Abstract
Monocultures of functional equivalent species often negatively affect nutrient cycling and overall biodiversity of aquatic ecosystems. The importance of water and sediment nutrients for the occurrence of monocultures was analysed using field data from drainage ditches. Ranges of nutrients were identified that best explained the occurrence of monocultures of Elodea nuttallii (Planch.) St. John (Waterweed type), monocultures of duckweed (Duckweed type) and the occurrence of a diverse submerged vegetation (Mixed type). Results indicated these three vegetation types occurred at distinctive ranges of phosphorus in water and sediment. Sediment phosphorus distinguished monocultures from the Mixed type, with the two monocultures occurring at two to four times higher concentrations. The Waterweed type occurred at higher sediment phosphorus levels than the mixed type, showed a higher degree of dominance and lower number of red list species. Phosphorus concentrations in water were four to six times higher in the Duckweed type compared to the Waterweed and Mixed type. The three vegetation types had comparable total biomass which was unexpected. This comparability was likely caused by duckweed only growing at the water surface at the highest nutrient levels and the limited space in drainage ditches for increased submerged biomass development at high nutrient availability. Possible measures to limit the occurrence of monocultures, and thereby increasing the ecological quality, are discussed with focus on lowering phosphorus concentrations in both water and sediment and on removal of plant species that develop into monocultures.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-2-564) contains supplementary material, which is available to authorized users.
Highlights
Environmental change in ecosystems due to anthropogenic stressors generally leads to a loss of community diversity and is often combined with an increased dominance of one or a few species (Hillebrand et al 2008)
Characteristics of vegetation types Based on biomass composition, 20, 17 and 13 ditches were designated as Duckweed, Waterweed and Mixed, respectively
Both in June and September the Duckweed and Waterweed ditches contained the highest biomass of duckweed and E. nuttallii respectively, while Mixed ditches contained the highest biomass of plants other than E. nuttallii or duckweed (Table 1)
Summary
Environmental change in ecosystems due to anthropogenic stressors generally leads to a loss of community diversity and is often combined with an increased dominance of one or a few species (Hillebrand et al 2008). An aquatic vegetation dominated by for instance several duckweed species can be considered a monoculture as the species are functionally comparable and influence the ecosystem in a comparable way (Hubbell 2005). In lakes for example, eutrophication and related phytoplankton dominance prevents submerged macrophyte development, which leads to an overall loss of biodiversity (Scheffer et al 1993). Small aquatic systems such as streams and drainage ditches can develop monocultures of fast growing submerged species like Elodea nuttallii (Planch.) St. John or duckweed
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