Aquatic Plant Diversity Research Articles

Moose Grazing Decreases Aquatic Plant Diversity

ABSTRACT We excluded moose from ten 2×2 meter areas of Feldtmann Lake on Isle Royale, Michigan, USA, in the beginning of the summer and measured total biomass, plant species richness, and plant species diversity in the three exclosures that were still intact at the end of the summer. Plant biomass, species richness, and species diversity all were lower in grazed areas compared to non-grazed exclosures. Thus, herbivory by moose has the potential to significantly affect both standing biomass and species composition of macrophytes in certain aquatic systems.

Area, altitude and aquatic plant diversity

Several explanations have been given for the decline in species richness with altitude. However, separating the influences of altitude, area, and isolation is difficult because of the conical shape of mountains. We used species lists of aquatic plants from >300 lakes in a small geographical area to investigate the influence of altitude on species richness. Altitude and/or surface area were better predictors of species richness than any measure of water chemistry. The surface area and depth of individual lakes were not related to altitude, neither was the degree of isolation from other waterbodies. Although species range size increased with altitude, range sizes of all but the rarer species (in the data set) encompassed the lowest altitudes, indicating species loss rather than turnover and no influence of the Rapoport rescue effect. Nevertheless we found a decline in species richness with altitude, additive to the effect of area. Species were ascribed to attribute groups according to an a priori classification based on morphological and life‐history traits. The number of attribute groups and number of species within each group increased with area, suggesting both increased diversity and coexistence within niches. With altitude, the number of attribute groups declined, but the number of species per group increased, consistent with a loss of richness and reduced competition. The species remaining at high altitudes were characterised by stress tolerant traits, associated with sites of low productivity.Our results suggest an absolute effect of altitude on species richness, irrespective of other influences and consistent with a decline in productivity.

THE EFFECT OF AQUATIC PLANT SPECIES RICHNESS ON WETLAND ECOSYSTEM PROCESSES

Rapid environmental changes have fostered debates and motivated research on how to effectively preserve or restore ecosystem processes. One such debate deals with the effects of biodiversity, and the loss thereof, on ecosystem processes. Recent studies demonstrate that resource-use complementarity, now known as the effect, and the presence of a competitive species with strong effects on ecosystem pro- cesses, now known as the effect, can explain why productivity and nutrient retention are sometimes enhanced with increasing species richness. In a well-replicated outdoor mesocosm experiment, we tested these and other alternative mechanisms that could explain the effects of submersed aquatic plant (macrophyte) diversity on wetland ecosystem processes. Algal biomass increased and phosphorus loss decreased as species richness increased. This result can best be explained by an indirect sampling caused by one of the weakest competitors, which appeared to facilitate algal growth and thereby filtering of particles, and thus phosphorus, from the water column. The dominant competitor also appeared to decrease phosphorus loss through direct effects on phosphorus availability in the soil and water. Thus, the effects by one of the weakest and the most dominant competitors combine to produce a diversity on phosphorus loss. Macrophyte biomass was not enhanced, but converged toward the intermediate biomass of the most competitive species. Such an sampling effect may be produced when the most competitive species is not the most productive species owing to species-specific feedbacks and adaptations to the wetland environment. In summary, we reject the niche-differentiation as the dominant mechanism in our macrophyte communities and expand on the role of sampling effects in explaining the relationship between plant communities and ecosystem processes. In particular, indirect and inverse sampling effects combine to drive the relationship between species richness and wetland ecosystem processes. Thus, we demonstrate that plant diversity may affect wetland ecosystem processes when inferior competitors drive system produc- tivity and nutrient retention. To ensure coexistence of such species with superior compet- itors, wetland systems may need to be maintained in a nonequilibrium state, such as with hydrologic disturbances, which would maintain both higher diversity and enhance ecosys- tem functioning.

Ditch communities: a major contributor to floodplain biodiversity

Abstract Chalk stream floodplains are extensively managed and the high degree of connectivity associated with water meadows has been severely reduced. The main contributor to aquatic biodiversity is perceived to be the river itself. Ditches in these areas have been largely ignored as a contributor to total diversity. Separate surveys of instream, bankside and ditch macroinvertebrates in a small area of floodplain provided a unique opportunity to assess the relative contribution of each locality to total aquatic diversity. The fauna and flora of a ditch on the lower River Frome floodplain was examined and compared with studies of adjacent bankside and instream habitat. A total of 145 macroinvertebrate taxa and 61 plant species were recorded from the ditch. Faunal abundance and richness were positively related to the diversity of aquatic plants. The ditch showed a clear linear trend in community type that appeared to be partly related to the acidic seepage from tertiary deposits at the source and percentage cover of vegetation. There were large differences in the numbers of taxa collected in ditch, bankside, instream mesohabitat and RIVPACS surveys. Of the total 202 taxa recorded in the four surveys, the ditch contributed 59 unique taxa with 25 from the bankside and two and three from the mesohabitat and RIVPACS surveys, respectively. The large contribution of the Rushton Ditch to aquatic biodiversity on the floodplain is due to three main factors: the chemically different and slow‐flowing environment, the connection to the main river, and a management regime which has halted hydroseral succession at a point where vegetation structure is for the most part open and able to support a wide range of ecological niches. The maintenance of these conditions requires sensitive management and further knowledge of the needs and interactions of faunal communities with vegetation. Copyright © 2002 John Wiley & Sons, Ltd.

Effects of macrophyte species richness on wetland ecosystem functioning and services.

Wetlands provide many important ecosystem services to human society, which may depend on how plant diversity influences biomass production and nutrient retention. Vascular aquatic plant diversity may not necessarily enhance wetland ecosystem functioning, however, because competition among these plant species can be strong, often resulting in the local dominance of a single species. Here we have manipulated the species richness of rooted, submerged aquatic plant (macrophyte) communities in experimental wetland mesocosms. We found higher algal and total plant (algal plus macrophyte) biomass, as well as lower loss of total phosphorus, in mesocosms with a greater richness of macrophyte species. Greater plant biomass resulted from a sampling effect; that is, the increased chance in species mixtures that algal production would be facilitated by the presence of a less competitive species-in this case, crisped pondweed. Lower losses of total phosphorus resulted from the greater chance in species mixtures of a high algal biomass and the presence of sago pondweed, which physically filter particulate phosphorus from the water. These indirect and direct effects of macrophyte species richness on algal production, total plant biomass and phosphorus loss suggest that management practices that maintain macrophyte diversity may enhance the functioning and associated services of wetland ecosystems.

Aquatic plant diversity in four river floodplains: a comparison at two hierarchical levels

The present study focuses on the role of environmental factors in plant diversity and community organization at both water-body and river floodplain levels. The cover of each plant species was measured at 841 sampling plots along 63 cut-off channels located in four river floodplains. Environmental variables were documented either at river level (suspended matter, water physico-chemistry, river slope) or at cut- off channel level (channel capacity, slope, substrate grain-size). At both river and cut-off channel levels, increasing slope (i.e. increasing erosion during floods) and decreasing nutrient-content of the water raise species richness and uniqueness (number of species found only in one river), according to hypotheses on the combined role of disturbances and productivity in biodiversity. Rivers that are not eroded during floods are nutrient-rich and present the lowest richness and uniqueness at the river level, but dewatering combined with high connectivity increase richness at the cut-off channel level.

Antagonistic and cumulative effects of connectivity: a predictive model based on aquatic vegetation in riverine wetlands

The effects of connectivity cannot be reduced to a simple gradient. River overflows disturb the vegetation of connected wetlands but, reducing competition, promote plant diversity, Overflows also bring nutrients, silt and plant propagules. Nutrients increase eutrophication and promote phytoplankton development, which reduces water transparency and impedes the growth of rooted plants. Silt inputs accelerate terrestrialization but provide regeneration niches that favour the recruitment of allochthonous propagules. These multiple effects are combined into a model that predicts diversity and life-history traits of aquatic plants (growth form, potential size, phenology and frequency of flowering, vegetative reproduction and defence against herbivores) in relation to the connectivity of the riverine wetlands.

Percentage land use in the watershed determines the water and sediment quality of 22 marshes in the Great Lakes basin

Data from 22 Ontario marshes were used to test the hypothesis that distribution of forested, agricultural, and urban land in the watershed determines the water and sediment quality of Great Lakes wetlands. The first three components of the principal components analysis explained 82% of the overall variation. PC1 ordinated wetlands along a trophic gradient; species richness of submergent vegetation decreased with PC1 scores. PC2 reflected the content of inorganic solids and phosphorus in sediment and the ionic strength of the water. Both PC1 and PC2 scores were positively correlated with percent agricultural land, whereas PC1 scores were negatively correlated with forested land. Correlation between PC1 and agricultural land improved when best-management practices were considered. Accounting for common carp (Cyprinus carpio) disturbance did not confound the relationship between land use and water quality. PC3, driven by soluble reactive phosphorus and nitrate nitrogen concentration in the water, was not correlated with land use. Concentrations of polycyclic aromatic hydrocarbons and Metolachlor were correlated with urban and agricultural land, respectively, and may be useful as land use surrogates. Watershed management favouring the retention of forested land, or creation of buffer strips to trap agricultural runoff in the drainage basin, should help maintain aquatic plant diversity in coastal wetlands.

Aquatic plant diversity in riverine wetlands: the role of connectivity

1. The hypothesis was tested that intermediate connectivity to a river results in propagule inputs to wetlands, whereas excessive connectivity impedes recruitment, and insufficient connectivity causes less competitive species to be eliminated, with no recruitment of new species. As a consequence, very low or very high nutrient levels should decrease species richness by selecting specialized species, whereas intermediate nutrient levels should favour the co‐occurrence of species with contrasting nutrient requirements.2. Among cut‐off channels with high sinuosity and which are infrequently flooded by the river (low flood scouring), one example possesses high species richness because most species are saved from extinction by long‐term isolation of the channel and cold groundwater supplies. Other channels are poorly supplied with groundwater and show a lower richness of species, because of low propagule inputs and low recruitment potential.3. Cut‐off channels with low sinuosity and which are flooded at intermediate frequencies were divided into three groups. The first group was species‐poor, being closely connected to the river through downstream backflows which maintain nutrient‐rich and turbid waters, in keeping with the hypothesis. The second group presents intermediate richness caused by: (i) lower river backflows; and (ii) floods that partly scour substrate and plants, and afford regeneration niches for transported propagules. The third group was species‐poor because of excessive groundwater supplies, which probably acted as a limiting factor for species growth and recruitment.4. The most frequently flooded channel shows the highest species richness, and occurrence of rare and fugitive species, because of floods which compensate competition by scouring sediments and plants, and afford regeneration niches for propagules. In this case, conservation of biodiversity necessitates propagule sources at the level of the river landscape.

Vertical and Horizontal Structure of the Urban Park Ponds as Habitat for Aquatic Plants

The authors investigated the effect of vertical and horizontal pond structure on aquatic plant diversity in nine urban parks in eastern part of Honshu, Japan. The structural parameters that we measured were coverage of each plant species, water depth and bottom material. Water quality parameters such as water temperature, pH, electric conductivity, dissolved oxygen, suspended solid, COD, total nitrogen and total phosphorus were also measured. We performed multivariate correlation analysis to examine the effect of these parameters on the diversity of aquatic plants.The results were as follows:(1) Most of investigated ponds were eutrophicated.(2) The number of emergent plant species was positively correlated with the pond figure index and the size of pond, and negatively correlated with the slope of the bottom near shoreline.Generally, each aquatic plant appeared in a particular set of habitat type expressed as the combination of the water depth and the bottom material. Technical suggestions for constructing and/or managing urban park ponds to make them better as the habitats of aquatic plants are as follows:(1) The figure of the pond should be complex, rather than being simple figures like circle.(2) The size of the pond should be as large as possible.(3) Suitable bottom materials are coarse sand, fine sand, silt and clay. Each material should be used in an appropriate part of the pond.(4) The slope of the bottom near the shore should be less than 10% and should never exceed 15%.

Environmental Assessment by Plant Indicators.

A number of plant indicators have been used in agriculture from early times because the vegetation reflects soil pH, soil moisture, soil fertility, etc. During the decades of 1960s and 1970s Japan has experienced severe environmental degradation such as air, water and soil pollution. Plant indicators, in those days, were considered to be a substitute for the physical and/or chemical measurement. Plant indicators practically used in those days were a visible injury to plants, a combination and/or diversity of epiphytes, aquatic plants and algae, a distribution of heavy metal resistant plants, etc. Environmental pollutants absorbed or adsorbed by plants, e. g., heavy metals, sulfur, fluoride, etc., have been considered as indices of environmental pollution. Dendrochronology was established, in the early years of the twentieth century in the U. S. A., to study past environmental changes. Although some pioneer studies on tree-ring information have been carried out in Japan, since 1920s, most of the early studies were not free from the dating error. In Japan, dendrochronology in the strict sense, was started in 1960s and has been rapidly progressed since 1970s. Besides environmental pollution, past natural disasters such as landslide, typhoon, and flood are also clarified by the dendrochronological studies. Another aspect of plant indicators is focused on future environment. Today, the decreasing biological diversity is recognized as one of the most serious global environmental problems. In this context, plant indicators in these days are not merely a substitute for the physical and/or chemical monitoring system but also the indicator for past environment and the goal of future environment.

Reduction in Diversity of Aquatic Plants in a Spanish Wetland: The Effect of the Size of Inundated Area

ABSTRACT The effect of subsequent decreases in inundated area on the reduction in diversity of aquatic plants in Las Tablas de Daimiel National Park was examined. This Spanish wetland was declared a national park in 1973 in an attempt to protect it from degradation. However, human actions, such as canalization of superficial waters and extraction of subterranean waters, together with the cumulative effects of successive years of low rainfall, resulted in a marked decline in both surface and groundwater resources during the 1980s and 1990s. Diversity of aquatic plants (number of hydrophyte species, genera and families) and size of inundated area (ha) in 1956, 1975 and 1994 were estimated. The power function model S = CAz (or log S = log C+ z log A) was applied to detect a linear relationship between hydrophyte diversity and inundated area. The number of hydrophyte species, genera, and families decreased with decreasing the size of inundated area; the highest values were estimated in 1956 whereas the lowest values were estimated in 1994. This linear relationship implies that a tenfold decrease in inundated area approximately cuts hydrophyte diversity in half.

The Aquatic Macrophyte Community of Onondaga Lake: Field Survey and Plant Growth Bioassays of Lake Sediments

ABSTRACT Onondaga Lake, located in the Syracuse metropolitan area of upstate New York, has been heavily impacted by domestic and industrial waste effluents, resulting in a lake with high salinity, low light availability, and a highly calcareous, nutrient-poor sediment. These factors appear interrelated in reducing the cover, distribution and diversity of aquatic plants between 1940 and 1990. A quantitative survey in 1991 found that only 13% of the littoral zone had any aquatic plants. The plant community was dominated by Potamogeton pectinatus (11%), with four other submersed aquatic plants found: Ceratophyllum demersum, Heteranihera dubia, Myriophyllum spicatum, and Potamogeton crispus. Aquatic plants were found less often than expected on the calcium-carbonate oncolite sediments, which are formed from precipitated calcium carbonate, compared to other sediment types in the lake. Laboratory studies were developed to evaluate the role of sediments in limiting plant growth. These studies showed that Onondag...

Patterns and prediction of α and β diversity of aquatic plants in Adirondack (New York) lakes

Patterns in α diversity (species richness) of submersed and floating-leafed aquatic plants were investigated for 45 lakes in the Adirondack region of northern New York State. Multiple linear regressions were used to build predictive models of species richness; the independent variables included lake surface area, approximate littoral zone area, pH, and measures of isolation and connectedness. The regression models that explained the most variance in species richness incorporated pH, a connectedness predictor, and either lake surface area or littoral zone area (r2 = 0.74). The two area measures accounted for a majority of the variance in species richness (about 57%), but neither was a superior predictor to the other. When acidic lakes were systematically removed from the multiple regression model, r2 tended to increase. The coefficient of determination was maximized (at r2 = 0.822) when we limited the data set to lakes with pH > 5.6. As there was no significant correlation between pH and any of the isolation or connectedness measures we used (maximum r = 0.18), acidic lakes are not more isolated than circumneutral lakes. Point β diversity (the heterogeneity of species composition among sites) was measured for each pair of lakes. It was not strongly correlated to either the difference in surface area or the difference in pH between pairs of lakes. Standardized nestedness was calculated following Wright and Reeves (1992, Oecologia 92 : 416 – 428). Adirondack lakes are moderately nested. An implication of this is that species that are found in less diverse lakes have a 44% probability of being found in more diverse lakes. Key words: Adirondacks, aquatic plant, β diversity, biogeography, lake, nestedness, pH, species richness.

Species diversity in aquatic angiosperms: latitudinal patterns

Preliminary studies of aquatic plants in numerous tropical aquatic habitats in Costa Rica indicate a low level of diversity, and such a level of species richness appears to be in direct conflict with the general viewpoint that tropical ecosystems are exceedingly diverse. Furthermore, there is a strong tendency for dominance of particular plant species within tropical aquatic ecosystems, whereas in tropical forest ecosystems, individuals of a species tend to be scattered rather than to express dominance. A comparison of aquatic plant diversity on a latitudinal basis reveals a higher level of diversity at warm temperature latitudes and a surprisingly high, if not highest, level at cool temperature latitudes. This appears to be true when comparing representative aquatic families as well as aquatic habitats. Standardized data on biodiversity in aquatic ecosystems are needed for further comparative purposes. Additionally, aquatics are poorly known for tropical regions; thus, there is a great need for field work to be conducted in aquatic habitats of the tropics.