Standing crop of Sagittaria in the Upper Mississippi River

Abstract

Aboveground and belowground standing crops of Sagittaria latifolia and Sagittaria rigida were 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 (30.1 ± 2.1 cm) than in backwaters (16.5 ± 1.5 cm). The average water depth of 35.1 in S. rigida stands was deeper than the average of 26.4 cm in S. latifolia beds. Sediments in backwaters had significantly greater proportions of clay- and silt-sized particles than sediments in open waters. Density of S. latifolia in open water was 31.0 ± 1.3 compared with 22.7 ± 1.6/m² in backwaters. Peak aboveground standing crop of S. latifolia in open water (683.4 ± 41.4 g/m²) was greater than in backwaters (430.9 ± 25.7 g/m²) and varied directly with differences in water depths in stands among years. Belowground standing crop of S. latifolia in open water (58.6 ± 4.3 g/0.25 m²) was also greater than in backwaters (40.9 ± 6.6 g/0.25 m²). During the growing season, approximately 46% of the belowground standing crop of this species was composed of tubers. Peak aboveground standing crop of S. rigida in open water (498.2 ± 35.5 g/m²) was greater than in backwaters (422.1 ± 26.3 g/m²), but a correlation with water depth was not found. Belowground standing crop of S. rigida in open water (39.3 ± 4.0 g/0.25 m²) was greater than in backwaters (25.6 ± 3.3 g/0.25 m²). Tubers constituted 61% of belowground standing crop of S. rigida, which was greater than the proportion for S. latifolia. Shallower water depth and finer particle size caused by siltation in backwater Sagittaria beds result in stands which are less productive.