ASIA/OCEANIA REPORT The contribution of Potamogeton crispus to the phosphorus budget of an urban shallow lake: Lake Monger, Western Australia Barbara Leoni 1 • Clelia Luisa Marti 2 • Elena Forasacco 1 • Matteo Mattavelli 1 • Valentina Soler 1 • Pietro Fumagalli 1 • Jo ¨rg Imberger 3 • Simone Rezzonico 1 • Letizia Garibaldi 1 Received: 19 May 2015 / Accepted: 31 July 2015 Ó The Japanese Society of Limnology 2015 Abstract Lake Monger (Perth, Western Australia) is a highly eutrophic lake, characterised by very low species richness of macrophytes with the dominance of Pota- mogeton crispus. Mesocosm experiments were performed using water and plants collected from the lake to determine the effects of vegetation decay on the phosphorus (P) con- centrations in the overlying waters. After 2 weeks of experimental incubation of mesocosms with and without re-oxygenation, P concentrations in the water column were significantly higher, showing a quite similar effect of P. crispus on the phosphorus release in different mesocosms. The results of our study provide clear evidence that the P concentrations in overlying waters mainly depend upon the plant P content and developmental stage. Although many sources contribute to the nutrient load of Lake Monger, macrophyte harvesting, prior to its senescence, might constitute a significant in-lake measure for reducing the internal P load. Keywords Phosphorus Á Macrophytes Á Decomposition Á Restoration Á Wetlands Introduction Submerged vegetation plays a central role in aquatic ecosystems because of their numerous functions in the nutrient and organic matter balance as well as in the food web regulation and the provision of habitat for aquatic biocoenosis (shelter, food, and spawning grounds; Hilt et al. 2010; Declerck et al. 2011; Lauridsen et al. 2015). Potamogeton crispus L. (curly pondweed) is a perennial submerged aquatic macrophyte distributed in a wide range of climatic regions (Heuschele and Gleason 2014) that can tolerate hypertrophic conditions and grows well in polluted water. P. crispus assimilates most of its nutrition through the roots, so biomass, shoot density, and tissue nutrient concentrations are primarily determined by sediment type (Chambers et al. 1989). Consequently, the growth of P. crispus may cause the depletion of phosphorus (P) and nitrogen (N), and a decrease of chemical oxygen demand (COD), along with an increase in water transparency and dissolved oxygen (DO) in the water column (Bakker et al. 2010; Menon and Holland 2014). These characteristics make it a suitable candidate for bioremediation of polluted waters (Mi et al. 2008). Eutrophication is an important indication of serious water pollution, and often P is a key factor enhancing the primary production (Bennett et al. 2004; Gan and Guo 2004; Menon and Holland 2014). Upon controlling the input of external P loading, the P in sediment (internal loading) becomes the main P source for any freshwater environment. Thus, the majority of freshwater lake restoration programmes are striving towards an improve- ment in water quality through the reduction of the within- lake total phosphorus (TP) concentrations (Menon and Holland 2014). The exchanges of P between water and sediment are highly complex, involving interrelated Handling Editor: Tomomi Inoue. & Barbara Leoni barbara.leoni@unimib.it 1 Dipartimento di Scienze dell’Ambiente e del Territorio e Scienze della Terra, Universita ` degli Studi di Milano Bicocca, Piazza della Scienza 1, 20126 Milan, Italy 2 Centre for Water Research, The University of Western Australia, Crawley, WA 6009, Australia 3 43 Goldsmith Rd, Dalkeith, Western Australia 6009, Australia 123 Limnology DOI 10.1007/s10201-015-0465-4