Upland Wetland Research Articles

Four principles for improved statistical ecology

Abstract Increasing attention has been drawn to the misuse of statistical methods over recent years, with particular concern about the prevalence of practices such as poor experimental design, cherry picking and inadequate reporting. These failures are largely unintentional and no more common in ecology than in other scientific disciplines, with many of them easily remedied given the right guidance. Originating from a discussion at the 2020 International Statistical Ecology Conference, we show how ecologists can build their research following four guiding principles for impactful statistical research practices: (1) define a focussed research question, then plan sampling and analysis to answer it; (2) develop a model that accounts for the distribution and dependence of your data; (3) emphasise effect sizes to replace statistical significance with ecological relevance; and (4) report your methods and findings in sufficient detail so that your research is valid and reproducible. These principles provide a framework for experimental design and reporting that guards against unsound practices. Starting with a well‐defined research question allows researchers to create an efficient study to answer it, and guards against poor research practices that lead to poor estimation of the direction, magnitude, and uncertainty of ecological relationships, and to poor replicability. Correct and appropriate statistical models give sound conclusions. Good reporting practices and a focus on ecological relevance make results impactful and replicable. Illustrated with two examples—an experiment to study the impact of disturbance on upland wetlands, and an observational study on blue tit colouring—this paper explains the rationale for the selection and use of effective statistical practices and provides practical guidance for ecologists seeking to improve their use of statistical methods.

Spatial variation of soil organic matter and metal mobility in wetland soils: Implications for biogeochemical processes in lateritic landscape

The evolution of the lateritic landscape over time changes the path of pedogenesis and soil hydrology. The occurrence of upland wetlands in the savannah flat plateau transforms well-drained lateritic soils into hydric soils enriched in organic matter. We investigated the composition of soil organic matter (SOM) produced in a wetland and their link with the mineral constituents of soil and their contribution to the mobility of Si, Fe, and Al in the soil. Six tranches were opened in a soil catena located from the plateau toward the center of the wetland, representing different hydromorphic features. Soil morphology was described, and chemical, physical and mineralogical analyses were performed to evaluate soil properties. Chemical fractionation of Soil Organic Matter (SOM) was performed and total organic carbon (TOC), dissolved organic carbon (DOC), particulate organic carbon (POC), and water-extractable organic matter (WEOM) were determined in the soil horizons. Metal complexing properties of DOM were determined using an excitation-emission matrix of fluorescence. The occurrence of Fe eluviation in the superficial horizons, Fe2O3 enrichment in the mottled horizons, and ferricrete formation in the center of the wetland were observed. Geochemical transfer assessment and the variation of oxides within the horizons showed that Fe2O3 and SiO2 were more mobile than Al2O3, whose variability in the gley horizon reflected the mobility of Fe2O3 and SiO2. The stability constants of Al and Cu showed an increase with the depth for WEOM and SOM. The pattern of the organic carbon fraction varied according to the level of hydromorphy and soil depth. It was also observed an increase in the C/N ratio with depth, possibly related to the reduced bioavailability of DOC due to its adsorption with soil solids.

Development of soil health benchmarks for managed and semi-natural landscapes

Efforts to improve soil health require that target values of key soil properties are established. No agreed targets exist but providing population data as benchmarks is a useful step to standardise soil health comparison between landscapes. We exploited nationally representative topsoil (0–15 cm) measurements to derive soil health benchmarks for managed and semi-natural environments across Great Britain. In total, 4587 soil organic matter (SOM), 3860 pH, 2908 bulk density (BD), and 465 earthworm abundance (EA) datapoints were used. As soil properties are sensitive to site-specific characteristics, data were stratified by habitat, soil type, and mean annual precipitation, with benchmarks defined as the middle 80 % of values in each distribution – yielding 135 benchmarks. BD and pH decreased with land management intensity (agriculture > semi-natural grasslands > woodlands > heathlands > wetlands), and vice versa for SOM and EA. Normalising benchmark ranges by medians revealed soil health indicator benchmark widths increased in the order: pH < BD < SOM < EA, while width increased with decreasing land management intensity. Arable and horticulture and improved grassland exhibited narrow benchmarks for SOM, pH and BD, yet the widest EA benchmark, suggesting additional drivers impact EA patterns. Upland wetlands had the widest BD benchmarks, important when determining carbon stocks. East Anglia currently possesses the largest proportions of atypical soils, including below typical SOM (19.2 %), above typical BD (17.4 %) and pH (39.1 %), and the smallest proportions of above typical SOM (2.4 %), and below typical BD (5.8 %) and pH (2.3 %). This is found even after land use, soil type and rainfall have been considered, underscoring how urgently soil health should be addressed here. Our benchmarking framework allows landowners to compare where their measured soil health indicators fall within expected ranges and is applicable to other biomes, national and multinational contexts.

Nesting habits of grey crowned craneBalearica regulorumin Lake Ol’ Bolossat basin, Kenya

AbstractInformation on breeding habits of grey crowned crane (Balearica regulorum) in Kenya is currently lacking. Investigations were therefore carried out between 2017 and 2020 to determine its nesting habits in Lake Ol’ Bolossat basin including nest‐site features, number and distribution of territorial pairs, clutch size, eggs, and duration of breeding cycle. While 103 pairs were observed in the lake marshlands (mean density 5.00 pairs/km2), only 20 were found in upland wetlands. The number of pairs and densities (pairs/km2) in each of the lake's sections were as follows: north (24; 3.23), middle (47; 5.42), and south (32; 6.24). During this study, 61% (n = 63) of the lake marshland pairs attempted to breed compared to 80% (n = 16) in the upland wetlands. A mean of 2.23 eggs/clutch and a modal clutch of three eggs was recorded in 33 accessible nests. The range of influential factors in nest‐site selection were as follows: water depth (50–100 cm), vegetation height around the nest (60–90 cm), and an offshore distance of &gt;100 m. Breeding cycle showed phenotypic plasticity in response to variations in local weather conditions. The number and density of cranes in this study area show its importance in the recovery and survival of the species, and which should subsequently be accorded effective protection.

Challenges and opportunities of participatory management of Upland Wetland in Kiambu County, Kenya

Abstract. Kinyariro MS, Njuguna SG, Macharia G. 2019. Challenges and opportunities of participatory management of Upland Wetland in kiambu county, Kenya. Bonorowo Wetlands 10: 52-65. Wetlands are continuously degraded through agricultural activities, pollution, and settlements. For example, in the Lari sub-district, increased population pressure decreased soil fertility, unreliable rainfall, and the search for food security forced farmers to encroach on the seemingly idle Upland Wetlands. Opportunities for wetland conservation lie in participatory approaches that can be applied at the local level to assist in conserving this vital natural resource. The main water of the Ruiru river comes from the Upland Wetlands harvested by the Nairobi Water and Waste Company in the Githunguri sub-district at the Ruiru dam. This research is critical because the water company does not have in-depth information about its catchment area, which leads to encroachment and ultimately rationing of water in the city of Nairobi. This study aims to document the causes of wetland degradation in the highlands, assess the level of community participation, and determine the level of awareness of the importance of wetlands and the possible contribution of farmer involvement in catchment management. The sampling method used to select the research unit was stratified and random sampling where farmers and Ruiru dam workers were given a questionnaire. Purposive sampling was used to determine the WARMA manager, WRUA officer, and six older people who were interviewed. 40 farmers from the Lari 107 settlement scheme where the wetlands are located and four workers of the Ruiru dam were given questionnaires. Data analysis was performed using the Chi-square package computer, T-test, and SPSS. Percentages for qualitative data are presented using tables, bar charts, and pie charts. The wetland mapping was carried out using GIS and Google Earth. The study results found that the total land cover of upland rice fields was 129.6 Ha after deducting 105.4. Ha for the last thirty years due to encroachment. The study revealed that 65% of respondents had lived in the area for more than 20 years. Farmers drain wetlands primarily for food supply (50%), generate income (25%), while 10% do so to control waterborne diseases. Participation rates are negligible, with only 2.5% of respondents ever participating in wetland conservation. Community-based conservation groups like WRUA still lack in this area. Environmental impacts include loss of biodiversity, destruction of ornithological habitat, and loss of hydro plant species. Social effects include outbreaks of waterborne diseases such as typhoid, water pollution, and weak community conservation infrastructure. However, there is a chance for community involvement, where the majority of the population is ready to carry out conservation (X2 = 0.127, p = 0.001). The formation of community-based conservation groups such as the Water Resources Users Association, the Association of Riverland Owners, and the Watershed Advisory Committee was proposed as the primary solution. Devolution of water resources is also proposed to ensure local people benefit from selling water to city residents. Such efforts would provide an adequate supply of water to Nairobi and the surrounding satellite cities.

Surface Water Quality Differs between Functionally Similar Restored and Natural Wetlands of the Saint Lawrence River Valley in New York

We tested the hypothesis that upland wetland restorations provide the same quality of wetland, in terms of ecosystem services and biodiversity, as natural wetlands in the St. Lawrence River Valley. Water quality (pH, alkalinity, colored dissolved organic matter, phytoplankton community composition, chlorophyll-a, fecal coliform, total phosphorus, dissolved nitrate, turbidity, specific conductivity) in 17 natural and 45 restored wetlands was compared to determine whether wetland restoration provided similar physicochemical conditions as natural wetlands in the Saint Lawrence River Valley of northeastern New York State. Natural wetlands were more acidic, which was hypothesized to result from the avoidance of naturally acidic regions by farmers seeking to drain wetlands for crop and pasture use. Natural wetlands had significantly greater fecal coliform concentrations. Restored wetlands had significantly greater specific conductivity and related ions, and this is attributed to the creation of wetlands upon marine clay deposits. Other water quality indicators did not differ between restored and natural wetlands. These findings confirm other research at these same wetlands showing no substantial differences between restored and natural wetlands in major biotic indicators. Thus, we conclude that wetland restoration does result in wetlands that are functionally the same as the natural wetlands they were designed to replicate.

Vegetation change in semi-permanent or ephemeral montane marshes (lagoons) of the New England Tablelands Bioregion

The vegetation communities within semi-permanent or ephemeral montane marshes colloquially known as lagoons are an under investigated wetland type of the New England Tablelands Bioregion (NETB) yet they are listed (Upland Wetlands) on both state and federal acts as endangered. Lack of survey and analysis of plot data has meant that the variation in vegetation due to zonation, seasonality and unpredictable wetting and drying cycles are poorly understood. Here, 317 full floristic 2 × 2-m plots were placed across 13 lagoons. The plot data were classified to allow description of native and novel vegetation types using the hierarchical EcoVeg schema. The updated classification includes one Division and Macrogroup with 15 Alliances and 47 Associations. Permanent 50-m transects with a 1 × 1-m plot at every 5 m (10 per transect) were placed within lagoons. Five lagoons were resurveyed annually for 3 years. Within transects, each plot was assigned an Association after each survey period. Approximately one third of transect plots changed in vegetation type each year, often at the Alliance level. Over the 3-year period the number of Associations reduced by ~30% across transects associated with increasing drought and drying out of the wetlands. Transitional environments with the greatest level of hydrological periodicity had the greatest variety of Associations recorded. Highly dynamic systems with increased temporal turnover are likely to require increased sampling effort both spatially and temporally than more stable vegetated systems. The constant changing nature of these communities poses significant issues for management and conservation planning, including benchmarking and offsetting, which may require novel solutions.

Extent and effect of the 2019-20 Australian bushfires on upland peat swamps in the Blue Mountains, NSW

The devastating bushfires of the 2019–20 summer are arguably the most costly natural disaster in Australian recorded history. What is little known is that these fires severely affected the temperate highland peat swamps on sandstone (THPSS), a form of upland wetland that occurs in the water supply catchments of Sydney in the Greater Blue Mountains World Heritage Area and National Park. During the fires, 59% of THPSS was burnt and 72% of those by a high severity burn. Upland swamps at Newnes were the most affected, with 96% of swamps burnt and 84% of these experiencing a very high burn severity. We present an analysis of the spatial extent and severity of the bushfire on the THPSS and discuss some of the likely consequences on their geomorphological, hydrological and ecological structure, function and recovery potential.

Condition thresholds in Australia’s threatened ecological community listings hinder conservation of dynamic ecosystems

Environmental degradation is threatening biodiversity and ecosystem function globally. Mandating ecosystem-level protection in policy and legislative frameworks is essential to prevent biodiversity loss. Australia’s Environment Protection and Biodiversity Conservation Act 1999 is the key legislative mechanism for supporting biodiversity at the national level, but has so far been ineffective at protecting habitat and ecological communities. Here we identify a major flaw in the current approach to listing threatened ecological communities (TECs): restrictive condition thresholds that threaten ecosystem function in dynamic ecosystems. Using two wetland TECs as a case study (Upland Wetlands and Coolibah-Black Box Woodlands), we argue that Australia’s environmental legislation should adopt a landscape-scale approach to TEC protection that acknowledges ecosystem function, accounts for different states in temporally dynamic systems, and sustains landscape connectivity of TEC distribution. We present a state-and-transition model for each TEC to show how human activities affect the reference-state continuum of wet and dry phases. We also show that the current listed condition thresholds do not acknowledge alternative ecosystem states and exclude areas that may be important for restoration and conservation of the TEC at the landscape-scale. Description of alternative and transitional states for dynamic systems, including how, when and why ecological communities shift between different states, should be formally integrated into the TEC listing process to protect Australia’s vulnerable ecosystems from further degradation and loss.

Importance of boreal forested wetlands for epiphytic macrolichen communities

Forested wetlands provide ecosystem services and often support elevated levels of biodiversity and rare species. However, forested wetlands are understudied and face threats such as logging and land conversion. Epiphytic lichens are abundant in forested wetlands and may be useful to help delineate microhabitats across wetland–upland gradients. We investigated epiphytic macrolichen richness, diversity, and community composition in 15 sites in the Avalon Forest Ecoregion, Newfoundland, Canada. Within each site, we set up three parallel 40 m transects in (i) the forested wetland, (ii) the ecotone, and (iii) the upland forest. Along each transect, we selected five balsam fir (Abies balsamea (L.) Mill.) trees 10 m apart and surveyed for macrolichens on the lower bole. We collected data on tree height and tree diameter at breast height, which differed significantly among forest types. We also collected data on tree age and canopy cover, which did not differ significantly among forest types. Contrary to hypotheses suggesting that biodiversity is highest in ecotones, we found that mean macrolichen richness was significantly higher in wetlands, lower in the ecotones, and lowest in upland forests, and macrolichen diversity followed a similar pattern but with no significant difference among groups. Macrolichen community composition significantly differed among wetlands, ecotones, and upland forests. A lichen of conservation concern, Erioderma pedicellatum (Hue) P.M. Jørg., was detected primarily in forested wetlands, highlighting wetlands as key habitats for rare epiphytic macrolichens.

Amphibian chytrid prevalence on boreal toads in SE Alaska and NW British Columbia: tests of habitat, life stages, and temporal trends.

Tracking and understanding variation in pathogens such as Batrachochytrium dendrobatidis (Bd), the agent of amphibian chytridiomycosis which has caused population declines globally, is a priority for many land managers. However, relatively little sampling of amphibian communities has occurred at high latitudes. We used skin swabs collected during 2005-2017 from boreal toads Anaxyrus boreas (n = 248), in southeast Alaska (USA; primarily in and near Klondike Gold Rush National Historical Park [KLGO]) and northwest British Columbia (Canada) to determine how Bd prevalence varied across life stages, habitat characteristics, local species richness, and time. Across all years, Bd prevalence peaked in June and was >3 times greater for adult toads (37.5%) vs. juveniles and metamorphs (11.2%). Bd prevalence for toads in the KLGO area, where other amphibian species are rare or absent, was highest from river habitats (55.0%), followed by human-modified upland wetlands (32.3%) and natural upland wetlands (12.7%)-the same rank-order these habitats are used for toad breeding. None of the 12 Columbia spotted frogs Rana luteiventris or 2 wood frogs R. sylvatica from the study area tested Bd-positive, although all were from an area of low host density where Bd has not been detected. Prevalence of Bd on toads in the KLGO area decreased during 2005-2015. This trend from a largely single-species system may be encouraging or concerning, depending on how Bd is affecting vital rates, and emphasizes the need to understand effects of pathogens before translating disease prevalence into management actions.

The floristic relationship between the upland and lowland Carboniferous wetlands of Variscan Euramerica \u2014 Evidence from some medullosalean pteridosperm fronds

Alethopteris grandinii represents remains of fronds of a medullosalean pteridosperm (probably a small tree) that rapidly migrated across the lowland wetland habitats of Variscan Euramerica in middle Asturian (late Moscovian) times. This was probably caused by changing drainage patterns within the lowland coal swamps, in response to climate and landscape changes. However, these medullosaleans had first appeared rather earlier, in early Bolsovian (early Moscovian) times, in upland wetland habitats. These upland habitats may have pre-adapted these plants to the changed condition in the lowland coal swamps.

Dissolved organic matter variations in coastal plain wetland watersheds: The integrated role of hydrological connectivity, land use, and seasonality

AbstractDissolved organic matter (DOM) is integral to fluvial biogeochemical functions, and wetlands are broadly recognized as substantial sources of aromatic DOM to fluvial networks. Yet how land use change alters biogeochemical connectivity of upland wetlands to streams remains unclear. We studied depressional geographically isolated wetlands on the Delmarva Peninsula (USA) that are seasonally connected to downstream perennial waters via temporary channels. Composition and quantity of DOM from 4 forested, 4 agricultural, and 4 restored wetlands were assessed. Twenty perennial streams with watersheds containing wetlands were also sampled for DOM during times when surface connections were present versus absent. Perennial watersheds had varying amounts of forested wetland (0.4–82%) and agricultural (1–89%) cover. DOM was analysed with ultraviolet–visible spectroscopy, fluorescence spectroscopy, dissolved organic carbon (DOC) concentration, and bioassays. Forested wetlands exported more DOM that was more aromatic‐rich compared with agricultural and restored wetlands. DOM from the latter two could not be distinguished suggesting limited recovery of restored wetlands; DOM from both was more protein‐like than forested wetland DOM. Perennial streams with the highest wetland watershed cover had the highest DOC levels during all seasons; however, in fall and winter when temporary streams connect forested wetlands to perennial channels, perennial DOC concentrations peaked, and composition was linked to forested wetlands. In summer, when temporary stream connections were dry, perennial DOC concentrations were the lowest and protein‐like DOM levels the highest. Overall, DOC levels in perennial streams were linked to total wetland land cover, but the timing of peak fluxes of DOM was driven by wetland connectivity to perennial streams. Bioassays showed that DOM linked to wetlands was less available for microbial use than protein‐like DOM linked to agricultural land use. Together, this evidence indicates that geographically isolated wetlands have a significant impact on downstream water quality and ecosystem function mediated by temporary stream surface connections.

Geomorphic controls on fluvial carbon exports and emissions from upland swamps in eastern Australia

Temperate Highland Peat Swamps on Sandstone (THPSS) are upland wetlands, similar to fens in the Northern Hemisphere and are found at the headwaters of low-order streams on the plateaus of Eastern Australia. They are classified as endangered ecological communities under State and National legislation. Previous works have identified particular geomorphic characteristics that are important to carbon storage in these low energy sediment accumulation zones. Changes in the geomorphic structure of THPSS, such as channelisation, may have profound implications for carbon storage. To assess the effect of channelisation on carbon budgets in these ecosystems it is essential to identify and quantify differences in carbon export, emissions and stocks of carbon of intact swamps and those that have become channelised. We undertook seasonal sampling of the perched swamp aquifers and surface waters of two intact swamps and two channelised fills in the Blue Mountains of New South Wales, Australia, to investigate differences in carbon exports and emissions between the two swamp types. We found that channelised fills' mean CO2 emissions were almost four times higher than intact swamps with mean CH4 emissions up to five times higher. Annual fluvial carbon exports for channelised fills were up to 18 times that of intact swamps. Channelised fill exports and emissions can represent up to 2% of the total swamp carbon stocks per annum which is 40 times higher than the intact swamps. This work clearly demonstrates that changes in geomorphic structure brought about by incision and channelisation results in profound changes to the carbon storage function of THPSS.

Distinguishing Pennsylvanian-age lowland, extra-basinal and upland vegetation

The palaeobotanical record associated with the coal-bearing sequences of Euramerica has historically been taken to epitomise Pennsylvanian (late Carboniferous) vegetation. However, both the macrofloral and the palynological record reveals a much more complex picture of low-latitude vegetational habitats of this age. Many of these other vegetation types have been traditionally referred to as “upland” but with no real justification, and recently, the term “extra-basinal” has been increasingly used. However, the evidence in fact points to the existence of a complex of lowland–wetland, lowland–dryland, upland–wetland and upland–dryland vegetation at this time, together with a number of intermediate vegetation types. Understanding this complex of habitats is essential for a true understanding of late Palaeozoic, especially Pennsylvanian, vegetation history.

Microbial and Environmental Controls of Methane Fluxes Along a Soil Moisture Gradient in a Pacific Coastal Temperate Rainforest

Most studies of greenhouse gas fluxes from forest soils in the coastal rainforest have considered carbon dioxide (CO2), whereas methane (CH4) has not received the same attention. Soil hydrology is a key driver of CH4 dynamics in ecosystems, but the impact on the function and distribution of the underlying microbial communities involved in CH4 cycling and the resultant net CH4 exchange is not well understood at this scale. We studied the growing season variations of in situ CH4 fluxes, microbial gene abundances of methanotrophs (CH4 oxidizers) and methanogens (CH4 producers), soil hydrology, and nutrient availability in three typical forest types across a soil moisture gradient. CH4 displayed a spatial variability changing from a net uptake in the upland soils (3.9–46 µmol CH4 m−2 h−1) to a net emission in the wetter soils (0–90 μmol CH4 m−2 h−1). Seasonal variations of CH4 fluxes were related to soil hydrology in both upland and wet soils. Thus, in the upland soils, uptake rates increased with the decreasing soil moisture, whereas CH4 emission was inversely related to the water table depth in the wet soils. Spatial variability of CH4 exchange was related to the abundance of genes involved in CH4 oxidation and production, but there was no indication of a temporal link between microbial groups and CH4 exchange. Our data show that the abundances of genes involved in CH4 oxidation and production are strongly influenced by soil moisture and each other and grouped by the upland–wetland classification but not forest type.

Aboriginal resources change through time in New England upland wetlands, south‐east Australia

AbstractIt has previously been assumed that New England high‐country environments were not conducive to intense Aboriginal occupation and associated ceremonial activities. How productive were upland wetlands (lagoons) for Aboriginal occupation of high country in eastern Australia through time? Especially during their intermittent phases, upland lagoons provide a diverse and changing mix of deep water, marsh and the green pick of recently exposed lake bed, a rich aggregation of both plant and animal resources not available in other environments. Upland wetlands can be a surprisingly productive Aboriginal resource in an otherwise harsh country, and would at times allow for high population aggregations, such as for ceremonies. We surveyed the ecological literature on New England lagoon characteristics, on vegetation and on birds and other fauna used as resources by Aboriginal people. This was then compared with palaeo‐environmental data to prepare an account of potential resources for the New England region over time. We found that overall productivity of lagoons can be high, with large numbers of plant and animal species present in the wetland environment, especially in the early and very late Holocene. Productivity is highest not at the lake‐full stage, but when the moist littoral zones are at their most extensive. The reasons for the apparent sparseness of occupation of the high country before the mid‐Holocene are unresolved but open to informed speculation about the changing resource inventory of the wetlands, and the mid‐Holocene appearance of new technologies that may have enabled more efficient use of resources. In the later Holocene, Aboriginal occupation in upland areas became visible in the record, and included an exceptionally high number of ceremonial sites juxtaposed with the areas of greatest lagoon concentration. This suggests either that these wetlands had become more productive and diverse over time or that people had learnt how to make better use of the available wetland resources, to the point of supporting the larger numbers often associated with ceremonial activity. More research into the location and chronology of wetland archaeological sites is required to resolve the question of whether the apparent early lack of sites is a question of visibility or a real hiatus.

Upland wetlands in the Namoi Catchment: mapping distribution and disturbance classes of fens, bogs and lagoons.

To assist with planning and conservation strategies, mapping of wetlands above 700 m elevation across the Namoi Catchment (east of Tamworth) was undertaken. The number of hectares of each type within this high-elevation region, the area currently in conservation reserves and the status of these remnants was assessed. 1 001 wetlands were mapped and allocated to three wetland types (fens, bogs and lagoons) and six disturbance groups (based on agricultural clearing and presence of dams). Total wetlands cover was 4 490 ha, of which fens were the most common, followed by bogs and a single lagoon. The smallest wetland was 0.12 ha in size, the largest 113 ha and the average 5 ha. Only 10% of all wetlands were considered to be in near natural state with only 5.5% of all wetland area protected within conservation reserves. Cunninghamia (2013) 13: 331-335 doi: 10.7751/cunninghamia2013.009

Understanding barite and gypsum precipitation in upland acid-sulfate soils: An example from a Lufkin Series toposequence, south-central Texas, USA

Although low-temperature barite precipitation has been previously documented in soils and paleosols, pedogenic barite precipitation remains poorly understood. This study characterizes the micromorphology, elemental trends, and stable isotope geochemistry of sulfates in a barite-bearing soil (Lufkin Series) toposequence using optical microscopy, XRD, ICP-MS, and stable S and O isotope data. Synthesized data indicate that fluctuating redox processes and microbial activity resulting from epiaquatic and evaporative conditions lead to the precipitation of sulfates in the Lufkin soils. Stable sulfur and oxygen isotopes indicate that the primary source of sulfur is the partial dissolution of jarosite during microbial sulfate reduction. Barium-rich parent material provides adequate barium for barite precipitation. Barium is mobilized and concentrated in Btg horizons ~100–160cm below the surface. The presence of humic acids in profiles lower on the landscape prevents barite precipitation and drives the precipitation of gypsum between saturated, anoxic conditions (November to May) and drier, more oxic conditions (May to November). Barite precipitation is a slow, punctuated process. Micromorphological data reveal that barite precipitates first along evacuated macropores and then in the adjacent matrix. In general, optimal conditions for pedogenic barite precipitation in upland wetland acid-sulfate soils are: 1) warm soil temperature that supports active sulfur-reducing and sulfur oxidizing microbes; 2) distinct wet/dry seasons that allow alternating redox conditions; 3) low-gradient landscape; 4) parent material that contains barium- and sulfur-rich constituents; and 5) a long-lived, stable landscape.

How Wetlands Affect Floods

It is widely recognised that wetlands play an important role in the hydrological cycle, influencing groundwater recharge, low flows, evaporation and floods. This has led to policies being formulated world-wide to conserve and manage wetlands to deliver these key services, especially flood risk reduction. Generic statements have often been published about wetland hydrological services but the term “wetlands” covers many land types, including wet woodlands, reedbeds, peat bogs, fens, and salt marshes. Each of these wetland types can have a hydrological function that is subtly different, making it difficult to generalise the flood reduction services of wetlands. In this paper we focus on two example wetland types (upland rain-fed wetlands and floodplain wetlands) to demonstrate why there are differences in flood functions both within and between wetland types. Upland wetlands generally tend to be flood generating areas while floodplain wetlands have a greater potential to reduce floods. However, landscape location and configuration, soil characteristics, topography, soil moisture status and management all influence whether these wetlands provide flood reduction services.