Effect of Macrophyte Species on Subsurface Flow Wetland Performance in Cold Climate

Abstract

Horizontal subsurface flow constructed wetlands (HSSCW) allows organic matter and nitrogen removal of fish farm effluent prior to streams discharge. The effect of macrophyte species on HSSCW efficiency was tested in ten units in a greenhouse experiment, in summer and winter. Planted units were at least 5% more efficient in pollutant removal than unplanted units in summer and at least 10% in winter. The increase in removal efficiency for planted units was small, mainly because of the low loading conditions of the fish farm effluent. TKN (96% in summer and 88% in winter) and COD (96% in summer) removal were more efficient for Phragmites and Typha, the two species with large rhizomes. Phalaris was more efficient than the others with COD and BOD removal at 95% in winter. Calamagrostis was the least efficient species, with the largest difference being for winter nutrient removal. It was also the species with the lowest belowground: aboveground biomass ratio, around 0.25 compared to above 2 for Typha. Units planted with macrophytes with large belowground biomass showed less seasonal variability.

Significant Increase in Nutrient Stocks Following Phragmites australis Invasion of Freshwater Meadow Marsh but Not of Cattail Marsh

“…aboveground biomass was positively related to water depth in a Great Lakes wetland. Our results also differ from previous studies that did not find a difference in belowground biomass between cattail and P. australis-invaded communities (Ouellet-Plamondon et al, 2004;Rothman and Bouchard, 2007). A major difference between our study and others examining below ground biomass in P. australis-invaded marhes (e.g., Farnsworth and Meyerson, 2003;Rothman and Bouchard, 2007) is that we used the in-growth core technique because our interest was in annual standing stocks, whereas other field studies typically used traditional soil core methods to measure total belowground standing crop biomass.…”

“…and P. australis measured in our study, this inferior nutrient assimilation is likely attributable to lower standing crop biomass in meadow marsh. Indeed, the aboveground biomass in meadow marsh reported in our study is similar to that reported in a greenhouse experiment (1,057 ± 12 g/m 2 ; Ouellet-Plamondon et al, 2004), and lies well below the standing crop biomass values for cattail marsh and P. australis-invaded marsh.…”

“…A major difference between our study and others examining below ground biomass in P. australis-invaded marhes (e.g., Farnsworth and Meyerson, 2003;Rothman and Bouchard, 2007) is that we used the in-growth core technique because our interest was in annual standing stocks, whereas other field studies typically used traditional soil core methods to measure total belowground standing crop biomass. Our approach would exclude any roots and rhizomes produced during previous seasons, and consequently yields lower estimates of belowground biomass than many other studies (e.g., Farnsworth and Meyerson, 2003;Ouellet-Plamondon et al, 2004;Rothman and Bouchard, 2007).…”

“…Indeed, in its native range, P. australis is often used in constructed wetlands to remove nutrient pollution (Gumbricht, 1993;Bhatia and Goyal, 2014), suggesting it could provide an important water quality improvement function where it has invaded. Yet, despite the importance of carbon and macronutrients phosphorus, potassium, calcium, and magnesium (Ehrenfeld, 2010), research on P. australis invasion and its effects on nutrient stocks in freshwater coastal marsh has primarily focused on nitrogen (but see Findlay et al, 2002;Ouellet-Plamondon et al, 2004). In addition, prior work has focused on differences between Typha spp.…”