Invasive Macrophyte Research Articles

Pervasive changes to the lower aquatic food web following Nitellopsis obtusa establishment in a large, shallow lake

Abstract Nitellopsis obtusa was first reported in North America in 1974. The overall ecological threat that N. obtusa poses towards freshwater ecosystems in its non‐native range is thought to be similar to other invasive macrophyte species. However, few studies have evaluated the impacts to aquatic communities upon successful establishment of this species in North America. Despite N. obtusa being a non‐native invasive species in North America, it is considered a beneficial macrophyte within its native range in Eurasia We evaluated the impacts associated with the non‐native invasive charophyte N. obtusa on the lower aquatic food web (LAFW) communities (phytoplankton, macroinvertebrates, and macrophytes) in a large, shallow lake in Ontario, Canada. To tease apart abiotic and biotic factors that influence LAFW species assemblages, a generalised linear latent variable model (GLLVM) was used. Over the course of the 4‐year study period, N. obtusa abundance significantly increased throughout the lake (pairwise comparison, p < 0.001) and notable shifts in community composition occurred across years (PERMANOVA, p < 0.001), especially for the phytoplankton and macrophyte communities. Nitellopsis obtusa was also found to be associated with a decline in diversity, where Simpson's diversity indices across all LAFW communities decreased as a function of increasing N. obtusa biomass. The GLLVM analysis revealed significant negative associations between N. obtusa and the majority of LAFW taxa. Most notably, there was a significant (p < 0.001) negative relationship between Myriophyllum spicatum, a previously established non‐native invasive macrophyte, and N. obtusa. The GLLVM model also demonstrated that N. obtusa had positive co‐occurrence relationships with other members of the macrophyte community including Utricularia vulgaris, Najas flexilis, Potamogeton crispus, and Stuckenia pectinata. These results show for the first‐time significant impacts to the LAFW in an invaded ecosystem, which raises major concerns for fish communities that depend on the LAFW for food and habitat. Further studies are necessary to confirm the extent of these impacts in other invaded lakes.

The success of an invasive Poaceae explained by drought resilience but not by higher competitive ability

Invasions are occurring very rapidly and they may be enhanced by alterations associated with climate change. Environments exposed to stronger droughts (supposed to occur in some regions in response to climate change) may become more susceptible to the invasion of certain species of plants. We experimentally measured the recovery of a native (Hymenachne pernambucensis) and a non-native invasive (Urochloa arrecta) macrophyte to extreme drought, and we evaluated whether the interspecific competition is affected by the drought stress or not. We found that the invasive species recovered biomass from drought more efficiently than the native species when they grew in monocultures. In contrast, the data of aboveground biomass showed that the invasive species was more negatively affected by interspecific competition than the native one. These results indicate that the invasive species is more resilient to droughts than the native, but the native species has a greater competitive ability than the invasive. Thus, the high dominance of U. arrecta observed in several aquatic ecosystems can be explained by its resilience to drought disturbances. Our findings also demonstrate the importance of biotic resistance since the invasive species does not grow well in the presence of native neighbors.

Divergent effects of invasive macrophytes on population dynamics of a snail intermediate host of Schistosoma Mansoni

Vectors and intermediate hosts of globally impactful human parasites are sensitive to changes in the ecological communities in which they are embedded. Sites of endemic transmission of human schistosome can also be invaded by nonnative species, especially aquatic plants (macrophytes). We tested the effects on macrophyte invasions on experiment snail and schistosome populations created in 100 L mesocosm tanks. We established macrophyte-free mesocosms and those containing one of four widespread macrophyte species that are inedible to snails (duckweed, hornwort, water lettuce, or water hyacinth) and then tracked edible resources (periphyton algae) and the abundance, reproduction, and infection of snail intermediate hosts for 16 weeks. We predicted that the three floating macrophytes would reduce periphyton, thereby reducing snail reproduction, abundance, and infections. In contrast, we predicted that hornwort, which is submerged and provides substrate for periphyton growth, would increase snail reproduction and abundance. As predicted, all floating macrophytes decreased periphyton, but only water hyacinth significantly decreased snail reproduction and abundance. Snail abundance increased significantly only with water lettuce. We hypothesize that this unanticipated increase in snails occurred because water lettuce produced abundant and/or high quality detritus, subsidizing snails despite low periphyton availability. Unfortunately, we detected too few infections to analyze. Aquatic macrophytes exert strong species-specific effects on snail populations. Therefore, efforts to manage invasive plants in endemic sites should evaluate changes in resources, snails, and transmission potential. We recommend caution with management efforts that produce large amounts of detritus, which might stimulate snail populations and therefore risk of human exposure.

Fish grazing enhanced by nutrient enrichment may limit invasive seagrass expansion

The success of invasive macrophytes can depend on local nutrient availability and consumer pressure, which may interact. We therefore experimentally investigated the interacting effects of nutrient (nitrogen and phosphorus) addition, the exclusion of large herbivorous fishes and mimicked grazing on the expansion rates of the invasive seagrass Halophila stipulacea. The experiments were established on Bonaire and Aruba, two islands in the southern Caribbean, which differ in fish community structure. We observed that multiple Caribbean fish species feed on H. stipulacea. At both study sites, nutrient enrichment decreased invasive leaf carbon:nitrogen ratios. However only on Bonaire, where herbivore fish abundance was 7 times higher and diversity was 4.5 times higher, did nutrient enrichment result in a significant reduction of H. stipulacea expansion into native Thalassia testudinum meadows. This effect was likely due to increased herbivory on nutrient enriched seagrass leaves, as we found that excluding large herbivorous fish (e.g. parrotfish) doubled invasive expansion rates in bare patches on Bonaire. On Aruba, H. stipulacea expansion rates were higher overall, which coincided with lower abundances and diversity of native fishes, and were limited by mimicked fish grazing. We suggest that top-down control by the native fish community may counteract eutrophication effects by increased grazing pressure on nutrient-rich invasive seagrass leaves. We conclude that diverse and abundant herbivore communities likely play an important role in limiting invasion success and their conservation and restoration may serve as a tool to slow down seagrass invasions.

Invasive Nitellopsis obtusa (starry stonewort) has distinct late-season phenology compared to native and other invasive macrophytes in Minnesota, USA

Understanding the phenology of the invasive macroalga Nitellopsis obtusa (starry stonewort) is critical for evaluating and predicting its impacts on native macrophytes and timing control efforts. We tracked N. obtusa phenology in two Minnesota (USA) lakes from 2017 to 2018. We measured N. obtusa biomass and counted bulbils (asexual reproductive structures) throughout the growing season and in winter, under ice. Additionally, we compared phenology of N. obtusa to other invasive and native macrophytes using a long-term, Minnesota statewide dataset. We found consistent late-season peaks in N. obtusa biomass in both lakes, and this extended growth distinguished it from common native and invasive macrophytes in the region. Phenological asynchrony of N. obtusa relative to native macrophytes indicates use of a distinct temporal niche that may contribute to its invasion success. Bulbil counts were lowest early to mid-summer and increased through fall; however, high variability in this relationship warrants more intensive sampling to clarify seasonal trends. Late-season growth of N. obtusa poses challenges for timing control efforts, as early-season treatments may be limited to avoid harming native species. Treatment during peak biomass, before peak bulbil abundance, may improve control.

Using a DNA barcoding approach to facilitate biosecurity: Identifying invasive alien macrophytes traded within the South African aquarium and pond plant industry

South Africa's water bodies have been invaded multiple times by various alien macrophytes in the last 200 years and this trend is set to continue – posing a significant threat to the already fragile indigenous aquatic ecosystems and the services they provide. The aquarium and ornamental pond plant industry has been found to serve as a primary pathway for the continued introduction of high-risk taxa. Although regulations like the National Environmental Management: Biodiversity Act (NEM:BA) 10 of 2004 together with some national programmes are currently in place to ensure compliance by the different industry role players, adequate enforcement is hampered by challenges inherent to definitive species identification. In this study, the utility of a DNA barcoding approach to aid in addressing these issues was assessed. An extensive macrophyte core barcode (matK and rbcLa) reference library was compiled and tested to: (i) establish if a “barcode gap” was present, ii) determine the optimised threshold for species delimitation and (iii) assess identification efficiency using different distance based metrices. This reference library was subsequently used to identify plants collected during a survey of ten macrophyte retailer shops in and around the Johannesburg metropolitan area for which DNA barcodes could be generated. Results obtained indicate the presence of considerable interspecific and curbed intraspecific distance between the marker combinations tested and demonstrate high species identification rates. Additionally, multiple alien aquatic plants currently in trade under the following NEM:BA categories were recovered: 1a (invasive species), 1b (invasive species controlled by program) and species prohibited in terms of section 67(1). A surprisingly large number of first-time invasive alien macrophytes not currently on the NEM:BA lists were also identified. The dataset and findings presented in this study have important implications for informing pre-emptive invasive macrophyte management in South Africa e.g. tracking the country's commitments towards achieving the Convention on Biological Diversity's (CBD) Aichi Biodiversity Target 9 (as well as its inheritor post-2020) and providing recommendations for updates to the NEM:BA alien and invasive species lists. The library also presents opportunities for exploring the utility of spin-off applications that rely on robust molecular datasets (e.g. eDNA monitoring).

Low Benthic Oxygen and High Internal Phosphorus-Loading are Strongly Associated With the Invasive Macrophyte Nitellopsis obtusa (starry stonewort) in a Large, Polymictic Lake

Lake Scugog is an important headwater to the Trent Severn-Waterway in Ontario, Canada. In recent years, notable ecosystem-level changes have occurred coinciding with the emergence of the non-native invasive charophyte Nitellopsis obtusa. Despite N. obtusa arriving in North America in the early 1970s, studies documenting the impact of N. obtusa on invaded ecosystems are scarce. Given the increasing dominance of N. obtusa in inland waters of the Great Lakes basin, we investigated the ecosystem-level impacts of N. obtusa in Lake Scugog over a 3-year period. We show for the first time a strong association between N. obtusa occurrence and biomass with benthic anoxia in this shallow, polymictic lake. Benthic dissolved oxygen concentrations were significantly lower (p-value < 0.001) at sites with N. obtusa compared to sites without N. obtusa. Additionally, N. obtusa biomass was a negative predictor of near-bed oxygen concentration (R2 = 0.59, p-value < 0.001). Knowing that anoxia can promote the internal loading of phosphorus, we measured soluble reactive phosphorus (SRP) in the pore-water of sediments at each site, and found N. obtusa biomass explained 90% of sediment pore-water SRP (R2 = 0.90, p-value < 0.001). These notable associations between N. obtusa and key lake elements indicates that N. obtusa may be acting as an ecosystem engineer in invaded lakes by altering the biogeochemical fate of oxygen and phosphorus.

The success of the invasive macrophyte Hydrilla verticillata and its interactions with the native Egeria najas in response to environmental factors and plant abundance in a subtropical reservoir

The invasion success of non-native species depends on a variety of factors, and abiotic characteristics of invasive ranges and their native populations can offer resistance to non-native species establishment. Reservoirs, compared to natural lakes, can facilitate submerged macrophyte invasion because they provide favorable abiotic conditions to macrophyte establishment and development. However, previous colonization of native species can hamper the development of invasive ones through priority effects. In this investigation we used large data-set obtained in the Itaipu Reservoir (Brazil/Paraguay) to assess the relationship between the abundance of the native submerged macrophyte Egeria najas and of the invasive Hydrilla verticillata and water level, littoral slope and Secchi disk depth. We also investigated how the concomitant and previous abundance of both macrophytes correlates. A Bayesian modeling was applied, controlling the effect of spatial-temporal autocorrelation. Our results indicate an important role of water transparency, littoral slope and water level oscillations in a short period of time (30 days) for the temporal dynamics of these species’ abundances. Fluctuations of water levels and littoral slope affected H. verticillata to a greater extent than E. najas. In addition, the abundance of each species was related with its own abundance in previous samplings, highlighting the possible importance of habitat suitability, vegetative propagule pressure and resistance structures for population recovery. In low abundances, there was a possible facilitation between both species, while high abundances probably increased competition. The great importance of water level oscillations on these species’ abundances indicate that this strategy can be used as management tool.

Habitat heterogeneity enables spatial and temporal coexistence of native and invasive macrophytes in shallow lake landscapes

AbstractMacrophyte invasive alien species (IAS) fitness is often hypothesised to be associated with beneficial environmental conditions (environmental matching) or species‐poor communities. However, positive correlations between macrophyte IAS abundance and native plant richness can also arise, due to habitat heterogeneity (defined here as variation in abiotic and native biotic conditions over space and time). We analysed survey and palaeoecological data for macrophytes in satellite lakes along the Upper Lough Erne (ULE) system (Northern Ireland, UK), covering a gradient of eutrophication and connectivity to partition how environmental conditions, macrophyte diversity and habitat heterogeneity explained the abundance of Elodea canadensis, a widely distributed non‐native macrophyte in Europe. E. canadensis abundance positively correlated with macrophyte richness at both the within‐ and between‐lake scales indicating coexistence of native and invasive species over time. E. canadensis was also more prolific in highly connected and macrophyte‐rich lakes, but sparser in the more eutrophic‐isolated ones. Partial boosted regression trees revealed that in eutrophic‐isolated lakes, E. canadensis abundances correlated with water clarity (negatively), plant diversity (positively), and plant cover (negatively) whereas in diverse‐connected lakes, beta diversity (both positively and negatively) related to most greatly E. canadensis abundance. Dense macrophyte cover and unfavourable environmental conditions thus appear to confer invasibility resistance and sufficient habitat heterogeneity to mask any single effect of native biodiversity or environmental matching in controlling E. canadensis abundance. Therefore, in shallow lake landscapes, habitat heterogeneity variously enables the coexistence of native macrophytes and E. canadensis, reducing the often‐described homogenisation effects of invasive macrophytes.

Reciprocal competitive effects of congeneric invaders, Trapa natans L. and Trapa bispinosa Roxb. var. iinumai Nakano, in established freshwater plant cultures

Plant diversity is a known indicator of healthy ecosystems, therefore understanding interspecific relationships that structure plant communities is critical for invasive species management. A cryptic introduction of invasive macrophyte water chestnut (Trapa bispinosa var. iinumai) into the northeastern United States prompted investigation into potential competitive interactions between it and two common submersed species in the Chesapeake Bay watershed, Vallisneria americana and Hydrilla verticillata. Because the congeneric invader Trapa natans co-occurs in the same watershed with a documented history of negative environmental impacts, it was included for comparison. Reciprocal pairwise competitive effects between water chestnut and resident species were determined by additive reciprocal design, plants were grow in monoculture and biculture under controlled greenhouse conditions for one year. Competitive reciprocal effects between species were evident. Vallisneria americana produced 1.7 X more ramets in monoculture than in combination with Trapa spp. and tuber production was reduced by 37 % in biculture, independent of Trapa competitor. Trapa bispinosa var. iinumai fruit production was reduced by 80 % when grown in biculture with V. americana, and no fruits were produced when grown with H. verticillata. Biculture T. natans fruit production was impacted with less production observed for H. verticillata (54 %) than V. americana (25 %). Trapa bispinosa var. iinumai produced nearly 150 % more biomass in monoculture than T. natans, suggesting increased impacts in species-poor or disturbed areas. Findings suggest established monocultures of V. americana and H. verticillata may be vulnerable to invasion by either species of Trapa, but long-term competitive effects of invasion may not preclude co-existence.

Hydrological alteration induced changes on macrophyte community composition in sub-tropical floodplain wetlands of Nepal

In wetland ecosystems, macrophytes are sensitive to water level fluctuations. However, studies specific to the effects of water level fluctuations on distribution and composition of macrophytes are limited in sub-tropical floodplain wetlands of Nepal. This study aimed to examine the association between macrophytes and water levels in the floodplain wetlands of Koshi Tappu, in south-eastern Nepal. Sixty-four samples of macrophyte, along with twelve water quality parameters, five soil parameters and weekly water level information were collected from four shallow wetlands during summer, autumn, winter and spring over 2018 and 2019. Altogether, 52 macrophyte species belonging to 25 families were documented. Of them, 15, 6, 5 and 26 were emergent, submerged, floating and amphibian species, respectively. 10 species (5 emergent, 2 submerged, 2 floating and 1 amphibian species) were common across seasons. Regression analysis showed the decreasing trend in diversity, richness and evenness with increased water levels while at the same time overall macrophyte biomass increased. During summer, high water level supported the growth of floating invasive macrophytes, while medium and low water level during autumn and winter, respectively, supported submerged macrophytes. However, low-water level during spring supported emergent and amphibian macrophyte species. Canonical correspondence analysis (CCA) indicated that water depth and physico-chemical parameters such as water temperature, dissolved oxygen, pH, conductivity, nitrate-nitrogen, and phosphate were highly correlated with macrophyte assemblages across the wetlands. The study elucidated that management of water levels can ensure ecological integrity of wetlands and hence maintain biodiversity, and provide key indicators of water quality change.

Effects of invasive wetland macrophytes on habitat selection and movement by freshwater turtles

Invasive species can significantly impact native wildlife by structurally altering habitats and access to resources. Understanding how native species respond to habitat modification by invasive species can inform effective habitat restoration, avoiding inadvertent harm to species at risk. The invasive graminoids Phragmites australis australis (hereafter Phragmites) and Typha × glauca are increasingly dominating Nearctic wetlands, often outcompeting native vegetation. Previous research suggests that turtles may avoid invasive Phragmites when moving through their home ranges, but the mechanisms driving avoidance are unclear. We tested two hypotheses that could explain avoidance of invaded habitat: (1) that stands of invasive macrophytes (Phragmites and Typha x glauca) impede movement, and (2) that they provide inadequate thermal conditions for turtles. We quantified active-season movements of E. blandingii (n = 14, 1328 relocations) and spotted turtles (Clemmys guttata; n = 12, 2295 relocations) in a coastal wetland in the Laurentian Great Lakes. Neither hypothesis was supported by the data. Phragmites and mixed-species Typha stands occurred within the home ranges of mature, active E. blandingii and C. guttata, and were used similarly to most other available habitats, regardless of macrophyte stem density. Turtles using stands of invasive macrophytes did not experience restricted movements or cooler shell temperatures compared to other wetland habitat types. Control of invasive macrophytes can restore habitat heterogeneity and benefit native wetland species. However, such restoration work should be informed by the presence of at-risk turtles, as heavy machinery used for control or removal may injure turtles that use these stands as habitat.

Toxicity of rhizomes of the invasive Hedychium coronarium (Zingiberaceae) on aquatic species

The production and release of chemical compounds by invasive plants can affect competitors and native species overall, destabilizing ecological interactions and harming ecosystem functioning. Hedychium coronarium is an invasive macrophyte common on Brazilian riparian areas that produces a wide variety of allelochemicals, but little is known about their effect on aquatic species. Here, we identified the major chemical compounds of the aqueous extract of H. coronarium rhizomes and assessed its toxicity, evaluating the growth inhibition of one alga (Raphidocelis subcapitata) and one macrophyte (Lemna minor), and the lethality of cladoceran (Ceriodaphnia silvestrii and Daphnia similis) and Chironomidae larvae (Chironomus sancticaroli). The majoritarian compounds of H. coronarium rhizomes were Coronarin D and Coronarin D Ethyl Ether. The aqueous extract was toxic for all tested species. We observed growth inhibition in R. subcapitata, as well as reduction in biomass in L. minor. Chironomus sancticaroli and cladoceran were the most sensible species. The aqueous extract of H. coronarium rhizomes was toxic on tested conditions, suggesting that the rhizome compounds may interfere on aquatic organisms and in the dynamic of trophic webs of aquatic ecosystems on invaded areas.

Alien invasive macrophyte put into the shade: The native floating‐leaved macrophyte Nymphoides indica reduces Cabomba caroliniana growth performance through competition for light

Abstract Alien invasive aquatic macrophytes tend to displace native species and transform diverse macrophyte communities into monospecific stands. It is often thought that superior competitiveness allows alien invaders to achieve this. Cabomba caroliniana is a submersed macrophyte that is highly invasive worldwide and frequently monopolises habitats. However, field observations in Queensland, Australia, found that the native floating attached Nymphoides indica can co‐exist with C. caroliniana, highlighting N. indica as a potential candidate for habitat restoration. To identify factors and processes that regulate the coexistence of these species, we conducted a field survey and two experiments in artificial mesocosms. We found that N. indica leaf areal coverage of the water surface significantly reduced C. caroliniana standing crop biomass in the field. C. caroliniana growth was also linked to water depth; N. indica was not able to grow beyond 2 m depth. There was a small reduction in N. indica root and shoot biomass when co‐cultured with C. caroliniana in our experiment. Therefore, there was reciprocal competitive inhibition between the two species. However, the effect of N. indica on C. caroliniana was much larger. There was evidence that a reduction of C. caroliniana biomass below a threshold of c. 300 g dry mass/m is critical for protecting native submersed macrophyte diversity and abundance. Once C. caroliniana biomass exceeds this threshold, it dominates plant communities and forms high biomass monocultures. The experimental work identified shading as the most important factor that reduces C. caroliniana biomass, corroborating the relationship between leaf areal cover and C. caroliniana biomass found in the field. Based on these findings, N. indica could be useful for restoring the shallow lake littoral habitat, because it suppresses biomass of the invasive species to a level that allows other macrophytes to coexist and additionally increases habitat heterogeneity. Similarly, N. indica could be suitable to restore areas where C. caroliniana was previously removed to reduce the likelihood of future habitat monopolisation by C. caroliniana and realise long‐term ecological benefits from invasive macrophyte management.

Effect of rhizome exposure to contrasting abiotic conditions on the performance of the invasive macrophyte Hedychium coronarium J. Koenig (Zingiberaceae)

Although invasive species are often better competitors than native species, broad environmental tolerance may also drive invasion success. Tolerance to abiotic heterogeneity in riparian ecosystems tends to favour the establishment of alien clonal species, as well as their dispersion by vegetative fragments. Hedychium coronarium J. Koenig is a rhizomatous emergent macrophyte native to Asia and has invaded Neotropical riparian ecosystems. We assessed the effect of H. coronarium rhizome exposure to distinct abiotic conditions on ramet growth. We exposed rhizomes to different desiccation periods (1–90 days), temperatures (15, 25 and 35 °C), and light regimes (0, 12, 16 h) and then assessed the effect of each of these variables on subsequent clonal growth (aboveground biomass production per plant and per ramet, and number and height of ramets) under ambient conditions. While no rhizome survived desiccation periods longer than 30 days, ramet growth among surviving rhizomes was not affected by the period of desiccation. Biomass production per rhizome, ramet biomass, and ramet height were significantly lower at 35 °C than at 25 °C. Constant darkness increased rhizome survival, but decreased ramet growth. Although rhizome exposure to extremes of each abiotic variable may hinder the invasion success of H. coronarium, the subsequent aboveground biomass production of surviving rhizomes did not decrease strongly in response to any treatment. This resilience may contribute to successful establishment of H. coronarium after dispersal through rhizome fragments and to varying abiotic conditions.

Tissue Hydrogen Peroxide Concentration Can Explain the Invasiveness of Aquatic Macrophytes: A Modeling Perspective

In recent years, an invasive macrophyte, Egeria densa, has overwhelmingly colonized some midstream reaches of Japanese rivers. This study was designed to determine how E. densa has been able to colonize these areas and to assess the environmental conditions that limit or even prevent colonization. Invasive species (E. densa and Elodea nuttallii), and Japanese native species (Myriophyllum spicatum, Ceratophyllum demersum, and Potamogeton crispuss) were kept in experimental tanks and a flume with different environmental conditions. Tissue hydrogen peroxide (H2O2) concentrations were measured responding to either individual or multiple environmental factors of light intensity, water temperature, and water flow velocity. In addition, plants were sampled in rivers across Japan, and environmental conditions were measured. The H2O2 concentration increased in parallel to the increment of unpreferable levels of each abiotic factor, and the trend was independent of other factors. The total H2O2 concentration is provided by the sum of contribution of each factor. Under increased total H2O2 concentration, plants first started to decrease in chlorophyll concentration, then reduce their growth rate, and subsequently reduce their biomass. The H2O2 concentration threshold, beyond which degradation is initiated, was between 15 and 20 µmol/gFW regardless of the environmental factors. These results highlight the potential efficacy of total H2O2 concentration as a proxy for the overall environmental condition. In Japanese rivers, major environmental factors limiting macrophyte colonization were identified as water temperature, high solar radiation, and flow velocity. The relationship between the unpreferable levels of these factors and H2O2 concentration was empirically obtained for these species. Then a mathematical model was developed to predict the colonization area of these species with environmental conditions. The tissue H2O2 concentration decreases with increasing temperature for E. densa and increases for other species, including native species. Therefore, native species grow intensively in spring; however, they often deteriorate in summer. For E. densa, on the other hand, H2O2 concentration decreases with high water temperature in summer, allowing intensive growth. High solar radiation increases the H2O2 concentration, deteriorating the plant. Although the H2O2 concentration of E. densa increases with low water temperature in winter, it can survive in deep water with low H2O2 concentration due to diffused solar radiation. Currently, river rehabilitation has created a deep zone in the channel, which supports the growth and spreading of E. densa.

Drivers of species richness, biomass, and dominance of invasive macrophytes in temperate lakes

Presence and abundance of invasive species depend on likelihood of introduction and environmental limitations to their distributions. Propagule pressure and anthropogenic disturbance are hypothesized to increase invasions, yet assessing the importance of propagule pressure and anthropogenic factors independently is challenging, and properties of invaded systems (e.g., habitat availability) likely contribute to invasions. We sampled macrophyte assemblages in 20 lakes in New York, varying in boater visitations and number of previous waterbodies visited, to test if increased propagule risk (proxy for propagule pressure measuring potential for introducing invasives from different sources) resulted in greater species richness, biomass (g/m2) and dominance (% invasive biomass) of invasive macrophytes. We then tested watershed land use, in-lake water properties, and lake morphology on presence, abundance, and dominance of invasive macrophytes. Increased propagule risk resulted in greater species richness of invasive macrophytes. In invaded lakes, increased abundance of invasive macrophytes was correlated with increased agriculture in watersheds and littoral:total area. Increased dominance of invasive macrophytes was observed in lakes with greater littoral:total areas. Results suggest propagule risk can explain spatial variability in macrophyte invasions, while area-specific biomass in invaded lakes can be correlated with watershed and in-lake water properties. In lakes with increased suitable habitat (relative proportion of littoral:total area ratio), invasive macrophytes may dominate aquatic plant assemblages. Many factors correlated with the abundance of invasive macrophytes are not easily managed (e.g., watershed agricultural land use and lake morphology). Limiting introductions of propagules is likely the best approach to prevent macrophyte invasions, especially at high risk lakes.

Weak non-linear influences of biotic and abiotic factors on invasive macrophyte occurrence

Weak non-linear influences of biotic and abiotic factors on invasive macrophyte occurrence

Impact of invasive alien plant species on aquatic biodiversity of Koshi Tappu Wetlands : Ramsar Site, Nepal

Koshi Tappu Wetlands play a significant role in the conservation of many rare and endangered species of flora and fauna. However, this wetland is threatened by several natural and anthropogenic stressors; among others, invasion by invasive species is the most serious problem. The objective of this study was to prepare an inventory list of wetlands, categorize the wetlands based on the coverage of alien species, identify the problematic aquatic invasive plant species, and assess their impact on water quality and aquatic biodiversity (fish and macroinvertebrates). This study was conducted in winter and spring seasons of 2018. Composite water samples were collected from the wetlands with different covers of invasive species. Macroinvertebrate samples were collected using hand net of 500µm mesh following the habitat specific sampling approach, and fishes were sampled using Cast Net. The analysis of water quality parameters, macroinvertebrates and fishes were performed for different levels of invasion. Altogether, 66 wetlands were documented in the Buffer Zone located in the east of eastern embankment of the KTWR. Out of the total 66 wetlands, 33.33% were found to be non-invaded while 66.67% were found to be invaded by the invasive macrophytes. The invaded wetlands were further subdivided into abundant 'A' (>75% coverage), common 'C' (50-75% coverage) frequent 'F' (25-50%coverage), occasional 'O' (5-25% coverage), and rare 'R' (1-5% coverage) which were found to have occupied 19.69%, 16.67%, 12.12%, 13.63% and 4.50%, respectively, of the invaded wetlands (66.61%). The most problematic invasive species were found to be Eichhornia crassipes and Ipomoea carnea. The dissolved oxygen (DO) decreased while the total alkalinity and free CO2 increased significantly with the increased coverage of invasive macrophytes. The macroinvertebrate diversity was observed high in common and abundant coverage, but the fish diversity was high in the frequent coverage of invasive species. The taxa compositions shifted from “Decapoda” and “Ephemeroptera” to “Odonata” and “Mollusca” in none to abundant coverage of invasive species. The findings of this research are expected to help wetland managers and related stakeholders to understand the level of impact of different coverage of invasive species on wetlands, help to develop the conservation strategy and action plans to mitigate the spread of these invasive species, and wise use of wetlands.

Phytoremediation of battery industry effluent through aquatic macrophytes

Research was conducted to quantify the level of copper (Cu), chromium (Cr), cadmium (Cd) and lead (Pb) contamination in battery industry effluent and to assess the remediation potential of three invasive aquatic macrophytes Eichhornia crassipes, Pistia stratiotes and Hydrocotyle umbellata by growing on industrial effluent collected from Lead acid Battery industry.The effluent was heavily contaminated with Pb (10mg/l) and sulphuric acid (pH 2- 2.1). Due to high Pb concentrations and low pH (2-2.2) the plants were unable to survive. Mortality rate of E. crassipes was 96 % while P. stratiotes and H. umbellata were 100% rotten. The experiment was repeated after adjusting the effluent pH to 7-7.5 to increase the plant life.Plant parts and wastewater samples were analyzed after every 3 days interval uptil 21st day. The amount of Cr, Cd and Cu in the effluent was 0.076 mg /L, 0.036 mg /L and 0.097 mg /L, which was in permissible limits of NEQs (1.0 mg/l, 0.1 mg/l and 1.0 mg/l) respectively. Pb was found 10 times higher i.e. 10 mg/l than the permissible limit 0.5 mg/l. E. crassipes removed Pb>Cr>Cu>Cd while P. stratiotes and H. umbellata reduced Cd, Cr, Cu more than Pb from the effluent. E. crassipes was most efficient Pb removing plant in 21 days of experiment. Â