Marginal Wetlands Research Articles

Flood Hydrology and Methylmercury Availability in Coastal Plain Rivers

Mercury (Hg) burdens in top-predator fish differ substantially between adjacent South Carolina Coastal Plain river basins with similar wetlands coverage. In the Congaree River, floodwaters frequently originate in the Blue Ridge and Piedmont regions, where wetlands coverage and surface water dissolved methylmercury (MeHg) concentrations are low. Piedmont-driven flood events can lead to downward hydraulic gradients in the Coastal Plain riparian wetland margins, inhibiting MeHg transport from wetland sediments, and decreasing MeHg availability in the Congaree River habitat. In the adjacent Edisto River basin, floodwaters originate only within Coastal Plain sediments, maintaining upward hydraulic gradients even during flood events, promoting MeHg transport to the water column, and enhancing MeHg availability in the Edisto River habitat. These results indicate that flood hydrodynamics contribute to the variability in Hg vulnerability between Coastal Plain rivers and that comprehensive regional assessment of the relationship between flood hydrodynamics and Hg risk in Coastal Plain streams is warranted.

Interannual, seasonal, and diel variation in soil respiration relative to ecosystem respiration at a wetland to upland slope at Harvard Forest

Soil carbon dioxide efflux (soil respiration, SR) was measured with eight autochambers at two locations along a wetland to upland slope at Harvard Forest over a 4 year period, 2003–2007. SR was consistently higher in the upland plots than at the wetland margin during the late summer/early fall. Seasonal and diel hystereses with respect to soil temperatures were of sufficient magnitude to prevent quantification of the influence of soil moisture, although apparent short‐term responses of SR to precipitation occurred. Calculations of annual cumulative SR illustrated a decreasing trend in SR over the 5 year period, which were correlated with decreasing springtime mean soil temperatures. Spring soil temperatures decreased despite rising air temperatures over the same period, possibly as an effect of earlier leaf expansion and shading. The synchronous decrease in spring soil temperatures and SR during regional warming of air temperatures may represent a negative feedback on a warming climate by reducing CO2 production from soils. SR reached a maximum later in the year than total ecosystem respiration (ER) measured at a nearby eddy covariance flux tower, and the seasonality of their temperature response patterns were roughly opposite. SR, particularly in the upland, exceeded ER in the late summer/early fall in each year, suggesting that areas of lower efflux such as the wetland may be significant in the flux tower footprint or that long‐term bias in either estimate may create a mismatch. Annual estimates of ER decreased over the same period and were highly correlated with SR.

Vegetation heterogeneity on a Late Pennsylvanian braided-river plain draining the Variscan Mountains, La Magdalena Coalfield, northwestern Spain

The spatial heterogeneity and community ecology is reconstructed for Late Pennsylvanian (Stephanian B sensu lato) vegetation preserved in La Magdalena Coalfield, northwestern Spain. The ≈ 1500 m thick basin-fill accumulated rapidly along the margin of the Variscan Mountains, and the principal sedimentary facies comprise the deposits of large braided streams that dissected extensive wetlands containing large lakes. Quadrat analysis of 93 mostly (par)autochthonous megafloral assemblages indicates that pteridosperms and ferns dominated communities, with three taxa ( Pecopteris spp., Callipteridium pteridium, and Neuropteris ovata) accounting for ≈ 58% of all plant remains. Sphenopsids and lycopsids were less common but widespread, and cordaitaleans were rare. At the local scale, laterally exposed bedding planes reveal that communities comprised a complex and heterogeneous mosaic of species. At the landscape scale, ecological gradients are evident from multivariate analyses of quadrats in a facies context. Pteridosperms dominated marginal wetlands adjacent to steep basin margins. A greater proportion of ferns occurred in or adjacent to braided channel belts, consistent with their opportunistic growth and prolific reproductive capacity, characteristics advantageous in frequently disturbed habitats. In interfluve wetlands distant from channel influence, communities consisted of low-diversity or monospecific patches of slow-growing pteridosperms enclosed in a fern-dominated matrix. Pteridosperms in interfluve wetlands were arranged along an environmental gradient: Alethopteris and Pseudomariopteris preferred more disturbed sites, Neuropteris, Linopteris, and Odontopteris occupied more stable settings, and Callipteridium was cosmopolitan. Ephemeral wetland swamps were dominated by tree ferns with lesser Sigillaria, and Omphalophloios was a major constituent in long-lived rheotrophic mires that resulted in thick coal seams. In addition to improving knowledge of Late Pennsylvanian tropical ecosystems in marginal settings, the findings demonstrate how the spatial structure of ancient plant communities can be reconstructed from multiple quadrats sampling a vertical succession.

Trends in agricultural impact and recovery of wetlands in prairie Canada

Despite widespread recognition that they provide valuable ecosystem services and contribute significantly to global biodiversity, over half of the world's wetlands have been lost, primarily to agriculture. Wetland loss is evident in prairie Canada, but comprehensive information about causes of ongoing impact for existing wetlands is lacking. Habitat data collected for approximately 10,500 wetlands during annual waterfowl surveys (1985-2005) were analyzed using multistate models to estimate rates of wetland impact and recovery from agricultural activities in the Canadian prairies. An impact was defined as an agricultural activity that visibly altered a wetland margin (natural vegetation surrounding wetland interiors) or basin (interior depression capable of holding water), whereas recovery was deemed to have occurred if agricultural activities had ceased and effects were no longer visibly apparent. We estimated separate impact and recovery rates for wetland basins and wetland margins and considered covariates such as location, time, wetness indices, land use, and wetland permanence. Results indicate that impact rates for wetland margins have declined over time, likely due to a decreasing percentage of unaffected wetlands on the landscape. Recovery rates for margins were always lower than impact rates, suggesting progressive incidence of impacts to wetlands over time. Unlike margins, impact and recovery rates for basins fluctuated with May pond densities, which we used as a wetness index. Shallow ephemeral wetlands located in agricultural fields had the highest impact and lowest recovery rates relative to wetlands with higher water permanence or situated in areas of lower agricultural intensity. High rates and incidence of wetland impact in conjunction with low recovery rates clearly demonstrate the need for stronger wetland protection in prairie Canada.

Earthworm fauna of the western Mazandaran province, Iran

In the present study, earthworms were collected from the margins of rivers, forests, and wetlands of the Western Mazandaran province, Iran, from April 2007 to April 2008 at 18 designated stations. The following ten species were identified: Aporrectodea caliginosa, Ap. jassyensis, Dendrobaena byblica complex, D. hortensis, D. octaedra, D. veneta, Eisenia fetida, Eiseniella tetraedra, Perelia kaznakovi (all family Lumbricidae) and Amynthas corticis (family Megascolecidae). The Ei. tetraedra species comprises a new record for the studied region.

Contiguous multi‐proxy analyses (X‐radiography, diatom, pollen, and microcharcoal) of Holocene archaeological features at Kuk Swamp, Upper Wahgi Valley, Papua New Guinea

AbstractContiguous multi‐proxy analyses (X‐radiography, diatom, pollen, and microcharcoal) have been conducted on the fills of early, mid‐, and mid‐late Holocene features at Kuk Swamp, Upper Wahgi Valley, Papua New Guinea. The features are associated with key periods of archaeological interest: plant exploitation (ca. 10,000 cal yr B.P.), earliest cultivation (6950–6440 cal yr B.P.), and earliest ditches (ca. 4000 cal yr B.P.). The analyses are designed to clarify uncertainties regarding the reliability and association of different samples within feature fills for the interpretation of human activities on the wetland in the past. Methodologically, these investigations have clarified site formation processes, including pedogenesis within feature fills, which enable a better determination of archaeological associations for different samples within those fills. Substantively, the results provide higher resolution interpretations of paleoenvironments and past human activities on the wetland margin. © 2009 Wiley Periodicals, Inc.

Whole Ecosystem Evidence of Eutrophication Enhancement by Wetland Dredging in a Shallow Tropical Lake

The purpose of this research was to assess the effects of dredging performed in a marginal wetland colonized by aquatic macrophytes on eutrophication of the adjacent shallow tropical lake (Imboassica Lake, Brazil). The river mouth of the Imboassica River that drains into Imboassica Lake had been densely colonized by aquatic vegetation dominated by Typha domingensis (Pers.) when it was dredged. Total and dissolved nitrogen and phosphorus concentrations were measured monthly over 13 years at four stations in the Imboassica river-lake system. Dredging activities reduced phosphorus and nitrogen retention at the river mouth and subsequently increased these nutrient stocks in the lake waters. Nutrient retention by non-dredged wetland was estimated to be ca. 1,200 kg year−1 (87.3 g m−2 year−1) for nitrogen and 60 kg year−1 (4.5 g m−2 year−1) for phosphorus. Our whole-lake approach suggested that dredging might intensify rather than mitigate eutrophication in shallow tropical lakes when the removal of aquatic macrophytes is coupled to the persistence of anthropogenic nutrient inputs from the watershed.

Inductively mapping expert-derived soil-landscape units within dambo wetland catenae using multispectral and topographic data

Constructing a cost-effective and detailed digital soil map of Africa will require the extensive utilization of both legacy soil data and legacy soil-landscape knowledge — which in Africa is primarily available from reconnaissance-scale catena or association maps and related studies. We evaluated a hybrid approach for disaggregating reconnaissance scale soil maps: rapid and inexpensive delineation of representative soil-landscape units in the field using expert knowledge, followed by the use of inductive, empirical, and correlative modeling techniques to map these landscape units. Our 2214 km 2 study area, located in central Uganda, consisted predominantly of catenae that terminate in seasonal valley floor wetlands called dambos — a type of landscape that can be found throughout the African continent. For model training and validation, we identified four landscape classes in the field using published expert knowledge: well-drained uplands (red soils); sloping dambo wetland margins (gradient > 2%), frequently inundated dambo bottoms (hummocky microtopography), and flat dambo floors (default). Using binary decision trees (BDT) with multispectral and topographic remote sensing covariates, we created a 20 m resolution map of these four classes. Multispectral inputs included reflectance values, vegetation indices, and spectral mixture modeling fractions from Système Pour l'Observacion de la Terre (SPOT) 4 satellite images acquired in December, 2006 and February, 2007. Topographic inputs consisted of a digital elevation model (DEM) from Shuttle Radar Topography Mission (SRTM) data, slope, and 20 relative elevation layers calculated using moving windows of various sizes. Decision rules were based upon the following input variables: the Normalized Difference Vegetation Index (NDVI), the Normalized Difference Infrared Index (NDII), the shortwave infrared (SWIR) reflectance, northing, slope, and two relative elevation layers. The overall classification accuracy of 75.5% and Kappa coefficient of 0.67 suggest that a combination of multispectral, topographic, and spatial data may be used to reliably classify landscape classes for dambo-terminated catenae. At 59% of the 2214 km 2 study area, the upland class was by far the most abundant, with margins at 21%, floors at 12% and bottoms at 8%. A statistical analysis of soil property data from a small catchment located within the study area showed significant class differences in soil texture, color, organic carbon (SOC), base saturation, pH, effective cation exchange capacity (ECEC), and clay mineralogy. Though detailed soil maps are rare in Africa, reconnaissance soil maps can be inexpensively disaggregated to provide a valuable starting point for digital soil mapping.

Groundwater-wetland ecosystem interaction in the semiarid glaciated plains of North America

The prairie wetlands of northern USA and Canada exist in numerous topographical depressions within the glaciated landscape. The wetlands are disconnected from each other most of the time with respect to surface-water drainage. The wetland water balance is controlled by snowmelt runoff and snowdrift from the surrounding uplands, precipitation, evapotranspiration, groundwater exchange, and occasional “fill-spill” connections to other wetlands. Salinity of water and the seasonal variability of water level in these wetlands have a strong influence on the ecosystem. Clay-rich glacial tills, covering much of the region, have very low (0.001–0.01 m/yr) hydraulic conductivity, except for the top several meters where the factures and macropores increase conductivity up to 1,000 m/yr. Transpiration in the wetland margin induces infiltration and lateral flow of shallow groundwater from wetland ponds through the high-conductivity zone, which strongly affects the water balance of wetlands. In contrast, groundwater flow in the deeper low-conductivity till has minor effects on water balance, but has a strong influence on salinity because the flow direction determines if the salts accumulate in wetlands (upward flow) or are leached out (downward flow) under wetlands. Understanding of the roles of shallow and deep groundwater systems will improve the hydrological conceptual framework for the management of wetland ecosystems.

A 'Sportsman's Paradise': The Effects of Hunting on the Avifauna of the Gippsland Lakes

Abstract The Gippsland Lakes form an extensive lake system in south-eastern Australia that is fed by rivers draining the Australian Alps. Until the engineered opening of a permanent entrance to the sea in 1889 they were predominantly a freshwater system, regularly inundated by floodwaters that formed marginal wetlands locally known as morasses. Historical sources document an environment of avifaunal abundance, particularly of waterfowl. Although scientists have explained Australian avifaunal decline on habitat modification, historical sources suggest that on the Gippsland Lakes European interaction with nature in the form of hunting had a significant impact in the period before widespread habitat modification in the twentieth century.

Natural and constructed littoral zones as nutrient traps in eutrophicated shallow lakes

It is generally known that the water quality of shallow lakes can be influenced significantly by marginal wetlands. In order to study the efficacy of constructed littoral wetlands in the IJsselmeer area (The Netherlands) for water quality improvement, a field survey was carried out in 2003. Vegetation, soil, pore water and surface water characteristics were measured in spring and summer in two types of littoral zones: natural and constructed for 8–16 years. The study showed that constructed wetlands perform well and are suitable to enlarge the vegetated littoral zone in the IJsselmeer area. In both natural and constructed sites vegetation biomass varied between 2,200 g m−2 for helophyte vegetation and 1,300 g m−2 for low herbaceous vegetation. Nutrient concentrations in the pore water of constructed sites tended to be higher than in natural sites. \( {\text{PO}}^{{3 - }}_{4} \) and \( {\text{NH}}^{ + }_{4} \) concentrations in pore water were much lower when vegetation was present, probably as a result of plant uptake. The N and P accumulation rate in the soil of constructed wetlands was 20 g N m−2 y−1 and 3 g P m−2 y−1 in vegetated plots; without vegetation the rate was much lower (8 g N m−2 y−1 and 1.8 g P m−2 y−1). We conclude that concerning their effect on water quality, constructed sites may replace natural sites, at least after 8–16 years. Principal component analysis showed a relationship between vegetation biomass and flooding, and nutrient concentrations in soil and pore water. Biomass was negatively correlated with extractable nutrients and positively with soil total N and P content. Flooding duration was negatively related to pore water salinity and positively to pore water nutrients. Due to their high biomass, helophyte stands retained significantly more nutrients than low pioneer vegetation and are therefore more suitable for improving water quality.

Effect of climate fluctuations on long-term vegetation dynamics in Carolina bay wetlands

Carolina bays and similar depression wetlands of the U.S. Southeastern Coastal Plain have hydrologic regimes that are driven primarily by rainfall. Therefore, climate fluctuations such as drought cycles have the potential to shape long-term vegetation dynamics. Models suggest two potential long-term responses to hydrologic fluctuations, either cyclic change maintaining open emergent vegetation, or directional succession toward forest vegetation. In seven Carolina bay wetlands on the Savannah River Site, South Carolina, we assessed hydrologic variation and vegetation response over a 15-year period spanning two drought and reinundation cycles. Changes in pond stage (water depth) were monitored bi-weekly to monthly each year from 1989–2003. Vegetation composition was sampled in three years (1989, 1993, and 2003) and analyzed in relation to changes in hydrologic conditions. Multi-year droughts occurred prior to the 1989 and 2003 sampling years, whereas 1993 coincided with a wet period. Wetland plant species generally maintained dominance after both wet and dry conditions, but the abundances of different plant growth forms and species indicator categories shifted over the 15-year period. Decreased hydroperiods and water depths during droughts led to increased cover of grass, upland, and woody species, particularly at the shallower wetland margins. Conversely, reinundation and longer hydroperiods resulted in expansion of aquatic and emergent species and reduced the cover of flood-intolerant woody and upland species. These semi-permanent Upper Coastal Plain bays generally exhibited cyclic vegetation dynamics in response to climate fluctuation, with wet periods favoring dominance by herbaceous species. Large basin morphology and deep ponding, paired with surrounding upland forest dominated by flood-intolerant pines, were features contributing to persistence of herbaceous vegetation. Drought cycles may promote directional succession to forest in bays that are smaller, shallower, or colonized by flood-tolerant hardwoods.

A conceptual hydrologic model for a forested Carolina bay depressional wetland on the Coastal Plain of South Carolina, USA

AbstractThis paper describes how climate influences the hydrology of an ephemeral depressional wetland. Surface water and groundwater elevation data were collected for 7 years in a Coastal Plain watershed in South Carolina USA containing depressional wetlands, known as Carolina bays. Rainfall and temperature data were compared with water‐table well and piezometer data in and around one wetland. Using these data a conceptual model was created that describes the hydrology of the system under wet, dry, and drought conditions. The data suggest this wetland operates as a focal point for groundwater recharge under most climate conditions. During years of below‐normal to normal rainfall the hydraulic gradient indicated the potential for groundwater recharge from the depression, whereas during years of above‐normal rainfall, the hydraulic gradient between the adjacent upland, the wetland margin, and the wetland centre showed the potential for groundwater discharge into the wetland. Using high‐resolution water‐level measurements, this groundwater discharge condition was found to hold true even during individual rainfall events, especially under wet antecedent soil conditions. The dynamic nature of the hydrology in this Carolina bay clearly indicates it is not an isolated system as previously believed, and our groundwater data expand upon previous hydrologic investigations at similar sites which do not account for the role of groundwater in estimating the water budget of such systems. Copyright © 2007 John Wiley & Sons, Ltd.

Diversity of chironomid larvae in a marginal fluvial wetland of the Middle Paraná River floodplain, Argentina.

The diversity of chironomid larvae in relation to flooding and drought phases in a marginal fluvial wetland of the Middle Parana River floodplain was analyzed. Four sampling stations in the right bank of the Tiradero Viejo River towards the interior of the marginal wetland were established: one at the riverside, and three more at 10, 30 and 40 m from the river. Bottom sediment samples were extracted during the hydrosedimentological cycle of 2001. A total of 25 taxa of Chironomidae were recorded. The values of taxonomic richness, density and diversity were higher in the marginal fluvial wetland than in the riverside, increasing when the wetland is disconnecting from the river. Polypedilum (Tripodura) spp., Polypedilum (Polypedilum) spp., Ablabesmyia (Karelia) spp., Coelotanypus sp., Monopelopia cf. boliekae, Goeldichironomus holoprasinus and Chironomus gr. decorus spp. were dominant in marginal wetlands. The results indicate that the variations in the hydrosedimentological regime, the degree of disconnection with the river and the progressive desiccation at each one of the stations of the marginal fluvial wetland are limitant factors in the distribution and abundance of aquatic chironomids. The different assemblages of Chironomidae were strongly conditioned by temporal changes related to the gradient of inundation-drought and to the hydroperiod dynamics.

A Development Principle for the Marginal Wetlands

A Development Principle for the Marginal Wetlands

Upland Forest Linkages to Seasonal Wetlands: Litter Flux, Processing, and Food Quality

The flux of materials across ecosystem boundaries has significant effects on recipient systems. Because of edge effects, seasonal wetlands in upland forest are good systems to explore these linkages. The purpose of this study was to examine flux of coarse particulate organic matter as litter fall into seasonal wetlands in Minnesota, and the relationship of this flux to development of mosquitoes (Aedes aegypti). We hypothesized that litter flux into seasonal wetlands was dominated by upland plant litter that was lower quality and slower to breakdown than wetland litter, and that development rate of mosquitoes reared on upland litter was less than those reared on wetland litter. Of total litter fall into the wetlands, 71% originated in upland forest. Carbon to nitrogen ratios differed between upland litter (mostly sugar maple (Acer saccharum) and trembling aspen (Populus tremuloides) leaves) and wetland litter (mostly black ash (Fraxinus nirgra) leaves), averaging 63.9 and 47.7, respectively over two years. Breakdown rate of black ash leaves was faster than upland leaves (k (day−1) = 0.00329 and 0.00156, respectively), based on the average between wetland margins and centers. Development of mosquito larvae fed black ash leaves was faster than larvae fed upland leaves. Our results demonstrate linkages between upland forests and seasonal wetlands through litter fall. The abundance of upland litter in the wetlands may influence litter breakdown and carbon assimilation by invertebrates. Wetlands receiving high amounts of upland versus wetland litter may be lower quality habitats for invertebrates that depend on detrital pools for their development.

The measurement and analysis of denitrification rates obtained using soil columns from river marginal wetlands

Soil cores from river marginal wetlands from three sites in the UK (Torridge and Severn catchments), sampled and restrained in PVC piping, were flooded with dilute aqueous potassium nitrate. Half of the cores were sterilized prior to flooding to destroy the denitrifying bacteria. The change in nitrate concentration in the flood-water was measured over time. It is argued that the observed nitrate depletion rates (from 1.2 to 4.7 kg ha -1 d -1 ) is the result of microbially-mediated denitrification. The results show the method to be a simple and direct procedure for the assessment of spatial variation in nitrate-sink capacity. The depth of the denitrifying layer at the soil-water interface was confirmed to be of the order of a few mm only. A one-dimensional model for the diffusive flux in the flooded soil was developed which, on differentiation, gave a predictive expression for denitrification rate in terms of the effective soil diffusion coefficient for nitrate, the flood-water depth and concentration, and the thickness of the microbially active zone.

Seed germination of Cirsium arvense and Lepidium latifolium: Implications for management of montane wetlands

Cirsium arvense and Lepidium latifolium are species that can aggressively invade wetland margins and potentially reduce biodiversity and alter ecosystem function. Although expansion of these species primarily occurs via rhizomatous growth, seeds are thought to be important in initial establishment. We conducted this study to investigate differences in seed germination of C. arvense and L. latifolium in montane wetlands of Colorado and Wyoming, USA. We used germination chambers to simulate environmental conditions (photoperiod, day/night temperature) during three periods of the growing season at each site and evaluated seed germination in relation to three soil moisture levels and two soil depths. A combination of shallow (<1 cm) seed burial and wet conditions resulted in the greatest germination probability of C. arvense (x = 63.0%), 95% CI = 41.2–80.5%), whereas deep (2–3 cm) seed burial and saturated moisture conditions resulted in almost no germination (x = 0.3%, 95% CI = 0.1–1.3%). The maximum germination probability of 44.0% (CI = 28.1–61.4%) for L. latifolium also occurred in the shallow burial and wet treatment; however, only effects of seed burial were significant (P < 0.05). The estimated mean germination probability of deeply buried seeds was < 1.0% (CI = 0.3–1.4%) compared to 32% (CI = 19.7–47.9%) for shallowly buried seeds. Our results suggest that each species has the ability to germinate at similar rates throughout the growing season and across a large portion of the moisture gradient. This suggests that management actions, including water-level manipulations, at any time during the growing season may stimulate germination. Although burial of seed to depths of 2–3 cm reduced the germination potential of both species, the use of mechanical implements may be problematic in established stands because new plants of both species easily sprout from root buds. Further, disturbance resulting from such actions diminishes the density and vigor of other plants already present, which may ultimately decrease the competitive resistance of the disturbed environment to invasion by outside species. Detection of new invasions is a critical component of any integrated weed management program. Our results indicate that the incidence of C. arvense and L. latifolium germination is most likely in areas with seeds that are within 1 cm of the soil surface and soil moisture is 75–100% of field capacity for extended periods.

Early and mid Holocene tool-use and processing of taro ( Colocasia esculenta), yam ( Dioscorea sp.) and other plants at Kuk Swamp in the highlands of Papua New Guinea

Recent multidisciplinary investigations document an independent emergence of agriculture at Kuk Swamp in the highlands of Papua New Guinea. In this paper we report preliminary usewear analysis and details of prehistoric use of stone tools for processing starchy food and other plants at Kuk Swamp. Morphological diagnostics for starch granules are reported for two potentially significant economic species, taro ( Colocasia esculenta) and yam ( Dioscorea sp.), following comparisons between prehistoric and botanical reference specimens. Usewear and residue analyses of starch granules indicate that both these species were processed on the wetland margin during the early and mid Holocene. We argue that processing of taro and yam commences by at least 10,200 calibrated years before present (cal BP), although the taro and yam starch granules do not permit us to distinguish between wild or cultivated forms. From at least 6950 to 6440 cal BP the processing of taro, yam and other plants indicates that they are likely to have been integrated into cultivation practices on the wetland edge.

Impacts of mosquitofish, Gambusia affinis, on black mudfish, Neochanna diversus

The potential for western mosquitofish, Gambusia affinis, to negatively affect populations of black mudfish in New Zealand wetlands was investigated with annual fishing surveys of the Whangamarino wetland and by laboratory experiments evaluating competition and predation of mosquitofish on mudfish adults and larvae. Abundance of mudfish juveniles was reduced in the presence of mosquitofish at marginal wetland sites close to permanent water, but mosquitofish were not found at ephemeral adult mudfish habitats. In constructed wetland microcosms, mosquitofish reduced both growth and condition of post‐larval mudfish but did not attack or kill mudfish. In laboratory aquaria, mosquitofish rapidly consumed mudfish fry but survival time of the latter was significantly extended by an increase in density of submerged structures and by the presence of an alternative food source for mosquitofish. Because mosquitofish cannot survive in ephemeral wetlands that dry over summer, the impacts of mosquitofish on mudfish are likely to be minimal except in habitats where mosquitofish can survive year‐round owing to the presence of permanent standing water.