Field-based Evidence Research Articles

Excess ice loads in the Indian Ocean sector of East Antarctica during the last glacial period

Abstract An accurate reconstruction of the Antarctic Ice Sheet is essential in order to develop an understanding of ice-sheet responses to global climate changes. However, the erosive nature of ice-sheet expansion and the difficulty of accessing much of Antarctica make it challenging to obtain field-based evidence of ice-sheet and sea-level changes before the Last Glacial Maximum. Limited sedimentary records from Lützow-Holm and Prydz Bays in East Antarctica demonstrate that the sea level during Marine Isotope Stage 3 was close to the present level despite the global sea-level drop lower than −40 m. We demonstrate glacial isostatic adjustment modeling with refined Antarctic Ice Sheet loading histories. Our experiments reveal that the Indian Ocean sector of the Antarctic Ice Sheet would have been required to experience excess ice loads before the Last Glacial Maximum in order to explain the observed sea-level highstands during Marine Isotope Stage 3. As such, we suggest that the Antarctic Ice Sheet partly reached its maximum thickness before the global Last Glacial Maximum.

What controls the remobilization and deformation of surficial sediment by seismic shaking? Linking lacustrine slope stratigraphy to great earthquakes in South-Central Chile.

Remobilization and deformation of surficial subaqueous slope sediments create turbidites and soft sediment deformation structures, which are common features in many depositional records. Palaeoseismic studies have used seismically‐induced turbidites and soft sediment deformation structures preserved in sedimentary sequences to reconstruct recurrence patterns and – in some cases – allow quantifying rupture location and magnitude of past earthquakes. However, current understanding of earthquake‐triggered remobilization and deformation lacks studies targeting where these processes take place, the subaqueous slope and involving direct comparison of sedimentary fingerprint with well‐documented historical earthquakes. This study investigates the sedimentary imprint of six megathrust earthquakes with varying rupture characteristics in 17 slope sediment cores from two Chilean lakes, Riñihue and Calafquén, and evaluates how it links to seismic intensity, peak ground acceleration, bracketed duration and slope angle. Centimetre‐scale stratigraphic gaps ranging from ca 1 to 20 cm – caused by remobilization of surficial slope sediment – were identified using high‐resolution multi‐proxy core correlation of slope to basin cores, and six types of soft sediment deformation structures ranging from ca 1 to 25 cm thickness using high‐resolution three‐dimensional X‐ray computed tomography data. Stratigraphic gaps occur on slope angles of ≥2.3°, whereas deformation already occurs from slope angle 0.2°. The thickness of both stratigraphic gaps and soft sediment deformation structures increases with slope angle, suggesting that increased gravitational shear stress promotes both surficial remobilization and deformation. Seismic shaking is the dominant trigger for surficial remobilization and deformation at the studied lakes. Total remobilization depth correlates best with bracketed duration and is highest in both lakes for the strongest earthquakes (M w ca 9.5). In lake Riñihue, soft sediment deformation structure thickness and type correlate best with peak ground acceleration providing the first field‐based evidence of progressive soft sediment deformation structure development with increasing peak ground acceleration for soft sediment deformation structures caused by Kelvin‐Helmholtz instability. The authors propose that long duration and low frequency content of seismic shaking favours surficial remobilization, whereas ground motion amplitude controls Kelvin‐Helmholtz instability‐related soft sediment deformation structure development.

Rapid hydraulic collapse as cause of drought-induced mortality in conifers

Understanding the vulnerability of trees to drought-induced mortality is key to predicting the fate of forests in a future climate with more frequent and intense droughts, although the underlying mechanisms are difficult to study in adult trees. Here, we explored the dynamic changes of water relations and limits of hydraulic function in dying adults of Norway spruce (Picea abies L.) during the progression of the record-breaking 2018 Central European drought. In trees on the trajectory to drought-induced mortality, we observed rapid, nonlinear declines of xylem pressure that commenced at the early onset of xylem cavitation and caused a complete loss of xylem hydraulic conductance within a very short time. We also observed severe depletions of nonstructural carbohydrates, though carbon starvation could be ruled out as the cause of the observed tree death, as both dying and surviving trees showed these metabolic limitations. Our observations provide striking field-based evidence for fast dehydration and hydraulic collapse as the cause of drought-induced mortality in adult Norway spruce. The nonlinear decline of tree water relations suggests that considering the temporal dynamics of dehydration is critical for predicting tree death. The collapse of the hydraulic system within a short time demonstrates that trees can rapidly be pushed out of the zone of hydraulic safety during the progression of a severe drought. In summary, our findings point toward a higher mortality risk for Norway spruce than previously assumed, which is in line with current reports of unprecedented levels of drought-induced mortality in this major European tree species.

Hybrid watermilfoil (Myriophyllum spicatum\u2009\xd7\u2009Myriophyllum sibiricum) exhibits traits associated with greater invasiveness than its introduced and native parental taxa

Hybridization has been associated with increased invasiveness in plants. In North America, the hybrid aquatic plant Myriophyllum spicatum × Myriophyllum sibiricum (hybrid watermilfoil, hereafter HWM) is a cross between non-native invasive Eurasian watermilfoil (M. spicatum, EWM) and native northern watermilfoil (M. sibiricum, NWM). Lab-based trials have demonstrated higher growth rates in HWM compared to EWM and NWM, but these patterns have not been systematically examined in the field. In this study, we compared the invasiveness of HWM to its parental taxa, EWM and NWM, by examining the amount and timing of: (1) flowering, (2) surface cover, and (3) biomass (using stem counts as a proxy). We conducted repeat surveys of Myriophyllum beds at eight lakes (2–3 lakes/taxon) in the Minneapolis–St. Paul Metropolitan area (Minnesota, USA) between June 2017 and November 2018. HWM produced more flower spikes earlier and overall, and maintained consistently more flower spikes throughout the growing season than EWM and NWM. In addition, surface cover reached greater annual peaks and was higher for longer throughout the growing season for HWM than for both parental taxa. We did not observe a significant difference in stem counts among the three taxa, but HWM did reach a higher maximum number of stems than either parental taxon. This study provides field-based evidence of increased invasiveness associated with hybridization between EWM and NWM; specifically, greater reproductive potential via flowering and greater surface cover may increase HWM spread, have greater impacts on native species, and pose more of a nuisance to lake users.

The influence of land cover and storm magnitude on hydrologic flowpath activation and runoff generation in steep tropical catchments of central Panama

Despite abundant research documenting that land use/land cover (LULC) have substantial impacts on the hydrology of humid tropical systems, field-based evidence for the physical mechanisms behind these impacts are still lacking. In particular, our understanding of the hydrologic flowpaths that generate runoff in these systems, and how they vary with respect to LULC is insufficient to inform both physically-based hydrologic modeling and land-use decision-making. In this study, we use end-member mixing analysis (EMMA) of stream chemistry, and hydrometric characterizations of hillslope soil moisture to identify hydrologic flowpaths in humid tropical steep-land catchments of varying LULC: mature tropical forest, young secondary tropical forest, cattle pasture. EMMA was applied to data from 14 storm events (six at the mature forest, five at the young secondary forest, and three at the cattle pasture) that were intensively sampled during the 2017 wet season representing a wide range of rainfall magnitudes and intensities. Additionally, volumetric-soil-moisture responses at multiple depths were characterized during and after 74 storm events occurring from 2015 to 2017. EMMA results indicated that lateral preferential flow within the top 30 cm of the soil profile was a dominant source of runoff generation at the two forested catchments, with the contribution of this flow path increasing with rainfall magnitude and intensity. This was corroborated by volumetric-soil-moisture data, that showed that a perched zone of saturation developed at 30 cm at the time of peak storm runoff during the largest events and lasted for the remaining duration of the event. EMMA indicated that runoff was a combination of infiltration-excess overland flow and lateral subsurface flow in the actively grazed pastoral catchment. There, overland flow contributed 62 % of runoff during the highest runoff rate sampled (35.3 mm/hr) and this contribution increased substantially with storm magnitude. This flowpath identification was also supported by volumetric-soil-moisture data at the pasture, with peak saturation at all depths during the largest storm events occurring up to 30 min after peak runoff. These results provide a mechanistic explanation for previously observed hydrologic differences among tropical LULCs. Additionally, the wide range of hydrologic conditions during these storm events provide a basis for understanding how future changes to this, and similar humid tropical regions will impact hydrological processes and water availability.

Bathymetry data and water column profiles in the shallow waters of Langhovde in Lützow-Holm Bay, East Antarctica

The sediments of shallow marine waters and lakes around Antarctica provide valuable records of sea-level changes. Understanding the timing and amplitude of Antarctic Ice Sheet changes during the last deglaciation is essential to assess the effect of glacial isostatic adjustments on the present ice-sheet mass balance. However, the difficulty in accessing Antarctica makes it challenging to obtain field-based evidence of ice-sheet and sea-level change during the last deglaciation. We used a portable sonar system to measure bathymetry and water column profiles (sea temperature, salinity, dissolved oxygen, and turbidity) in Lake Nurume and shallow marine waters of Langhovde, East Antarctica, to collect baseline data for sea-level reconstruction from the Last Glacial Maximum (~20 ka). The bathymetry data reveals the surveyed shallow marine waters of Langhovde have basins of 100 m water depth with approximately −67 and −92 m sills, in which sediments provide a potentially useful sea-level archive for the last deglaciation. The water column profile in Lake Nurume reveals a chemocline at ~11 m water depth and anoxic condition below that depth. These baseline data will be useful to reconstruct sea-level and ice-sheet changes in East Antarctica.

1750–1710 Ma deformation along the eastern margin of the North Australia Craton

In this contribution, we present field-based evidence that in the Mary Kathleen Domain from the Eastern Fold Belt of the Mount Isa Inlier the 1790–1750 Ma metasediments of the Leichhardt Superbasin were sheared and folded between 1750 and 1710 Ma. The Mary Kathleen Domain consists of a series of anastomosing high and low strain domains intruded syn- to late-tectonically by a series of 1740–1710 Ma felsic and mafic plutons and dykes. The timing relationships in the high strain domains are unclear due to mylonitisation and transposition but in the lower strain domains are well-preserved. The earliest deformation, D1, consists of a series of low angle truncation surfaces and shear zones that are folded around large scale N-S trending upright folds during D2. The D2 folds were refolded during D3 along NW to EW trending fold axes. An undeformed granitic pluton from the Mt Godkin area dated at ~1710 Ma that crosscuts the D2-D3 folds and the youngest detrital zircon population of ~1750 Ma constrains the timing of D1-D3 deformation between 1750 and 1710 Ma. Later, N-S (D4) and N-E (D5) trending brittle-ductile shears are interpreted to indicate a late Isan Orogeny overprint. The occurrence of contemporaneous folding in the Western Fold Belt suggests that between 1750 and 1710 Ma the eastern margin of the North Australia Craton was experiencing a significant deformation event that can be correlated with similarly aged deformation events from other parts of the North Australia Craton, from South Australia Craton and from East Antarctica. Following the assembly of most of the Nuna Supercontinent by 1.8 Ga, we postulate that the 1750–1710 Ma deformation and plutonism observed in Mount Isa Inlier is part of a series of worldwide orogenic events that contributed to the final configuration of the Nuna Supercontinent.

Soil organic carbon becomes newer under warming at a permafrost site on the Tibetan Plateau

Permafrost areas are experiencing fast and dramatic changes under global warming. Increased primary production and stimulated microbial activity have been widely observed in warming permafrost. However, the fate of permafrost soil organic carbon (SOC) remains elusive, and the potential mechanisms underlying warming-mediated SOC formation and old C decomposition are poorly understood. Here, using in situ six-year manipulative warming experiments with two scenarios (+2.4 °C and +4.9 °C for lower and higher scenarios, respectively, above the ambient temperature) at a permafrost site in the Tibetan Plateau, we observed that soil C sink increased in the surface 5 cm layer under the two warming scenarios. SOC exhibited a linear increase with warming duration at rates of 6.8% and 6.4% annually in the silt & clay fractions and aggregates, respectively. Warming-induced accumulations of SOC in the aggregates and silt & clay fractions were contributed mainly by plant-derived C and minorly by microbial necromass. However, the increased input of new plant-derived C was accompanied with an increasing loss of old C via enhanced respiration under warming, likely due to the mobilization and degradation of C in the aggregates and silt & clay fractions. Our study provides field-based evidence of the enhanced SOC accumulation in the Tibetan permafrost regions under warming, and improves process-based understanding of warming-induced new plant-derived C that could replace the protected old C in the aggregates and silt & clay fractions.

Field-based Evidence of the Black Coffee Twig Borer infesting Maesopsis eminii in Coffee Agro-systems in Kiboga District, Uganda

Despite Ugandan coffee farmers’ preference for Maesopsis eminii as a shade tree, the species is an alternate host for the black coffee twig borer, Xylosandrus compactus (Eichhoff)—a major insect pest of coffee in the country. Wilting and drying of leaves and branches of young M. eminii trees (<5 m tall) observed in Kiboga District, Uganda. The branches were trimmed off the trees, separated into primary and secondary branches and then the percentage of those possessing characteristic X. compactus entry holes determined separately. Additionally, the number of entry holes on both primary and secondly branches was established to determine the extent of damage of X. compactus. X. compactus characteristic holes were observed on both primary and secondary branches of M. eminii - percentage of branches having entry holes and the number of entry holes higher on primary than secondary branches. Dissecting the branches at the entry holes revealed various life stages of X.compactus in the gallery, proving that the damage was due to the pest. Presence of this pest on trees that are inter-planted in the coffee agroforestry systems presents a dilemma in managing it. Therefore, research should be geared towards designing management strategies for the pest in the coffee agroforestry systems. In the meantime, farmers should always trim-off and burn all infested parts from coffee and other plants inter-planted in it.

Comparing farmers’ perceptions of climate change with meteorological trends and examining farm adaptation measures in hazard-prone districts of northwest Bangladesh

Consistency between farmers’ perceptions of climate change (CC) and meteorological trends leads to effective farm adaptation strategies. This study was conducted in hazard-prone districts, Kurigram (riverbank erosion-prone) and Nilphamari (drought-prone), of the northwest region of Bangladesh to compare farmers’ perceptions of CC with meteorological trends, and to examine farm adaptation measures. A total of 252 smallholder households were interviewed. Household survey, key informant interviews, focus group discussions and field observations were carried out to collect the primary data. The findings revealed that farmers’ perceptions of CC were consistent with the meteorological trends of the past 30 years (1986–2015) and showed increasing temperature parameters and decreasing rainfall parameters. Farmers perceived negative impacts were increased summer temperature and length of summer days, decreased rainfall intensity, number of rainy days and length of winter days as well as increased intensity of floods, droughts, riverbank erosion and other natural hazards. The farmers also noted significant moderate to high impact of CC on agricultural production. The practiced adaptation strategies were low to medium, and almost all the households applied traditional strategies including compost and manure in their fields and practiced crop rotation as well as homestead gardening to minimize the adverse impact of CC. The study recommends bridging information gaps between the scientific community and farmers about CC adaptation options to meet challenges posed by CC. This study also provides field-based evidence for devising CC mitigation and adaptation policies.

Applications of glacial geomorphological and lichenometric studies for reconstructing the Late Holocene glacial history of the Hoksar valley, Kashmir Himalaya, India

ABSTRACT In this study, the lichenometry studies of the Hoksar Glacier valley in Kashmir Himalaya, India supported by the extensive ground- and remote sensing-based glacial geomorphological mapping enabled the identification of the six episodes of glacier advances in the valley. Field-based geomorphologic evidence suggests that the glacial episode 1 (GEI) experienced the most extensive glaciation in the Hoksar valley extending ∼1 km down the valley (altitude 3565 m) from the current snout position of the Hoksar Glacier (altitude 3680m). Lichenometric dating of the moraines suggests that the GE1 episode is chronologically the oldest (∼480 ± 25 years) and GE6 episode the youngest (∼245 ± 10 years). The mean equilibrium line altitude (ELA) during the GE1 episode was calculated as 3755 ± 4 m compared to the observed present ELA position of 4060 ± 5 m, an upward shift of 305 m observed during the period. The spatio-temporal changes of the Hoksar Glacier during different episodes of the glacier advances until 2018 showed that the glacier area has shrunk from ∼212 ha during the GE1 to 100 ha at present losing an area of 112 ha (52%) during the period mainly as a result of the recent climate change. The recent observed glacier recession (1980–2018) is much higher (11 000 m2 a−1) compared to the past recession (1300 m2 a−1). The study provides valuable insights about the glacier recession in the Kashmir Himalayan region during the Late Holocene where knowledge about the past glacial history on a regional scale is generally poorly investigated.

Effectiveness of terracing techniques for controlling soil erosion by water in Rwanda

Despite long-standing efforts in terracing, limited field-based evidence of its effectiveness as implemented within rural farming systems of humid tropical regions, such as Rwanda, is available. This study aimed to reveal regional differences in effectiveness of two widely used terracing techniques. Traditional slope farming (NP) was compared to bench (BT) and farmers’ based progressive terraces (PT) in terms of runoff, soil losses, and topsoil fertility in two contrasting agro-ecological zones, the Eastern Plateau (Murehe) and Buberuka Highlands (Tangata). During four consecutive rainy seasons, event-based data were collected using erosion plots (5 m width x 22.2 m length). Effectiveness indices of both terracing systems, as well as (R)USLE P-factor values, were calculated. The annual average soil losses under NP ranged from 4.71 ± 5.02 ton ha−1 to 46.01 ± 7.28 ton ha−1 in Murehe (14% slope gradient) and Tangata (43% slope gradient), respectively. Bench terracing clearly outperformed the farmer-based progressive terrace at both locations, leading to negligible soil losses. In terms of runoff reduction, an effectiveness of 70 and 85% respectively, was observed at Murehe and Tangata. The effectiveness of PT reached 52% for runoff control and 93% for soil loss control at Tangata, thereby confirming its huge potential as erosion control measure, even in mountainous areas. In the hilly landscape of Murehe, the runoff generated by PT – in some years - can exceed that under traditional farming, while the measure reduced soil losses by half on average. Associated USLE P-factors varied between seasons with an annual average values of 0.001–0.02 for BT, and 0.07 to 0.55 for PT at Tangata and Murehe, respectively. These variations in performance by site and terracing system also resulted in differences in topsoil chemical fertility, with BT generally outperforming both PT and NP at Tangata. At Murehe, PT showed a significantly lower chemical fertility compared to BT and NP. Poor quality risers explained the overall lower performance of PT at Murehe. The study thus confirmed the huge potential of (bench) terraces to sustainably reduce soil erosion rates when established within an integrated approach, paying attention to correct installation and fertility-supporting agronomic practices. More attention should be given to riser installation (e.g. distance) and maintenance of PT. Adoption of these erosion control measures can be recommended to similar agro-ecological zones for sustainably protecting the lands while mitigating or adapting the effects of climate change.

The abundance of arbuscular mycorrhiza in soils is linked to the total length of roots colonized at ecosystem level.

Arbuscular mycorrhizal fungi (AMF) strongly affect ecosystem functioning. To understand and quantify the mechanisms of this control, knowledge about the relationship between the actual abundance and community composition of AMF in the soil and in plant roots is needed. We collected soil and root samples in a natural dune grassland to test whether, across a plant community, the abundance of AMF in host roots (measured as the total length of roots colonized) is related to soil AMF abundance (using the neutral lipid fatty acids (NLFA) 16:1ω5 as proxy). Next-generation sequencing was used to explore the role of community composition in abundance patterns. We found a strong positive relationship between the total length of roots colonized by AMF and the amount of NLFA 16:1ω5 in the soil. We provide the first field-based evidence of proportional biomass allocation between intra-and extraradical AMF mycelium, at ecosystem level. We suggest that this phenomenon is made possible by compensatory colonization strategies of individual fungal species. Finally, our findings open the possibility of using AMF total root colonization as a proxy for soil AMF abundances, aiding further exploration of the AMF impacts on ecosystems functioning.

The social and cultural dynamics of Zimbabwe’s land reform programme on the ‘new generation’ of farmers: a transformative social policy perspective

ABSTRACT This article examines the socio-cultural dynamics of redistributive land reform on the ‘new generation’ after Zimbabwe’s fast track land reform programme (FTLRP). Firstly, using the transformative social policy conceptual framework (TSP) as a heuristic and evaluative tool, it makes a conceptual contribution that land and agrarian reforms are a social policy instrument that can transform the welfare and wellbeing of citizens. This marks a departure from conservative ideologies and doctrines on welfare which have seen social policies having a neo-liberal orientation which wrongly assume that the welfare needs of citizens are met through the market. Secondly, it presents field-based evidence which shows that for the new generation, land reform has transformed socio-economic and cultural relations while enhancing their productive capacities. The article is informed by data which was gathered from Goromonzi District. It employed an interpretive research paradigm and a qualitative life history approach which entailed the use of several data-gathering instruments. Findings suggest that in addition to the generational transfer of land, there are some outcomes of the FTLRP which have not been subjected to rigorous empirical interrogation. Due to the FTLRP, it shows that in the resettlement areas; cultures, rituals and traditions are being undertaken by the new generation. These practices are of sentimental, symbolic and practical significance creating a bond and sense of identity between resettled households and the land. From a TSP perspective, it can be shown that access to land has had multiple-interrelated outcomes which include production, reproduction, protection, redistribution and social cohesion outcomes.

Pathogen flows from on-site sanitation systems in low-income urban neighborhoods, Dhaka: A quantitative environmental assessment.

Despite wide usage of on-site sanitation, there is limited field-based evidence on the removal or release of pathogens from septic tanks and other primary treatment systems, such as anaerobic baffled reactors (ABR). In two low-income areas in Dhaka, we conducted a cross-sectional study to explore pathogen loads discharged from commonly used on-site sanitation-systems and their transport in nearby drains and waterways. We collected samples of drain water, drain sediment, canal water, and floodwater from April-October 2019. Sludge, supernatant, and effluent samples were also collected from septic tanks and ABRs. We investigated the presence and concentration of selected enteric pathogens (Shigella, Vibrio cholerae (V. cholerae), Salmonella Typhi (S. Typhi), Norovirus Genogroup-II (NoV-GII), and Giardia) and presence of Cryptosporidium in these samples using quantitative polymerase chain reaction (qPCR).The equivalent genome copies (EGC) of individual pathogens were estimated in each sample by interpolation of the mean Ct value to the corresponding standard curve and the dilution factor for each sample type. Absolute quantification was expressed as log10 EGC per 100mL for the water samples and log10 EGC per gram for the sediment samples. Among all samples tested (N=151), 89% were contaminated with Shigella, 68% with V. cholerae and NoV-GII, 32% with Giardia, 17% with S. Typhi and 6% with Cryptosporidium. A wide range of concentration of pathogens [range: mean log10 concentration of Giardia=0.74 EGC/100mL in drain ultrafiltration samples to mean log10 concentration of NoV-GII and Giardia=7.11 EGC/100mL in ABR sludge] was found in all environmental samples. The highest pathogen concentrations were detected in open drains [range: mean log10 concentration=2.50-4.94 EGC/100mL], septic tank effluent [range: mean log10 concentration=3.32-4.65 EGC/100mL], and ABR effluent [range: mean log10 concentration=2.72-5.13 EGC/100mL]. High concentrations of pathogens (particularly NoV-GII, V.cholerae and Shigella) were frequently detected in environmental samples from two low-income urban neighbourhoods of Dhaka city. The numerous environmental exposure pathways for children and adults make these findings of public health concern. These results should prompt rethinking of how to achieve safe sanitation solutions that protect public health in dense low-income areas. In particular, improved management and maintenance regimes, further treatment of liquid effluent from primary treatment processes, and appropriate application of onsite, decentralised and offsite sanitation systems given the local context.

Agroforestry Benefits and Challenges for Adoption in Europe and Beyond

Soil degradation is a global concern, decreasing the soil’s ability to perform a multitude of functions. In Europe, one of the leading causes of soil degradation is unsustainable agricultural practices. Hence, there is a need to explore alternative production systems for enhanced agronomic productivity and environmental performance, such as agroforestry systems (AFS). Given this, the objective of the study is to enumerate the major benefits and challenges in the adoption of AFS. AFS can improve agronomic productivity, carbon sequestration, nutrient cycling, soil biodiversity, water retention, and pollination. Furthermore, they can reduce soil erosion and incidence of fire and provide recreational and cultural benefits. There are several challenges to the adoption and uptake of AFS in Europe, including high costs for implementation, lack of financial incentives, limited AFS product marketing, lack of education, awareness, and field demonstrations. Policies for financial incentives such as subsidies and payments for ecosystem services provided by AFS must be introduced or amended. Awareness of AFS products must be increased for consumers through appropriate marketing strategies, and landowners need more opportunities for education on how to successfully manage diverse, economically viable AFS. Finally, field-based evidence is required for informed decision-making by farmers, advisory services, and policy-making bodies.

Impacts of warming winters on recharge in a seasonally frozen bedrock aquifer

Under conditions of a changing climate, winters are predicted to be warmer and wetter in the northern hemisphere. Yet, the impacts of increasing midwinter snowmelt and rain-on-snow (ROS) events on groundwater recharge are poorly understood, particularly in seasonally frozen shallow bedrock. To characterize the mechanisms and antecedent conditions inhibiting or enabling winter recharge in seasonally frozen bedrock, a field investigation was conducted in eastern Ontario, Canada over the winter of 2019–2020. Since rock outcrops are known areas of recharge in nonwinter months, a low-lying granitic outcrop and adjacent soils were heavily instrumented. Both hydrogeologic and cryospheric conditions of the surface, unsaturated and saturated zones were monitored at a high temporal resolution (10–15-minute intervals). Climate data collected during the study indicated that winter conditions were warmer and wetter than long-term (30 year) averages, which allows for parallels to be drawn between observations from this winter and what could be expected for future winter conditions under climate change. Hydraulic head and temperature measurements in two bedrock wells indicated rapid midwinter recharge occurred in response to most ROS and snowmelt events despite the presence of basal ice in the snowpack and shallow frozen ground. Volumetric water content and temperature measurements in two soil profiles revealed that where the soil-bedrock interface was unfrozen, this became the primary pathway permitting infiltration to bypass the frozen surface layer. A major midwinter ROS event generated ponding on surface which subsequently froze, ultimately reducing effective recharge from the event and inhibiting future snowmelt recharge. Estimates of net recharge per ROS and/or snowmelt event indicated that moderate events were more effective at recharging the bedrock aquifer than higher intensity events and events in winter were more effective than in fall. Implications of these findings suggest that rock outcrops provide a window for rapid localized recharge during midwinter warming or ROS, where basal ice or frozen soil would otherwise inhibit vertical infiltration. Study results provide field-based evidence for both enhanced and impeded winter recharge in seasonally frozen bedrock aquifers due to warming winters under climate change.

Where does the salt marsh start? Field-based evidence for the lack of a transitional area between a gradually sloping intertidal flat and salt marsh

Salt marshes are vegetated ecosystems between land and sea, hosting unique plant and animal communities, contributing to crucial habitats for birds and providing numerous other ecosystem services. They form a sustainable nature-based coastal protection, and its protective value increases with the width of the system. Salt marshes and their adjoining tidal flats are often studied separately. At present, there is a lack of studies that describe the features of these two systems in unison and in relation to each other. This study descriptively assesses an array of abiotic and biotic variables that potentially affect successful vegetation establishment. Unfavourable soil conditions may limit establishment as well as bioturbation of infauna. This is related to the marsh expansion potential and could aid in salt marsh restoration and marsh growth stimulation projects. In a naturally developing salt marsh, we sampled the elevation gradient from the tidal flat to the low marsh for benthic species composition, plant seed availability and abiotic variables. The abundance of benthos was highest landwards of the transition zone, in the pioneer zone. Distinct meiobenthic groups occurred in the different zones along the tidal flat to low marsh gradient, but macrobenthos was largely absent from the muddy soil. In the sparsely vegetated transition zone, the abundance of salt-marsh seeds was low, similar to the tidal flat. It suggests that, even though a seed source was in proximity, seed availability in spring was insufficient to achieve lateral marsh expansion. Clustering and nMDS analyses showed that an identifiable transition zone was lacking. The transition zone resembled the bare tidal flat in terms of its abiotic and biotic conditions. This was mainly driven by significant changes in soil oxygenation and seed availability.

Prediction of plant species occurrence as affected by nitrogen deposition and climate change on a European scale

Plant species occurrence in Europe is affected by changes in nitrogen deposition and climate. Insight into potential future effects of those changes can be derived by a model approach based on field-based empirical evidence on a continental scale. In this paper, we present a newly developed empirical model PROPS, predicting the occurrence probabilities of plant species in response to a combination of climatic factors, nitrogen deposition and soil properties. Parameters included were temperature, precipitation, nitrogen deposition, soil pH and soil C/N ratio. The PROPS model was fitted to plant species occurrence data of about 800,000 European relevés with estimated values for pH and soil C/N ratio and interpolated climate and modelled N deposition data obtained from the Ensemble meteo data set and EMEP model results, respectively. The model was validated on an independent data set. The test of ten species against field data gave an average Pearson’s r-value of 0.79.PROPS was applied to a grassland and a heathland site to evaluate the effect of scenarios for nitrogen deposition and climate change on the Habitat Suitability Index (HSI), being the average of the relative probabilities, compared to the maximum probability, of all target species in a habitat. Results for the period 1930–2050 showed that an initial increase and later decrease in nitrogen deposition led to a pronounced decrease in HSI, and with dropping nitrogen deposition to an increase of the HSI. The effect of climate change appeared to be limited, resulting in a slight increase in HSI.

Productivity and Economic Evaluation of Agroforestry Systems for Sustainable Production of Food and Non-Food Products

Agroforestry systems have multifunctional roles in enhancing agronomic productivity, co-production of diversity of food and non-food products and provision of ecosystem services. The knowledge of the performance of agroforestry systems compared with monoculture is scarce and scattered. Hence, the objective of the study was to analyze the agronomic productivity and economic viability of diverse agroforestry systems in Europe. A network of five agroforestry systems integrating arable crops, livestock and biomass trees was investigated to assess the range of agricultural products in each agroforestry system. Land Equivalent Ratio (LER) was used to measure the agronomic productivity, whereas gross margin was used as an indicator for economic viability assessment. LER values ranged from 1.36–2.00, indicating that agroforestry systems were more productive by 36–100% compared to monocultures. Agroforestry gross margin was lower in Denmark (€112 ha−1 year−1) compared to United Kingdom (€5083 ha−1 year−1) and the crop component yielded higher returns compared to negative returns from the tree component in agroforestry. Hence, the study provided robust field-based evidence on agronomic productivity and economic viability assessment of agroforestry systems in diverse contexts for informed decision making by land managers, advisory services, farmers and policymakers.