Aboveground and belowground standing crops ofSagittaria latifoliaandSagittaria rigidawere related to water depths and substrate particle-size distribution, in differing parts of Pool 9 of the Upper Mississippi River. Average water depth during the growing season was greater in stands in open-water areas (30.1ensp;plusmn;ensp;2.1ensp;cm) than in backwaters (16.5ensp;plusmn;ensp;1.5ensp;cm). The average water depth of 35.1 inS.rigidastands was deeper than the average of 26.4ensp;cm inS.latifoliabeds. Sediments in backwaters had significantly greater proportions of clay- and silt-sized particles than sediments in open waters. Density ofS.latifoliain open water was 31.0ensp;plusmn;ensp;1.3 compared with 22.7ensp;plusmn;ensp;1.6/m2in backwaters. Peak aboveground standing crop ofS.latifoliain open water (683.4ensp;plusmn;ensp;41.4ensp;g/m2) was greater than in backwaters (430.9ensp;plusmn;ensp;25.7ensp;g/m2) and varied directly with differences in water depths in stands among years. Belowground standing crop ofS.latifoliain open water (58.6ensp;plusmn;ensp;4.3ensp;g/0.25ensp;m2) was also greater than in backwaters (40.9ensp;plusmn;ensp;6.6ensp;g/0.25ensp;m2). During the growing season, approximately 46 of the belowground standing crop of this species was composed of tubers. Peak aboveground standing crop ofS.rigidain open water (498.2ensp;plusmn;ensp;35.5ensp;g/m2) was greater than in backwaters (422.1ensp;plusmn;ensp;26.3ensp;g/m2), but a correlation with water depth was not found. Belowground standing crop ofS.rigidain open water (39.3ensp;plusmn;ensp;4.0ensp;g/0.25ensp;m2) was greater than in backwaters (25.6ensp;plusmn;ensp;3.3ensp;g/0.25ensp;m2). Tubers constituted 61 of belowground standing crop ofS.rigida, which was greater than the proportion forS.latifolia. Shallower water depth and finer particle size caused by siltation in backwaterSagittariabeds result in stands which are less productive.
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