. Bulletin. Natural history; Natural history. August 1941 BELLROSE: DUCK FOOD PLANTS 257 Fluctuating water levels affect such marsh and moist-soil plants as wild and Walter's millets, figs. 19-20, chufa. rice cut-grass, certain smartweeds and pigweed, as well as aquatic plants. \Vhen these plants are inundated in their immature more turbid the waters, the shallower be- comes the maximum depth at which vari- ous species of aquatic plants are able to live. During the summer of 1939 and 1940, the transparency of many lakes along the. Fig. 16. — Remnant ut .i bed ot duck, potato iScigit/cuiii lali
. Bulletin. Natural history; Natural history. August 1941 BELLROSE: DUCK FOOD PLANTS 257 Fluctuating water levels affect such marsh and moist-soil plants as wild and Walter's millets, figs. 19-20, chufa. rice cut-grass, certain smartweeds and pigweed, as well as aquatic plants. \Vhen these plants are inundated in their immature more turbid the waters, the shallower be- comes the maximum depth at which vari- ous species of aquatic plants are able to live. During the summer of 1939 and 1940, the transparency of many lakes along the. Fig. 16. — Remnant ut .i bed ot duck, potato iScigit/cuiii lalijiiiui] being cncro-ichtd upon by r bulrush (Scirpiis fliivinlilisi in an area from which water has receded. stages, as they frequently are during the summer, they drown through lack of suf- ficient carbon dioxide and oxygen. The more mature these plants become, the longer they are able to tolerate flooding. In 1938 and 1939, many seedling Japan- ese millet patches planted by duck clubs failed to develop because of inundation in July or August. Factors Influencing Turbidity ^Vith the exception of fluctuating water levels, turbidity is apparently the most potent factor affecting aquatic plant beds in the Illinois River region. Turbidity in- hibits light penetration. The depth to which submerged and floating aquatic plants grow is dependent largely upon the amount of sunlight they obtain. Thus, the Illinois River was measured by means of a Secchi disc. This disc is 10 centimeters (4 inches) in diameter and white in color. The maximum distance below the water surface that the outline of the disc is visible in the shade is used as a measure of the degree of transparency. Fluctuating Water Levels. — Physical factors may change the transparency of part of a lake or an entire lake within a few hours. In order to compare transpar- encies as affected by water levels, it was necessary to consider only those readings not influenced by other factors. The transparency readings at Lake C
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Keywords: ., booka, bookcentury1900, bookdecade1910, booksubjectnaturalhistory
