Search

Murray-Darling Freshwater Research CentreMDFRC item.We investigated the importance of lacunar gas transport for the release of methane from beds of Eleocharis sphacelata R. Br. in a freshwater wetland in southeastern Australia. Gases were transported in the E. sphacelata lacunar system by pressurized convective flow, which was apparently driven by humidity induced pressurization. Internal culm temperatures were 1.9–4.2° C lower than at the external culm surface, suggesting that thermal transpiration was not responsible for lacunar pressurization. Some of the culms (influx culms) provide a net gas flux from the atmosphere into the plant, whereas others (efflux culms) act as conduits for flux from the rhizosphere to the atmosphere. The mean gas influx was 1.0±0.2 (SE) ml min−1 per culm, and the mean gas efflux was 0.2±0.0 (SE) ml min−1 per culm. The difference in influx and efflux flow rates is due to unequal numbers of the two culm types, and the total gas flux through three adjacent E. sphacelata beds was estimated from this flow ratio and the total culm density. It ranged from 1.1 to 2.5 1 m−2 h−1. The methane concentration in the efflux culms was 2–3%, resulting in a total methane efflux from E. sphacelata of 22–75 ml CH4 m−2 h−1. These rates represented 1–15 times the rate of methane release from the E. sphacelata beds by ebullition of methane in bubbles released from the sediment. Diffusive methane fluxes in the lacunar s system (< 300 μl m−2 h−1) were an insignificant mechanism of methane release compared with lacunar convective flow and ebullition fluxes from sediments. The interstitial methane concentration in sediments from E. sphacelata beds was approximately 0.6 times that of adjacent unvegetated sediment, highlighting the role of convective flow by E. sphacelata in accelerating methane release from sediments.

MDFRC item.Internal pressurization and convective through-flow are demonstrated to be common attributes of wetland plants with cylindrical culms or linear leaves. Eight of 14 species tested produced static internal gas pressure differentials of 200-1,300 Pa relative to ambient and internal convective airflows of 0.2 to > 10 cm3 min-1 culm-1, depending on species. Four species produced internal static pressure differentials of < 100 Pa. Two species did not pressurize. The driving forces are gradients in temperature and water vapor between the internal gas spaces of the plants and the ambient atmosphere (thermal transpiration and humidity-induced pressurization). A clear diel variation in pressurization and convective flow was observed; rates were highest in the afternoon and lowest at night, responding to ambient changes in light, temperature, and humidity. The resistance to airflow at the stem-rhizome junction was very high for some species, resulting in a low ability to convert internal pressurization into convective airflow through the rhizomes. Species with a high potential for internal pressurization and a low internal resistance to convective flow seem to have a competitive advantage over species that rely exclusively on diffusive gas transport, which allows them to grow in deeper waters.

Murray-Darling Freshwater Research CentreMDFRC item.1. We examined the temporal (seasonal and diel) and spatial variation in methane flux from sediments of a billabong in south-eastern Australia, and related it to variations in the rate of organic matter decay, concentration of interstitial metabolites, and sediment redox.2. Total gas ebullition ranged from 59mlm−2h−1, and was highest in the summer months when water temperatures were >25°C. These rates are equivalent to carbon fluxes of about 16–30gC—CH4m−2yr−1. Ebullition was greater from unvegetated sediments than from sediments colonized by the emergent macrophyte Eleockaris sphacelata, R, Br. or the submerged macrophyte Vallisneria gigantea Graeb. There were no consistent differences in the rate of ebullition over the day and the night.3. Methane accounted for about 42–45% of total sediment gas in the vegetated sediments, but about 60% in the unvegetated sediments. These ratios did not vary greatly throughout the year. Carbon dioxide was a minor component of sediment gas, usually comprising

Murray-Darling Freshwater Research CentreMDFRC item.1. We examined the effects of an emergent macrophyte (Eleocharis sphacelata R. Br., Cyperaceae) and a submerged macrophyte (Vallisneria gigantea Graeb., Hydrocharitaceae) on the biogeochemistry of the sediments of a billabong in south-eastern Australia.2. Sediments from an E. sphacelata bed had significantly lower concentrations of exchangeable phosphorus than did sediments from a nearby bare area or a V. gigantea bed, but neither macrophyte had a measureable effect on their sediment's exchangeable ammonium content.3. The redox potential in the upper 10cm of E. sphacelata sediments was about 100 mV higher than that of bare sediments, or of sediments colonized by V. gigantea.4. There were few consistent differences between vegetated and bare sediments in terms of the activity of extracellular enzymes, such as α-amylase, protease, β-d glucosidase, lipase or alkaline phosphatase. Rates of alkaline phosphatase activity (235–306μmol (g dry wt)−1 day−1) were markedly higher than those commonly reported for sediments or soils.5. Rates of gas release were higher from bare sediments (21–93 ml m−2 h−1) than from E. sphacelata or V. gigantea sediments (17–23 and 21-24ml m−2 h−1, respectively). Gas bubbles consisted mainly of methane (26–66%) and nitrogen (15–68%). Rates of methane ebullition varied from 5 to 60ml m−2 h−1.6. In-vitro methanogenesis was most rapid in samples of the upper flocculent sediment. Methanogenesis was slower in V. gigantea sediments than in bare area or E. sphacelata sediments, but was markedly accelerated by additions of acetate and/or H2/CO2 in all sites.7. Profiles of total extractable fatty acids and phospholipid fatty acids demonstrated that material derived from higher plants dominated the sediment organic matter in all sites. Bacteria were also a significant component of sediment organic matter, as fatty acids for which bacteria can be assumed the sole source accounted for 18–30% of total fatty acid content. Biomarkers for sulphate-reducing bacteria (Desulfobacter spp.) were detected, and for type II methanotrophic bacteria.

Murray-Darling Freshwater Research CentreMDFRC item.Methane emissions were quantified from beds of Eleocharis sphacelata R.Br., Myriophyllum sp., and Vallisneria gigantea Graeb. in a small floodplain lake (Ryans 1 Billabong; 36°07′S, 146°58′E) in south-eastern Australia over a 15-mo period, from March 1993 to May 1994. Gas from sediments of Vallisneria beds had the highest methane concentrations (about 60-90% v/v); methane concentrations in gas from sediments of Myriophyllum beds were the lowest (falling to 17 ± 3% v/v in May 1994), and concentrations in sediments of Eleocharis beds varied from about 25% v/v in winter to about 60-82% v/v in summer-autumn. Total water-atmosphere methane fluxes, measured with 0.8 m3 static chambers, varied from -2 h-1 in Eleocharis beds, -2 h-1 in Myriophyllum beds, and -2 h-1 in areas of open water colonised by Vallisneria. Total fluxes were highly seasonal, being greatest in summer-autumn, when sediment temperatures exceeded 20°C. Strong diurnal and diel variations were also observed, especially in Eleocharis beds during the warmer months. Ebullition rates varied from -2 h-1 and, like total water-atmosphere fluxes, fluctuated according to season, being lowest in winter and highest in summer-autumn. Ebullition seemingly accounted for 6-15% of total methane fluxes from Eleocharis beds in the cooler months, and 30-90% in the warmer months. Eleocharis shoots could generate pressures of up to 550 Pa during summer days, and the seasonal pattern to plant pressurization matched closely the seasonality of total methane emissions from Eleocharis beds. Manipulative experiments provided additional evidence that emergent shoots of Eleocharis were a significant pathway for methane transport from the benthos to the atmosphere, because cutting shoots below the water decreased emissions.

Ice algae are key contributors to primary production and carbon fixation in the Arctic, and light availability is assumed to limit their growth and productivity. We investigated photo-physiological responses in sea ice algae to increased irradiance during a spring bloom in West Greenland. During a 14 d field experiment, light transmittance through sea ice was manipulated to provide 3 under-ice irradiance regimes: low (0.04), medium (0.08), and high (0.16) transmittances. Chlorophyll a decreased with elevated light availability relative to the control. Maximum dark-adapted photosynthetic efficiency (ΦPSII_max) showed an initially healthy and productive ice algae community (ΦPSII_max > 0.6), with ΦPSII_max decreasing markedly under high-light treatments. This was accompanied by a decrease in the light utilization coefficient (α) and photosynthetic capacity (maximum relative electron transfer rate), and a decrease in the ratio of mono- to polyunsaturated fatty acids. This was partly explained by a corresponding increase of photoprotective pigments (diadinoxanthin and diatoxanthin), and a development of mycosporine-like amino acids as identified from a distinctive spectral absorption peak at 360 nm. After 14 d, in situ fluorescence imaging revealed significant differences in ΦPSII_max between treatments of dark-adapted cells (i.e. those sampled before sunrise and after sunset), during diel cycles, with clear chronic photoinhibition in high and medium treatments. Data demonstrate the high sensitivity of spring-blooming Arctic sea ice algae to elevated irradiance caused by loss of snow cover. The predicted loss of snow cover on landfast ice will negatively impact ice algae, their potential primary production, and nutritional quality for higher trophic levels.

Tall wetland graminoids with rapid growth, high productivity and wide tolerance of biotic and abiotic stresses are potentially valuable bioenergy crops, especially when grown in rewetted peat soils for biomass (paludiculture). Using wetland plants as renewable bioenergy crops instead of fossil fuels has the ecological benefits of reducing greenhouse gas (GHG) emissions, improving water quality and conserving peat soils. As these potential crops will grow in peat that differs in nutrient availability, not only will their biomass productivity be affected, but also the biomass quality for bioenergy may be altered. We set up five different nutrient availability treatments in waterlogged peat soil to simulate different nutrient environments for wetland plant cultivation. Seven wetland plants suitable for paludiculture (Typha latifolia, Arundo plinii, Arundo donax and four distinct genotypes of Phragmites australis from Denmark, The Netherlands, Romania and Italy) were selected to test responses of biomass production and tissue quality to different nutrient availability. Due to their high biomass productivity, T. latifolia, A. donax, Dutch (NL) and Romanian (RO) P. australis had the greatest potential to produce bioenergy feedstock. All taxa survived when cultivated with very low nutrient availability, especially NL and RO P. australis and T. latifolia. Moreover, biomass quality was both species-specific and element-specific, affected by increasing nutrient availability. Overall, T. latifolia had the lowest tissue concentrations of S and Si as well as high concentrations of Ca, and therefore the best tissue quality for combustion both at low and high nutrient availability. These results will provide crucial information for choosing appropriate crops and managements and promote the success of culturing wetland plants as bioenergy feedstock.

Background Coastal wetlands are threatened by the increased salinity that may result from sea level rise. Salinity stress alters species zonation patterns through changes in competitive outcome between species differing in salinity tolerance. This study therefore aimed to understand how salinity and light affect two dominant and competing coastal wetland grasses that differ in salt tolerance, height and photosynthetic metabolism. Methods The C4 species Spartina anglica and the C3 species Phragmites australis were grown at five salinity levels (0, 7, 14, 21 and 28 ppt) and two light fluxes (100 % and 50 % of natural daylight) in an outdoor experimental setup for 102 d with full access to nutrients. Key Results Salinity reduced the biomass, height and shoot density of P. australis from 81.7 g dry weight (DW), 0.73 m and 37 shoots per pot at a salinity of 0 ppt to 16.8 gDW, 0.3 m and 14 shoots per pot at a salinity of 28 ppt. Biomass, height and shoot density of S. anglica did not respond or were only slightly reduced at the highest salinity of 28 ppt. High salinity also resulted in a higher tissue concentration of N and P in P. australis. Both species had low ability to acclimate to the lower light flux. Shade acclimation in S. anglica occurred via modest changes in specific leaf area, pigment content and biomass allocation. Conclusions High salinity reduced traits important for light competition and increased the nutrient concentration in P. australis leaf and root biomass, while this was overall unaffected in S. anglica. This is likely to reduce the competitive ability of P. australis over S. anglica for light because at high salinities the former cannot effectively shade the lower-growing S. anglica. Neither species effectively acclimates to shade, which could explain why S. anglica does not occur in the understorey of P. australis at low salinities.

We immersed the root systems of three emergent aquatic monocots (Cyperus involucratus Rottb., Eleocharis sphacelata R. Br. (both Cyperaceae), and Juncus ingens N. A. Wakef. (Juncaceae)) in nutrient agar gels with pH indicators and pH microelectrodes to study H

Small-scale variation in the physical and biological properties of sea ice was examined by collecting nine sea ice cores within 1 m2 in a land-fast first-year ice in southwest Greenland in late winter. Cores were sectioned in four segments and sea ice physical, biological, and photobiological parameters were measured. The main purpose was to explore the decimeter-scale horizontal and vertical variations in common sea ice parameters. ANOVA analyses revealed significant within-core variations for bulk salinity, brine salinity, brine volume, gas volume, chlorophyll a (Chl a), and the maximum light-limited photosynthetic efficiency (&alpha, ). Only temperature and bulk salinity variations were significant between cores, and no significant variations were found within or between cores for other photobiological parameters. Power analyses were applied to determine the number of replicates needed to achieve a significance at p &lt, 0.05 with sufficient power, and showed a minimum of four and preferably five replicate cores to detect the observed variability in this first-year ice. It is emphasized that these results only apply to this type of first-year ice in late winter/early spring, and that different variations may apply to other types of ice.

Aquatic macrophytes grow abundantly in many lowland streams and play a key role in ecosystem functioning, such as nutrient retention. In this study, we performed a microcosm experiment to quantify and compare the contribution of two freshwater macrophyte growth forms to nutrient cycling. We measured and compared inorganic nitrogen (NH4–N and NO3–N) and phosphorus (PO4–P) uptake kinetic parameters (Vmax and Cmin) in 12 submerged and seven amphibious plant species. We tested whether relative growth rate (RGR) was related to high Vmax and low Cmin, and quantified changes in nutrient uptake kinetic in a subset of six out of 19 plants species during the growth season. Uptake rates of NH4–N were higher in submerged compared to amphibious plants, whereas uptake rates of NO3–N were significantly higher in amphibious species; PO4–P uptake kinetics were not significantly different between the two growth forms. There were also significant seasonal differences in Vmax NH4–N rate among both submerged and amphibious species and in Vmax NO3–N among amphibious species. Highest uptake rates were observed in summer for both submerged and amphibious species. Overall, we found that nutrient uptake kinetics differed between the two growth forms within and between seasons. Consequently, the presence of both growth forms should extend the period of nutrient uptake across the year and enhance nutrient uptake within seasons. We conclude that higher functional diversity enhances annual nutrient uptake in streams and that stream restoration efforts should consider increasing the niche space available for both submerged and amphibious species.

This study examined the acclimation to temperature of two globally invasive species Iris pseudacorus and Lythrum salicaria, which share the same habitat type but differ in morphology. Iris pseudacorus has long vertical leaves, allowing light penetration through the canopy, while L. salicaria has stems with small horizontal leaves, creating significant self-shading. We aimed to build a physiological understanding of how these two species respond to different growth temperatures with regard to growth and gas exchange-related traits over the canopy. Growth and gas exchange-related traits in response to low (15 °C) and high (25 °C) growth temperature regimes were compared. Plants were grown in growth chambers, and light response curves were measured with infrared gas analysers after 23–33 days at three leaf positions on each plant, following the vertical light gradient through the canopy. After 37 days of growth, above-ground biomass, photosynthetic pigments and leaf N concentration were determined. The maximum photosynthesis rate was lower in lower leaf positions but did not differ significantly between temperatures. Iris pseudacorus photosynthesis decreased with decreasing leaf position, more so than L. salicaria. This was explained by decreasing N and chlorophyll concentrations towards the leaf base in I. pseudacorus, while pigment concentrations increased towards the lower canopy in L. salicaria. Biomass, shoot height and specific leaf area increased with temperature, more so in I. pseudacorus than in L. salicaria. Light response curves revealed that L. salicaria had a higher degree of shade acclimation than I. pseudacorus, probably due to self-shading in L. salicaria. High temperature decreased C assimilation at the bottom of the canopy in L. salicaria, while C assimilation in I. pseudacorus was less affected by temperature. As vegetative growth and flowering was stimulated by temperature, the invasive potential of these species is predicted to increase under global warming., Photosynthetic carbon gain throughout the canopy was affected differently by temperature in the invasive yellow flag iris (Iris pseudacorus) and purple loosestrife (Lyhtum salicaria). While unaffected in I. pseudacorus, lower canopy photosynthesis decreased with high temperature in L. salicaria. Lythrum salicaria showed typical shade-acclimated responses in leaf pigment content and light response curves which were attributed to adaptations to self-shading. Iris pseudacorus did not show any such adaptations, revealing different invasive photosynthetic strategies in the two species. Overall, both species benefited from elevated temperatures with increased biomass and shoot height as well as flowering rate in L. salicaria.

The study is based on a very extensive data-set of physical, biological, and optical parameters from below the sea ice in the western Amundsen Basin, central Arctic Ocean, in August–September 2012 during the record low sea ice extent. The water column was strongly stratified at all stations related to salinity differences between a surface layer of reduced salinities (34). A nitrate utilization-based budget in the surface layer gave a primary production of 67.5 mg C m− 2 d− 1, which reduced to 3.9 mg C m− 2 d− 1 in August 2012. Amundsen Basin primary production rates are lower than rates determined for other Arctic Ocean deep-water basins, and also lower compared to rates on the shelf. Below ice phytoplankton was well adapted to low light conditions in the Amundsen Basin and the photosynthetic potential was high, but limited by the low nutrient fluxes induced by the strong stratification. Amundsen Basin is foreseen to be ice-free in summer in 3–4 decades, and the question whether primary production will increase when ice-free was resolved with a coupled physical-biogeochemical model. Results showed that production will increase 10 to 14 times from the present 3.9 mg C m− 2 d− 1 to 37.4 and 55.2 mg C m− 2 d− 1 for an ice-free August and July–August, respectively. The study substantiates that both present and future ice-free low production rates were related to the strong stratification, reduced nutrient fluxes, and deep lying nutrient rich waters. Low production rates and strong stratification are discussed in the view of parameters that increase this stratification as higher freshwater run off or reduce stratification as wind.

Large blooms of purple-brownish pigmented glacier algae cover the ablation zones of the Greenland Ice Sheet (GrIS) and amplify its melt by lowering the ice surface albedo and increasing its solar radiation absorption. The darkening effect of these Zygnematophycean algae can be mainly attributed to their phenolic pigments, which absorb in the visible (VIS) and UV light ranges. Currently, a mechanistic understanding of the factors regulating the production of these pigments and their implications for the large-scale biologically-driven albedo reduction on the GrIS is missing. Here, we reveal how light (VIS vs. UV range) controls the phenolic pigment production, endo- and exometabolome, gene expression and photosynthetic performance of glacier algae. Two different algal communities (a mixed natural microbial community collected from snow-free ice and a laboratory-grown community of the ice algae Mesotaenium berggrenii without its original dark pigmentation) were used for a set of in situ incubations on Mittivakkat glacier in SE-Greenland. Pulse-amplitude-modulated (PAM) fluorometry revealed an overall higher photosynthetic performance (electron transport rate) at higher irradiances for the field population containing purpurogallin-like pigments compared to the lab community without dark pigmentation. The lab population showed a low maximum quantum efficiency of photosystem II under in situ light conditions, indicating a photo-damaging effect from high intensities of UV light in the absence of purpurogallin-derived phenolic pigments. Our study highlights the intracellular shading effect by purpurogallin-derived pigments, which are key for the survival of glacier algae on the ice and forms a cornerstone of understanding the large-scale variability in the biological darkening of the GrIS.

Paludiculture („palus" lat. swamp) is the sustainable use of wet and rewetted peatlands which maintains the peatbody for carbon storage. Worldwide, drained peatlands cover only 0.3 percent of the land area but emit almost 5 percent of all anthropogenic greenhouse gas emissions. Rewetting of drained peatlands is therefore an urgent need for climate change mitigation. The production of biomass for the use as solid biofuel for combustion, is one promising utilisation option.Compared to wood, herbaceous biomass (e.g. grasses and reeds) contains higher concentrations of critical elements (N, S, Cl or K) that leads to higher emissions (SOx, NOx) or to the destruction of boilers or parts of it (corrosion). Late harvest in winter is often recommended for grass species to improve fuel quality and also storage stability. Nutrients and other elements will be reduced in plant tissues by leaching or translocation processes during plant die-off. Water content that is crucial for storage will also decrease. Combustion quality of herbaceous biomass depends on plant species, site specific parameters and harvest time. There are only a few studies for the suitability of Paludiculture plants for combustion, and little is known about the effects of nutrient supply.In our study we focused on fuel quality parameters of Typha latifolia, Typha angustifolia, Arundo donax, and four European clones of Phragmites australis (Denmark, Netherlands, Romania, and Italy) grown in mesocosms on three different nutrient levels (0, 75 and 500 kg N/ha/a). We analysed the total concentrations of C, H, N, O, S, Cl, K, Na, P, Ca, Si and ash content as well as higher heating value in the above ground biomass.Winter harvested P. australis (Italy), T. angustifolia as well as T. latifolia could meet the required treasure values for N concentrations at all nutrient levels. S concentrations were only for T. angustifolia and T. latifolia below the treasure values at summer harvest, but for all plant species at winter harvest. Ash contents were very high for all plant species in summer (>6 %) – except for A. donax and P. australis (Netherlands). Effects of nutrient levels on biofuel quality were stronger in summer than in winter.A comparison of plant species, harvest time (summer and winter) and nutrient levels will be used to decide for an optimal cultivation type and management strategy for Paludiculture purposes. The main aim is to provide biomass for combustion with high energy yields per hectare combined with the highest possible fuel quality.

Constructed wetlands have become a widespread mean to reduce nutrient loading from tile drained agricultural areas. As a supplement to emergent plants usually present in these wetlands, submerged plants may, if present, enhance nutrient retention by occupying the deeper zones of the wetland basins. The nutrient retention efficiency may, however, vary among submerged species and also vary between multi-species communities compared to single-species communities. In this study we performed a mesocosm experiment to quantify the inorganic nitrogen (NH4-N and NO3-N) and phosphorus (PO4-P) uptake kinetic parameters (Vmax and Cmin) in constructed wetlands (1) in habitats with and without plants; and (2) in multi-species communities and single-species communities using four submerged plant species relevant for use in these wetlands. We found that uptake rates of PO4-P and NH4-N was three and five times higher, respectively, in habitats with plants compared to habitats without plants, whereas the uptake rates of NO3-N was similar. Multi-species communities were not more efficient in nutrient retention than single-species communities, although a residual analysis indicated that multi-species communities might be better in taking up and depleting NH4-N but not PO4-P and NO3-N. Overall, our study shows that submerged plants in deeper waters of drainage wetlands can be an important nutrient retaining component, and that a high biomass of one efficient plant species (e.g. R. aquatilis) is working similarly well as multi-species communities in this context.

Estuaries are dynamic and selective environments that provide frequent opportunities for the turnover of Phragmites australis populations. We studied Phragmites genetic diversity patterns in three of the major deltas of China, viz. the Yellow River, the Yangtze and the Liaohe, in relation to Phragmites global phylogeography and soil salinity. We found that two distantly related P. australis haplotypes, each with intercontinental distribution, co-occur in these deltas in China. One is European Phragmites (Haplotype O) and is related to P. japonicus; the other (Haplotype P) has its range in East Asia and Australia and is related to the Asian tropical species P. karka. The two haplotypes have differing salt tolerance, with Haplotype O in areas with the highest salinity and Haplotype P in areas with the lowest. Introgressed hybrids of Haplotype P with P. karka, and F1 hybrids with Haplotype O, have higher salt tolerance than Haplotype P. Phylogenetic diversity appears as the factor that better explains population structure and salinity tolerance in these estuaries. Future research may explain whether the two P. australis haplotypes evolved in East Asia, and East Asia is a center of Phragmites diversity, or are introduced and a threat to P. japonicus and P. karka.

Combining peatland rewetting with biomass cropping (paludiculture) is one strategy to remove nutrient surpluses from soil/water and stimulate peat-forming vegetation. This approach was tested in the Massaciuccoli Lake Basin (Tuscany, Italy), a coastal floodplain artificially drained for agricultural purposes since 1930, where land reclamation and continuous cropping have contributed to considerable peat degradation and water eutrophication due to nutrient enrichment of surface waters. An experimental trial was established in spring 2012 with three perennial rhizomatous grasses (PRG) (Phragmites australis, Miscanthus × giganteus, Arundo donax) and two woody species managed as short-rotation coppice (SRC) (Salix alba “Dimitrios”, Populus × canadensis “Oudenberg”), aimed to provide biomass for various bioenergy supply chains. A conventionally cultivated annual crop (maize) was the control. The aim of this study was to compare the sustainability of the proposed paludiculture systems to that of conventional annual crops on the basis of yield and nutrient-removal capability. This two-year field study evaluated yields, nutrient concentrations and uptake (N and P) of the crops. Over the two years, A. donax had the highest mean biomass yield (35 Mg ha−1), N uptake (367 kg ha−1), and P uptake (54 kg ha−1). SRCs had the lowest nutrient uptake in both years. Among grasses, the highest N concentration was recorded in A. donax leaves in 2013 (N: 2.41%), while P concentration was greater in S. alba branches (P: 0.39%). The average aboveground biomass of maize was 17.5 Mg ha−1, while the nutrient uptakes were equal to 194 and 27 kg ha−1 for N and P, respectively. Thus, the performances of paludiculture systems were generally encouraging and could represent an important alternative for restoring and managing former drained peatlands in a suitable product chain.

This chapter describes a period of low air temperatures, darkness or very little light, cold ice, minimum brine volumes, and strongly reduced ice permeability. The first section provides an overview of the physical and optical conditions of this winter ice (3.1). Both snowfall and snowdrift are frequent during winter and an overview of the effects of a thick snow cover on sea ice is provided (3.2). Increased colonization of the sea ice bottom by bacteria and ice algae is initiated in late winter around first light, and an example is given (3.3). Once these microorganisms have colonized the ice the important growth limitations of bacteria and algae are considered (3.4), along with how they are able to adapt to these extreme conditions, and their seasonal species succession (3.5). The purposes of EPS and the functioning of different pigments found in ice algae are described (3.6). This is combined with a description of low light conditions and related photosynthesis (3.7), and exemplified with a case study from Station North, NE Greenland (3.8).

This chapter is a description of the field and laboratory methods that are generally applied in sea ice ecological research. The first section describes sampling techniques and handling of sea ice samples (6.1). Calculations of brine and gas volumes are dealt with in (6.2), and how to measure and calculate optical parameters (6.3). Sampling, handling, and calculation of ice bacterial production are described (6.4), and methods for ice algae biomass spatial distributions are dealt with in (6.5). Measuring photosynthesis and ice algae primary production are described (6.6), and the determination of Chl a content is explained (6.7). The recently developed fluorescence imaging of ice algae distributions and derived photosynthetic parameters are described (6.8). This is followed by a description of the IP25, a substance synthesized by ice algae and applied for mapping sea ice and food web studies (6.9).

This chapter describes the period of development of new ice during autumn freeze-up, different ice types, and development of the brine channels (2.1). Optical properties of young and developing sea ice are described in terms of the transition from open water to bare sea ice, that later can be covered by snow (2.2). The incorporation and scavenging of ice algae, bacteria and meiofauna from the water column during ice growth and freeze-up are then described (2.3). Development of platelet ice, a prominent under-ice feature in Antarctica and recently observed in the Arctic, is described (2.4). The final section describes frost flowers and brine skim development, and the dynamics of the bacteria communities in the frost flowers and brine skim on top of newly formed sea ice (2.5).

This chapter describes the structure of the book and the diverse significance and importance of sea ice. The first section explains how and why the book is structured following the seasonal events governing the abiotic and biotic parameters in sea ice (1.1). The second section places sea ice into a physical and geopolitical perspective with the new and developing international borders in the Arctic Ocean (1.2). Sea ice ecosystems are then compared to other ecosystems (1.3), followed by a section describing the important and global ecological features of sea ice (1.4).

This chapter describes one of the most dynamic and ecological important seasons. The onset of ice melt initiates significant changes in the physical properties of the ice (4.1), and the related biotic processes in the spring/summer sea ice are addressed (4.2). Ice algal spring blooms are described and exemplified with two studies from contrasting Arctic sites (4.3). A Case Study 2 has a focus on effects and consequences for ice algae of increased irradiances at the ice bottom in terms of pigments, fatty acids, and MAAs (4.4). Ice algae bloom dynamics are investigated in a combined model and field study (4.5). Melt ponds termed “windows to the ocean” develop on the surface of the ice with increased light transmittance (4.6). Seeding of the ice or water column below with viable ice algae can initiate ice algae or pelagic blooms, and mechanisms are explored in model and field studies (4.7). Case study 3 show that species of meiofauna graze directly on the ice algae, and that the meiofauna establishes an important ecological component in the sea ice (4.8).

This chapter is a description of the role and importance of sea ice and sea ice biota on large scales and in relation to the effects of climate change. The decrease in summer sea ice extent and thickness are evident and described in (5.1). A Case Study 4 based on our observations in the Fram Strait and the Arctic Ocean illustrates some of the consequences and effects of increased inflow of warm Atlantic water (5.2). The question whether more light in an ice-free water column will increase pelagic primary production in the Arctic Ocean, is addressed with a model (5.3). Sea ice plays an important role in the exchange of CO2 between ocean and atmosphere and the sea ice CO2 pump is described in (5.4).

It is a generally accepted theory that ecological functions are enhanced with increased diversity in plant communities due to species complementarity effects. We tested this theory in a mesocosm study using freshwater submerged plant beds to determine if increasing species number caused overyielding and species complementarity. We applied a maximum of four species in the plant beds corresponding to the typical species number in natural freshwater plant beds. We found no clear effects of species number (1–4) on biomass production and thus no conclusive overyielding and complementarity effect. This may be explained by low species differentiation among the four species in plant traits relevant for resource acquisition in freshwater, or that other species interactions, e.g. allelopathy, were inhibiting overyielding. The existing knowledge on species complementarity in aquatic plant communities is sparse and inconclusive and calls for more research.

To comprehensively assess the effects of ZnO nanoparticles on freshwater decomposition processes under natural sunlight, we conducted an indoor microcosm experiment on Populus nigra L. leaf decomposition with ZnO nanoparticles (5, 10, and 20 mg L-1) under simulated sunlight. A significant and negative relationship between decomposition rate and ZnO nanoparticle concentrations was observed after 30 days of exposure. ZnO nanoparticles significantly inhibited extracellular enzyme activities, dehydrogenase activities and fungal biomass as well as impacting fungal community structures. Additionally, the exposure to ZnO nanoparticles increased microbial antioxidant activities and 5 mg L-1 of ZnO nanoparticles led to the greatest increase. Importantly, the activities of carbon-related enzymes were significantly inhibited by ZnO nanoparticles, but leaf carbon decomposition was stimulated in the microcosms containing 10 and 20 mg L-1 of ZnO nanoparticles, suggesting the possible contribution of ZnO nanoparticles' physicochemical properties under sunlight to leaf decomposition. The information provided here on the effects of different concentrations of ZnO nanoparticles under sunlight will help us to better evaluate the impacts of ZnO nanoparticles on stream functioning.

The condition of New Zealand's remnant wetlands has been documented by landscape-scale assessments such as the Index of Ecological Integrity and Wetland Condition Index. We explored the potential for microscopic aquatic biota (epiphytic diatoms) to provide complementary information about wetland condition using data from 77 lowland sites (mainly palustrine swamps) with circumneutral pH. In the South Island, correspondence between diatoms and wetland indices or water quality was weak. In the North Island, conductivity and total dissolved nitrogen (TDN) together explained 49% of the variance in assemblage composition and several diatom genera were indicative of high or low conductivity, dissolved phosphorus and TDN. Changes in these water quality variables may trigger changes in wetland condition, which are eventually reflected by the landscape-scale indices. Diatoms respond rapidly to water quality changes suggesting potential for diatom indicator taxa to provide early warning of wetland degradation or to track restoration.

Colonization by ice algae at the bottom of the sea ice is important ecologically as these algae are the major carbon source for zooplankton and the Polar food chains from early spring and until ice break-up several months later. At that time, ice algae can seed the water column promoting the pelagic production. We collected a time-series of ice growth, surface roughness, ice algae biomass (Chl-a), photosynthetic performance, primary production, irradiance, species composition, under ice ADCP data, nutrients, and ice algae spatial distribution in Kangerlussuaq, Greenland. A significant increase in biomass, primary production, and photosynthetic performance was observed at the bottom of the first-year sea ice. This colonization was not related to any change in light or nutrient availability, but instead occurred over a few days after which all parameters remained stable and constant. Colonization was concurrent with active ice growth associated with a period of very cold air temperatures as low as minus 35 °C. This new ice growth featured ice crystals and dendrites that significantly increased the surface roughness of the bottom, which facilitated the colonization. The dendrites are about 0.5 mm high and with a similar distance between the crests. The species composition of ice algae was similar in the water below and at the ice bottom, though biomass remained significantly lower in the water, and was dominated by Fragilariopsis oceanica and Navicula vanhoeefi. It is concluded that the colonization of the bottom of the sea ice is solely related to the increase in surface roughness initiated in the growing ice.

Sea level rise and more frequent storm and precipitation events associated with climate change are predicted to increase salinity fluctuations in estuarine and inshore areas, where foundation species such as eelgrass (Zostera marina L.) will be exposed to more frequent salinity changes. Effects of acute hyposalinity exposure on seagrasses remain poorly understood compared to the effects of more prolonged, constant salinity. Here, we examined growth and photo-physiological responses of Z. marina to 5 levels of stable salinity (5, 12 19, 25, 33) and compared effects of prolonged (16 days) versus acute (24 and 48 hours) exposure to hyposalinity (salinity 5 and 12) using fluorescence imaging. We also examined if fluorescence kinetics were affected by age differences across leaves. Growth reached an optimum at salinity 19 and was more affected by hyposalinity than hypersalinity. Rapid reduction from salinity 25 to 5 decreased the maximum quantum yield (Fv/Fm) after just 48 h. In contrast with prolonged exposure, non-photochemical quenching processes were not increased at salinity 5 after 48 h. Young leaves were more susceptible to extreme hyposalinity than older leaves (e.g., lower photosynthetic quantum yield), which emphasizes the importance of considering shoot-scale and within-shoot variations in studies of stress response patterns. Differences between hyposalinity and hypersalinity responses were generally replicated in the literature, but we were not able to detect any differences across studies. Overall, these results suggest that eelgrass is tolerant to large fluctuations in salinity, but sudden extreme reductions may act as a severe co-stressor, and contribute to accumulated stress-exposure effects (chronic or lasting effects).

In constructed wetlands (CWs) with forced aeration and vertical flow, plants can suffer from iron (Fe) deficiency due to Fe immobilization in the gravel substrate as a consequence of the oxic condition. The common reed (Phragmites australis) is the most commonly used plant species in CWs and frequently displays Fe-deficiency symptoms particularly in new-established systems. The aim of this study was therefore to study the Fe-nutrition of P. australis in order to gain knowledge on how Fe-deficiency in P. australis can be alleviated. For this purpose, we grew two genetically distinct phylogeographic groups of P. australis hydroponically with seven different Fe concentrations (0, 0.1, 0.2, 0.5, 1.0, 5.0 and 20.0 mg Fe-EDDHA ([iron (3+) ethylenediamine di (o-hydroxyphenylacetic) acid]) L−1) in a phytotron. Both groups responded strongly to the increasing Fe supply. The belowground biomass allocation ratio, light-saturated photosynthesis rates, chlorophyll content and leaf Fe tissue concentration all significantly increased with increasing Fe availability. Phragmites australis in the 0 mg Fe-EDDHA L−1 treatment suffered strongly from Fe deficiency, and plants in the high 20.0 mg Fe-EDDHA L−1 treatment also had reduced growth and Fe toxicity symptoms. The ‘critical deficiency concentration’ of Fe in leaves of juvenile P. australis was 40–50 mg kg−1 DM, and the ‘critical toxicity concentration’ of Fe in leaves of juvenile P. australis were approximately 150 mg kg−1 DM. Overall the two genetically distinct P. australis groups differed in their ecophysiological traits, and the two groups also responded differently to the different Fe-supply rates which may be the result of adaptations obtained in their native growth habitats. We suggest that the Fe-deficiency in CW systems with unsaturated vertical flow and/or forced aeration can be alleviated by application of a foliar spray containing chelated iron. However, the application rate and frequency should be further studied.

Here we describe the design, performance and field tests of a lightweight (13.1 kg), low-cost (15.000 USD), and portable remotely operated vehicle (ROV) of dimensions 55 x 43 x 34 cm (L x H x W), with a new optical based positioning system. The ROV is designed for deployments and measurements of the irradiance field at a short distance below sea ice bottom in landfast level sea ice at calm under ice conditions. It is equipped with two cameras (front and rear) for optical positioning based on reference poles with LED lights below the ice. A third upward camera is for guiding during deployment and positioning. The ROV is equipped with spacer poles to maintain a constant distance between ROV with onboard optical sensors and bottom of the ice. All pre-tests of housing, thrusters, optical positioning, and ROV maneuverability were carried out in freshwater basins prior to field trials and tests. These were conducted at Kangerlussuaq, West Greenland on landfast first-year 79-80 cm thick ice with a variable (1-12 cm) snow cover in March 2016. The ROV was easily deployed through a hole (75 x 50 cm) in the ice and easy to maneuver below the ice. Test of positioning system showed an average deviation of 28 +/- 5 cm between optically based position and actual position with an average offset from center line of 16 +/- 5 cm. The ROV was applied for measuring the under-ice irradiance field and results demonstrated a solid negative correlation between snow depth and PAR transmittance. We derived a Normalized Differences Index (NDI) for snow depths: NDIsnow (depth) = [E(610 nm) - E(490 nm)]/[E(610 nm) + E(490 nm)] with minimum attenuation at 490 nm and maximum at 610 nm. It is discussed that the correlations for both PAR transmittance and the NDI with snow depths are due to a combination of a constant distance between optical sensor and ice bottom, and accurate positioning. A test showed that the wakes of thrusters removed parts of the ice algae biomass, but the study demonstrates the applicability of this ROV design for measurements of the under-ice irradiance field below landfast sea ice with a new optical based positioning system.

The estuary is dominated by sea ice and snow cover from winter to spring, and a highly turbid meltwater plume during summer. The aims were to quantify the variability in optical conditions, inorganic nutrients, and primary production between these two extremes, and identify the drivers of variability. Data were obtained during a summer cruise along a transect in the estuary in August 2007, and a spring campaign on the ice in March 2011. The study comprises conductivity, temperature, and depth (CTD), K-d (PAR), K-d (A), PAR transmittance, photic depth, chl-a, nutrients (NO3, NO2, NH3 , PO4, and SiO2), primary production, and sediment concentrations. PAR transmittance varied between 5% below snow and ice and 85% in clear water with 44% in turbid meltwater. Primary production rates were similar below the ice in March (76.8 mg C m(-2) d(-1)) and in the highly turbid meltwater in August (94.8 mg C m(-2) d(-1)), but higher (246.6 mg C m(-2) d(-1)) at the mouth of the fjord. Meltwater inflow was the main driver of variability during summer and the snow and sea ice during spring. Under-ice primary production will increase three-fold with less snow on the sea ice, and the higher meltwater turbidity with increased melting of glacial ice and runoff will only reduce primary production slightly.

Aerenchymatous plants can affect methane (CH4) emissions from wetland soils differently, and there is a need to understand specifically under which conditions plants enhance or attenuate CH4 emissions. We used a mesocosm set-up to assess the interactive effect of three water table positions (0 cm, −10 cm and −20 cm) and the presence or absence of Juncus effusus L on in vitro soil methanogenesis and methane emissions. Soil methanogenesis and CH4 emission rates were significantly affected by water table position and vegetation, and the effect of vegetation depended on the water table position. At high water tables (−10 cm and 0 cm) soil methanogenesis and CH4 emissions were high and not significantly affected by vegetation, whereas at the low water table (−20 cm), methanogenesis and CH4 emission rates were lower in unvegetated soils than in soils with J. effusus. Methane emissions from organic wetland soils at low water tables may be enhanced by J. effusus because of increased methanogenesis and because CH4 enters the roots in the deeper anaerobic layers and are transported through the aerenchymatous tissue of the plants to the atmosphere bypassing the methanotrophic upper layers of the soils.

A wetland condition index (WCI) has been developed for state of the environment monitoring and reporting in New Zealand's terrestrial wetlands. The WCI is a semiquantitative metric comprising five ecological indicators based on the major threats and stressors known to degrade wetlands. These are compared and scored against an assumed natural or reference state set at before European settlement, c.1840. The indicators are (1) hydrological integrity, (2) physicochemical parameters, (3) ecosystem intactness, (4) browsing, predation, and harvesting (a measure of introduced animal and human impacts), and (5) dominance of native plants. The WCI is out of a maximum of 25; the higher the score, the better the ecological condition. It is derived from a process involving wetland classification, mapping and delineation of vegetation types, field reconnaissance, ground-truthing, establishing representative plots, and collection of data to facilitate informed assessment of the indicators. The WCI can be used to compare changes at different levels and scales, for example, within an individual wetland or across a wetland type in a watershed, region, or nationwide to gauge the effectiveness of policies, rules, and other legislation. In recent years, the system has been refined to cater to changes in monitoring and reporting requirements. It was also the basis for the development of community-based and additional monitoring systems.

The effects of inorganic nitrogen (N) forms (NH 4 + , NO 3 − or both) at equimolar (0.5 mM) concentrations on growth, biomass allocation, photosynthesis, nitrate reductase activity (NRA) and N uptake rates of Arundo donax were investigated in hydroponic culture. Plants supplied with NH 4 + , or NH 4 NO 3 had significantly higher above-ground biomass, leaf length, shoot number and shoot production rates than NO 3 − fed plants, whereas the relative growth rates, below-ground biomass, and other plant morphological parameters were indifferent to N nutrition. Leaf photosynthetic pigment concentrations and leaf specific area of NO 3 − −fed plants were lower than those of plants grown on NH 4 + , or NH 4 NO 3 . In addition, NH 4 + and NH 4 NO 3 fed plants had higher light-saturated rate of photosynthesis and stomatal conductance than NO 3 − fed plants and there were no differences in leaf dark respiration among N-form treatments. Both leaves and roots of A. donax had NRA, but NRA was much greater in leaves, particularly when plants were fed with NO 3 − . The N uptake rate of A. donax was greatest when supplied as NH 4 NO 3 (1.10 ± 0.34 mg N g −1 root DM h −1 ) although not different from the N uptake rate with NH 4 + alone (0.61 ± 0.08 mg N g −1 root DM h −1 ), whilst NO 3 − uptake velocities were similar among N-form treatments. Our results indicate that although some traits perform better in the presence of NH 4 + , presumably due to lower energetic costs of NH 4 + uptake, A. donax grows well with either NH 4 + or NO 3 − . This reflects its ability to grow well in both wetland and terrestrial soil types, which is an important consideration for its use as a candidate species for paludiculture.

Meltwater ponds are important biodiversity elements in continental Antarctica. Many occupy closed basins and are vulnerable to changes in the balance between water accrual, through melting of ice and snow, and water loss by ablation and evaporation. We use a two-decade long record of ponds on the McMurdo Ice Shelf to assess temporal variability in key limnological variables. Ponds underwent many-fold change in biologically conservative variables, such as conductivity, and changes were similar in ponds from different catchments but of comparable area. In contrast, biologically active variables (pH, inorganic nutrients and planktonic/benthic biomass) are buffered by in-pond processes and show consistency between years and no coherence across catchments. Coherent behaviour across catchments implies an overarching, climatic effect. However, we could identify no signature of summer air temperature or irradiance in pond dynamics, although winter snow deposition may leave a legacy of low conductivity to the following summer. While ponds are clearly affected by climate, our data show that ecosystem responses are complex and highlight the need for system-appropriate, long-term observation if directional environmental change is to be separated from inherent variability in systems that respond to multiple climatic variables and which have significant biological buffering capacity.

Apart from playing a key role in important biochemical reactions, molecular oxygen (O2) and its by-products also have crucial signaling roles in shaping plant developmental programs and environmental responses. Even under normal conditions, sharp O2 gradients can occur within the plant when cellular O2 demand exceeds supply, especially in dense organs such as tubers, seeds and fruits. Spatial and temporal variations in O2 concentrations are important cues for plants to modulate development (van Dongen & Licausi, 2015; Considine et al., 2016). Environmental conditions can also expand the low O2 regions within the plant. For example, excessive rainfall can lead to partial or complete plant submergence resulting in O2 deficiency in the root or the entire plant (Voesenek & Bailey-Serres, 2015). Climate change-associated increases in precipitation events have made flooding a major abiotic stress threatening crop production and food sustainability. This increased flooding and associated crop losses highlight the urgency of understanding plant flooding responses and tolerance mechanisms. Timely manifestation of physiological and morphological changes triggering developmental adjustments or flooding survival strategies requires accurate sensing of O2 levels. Despite progress in understanding how plants sense and respond to changes in intracellular O2 concentrations (van Dongen & Licausi, 2015), several questions remain unanswered due to a lack of high resolution tools to accurately and noninvasively monitor (sub)cellular O2 concentrations. In the absence of such tools, it is therefore critical for researchers in the field to be aware of how experimental conditions can influence plant O2 levels, and thus on the importance of accurately reporting specific experimental details. This also requires a consensus on the definition of frequently used terms. At the 15th New Phytologist Workshop on Flooding stress (Voesenek et al., 2016), community members discussed and agreed on unified nomenclature and standard norms for low O2 and flooding stress research. This consensus on terminology and experimental guidelines is presented here. We expect that these norms will facilitate more effective interpretation, comparison and reproducibility of research in this field. We also highlight the current challenges in noninvasively monitoring and measuring O2 concentrations in plant cells, outlining the technologies currently available, their strengths and drawbacks, and their suitability for use in flooding and low O2 research.