Eutrophic Wetland Research Articles

Linking fish bioturbation to life history in a eutrophic wetland: An analysis of fish contributions to internal nutrient loading

Abstract Bioturbation (sediment disturbance by animal actions) effects on nutrient cycling and nutrient levels in surface waters are difficult to quantify, in part because the diversity and magnitude of species‐specific influences are poorly understood. These influences may have consequences for the management of the trophic state of freshwater ecosystems. Fish cause bioturbation in freshwater and marine ecosystems by digging in benthic sediments, manipulating periphyton mats while searching for prey and scraping hard substrates while feeding. We used experimental enclosures (2.25 m2) to quantify bioturbation‐mediated phosphorus (P) and nitrogen (N) regeneration from sediment by three species of fish that differ in interactions with the benthos (largemouth bass, Micropterus salmoides; tilapia, Oreochromis spp.; and sailfin catfish, Pterogoplichthys spp.) in shallow eutrophic wetlands in Southern Florida. Tilapia are omnivores that include detritus in their diet (winnowing or ingesting sediments) and dig nests in soft sediments year round, sailfin catfish actively burrow into substrate and consume detritus (digging and ingesting sediments), and largemouth bass are piscivores that do not routinely interact with the benthos when feeding but may dig nests in soft sediment in spawning season (January–April). We quantified the amount of suspended flocculent organic matter and changes in water column nutrients (total phosphorus [TP] and total nitrogen [TN]) in 2‐week trials for each species and estimated the portion of nutrient increases relative to fishless controls that could be attributed to bioturbation‐mediated internal nutrient loading through suspension of organic matter (as opposed to excretion or other sources of nutrient loading). Water column nutrient concentrations increased with increasing biomass for all species, but the bioturbation contribution differed by species. Largemouth bass increased water column nutrient concentrations (TP: 86% and TN: 5% relative to controls) but did not influence water column suspended particulate matter through bioturbation of sediment. Tilapia increased water column nutrients a modest amount (TP: 8%; TN: 15%), of which a small portion was attributed to bioturbation (c. 18% of TP). Sailfin catfish raised water column nutrients substantially (TP: 105%; TN: 46%) and up to 100% of the increased TP was attributed to bioturbation. Sailfin catfish also suppressed algal growth and TP accumulation on the sides of the enclosures and reduced nutrient concentrations of the flocculent sediments. Our results were consistent with our hypothesis that behaviour and foraging traits affect bioturbation contributions to nutrient loading. The results also demonstrated that species with similar net effects like largemouth bass and sailfin catfish, added nutrients via different mechanisms (i.e. excretion vs. bioturbation). Considering the feeding strategies and interactions with the substrate of common fish species may assist managers in meeting nutrient reduction goals for eutrophic wetlands and managed freshwater systems.

Rhizosphere-Associated Anammox Bacterial Diversity and Abundance of Nitrogen Cycle-Related Functional Genes of Emergent Macrophytes in Eutrophic Wetlands.

Rhizospheric microbial community of emergent macrophytes plays an important role in nitrogen removal, especially in the eutrophic wetlands. The objective of this study was to identify the differences in anammox bacterial community composition among different emergent macrophytes and investigate revealed the the main factors affecting on the composition, diversity, and abundance of anammox bacterial community. Results showed that the composition, diversity, and abundance of the anammox community were significantly different between the vegetated sediments of three emergent macrophytes and unvegetated sediment. The composition of the anammox bacterial community was different in the vegetated sediments of different emergent macrophytes. Also, the abundance of nitrogen cycle-related functional genes in the vegetated sediments was found to be higher than that in the unvegetated sediment. Canonical correspondence analysis (CCA) and structural equation models analysis (SEM) showed that salinity and pH were the main environmental factors influencing the composition and diversity of the anammox bacterial community and NO2--N indirectly affected anammox bacterial community diversity by affecting TOC. nirK-type denitrifying bacteria abundance had significant effects on the bacterial community composition, diversity, and abundance of anammox bacteria. The community composition of anammox bacteria varies with emergent macrophyte species. The rhizosphere of emergent macrophytes provides a favorable environment and promotes the growth of nitrogen cycling-related microorganisms that likely accelerate nitrogen removal in eutrophic wetlands.

Whole genome sequence of denitrifying bacterium Stutzerimonas stutzeri strain NGHE31, collected from an eutrophic wetland in Sunamganj, Bangladesh, following the 2017 flash floods.

Here, we report the whole genome sequence of Stutzerimonas stutzeri strain NGHE31, isolated from Dekhar Haor, following the 2017 flash flood that resulted in mass die-offs of local wildlife. The predicted genome size is 4,434,670 bp, with 63.97% GC content, 4,035 coding sequences, 3 rRNAs, and 50 tRNAs.

Diversity and Seasonal Variation of Fish Assemblages of Dingapota Haor an Eutrophic Wetland of Northeastern Bangladesh

Diversity and Seasonal Variation of Fish Assemblages of Dingapota Haor an Eutrophic Wetland of Northeastern Bangladesh

Macrophyte growth forms and hydrological connectivity affect greenhouse gas concentration in small eutrophic wetlands

In eutrophic freshwater ecosystems, submerged macrophyte communities are replaced by phytoplankton or free-floating plants. In isolated wetlands, vegetation shift occurs over short time scales and leads to water deoxygenation and chemically reduced sediments, conditions that favor the generation, accumulation and degassing of greenhouse gases (GHGs, i.e. CH4, CO2 and N2O) to the atmosphere. However, the relationship between primary producer’s growth forms, hydrological connectivity and GHGs concentration is poorly studied in the literature. A set of 18 freshwater wetlands including isolated and river-connected oxbow lakes, marshes and ponds with different vegetation growth forms was therefore monitored monthly on the annual scale. Potential GHGs diffusive fluxes towards the atmosphere were calculated and compared with direct measurements reported in peer-reviewed papers within a meta-analysis. Our results demonstrate a strong link between the colonization of free-floating plants and the onset of hypoxic conditions and accumulation of dissolved methane. Methane and carbon dioxide concentration peaked in late summer, when floating-leaved and free-floating vegetation covered 100% of the water surface. Carbon dioxide accumulation was particularly evident at hydrological connected wetlands, where nitrate pollution was likely responsible for the concomitant increment of dissolved nitrous oxide. As an increasing number of studies focuses on unravelling environmental drivers of GHGs emission from small lakes and ponds, we encourage to systematically consider the vegetation growth forms and the hydrological connectivity as major drivers of GHGs accumulation and evasion rates.

Carlson's Trophic State Index for the Assessment of Trophic state of Phewa, Begnas and Rupa Lakes in Kaski district, Nepal

Eutrophication of wetlands has been considered as a global level environmental problem due to wide range of environmental impacts caused by it. All the lake bodies are subjected to natural eutrophication process but anthropogenic activities like excessive utilization of inorganic fertilizers containing phosphorus and nitrogen in the farmlands which ultimately reach to water bodies through runoff during rainfall further maximizes the eutrophication. The research was conducted to find the trophic state of Lake Phewa, Lake Begnas and Lake Rupa which are three major lakes of Lake Clusters of Pokhara Valley, a Ramsar listed wetland from mid-hills of Nepal. Trophic state of lakes were classified on the basis of Carlson’s Trophic State Index. This index was calculated with the measurement of Secchi depth, Chlorophyll-a, and Total Phosphorus using standard methods. Study revealed that all three lakes were mesotrophic in both pre-monsoon and monsoon season. Lake Rupa had the highest Carlson Trophic State Index (CTSI) and Lake Begnas had lowest CTSI in both the season. Development of lake from oligotrophic to eutrophic state is a natural and gradual process and hence these lakes have increased chances of being eutrophic naturally along with natural process being crucially altered by cultural eutrophication which shortens the life expectancy of the affected aquatic body. Suitable conservation measures are needed to reduce organic load from lake to prevent from being further degraded.

Extensive Carbon Contribution of Inundated Terrestrial Plants to Zooplankton Biomass in a Eutrophic Lake.

Organic carbon derived from terrestrial plants contributes to aquatic consumers, e.g., zooplankton in lakes. The degree of the contribution depends on the availability of terrestrial organic carbon in lake organic pool and the transfer efficiency of the carbon. Terrestrial organic carbon is poor-quality food for zooplankton with a mismatch of nutrition content and was incorporated to zooplankton with much lower efficiency than phytoplankton. Contributions of terrestrial carbon to zooplankton generally decrease with an increase in phytoplankton production, indicating a preferential incorporation of phytoplankton in previous investigations. However, in eutrophic lakes, the dominating cyanobacteria were of poor quality and incorporated to consumers inefficiently too. In that case, zooplankton in eutrophic wetlands, where cyanobacteria dominate the phytoplankton production and massive terrestrial plants are inundated, may not preferentially incorporate poor food-quality phytoplankton resource to their biomass. Therefore, we hypothesize that carbon contributions of terrestrial vegetation to zooplankton and to lake particulate organic pool should be similar in such aquatic ecosystems. We tested this hypothesis by sampling zooplankton and carbon sources in Ming Lake (Jinan University Campus, southern China) which was overgrown by terrestrial plants after drying and re-flooded. After 60days of observations at weekly (or biweekly) intervals, applying stable carbon (13C), nitrogen (15N), and hydrogen (2H) isotopic analysis and a stable isotope mixing model, we estimated the occurrence of extensive carbon contribution (≥ 50%) of flooded terrestrial plants to cladocerans and copepods. Contribution of inundated terrestrial plants to cladocerans was similar to that to lake particulate organic pool. Thus, our study quantified the role of terrestrial carbon in eutrophic wetlands, enhancing our understanding of cross-ecosystem interactions in food webs with an emphasis on the resource quality.

Nutrient Remediation Efficiency of the Sedge Plant (Cyperus alopecuroides Rottb.) to Restore Eutrophic Freshwater Ecosystems

The current study investigated the nutrients removal efficiency of the sedge macrophyte Cyperus alopecuroides to treat water eutrophication, besides evaluating the recycling possibility of the harvested material. Samples of sediment, water, and plant tissues were taken seasonally from six polluted and three unpolluted locations for this investigation. The growth properties of C. alopecuroides showed remarkable seasonal differences in plant density and biomass, with the maximum values (7.1 individual/m2 and 889.6 g/m2, respectively) obtained during summer and the minimum (4.1 individual/m2 and 547.2 g/m2, respectively) in winter. In polluted locations, the above-ground tissues had an efficiency to remove more contents of N and P (11.9 and 3.8 g/m2, respectively) than in unpolluted ones (7.1 and 3.4 g/m2, respectively). The high-nutrient standing stock of C. alopecuroides supports its potential use for nutrient removal from eutrophic wetlands. The tissues of C. alopecuroides had the maximum nutrients removal efficiency to remediate great amounts of Na, K, and N in summer, and Ca, P, and Mg in spring. Above- and below-ground parts of C. alopecuroides from unpolluted locations can be considered as a rough forage for beef cattle, dairy cattle, goats, and sheep. The present study indicated the potential of C. alopecuroides in restoring eutrophic freshwater ecosystems, and, thus, it can be used in similar habitats worldwide.

Spatiotemporal Evaluation of Eutrophication State in The Hammar Marsh Using A Satellite-Based Model

Water pollution is now a major threat to the existence of living beings. Accordingly, Water quality monitoring is an important activity toward restoring water quality. As wetland eutrophication is one of the essential ecosystem elements, devastation of this element is a significant issue. The Trophic State Index (TSI) provides information about trophic condition of water bodies. This paper aims to conduct spatiotemporal monitoring for the eutrophication of the west part of Al-Hammar Marsh for the period 2013-2020. To this end, a satellite-based TSI computation model was developed and implemented by using a series of OLI Landsat satellite images. The results showed that there was no improvement in the eutrophication state in the marsh, the percentage of the low class of TSI decreased in 2015 and 2018 to 7.9% and 2.6% and increased in 2017 and 2020 to 39.8%, and 56.3%. In general, the TSI was in the poor class in all the considered periods. Fluctuation of quantity and quality of the inflow prevents restoring the eutrophication of the marsh because this process requires stability in the levels of inundation above the critical limits for the water depth and periods. Therefore, it is necessary to find suitable alternatives to provide water drainage in quantities and quality that ensure the sustainability of the marsh ecosystem.

How Waterlogged Conditions Influence the Nitrogen Dynamics in a Soil–Water–Plant System: Implications for Wetland Restoration

Growing populations and industrialization have led to increased nitrogen (N) loads in wetland ecosystems. A micro-constructed wetland planted with Lythrum salicaria L. to treat artificial wastewater was used to investigate the short-term variations in the plant biomass and dynamics of total nitrogen (TN) content. Our results showed that the biomass of Lythrum salicaria L. rapidly increased during the experiment due to their extensive root system and vigorous spread, and waterlogged conditions had little effect on the relationship between biomass and the TN content in soil and effluent. Under different waterlogged conditions, the TN removal rates in the water were all greater than 60%, providing a reference for the waterlogged conditions used in wetland eutrophication restoration.

The contribution of sediment desiccation and rewetting process to eutrophication in the presence and absence of emergent macrophytes.

The purpose of current study was to investigate the effects of sediment desiccation on nutrient dynamics and eutrophication in wetlands during the presence or absence of wiry and sturdy rooted emergent macrophytes, based on the hypothesis that sediment desiccation negatively correlated with plants nutrient uptake abilities and positively with nutrients fluxes at sediment-water interface. Growth of four emergent macrophytes, including two wiry rooted plants, i.e., Alocasia cucullata and Aglaonema commutatum, and two sturdy rooted plants, i.e., Cannabis indica and Acorus calamus, were grown and investigated in dried-rewetted sediments (DS) and constantly wet sediments (WS), respectively, for 6 months. The findings revealed that sediment drying and rewetting process significantly decreased the diffusion of overlying nutrient into sediment and the particle size density, porosity, and nutrients' repository ability in DS treatments, while the sediment bulk density and mineralization of organic macronutrients increased. Compared to WS treatments, the DS treatments impaired plant growth, root biomass, shoot biomass, and stimulated higher fluxes of ammonium nitrogen ([Formula: see text]-N, 0.042-0.081 mg m - 2 d - 1) and phosphate (P[Formula: see text] 0.009-0.030 mg m-2 d-1) at sediment-water interface upon rewetting. The higher internal release of macronutrients and dissolved organic carbon (DOC) from DS led to the higher chlorophyll-a (Chl-a) concentrations (34.47-21.28 to 41.76-33.36 μg L-1) in their water column than in the water column of WS. The wiry rooted plants with higher root biomass displayed lower internal release of [Formula: see text]-N, PO43-P and DOC and water column Chl-a concentrations than the sturdy rooted plants in two sediment types. Root biomass of plants correlated positively with TN (63-87%) and TP (56-78%) removal percentages from WS and DS. These results demonstrated that sediment desiccation process reduced plant growth and enhanced internal loading of nutrients and consequently accelerated eutrophication in these wetlands.

Floodplain wetlands of eastern India in a changing climate: Trophic characterization, ecological status, and implications for fisheries

AbstractIndia is endowed with vast floodplain wetland resources (0.5 million ha), which provide both livelihood and nutritional security to much of the rural populace. These biologically sensitive ecosystems are threatened by a range of anthropogenic and climatic factors. Assessment of their ecological vulnerability, and of the environmental threats that they face, is essential both in evaluating the health of these ecosystems and in developing sustainable management strategies for conservation and fisheries enhancement. In this context, eight wetlands in the Ganga basin were studied for two consecutive years across the seasons and were characterized ecologically based on chlorophyll a, primary productivity, and trophic state index. A warming temperature (+0.20 – +0.47 °C) and a decreasing total annual rainfall (257–580 mm) have been observed along the Ganga basin in the last three decades. The chlorophyll a (mean ± S.E.) content of the water varied from 4.08 ± 1.04 to 38.0 ± 14.11 µg l-1. The high primary productivity, gross primary productivity/plankton respiration ratio and trophic state index correlated positively with the high fish yield in the wetlands. Analysis of data based on Carlson's method revealed five wetlands in the eutrophic category, whereas based on Lamparelli's method, two wetlands fall into the eutrophic category. The Lamparelli TSI value ranged from 54.1 in Majharia to 65.8 in Kararia among the wetlands. The Bishnupur wetland in West Bengal and Kararia wetland in Bihar were found to be eutrophic due to cascading sewage incursion from nearby towns. These altered ecosystems with high TSI values were prudently exploited by selecting suitable fish species for high fish production, and a fish yield of 1200 kg ha-1 yr-1 was achieved in Bishnupur. The study revealed that eutrophic wetlands can be strategically managed for maintaining both ecosystem services and fish production. Careful selection of suitable fish species and stocking rate is crucial. The planned disposal and treatment of sewage is recommended to maintain the ecological health of floodplain wetlands for sustainable fisheries management in the context of a changing climate.

Diversity of active anaerobic ammonium oxidation (ANAMMOX) and nirK-type denitrifying bacteria in macrophyte roots in a eutrophic wetland

Wetland eutrophication is a global ecological problem. Anaerobic oxidation of ammonium (ANAMMOX) and denitrification are the two major pathways of nitrogen removal in wetlands. However, little is known about the associated bacteria that are present around emergent macrophytes and their transcriptional activities. Here, we examine the transcriptional activity of bacteria that perform ANAMMOX and denitrification in the roots and vegetated sediments of three emergent macrophytes and in unvegetated sediment from a eutrophic wetland. Roots and vegetated sediments of three emergent macrophytes (Phragmites australis, Typha angustifolia, and Scirpus triqueter) and unvegetated sediment were collected from Wuliangsuhai wetland, China. The community structure and transcriptional activity of ANAMMOX and denitrifying bacteria were examined at the DNA and RNA levels. Additionally, the sediment physicochemical properties were determined. ANAMMOX (hzsB) and denitrifying bacteria (nirK, nirS, and nirSII) were detected in all sediments and roots at the DNA level. However, at the RNA level, root-associated ANAMMOX bacteria, including Candidatus Jettenia and Candidatus Brocadia, were detected only in the roots of P. australis. In contrast, nirK-carrying active denitrifiers, such as uncultured bacteria, Sinorhizobium, Rhizobiales, Mesorhizobium, Rhizobium, Devosia, and Bosea (all Rhizobiales), were detected in the roots of T. angustifolia and S. triqueter. The reduction of nitrogen concentration in the sediments of the vegetation zone was probably associated with active ANAMMOX bacteria and denitrifiers. Active root-associated ANAMMOX bacteria and nirK-type denitrifiers were influenced by plant species, and they likely contribute to nitrogen removal in eutrophic wetlands.

A Case Study of the Effects of Management Interventions on the Phosphorus Dynamics at a Coastal, Eutrophic, Caribbean lagoon (Laguna Cartagena, Puerto Rico)

Laguna Cartagena is a coastal, eutrophic, shallow lake and freshwater wetland in southwestern Puerto Rico, managed by the US Fish and Wildlife Service. This ecosystem has been impacted by phosphorus loading from adjacent agricultural areas since the 1950s, causing eutrophication and deteriorating wildlife habitats. Herein, we describe phosphorus input and export during September 2010–September 2011 (Phase One) and October 2013–November 2014 (Phase Two). These two phases bracket a period of intensified management interventions including excavation and removal of sediment and vegetation, draining, and burning during the summers of 2012 and 2013. Results indicate that Laguna Cartagena retains a phosphorus (sink) in its sediments, and exhibits nutrient-releasing events (source, mainly total phosphorus) to the lagoon water column, which are associated with rainfall and rising water levels. External factors including water level fluctuations and rainfall influenced phosphorus export during Phase One, but after management interventions (Phase Two), internal processes influenced sink/source dynamics, releasing elevated phosphorus concentrations to the water column. When exposed sediments were re-flooded, phosphorus concentrations to the water column increased, releasing elevated P concentrations downstream to an estuarine wetlands area and the Caribbean Sea. Herein we offer management recommendations to optimize wildlife habitat without elevating phosphorus concentrations.

Nutrient sequestration potential of water primrose Ludwigia stolinefera (Guill. & Perr.) P.H. Raven: A strategy for restoring wetland eutrophication.

The current work investigates the capacity of the water primrose (Ludwigia stolinefera) to sequester inorganic and organic nutrients in its biomass to restore eutrophic wetlands, besides its nutritive quality as fodder for animals. The nutrient elements and nutritive value of the water primrose were assessed seasonally in polluted and unpolluted watercourses. The water primrose plants’ highest biomass was attained during summer; then, it was significantly reduced till it reached its lowest value during winter. In the polluted canal, the plant root and shoot accumulated higher contents of all nutrient elements (except Na and Mg) rather than in the unpolluted Nile. They accumulated most investigated nutrients in the growing season during summer. The shoots accumulated higher contents of N, P, Ca, and Mg than the root, which accumulated higher concentrations of Na and K. Therefore, summer season is the ideal time to harvest water primrose for removing the maximum nutrients for restoring eutrophic watercourses. The aboveground tissues had the highest values of ether extract (EE) during spring and the highest crude fibers (CF) and total proteins (TP) during summer. In contrast, the belowground tissues had the lowest EE, CF, and TP during winter. In spring, autumn, and winter seasons, the protein content in the grazeable parts (shoots) of the water primrose was within the range, while in summer, it was higher than the minimum requirement for the maintenance of animals. There was a decrease in crude fibers and total proteins, while an increase in soluble carbohydrates content in the below- and above-ground tissues of water primrose under pollution stress. The total protein, lipids, and crude fibers of the aboveground parts of water primrose support this plant as a rough forage.

Selecting submerged macrophyte species for replanting in Mediterranean eutrophic wetlands

The criteria to select submerged plant species for restoration still need further evaluations for a better understanding of their suitability prior to undertaking large plantings which represent a large effort in terms of economical and human resources. In this study, previously to the restoration of a eutrophic area (Tancat de la Pipa) within the Albufera de València Natural Park, the growth of three submerged plants (Ceratophyllum demersum, Myriophyllum spicatum and Stuckenia pectinata), an amphibious species (Ranunculus sceleratus), and three charophytes species (Chara vulgaris, Tolypella glomerata and Nitella hyalina) has been evaluated under controlled laboratory conditions in order to rank their overall performance, based on their growth traits (total height reached, production of roots, etc.). The ranking was in the order of M. spicatum ~ S. pectinata > C. demersum and within the charophytes C. vulgaris > T. glomerata > N. hyalina. Moreover, considering the relationships of these species with other biotic factors (bird, fish and crayfish disturbance and herbivory) which can prevent the success of the revegetation, we propose starting the planting with M. spicatum, S. pectinata, R. sceleratus and C. vulgaris, which are available, are very easy to cultivate by vegetative reproduction from shoot tips and small specimens, have appropriate growth traits and certain degree of resistance to biotic factors. The other species (C. demersum, N. hyalina and T. glomerata) could be used subsequently once a suitable cover of submerged vegetation is settled in the area to enhance biodiversity, trying to reach the diversity which existed in the past in that area. Hence, the structural and functional complexity of the system under restoration might be achieved.

Seasonal potential of Phragmites australis in nutrient removal to eliminate the eutrophication in Lake Burullus, Egypt

The present study was conducted to investigate the potential of the emergent macrophytes Phragmites australis to remediate nutrients and restore an eutrophic wetland (Lake Burullus, Egypt). The plant was sampled monthly for one year from 6 sites distributed equally along the northern and southern parts of this lake. Monthly significant variation in all investigated sediment and water nutrients for the northern and southern sites was recorded. The biomass of P. australis in the southern sites was greater than that of the northern sites; in addition, the above-ground biomass was greater than the below-ground biomass. The above-ground biomass increased from February until it reached its maximum during August and then decreased again. Likewise, the highest nutrient concentrations in the different tissues were recorded at the beginning of the growing season during winter and early spring and then gradually decreased with increasing plant biomass. Moreover, the nutrient content (g/m2) increased from the early growing season (February) and reached its peak during April–August and then decreased. Based on our results, P. australis could be used for the extraction of nutrients to reduce the eutrophication in Lake Burullus, if the above-ground biomass is harvested at its maximum value in August, as was the case regarding the maximum content of most nutrients.

Diversity of active root-associated methanotrophs of\xa0three\xa0emergent\xa0plants in\xa0a eutrophic wetland in northern China

Root-associated aerobic methanotrophs play an important role in regulating methane emissions from the wetlands. However, the influences of the plant genotype on root-associated methanotrophic structures, especially on active flora, remain poorly understood. Transcription of the pmoA gene, encoding particulate methane monooxygenase in methanotrophs, was analyzed by reverse transcription PCR (RT-PCR) of mRNA isolated from root samples of three emergent macrophytes, including Phragmites australis, Typha angustifolia, and Schoenoplectus triqueter (syn. Scirpus triqueter L.) from a eutrophic wetland. High-throughput sequencing of pmoA based on DNA and cDNA was used to analyze the methanotrophic community. Sequencing of cDNA pmoA amplicons confirmed that the structure of active methanotrophic was not always consistent with DNA. A type I methanotroph, Methylomonas, was the most active group in P. australis, whereas Methylocystis, a type II methanotroph, was the dominant group in S. triqueter. In T. angustifolia, these two types of methanotroph existed in similar proportions. However, at the DNA level, Methylomonas was predominant in the roots of all three plants. In addition, vegetation type could have a profound impact on root-associated methanotrophic community at both DNA and cDNA levels. These results indicate that members of the genera Methylomonas (type I) and Methylocystis (type II) can significantly contribute to aerobic methane oxidation in a eutrophic wetland.

Enrichment of Type I Methanotrophs with <i>nirS</i> Genes of Three Emergent Macrophytes in a Eutrophic Wetland in China

The pmoA gene, encoding particulate methane monooxygenase in methanotrophs, and nirS and nirK genes, encoding bacterial nitrite reductases, were examined in the root and rhizosphere sediment of three common emergent macrophytes (Phragmites australis, Typha angustifolia, and Scirpus triqueter) and unvegetated sediment from eutrophic Wuliangsuhai Lake in China. Sequencing analyses indicated that 334 out of 351 cloned pmoA sequences were phylogenetically the most closely related to type I methanotrophs (Gammaproteobacteria), and Methylomonas denitrificans-like organisms accounted for 44.4% of the total community. In addition, 244 out of 250 cloned nirS gene sequences belonged to type I methanotrophs, and 31.2% of nirS genes were the most closely related to paddy rice soil clone SP-2-12 in Methylomonas of the total community. Three genera of type I methanotrophs, Methylomonas, Methylobacter, and Methylovulum, were common in both pmoA and nirS clone libraries in each sample. A quantitative PCR (qPCR) analysis demonstrated that the copy numbers of the nirS and nirK genes were significantly higher in rhizosphere sediments than in unvegetated sediments in P. australis and T. angustifolia plants. In the same sample, the nirS gene copy number was significantly higher than that of nirK. Furthermore, type I methanotrophs were localized in the root tissues according to catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH). Thus, nirS-carrying type I methanotrophs were enriched in macrophyte root and rhizosphere sediment and are expected to play important roles in carbon/nitrogen cycles in a eutrophic wetland.

Alien predation in wetlands – the Raccoon Dog and water birds breeding success

Alien predators are known to potentially strongly affect their prey populations. We studied the impact of raccoon dogs (Nyctereutes procyonoides) on waterbird breeding success in eight semi-urban wetlands in Finland. We manipulated raccoon dog density in two wetlands by removing individuals (2002 protection year, 2003 and 2004 removal years). We additionally performed nest predation experiments. We monitored raccoon dog density, estimated hunting bag size and observed waterbird breeding success. Our hypothesis predicts that the omnivorous raccoon dog plays a role in waterbird breeding success by depredating nests. Our experiments shown that the raccoon dog hunting bag in eutrophic wetlands may be large, as we removed 8.6–20.0 animals per km2. Both our nest predation experiment and field data indicated that raccoon dogs affect the breeding success of waterbirds. We found a significant relationship between raccoon dog density index and predation rate of the artificial nests, but not between red fox (Vulpes vulpes) density and predation on artificial nests. We did not find an association between raccoon dog abundance and the breeding success of mallards (Anas platyrhynchos) and great crested grebes (Podiceps cristatus). However, our study shows that birds species with different breeding strategies – e.g. great crested grebe, mute swan (Cygnus olor), mallard, Eurasian wigeon (Mareca penelope), coot (Fulica atra), lapwing (Vanellus vanellus) and marsh harrier (Circus aeruginosus) – when considered together showed higher breeding success both in 2003 and 2004 when compared to breeding success before removal. There was, however, variation in how strongly the species responded to raccoon dog removal. Our results indicate that the removal of alien raccoon dogs can be an important tool in wetland management.
 Keywords: ducks, invasive species, lapwing, nest predation experiment, Nyctereutes procyonoides, predator removal