Microrefuges from drying for invertebrates in a seasonal wetland

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Relationship between the hydrological conditions and the distribution of vegetation communities within the Poyang Lake National Nature Reserve,China

Hydrological characteristics have been recognized as major driving forces for wetland vegetation. The water cycle and hydrological processes of wetland are increasingly influenced by the ongoing climate change and more intensive human activities, which may in turn affect the distribution and structure of vegetation communities. Poyang Lake, located on the south bank of the lower reach of Yangtze River, receives inflows from five tributaries and discharges to the Yangtze River. The unique hydrological conditions of the Poyang Lake wetland create abundant wetland vegetation communities. As a major national hydraulic project, the Three Gorges Dam across the Yangtze River has changed the water regime of Poyang Lake and hence may affect the vegetation distribution. This work aims to investigate the influences of hydrological properties on vegetation structure at broad spatial and temporal scales. Histograms and sensitivity index are used to link the hydrological processes with the vegetation distribution across the Poyang Lake National Nature Reserve. The results show that different vegetation communities react differently to the hydrological conditions. Specifically, certain communities, e.g. Carex and Eremochloa ophiuroides, are able to survive a wide variety of mean water depth and percent time inundated, while others, like Carex–Polygonum criopolitanum, are found to be relatively sensitive to hydrological conditions. It is suggested that this work provides a new insight for evaluating the impact of hydro-engineering projects on vegetation communities and wetland vegetation restoration.     

鄱阳湖南矶湿地优势植物群落及土壤有机质和营养元素分布特征

湿地植物和土壤是承担湿地诸多生态功能的主要基质和载体,相互之间有着强烈的影响。湿地土壤影响植物的种类、数量、生长发育、形态和分布,湿地植物又影响土壤中元素的分布与变化。鄱阳湖湿地的植物和土壤的特征及由他们带来的候鸟栖息地价值都受到他们之间的相互作用以及湖泊水位不同频率和幅度波动的影响。研究鄱阳湖湿地植物和土壤的特征及其形成原因和相互关系。为此,从2010年10月到2011年10月,对鄱阳湖湿地不同水位梯度下分布的芦苇、南荻、苔草、虉草和刚毛荸荠5个优势植物群落中57个定点样方展开了月度植被调查并且对5个不同植物群落下的135个土壤样品进行了实验室分析,研究了鄱阳湖优势植物群落及湿地土壤中有机质、全氮、全磷、全钾含量的分布特征及其相互关系。研究结果表明,鄱阳湖湿地优势植物群落分布特征受湿地土壤元素分布特征、湖面水位波动及植物生长特性和土壤沉积及土壤养分的综合影响,呈现了沿水位和海拔梯度明显的条带状或弧状分布、从湖岸到湖心依次分布为:狗牙根群落、芦苇群落、南荻群落、苔草群落、虉草群落、刚毛荸荠群落,最后是水生植物。同时植物群落的组成和分布特征也随季节性水位涨落的变化而变化;土壤有机质及其他各元素含量特征受植物群落分布、水位波动规律及湿地土壤特性等各种因素的影响,呈现出相对一致的分布规律,在0—20cm土壤层含量较高,20cm层后随土壤深度的增加含量逐渐减小,减小的速度先快后慢直至40cm层后趋于稳定;不同植物群落对土壤有机质、全氮、全磷、全钾的含量及变化具有很大的影响,不同植物群落下同种元素含量差异显著,并且各自随土壤深度和植物群落的变化呈现出层状、带状或弧状富集特征。不同植物群落对土壤养分元素含量影响程度不同,苔草群落对各元素吸收和滞留能力最强、影响最大,刚毛荸荠群落对土壤营养元素影响最弱。湿地植物群落和土壤之间彼此有着强烈的影响,其中植株的重量和土壤的SOC、TN及TP含量有非常显著的负相关关系,与土壤TK含量则有较强的正相关关系,同时,植株的重量和高度与土壤地下水埋深也有微弱的负相关关系。     

Within-lake patterns in depth penetration of emergent vegetation

SUMMARY. 1. Within-lake relations of wave exposure (WE), and substratum softness (cone penetration depth; CPD) and organic content (loss on ignition; LOI), to water depth penetration of the emergent vegetation (DPE) was investigated in seven eutrophic lakes in southern Sweden, ranging in area from 1 to 46km².
2. There was a positive relationship between WE and DPE within lakes. This relationship, however, only occurred for sites with relatively soft substrata, for which CPD and LOI were negatively related to both WE and DPE.
3. Analysis of aerial photographs revealed that expansion of the emergent vegetation towards open water, or recession from open water, was not related to wave exposure or water depth, except in one lake where expansion mainly occurred at high exposures.
4. For relatively static vegetation on soft substrata, regressions with CPD°.⁵ explained 62–88% of the within-lake variation of DPE. These regressions did not differ among lakes. Expanding and recessing vegetation were significantly dislocated towards shallower and deeper water, respectively, than predicted from the regression models for static vegetation.
5. Phragmites australis dominated at the lakeward edge of the emergent vegetation, followed in frequency by Typha angustifolia . More broad-leaved species were generally restricted to shallow water and very soft substrata.
6. The results suggest that changes in the distribution of emergent vegetation in moderately wave exposed eutrophic lakes can be predicted largely from substratum character and water depth.     

Evaluating the ecological performance of wetland restoration in the Yellow River Delta,China

Long-term monitoring is essential to evaluate the effects of wetland restoration projects. A monitoring program before and after restoration has been carried out in the study area located in the Yellow River Delta since 2001. Water quality, soil salinity, soil organic matter, plant community, and bird species were chosen as indicators in this program. During the past seven years, the restored wetland showed increasing efficiency in reducing water pollution levels. Soil quality was constantly improved through salinity reduction and soil organic matter accumulation. The vegetation community quickly re-established after the restoration was initiated in 2002. The restored vegetation communities provide favorable habitat conditions for birds and thirty-seven bird species were observed in October 2007. Based on Canonical Correspondence Analysis (CCA), plant species and vegetation community are mainly influenced by soil salinity and water depth. These indicate that conducting freshwater to the project area is an efficient measure for vegetation restoration. While monitoring results show that the restoration project had positive effects on the wetland ecosystem over the past seven years, two issues remain for future study: (1) the contribution of harvesting vegetation to stabilizing nutrient removal rate and the accumulation of soil organic matter in the soil; and (2) the effects of excessive propagation of Phragmites australis on spatial heterogeneity and plant diversity.     

Restoration of dredged canals in wetlands: a comparison of methods

A comparison of two methods for restoring dredged canals to wetlands was examined at the Jean Lafitte National Historical Park and Preserve’s Barataria Preserve Unit near New Orleans, LA. Both northern and southern canals had the remnant dredged spoil material returned to the canal, but the southern canal had additional sediment pumped in from a nearby lake. The water depth in the southern canal shallowed significantly from 1.2 to 0.4 m following backfilling and sediment addition, while the depth of the northern canal (which received no additional sediment) remained unchanged following backfilling. Neither site had complete soil restoration, but the former spoil areas of the northern canal showed greater restoration than the southern canal. The vegetation on the former spoil areas of the northern canal closely resembled that of the reference marsh, while the former spoil areas of the southern canal had species indicative of spoil banks and other elevated areas. After 3 years wetland vegetation was established on approximately 65% of the former spoil areas at both sites and 20–25% of the open water areas. Sediment addition to the southern canal raised costs by a factor of eight times compared to that of the northern canal. The results of this study document the restoration potential of both methods, but also show that backfilling without supplemental sediment additions can restore abandoned canals at a fraction of the cost of other methods.     

The impact of desiccation of a freshwater marsh (Garcines Nord,Camargue, France) on sediment-water-vegetation interactions

The impact of desiccation on a marsh sediment was studied both in the laboratory and in the field. Changes in the sediment chemistry of a homogenized sediment suspension during desiccation were studied in the laboratory. FeS was oxidized completely. A considerable mineralization of organic phosphate took place, from both the acid soluble organic phosphate fraction and from the residual organic phosphate fraction, but no significant mineralization of organic matter was observed. The o-P formed during the mineralization was recovered partly in the Fe(OOH) ≈P fraction and partly in the CaC₃≈P fraction. An upward flux was found. During spring and summer 1990 the water inlet to a shallow permanent freshwater marsh with a surface of about 1.5 hectares was blocked, in order to desiccate the marsh by evaporation. The sediments initially consisted of a black anoxic organic top layer and a less organic anoxic gray layer. During the desiccation of the sediment a brown oxic surface layer was formed from the black layer and an increase of pH and Eh occurred. Subsequent rainfall made the Eh increase further but caused a decrease in pH indicating an increase in bacterial activity. A progressive oxidation of FeS was observed. An increase in Tot-P in the surface layer and a decrease in the gray and the black layer of the sediment occurred, probably due to a capillary upward flux. A mineralization of organic matter was observed in the two deeper layers. In the upper brown layer this mineralization was less evident, probably because it has been masked by the capillary movement. A net C loss of 40% was calculated to have occurred in the layer 0–40 cm. In the deeper layers a decrease in Tot-N was observed, whereas no important increase occurred in the top layer. Over a sediment layer of 40 cm a N loss of 50% was calculated. C- and N losses occurred simultaneously, suggesting the importance of mineralization as a source of inorg-N for denitrification. The chemical and physical changes in the sediment during desiccation affected layers down to 40 cm. This means that not only the top layer of a sediment but also deeper layers are active in systems of which part of the sediment dries occasionally. Fractionation of the surface sediment phosphate showed an increase of Fe(OOH) ≈ P in the top layer due to the oxidation of FeS to Fe(OOH), enlarging the P-adsorption capacity of the sediment. A mineralization of about 50% of acid soluble organic phosphate occurred. After rainfall, a net increase in residual organic phosphate occured presumably due to an increase of bacterial activity. Drying may therefore be utilized as a tool, in wetland management, to eliminate organic nitrogen and carbon from the sediment. In rice culture, it may be used to make part of the organic nitrogen available to the rice.     

Solute dynamics in a North Brazilian mangrove: the influence of sediment permeability and freshwater input

Although water in mangrove sediments influences nutrient cycling in both, mangrove forest and estuary, little information exists on seasonal and vertical distribution of dissolved organic and inorganic compounds in the sediment column. We studied the influence of sediment texture and chemistry, permeability (K), tides, and rainfall on dissolved organic carbon (DOC) and nitrogen (DON), dissolved inorganic phosphate (DIP) and salinity in creek and sediment waters of a mangrove in Pará, Brazil. Water samples were taken from boreholes and piezometers in the mangrove forest and from an adjacent tidal creek at neap and spring tides, during the dry and rainy season. Forest sediment was analysed for carbon (C), nitrogen (N), salinity and permeability. Clay, C and N decreased with depth. Sediment permeability (K) was lowest (<0.1 m day⁻¹) in the upper, clay-rich and crab-burrow-free mud layer. In the deeper, fine sand strata, K ranged from 0.7 to 1.8 m day⁻¹. Tidal range in the creek was 3.5 and 5.5 m for neap and spring tides, respectively. Salinity, DOC, DON and DIP in creek water were inversely related to tidal height. Piezometer data revealed significant water level changes in deeper, sandy sediment layer, which followed, time-lagged, the tidal fluctuations. In contrast, tide did not affect the water level in the upper sediment due to low permeability. Compared with creek water, sediment water was enriched in DOC, DON and DIP because of organic matter input and mineralization. In deeper layers, solute concentration was most likely affected by sorption processes (DOC and DIP) and reduction reactions (DIP). During the rainy season, DOC and DON in creek and sediment water were higher than in the dry season. DIP appeared invariant to seasonal changes. In the rainy season, salt flushing from surface sediments resulted in higher salinities at intermediate sediment depths, while in the deeper layers salinity was lower due to exchange with water from the tidal creek.     

Physical and chemical characteristics of the sediment in the estuarine region of Cananéia (SP), Brazil

Physical and chemical characteristics of sediment were analyzed at eight sampling areas in the estuarine region of Cananéia (SP), Brazil. The samples were collected in 1995 during four periods; summer, autumn, winter and spring. Total nitrogen and phosphorus concentrations, redox potential, water and organic matter percentage, sand and silt percentage and grain size were determined in six different layers of 20 cm deep columns of sediment. In general, the nutrient concentration and the percentage of organic matter decreased with depth and greater variations were observed in the first centimeter of the samples. Differences in nutrient concentration and organic matter were also observed during the study period. The highest concentrations were recorded during the rainy season (February) as a consequence of an accumulation of organic matter brought into the system by rivers and adjacent flooded areas. In general, the sediments had oxidized characteristics until the 5 or 10 cm depth in areas near the rich coastal vegetation. However, in areas open to the ocean, the entire sediment columns were almost completely oxidized.     

Convective gas flow development and the maximum depths achieved by helophyte vegetation in lakes

Background and Aims

Convective gas flow in helophytes (emergent aquatic plants) is thought to be an important adaptation for the ability to colonize deep water. In this study, the maximum depths achieved by seven helophytes were compared in 17 lakes differing in nutrient enrichment, light attenuation, shoreline exposure and sediment characteristics to establish the importance of convective flow for their ability to form the deepest helophyte vegetation in different environments.

Methods

Convective gas flow development was compared amongst the seven species, and species were allocated to ‘flow absent’, ‘low flow’ and ‘high flow’ categories. Regression tree analysis and quantile regression analysis were used to determine the roles of flow category, lake water quality, light attenuation and shoreline exposure on maximum helophyte depths.

Key Results

Two ‘flow absent’ species were restricted to very shallow water in all lakes and their depths were not affected by any environmental parameters. Three ‘low flow’ and two ‘high flow’ species had wide depth ranges, but ‘high flow’ species formed the deepest vegetation far more frequently than ‘low flow’ species. The ‘low flow’ species formed the deepest vegetation most commonly in oligotrophic lakes where oxygen demands in sediments were low, especially on exposed shorelines. The ‘high flow’ species were almost always those forming the deepest vegetation in eutrophic lakes, with Eleocharis sphacelata predominant when light attenuation was low, and Typha orientalis when light attenuation was high. Depths achieved by all five species with convective flow were limited by shoreline exposure, but T. orientalis was the least exposure-sensitive species.

Conclusions

Development of convective flow appears to be essential for dominance of helophyte species in >0·5 m depth, especially under eutrophic conditions. Exposure, sediment characteristics and light attenuation frequently constrain them to a shallower depth than their flow capacity permits.Key words: Aeration, convective flow, exposure, helophytes, lakes, lakeshore vegetation, light attenuation, redox, regression tree, sediment motion, trophic state, waves     

Bio-energetic data show weak spatial but strong seasonal differences in wetland quality for waders in a Mediterranean migration bottleneck

1. Assessing the quality of wetlands as refuelling areas for migrating waterbirds based on resource distribution patterns is challenging. Resources in wetlands can vary both horizontally and vertically and may be differentially available to different bird species at different times of the year. Therefore, the extent to which wetland quality can be generalised across seasons and for a diversity of birds remains unresolved.
2. Spatiotemporal variation in abundance and quality of macrobenthos as food for migrating waders was studied in a set of wetland areas near a Mediterranean migration bottleneck in the Balkan peninsula, during both spring and autumn migration. Samples were subdivided into different depth layers to differentiate between parts of the sediment that are accessible to different groups of wader species. To quantify food availability and the resulting refuelling capacity in different wetland habitat types, abundance, wet weight, and lipid and protein content of invertebrate taxa were determined for each sample.
3. Invertebrate food availability and quality were markedly higher in spring than in autumn. Given the higher abundance and protein and lipid content of prey in spring, the total energy that could be harvested in spring (3.81 ± 0.79 kJ/m²) was about 7 times higher than in autumn (0.56 ± 0.12 kJ/m²). Most prey were found in the top layer of the sediment (0–22 mm depth), but about a third of the total energy was present in the deepest soil layer that only longer-billed species could reach (55–200 mm depth). Higher quality prey items such as larger-bodied and heavier polychaetes and bivalves were found in the deeper sediment layers.
4. For other taxa, there was no evident vertical pattern of increasing individual body size. Prey abundance differed between certain habitat types but, overall, food availability could not be linked to distinct habitats. In spring, redox potential tended to be higher, while pH, vegetation cover, conductivity, and temperature were lower than in autumn.
5. Different wetland habitat classes used in a conservation framework may provide similar food resources for waders. As a result, linking food availability to habitat classifications is not straightforward. Furthermore, seasonal variation in wetland quality requires a re-evaluation of the importance of wetland areas during spring and autumn migration. Finally, nutritional analyses are essential for determining the capacity of wetlands to support refuelling by migratory waterbirds.

     

Carbon Dioxide Dynamics and Controls in a Deep-water Wetland on the Qinghai-Tibetan Plateau

To initially characterize the dynamics and environmental controls of CO₂, ecosystem CO₂ fluxes were measured for different vegetation zones in a deep-water wetland on the Qinghai-Tibetan Plateau during the growing season of 2002. Four zones of vegetation along a gradient from shallow to deep water were dominated, respectively by the emergent species Carex allivescens V. Krez., Scirpus distigmaticus L., Hippuris vulgaris L., and the submerged species Potamogeton pectinatus L. Gross primary production (GPP), ecosystem respiration (Re), and net ecosystem production (NEP) were markedly different among the vegetation zones, with lower Re and GPP in deeper water. NEP was highest in the Scirpus-dominated zone with moderate water depth, but lowest in the Potamogeton-zone that occupied approximately 75% of the total wetland area. Diurnal variation in CO₂ flux was highly correlated with variation in light intensity and soil temperature. The relationship between CO₂ flux and these environmental variables varied among the vegetation zones. Seasonal CO₂ fluxes, including GPP, Re, and NEP, were strongly correlated with aboveground biomass, which was in turn determined by water depth. In the early growing season, temperature sensitivity (Q₁₀) for Re varied from 6.0 to 8.9 depending on vegetation zone. Q₁₀ decreased in the late growing season. Estimated NEP for the whole deep-water wetland over the growing season was 24 g C m⁻². Our results suggest that water depth is the major environmental control of seasonal variation in CO₂ flux, whereas photosynthetic photon flux density (PPFD) controls diurnal dynamics.     

Wetland Selection by Mallard Broods in Canada's Prairie-Parklands

ABSTRACT Although brood survival has a pronounced effect on population growth in mallards (Anas platyrhynchos), knowledge of brood ecology is more limited than for other vital rates. During 1993–1997 we collected wetland selection data from 210 radiomarked mallard broods on 15 study areas located throughout the Canadian Prairie-Parklands. We used information-theoretic approaches to select the best-approximating model of habitat selection in relation to wetland characteristics. Wetland permanence, cover type, width of flooded emergent vegetation, and interactions between these variables and date, moisture level, and dominant species of emergent vegetation were all important predictors of wetland selection. Mallard broods selected deeper wetlands, especially later in the brood-rearing season. Mallard broods also selected wetlands with large central expanses of open water and wide peripheral zones of flooded emergent cover. These habitat characteristics can most easily be met in landscapes that already contain an abundance and diversity of natural wetland habitats. Where such wetlands are unavailable, restoration or management of deeper wetlands may be necessary to meet the habitat requirements of mallard ducklings.     

Net primary productivity and spatial distribution of vegetation in an alpine wetland,Qinghai-Tibetan Plateau

To initially describe vegetation structure and spatial variation in plant biomass in a typical alpine wetland of the Qinghai-Tibetan Plateau, net primary productivity and vegetation in relationship to environmental factors were investigated. In 2002, the wetland remained flooded to an average water depth of 25 cm during the growing season, from July to mid-September. We mapped the floodline and vegetation distribution using GPS (global positioning system). Coverage of vegetation in the wetland was 100%, and the vegetation was zonally distributed along a water depth gradient, with three emergent plant zones (Hippuris vulgaris-dominated zone, Scirpus distigmaticus-dominated zone, and Carex allivescers-dominated zone) and one submerged plant zone (Potamogeton pectinatus-dominated zone). Both aboveground and belowground biomass varied temporally within and among the vegetation zones. Further, net primary productivity (NPP) as estimated by peak biomass also differed among the vegetation zones; aboveground NPP was highest in the Carex-dominated zone with shallowest water and lowest in the Potamogeton zone with deepest water. The area occupied by each zone was 73.5% for P. pectinatus, 2.6% for H. vulgaris, 20.5% for S. distigmaticus, and 3.4% for C. allivescers. Morphological features in relationship to gas-transport efficiency of the aerial part differed among the emergent plants. Of the three emergent plants, H. vulgaris, which dominated in the deeper water, showed greater morphological adaptability to deep water than the other two emergent plants.     

Plant community,primary productivity,and environmental conditions following wetland re-establishment in the Sacramento-San Joaquin Delta,California

Wetland restoration can mitigate aerobic decomposition of subsided organic soils, as well as re-establish conditions favorable for carbon storage. Rates of carbon storage result from the balance of inputs and losses, both of which are affected by wetland hydrology. We followed the effect of water depth (25 and 55 cm) on the plant community, primary production, and changes in two re-established wetlands in the Sacramento San-Joaquin River Delta, California for 9 years after flooding to determine how relatively small differences in water depth affect carbon storage rates over time. To estimate annual carbon inputs, plant species cover, standing above- and below-ground plant biomass, and annual biomass turnover rates were measured, and allometric biomass models for Schoenoplectus (Scirpus) acutus and Typha spp., the emergent marsh dominants, were developed. As the wetlands developed, environmental factors, including water temperature, depth, and pH were measured. Emergent marsh vegetation colonized the shallow wetland more rapidly than the deeper wetland. This is important to potential carbon storage because emergent marsh vegetation is more productive, and less labile, than submerged and floating vegetation. Primary production of emergent marsh vegetation ranged from 1.3 to 3.2 kg of carbon per square meter annually; and, mid-season standing live biomass represented about half of the annual primary production. Changes in species composition occurred in both submerged and emergent plant communities as the wetlands matured. Water depth, temperature, and pH were lower in areas with emergent marsh vegetation compared to submerged vegetation, all of which, in turn, can affect carbon cycling and storage rates.     

Metal retention and distribution in the sediment of a constructed wetland for industrial wastewater treatment

A free water surface wetland was built in 2002 to treat wastewater from a tool factory containing metals (Cr, Ni, Zn and Fe), nutrients and organic matter. Until 2006, the last reported period, the wetland retained metals and stored them primarily in the bottom sediment and in the biomass of macrophytes secondarily. The aim of this work was to study metal retention and distribution in the sediment of a constructed wetland for industrial wastewater treatment. Total concentrations and fractions (exchangeable, carbonate-bound, Fe-Mn oxides-bound, organic matter-bound and residual) of metals in sediment were analyzed in this treatment wetland, in order to estimate the fate of metals over time. Metal concentrations were significantly higher in the inlet than in the outlet sediment; concentrations in the latter remained without significant differences throughout the testing period. Metal concentrations and redox potential decreased with depth within the sediment. The lowest metal concentrations and pH and the highest redox values were attained in spring, in agreement with the period of maximum macrophyte growth. Ni and Zn were mainly stored associated with the carbonate fraction; Cr was mainly associated with the Fe-Mn oxides fraction, while Fe was mainly associated with the residual fraction, probably as pyrite. The incoming wastewater composition containing high pH, carbonate, calcium and Fe concentrations favored the observed association in the surface sediment. It would be expected that sediment will continue retaining metals in fractions that will not release them into the water while the chemical and environmental conditions remain unchanged.     

Impact of land use in catchment and human activities on water, sediment and vegetation of Mediterranean temporary pools

The vegetation and physical and chemical characteristics of the water and sediment in ten temporary pools submitted to various anthropogenic disturbance were studied in Morocco over two hydrological cycles (1997-1998 and 1998-1999). Results of multivariate and parametric analyses show that disturbance has a significant impact on water and sediment. Agriculture in the catchment resulted in higher levels of N and the use of detergent to higher levels of phosphorus in both water and sediment. Mineral extraction resulted in higher depth and longer duration of flooding. Vegetation characteristics were better correlated to hydrology (water depth, duration of flooding) than to nutrient variables. These results suggest that although agriculture in the catchment contribute in modifying the sediment characteristics, the impact on vegetation and its conservation value is limited. However, care should be taken of the long-term effects of agriculture through cumulative effects and of the possible consequences of changing the agricultural practices.     

Colonisation by Dreissena of Great Lakes coastal ecosystems: how suitable are wetlands?

1.  Invasive zebra ( Dreissena polymorpha ) and quagga mussels ( Dreissena bugensis ) have become widespread throughout the Great Lakes basin. However, some types of Great Lakes coastal wetlands may be unsuitable for Dreissena invasion.
2.  To test this observation, artificial substrata were placed in wetlands (with emergent vegetation) and in adjacent open water (without emergent vegetation) habitats in two types of Great Lakes coastal ecosystems: drowned river mouth (DRM) and coastal fringing systems. Wetlands in DRM systems generally have deep organic sediment and limited water movement, whereas coastal fringing wetlands generally have low to moderate amounts of organic sediment and intense wind and wave action.
3.  We did not find a significant difference in Dreissena colonisation between wetlands and adjacent open water habitat in fringing systems. However, Dreissena colonisation was significantly lower in DRM wetlands than in the adjacent open water. We also found significantly lower survival in DRM wetlands than adjacent open water habitats, whereas survival did not differ significantly in coastal fringing wetlands and the adjacent open water.
4.  Our results suggest that vulnerability to Dreissena invasion varied among wetland types with DRM wetlands being less suitable than fringing wetlands. We suggest that colonisation and survival of Dreissena is lower in wetlands with deep organic sediment and less turbulent water.