Changes In Macrophyte Communities Research Articles

Ecological sensitivity of marl lakes to nutrient enrichment: evidence from Hawes Water, UK

Summary Highly calcareous (marl) lakes are infrequent but important freshwater ecosystems, protected under the EU Habitats and Species Directive. Chara lakes have been considered resistant to eutrophication owing to the self‐stabilising properties of charophyte meadows. However, the opposite is suggested by the large‐scale biodiversity declines in marl lake taxa in Europe, and evidence of charophyte sensitivity to eutrophication. We combined contemporary, palaeolimnological and archival methods to investigate the eutrophication of Hawes Water, a shallow marl lake in north‐west England (U.K.). Changes in aquatic macrophyte and invertebrate communities were reconstructed through the analysis of historical macrophyte surveys and sedimentary plant and animal macrofossils in two dated sediment cores from the littoral and deep zones of the lake. In addition, chlorophyll and carotenoid pigments were analysed to track changes in primary production from benthic and pelagic areas. Substantial changes in macrophyte communities were detected over centennial timescales, suggesting high ecosystem sensitivity considering the presently moderate phosphorus concentrations in Hawes Water (mean annual total phosphorus 20 μg L−1). Two apparent periods of threshold‐like change were identified from the sediment record: (i) changes in cyanobacteria (aphanizophyll + myxoxanthophyll to canthaxanthin + zeaxanthin) and potentially in nutrient stoichiometry, reductions in the maximum macrophyte colonisation depth and water clarity, reduced charophyte and Potamogeton diversity, and increases in Nymphaeaceae; and (ii) severe reductions in light availability inferred from subdecadal doubling in phytoplankton abundance, substantial increases in Daphnia abundance and the extinction of charophytes from higher water depths. Further, change in both the littoral and deeper water has confined key marl lake taxa to smaller niches. In the littoral, increasing siltation and reed and Nymphaeaceae densities caused extinction of Littorella uniflora in the early 1900s and have reduced the evenness of Characeae with suspected imminent extinction of two highly localised Chara spp. In the deeper water, upslope creep of maximum colonisation depth has reduced habitat for intermediate‐depth marl lake taxa leading to the loss of four Potamogeton and one Chara species, and replacement of these taxa by Nuphar lutea. The large changes in macrophyte community composition and increased incidences of turbid water have reduced the distinctive and valued marl lake features of Hawes Water, indicating that marl lakes can, as a habitat type, be highly sensitive to eutrophication. The persistence of abundant generalist macrophyte species at considerable water depth may be a feature of high‐alkalinity lakes in clearwater, macrophyte‐dominated states, but is a distinct eutrophication response in marl lakes rather than an indication of resistance to eutrophication.

Periphytic algal community structure in relation to seasonal variation and macrophyte richness in a shallow tropical reservoir

The macrophyte structure can influence the development of periphytic algal community in a shallow ecosystem. We investigated the interrelationship between periphytic algal community on artificial substrate and macrophyte species richness during four seasons in a tropical shallow reservoir. The periphyton was evaluated by biomass (as AFDM), algal abundance, species composition, and species richness. Limnological variables and macrophyte coverage were determined at sites with different macrophytes richness in littoral zone. Glass slides were used as the substrate and colonization time was 30 days. Periphytic algal structure was significantly influenced by seasonality and macrophyte richness, as well as the interaction of two factors. Periphytic algal density on natural and artificial substrates was negatively correlated with macrophyte richness and coverage. High biomass, algal biovolume and dominance of Zygnemaphyceae occurred when there was an increase of Utricularia foliosa coverage (summer). Our results showed that the seasonality, and to a lesser extent macrophyte species richness, explained significant portion of the variability of periphyton biomass, algal abundance, and taxonomic composition on artificial substrate. The changes in macrophyte community may have direct consequences on the periphyton structure in a shallow tropical reservoir.

Changes in macrophyte communities in Lake Swarzędzkie after the first year of restoration

Abstract Lake Swarzędzkie, near Poznań, was a hypertrophic lake because of its high nutrient content, cyanobacteria blooms, and disruptive recreational use, especially swimming, which was popular there. This is why protection measures have been in place since 1991, and a restoration program has been ongoing since fall 2011. The evaluation of the presence and distribution of macrophytes as an important element of lake ecosystem was conducted in August 2012. Nine plant communities were observed: Phragmitetum communis; Typhetum angustifoliae; Nupharo-Nymphaeetum albae; Hydrocharitetum morsus-ranae; Thelypteridi-Phragmitetum; Cicuto-Caricetum pseudocyperi; Acoretum calami; Ceratophylletum demersi; Potametum lucentis. The first three were dominating associations. The presence of submerged vegetation appears to verify the positive impact of the applied conservation and restoration measures. Improvement is confirmed by the significant decrease in concentrations of chlorophyll-a and total nitrogen, as well as the gradual decrease in total suspended solids and increased transparency.

Changes in aquatic macrophyte communities in Loch Leven: evidence of recovery from eutrophication?

This article assesses changes in the macrophyte community of Loch Leven over a period of 100 years. Evidence is presented that shows that these changes are associated with eutrophication and with subsequent recovery from eutrophication when anthropogenic nutrient inputs to the loch were reduced. This study uses macrophyte survey data from 1905, 1966, 1972, 1975, 1986, 1993, 1999 and 2008. In each of the four most modern surveys, the loch was divided into 19 sectors, each with at least one transect ranging from the shallowest to the deepest occurrence of macrophytes. From these data, a range of indicators of recovery were derived at the whole lake scale: the relative abundance of taxa, taxon richness and evenness. All of these metrics showed an improvement since 1972. Species richness, measured at the scales of survey sector and individual samples, also appeared to have increased in recent years. All of these measures, coupled with ordination of the presence/absence composition data from all survey years, indicate that the macrophyte community in the loch is recovering towards the state that was recorded in 1905.

Historical changes in the macrophyte community of a Norwegian softwater lake

Changes in macrophyte communities have occurred over the past decades in many oligotrophic softwater lakes with low carbon availability. Slow-growing isoetid species have been replaced by faster-growing elodeid species. Commonly, these changes are explained by anthropogenic nutrient enrichment or acidification of the lake water. Here we present a multi-proxy study in which we analysed plant macrofossils, pollen and spores, as well as sedimentological data from several cores taken from a SW Norwegian softwater lake. Our results indicate that the elodeid macrophyte Callitriche hamulata first appeared in this lake in the 1970s. Proliferation of C. hamulata occurred in the 1990s, replacing the hitherto dominant submerged Isoëtes macrophyte vegetation. Independent lines of evidence, such as diatom-inferred TP and pH reconstructions, showed no change during the past 200 years, therefore ruling out both acidification and phosphorus enrichment of the lake as possible causes for the observed change in the macrophyte community. Alternatively, expansion of Callitriche at the expense of Isoëtes may have been related to increased aquatic carbon availability, although nitrogen enrichment may also have been important.

Submerged macrophytes as indicators of the ecological quality of lakes

Summary1. We analysed submerged macrophyte communities from 300 Danish lakes to determine the efficacy of different species, maximum colonisation depth (Cmax) of plants as well as coverage and plant volume inhabited (PVI) as indicators of eutrophication.2. Most species occurred at a wide range of phosphorus and chlorophyll a (Chla) concentrations, but some species of isoetids (Lobelia, Isoëtes) and Potamogeton (Potamogeton gramineus, Potamogeton alpinus and Potamogeton filiformis) were mainly found at low nutrient concentrations and hence may be considered as indicators of nutrient poor conditions. However, species typically found in nutrient‐rich conditions, such as Elodea canadensis and Potamogeton pectinatus, were also found at total phosphorus (TP) <0.02 mg P L−1 and Chla <5 μg L−1 and therefore cannot be considered as reliable indicators of eutrophic conditions.3. Submerged macrophyte coverage, PVI and the Cmax were negatively correlated with TP and Chla. However, variability among lakes was high and no clear thresholds were observed. At TP between 0.03 and 0.07 mg P L−1 plant coverage in shallow lakes ranged from nearly 0 to 100%, whilst at concentrations between 0.10 and 0.20 mg P L−1 only 29% of the lakes had coverage >10%. Cmax was found to be a useful indicator only in deep lakes with unvegetated areas in the deeper part, whereas the use of coverage was restricted to shallow lakes or shallow areas of deep lakes.4. Overall, submerged macrophytes responded clearly to eutrophication, but the metrics investigated here showed no well‐defined thresholds. We developed a simple index based on species richness, presence of indicator species, coverage and Cmax, which might be used to track major changes in macrophyte communities and for lake classification.

Influence of disturbance on habitats and biological communities in lowland streams

We studied 68 small lowland streams in Denmark of which the majority were affected by physical and chemical stress or a combination of both. Using DCA analyses, we analysed macrophyte and macroinvertebrate communities along a combined disturbance gradient. Both macrophytes and macroinvertebrate communities responded to the combined pressure gradient. We used a rigorous classification of the 68 sites, into 5 disturbance groups, with respect to physical and chemical disturbance and studied the effects of disturbance on physical habitat structure and density and diversity of macrophytes, macroinvertebrates and fish. Physical habitat structure in the disturbed streams was similar, except for variations in width which was lowest, and coverage of mud, which was highest in heavily disturbed streams. Macrophyte communities were impacted by disturbance. Average species richness and diversity were significantly lower in disturbed streams (8.6 and 2.8) than in relatively undisturbed streams (15.3 and 5.6). The total number of Ephemeroptera, Plecoptera and Trichoptera taxa (EPT) was significantly lower in disturbed streams (4.1) compared to streams experiencing intermediate disturbance (6.0-7.6) and undisturbed streams (7.0). Taxa associated with stable substrata, such as Leuctra sp. and Baetis sp., were reduced in abundance by approximately 50% on disturbed sites. Density of trout (Salmo trutta L.) was markedly lower in disturbed streams (14 per 100 m 2 ) than in undisturbed streams (55-204 per 100 m 2 ). The results indicate that disturbance cascades through the stream ecosystem, primarily meditated by changes in macrophyte communities that are essential providers of habitat in unshaded lowland streams in which other structural elements, as coarse inorganic substrates and woody debris, are scarce. The analyses also show that the community variable responses to the combined stressors are not linear, which is an important issue implementing the ecological classification in the Water Framework Directive.