Water Levels In Wetlands Research Articles

The potential impact of climate change on groundwater‐fed wetlands in eastern England

ABSTRACTWetlands are fragile ecosystems that provide a range of useful functions. However, such ecosystems have been experiencing persistent pressures and stresses from a range of socio‐economic drivers in the last few centuries. In the 21st century, changes in global climate are expected to have impacts on hydrological and water supply regimes, which will in turn impose additional pressures on wetlands. Consequently, the need for quantitative methods to evaluate the likely impact of climate change is essential if appropriate conservation strategies and integrated water management regimes are to be developed. In this paper, a methodology is presented to evaluate the implications of potential climate change on groundwater‐fed wetlands underlain by an unconfined limestone (Chalk) aquifer in eastern England, one of the most vulnerable regions to climate change in the UK. A daily weather generator, a recharge model and a groundwater model have been coupled to investigate the most extreme consequences of future climate change as described by the UKCIP02 ‘high’ greenhouse gas emissions scenario. Simulations showed that a declining trend in wetland water levels could result in loss of species with a small tolerance to dry conditions by the end of the 21st century. Copyright © 2011 John Wiley & Sons, Ltd.

The wetland water level process and habitat of migratory birds in Lake Poyang

鄱阳湖越冬候鸟保护最重要的环节是保护栖息地, 候鸟栖息地的面积和空间分布随水位过程而变化.在分析认定鄱阳湖湿地景观分类中水陆过渡带及其上下摆动区(稀疏草滩区和浅水区)为越冬候鸟主要栖息地的基础上, 选择不同水位的遥感影像资料, 经解译定量分析不同水位水陆过渡带面积及其空间分布, 从而分析不同水位条件对候鸟栖息地的影响.进而分析研究鄱阳湖国家级自然保护区微地形水位过程候鸟栖息地变化及对候鸟越冬的影响, 提出湖泊湿地候鸟栖息地(水陆过渡带)水位过程的自然变化, 尤其是湖泊湿地微地形水位过程变化是保证候鸟(尤其是水禽)越冬的重要影响因素.枯水期鄱阳湖水位14.18m(星子站, 黄海高程)以上时, 水陆过渡带将缩小乃至消失, 鄱阳湖湿地作为越冬侯鸟柄息地的功能将丧失。;The habitat preservation is important for the protection of migratory birds wintering in Lake Poyang, while the bird habitat area and spatial distribution change along with water Level processes.This paper analyzed the topography classification of wetland transitional zone of Lake Poyang and fluctuating area in the water and land(sparse marsh areas and shallow water) as wintering habitat for migratory birds.Then we selected remote-sensing image data under different water level and obtained dififerent water surface area of the transitional zone and its spatial distribution, and analyzed various water level conditions influence on the habitat of migratory birds.Through analysis of Lake Poyang National Nature Reserve, under the topography of water level processes, changes in migratory birds and their habitat of migratory birds wintering in the impact of the proposed wetland birds on the lake habitat (land and water trangition zone), the natural water level process was important measures for ensuring the migratory birds(especially waterfowl)living through the winter in Lake Poyang.

Response of waterbird species to fluctuating water levels in tropical coastal wetlands

AbstractRecent upsurges in the incidence of dam construction over rivers for farming and hydro electric power in the West African sub‐region is a known promoter of fluctuating water levels on tropical coastal wetlands. Waterbirds, being one of the dominant fauna on wetlands, are key species that can be affected by fluctuating water levels. Waterbird census and water level monitoring at four coastal wetlands in Ghana revealed that different guilds (species assemblages) of waterbirds responded differently to fluctuating water levels. The populations density of birds in guilds 1 (ducks and cormorants), 3 (tactile surface foraging waders), 4 (pelagic foraging waders) and 5 (stalking herons and egrets) significantly (P < 0.05) increased linearly with decreasing water levels. The population density of birds in guilds 2 (visual surface foraging waders) and 7 (fishing terns) responded significantly (P < 0.05) in a second order polynomial function with optimum numbers occurring when water levels were neither too high nor too low. As far as farming and energy requirement are met from these dams, it is important that the ecological needs of waterbirds on wetlands are incorporated into the management of these dams so as to maintain appropriate water levels beneficial to waterbird populations.

Plant adaptations and microbial processes in wetlands

Wetlands are terrestrial ecosystems characterized by high and fluctuating water tables. The spatial and temporal differences in the degree to which wetland soils are waterlogged create a very dynamic soil environment with, on average, lower oxygen concentrations than unsaturated soils. Wetland soils are characterized by gradients in redox conditions from totally oxidized to extremely reduced. These conditions require special adaptations for the plant and microbial species in the wetland. Wetland plants, particularly in wetlands with strongly fluctuating water tables, need adaptations to the shortage of oxygen in the root zone, but also to extended periods of dry conditions during low-water phases. Microbial communities are strongly coupled to redox cycles, in which alternative electron acceptors are used, for example nitrate, iron, manganese, sulphate and carbon dioxide. Plant–microbe interactions add to the complexity of the functioning of the wetland soil system. This Highlight section of Annals of Botany addresses the adaptations of plants and microbes in wetlands with fluctuating water levels, following a broad perspective. It contains three review papers and three primary scientific papers with experiments and field comparisons. The review by Parolin et al. gives an overview of adaptations of wetland plants in Amazonian floodplains to drought. The annual water cycle in these wetlands is quite predictable but shows an amplitude of 8 m, giving rise to a long flooded period as well as a long dry period each year. Previously, most emphasis in the evaluation of plant adaptations in these environments had been on the wet phase, focusing on the difficulty of overcoming long periods of waterlogged soil and (partial) submergence of the above-ground parts of plants. This paper for the first time evaluates plant adaptations to the dry period, in the context of the total annual cycle. The review paper by Laanbroek investigates how methane emission from wetland systems is controlled by microbial processes and influenced by wetland vegetation. The complex coupling of the various microbially mediated redox cycles, the leakage of oxygen from the internal plant gas system and the ‘escape’ of methane through this gas system to the atmosphere are evaluated. The review by Verhoeven and Setter deals with human control of water levels in wetlands to promote agricultural use. The emphasis is on the difference between sustainable and non-sustainable uses of wetlands for agriculture. Drainage of peatlands has led to severe soil subsidence and greenhouse gas emissions, whereas floodplains and rice fields are suitable for a more sustainable agricultural use. Developments in crop science, leading to increasingly waterlogging-tolerant crops are also discussed in this context. The paper by Sorrell and Hawes evaluates the importance of convective gas flow in the lacunae of helophytes for the occupation of relatively deep-water habitats. In their study, plant species lacking convective flow occurred in very shallow water only, whereas species with high rates of convective flow were able to grow in deep water, even in eutrophic habitats where the organic soil has a high oxygen demand. Li et al. carried out an experiment with Typha domingensis to test the ability of this species to grow in nutrient-rich, strongly reduced sediments. Growth was adversely affected by low redox potentials, but high availability of phosphates moderated this negative effect. The results are discussed in the context of competitive replacement of Cladium jamaicense by Typha domingensis in parts of the Everglades affected by high agricultural run-off. Finally, Yu and Ehrenfeld have studied the way in which the plant and microbe community structure was affected by water-level fluctuations and soil characteristics in New England forested wetlands. Both median level and variability in water tables turned out to affect plant and microbe communities; however, soil genesis, a result of both water-table position and geologic history, appeared to be even more important.

Litter accumulation promotes dominance of invasive species of cattails (Typha spp.) in Lake Ontario wetlands

Wetlands of the Great Lakes region are increasingly dominated by invasive cattails (Typha angustifolia and Typha X glauca) which form dense stands of live and dead biomass that may reduce plant diversity. We hypothesized that differences in plant litter accumulation explain cattail dominance under certain hydrologic regimes related to wetland hydrogeologic setting. We investigated cattail abundance, litter accumulation, and species density in three bayside wetlands hydrologically connected and three protected wetlands hydrologically isolated from Lake Ontario. Mean litter biomass was higher in bayside wetlands (1.7-2.6 vs. 0.4-1.2 kg/m 2 ) and negatively related to species density (p 5 0.004) in both settings. A litter addition experiment demonstrated that fallen litter negatively influenced seedling survival (p 5 0.061) and species density (p 5 0.024). Decomposition rates accounted only partially for higher overall litter accumulation in bayside wetlands. Growing season water levels in bayside wetlands tracked Lake Ontario levels and showed less variation than protected wetlands. More stable water levels and higher density of standing dead stems in bayside wetlands may limit litter fragmentation, resulting in greater litter accumulation. Thus, anthropogenic and natural factors affecting cattail litter production, fragmentation, and decomposition could influence species diversity in coastal wetlands.

Louisiana Wetland Water Level Monitoring Using Retracked TOPEX/POSEIDON Altimetry

Previous studies using satellite radar altimetry to observe inland river and wetland water level changes usually spatially average high-rate (10-Hz for TOPEX, 18-Hz for Envisat) measurements. Here we develop a technique to apply retracking of TOPEX waveforms by optimizing the estimated retracked gate positions using the Offset Center of Gravity retracker. This study, for the first time, utilizes stacking of retracked TOPEX data over Louisiana wetland and concludes that the water level observed by each of 10-Hz data with along-track sampling of ∼660 m exhibit variations, indicating detection of wetland dynamics. After further validations using nearby river gauges, we conclude that TOPEX is capable of measuring accurate water level changes beneath heavy-vegetation canopy region (swamp forest), and that it revealed wetland dynamic flow characteristics along track with spatial scale of 660 m or longer.

Helmand River Hydrologic Studies Using ALOS PALSAR InSAR and ENVISAT Altimetry

The Helmand River wetland represents the only fresh-water resource in southern Afghanistan and one of the least mapped water basins in the world. The relatively narrow wetland consists of mostly marshes surrounded by dry lands. In this study, we demonstrate the use of the Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) Interferometric SAR (InSAR) to detect the changes of the Helmand River wetland water level. InSAR images are combined with the geocentric water level measurements from the retracked high-rate (18-Hz) Environmental Satellite (Envisat) radar altimetry to construct absolute water level changes over the marshes. It is demonstrated that the integration of the altimeter and InSAR can provide spatio-temporal measurements of water level variation over the Helmand River marshes where in situ measurements are absent.

Adaptation of farming practices could buffer effects of climate change on Northern Prairie wetlands

Wetlands of the Prairie Pothole Region of North America are vulnerable to climate change. Adaptation of farming practices to mitigate adverse impacts of climate change on wetland water levels is a potential watershed management option. We chose a modeling approach (WETSIM 3.2) to examine the effects of changes in climate and watershed cover on the water levels of a semi-permanent wetland in eastern South Dakota. Land-use practices simulated were unmanaged grassland, grassland managed with moderately heavy grazing, and cultivated crops. Climate scenarios were developed by adjusting the historical climate in combinations of 2°C and 4°C air temperature and ±10% precipitation. For these climate change scenarios, simulations of land use that produced water levels equal to or greater than unmanaged grassland under historical climate were judged to have mitigative potential against a drier climate. Water levels in wetlands surrounded by managed grasslands were significantly greater than those surrounded by unmanaged grassland. Management reduced both the proportion of years the wetland went dry and the frequency of dry periods, producing the most dynamic vegetation cycle for this modeled wetland. Both cultivated crops and managed grassland achieved water levels that were equal or greater than unmanaged grassland under historical climate for the 2°C rise in air temperature, and the 2°C rise plus 10% increase in precipitation scenarios. Managed grassland also produced water levels that were equal or greater than unmanaged grassland under historical climate for the 4°C rise plus 10% increase in precipitation scenario. Although these modeling results stand as hypotheses, they indicate that amelioration potential exists for a change in climate up to an increase of 2°C or 4°C with a concomitant 10% increase in precipitation. Few empirical data exist to verify the results of such land-use simulations; however, adaptation of farming practices is one possible mitigation avenue available for prairie wetlands.

Waterbird Assemblages and Habitat Characteristics in Wetlands: Influence of Temporal Variability on Species-Habitat Relationships

Abstract. Patterns of spatial and temporal variation in species richness, abundance and diversity were evaluated in eight wetlands in Central-South Chile in relation to nine wetland characteristics. Twenty-six bird species were recorded, among the most representative families were Rallidae, Ardeidae and Anatidae with five species each. Stepwise regression analyses identified wetland area and water level fluctuations as the most important variables determining bird abundance. Variations in species richness were explained by wetland area, shoreline length, vegetation cover and water-level fluctuations. Shoreline development, shoreline length and wetland area lower than one-meter depth were especially important in determining species diversity. Cluster analyses showed similar results. Shoreline length was an important feature influencing total species number, but simple regression analysis showed that the species area relationship occurs in wetlands too. This study concludes that species richness, bird abund...

Current status of Peruvian Terns Sternula lorata in Perú: threats, conservation and research priorities

SummaryPeruvian Terns Sternula lorata breed in the sand desert plains of the coast of Perú and northern Chile. Because of their long-term population decline, Peruvian Tern is categorized as ‘Endangered’ on the IUCN Red List. The observations that formed the basis for that decision were made in the 1970s and 1990s. In this study, we compile information on distribution, numbers, habitat use and threats of Peruvian Terns that has become available between 2003 and 2008 from 14 localities on the Peruvian coast. Peruvian Tern sites are located between the mangroves of San Pedro de Vice in the north (5o31’S) and the wetlands of Ite in the south (17o56’S). From the 14 locations, five are reported for first time: Virrilá, Eten, Huanchaco, isla Mazorca and Ite. There were only four active breeding sites: Pacasmayo, Paraíso, Pampa Lechuzas and Tres Hermanas-Yanyarina; however, some localities were visited outside the breeding season and should be surveyed between October and February to search for nests. The presence of 283 individuals was confirmed at the 14 sites in an area of approximately 1,388 ha (which represents only 0.35% of the total suitable area for nesting along the Peruvian coast). Thus, the number of Peruvian Terns in Perú should increase with systematic surveys. Here for the first time we report the importance of wetlands for the Peruvian Terns (43% of the sightings occurred in this habitat). Wetlands can offer optimal conditions for feeding, but the cost of using them is becoming higher with a sharp increase of human expansion into coastal areas and urban development around wetlands. We identified the following threats affecting Peruvian Terns on their feeding and breeding grounds: 1) recreational activities; 2) off-road driving by fishermen and tourists; 3) wetland pollution and water use for irrigation; 4) conversion of desert plains to agricultural land; 5) management of wetland water levels; 6) presence of feral cats and dogs, and 7) oil exploration on the desert plains. These adverse factors can be eradicated by the protection of tern sites and public awareness and education. Conservation actions, monitoring and research priorities are suggested.

Macroinvertebrate cycles of decline and recovery in Swan Coastal Plain (Western Australia) wetlands affected by drought-induced acidification

Management of wetlands influenced by the Gnangara groundwater mound, Western Australia, is becoming increasingly challenging due to an ongoing decline in the regional groundwater table. A number of these groundwater-dependent wetlands have acidified (with adverse effects on the extant macroinvertebrate fauna) due to the oxidation of pyritic sediments. One management option in such cases is artificial augmentation of surface water in order to maintain or reinstate anaerobia in the sediments. This paper documents cycles of macroinvertebrate decline and recovery over 12 years of monitoring in three Gnangara mound wetlands affected by drought-induced acidification, one of which is being artificially augmented. Acidification did not result in a reduction of the total number of macroinvertebrate families present, however, there were clearly identifiable groups of acid-sensitive taxa (amphipods and isopods, ostracods, chydorid and daphnid cladocerans, mayflies, oligochaetes, clams and snails) and acid-tolerant taxa (sandfly larvae, macrothricid cladocerans and water boatmen). In the artificially augmented wetland, the effects of acidification were reversed: acid-sensitive taxa reappeared and acid-tolerant taxa decreased in numbers. Moreover, there were a number of taxa that appeared for the first time since augmentation, and summer family richness increased markedly. This study has shown that artificial augmentation of wetland water levels can be a successful recovery strategy for recently acidified systems, but this will depend on a number of factors, and the ‘recovered’ state will be at least slightly different from the original state.

L’utilisation des bilans d’eau dans les zones humides pour relier les processus hydrogéologiques aux conséquences écologiques

A methodology for modelling wetland water levels using the water balance approach was developed for Pulborough Brooks Site of Special Scientific Interest in West Sussex, in the UK. The methodology was applied to assess potential groundwater abstraction impacts on communities and species of ecological importance in the wetland. The modelling methodology links regional hydrogeological processes to wetland hydrology and ecology that is typically influenced by processes that take place at a more reduced spatial scale. To assess impacts, it is necessary to understand the hydrological sources of water that are affected by abstraction as well as to consider how the magnitude of these processes relates to other processes that influence wetland water levels. Water levels are commonly the most important factor determining the presence or absence of species or communities in a wetland and the model predicts wetland water levels and assesses how suitable these water levels are for species of ecological significance. Model results show that typical historic rates of abstraction have not resulted in an adverse effect on the integrity of the Pulborough Brooks relative to a ‘natural’ (no abstraction) scenario.

Assessment of the impacts of hydrological fluctuations and salt pans abandonment on Greater flamingos in the Camargue, South of France

Flamingos forage in both commercial salt pans and natural marshes and lagoons along the French Mediterranean coast. In order to assess the impact of changes in management of commercial salt pans and hydrological fluctuations on this flagship species, we evaluated the foraging areas of breeding flamingos using the resightings of 283 breeding flamingos marked with dye at the colony in 1987 and 1989, two years with contrasting hydrological conditions. Teams of observers searched all suitable habitats within 80 km of the colony during the four days following marking and recorded presence of off-duty flamingos. About one-third of the birds were found within 10 km of the colony, but some were seen up to 70 km away. About 24–54% of the birds were found in permanent brackish lagoons and 18–60% in the salt pans, the two most important habitats. In 1989, a dry year with lower water levels in the natural wetlands, the proportion of breeding flamingos using salt pans was twice as high [53%, range (47–60%)] as in 1987 [26%, range (18–29%)], this habitat thus acting as a refuge. Most of the feeding areas shown to be important for flamingos breeding in the Camargue are thus susceptible to variations according to rainfall and to transformations or drying out if the salt pans are abandoned. Our results provide essential benchmarks to reconsider the conservation of this flagship species when management of commercial salt pans changes.

Comparison of mosquito (Diptera: Culicidae) populations by wetland type and year in the lower River Dalälven region, Central Sweden

We studied adult mosquito assemblages in six wetlands, representing three types (wet meadow, alder swamp, and bog), in the lower part of the River Dalälven in Central Sweden during three consecutive years (2000-2002) and evaluated the influence of wetland type and year. Mosquito abundance differed significantly between years but not between wetland types. Mosquito species richness showed no significant variation between years or wetland types. Cluster analysis based on percentage of similarity resulted in three clusters, with high similarity between all wetlands in 2000. Ordination analysis showed that mosquito assemblages were mainly correlated with wetland type and water level increase in the previous month. Hydrological conditions varied between the years and between the wetland types, and our collections also included a year (2000) with extreme flood situations. The floodwater mosquito species Ochlerotatus sticticus was the predominant species with a strong influence on the whole study due to its long-range dispersal ability. The entire region suffered from enormous numbers of Oc. sticticus in 2000. The data from this study provided the basis for the initiation of a mosquito control project in the region.

Impact of photosynthesis and transpiration on nitrogen removal in constructed wetlands

To determine the impact of photosynthesis and transpiration on nitrogen removal in wetlands, an artificial wetland planted with reeds was constructed to treat highly concentrated domestic wastewater. Under different meteorological and hydraulic conditions, the daily changes of photosynthesis and transpiration of reeds, as well as nitrogen removal efficiency were measured. It was found that net photosynthesis rate per unit leaf area was maintained on a high level (average 19.0 μmol CO2/(m2·s)) from 10:00 to 14:00 in July 2004 and reached a peak of 21.1 μmol CO2/(m2·s) when Photon Flux Density was high during the day. Meanwhile, TN and NH4 +-N removal efficiency rose to 79.6% and 89.6%, respectively—the maximum values observed in the test. Correlation coefficient analysis demonstrated a positive correlation among photon flux density, net photosynthetic rate, transpiration rate, and TN and NH4 +-N removal efficiency. In contrast, there was a negative correlation between stomatal conductance and TN and NH4 +-N removal efficiency. Results suggest that the photosynthesis and transpiration of wetland plants have a great impact on nitrogen removal efficiency of wetlands, which can be enhanced by an increase in the photosynthesis and transpiration rate. In addition, the efficiency of water usage by reeds and nitrogen removal efficiency could be affected by the water level in wetlands; a higher level boosts nitrogen removal efficiency.

Global inundation dynamics inferred from multiple satellite observations, 1993–2000

Wetlands and surface waters are recognized to play important roles in climate, hydrologic and biogeochemical cycles, and availability of water resources. Until now, quantitative, global time series of spatial and temporal dynamics of inundation have been unavailable. This study presents the first global estimate of monthly inundated areas for 1993–2000. The data set is derived from a multisatellite method employing passive microwave land surface emissivities calculated from SSM/I and ISCCP observations, ERS scatterometer responses, and AVHRR visible and near‐infrared reflectances. The satellite data are used to calculate inundated fractions of equal area grid cells (0.25° × 0.25° at the equator), taking into account the contribution of vegetation to the passive microwave signal. Global inundated area varies from a maximum of 5.86 × 106 km2 (average for 1993–2000) to a mean minimum of 2.12 × 106 km2. These values are considered consistent with existing independent, static inventories. The new multisatellite estimates also show good agreement with regional high‐resolution SAR observations over the Amazon basin. The seasonal and interannual variations in inundation have been evaluated against rain rate estimates from the Global Precipitation Climatology Project (GPCP) and water levels in wetlands, lakes, and rivers measured with satellite altimeters. The inundation data base is now being used for hydrology modeling and methane studies in GCMs.

MODEL ESTIMATION OF LAND-USE EFFECTS ON WATER LEVELS OF NORTHERN PRAIRIE WETLANDS

Wetlands of the Prairie Pothole Region exist in a matrix of grassland dominated by intensive pastoral and cultivation agriculture. Recent conservation management has emphasized the conversion of cultivated farmland and degraded pastures to intact grassland to improve upland nesting habitat. The consequences of changes in land-use cover that alter watershed processes have not been evaluated relative to their effect on the water budgets and vegetation dynamics of associated wetlands. We simulated the effect of upland agricultural practices on the water budget and vegetation of a semipermanent prairie wetland by modifying a previously published mathematical model (WETSIM). Watershed cover/land-use practices were categorized as unmanaged grassland (native grass, smooth brome), managed grassland (moderately heavily grazed, prescribed burned), cultivated crops (row crop, small grain), and alfalfa hayland. Model simulations showed that differing rates of evapotranspiration and runoff associated with different upland plant-cover categories in the surrounding catchment produced differences in wetland water budgets and linked ecological dynamics. Wetland water levels were highest and vegetation the most dynamic under the managed-grassland simulations, while water levels were the lowest and vegetation the least dynamic under the unmanaged-grassland simulations. The modeling results suggest that unmanaged grassland, often planted for waterfowl nesting, may produce the least favorable wetland conditions for birds, especially in drier regions of the Prairie Pothole Region. These results stand as hypotheses that urgently need to be verified with empirical data.

Effects of capillarity and microtopography on wetland specific yield

Hydrologic models aid in describing water flows and levels in wetlands. Frequently, these models use a specific yield conceptualization to relate water flows to water level changes. Traditionally, a simple conceptualization of specific yield is used, composed of two constant values for above- and below-surface water levels and neglecting the effects of soil capillarity and land surface microtopography. The effects of capillarity and microtopography on specific yield were evaluated at three wetland sites in the Florida Everglades. The effect of capillarity on specific yield was incorporated based on the fillable pore space within a soil moisture profile at hydrostatic equilibrium with the water table. The effect of microtopography was based on areal averaging of topographically varying values of specific yield. The results indicate that a more physically-based conceptualization of specific yield incorporating capillary and microtopographic considerations can be substantially different from the traditional two-part conceptualization, and from simpler conceptualizations incorporating only capillarity or only microtopography. For the sites considered, traditional estimates of specific yield could underor over-estimate the more physically based estimates by a factor of two or more. The results suggest that consideration of both capillarity and microtopography is important to the formulation of specific yield in physically based hydrologic models of wetlands.

Effects of variable hydroperiods and water level fluctuations on denitrification capacity, nitrate removal, and benthic-microbial community structure in constructed wetlands

The hydrologic character of wetlands is one of the attributes by which they are defined. There are, however, conflicting reports about the detrimental versus beneficial responses of wetland systems to water level fluctuations and variable hydroperiods. We conducted water level and hydroperiod fluctuation studies in full-scale experimental wetlands in order to determine the effects of hydraulic operation on wetland performance (in terms of nutrient removal), and benthic-bacterial community function (in terms of denitrification potential, DNP) and structure (via terminal restriction fragment length polymorphisms, T-RFLP). In our comparison, detention time was the controlling factor for nitrate removal at the system level. However, widely fluctuating water levels and variable hydroperiods did not diminish either the nitrate removal capacity of the experimental wetlands, or the size or composition of benthic-bacterial communities relative to the more stable water level systems. Rather, significant differences in denitrification potential rates, bacterial cell densities, and benthic community structure were a function of sampling location within the experimental wetlands regardless of hydraulic operation. The results of this study support the need for reconsidering the hydraulic criteria for wetland delineation.

Hydrologic interactions between an alluvial fan and a slope wetland in the central Rocky Mountains, USA

Slope wetlands generally occur at breaks in slope where discharging ground water maintains moist soil conditions. They often are found on the perimeter of highly permeable alluvial fans, but there have been no detailed hydrologic studies of these particular wetlands. We combined stream and spring flow measurements with five years of water-level and piezometric data to understand the hydrology of a 1.6 ha slope wetland at the base of a 5.2 ha alluvial fan in the central Rocky Mountains of Colorado. Step changes in streamflow inputs resulting from an upstream water diversion helped confirm the linkages inferred from the hydrometric data. Nearly 30% of the streamflow along a 180-m reach on the alluvial fan was lost to seepage. Discharge from two springs at the toe of the alluvial fan was eliminated and the piezometric head in the toe of the fan decreased by more than 80 cm within 1-2 days after the stream was diverted, indicating that stream seepage is the primary source of ground-water recharge for the alluvial fan. Streamflow and ground water discharging at the base of the alluvial fan were the primary wetland inflows, with summer precipitation playing a relatively minor role. Consequently, wetland water levels declined by up to 75 cm after the diversion began operating. The largest declines were in the lower part of the wetland, where surface sheet flow from the stream was the main water source. Continuing ground-water discharge into the upper part of the wetland limited the water level declines to less than 40 cm. The importance of streamflow as a water source distinguishes slope wetlands adjacent to alluvial fans from those found in other settings and makes them particularly vulnerable to upstream water diversions.