Effects of vegetation management in constructed wetland treatment cells on water quality and mosquito production

Abstract

The impact of three vegetation management strategies on wetland treatment function and mosquito production was assessed in eight free water surface wetland test cells in southern California during 1998-1999. The effectiveness of the strategies to limit bulrush Schoenoplectus californicus culm density within the cells was also investigated. Removing accumulated emergent biomass and physically limiting the area in which vegetation could reestablish, significantly improved the ammonia-nitrogen removal efficiency of the wetland cells, which received an ammoniadominated municipal wastewater effluent (average loading rate = 9.88 kg/ha per day NH 4 -N). We determined that interspersing open water with emergent vegetation is critical for maintaining the wetland's treatment capability, particularly for systems high in NH 4 -N. Burning aboveground plant parts and thinning rhizomes only temporarily curtailed vegetation proliferation in shallow zones, whereas creating hummocks surrounded by deeper water successfully restricted the emergent vegetation to the shallower hummock areas. Since the hummock configuration kept open water areas interspersed throughout the stands of emergent vegetation, the strategy was also effective in reducing mosquito production. Decreasing vegetation biomass reduced mosquito refuge areas while increasing mosquito predator habitat. Therefore, the combined goals of water quality improvement and mosquito management were achieved by managing the spatial pattern of emergent vegetation to mimic an early successional growth stage, i.e. actively growing plants interspersed with open water.

Tropical treatment wetlands dominated by free-floating macrophytes for water quality improvement in Costa Rica

“…Few mosquitoes were observed in the wetlands during this study, with the exception of the Relleno Sanitario, the shallowest wetland. This concurs with several other studies that report that deep-water wetlands (>0.2-0.6 m) supported less mosquito larvae compared to shallow-water wetlands (Walton and Workman, 1998;Thullen et al, 2002;Diemont, 2006). Deep-water wetlands also provide habitat for fish that commonly occur, such as tilapia, which can be harvested as a salable product, thus potentially increasing the economic efficiency of these tropical treatment wetlands.…”

“…It is recommended that caution be taken when constructing treatment wetlands so that favorable conditions for the proliferation of mosquitoes are not met; wetlands should have consistent flow, a minimum of 30% open water (Greenway et al, 2003), and should be greater than 0.2-0.6 m in depth (Walton and Workman, 1998;Thullen et al, 2002;Diemont, 2006). The treatment wetland alternative also provides a relatively inexpensive approach for small-scale farmers to continue to operate in the face of appropriately stronger water quality standards.…”

Integrated Mosquito Management in Experimental Constructed Wetlands: Efficacy of Small-Stature Macrophytes and Fluctuating Hydroperiod

“…Managing vegetation in constructed treatment wetlands is controversial (see discussion in [41]) and can be expensive. Large macrophytes require thinning if water quality performance declines or if mosquito production reaches problematic levels [6,[41][42][43].…”

“…Large macrophytes require thinning if water quality performance declines or if mosquito production reaches problematic levels [6,[41][42][43]. Drying the wetland is necessary if heavy equipment is used to knock down and move dried vegetation.…”

“…After establishment, dense stands of B. maritimus are somewhat resistant to invasion by other macrophyte species [28,44]. Raised planting beds (hummocks) separated by deeper open water zones [41] is one wetland design that might facilitate proliferation of B. maritimus in new constructed wetlands and should be conducive to IMM strategies designed to reduce the use of chemical pesticides [6,42]. Bolboschoenus maritimus and closely related species (i.e., B. robustus (Pursh) M.T.…”