Impact of Municipal Wastewater Effluent on Seed Bank Response and Soils Excavated from a Wetland Impoundment

Authors: FINOCCHIARO, RAYMOND - University Of Missouri; Kremer, Robert; FREDRICKSON, LEIGH - University Of Missouri

Submitted to: Wetlands
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2009
Publication Date: 6/8/2009
Citation: Finocchiaro, R.G., Kremer, R.J., Fredrickson, L.H. 2009. Impact of Municipal Wastewater Effluent on Seed Bank Response and Soils Excavated from a Wetland Impoundment. Wetlands. 29(2):713-723.

Interpretive Summary: Constructed wetlands are important for restoring wildlife habitat and reducing flooding in river floodplains. The Eagle Bluffs Conservation Area (EBCA) was established in the Missouri River floodplain near Columbia, MO, to serve as a wildlife refuge and public access for observing and hunting wildlife. Because it is a seasonal wetland, EBCA is flooded during autumn by irrigation with treated wastewater effluent from the nearby Columbia City Wastewater Treatment Facility. Rather than being discharged into the river, wastewater effluent (WWE) serves as a valuable source of water during the flooded stage of the wetland (hydroperiod). Although treated wastewater effluent poses little or no human health concern, its impact on establishment and growth of vegetation used as food sources and habitats for wildlife has received little attention. After treatment, wastewater effluent can contain high salt contents, which may accumulate in flooded soils and detrimentally affect germination of seeds in the soil and subsequent growth of vegetation that provides wildlife habitat. Our objective was to determine the response of seeds in the soil (“seed bank”) to WWE used to flood constructed wetlands at EBCA by measuring changes in the plant community that developed from the seed bank. We found that repeated irrigation with WWE of soils originating from the wetland site at EBCA decreased vegetative diversity, plant density and biomass originating from the seed bank. Seed germination and seedling development in WWE-irrigated soils were probably inhibited by the substantial increase in salts, particularly sodium, that accumulated in the soil, which was four times higher than river water. Our study suggests that wastewater effluent used for constructed wetlands should be monitored for high salt content and that remedial practices such as integrating periodic flooding with a non-saline water source may be necessary to avoid detrimental effects on establishment and growth of a diversity of plant species necessary for wildlife habitat in wetland soils. This information has important implications for scientists, wildlife conservation personnel, and wetland managers because it helps to focus investigative research aimed at anticipating potential problems with using novel water sources such as wastewater effluent for wetland flooding. Furthermore, the information could be used to develop water management systems that include alternate irrigation with non-WWE sources to avoid potential salt buildup involved in disrupting wetland vegetation communities.

Technical Abstract: Intensive management of wetlands typically includes the manipulation of water depth, duration, and timing to promote desired vegetation communities. Increased demand for water may encourage the use of alternative sources such as wastewater effluents in managed wetlands. However, water quality is commonly overlooked as an influence on wetland soil seed banks and soils. We examined the effects of municipal wastewater effluent (WWE) on vegetation of wetland seed banks and soils through a series of greenhouse trials. We used microcosms filled with one of two soils and irrigated with WWE, Missouri River water (MOR), or deionized water to simulate moist-soil conditions. Vegetation that germinated from the soil seed bank was allowed to grow in microcosms for approximately 100 d. Vegetative taxa richness, plant density, and biomass were significantly reduced in WWE-irrigated soils compared with other water sources. Salinity and sodicity rapidly increased in WWE-irrigated microcosms and probably was responsible for inhibiting germination or interfering with seedling development. Our results indicate that irrigation with WWE promoted saline-sodic soil conditions, which altered the vegetation community by inhibiting germination or seedling development.