The plants, through their roots draw much water, especially from greater depths, then 

 evaporate it again. The thicker their growth and the longer they are allov;ed to grow, the 

 better v.111 the bottom be dried out and the better will it be aired. 



Tlie top layers will reiaain moist nevertheless, on accoiont of sfiading by the plants. 

 This is quite necessary for the completely (and favorably) changed world of bacteria, 

 especially for the aerobic fission fungi, so valuable for the decomposition of cellulose. 



Chapter II 



COUSTiDCTIOi: OF PONES 



In Geimany the term "pond" is popularly misconstrued, so that it can no longer be 

 exactly defined. It does not mean only snail, only drainable or cnly flat bodies of water. 

 In pond industry the "fish pcnd" always signifies a drainable Hat body of water; but also, 

 the only conditionally drainable nill-^jonds, hydraulic-hammer ponds, fire protection ponds, 

 drinking-v.ater ponds, and the non-drainable dammed ponds for pOTver production, village 

 ponds, irrigation ponds, paric ponds, peat cuts, and other ponds should be included when 

 possible in "pond industry" . 



Pond culture is profitable only under favorable fishing conditions, i.e., where 

 drainage of ponds or fishing v.lth nets is possible. Non-drainable ponds, with the exception 

 of village ponds and of irrigation ponds (always supplied with organic substances) are 

 little productive; hence, they are less profitable than drainable ones. 



We divide ponds into the following classes: 



(1) Non-drainable or at least not periodically water-covered pcxids. 



(2) Drainable, i.e., periodically water covered ponds, "fish ponds". 



Cbly the latter will be considered for the following discussions on pond construction. 

 The fish ponds iigain are divided — according to the nature of their water supply — into: 



(1) Spring water ponds (including underground-water ponds). 



(2) Rain water ponds. 



(3) Brook ponds: 



a. Dike ponds 



b. Feeder ponds 



(4) River ponds. 



Ponds under 3a are possible only in regions, free from the danger of floods. 



T.-hen makint' a choice for the location of a pond, it should be kept in mind that a _ 

 locati^'upon s^ndyTTS^ddTsoil is profitable for the reason that such a soil is practical- 

 ly unusable for other purposes. Since the construction of a pond requires capital, such an 

 undertaking will only be profitable if the pcnd ensur.es a better inco.Tie than any other use 

 of the soil. 



Ttie bottom must be not too porous, since an artificial packing with clay ydll be of 

 benefit only in small trout ponds. At the point of dam construction, the underground must 

 be solid and absolutely ii^permeable for water. Dam construction upon quick sand or upon 

 filled-in ground is to be avoided. 



Aside from small trout ponds— which occasionally can even be dug out and arranged 

 re<nilarly side by side, the location must be such that the investment for the rather costly 

 dal is low ir. proportion to the ultimately obtained pond surface, so that interest and sink- 

 inr fund may be recovered froir. the expected returns. 



61 



