Alkali and alkaline earth metals in decomposing macrophytes in a wetland system P.A. Azeez a, * , B.A.K. Prusty a, * , E.P. Jagadeesh b a Environmental Impact Assessment Division, Sálim Ali Centre for Ornithology and Natural History, Anaikatty (PO), Coimbatore 641 108, India b Department of Chemistry, Government Engineering College, Thrissur, Kerala, India article info Keywords: Alkali metals Macrophytes Decomposition Wetland abstract The background concentration of selected alkali and alkaline earth metals (sodium, potassium, calcium and magnesium) in some macrophytes was explored in the wetland system of Keoladeo National Park, Bharatpur, India. Changes in the concentration of these elements in the course of macrophyte decompo- sition were also studied. The species selected were Paspalum distichum, Paspalidium punctatum, Cyperus alopecuroides, Pseudoraphis spinescens, Ipomoea aquatica, Neptunia oleracea and Hydrilla verticillata, which dominate the aquatic vegetation of the Park. Litterbag decomposition experiments were carried out with nylon bags of two different mesh sizes (0.14 and 0.375 mm) in the laboratory and in the field. Among the macrophytes, Hydrilla was the fastest decaying species with the lowest half-life (12.65 days) and Paspal- idium the slowest with the highest half-life (385.08 days). Overall, the grasses had low decay rate and high half-life. Background concentration of Na, K, Ca and Mg varied among the plant species. During decomposition and towards the end of the experiment, Na, K and Ca gradually declined whereas Mg increased. The variation was significant (ANOVA, P <0.05) among metals and macrophytes. Na showed no correlation with the weight loss of decomposing macrophytes in the field or in the laboratory tanks. In the field, the K concentration, in contrast with the observations in the tanks, was negatively correlated with the biomass and positively correlated with Ca content. Ca concentration in the biomass was nega- tively correlated with the weight of the remaining biomass, while Mg was positively correlated with the biomass in the litterbags. Ó 2009 Ecological Society of China. Published by Elsevier B.V. All rights reserved. 1. Introduction Wetlands, one of the highly productive ecosystems [1–6], pro- vide several ecological services [7–11]. One of such valuable ser- vices is receiving and filtering waste and runoff water, and helping in the natural purification. Macrophytes occupying an important position in the structure and function of aquatic ecosys- tems [12] play vital roles in the wetland’s function as a natural purification system. The occurrence and growth of macrophytes are affected by a variety of abiotic conditions such as water quality, sediment properties, temperature conditions and water level fluc- tuations [13]. Litter decomposition plays an important role in nutrient cycles of wetland ecosystems. The nutrient dynamics of litter are related to the decomposition rates, and directly deter- mine the wetland’s nutrient status, thereby exerting a critical con- trol on the vegetation productivity [14,15]. Existing evidences show that decomposition and nutrient dynamics are regulated by microbial activities [16], which depend on the physical and chem- ical environmental factors, including temperature, hydrological conditions, water quality and litter biochemical quality [17–21]. Over the past decades alkali metals have been widely used in industry and agriculture. Particularly millions of tons of fertilizers containing alkali metals have been used world wide to increase agricultural productivity [22]. In this paper, we reported the natu- ral background concentrations of common alkali and alkaline earth metals, sodium (Na), potassium (K), calcium (Ca) and magnesium (Mg) in select macrophytes. Decomposition of these macrophytes, changes in the metals in the plants during the course of the decom- position, and its influence on water quality were also reported. 2. Study area The study was carried out in Keoladeo National Park (Fig. 1), Bharatpur, Rajasthan, India. The 29 km 2 park (27°7.6 0 –27°12.2 0 N and 77°29.5 0 –77°33.9 0 E; almost equidistant from Delhi and Jaipur) is one of the important waterfowl habitats in the country, which has existed for more than 250 years [23] and is one of the early Ramsar sites [24]. About 8.5 km 2 large central area of the park is occupied by wetlands, while the rest is covered by grassland and woodland [4,25]. The wetland portion is apparently the most critical part of the Park ecosystem. The total area of the park KNP is segmented into several blocks or compartments (named from A to O), and separated by earthen dykes or muddy trails for the 1872-2032/$ - see front matter Ó 2009 Ecological Society of China. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.chnaes.2009.04.003 * Corresponding authors. E-mail addresses: azeezpa@gmail.com (P.A. Azeez), anjaneia@gmail.com (B.A.K. Prusty). Acta Ecologica Sinica 29 (2009) 13–19 Contents lists available at ScienceDirect Acta Ecologica Sinica journal homepage: www.elsevier.com/locate/chnaes