taining structure contains mineral and orgarJ.c matter as solid substances 

 which^ by chemical and biological actions^ influence the composition of the 

 water. In addition to this^ Neess (19U9) pointed out the function of the 

 bottom colloidal fraction (humic substances^ ferric gels^ clay) which ab- 

 sorbs and regulates the distribution of certain soluble nutrients, and 

 also facilitates chemical deconposition and transformation by nicroorganic 

 life occurring therein. As in agriculture, fertile soils are indicative of 

 high productivity. Schaeperclaus (1933), Meehean (1935) j and Lawson (1937) 

 discussed the quality of the substratec The bottom^ at least in shallow 

 water, acts as a nutrient storehouse,, center of biological activity, and 

 area of chemical transformations « Topsoil, and soils rich in humus, are 

 most desirable. Marl„ clay_. sand, and rock follow a general order of de- 

 creasing richness o The vrater contains dissolved gases and solids, and sus- 

 pended particulate matter,, which are in continuous exchange with the sub- 

 strate. Oxygen and carbon dioxide are gases most abundant and vital to life 

 processes.- Methane„ hydrogen, nitrogen^ ammonia, and hydrogen sulfide may 

 be present in small quantities,, The last three gases and carbon dioxide may 

 be toxic in large amounts. Suspended solids can be divided into organic (as 

 detritus) and inorganic (silt) coniponentso Dissolved solids comprise a 

 wide range of compounds containing most elements that are in some way soluble 

 in water. These are also inorganic, or complex organic, compounds. A cer- 

 tain proportion of each compound, depending upon its chemical characteris- 

 tics, and those of the solvent, exists as ions in dissociation- this in 

 t'orn affects pH, chemical reactions, and nutrient absorption. 



The hydrogen-ion concentration (pH) , a result of many obscure chemical 

 conditions, is one of the singularly significant factors affecting aquatic 

 productivity. Both soil and water should show an alkaline reaction 

 (TflE-esner, 1937). Smith (1933) found the decomposition rate of fish meal 

 noticeably lowered above pH 9oO= Schaeperclaus (1933) termed pH 9=0 the 

 alkaline danger point, and further recommended raising the pH of waters 

 rated 6,5 or lower. It is well known that acid waters are ooor producers. 

 Tne optimal range of pH can thus be established at 7oO to 8,5- To main- 

 bain a constant pH, water and soil must show a buffering action caused by 

 the presence of calcium and magnesium carbonates. Schaeperclaus (1933) and 

 Wiesner (1937) regarded this buffer action as the acid combining capacity 

 (A.CCo) of the water. The A.C.C, (corresponding to our methyl orange 

 alkalinity) is the number of cubic centimeters of 0,1 N hydrochloric acid 

 that can be neutralized by 1 liter of water. Waters of 2 to 5 A=C.C, vary 

 only slightly in pH and are rated as "very productive." 



The next step is to relate chemical nutrients to aquatic organisms. 

 Liebig's law of the minimum, directed toward plant crops, has also been 

 applied to fish crops. It states, in essence, that plants require certain 

 nutrients J the presence of any one in minimal quantity will lower the 

 total productivity. Early work in nutrient enrichment carried the 

 results of agriculture to aquiculture„ From its inception to the present 

 time, aquatic fertilization has dealt almost exclusively with organic 

 matter and four chemical elements? nitrogen, phosphorous, potassium, and 



