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At least 811 records · Page 45Linked to original sources

USGS2018

Wetland stratigraphic evidence for variable megathrust earthquake rupture modes at the Cascadia subduction zone

Although widespread agreement that the Cascadia subduction zone produces great earthquakes of magnitude 8 to 9 was reached decades ago, debate continues about the rupture lengths, magnitudes, and frequency of megathrust earthquakes recorded by wetland stratigraphy fringing Cascadia’s estuaries. Correlation of such coastal earthquake evidence along the subduction zone has largely relied on relative position in a stratigraphic sequence and maximum-limiting 14C ages with errors of decades to hundreds of years. Offshore, a 10,000-year record of turbidites in marine cores is interpreted as an archive of strong shaking from great earthquakes, with an average frequency of about 500 years in northern Cascadia versus 200-300 years in southern Oregon and northern California. Onshore, fewer events marked by sharp (<3 mm) peat-mud (mud-over-peat) contacts in tidal wetland stratigraphic sequences have been widely inferred to record sudden relative sea-level rise due to coseismic subsidence during megathrust earthquakes: 4-7 sharp subsidence contacts in 3500 years at estuaries in northern Oregon and southern Washington (500-800 year average recurrence), and 9-12 sharp subsidence contacts in over 6000 years in sequences in central and southern Oregon (500-900 year average recurrence). Improved understanding of the onshore and offshore records is critical to the assessment of earthquake hazard in western North America and of tsunami hazard in the Pacific basin. However, because dating the turbidite record is inherently much less precise than are age models for subsidence events in the most thoroughly studied tidal wetland sequences, accurate reconstruction of the times of Cascadia’s great earthquakes depends on the ages from the onshore record. Although methods to reduce uncertainty in the limits of resolution of tidal stratigraphy for recording earthquakes of a particular magnitude, and ways to distinguish earthquake subsidence stratigraphic contacts from non-seismic contacts, have been discussed for decades (e.g., Nelson, 1992; Atwater, 1992; Darienzo et al., 1994; Nelson et al., 1996a; Atwater and Hemphill-Haley, 1997; Witter et al., 2001; Kelsey et al., 2002; Nelson et al., 2006; Graehl et al., 2014; Milker et al., 2016), consensus about the threshold of resolution (minimum identifiable evidence of an earthquake) of tidal stratigraphy and, therefore, the completeness of Cascadia’s coastal record of great earthquakes, remains elusive. Although the most distinct, widespread contacts likely record close to a meter of coastal subsidence during the greatest megathrust earthquakes (e.g., M8.8-M9), other contacts may record <0.5 m of subsidence onshore of patches of low stress release on the megathrust during great earthquakes, during lesser megathrust earthquakes (e.g., M8.2-8.6), or from localized subsidence near upper-plate faults that slip during or independently of megathrust earthquakes (Nelson et al., 1996b; Wang et al., 2013; Kemp et al., 2018). At the Siuslaw River estuary in central Oregon (lat. 43.97°) a stratigraphy of 9-12 peat-mud contacts, similar to those described from many Cascadia estuaries, may record a greater number of earthquakes during the past 2000 years than at any other of the tens of tidal wetland sites to the north and south. Here, as well as at many tens of other Cascadia tidal wetland sites, peat-mud contacts mark the tops of couplets of tidal flat and low marsh mud gradually shoaling upward into middle and high marsh peat. Along core transects across an 800-m-wide, island marsh in the Siuslaw River, we traced the 9 most continuous of 12-15 peaty beds dating from the past 2000 years for 250-500 m, but we had difficulty correlating the 3-6 intervening beds >50-100 m. We attribute the sharper, more extensive upper contacts on peaty beds—two capped by sandy beds probably deposited by tsunamis—to sudden coseismic subsidence of middle and high marshes, but origins for other upper and lower contacts boundi

Conference Paper↗

USGS2005

Historical subsidence and wetland loss in the Mississippi delta plain

Five representative areas of the Mississippi River delta plain were investigated using remote images, marsh elevations, water depths, sediment cores, and radiocarbon dates to estimate the timing, magnitudes, and relative rates of marsh erosion and land subsidence at geological and historical time scales. In the Terrebonne-Lafourche region of rapid interior-wetland loss, former marshes are now submerged beneath water that averages 0.5 to 1.0 m deep. Most of the permanent historical flooding was caused by rapid subsidence and collapse of the delta plain that occurred during the late 1960s and 1970s. Subsequent erosion of the submerged delta-plain marsh was relatively minor at most of the coring sites. Widespread nearly simultaneous collapse of marshes across the Mississippi delta plain appears to be unprecedented and not repeated in the geological record of the past 1,000 years. Surface and subsurface data strongly indicate that the rapid subsidence and associated wetland loss were largely induced by extraction of hydrocarbons and associated formation water. Average historical rates of subsidence between 1965 and 1993 were about 8 to 12 mm/yr, whereas average geological rates of subsidence for the past 5,000 years were about 1 to 5 mm/yr. Natural processes such as deep-seated salt migration and fault movement cannot be discounted entirely, but there is no compelling evidence that these processes were responsible for the observed historical changes. Results of this study provide a basis for determining the relative importance of subsidence and shoreline erosion as causes of past wetland loss and for predicting sites and probable mechanisms of future wetland loss. This information should improve the selection of project sites and designs for wetland-loss mitigation and coastal restoration in south Louisiana.

Louisiana↗

USGS2009

Quantifying biophysical conditions of herbaceous wetland vegetation in Poyang Lake of coastal China via multi-temporal SAR imagery and in-situ measurements

Wetland ecosystems, known as the “kidneys of the earth,” are an important habitat for aquatic fl ora and fauna and provide valuable services and goods for the human beings. The wetlands in Poyang Lake of the Southeast China coastal region are one of the fi rst national natural reserves listed in the Ramsar convention in 1992. Poyang Lake is the largest freshwater lake in China and its natural wetland area covers over 4000 km2 with diverse species of plants and vertebrate. Every year several million migratory birds live through the winter in this region (Liu and Ye, 2000). The Lake also plays an important role in fl ood control along the Yangtze River watershed. In the last several decades, however, overexploitation of the wetlands in Poyang Lake has altered seriously the ecosystem and reduced biodiversity. The area of wetlands in the Poyang Lake region has decreased by over 1000 km2 and total water storage decreased by 6000 million m3 due to reclamation (Wang et al., 2004).

Poyang Lake↗

USGS1995

The role of wetlands as nearshore habitat in Lake Huron

Wetlands are generally considered to be among the most productive habitats on earth. As the landscape connection between upland and aquatic ecosystems, they posess many of the attributes of both systems and perform functions that extend beyond the wetland boundary into both systems. In Lake Huron, wetlands comprise a small fraction of the total area, but they provide nearshore habitat for many plant and animal species that are deemed important for the lake as a whole. Thus, their role is an important one. In this paper, after describing the general functions and types of wetlands, I will explore the importance of wetland habitat in Lake Huron by defining its extent, describing physical and biological processes, summarizing biological uses, and detailing management problems.

Book chapter↗

USGS1992

A new device for collection of interstitial water from wetland sediments

A sampler for collection of interstitial water from wetland sediments is described. It differs from other sampling devices because it does not have to be filled with solution to facilitate diffusion, it does not have to be removed from the wetland to collect samples, and it can be used to draw repeated samples over time from identical locations. The device facilitates “in situ” measurement of a wide range of abiotic parameters such as electrical conductivity, redox potential, and pH in wetland sediments. The device has application in ecological investigations of sediment-borne wildlife diseases, studies of benthic invertebrates, measurement of nutrient exchange, and other aspects of wetland ecology.

Wetlands Ecology and Management↗

USGS1985

Disturbance in a cypress-tupelo wetland: an interaction between thermal loading and hydrology

The interaction between thermal loading and hydrology was examined in a forested wetland. As a result of flooding, portions of the wetland are periodically exposed to elevated water temperatures, resulting in progressive deterioration of the canopy. We chose three study sites along a gradient of canopy disturbance: most disturbed, intermediate disturbance and a least disturbed site. The timing of flooding has important effects on this wetland: floods which occur late in the growing season have greater impact on the timing of litterfall and the extent of tree mortality. Following a flood in May, there was no observed increase in litterfall, and woody detrital production (tree mortality) eliminated only o.4% and 1.1% of the aboveground woody biomass at the intermediate and least disturbed sites, respectively. In contrast. premature leaf senescence and literfall were observed at the intermediate site following an August flood, and tree mortality at the intermediate and least disturbed sites eliminated 10% and 8%, respectively, of the aboveground woody biomass. At the most disturbed site, where the majority of trees were already dead, no additional mortality was recorded during the study. Long-term effects of this disturbance regime are the loss of small stems and increased stem production of trees which remain. While stem production at the intermediate site (413 g.m −2 .yr −1 ) exceeded that at the least disturbed site (373 g.m −2 .y −1 ), total aboveground net primary production was highest at the least disturbed site (788 g·m −2 · yr −1 ), primarily because of the greater stem density. Portions of this wetland continue to deteriorate after more than 30 years of thermal loading.

Wetlands↗

USGS1997

A rop net and removable walkway used to quantitatively sample fishes over wetland surfaces in the dwarf mangrove of the Southern Everglades

We describe a 9 m 2 drop net and removable walkways designed to quantify densities of small fishes in wetland habitats with low to moderate vegetation density. The method permits the collection of small, quantitative, discrete samples in ecologically sensitive areas by combining rapid net deployment from fixed sites with the carefully contained use of the fish toxicant rotenone. This method requires very little contact with the substrate, causes minimal alteration to the habitat being sampled, samples small fishes in an unbiased manner, and allows for differential sampling of microhabitats within a wetland. When used in dwarf red mangrove ( Rhizophora mangle ) habitat in southern Everglades National Park and adjacent areas (September 1990 to March 1993), we achieved high recovery efficiencies (78–90%) for five common species <110 mm in length. We captured 20,193 individuals of 26 species. The most abundant fishes were sheepshead minnow Cyprinodon variegatus , goldspotted killifish Floridichthys carpio , rainwater killifish Lucania parva , sailfin molly Poecilia latipinna , and the exotic Mayan cichlid Cichlasoma urophthalmus . The 9 m 2 drop net and associated removable walkways are versatile and can be used in a variety of wetland types, including both interior and coastal wetlands with either herbaceous or woody vegetation.

Wetlands↗

USGS1999

Characterizing hydrology and the importance of ground-water discharge in natural and constructed wetlands

Although considered the most important component for the establishment and persistence of wetlands, hydrology has been hard to characterize and linkages between hydrology and other environmental conditions are often poorly understood. In this work, methods for characterizing a wetland’s hydrology from hydrographs were developed, and the importance of ground water to the physical and geochemical conditions in the root zone was investigated. Detailed sampling of nearly continuous hydrographs showed that sites with greater ground-water discharge had higher water tables and more stable hydrographs. Subsampling of the continuous hydrograph failed to characterize the sites correctly, even though the wetland complex is located in a strong regional ground-water-discharge area. By comparing soil-moisture-potential measurements to the water-table hydrograph at one site, we noted that the amount of root-zone saturation was not necessarily driven by the water-table hydrograph but can be a result of other soil parameters (i.e., soil texture and associated capillary fringe). Ground-water discharge was not a significant determinant of maximum or average temperatures in the root zone. High ground-water discharge was associated with earliest date of thaw and shortest period of time that the root zone was frozen, however. Finally, the direction and magnitude of shallow ground-water flow was found to affect the migration and importance of a geochemical species. Areas of higher ground-water discharge had less downward penetration of CO 2 generated in the root zone. In contrast, biotically derived CO 2 was able to penetrate the deeper ground-water system in areas of ground-water recharge. Although ground-water flows are difficult to characterize, understanding these components is critical to the success of wetland restoration and creation efforts.

Wisconsin↗

USGS1999

Passing of northern pike and common carp through experimental barriers designed for use in wetland restoration

Restoration plans for Metzger Marsh, a coastal wetland on the south shore of western Lake Erie, incorporated a fish-control system designed to restrict access to the wetland by large common carp ( Cyprinus carpio ). Ingress fish passageways in the structure contain slots into which experimental grates of varying size and shape can be placed to selectively allow entry and transfer of other large fish species while minimizing the number of common carp to be handled. We tested different sizes and shapes of grates in experimental tanks in the laboratory to determine the best design for testing in the field. We also tested northern pike ( Esox lucius ) because lack of access to wetland spawning habitat has greatly reduced their populations in western Lake Erie. Based on our results, vertical bar grates were chosen for installation because common carp were able to pass through circular grates smaller than body height by compressing their soft abdomens; they passed through rectangular grates on the diagonal. Vertical bar grates with 5-cm spacing that were installed across much of the control structure should limit access of common carp larger than 34 cm total length (TL) and northern pike larger than 70 cm. Vertical bar grates selected for initial field trials in the fish passageway had spacings of 5.8 and 6.6 cm, which increased access by common carp to 40 and 47 cm TL and by northern pike to 76 and 81 cm, respectively. The percentage of potential common carp biomass (fish seeking entry) that must be handled in lift baskets in the passageway increased from 0.9 to 4.8 to 15.4 with each increase in spacing between bars. Further increases in spacing would greatly increase the number of common carp that would have to be handled. The results of field testing should be useful in designing selective fish-control systems for other wetland restoration sites adjacent to large water bodies.

Michigan↗

USGS2019

The importance of turtle populations to wetland restoration in the upper Mississippi embayment of the Mississippi Alluvial Valley

The Upper Mississippi Embayment (UME) ecoregion covers approximately 141,895 km2 and historically supported 9,712,455 ha of bottomland deciduous forests, swamps, bayous, and rivers. Only about 500 ha (< 0.01%) of pre-settlement bottomland hardwood forest habitat in the Mississippi Alluvial Valley (MAV) in the UME remained by the 1940s because the timber was clearcut and the wetlands drained for agriculture. By 1983 only a few scattered cypress-tupelo swamps remained. We studied the freshwater turtle community in Allred Lake, Missouri, a rare remnant of this ecosystem and compared these results to those from two other study sites in the MAV, Big Oak Tree State Park (BOTSP), Missouri, and Coldwater River National Wildlife Refuge (CRNWR), Mississippi. Species richness included six species commonly found throughout the MAV. One species (Red-eared Slider, Trachemys scripta elegans) dominated density and biomass in all three assemblages. The occurrence of the six species we studied in man-made restored wetlands such as those in BOTSP and CRNWR indicate these turtles would adapt to restored wetlands in the MAV in southeastern Missouri and elsewhere in the ecosystem. We provide information on habitat features that could be included in restoration design and construction that would benefit turtles. Given the ongoing worldwide decline of turtles, consideration of turtle ecology and behavior in wetland restoration projects in the MAV may be warranted.

Arkansas, Illinois, Kentucky, Louisiana, Mississip↗

USGS2022

Influences of seasonality and habitat quality on Great Lakes coastal wetland fish community composition and diets

Great Lakes coastal wetlands (GLCW) have been severely degraded by anthropogenic activity over the last several decades despite their critical role in fish production. Many Great Lakes fish species use coastal wetland habitats for spawning, feeding, shelter, and nurseries throughout the year. The goal of our study was to compare GLCW fish community composition in the spring, summer, and fall months and investigate how water quality relates to fish diversity, the presence of functional groups, and juvenile fish diets. We summarized fish data collected from GLCW across the basin and used the coastal wetland monitoring program’s water quality-land use indicator to quantify water quality. Basin-wide, we found taxonomic and functional group differences in community composition among three sampling seasons, as well as across the range of water quality. Water quality was positively associated with the abundance of small cyprinids and the relative abundance of some habitat and reproductive specialists. Seasonal differences were also observed for many of these functional groups, with more temperature- and pollution-sensitive fishes captured in the spring and more nest-spawning fishes captured in the summer and fall. In our diet study, we found that age-0 fish primarily consumed zooplankton in the fall, whereas age-1 fish primarily consumed macroinvertebrates in the spring. Moreover, wetland quality was positively associated with trichopteran prey abundance. We concluded that taxonomic and functional composition of fish communities in GLCW vary markedly with respect to water quality and season. Thus, a full understanding of communities across a gradient of quality requires multi-season sampling.

Great Lakes↗

USGS2013

Influence of drought on salamander occupancy of isolated wetlands on the southeastern Coastal Plain of the United States

In the southeastern U.S., changes in temperature and precipitation over the last three decades have been the most dramatic in winter and spring seasons. Continuation of these trends could negatively impact pond-breeding amphibians, especially those that rely on winter and spring rains to fill seasonal wetlands, trigger breeding, and ensure reproductive success. From 2009 to 2012, we monitored Spring and Fall presence of aquatic stages (larval and paedomorphic, gilled adult) of a winter-breeding amphibian (the mole salamander, Ambystoma talpoideum) and used multi-season models to estimate occupancy, local colonization and extinction. Seasonal estimates of occupancy, corrected for imperfect detection, declined from 22.3 % of ponds in Spring 2009 to 9.9 % in Fall 2012. Our best supported model suggested that changes in occupancy were driven by increased rates of extinction that corresponded with drought-related drying of ponds. Based on uncertainty in climate change projections for the Southeast, we present a conceptual model of predicted changes in wetland hydroperiods across a landscape with projected decreases and increases in future precipitation. Such precipitation changes could alter wetland hydroperiods, facilitate extinctions of species adapted to short, intermediate or long hydroperiod environments and, ultimately, modify the composition of amphibian communities within freshwater wetland ecosystems.

Florida↗

USGS2019

Perspective: Developing flow policies to balance the water needs of humans and wetlands requires a landscape scale approach inclusive of future scenarios and multiple timescales

Maintenance of the natural flow regime is essential for continued wetland integrity; however, the flow regime is greatly influenced by both natural and anthropogenic forces. Wetlands may be particularly susceptible to altered flow regimes as they are directly impacted by water flows at a variety of time scales. In Puerto Rico, contemporary water management is decreasing freshwater recharge to wetlands and contributes to the salinization of important coastal wetlands as sea levels rise. Further, downscaled climate models predict an increase in drought frequency, intensity, and duration by mid-century. Conflicts over water allocation seem imminent between human and ecological needs. Current minimum flow policies are insufficient given the complexities of ecosystem processes and the changes in precipitation patterns and sea level rise that are expected in the future. Improved flow policies need to be established that reflect the functional relationships between specific representative ecological resources and components of the natural flow regime across all relevant time scales. Similarly, flow policies need to be developed within a landscape scale to implicitly address the socio-ecological trade-offs as well as the complexities of water management. Multi-disciplinary collaborations will be essential for increasing our resiliency to anticipated future changes.

Wetlands↗

USGS2021

Wetland conservation: Challenges related to water law and farm policy

Water is essential for wetland function and sustaining migratory networks for wetland wildlife across broad landscapes. Groundwater declines and surface flow reductions that impact aquatic and wetland organisms are common in the western U.S. and increasingly in the eastern U.S. Agriculture is the largest consumptive water user in the U.S. and understanding economic incentives of water-use practices and the legal context of water rights is foundational to identifying meaningful water solutions. In this paper, we provide a brief legal overview of water rights in the U.S. and synthesize the literature to provide a broad overview of how federal farm policy influences water-use decisions. We conclude that the ultimate cause of many water-use conflicts is an inefficient, farm economy that is driven by several proximate factors, of which outdated water laws and subsidies that encourage increased water use are among the most important. Development of multi-scale water budgets to assess project impacts and by working more intensively at local watershed and aquifer scales can improve conservation efforts. Finally, detailed analyses to understand and minimize the impacts of specific federal policies on agricultural water use would enhance water conservation efforts, facilitate long-term food and water security, and provide greater protection for wetland and aquatic resources.

Wetlands↗

USGS2023

Doing the same thing over and over again and getting the same result: Assessing variance in wetland invertebrate assemblages

Past efforts to explain variation of invertebrate assemblages in freshwater wetlands have been less productive than anticipated. To explore why efforts are disappointing, we assembled large invertebrate data sets from North Dakota prairie potholes, California rock pools, and Georgia Carolina bay wetlands that addressed spatial (among wetlands) and temporal (among seasons and years) variation. We anticipated that these large data-set sizes would enable robust conclusions to be drawn, and each place had unique environmental conditions that might contribute to greater explanatory power. We used statistical techniques that partitioned variation in invertebrate assemblages into spatial and/or temporal components, and that also yielded a measure of the amount of unexplained variation; Permutational Multivariate Analysis of Variation and Principal Coordinates Analysis assessed whole assemblage variation, and Analysis of Variance or Analysis of Covariance assessed variation in taxon richness, total abundances, and abundances of wide-spread individual taxa. Across all locations, variation explained by spatial and temporal factors, and unexplained variation were of comparable magnitudes (i.e., similar R 2 values of ~ 50%). Review of other published studies indicate that this pattern is widespread. The 50% or more unexplained variation is typically ignored by researchers, who instead focus on explained fractions. We argue that, besides addressing explained spatial and temporal variation in invertebrate assemblages (e.g., control by hydrology, resources, predation), efforts to understand what contributes to currently unexplained variation, that is unrelated to local spatial or temporal controls (e.g., broad climatic and biogeographic patterns, organism physiology and behavior), will lead to a fuller comprehension of how invertebrates in freshwater wetlands are controlled.

Wetlands↗

USGS2026

Towards a refined definition of “tidal influence” for the coastal wetland sciences

The astronomical tide relates to lunar (and to a lesser extent solar) influences on rising and falling water bodies, and is a key control of many coastal processes. However, tides manifest along coastal margins in different ways to muddle application beyond Sir Isaac Newton’s first descriptions. Here, we argue that tide, or specifically “tidal,” has not been adequately defined for the coastal wetland sciences to facilitate contemporary interdisciplinary distinction for rapidly changing coastlines and future climate adaptation planning. We provide a brief history of the tidal concept, and we describe tides in a diversity of uncommonly recognized marginal coastal environments. Common astronomical tide manifestations are described through hydrographic examples, then expanded to include those tidal environments exposed additionally to fluvial, meteorological (wind), or groundwater influences. Our expanded definition of “tidal” is intended to be a forward-looking construct as environments will inevitably change with sea-level rise, water extraction, and anthropogenic flow alteration. Our definition of wetland tidal influence, which we broaden, includes those “wetlands affected by astronomic water level fluctuations within coastally restricted environments causing frequent or infrequent surface inundation or groundwater tidal variation that affects the biogeochemistry of the soil (e.g., ion exchange capacity, oxygen state, mineralization processes)”. Astronomic water level fluctuations are often amplified or dampened by non-astronomical events, such as wind. Expanding the definition of what is considered tidal by the scientific community is critical for improved understanding of coastal wetland function and the suite of ecosystem services they provide people and society, including climate mitigation opportunity, management, and adaptation.

Wetlands↗

USGS2000

Effects of roadside transect width on waterfowl and wetland estimates

Strip transects located along roads are commonly used to estimate waterfowl populations and characterize associated wetland habitat. We used data collected in May and early June, 1995, on forty-five 40-km 2 plots in North Dakota to evaluate bias of 800-m and 400-m wide roadside transects for sampling wetlands relative to a larger (40-km 2 ) scale and to compare duck abundance at the two widths. Densities of all basins combined and of seasonal basins considered alone were biased high for both transect widths, but mean bias did not differ from zero for temporary or semipermanent basins. Biases did not occur when excavated seasonal and temporary basins (i.e., road ditches) were excluded from the sample. Mean basin density was higher for the inner (400-m) transect width than for the outer transect width (area remaining of the 800-m transect, outside of center 400-m width) for all basins combined and for seasonal and temporary basins. We detected an area-related bias in the occurrence of basins in transects: smaller basins (0.08–1.6 ha) were over-represented in transect samples by 2.9–6.5%, and larger basins (≥11 ha) were under-represented in 800-m transects by 7.3% and in 400-m transects by 16.3%. We compared the distribution of ducks relative to water conditions in the inner and outer transect widths to evaluate whether they were affected by proximity to the road. Mallards ( Anas platyrhynchos L.), northern pintails ( A. acuta L.), and gadwall ( A. strepera L.) responded to water conditions equally in the inner and outer transect widths, but northern shovelers ( A. clypeata L.) and blue-winged teal ( A. discors L.) responded more strongly to wetlands on the inner than the outer transect width, indicating that estimates of these species would be higher from a 400-m wide transect than from an 800-m wide transect. Differences in an adjustment index, used to account for the portion of basin obscured from view, were highly variable between inner and outer transect widths but did not indicate that use of wider transects was hampered by visibility. Biases of transect sampling need to be carefully considered when extrapolating wetland basin or duck densities from transects to larger landscape scales.

Wetlands↗

USGS2004

Estimates of fetch-induced errors in Bowen-ratio energy-budget measurements of evapotranspiration from a prairie wetland, Cottonwood Lake Area, North Dakota, USA

Micrometeorological measurements of evapotranspiration ( ET ) often are affected to some degree by errors arising from limited fetch. A recently developed model was used to estimate fetch-induced errors in Bowen-ratio energy-budget measurements of ET made at a small wetland with fetch-to-height ratios ranging from 34 to 49. Estimated errors were small, averaging −1.90%±0.59%. The small errors are attributed primarily to the near-zero lower sensor height, and the negative bias reflects the greater Bowen ratios of the drier surrounding upland. Some of the variables and parameters affecting the error were not measured, but instead are estimated. A sensitivity analysis indicates that the uncertainty arising from these estimates is small. In general, fetch-induced error in measured wetland ET increases with decreasing fetch-to-height ratio, with increasing aridity and with increasing atmospheric stability over the wetland. Occurrence of standing water at a site is likely to increase the appropriate time step of data integration, for a given level of accuracy. Occurrence of extensive open water can increase accuracy or decrease the required fetch by allowing the lower sensor to be placed at the water surface. If fetch is highly variable and fetch-induced errors are significant, the variables affecting fetch (e.g., wind direction, water level) need to be measured. Fetch-induced error during the non-growing season may be greater or smaller than during the growing season, depending on how seasonal changes affect both the wetland and upland at a site.

North Dakota↗