Growth of softstem bulrush (Scirpus validus) in microcosms with different hydrologic regimes and media depths

Factors affecting growth of softstem bulrush (Scirpus validus), an obligate wetland plant frequently used in subsurface-flow constructed wetlands in N orth America, were studied in a controlled environmental chamber. Effects o f media depth (30- and 46-cm), hydraulic retention time (HRT) (2- and 6-day ), and water-level drawdown (drawdown vs. no drawdown) on plant growth in 2 4 microcosms were investigated. Weekly root and stem growth was measured an d stem health assessed to determine effects of treatments on plant vigor. W ater-level drawdown was detrimental to plant growth, increasing the percent age of dead stems. Stem production was higher in microcosms with a 46-cm me dia depth than those with a 30-cm depth and also higher in microcosms that were permanently flooded than in those with fluctuating water levels. Root production was greater in microcosms with a 30-cm media depth than in those with a 46-cm depth, and root production was also greater in microcosms tha t were constantly hooded than in those drawn down. Scirpus validus is a rob ust plant that grows well in gravel media microcosms; however, problems are experienced when rhizomes and roots dry out during water drainage.