Individual study: Effect of flooding with sewage water on three wetland sedges (Carex vesicaria, C.rostrata and C.gracilis) in the Trebon Biosphere Reserve, Czech Republic
Koncalová H., Kvet J., Pokorný J. & Hauser V. (1993) Effect of flooding with sewage water on three wetland sedges. Wetlands Ecology and Management, 2, 199-211
Three tall, wetland sedges, bladder sedge Carex vesicaria, beaked sedge C.rostrata and slender tufted-sedge C.gracilis, adapted to waterlogged soils of mesotrophic to eutrophic habitats, dominate periodically flooded wetlands in the Trebon Biosphere Reserve, Czech Republic, to which partially treated wastes from a large pig farm are applied as fertilizer at irregular intervals throughout the year. The study summarised here looked at the effects on these sedges of flooding with pig farm sewage water.
C. gracilis, C. rostrata and C. vesicaria plants were collected locally from a sedgegrass marsh on 12 April 1985. Tillers (shoot height about 10 cm; rhizome length 2-3 cm) were used as propagules, planted in pairs in 3.6 l glass flasks part-filled with a mix of sand and earth (1:1) to 15 cm in depth. They were grown outdoors from 12 April to 27 August 1985 (20 weeks). The substrate was kept flooded (water level maintained between 1 cm to 5 cm above the substrate surface) by adding water as required.
Nitrogen (N) and phosphorus (P) were supplied three times (8 May, 22 May, 7 June) to all flasks as 20 g urea (9.3 g N) and 20 g superphosphate (1.6 g P). One month after experiment initiation (12 May onwards) sewage water (liquid fraction of pig farm waste) applications were applied at one of four doses: 0, 50, 100 or 200 ml per flask, added at 2- to 3-week intervals (12 May, 31 May, 16 June, 1 July).
Growth responses and nutrient levels: Sedge growth was estimated from increases in dry weight of plants harvested at 2- or 3-week intervals; on each date, four to six randomly chosen C.vesicaria and C.rostrata plants were removed, washed free of the substrate with water, and divided into living shoots, living roots, living rhizomes and dead parts. On August 5, 14 and 27, 1985, roots were collected to determine their specific gravity (i.e. fresh weight per unit volume) and their water content. Mineral nutrient levels (N, P, K, Na, Ca, Mg) were analysed in the laboratory.
In all three sedge species, sewage water flooding altered the distribution of dry matter in favour of above-ground parts and increased content of major nutrients (N, P, K) in plant material. Root growth was depressed as was formation of gas spaces in the root cortex, differentiation of exodermis and endodermis, and formation of cortex starch grains.
The changes in root growth and structure are attributed to both high nutrient availability, and oxygen deficiency which developed in the substrate following sewage water addition.
These changes noted in sedge growth are considered unlikely to be the only limitations of the sewage water treatment, but they indicate that these three Carex species (and perhaps other Carex) unlike for example the grass, common reed Phragmites australis, are not well suited for use in the treatment of waste waters rich in mineral nutrients and organic matter.
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