Effect of flooding with sewage water on three wetland sedges

Plants of three wetland sedges, Carex vesicaria, C. rostrata, and C. gracilis, were subjected to flooding with diluted pig farm sewage water in a sand-culture experiment lasting for one growing season (20 weeks). Sewage water application altered growth dynamics and accumulation of dry matter in all three species; it shifted the distribution of dry matter in favor of above-ground parts; it depressed root growth both in dry mass and length; and it increased percentages of major nutrients (nitrogen, phosphorus, and potassium) in plant dry matter. In the root structure, sewage water application inhibited formation of gas spaces in the cortex, differentiation of exodermis and endodermis, and formation of starch grains in the cortex. The changes in root growth and structure are ascribed to the combination of (1) high nutrient availability, and (2) oxygen deficiency, which developed in the root medium following addition of sewage water. In view of these findings, Carex species are not well suited for use in the treatment of wastewaters rich in both mineral nutrients and organic matter.