from 0.51 ppm to 1 .0 ppm 

 although nitrogen appears to be only occasionally 

 a limiting factor in the productivity of Minnesota 

 waters. 



The basic compx^nents generally associated 

 with fertility were found in the present study to 

 equal or exceed those values described above 

 which are indicative of heavy fish production 

 and it is concluded that chemical fertility of the 

 upper Mississippi River is high and capable in 

 that regard of supporting a fish population at a 

 proportionate level . 



Bottom soils. --The importance of bottom 

 soils in fish culture in Europe is described by 

 Neess (38) in his review of numerous papers. 

 The bottom soil in area B was a silty clay in 

 texture and had a organic content of 7 .49 per- 

 cent (Table 33). The soils of both the side 

 channel adjacent to area B and the main channel 

 were of a coarser texture and contained less 

 organic material. 



In a series of Minnesota walleye rearing 

 ponds, Dobie (14) found higher fish production 

 in ponds with fine-textured soils than in those 

 with the bottom composed of coarse material . 

 Wood (68) concluded that the availability of 

 essential plant nutrients in the bottom soils 

 is one of the two most important factors 

 affecting the productivity of impoundments . 



The pressure of fine-textured soil with a 

 higher organic content than that associated with 

 the coarser soils of the adjacent lotic environ- 

 ments suggests that the backwater areas in the 

 upper Mississippi River represent a major 

 component of the entire fish-producing habitat. 



Food availability 



That fish production is directly related to 

 the abundance of food in plankton or macro- 

 invertebrate form has often been suggested. 



Surber (54) found an abundance of phyto- 

 plankton and rotifers in samples from upper 

 Mississippi River sloughs. He reported Cyclops, 

 chironomid larvae, and ostracods to be the 

 "animal staples" in these waters. 



9/ Analyses were run at the laboratory of 

 the Minnesota Department of Conservation, 

 Bureau of Research and Planning, St. Paul, 

 Minnesota. 



Comparison of bottom fauna and epifauna 

 production in 1929-30 with that in 1953 in three 

 sloughs located approximately 20 miles below 

 Fountain City was reported by the Upper 

 Mississippi River Conservation Committee (65) 

 (Table 34). In the 1953 samples, copepods. 



42 



