Shading by an invasive macrophyte has cascading effects on sediment chemistry (original) (raw)
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Effects of different submersed macrophytes on sediment biogeochemistry
Aquatic Botany, 1997
Porewater phosphate levels in submersed macrophyte grassbeds varied among years in the upper Chesapeake Bay (Maryland, USA) coincident with macrophyte species variation during these same years (1990, 1993, 1995). When native, deep-rooted Vallisneria americana Michx. was a codominant in the grassbed, the porewater phosphate concentrations were significantly lower (P < 0.001) than concentrations when the exotic, shallow-rooted species Hydrilla verticillata (L.f.) Royle and Myriophyllum spicatum L. were codominants. There were significant relationships (P < 0.001) between solid-phase inorganic phosphorus and reactive metals (Fe, Mn) in both native and exotic grassbeds. However, the slopes of the regression relationships between years were significantly different (P < 0.001), suggesting greater retention of inorganic phosphorus in sediments when V. americana was a codominant at the site. In addition, significant relationships between reactive manganese and iron in the sediments were observed, but the coefficient of determination was statistically greater (P <0.001) when V. americana was a codominant at the site. Furthermore, plant cores of V. americana and H. verticillata had noticeably different sediment redox profiles, with the oxidation-reduction status of V. americana sediments being more oxidized in the root zone (i.e., + 125 mV vs -5 mV at 4 cm depth). These data suggest that macrophyte species composition can alter sediment biogeochemistry resulting in varying porewater phosphate and solid-phase phosphorus and metal levels. Possible explanations for these biogeochemical differences may be attributed to morphological differences among macrophyte species (i.e., root/shoot ratio, canopy type, growth form) and differences in root oxygenation capabilities.
Water brownification may increase the invasibility of a submerged non-native macrophyte
Biological Invasions, 2012
Environmental conditions and human activities play a significant role in structuring novel assemblages of native and non-native species. Ongoing and future climatic change may alter the performance of native and non-native species and their biotic interactions. In the northern hemisphere, expected climate changes include warmer temperatures and higher precipitation, the latter of which may increase dissolved organic carbon (humic) concentrations, resulting in browner water in aquatic ecosystems (brownification). We tested the effects of elevated temperature (3°C) and brownification on native and non-native aquatic plant production in mesocosms over 56 days. Elodea canadensis, an aquatic invasive plant, had higher relative growth rate in terms of both length and weight, as well as higher weight to length ratio when grown in brown versus clear water; E. canadensis did not respond to temperature treatments. Different functional groups of native producers (phytoplankton, periphyton, macrophytes) showed different relationships to temperature and brownification treatments, with the macrophyte response being most notable because it was opposite to that of E. canadensis. Native macrophytes decreased in biomass in browner water, where they represented about 40 % of total biomass compared to 85 % in clear water. In regression analyses, E. canadensis length RGR was best predicted only by water color treatment, but biomass RGR and biomass per length were inversely correlated with native macrophyte biomass, which is consistent with competition. Our results unexpectedly showed water brownification to have more influence on lake invasion than climate warming at this temperature regime. Two pathways emerged for climate to interact with biological invasions in structuring novel communities: directly, if non-native species respond positively to climate change, and indirectly through species interactions, for instance, because water brownification impairs growth of native macrophytes and reduces biotic resistance to invasion.
Hydrobiologia, 2011
Redox potential is a significant factor in aquatic systems to regulate the availability of nutrients and some metals. To assess the driving variables regulating redox potential, background parameters (dissolved oxygen, pH, temperature, chlorophyll-a, soluble reactive and total phosphorus content of water, coverage and height of submerged macrophytes) and redox potential profiles around the sediment-water interface (SWI) were measured in simulated shallow lake ecosystems. There were two nutrient regimes (enriched and non-enriched) and three temperature scenarios (unheated; ?3.5°C; ?5°C) installed in the experimental setups, which were constructed to study the effects of global climate change. Temperature did not have any detectable effect on redox potentials, and we presume that nutrient addition had only indirect positive effects through triggering phytoplankton dominance which causes macrophyte absence. When submerged macrophytes were present in high density (80-100% coverage), redox potentials at the SWI varied between 60-215 mV and the mean redox potential was 133 ± 34 mV (mean ± 1 SD). In contrast to this, when phytoplankton dominance was coupled to low macrophyte density (0-20% coverage), the range of redox potentials at the SWI was 160-290 mV and the mean redox potential was 218 ± 34 mV. The results revealed the primary importance of submersed macrophytes; macrophyte coverage determined alone the redox potential of the sediment-water interface by 81%. This study suggests that possible positive effects of macrophytes on redox potential can be suppressed by their negative effects in case of 80-100% coverage and total inhabitation of the water column.
Can allelopathically active submerged macrophytes stabilise clear-water states in shallow lakes?
Basic and Applied Ecology, 2008
Inhibition of phytoplankton by allelochemicals released by submerged macrophytes is supposed to be one of the mechanisms that contribute to the stabilisation of clear-water states in shallow lakes. The relevance of this process at ecosystem level, however, is debated because in situ evidence is difficult to achieve. Our literature review indicates that allelopathically active species such as Myriophyllum, Ceratophyllum, Elodea and Najas or certain charophytes are among the most frequent submerged macrophytes in temperate shallow lakes. The most common experimental approach for allelopathic interference between macrophytes and phytoplankton has been the use of plant extracts or purified plant compounds. Final evidence, however, requires combination with more realistic in situ experiments. Such investigations have successfully been performed with selected species. In situ allelopathic activity is also influenced by the fact that phytoplankton species exhibit differential sensitivity against allelochemicals both between and within major taxonomic groups such as diatoms, cyanobacteria and chlorophytes. In general, epiphytic species apparently are less sensitive towards allelochemicals than phytoplankton despite living closely attached to the plants and being of key importance for macrophyte growth due to their shading. Light and nutrient availability potentially influence the sensitivity of target algae and cyanobacteria. Whether or not additional stressors such as nutrient limitation enhance or dampen allelopathic interactions still has to be clarified. We strongly propose allelopathy as an important mechanism in the interaction between submerged macrophytes and phytoplankton in shallow lakes based on the frequent occurrence of active species and the knowledge of potential target species. The role of allelopathy interfering with epiphyton development is less well understood. Including further levels of complexity, such as nutrient interference, grazing and climate, will extend this ecosystem-based view of in situ allelopathy. Zusammenfassung Die Inhibition von Phytoplankton durch Allelochemikalien aus submersen Makrophyten ist einer der potentiellen Mechanismen, die zur Stabilisierung von Klarwasserzusta¨nden in Makrophyten-dominierten Flachseen beitragen. Die Relevanz dieses Prozesses auf Ö kosystemebene ist jedoch umstritten, da der in situ Nachweis schwierig ist. Unsere Literaturu¨bersicht zeigt, dass allelopathisch aktive Arten wie Myriophyllum, Ceratophyllum, Elodea und Najas sowie bestimmte Characeen zu den ha¨ufigsten submersen Makrophyten in Flachseen der gema¨ßigten Breiten geho¨ren. Der experimentelle Nachweis allelopathischer Effekte auf Phytoplankton erfolgte bisher u¨berwiegend durch Pflanzenextrakte oder aufgereinigte Substanzen. Ein endgu¨ltiger Beweis erfordert jedoch zusa¨tzlich Experimente unter in situ Bedingungen,
Role of Macrophytes in a sewage fed urban lake
Institute of Integrative Omics and Applied Biotechnology, 2011
Corresponding author: Email: cestvr@ces.iisc.ernet.in; http://ces.iisc.ernet.in/energy ; Tel: +91-080-22933099; Fax: 23601428
Basic and Applied Ecology, 2008
Inhibition of phytoplankton by allelochemicals released by submerged macrophytes is supposed to be one of the mechanisms that contribute to the stabilisation of clear-water states in shallow lakes. The relevance of this process at ecosystem level, however, is debated because in situ evidence is difficult to achieve. Our literature review indicates that allelopathically active species such as Myriophyllum, Ceratophyllum, Elodea and Najas or certain charophytes are among the most frequent submerged macrophytes in temperate shallow lakes. The most common experimental approach for allelopathic interference between macrophytes and phytoplankton has been the use of plant extracts or purified plant compounds. Final evidence, however, requires combination with more realistic in situ experiments. Such investigations have successfully been performed with selected species. In situ allelopathic activity is also influenced by the fact that phytoplankton species exhibit differential sensitivity against allelochemicals both between and within major taxonomic groups such as diatoms, cyanobacteria and chlorophytes. In general, epiphytic species apparently are less sensitive towards allelochemicals than phytoplankton despite living closely attached to the plants and being of key importance for macrophyte growth due to their shading. Light and nutrient availability potentially influence the sensitivity of target algae and cyanobacteria. Whether or not additional stressors such as nutrient limitation enhance or dampen allelopathic interactions still has to be clarified. We strongly propose allelopathy as an important mechanism in the interaction between submerged macrophytes and phytoplankton in shallow lakes based on the frequent occurrence of active species and the knowledge of potential target species. The role of allelopathy interfering with epiphyton development is less well understood. Including further levels of complexity, such as nutrient interference, grazing and climate, will extend this ecosystem-based view of in situ allelopathy. Zusammenfassung Die Inhibition von Phytoplankton durch Allelochemikalien aus submersen Makrophyten ist einer der potentiellen Mechanismen, die zur Stabilisierung von Klarwasserzusta¨nden in Makrophyten-dominierten Flachseen beitragen. Die Relevanz dieses Prozesses auf Ö kosystemebene ist jedoch umstritten, da der in situ Nachweis schwierig ist. Unsere Literaturu¨bersicht zeigt, dass allelopathisch aktive Arten wie Myriophyllum, Ceratophyllum, Elodea und Najas sowie bestimmte Characeen zu den ha¨ufigsten submersen Makrophyten in Flachseen der gema¨ßigten Breiten geho¨ren. Der experimentelle Nachweis allelopathischer Effekte auf Phytoplankton erfolgte bisher u¨berwiegend durch Pflanzenextrakte oder aufgereinigte Substanzen. Ein endgu¨ltiger Beweis erfordert jedoch zusa¨tzlich Experimente unter in situ Bedingungen,