Mass invasion of non-nativeElodea canadensisMichx. in a large, clear-water, species-rich Norwegian lake – impact on macrophyte biodiversity

Abstract

-The impact of Elodea canadensis on aquatic macrophyte biodiversity in (Lake) Steinsfjord has been studied through extensive lake-wide surveys and photographic sampling. E. canadensis greatly expanded in Steinsfjord since its appearance in 1978 and still dominated the macrophyte community in 2004. The areal distribution of E. canadensis peaked within 6 years from invasion and has remained relatively stable since; however, stands no longer reach the water surface. E. canadensis significantly increased its depth range, but the cover-weighted mean depth remained unchanged, suggesting that 3-4 m is its optimal depth in Steinsfjord. Species richness has not changed significantly since the earliest survey in 1936-38. However, species composition has changed remarkably, from isoetid dominance in 1936-38 to a diverse community dominated by Najas flexilis in 1979-80 to a less diverse community dominated by E. canadensis in 2004, with Potamogeton berchtoldii and Myriophyllum alterniflorum as lake-wide subdominants. Regardless of their abundance at the onset of the E. canadensis invasion, taxa whose cover-weighted mean depth overlapped with E. canadensis's in 1979-80 greatly reduced their abundance in 2004, shifted to deeper or shallow water or disappeared from sampling stations. Our survey indicates that E. canadensis may be the reason for the decrease of N. flexilis, likely through depletion of CO 2 in the water column and reduced nutrients in sediments. The abilities to survive and grow in periodically exposed shallow areas, combined with minor herbivory by waterfowl, are likely important factors for the increase of M. alterniflorum in Steinsfjord's shallow waters.

Negative correlations between native macrophyte diversity and water hyacinth abundance are stronger in its introduced than in its native range

“…Previous studies have shown impacts of invasive macrophytes on native richness and species composition (Amorim, Umetsu, Toledo & Camargo, ; Chatterjee & Dewanji, ; Michelan, Thomaz, Mormul & Carvalho, ; Mjelde, Lombardo, Berge, & Johansen, ; Stiers et al, ), but few have compared these impacts with diversity responses of communities in the native range of the invasive species. Considering such comparison, it is possible to denote the impact intensity.…”

Effect of photosynthetically elevated pH on performance of surface flow-constructed wetland planted with Phragmites australis

“…Thus, a modified SFCW form, influ-ent→submerged plants→emergent plants→effluent, was introduced. Its enhancement for nitrogen removal has been theoretically proved by Weisner et al (1994), and the system could withstand the impact of temperature change because some submerged plants still grew when emergent macrophytes went through declining during winter (Mjelde et al 2012;Zhang et al 2009). Besides, emergent plantsʼ final position at collocation line could guarantee the purification efficiency.…”

Morphometric and biotic variables as potential predictors ofLudwigia sedoides(Humb. & Bonpl.) Hara in a large Amazonian reservoir

“…The excessive growth of aquatic macrophytes has attracted the interest of the scientific community and society, basically because excessive cover may compromise the use of some freshwater resources van Nes et al, 2002;Mjelde et al, 2012). However, macrophytes also play important ecological functions (Madsen et al, 2001;Engelhardt and Ritchie, 2002) as they provide habitat and resources for invertebrates, *Corresponding author: fmpelicice@gmail.com fish and other organisms (Pelicice et al, 2005;Agostinho et al, 2007a;Gualdoni et al, 2009;Thomaz and Cunha, 2010).…”