Coastal Plain Wetlands Research Articles

Long‐term differences in population structure, body size and distribution patterns of amphipods and isopods in wetlands with declining hydroperiods

Abstract In many regions, climatic drying is shortening hydroperiods and freshwater biodiversity is declining. Aquatic species that lack a desiccation‐resistant life stage are predicted to have the least ability to persist in drying climates, yet such species may occur in intermittent waterbodies. We examined the distribution of two crustacean species that lack desiccation‐resistant life stages: the isopod Paramphisopus palustris and amphipod Chiltoniidae sp.nov., before and after the commencement of severe climatic drying in Swan Coastal Plain wetlands, south‐western Australia. Historical distribution data for these species were obtained from studies of the same set of wetlands in 1989–1990. We determined whether population or body size differed between hydrological regimes (perennial, semi‐perennial, seasonal) between 1989–1990 and 2018–2019 for both species. Amphipods, isopods and environmental variables were sampled from 42 wetlands in 2018–2019. Thirty‐three wetlands (22 perennial, 11 seasonal) persisted with the same hydrological regime in both time periods and eight wetlands that were perennial in 1989–1990 had shifted to a drier hydrological regime (four became semi‐perennial, four became seasonal) by 2018–2019. Drying wetland hydrological regimes did not correspond to more limited spatial distributions for either species. Hydrological regime had no effect on amphipod counts, although abundances were lower in 2018–2019 than 1989–1990. In 2018–2019, male amphipods were larger than females in seasonal wetlands, but sexes were the same size in perennial wetlands and females were larger than males in semi‐perennial wetlands. Furthermore, amphipods of both sexes were considerably smaller in semi‐perennial than seasonal or perennial wetlands. Isopod distributions differed between the two sampling periods, with populations primarily lost from wetlands that remained perennial. This unexpected result was likely caused by prolonged periods of high summer–autumn water temperatures and stratification in shallow perennial wetlands that caused anoxia in bottom waters and made surface waters excessively hot for isopods. By contrast, drying seasonal wetlands seemingly offered suitable habitat in summer–autumn. Mean isopod head and body length did not differ between hydrological regimes or sexes, but became smaller between 1989–1990 and 2018–2019 (15 mm average body length in 1989 vs. 8.3 mm in 2018–2019; 17 mm maximum size in 1989–1990 vs. 13.2 mm in 2018–2019). The absence of population losses associated with drying hydrological regimes indicates that the current level of drying is within the tolerance range of both species. However, increased temperatures may be causing body size (and possibly fecundity) to decline for isopods. As global warming continues to shorten wetland hydroperiods in many regions, numerous species will struggle to complete their life cycles, leading to extirpation. Our findings suggest that climate change may also cause conditions in perennial wetlands to exceed the tolerances of species that lack desiccation resistance traits. This emphasises the need to better understand both environmental and habitat changes along the drying trajectory in wetlands and the fundamental life‐history and physiological traits that enable the survival of aquatic invertebrates that lack desiccation resistance. This includes not only species responses to drying, but also responses to other stressors (e.g., prolonged stratification) caused by global warming.

Patterns of Wetland Hydrologic Connectivity Across Coastal‐Plain Wetlandscapes

AbstractDepressional wetlands influence the functions of wetlandscapes by storing and releasing water, providing critical habitat, amplifying carbon and nutrient cycling, and influencing microclimate. Despite persistent subsurface connectivity, depressional wetlands are surrounded by uplands so only sporadically connect via surface pathways. However, the frequency, duration, and relative importance of surface connectivity in depressional wetlands remains poorly understood, limiting quantification of their landscape functions. Using multiple years of stage variation in 67 depressional wetlands across four contrasting wetlandscapes, we observed wetland spill elevation is exceeded 10%–40% of the time, with substantial variation within and between wetlandscapes. Moreover, surface connectivity increased water loss rates by 200%–350% on a depth basis and 350%–850% on a volumetric basis compared with subsurface water loss rates. This temporally disproportionate water export suggests that short‐lived surface connectivity is crucial for aggregate landscape export of water‐borne materials and numerous hydrologic and habitat services. Contrasting water loss rates above and below spill thresholds create homeostatic feedback that stabilizes water levels near the thresholds. We explored geomorphic, climatic, and vegetative influences on hydrologic connectivity, quantified as nighttime recession rates below the spill threshold for groundwater connectivity and percent time above thresholds for surface connectivity. Groundwater connectivity was consistently greater in deeper wetlands and wetlandscape identity was the primary factor explaining variation in surface and subsurface connectivity. Our results highlight the critical role of surface connectivity in coastal plain wetlands, illustrate the heterogeneity of those wetland functions within and across wetlandscapes, and provide hydrologic benchmarks for evaluating restoration of aggregate landscape functions.

Resilience and Adaptive Capacity of the Swan Coastal Plain Wetlands

An estimated 90% of the Swan Coastal Plain (SCP) wetlands, located in southwestern Australia, have been lost because of infilling or drainage. This loss continues despite the well-known causes, which include nutrient enrichment; the invasion of exotic flora and fauna; loss of fringing vegetation; and altered hydrological regimes caused by groundwater abstraction; urbanization; and a drying climate. Further loss is expected with climate change exacerbating the undesirable ecosystem changes of remaining wetlands. In this study, we consider these wetlands as examples of social-ecological systems (SES) which are characterized by a close interaction of the ecosystem with the social system. We take the theory of resilient SES as a starting point to identify the adaptive capacity and resilience of the wetlands. We argue that resilience provides a useful framework to analyze adaptation processes and to identify appropriate policy responses. We explore incremental adjustments and transformative action and demonstrate that policy responses arise across multiple scales and levels of jurisdiction and institution. By applying the theoretical framework of resilience to the SCP wetlands, we identified (un)desired ecosystem states of wetlands (hydrology and ecology) through different set of policy actions. Our results show that current wetland management is inadequate to maintain the ecosystem's functioning. We recommend cross-jurisdictional collaboration and the use of conceptual eco-hydrological models to depict gradual ecological change and types of regime shifts (thresholds, hysteresis, and irreversible changes). The different adaption options inform decision-makers to adequately adapt wetland management practices when uncertainty in ecosystem responses exist. Empirical data on how multiple jurisdictions operate and decide could help to further support decision-making. With this research we aim to narrow the science-policy interface which depends on corresponding cross-jurisdictional and institutional responses to coordinate wetland management policies and actions.

Distinct microbial communities alter litter decomposition rates in a fertilized coastal plain wetland

AbstractHuman activities have led to increased deposition of nitrogen (N) and phosphorus (P) into soils. Nutrient enrichment of soils is known to increase plant biomass and rates of microbial litter decomposition. However, interacting effects of hydrologic position and associated changes to soil moisture can constrain microbial activity and lead to unexpected nutrient feedbacks on microbial community structure–function relationships. Examining feedbacks of nutrient enrichment on decomposition rates is essential for predicting microbial contributions to carbon (C) cycling as atmospheric deposition of nutrients persists. This study explored how long‐term nutrient addition and contrasting litter chemical composition influenced soil bacterial community structure and function. We hypothesized that long‐term nutrient enrichment of low fertility soils alters bacterial community structure and leads to higher rates of litter decomposition especially for low C:N litter, but low‐nutrient and dry conditions limit microbial decomposition of high C:N ratio litter. We leveraged a long‐term fertilization experiment to test how nutrient enrichment and hydrologic manipulation (due to ditches) affected decomposition and soil bacterial community structure in a nutrient‐poor coastal plain wetland. We conducted a litter bag experiment and characterized litter‐associated and bulk soil microbiomes using 16S rRNA bacterial sequencing and quantified litter mass losses and soil physicochemical properties. Results revealed that distinct bacterial communities were involved in decomposing higher C:N ratio litter more quickly in fertilized compared to unfertilized soils especially under drier soil conditions, while decomposition rates of lower C:N ratio litter were similar between fertilized and unfertilized plots. Bacterial community structure in part explained litter decomposition rates, and long‐term fertilization and drier hydrologic status affected bacterial diversity and increased decomposition rates. However, community composition associated with high C:N litter was similar in wetter plots with available nitrate detected, regardless of fertilization treatment. This study provides insight into long‐term fertilization effects on soil bacterial diversity and composition, decomposition, and the increased potential for soil C loss as nutrient enrichment and hydrology interact to affect historically low‐nutrient ecosystems.

Biotic community and landscape changes around the Eocene–Oligocene transition at Shapaja, Peruvian Amazonia: Regional or global drivers?

Since 2012, we have investigated a stratigraphic section encompassing the late Eocene–earliest Oligocene interval at Shapaja (Tarapoto area, Peruvian Amazonia, ca. 7°S), through paleontological and geological fieldwork. The measured sedimentary series (120 m-thick [West] plus 90 m-thick [East]), assigned to the upper member of the Pozo Formation, records fluvial micro-conglomeratic lenses intercalated with floodplain and evaporite-rich fine red deposits, estuarine/coastal-plain tidally-influenced fine sandstones, and oxbow lake nodule-rich blue clays. This sedimentary shift coincides locally with the demise of the large Eocene coastal-plain wetland known as Pozo System. The late Eocene–early Oligocene Shapaja section was extensively sampled for chemostratigraphy (δ 13 C on dispersed organic matter and pedogenic carbonate nodules), which in turn allowed for refining the location of the Eocene-Oligocene Transition (EOT) and other climatic events recognized at a global scale (i.e., Oi-1 and Oi-1a). The section has yielded nine fossil localities with plant remains (leaves, wood, charophytes, and palynomorphs), mollusks, decapods, and/or vertebrates (selachians, actinopterygians, lungfishes, amphibians, sauropsids, and mammals), documenting ~130 distinct taxa. Four localities of the upper member of the Pozo Formation at Shapaja predate the EOT, one is clearly within the EOT, while four are earliest/early Oligocene in age. The small leaf impressions found along the Shapaja section could be indicative of dry and/or seasonal conditions for this region throughout and after the EOT. Monkeys, indicative of tropical rainforest environments, are only recorded in a latest Eocene locality (TAR-21). Two biotic turnovers are perceptible in the selachian, metatherian, and rodent communities, well before the EOT [~35–36 Ma] and a few hundred thousand years after the EOT [~33 Ma]. The latter turnover seems to be primarily related to a global sea-level drop (ichthyofauna: marine-littoral elements replaced by obligate freshwater taxa) and/or the onset of a drier and more seasonal climate in early Oligocene times (terrestrial components). Changes in the structure of the Shapaja paleocommunities were mostly driven by the flexural subsidence during the late Eocene, and then globally driven by the earliest Oligocene climatic deterioration. • The Shapaja section spans the late Eocene–early Oligocene interval ( ca. 36–32.5 Ma). • Micro- and macroremains of 129 plant and animal fossil taxa were recognized. • Two faunal turnovers are recorded on both sides of the Eocene-Oligocene transition. • Shapaja records the earliest occurrence of South American primates and sloth. • Community changes are locally- then globally-driven (late Eocene/earliest Oligocene).

Long‐Term Nutrient Enrichment, Mowing, and Ditch Drainage Interact in the Dynamics of a Wetland Plant Community

Photo 1: Plant community in a long-term study on the effects of fertilization, mowing, and hydrology in a coastal plain wetland (North Carolina, USA). Wetland specialist species such as Rhexia virginica, Calamagrostis coarctata, and Juncus spp. are present in a mowed, unfertilized, undrained plot. The unmowed plot visible in background is dominated by Nyssa sylvatica and other tree species. Photo credit: John W. Stiller (used with permission). Photo 2: Plant community in a long-term study on the effects of fertilization, mowing, and hydrology in a coastal plain wetland. The community in a mowed, fertilized, drained plot shows lower diversity and is dominated by an upland species, Rhus copallinum. Photo credit: John W. Stiller (used with permission). These photographs illustrate the article “Long-term nutrient enrichment, mowing, and ditch drainage interact in the dynamics of a wetland plant community” by Carol Goodwillie, Michael W. McCoy and Ariane L. Peralta published in Ecosphere. https://doi.org/10.1002/ecs2.3252.

Metagenomes from Experimental Hydrologic Manipulation of Restored Coastal Plain Wetland Soils (Tyrell County, North Carolina).

Hydrologic changes modify microbial community structure and ecosystem functions, especially in wetland systems. Here, we present 24 metagenomes from a coastal freshwater wetland experiment in which we manipulated hydrologic conditions and plant presence. These wetland soil metagenomes will deepen our understanding of how hydrology and vegetation influence microbial functional diversity.

Long‐term nutrient enrichment, mowing, and ditch drainage interact in the dynamics of a wetland plant community

AbstractFertilization studies have elucidated basic principles of the role of nutrients in shaping plant communities and demonstrated the potential effects of anthropogenic nutrient deposition. Yet less is known about how these effects are mediated by interacting ecological factors, particularly in nutrient‐poor wetland habitats. In a long‐term experiment in a coastal plain wetland, we examined how fertilization and mowing affected the diversity and composition of a plant community as it reestablished after major disturbance. A drainage ditch in proximity to the experimental plots allowed us also to consider the influence of hydrology and its interactions with nutrient addition. Fertilization decreased species richness, with wetland specialist species showing especially great losses, and several lines of evidence suggest that the effect was mediated by competition for light. Altered hydrology via ditch drainage had effects that were similar to fertilization, with more rapidly draining plots showing lower diversity and decreased abundance of wetland species. Plant community diversity and dynamics were influenced by complex interactions between fertilization, disturbance, and hydrology. The negative effect of fertilization on species richness was initially mitigated by mowing, but in later years was more evident in mowed than in unmowed plots. In the absence of disturbance, nutrient addition increased the rate of transition to primarily woody communities. Similarly, drained plots experienced increased rates of succession compared to wetter plots. Our results suggest that these interactions need to be considered to understand the potential effects of anthropogenic nutrient addition and hydrologic alterations to wetland ecosystems.

The Potential Long-Term Impacts of Climate Change on the Hydrologic Regimes of North Carolina’s Coastal Plain Non-Riverine Wetlands

HighlightsBased on current emissions, mean water table decline in these wetlands will likely range from 25 to 65 cm by 2100.Projected changes could lead to a decline or loss of the important ecosystem services that wetlands provide to society.Results indicate a potential need to allocate more resources to developing strategies for managing wetlands.Abstract. Wetlands are especially at risk from climate change because of their intermediate landscape position (i.e., transition between upland and aquatic environments), where small changes in precipitation and/or evapotranspiration can have substantial impacts on wetland hydrology. Because hydrology is the primary factor influencing wetland structure and function, the important ecosystem services that wetlands provide may be altered or lost as a result of climate change. While a great deal of uncertainty is associated with the projected impacts of climate change on wetlands, hydrologic models and downscaled climate model projections provide tools to reduce this uncertainty. DRAINMOD is one such process-based hydrologic model that has been successfully adapted to simulate the daily water level fluctuations in natural wetlands. The objective of this project was to determine the range of possible impacts of climate change on the hydrologic regimes of non-riverine, non-tidal Coastal Plain wetlands in North Carolina. DRAINMOD models were calibrated and validated for two minimally disturbed, natural wetland sites using observed water table and local weather data. Two representative concentration pathway (RCP) scenarios were evaluated: RCP4.5 and RCP8.5. Nine models were selected from an ensemble of 32 climate models to represent the range of possible changes in mean precipitation and temperature. Downscaled climate projections were obtained from the U.S. Bureau of Reclamation. Simulations were run from 1986 to 2099, and results were evaluated by comparing the projected mean water table levels between the base period (1986-2015) and two future evaluation periods: 2040-2069 and 2070-2099. The model simulation results indicated that the projected mean water table level may decline by as much as 25 to 84 cm by the end of this century (2070-2099) for the RCP8.5 scenario and may decline by 4 to 61 cm for the RCP4.5 scenario. In Coastal Plain wetlands, declines in water tables can lead to the subsidence of organic soils, which can lead to the loss of stored carbon and increased risk of peat fires. Lower mean water levels can also lead to shifts in vegetation community composition and loss of habitat functions for wetland-dependent fauna. These results provide an overview of the potential impacts of climate change on North Carolina wetlands, and they provide a range of scenarios to inform and guide possible changes to water management strategies in wetland ecosystems that can be implemented now to limit the loss of ecosystem services over the long term. Keywords: Climate change, DRAINMOD, Hydrology, Modeling, North Carolina, Wetlands.

Multi-temporal SAR image classification of coastal plain wetlands using a new feature selection method and random forests

ABSTRACTEfficient and reliable wetland mapping is essential for wetland resource management and conservation planning. Repeated attempts at classifying dense wetland vegetation has often failed to produce a high-quality product because of poor penetration of electromagnetic signals that cannot detect sub-surface water, and because of associated redundant information. In this study, a two-step classification procedure was developed for classifying typical coastal plain wetlands from multi-temporal Advanced Land Observing Satellite (ALOS)/Phased Array type L-band Synthetic Aperture Radar (PALSAR)-1 data. First, a new statistical strategy for feature selection was proposed by combining manual and automatic selection according to the backscattering mechanism differences between various land-cover types. Then the Random Forest (RF) classifier was applied to evaluate the established feature combinations for wetland classification. The experimental results show that the method described has high classification accuracies over the test site, with overall accuracies and kappa coefficients (κ) of above 89.79% and 0.88, respectively. This indicates that the presented technique is effective in dealing with high-dimensional feature space and may lead to significant improvements in multi-temporal Synthetic Aperture Radar (SAR) image-based wetland classification.

Linking variability in climate to wetland habitat suitability: is it possible to forecast regional responses from simple climate measures?

Temporary wetlands have value to both ecological and social systems. Interactions between local climate and the surrounding landscape result in patterns of hydrology that are unique to temporary wetlands. These seasonal and annual fluctuations in wetland inundation contribute to community composition and richness. Thus, predicting wetland community responses to environmental change is tied to the ability to predict wetland hydroregime. Detailed monitoring of wetland hydroregime is resource-intensive, limiting the scope and scale of forecasting. As an alternative, we determine which freely available measures of water availability best predict one component of wetland hydroregime, habitat suitability (i.e., the predictability of water in a wetland) within and among geographic regions. We used data from three North American regions to determine the climate index that best explained year-to-year variation in habitat suitability during a key phenological period—amphibian breeding. We demonstrate that simple, short-term climate indices based solely on precipitation data best predict habitat suitability in vernal pools in the northeast, montane wetlands in the west and coastal plain wetlands in the southeast. These relationships can help understand how changes in short-term precipitation patterns as a result of climate change may influence the overall hydroregime, and resulting biodiversity, of temporary wetlands across disparate biomes.

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.

Fertilizer legacies meet saltwater incursion: challenges and constraints for coastal plain wetland restoration

Coastal wetland restoration is an important tool for climate change adaptation and excess nutrient runoff mitigation. However, the capacity of restored coastal wetlands to provide multiple ecosystem services is limited by stressors, such as excess nutrients from upstream agricultural fields, high nutrient legacies on-site, and rising salinities downstream. The effects of these stressors are exacerbated by an accelerating hydrologic cycle, expected to cause longer droughts punctuated by more severe storms. We used seven years of surface water and six years of soil solution water chemistry from a large (440 ha) restored wetland to examine how fertilizer legacy, changes in hydrology, and drought-induced salinization affect dissolved nutrient and carbon concentrations. To better understand the recovery trajectory of the restored wetland, we also sampled an active agricultural field and two mature forested wetlands. Our results show that nitrogen (N) and phosphorus (P) concentrations in soil solution were 2–10 times higher in the restored wetland compared to two mature forested wetlands, presumably due to legacy fertilizer mobilized by reflooding. Despite elevated nutrient concentrations relative to reference wetlands, the restored wetland consistently attenuated N and P pulses delivered from an upstream farm. Even with continued loading, N and P concentrations in surface water throughout the restored wetland have decreased since the initial flooding. Our results suggest that high nutrient concentrations and export from wetlands restored on agricultural lands may be a severe but temporary problem. If field to wetland conversion is to become a more widespread method for ameliorating nutrient runoff and adapting coastal plain ecosystems to climate change, we should adopt new methods for minimizing the initial export phase of wetland restoration efforts.

Environmental isotopes applied to the evaluation and quantification of evaporation processes in wetlands: a case study in the Ajó Coastal Plain wetland, Argentina

In the Ajó coastal plain, which occurs in the south of the Samborombón Bay, Argentina, certain sectors of the wetland are influenced by the tidal flow, whereas others are not. In the tidally restricted Ajó wetlands, the evapotranspiration process is one of the most important components of the water balance due to fact that the flat morphology and low soil permeability make the flow of surface and groundwater difficult. Although evaporation is an important component of evapotranspiration, a quantitative estimation of this process is still lacking or poorly known. In this work, we quantify the evaporation term in the tidally restricted wetlands by applying isotopic modelling and assessing the hydrological response of the wetland by means of other methodologies, such as satellite imaging and level measurements. The results show that during deficit periods, the total evaporation ranges between 10 and 33 % of the local precipitation. In groundwater samples, it fluctuates between 2 and 13 %, whereas in surface water it varies between 8 and 20 %. Analyses of the water budget, satellite images and water level time series provide evidence on how evaporation processes regulate the hydrology of the wetland. The water balance suggests the occurrence of a deficit period, in which the satellite images show a reduction of the waterlogged areas and lakes, and a lowering in surface and groundwater level is recorded.

The floating gardens of Chan Cahal: Soils, water, and human interactions

Ancient Maya wetland agriculture has been studied since the 1960s, but there are still too few multiproxy excavations to adequately portray this phenomenon. This paper builds on multidisciplinary and multiproxy research near the ancient Maya site of Chan Cahal, near Blue Creek, Belize, with two new excavations, four new cores, 22 new AMS dates, and a new review of the site's water chemistry and archeology. A long-term study of the site's water chemistry has shown its pervasive impacts on wetland formation and limits to agricultural uses. We argue that a reservoir in the midst of the wetlands became inundated above a paleosol during the earliest Maya occupation in the Middle Preclassic, was dredged out during a time of population expansion sometime in the Late Preclassic to Early Classic, and was filled again with ‘Maya clay’ during and after the Classic period. Vibracores through two wetland fields and one canal corroborated our earlier model of Preclassic through Classic inundation of a paleosol by peat formation, flood sands, clay deposition, and gypsum precipitation. These cores produced new evidence for field and canal construction starting in the Late Preclassic. A later addition was a platform added at the very end or after the main occupation ended in the Terminal Classic. A new excavation at Sayap Ha on the Coastal Plain wetlands 7m lower than Chan Cahal experienced a similar history of inundation and aggradation. Here, Maya farmers reclaimed these wetlands with canals and raised fields late in the Late or Terminal Classic and abandoned them soon thereafter. The Sayap Hah fields thus parallel the BOP fields 9km south since both were built and abandoned at a late stage. As a comparison with other wetland field studies, the stable C isotopes of soil humin through soil profiles showed a strong Classic period to present influence of C4 species at Sayap Hah and an increase in C4 inputs in the upper 25cm at both Sayap Hah and the Chan Cahal platform, perhaps due to tropical pasture grasses prevalent here for the last 50years.

The effect of dilution and the use of a post-extraction nucleic acid purification column on the accuracy, precision, and inhibition of environmental DNA samples

Isolation of environmental DNA (eDNA) is an increasingly common method for detecting presence and assessing relative abundance of rare or elusive species in aquatic systems via the isolation of DNA from environmental samples and the amplification of species-specific sequences using quantitative PCR (qPCR). Co-extracted substances that inhibit qPCR can lead to inaccurate results and subsequent misinterpretation about a species’ status in the tested system. We tested three treatments (5-fold and 10-fold dilutions, and spin-column purification) for reducing qPCR inhibition from 21 partially and fully inhibited eDNA samples collected from coastal plain wetlands and mountain headwater streams in the southeastern USA. All treatments reduced the concentration of DNA in the samples. However, column purified samples retained the greatest sensitivity. For stream samples, all three treatments effectively reduced qPCR inhibition. However, for wetland samples, the 5-fold dilution was less effective than other treatments. Quantitative PCR results for column purified samples were more precise than the 5-fold and 10-fold dilutions by 2.2× and 3.7×, respectively. Column purified samples consistently underestimated qPCR-based DNA concentrations by approximately 25%, whereas the directional bias in qPCR-based DNA concentration estimates differed between stream and wetland samples for both dilution treatments. While the directional bias of qPCR-based DNA concentration estimates differed among treatments and locations, the magnitude of inaccuracy did not. Our results suggest that 10-fold dilution and column purification effectively reduce qPCR inhibition in mountain headwater stream and coastal plain wetland eDNA samples, and if applied to all samples in a study, column purification may provide the most accurate relative qPCR-based DNA concentrations estimates while retaining the greatest assay sensitivity.

Biogeochemical regime shifts in coastal landscapes: the contrasting effects of saltwater incursion and agricultural pollution on greenhouse gas emissions from a freshwater wetland

Many coastal plain wetlands receive nutrient pollution from agricultural fields and are particularly vulnerable to saltwater incursion. Although wetlands are a major source of the greenhouse gases methane (CH4) and nitrous oxide (N2O), the consequences of salinization for greenhouse gas emissions from wetlands with high agricultural pollution loads is rarely considered. Here, we asked how saltwater exposure alters greenhouse gas emissions from a restored freshwater wetland that receives nutrient loading from upstream farms. During March to November 2012, we measured greenhouse gases along a ~2 km inundated portion of the wetland. Sampling locations spanned a wide chemical gradient from sites receiving seasonal fertilizer nitrogen and sulfate (SO4 2−) loads to sites receiving seasonal increases in marine salts. Concentrations and fluxes of CH4 were low (<100 µg L−1 and <10 mg m−2 h−1) for all sites and sampling dates when SO4 2− was high (>10 mg L−1), regardless of whether the SO4 2− source was agriculture or saltwater. Elevated CH4 (as high as 1,500 µg L−1 and 45 mg m−2 h−1) was only observed on dates when air temperatures were >27 °C and SO4 2− was <10 mg L−1. Despite elevated ammonium (NH4 +) for saltwater exposed sites, concentrations of N2O remained low (<5 µg L−1 and <10 µg m−2 h−1), except when fertilizer derived nitrate (NO3 −) concentrations were high and N2O increased as high as 156 µg L−1. Our results suggest that although both saltwater and agriculture derived SO4 2− may suppress CH4, increases in N2O associated with fertilizer derived NO3 − may offset that reduction in wetlands exposed to both agricultural runoff and saltwater incursion.

Permian and Triassic microfloral assemblages from the Blue Nile Basin, central Ethiopia

Palynological investigation was carried out on surface samples from up to 400m thick continental siliciclastic sediments, here referred to as “Fincha Sandstone”, in the Blue Nile Basin, central Ethiopia. One hundred sixty species were identified from 15 productive samples collected along a continuous road-cut exposure. Six informal palynological assemblage zones have been identified. These assemblage zones, in ascending order, are: “Central Ethiopian Permian Assemblage Zone – CEPAZ I”, earliest Permian (Asselian–Sakmarian); “CEPAZ II”, late Early Permian (Artinskian–Kungurian); CEPAZ III – Late Permian (Kazanian–Tatarian); “CETAZ IV”, Lower Triassic (Olenekian Induan); “CETAZ V”, Middle Triassic (Anisian Ladinian); “CETAZ VI”, Late Triassic (Carnian Norian). Tentative age ranges proposed herein are compared with faunally calibrated palynological zones in Gondwana. The overall composition and vertical distribution of miospores throughout the studied section reveals a wide variation both qualitatively and quantitatively. The high frequency of monosaccate pollen in CEPAZ I may reflect a Glossopterid-dominated upland flora in the earliest Permian. The succeeding zone is dominated by straite/taeniate disaccate pollen and polyplicates, suggesting a notable increase in diversity of glossopterids. The decline in the diversity of taeniate disaccate pollen and the concomitant rise in abundance of non-taeniate disaccates in CEPAZ III may suggest the decline in Glossopteris diversity, though no additional evidence is available to equate this change with End-Permian extinction. More diverse and dominant non-taeniate, disaccate, seed fern pollen assignable to FalcisporitesAlisporites in CETAZ IV may represent an earliest Triassic recovery flora. The introduction of new disaccate forms with thick, rigid sacci, such as Staurosaccites and Cuneatisporites, in CETAZ V and VI may indicate the emergence of new gymnospermous plants that might have favourably adapted to coastal plain wetland environments with the return of humid conditions in the Middle to early Late Triassic. The present data constitute the first paleontologically substantiated record for the existence of Permian strata in the Blue Nile Basin. The new results allow for the first time a reliable biostratigraphic subdivision of the central Ethiopia Karoo and its correlation with coeval strata of adjacent regions in Gondwana. From a phytogeographic point of view, the overall microfloral evidence is in support of the position of central Ethiopia occupying the northern part of the southern Gondwana palynofloral province. In view of palaeoecological and paleoclimatic conditions, the microfloral change from the base to the top of the studied section may indicate a response to shifting climatic belts from warm- and cool-temparate climate in the earliest Permian to progressively drier seasonal conditions at successively higher palaeolatitudes during the Late Permian to Middle Triassic.

Estimating Above-Ground Carbon Biomass in a Newly Restored Coastal Plain Wetland Using Remote Sensing

Developing accurate but inexpensive methods for estimating above-ground carbon biomass is an important technical challenge that must be overcome before a carbon offset market can be successfully implemented in the United States. Previous studies have shown that LiDAR (light detection and ranging) is well-suited for modeling above-ground biomass in mature forests; however, there has been little previous research on the ability of LiDAR to model above-ground biomass in areas with young, aggrading vegetation. This study compared the abilities of discrete-return LiDAR and high resolution optical imagery to model above-ground carbon biomass at a young restored forested wetland site in eastern North Carolina. We found that the optical imagery model explained more of the observed variation in carbon biomass than the LiDAR model (adj-R2 values of 0.34 and 0.18 respectively; root mean squared errors of 0.14 Mg C/ha and 0.17 Mg C/ha respectively). Optical imagery was also better able to predict high and low biomass extremes than the LiDAR model. Combining both the optical and LiDAR improved upon the optical model but only marginally (adj-R2 of 0.37). These results suggest that the ability of discrete-return LiDAR to model above-ground biomass may be rather limited in areas with young, small trees and that high spatial resolution optical imagery may be the better tool in such areas.

Managing Conservation Reliant Species: Hawai'i's Endangered Endemic Waterbirds

Hawai'I's coastal plain wetlands are inhabited by five endangered endemic waterbird species. These include the Hawaiian Coot ('alae ke'oke'o), Hawaiian Duck (koloa maoli), Hawaiian Stilt (ae'o), Hawaiian Gallinule (Moorhen) ('alae 'ula), and Hawaiian Goose (nēnē). All five species are categorized as being “conservation reliant.” The current strategy to recover these endangered birds includes land protection and active management of wetlands. To assess the effectiveness of the current management paradigm, we compared species population trends across the state to those on six actively managed wetland national wildlife refuges (Refuges) thought to be critical for the survival of these endangered species. To perform the evaluation we relied on systematic semiannual population counts that have been conducted across most wetlands in the state and monthly population counts that have occurred on Refuges during the same time period. We found that statewide and Refuge populations of the Hawaiian Coot, Stilt and Gallinule have rebounded from historic lows and over the last 20 years have slowly increased or remained stable. We also documented that Refuges are important to each species year-round and that a disproportionately larger percentage of the population for each species is found on them. Understanding of why Refuges successfully house a disproportionate percentage of these “conservation reliant” species can inform current and future conservation efforts as well as ensure long-term population viability for these species.