Growth Rate of an Aquatic Bryophyte (Warnstorfia fluitans (Hedw.) Loeske) from a High Arctic Lake: Effect of Nutrient Concentration

The High Arctic is one of the regions most susceptible to climate change on a global scale. Increased temperature, precipitation, and cloud cover are anticipated in the region, with consequent increases in nutrient runoff to surface waters. Mosses are often the dominant submerged macrophyte in Arctic and High Arctic lakes. If the growth rate of mosses in these lakes is nutrient-limited, then production could increase with climate changes that result in higher nutrient concentrations. We conducted a laboratory study to 1) measure the growth response of Warnstorfia fluitans (Hedw.) Loeske from a High Arctic lake to nitrogen and phosphorus availability; and 2) determine whether growth rate was N- or P-limited by examining its relationship to internal P and N content. The growth rates of W. fluitans were generally low, ranging from 0.003 to 0.012 day-1. The growth rates increased with increasing plant P content, but not with increasing N content, indicating that moss growth was P-limited at low P availability in the experiment. Critical plant P concentration for maximum growth rate was 0.086% dry weight. This is the first time a critical P threshold has been calculated. The results imply that if climate changes result in increased P concentrations in surface waters, a higher production of moss could occur in High Arctic lakes.L’Extrême arctique est l’une des régions du monde les plus susceptibles au changement climatique. La région devrait enregistrer des hausses de températures, de précipitations et de couvertures nuageuses, ce qui se traduira par des augmentations conséquentes d’écoulement des nutriments dans les eaux de surface. Dans les lacs de l’Arctique et de l’Extrême arctique, les mousses constituent souvent le macrophyte submergé prédominant. Si le taux de croissance des mousses de ces lacs est restreint par les nutriments, la production pourrait alors augmenter avec les changements climatiques qui donnent des concentrations de nutriments plus grandes. Nous avons réalisé une étude en laboratoire dans le but 1) de mesurer la réponse de croissance de Warnstorfia fluitans (Hedw.) Loeske d’un lac de l’Extrême arctique vis-à-vis de la disponibilité en azote et en phosphore; et 2) de déterminer si le taux de croissance était restreint par N ou par P en examinant sa relation par rapport à sa teneur interne en N et en P. Les taux de croissance de W. fluitans étaient généralement faibles, allant de 0,003 à 0,012 jour-1. Les taux de croissance augmentaient en même temps que la teneur en N des plantes augmentait, mais pas en même temps que la teneur en P augmentait, ce qui laisse entrevoir que la croissance des mousses était restreinte par P en fonction de la faible disponibilité en P dans le cadre de l’expérience. La concentration critique en P dans les végétaux donnant lieu à un taux de croissance maximal était de 0,086 % du poids sec. Il s’agit de la première fois qu’un seuil critique de P a été calculé. Les résultats laissent entendre que si des changements climatiques se traduisent par des concentrations accrues en P dans les eaux de surface, une plus grande production de mousse pourrait se produire dans les lacs de l’Extrême arctique

Genetic diversity in three invasive clonal aquatic species in New Zealand

<p>Abstract</p> <p>Background</p> <p><it>Elodea canadensis, Egeria densa </it>and <it>Lagarosiphon major </it>are dioecious clonal species which are invasive in New Zealand and other regions. Unlike many other invasive species, the genetic variation in New Zealand is very limited. Clonal reproduction is often considered an evolutionary dead end, even though a certain amount of genetic divergence may arise due to somatic mutations. The successful growth and establishment of invasive clonal species may be explained not by adaptability but by pre-existing ecological traits that prove advantageous in the new environment. We studied the genetic diversity and population structure in the North Island of New Zealand using AFLPs and related the findings to the number of introductions and the evolution that has occurred in the introduced area.</p> <p>Results</p> <p>Low levels of genetic diversity were found in all three species and appeared to be due to highly homogeneous founding gene pools. <it>Elodea canadensis </it>was introduced in 1868, and its populations showed more genetic structure than those of the more recently introduced of <it>E. densa </it>(1946) and <it>L. major </it>(1950). <it>Elodea canadensis </it>and <it>L. major</it>, however, had similar phylogeographic patterns, in spite of the difference in time since introduction.</p> <p>Conclusions</p> <p>The presence of a certain level of geographically correlated genetic structure in the absence of sexual reproduction, and in spite of random human dispersal of vegetative propagules, can be reasonably attributed to post-dispersal somatic mutations. Direct evidence of such evolutionary events is, however, still insufficient.</p

Hydrological and environmental variables outperform spatial factors in structuring species, trait composition, and beta diversity of pelagic algae

There has been increasing interest in algae-based bioassessment, particularly, trait-based approaches are increasingly suggested. However, the main drivers, especially the contribution of hydrological variables, of species composition, trait composition, and beta diversity of algae communities are less studied. To link species and trait composition to multiple factors (i.e., hydrological variables, local environmental variables, and spatial factors) that potentially control species occurrence/abundance and to determine their relative roles in shaping species composition, trait composition, and beta diversities of pelagic algae communities, samples were collected from a German lowland catchment, where a well-proven ecohydrological modeling enabled to predict long-term discharges at each sampling site. Both trait and species composition showed significant correlations with hydrological, environmental, and spatial variables, and variation partitioning revealed that the hydrological and local environmental variables outperformed spatial variables. A higher variation of trait composition (57.0%) than species composition (37.5%) could be explained by abiotic factors. Mantel tests showed that both species and trait-based beta diversities were mostly related to hydrological and environmental heterogeneity with hydrological contributing more than environmental variables, while purely spatial impact was less important. Our findings revealed the relative importance of hydrological variables in shaping pelagic algae community and their spatial patterns of beta diversities, emphasizing the need to include hydrological variables in long-term biomonitoring campaigns and biodiversity conservation or restoration. A key implication for biodiversity conservation was that maintaining the instream flow regime and keeping various habitats among rivers are of vital importance. However, further investigations at multispatial and temporal scales are greatly needed

Stream restoration and ecosystem functioning in lowland streams

Restoration has been increasingly applied over the last decades as a way to improve the ecological conditions in stream ecosystems, but documentation of the impact of restoration on ecosystem functions is sparse. Here, we applied a space-for-time approach to explore effects of stream restoration on metabolism and organic matter decomposition in lowland agricultural streams. We included stream reaches that were restored >10 years ago and compared ecosystem functioning in these streams with those in channelized and naturally meandering stream reaches from the same geographical region. Specifically, we tested the following hypotheses: 1) rates of stream metabolism (gross primary production, GPP, and ecosystem respiration, ER) and organic matter decomposition in restored reaches resemble rates in naturally meandering reaches more than rates in channelized stream reaches and 2) higher resemblance in ecosystem metabolism and organic matter decomposition between restored reaches and meandering reaches can be attributed to the improved physical habitat conditions in the restored stream reaches. Overall, we did not find that stream metabolism or organic matter decomposition differed among restored, channelized and naturally meandering stream reaches even though habitat conditions differed among the three stream types. Instead, we found a large variation in ecosystem function characteristics across all sites. When analyzing all stream types combined, we found that GPP increased with increasing plant coverage and that ER increased with increasing stream size and with the coverage of coarse substratum on the stream bottom. Organic matter decomposition, on the other hand, only slightly increased with the number of plant species and declined with increasing concentrations of nutrients. Overall, our findings suggest that physical habitat improvements in restored stream reaches can affect ecosystem functions, but also that the restoration outcome is context-dependent since many of the physical characteristics playing a role for the measured functions were only to some extent affected by the restoration and/or clouded by interference with factors operating at a larger-scale.publishedVersio

SER: An R package to characterize environmental regimes

Environmental regimes (or environmental legacy or historical legacy) are the dynamics of environmental characteristics over a given (either long or short) time period, such as frequency of mean or extreme events and rate of change, which might be absent by using only contemporary variables. We present SER, an R package for estimating environmental regimes for different environmental variables. Using the data included in the package, several examples are shown. SER is suitable for any type of environmental or biotic variables, including nutrient concentration, light, and dissolved oxygen. In addition, by changing the argument "days_bf," it is possible to compute environmental regimes over any time period, such as days, months, or years. Our case study showed that the inclusion of environmental regimes increased the explained variation of temporal β-diversity and its components. Environmental regimes are expected to advance the "environment-community" relationships in ecological studies. They can further be implemented in other subjects such as social science, socioeconomics, and epidemiology

Epiphyton in Agricultural Streams: Structural Control and Comparison to Epilithon

Stream biofilms play an important role in the structure, functioning, and integrity of agricultural streams. In many lowland streams, macrophyte vegetation is abundant and functions as an important substrate for biofilm (epiphyton) in addition to the gravel and stone substrate for epilithon on the stream bed. We expect that reach-scale habitat conditions in streams (e.g., nutrient availability, hydraulic conditions) affect the epiphyton and epilithon biomass and composition, and that this effect will be substrate-specific (macrophytes and stones). The objectives of our study were (i) to describe concurrent changes in epiphyton and epilithon biomass and composition over a year in agricultural streams, and (ii) to determine the substrate specific reach-scale habitat drivers for the epiphyton and epilithon structure. We monitored epiphyton and epilithon biofilm biomass and composition at three-week intervals and reach-scale environmental conditions daily during a year for two agricultural steams. The results showed that epiphyton and epilithon communities differed in biomass, having high substrate specific biomass in epilithon compared to epiphyton. Epiphyton was mainly composed of diatom and green algae, while cyanobacteria were more important in epilithon, and the diatom species composition varied between the two biofilm types. Epiphyton structural properties were less influenced by reach-scale hydrology and nutrient availability compared to epilithon. The overall explanatory power of the measured environmental variables was low, probably due to micro-scale habitat effects and interactive processes within stream biofilms. Knowledge of biofilm control in agricultural streams is important in order to improve management strategies, and future studies should improve the understanding of micro-scale habitat conditions, interactive relationships within biofilms and between the biofilm and the substrates

Investigating emergent macrophytes establishment rate and propagation towards constructed wetlands efficacy optimization

Constructed wetlands have become a widely used tool for reducing nutrient loading from agriculture drainage water running to aquatic ecosystems. To ensure a high nutrient removal efficiency, it is often suggested to use macrophytes to retain or remove nutrients via uptake and through the denitrifying biofilm. In Europe, Phragmites australis and Typha spp are the most commonly used aquatic plants in constructed wetlands (CWs) with free surface flow, and these species often form monocultures in the wetlands. In order to achieve a more diverse vegetation, there is a need to introduce more plant species. Creating a mass production of plant material reduces both handling time and the risk of depleting and disturbing vegetation in natural habitats such as streams or lakes. However, a successful and continuous production of such material during growing seasons requires knowledge of the selected species' establishment and propagation. We examined the relative growth rate (RGR) of six emergent macrophyte species collected from streams and small lakes located in Mid Jutland (Denmark), in seasonal experiments from March to October in order to determine the most efficient time period for their propagation. We found that all species had highest RGR in June, and that several species showed high growth efficiency from April to August. The results showed that it is possible to have a full production of emergent macrophytes throughout the growing season, and therefore, we suggest to propagate plants for use in constructed wetlands in order to enhance biodiversity and ecosystem functioning

Nutrient uptake controls and limitation dynamics in north-east Greenland streams

Permafrost thaw induced by climate change will cause increased release of nutrients and organic matter from the active layer to Arctic streams and, with increased water temperature, will potentially enhance algal biomass and nutrient uptake. Although essential for accurately predicting the response of Arctic streams to environmental change, knowledge of nutrient release on current Arctic in-stream processing is limited. Addressing this research gap, we quantified nutrient uptake of short-term releases of NO3−, PO43- and NH4+ during peak snowmelt season in five streams of contrasting physiochemical characteristics (from unstable, highly turbid to highly stable, clear-water systems) in north-east Greenland to elucidate the major controls driving nutrient dynamics. Releases were plus or minus acetate to evaluate uptake dynamics with and without a dissolved organic carbon source. To substantiate limiting nutrients to algal biomass, nutrient-diffusing substrates were installed in the five streams for 16 days with NH4+, PO43- or NH4+ + PO43- on organic and inorganic substrates. Observed low uptake rates were due to a combination of low nutrient and DOC concentrations, combined with low water temperature and primary producer biomass, and substantial variation occurred between streams. N was found to be the primary limiting nutrient for biofilm, whilst streams displayed widespread PO43- limitation. This research has important implications for future changes in nutrient processing and export in Arctic streams, which are predicted to include increased nutrient uptake rates due to increased nutrient availability, warmer water temperatures and increased concentration of labile carbon. These changes could have ecosystem and landscape-wide impacts

Interactions between microplastics and benthic biofilms in fluvial ecosystems: Knowledge gaps and future trends

Plastics, especially microplastics (<5 mm in length), are anthropogenic polymer particles that have been detected in almost all environments. Microplastics are extremely persistent pollutants and act as long-lasting reactive surfaces for additives, organic matter, and toxic substances. Biofilms are microbial assemblages that act as a sink for particulate matter, including microplastics. They are ubiquitous in freshwater ecosystems and provide key services that promote biodiversity and help sustain ecosystem function. Here, we provide a conceptual framework to describe the transient storage of microplastics in fluvial biofilm and develop hypotheses to help explain how microplastics and biofilms interact in fluvial ecosystems. We identify lines of future research that need to be addressed to better manage microplastics and biofilms, including how the sorption and desorption of environmental contaminants in microplastics affect biofilms and how microbial exchange between microplastics and the biofilm matrix affects biofilm characteristics like antibiotic resistance, speciation, biodiversity, species composition, and function. We also address the uptake mechanisms of microplastics by consumers and their propagation through the food web