Ranunculus peltatus

Abstract: 1. Submerged macrophytes have important physical and structural effects on lowland streams. This study investigated the ability of submerged macrophytes to modify the near-bed flow and to retain mineral and organic particles in patches of four common macrophytes in shallow Danish streams during mid-summer. 2. In dense patches of Callitriche cophocarpa and Elodea canadensis, where near-bed velocity was reduced, the sediment surface was markedly raised and enriched with fine particles. In dense patches of Ranunculus peltatus, fine sediments were deposited among rooted shoots in the upstream part of the patches, while erosion and coarse sediments prevailed in the downstream part of the patches because of the strong vortices that formed at the rear and moved up under the trailing canopy. The open canopy of Sparganium emersum, with its streamlined leaves, had little effect on flow and sediment. 3. Patterns of sediment deposition and composition were closely related to the morphology and canopy structure of plant species and the presence of low velocity above the sediment among the rooted shoots. The mineral particles retained probably originate from bed-load, and the enrichment with finer particles within the patches probably results mainly from size-selective processes during erosion and transport of particles rather than during deposition. The mixed sediment composition within patches suggests that the flow-resistant shoots generate an environment conducive to deposition of all transported particles. 4. Fine sediments within macrophyte beds contained high concentrations of organic matter, carbon, nitrogen and phosphorus. The wide scatter in the relationships between mineral grain size and the content of organic matter and nutrients reflects the spatial and temporal complexity of erosion, transport and sedimentation of mineral and organic particles. 5. Enrichment of sediment within macrophyte beds relative to the surrounding substratum ranged from 780 g organic matter m–2, 30 g N m–2 and 25 g P m–2 for the flow-resistant dense canopies af Callitriche cophocarpa to 150 g organic matter m–2, 6.6 g N m–2 and 3.4 g P m–2 for the open canopies of Sparganium emersum. Retention of nutrient-rich particles within the macrophyte beds is probably of limited importance for plant growth in most lowland European streams, because macrophyte growth is rarely nutrient limited.

Abstract: During the last decades a strong decline has been noticed in the number of waters dominated by “Littorellion” species, mostly isoetids such as Lobelia dortmanna L., Isoetes lacustris L. and Littorella uniflora (L.) Aschers. Sixty-eight waters, which were known to be dominated by L. uniflora after 1950 were investigated. In 1980, L. uniflora appeared to be absent or to have strongly decreased in 53 (78%) of the waters. In 41 of them, Littorella had been replaced by submerged Juncus bulbosus L. and/or Sphagnum spp. These changes seem to have been caused by changed inorganic carbon budgets as a consequence of acidification. In the remaining 12 waters, eutrophication of the water and/or sediment seems to be responsible for the changes in the plant communities. Enrichment with phosphate of the mineral sediment alone, leads to luxurious growth of submerged, rooted macrophyte species such as Myriophyllum alterniflorum DC and Ranunculus peltatus Schrank, whereas phosphate-enrichment of both sediment and water leads to luxurious growth of pleustophytes such as Riccia fluitans L. and Lemna minor L. in small, shallow waters, and to plankton bloom and luxurious growth of epiphytes in larger, deeper waters. In these cases light limitation seems to be responsible for the disappearance or decline of the “Littorellion” species.

Abstract: Summary 1. Streams are subject to frequent natural and anthropogenic disturbances that cause sediment erosion and loss of submerged vegetation. This loss makes downstream transport and retention of vegetative propagules on the streambed very important for re-establishing vegetation cover. We measured dispersal and retention of macrophyte stem fragments (15–20 cm long) along 300 m long reaches of four small to medium sized Danish lowland streams. 2. The number of drifting stem fragments declined exponentially with distance below the point of release. This finding makes the retention coefficient (k, m−1) in the exponential equation a suitable measure for comparisons among different macrophyte species, and between stream reaches of different hydrology and vegetation cover. 3. Buoyancy of macrophyte tissue influenced retention. Elodea canadensis stems drifted below the water surface, and were more inclined to be retained in deeper water associated with submerged plants and obstacles in the streambed. Ranunculus peltatus stems were more buoyant, drifted at the water surface, and were more inclined to be trapped in shallow water and in riparian vegetation. 4. The retention coefficient of drifting stems increased with the relative contact between the flowing water and streambed, bank and vegetation. Thus, the retention coefficients were highest (0.02–0.12 m−1) in shallow reaches with a narrow, vegetation-free flow channel. Here there were no significant differences between E. canadensis and R. peltatus. Retention coefficients were lowest (0.0005–0.0135 m−1) in deeper reaches with wider vegetation-free flow channels. Retention of E. canadensis was up to 16 times more likely than retention of R. peltatus. 5. Overall, the longitudinal position in the stream system of source populations of species capable of producing numerous stems, the species-specific retention coefficients of stems, and the retention capacity of stream reaches should be important for species distribution in perturbed stream systems. Retention of stems is probably constrained in headwaters by the small downstream flux of stem fragments because of the restricted source area, and constrained in downstream reaches by small retention coefficients. Macrophyte retention may, consequently, peak in medium-sized streams.

Abstract: This work focuses on the potential of aquatic plants for bioindication and/or phytofiltration of arsenic from contaminated water. More than 71 species of aquatic plants were collected at 200 sampling points in running waters. The results for the 18 most representative plant species are presented here. The species Ranunculus trichophyllus, Ranunculus peltatus subsp. saniculifolius, Lemna minor, Azolla caroliniana and the leaves of Juncus effusus showed a very highly significant (P<0.001) positive correlation with the presence of arsenic in the water. These species may serve as arsenic indicators. The highest concentration of arsenic was found in Callitriche lusitanica (2346 mg/kg DW), Callitriche brutia (523 mg/kg DW), L. minor (430 mg/kg DW), A. caroliniana (397 mg/kg DW), R. trichophyllus (354 mg/kg DW), Callitriche stagnalis (354 mg/kg DW) and Fontinalis antipyretica (346 mg/kg DW). These results indicate the potential application of these species for phytofiltration of arsenic through constructed treatment wetlands or introduction of these plant species into natural water bodies.

Abstract: SUMMARY. The growth and recession of the macrophytes on an unshaded section of the R. Lambourn was documented by a mapping procedure from March 1971 to December 1976. The seasonal patterns were determined mainly by the dominant macrophytes. Ranunculus penicillatus var. calcareus and Ranunculus peltatus. Ranunculus grew rapidly in spring and early summer, mainly colonizing areas of gravel and reached a summer maximum. The greatest loss of plants was in August and September but losses continued through the winter to give minimum cover in March. Berula and Callitriche did not show regular seasonal growth patterns but their growth was largely confined to times when there was little growth of Ranunculus. Increase in area of Ranunculus in the spring was positively correlated with the mean discharge at that time. The growth of Ranunculus appeared to be restricted when shading was caused by turbid water due to dredging or by accumulation of epiphytic algae on the surface of the plants in years when discharge was low. Discharge also influenced the substrata underlying Ranunculus and the area of silt under Ranunculus beds was negatively correlated with discharge. The factors thought to influence growth of Ranunculus were used to develop a conceptual model of growth.