Pasture Sites Research Articles

Improved representation of soil moisture processes through incorporation of cosmic-ray neutron count measurements in a large-scale hydrologic model

Abstract. Profound knowledge of soil moisture and its variability plays a crucial role in hydrological modelling to support agricultural management, flood and drought monitoring and forecasting, and groundwater recharge estimation. Cosmic-ray neutron sensing (CRNS) has been recognised as a promising tool for soil moisture monitoring due to its hectare-scale footprint and decimetre-scale measurement depth. But since CRNS provides an integral measurement over several soil horizons, a direct comparison of observed and simulated soil moisture products is not possible. This study establishes a framework to assess the accuracy of soil moisture simulated by the mesoscale Hydrologic Model (mHM) by generating simulated neutron counts and comparing these with observed neutron measurements for the first time. We included three different approaches to estimate CRNS neutron counts in the mHM as a function of the simulated soil moisture profiles: two methods based on the Desilets equation and one based on the forward operator COSMIC (COsmic-ray Soil Moisture Interaction Code). For the Desilets method, we tested two different approaches to average the vertical soil moisture profiles: a uniform vs. a non-uniform weighting scheme depending on the CRNS measurement depth. The methods were tested at two agricultural sites, namely one pasture site and one forest site, in Germany. To explore the prior and posterior distributions of the mHM parameters when constrained by CRNS observations, we used a Monte Carlo method based on Latin hypercube sampling with a large sample size (S = 100 000). We found that all three methods performed well, with a Kling–Gupta efficiency > 0.75 and a percent bias < ± 10 % across the majority of investigated sites and for the best 1 % of parameter sets. The performance of the neutron forward models varied slightly across different land cover types. The non-uniform approach generally showed good performance, particularly at the agricultural sites. On the other hand, the COSMIC method performed slightly better at the forest site. The uniform approach showed slightly better results at the grassland site. We also demonstrated for the first time that the incorporation of CRNS measurements into the mHM could improve both the soil moisture and the evapotranspiration products of the mHM. This suggests that CRNS is capable of improving the model parameter space in general and adds a broader perspective on the potential of CRNS to support large-scale hydrological and land surface models.

Nitrogen leaching losses from pasture and winter forage crops in the West Matukituki Valley

In 2013 the Otago Regional Council (ORC) entered mediation with local farmers on changes to their Water Plan, Plan Change 6A, which sought to apply nitrogen load limits within the catchments of Lake Wanaka and Lake Hawea for all farm systems. There was little information available on nitrogen leaching losses in the high rainfall environments (c 2500 mm pa) of the South Island's high country. Agreement after mediation with the ORC and local farmers required a research project to examine differences between measured losses and outputs from OVERSEER® at a paddock and farm scale. To address this knowledge gap, a series of monitoring sites were set up in November 2014 in the West Matukituki Valley, west of Lake Wanaka. Porous soil solution samplers were installed to a depth of 50 cm in (i) a sheep- and cattle-grazed pasture, (ii) a cattle-grazed winter forage crop, and (iii) a native bush site. Results for 2015 showed that rainfall totalled 2240 mm, with calculated drainage estimated at 1330 mm. The total fluxes of dissolved N from the crop and pasture sites during the 12 months from June 2015 were 157 and 43 kg N/ha, respectively. Dissolved organic N (DON) made an unexpectedly large contribution to these fluxes, accounting for 20 and 67% of the total fluxes of dissolved N in drainage from the crop and pasture sites, respectively. Gaining a better understanding of the bioavailability of dissolved forms of organic N in leachate would help determine the risks that these forms of nutrients pose to water quality, and if they should be incorporated into models such as Overseer which do not account for DON. The project’s initial findings enabled an informed discussion on the use of modelled results from Overseer for the mitigation of N loss at a farm scale in the lakes’ catchments. It also focussed farmers’ attention on management of the nitrogen leaky parts of their farm systems, especially winter crops.

Dating and Interpreting Landscapes of Livestock Herding: Excavation of a Hut Site and Enclosure in Southwestern Ireland

ABSTRACT Grazing livestock in uplands was a widespread practice in late Medieval and early modern Europe, but there can be uncertainty about the date and function of archaeological sites associated with herding. This paper reviews fieldwork on such sites in northern and northwestern Europe and reports on the excavation of a hut and enclosure in the mountains of southwestern Ireland. The hut was found to have been built in the 16th or 17th centuries a.d. and was probably used to oversee dairy animals (likely cows). The enclosure was dated to the early 18th or early–mid-19th century a.d. and is more likely associated with goat milking. The excavations demonstrate that construction dates can be obtained for pastoral sites in uplands of northwestern Europe. Furthermore, with careful reading of features in the surrounding landscape and consideration of documentary and ethnographic evidence, fieldwork can help determine the nature of pastoral economies over time.

Bacterial community composition of Hungarian salt-affected soils under different land uses

Salinization and sodification are serious and worldwide growing threats to healthy soil functions. Although plants developed a plethora of traits to cope with high salinity, soil bacteria are also essential players of the adaptation process. However, there is still lack of knowledge on how other biotic and abiotic factors, such as land use or different soil properties, affect the bacterial community structure of these soils. Therefore, besides soil chemical and physical investigations, bacterial communities of differently managed salt-affected soils were analysed through 16S rRNA gene Illumina amplicon sequencing and compared. Results have shown that land use and soil texture were the main drivers in shaping the bacterial community structure of the Hungarian salt-affected soils. It was observed that at undisturbed pasture and meadow sites, soil texture and the ratio of vegetation cover were the determinative factors shaping the bacterial community structures, mainly at the level of phylum Acidobacteriota. Sandy soil texture promoted the high abundance of members of the class Blastocatellia, while at the slightly disturbed meadow soil showing high clay content was dominated by members of the class Acidobacteriia. The OTUs belonging to the class Ktedonobacteria, which were reported mostly in geothermal sediments, reached a relatively high abundance in the meadow soil.

Soil legacy phosphorus and loss risk in subtropical grasslands

The accumulation of soil legacy phosphorus (P) due to past fertilization practices poses a persistent challenge for agroecosystem management and water quality conservation. This study investigates the spatial distribution and risk assessment of soil legacy P in subtropical grasslands managed for cow-calf operations in Florida, with two pasture types along the intensity gradient: improved vs semi-native pastures. Soil samples from 1438 locations revealed substantial spatial variation in soil legacy P, with total P concentrations ranging from 11.46 to 619.54 mg/kg and Mehlich-1 P concentrations spanning 0.2–187.27 mg/kg. Our analyses revealed that most of the sites in semi-native pastures may function as P sinks by exhibiting positive Soil P Storage Capacity (SPSC) values, despite having high levels of soil total P. These locales of higher SPSC values were associated with high levels of aluminum, iron, and organic matter that can adsorb P. In addition, our results from spatial random forest modelling demonstrated that factors including elevation, soil organic matter, available water storage, pasture type, soil pH, and soil order are important to explain and predict spatial variations in SPSC. Incorporating SPSC into the Phosphorus Index (PI) spatial assessment, we further determined that only 3% of the study area was considered as high or very high PI categories indicative of a significant risk for P loss. Our evaluation of SPSC and PI underscores the complexity inherent in P dynamics, emphasizing the need for a holistic approach to assessing P loss risk. Insights from this work not only help optimize agronomic practices but also promote sustainable land management, thus ensuring the long-term health and sustainability of grass-dominated agroecosystems.

Tradeoffs in access to light and root networks of established host trees for restoration planting of the root hemiparasite Santalum paniculatum

Restoration of root hemiparasite trees, such as Hawaiʻi's endemic Santalum species (ʻiliahi), may benefit from underplanting in stands of suitable hosts like the nitrogen‐fixing native tree, Acacia koa (koa). At a pasture site on Hawaiʻi Island previously reforested with koa, we underplanted seedlings of the island‐endemic sandalwood species, Santalum paniculatum, to examine the tradeoff between access to an established root network (distance to the nearest koa tree) under variable overstory shading (8.8–90.1% canopy openness range) during regeneration establishment. We hypothesized that there is an optimal parasite–host spacing and canopy openness that balance parasitic resource transfer with light availability. ʻIliahi seedling survival was 96% with no survival treatment differences. ‘Iliahi seedling growth was positively related to canopy openness but negatively related to the distance to the nearest koa tree, and the slope of these relationships increased over time. Leaf photosynthetic light compensation points, light saturation points, and stomatal density mostly followed similar trends as growth. These results demonstrate that ‘iliahi can be successfully underplanted in an established koa stand, which benefits ‘iliahi plantings and contributes to diversifying initial restoration and reforestation plantings. There appears to be a significant tradeoff in planting distance between benefits from and competition with the host; however, the improvement in growth with increased canopy openness appeared to be much greater than the effect of planting distance. Underplanting into an established host stand with sufficient canopy openness can help restore functionally compatible and abundant ‘iliahi regeneration into forests.

The Productivity and Carbon Exchange of an Intensively Managed Pasture in Central Kentucky

Intensive pasture management that aims at providing season-long forage while minimizing soil degradation is increasingly becoming an important grazing strategy in Kentucky. Typically, it involves the use of high-yielding warm and cool season forage species that are well suited to local soil and climate conditions, meeting the dual-purpose provision of high nutritional value while remaining resilient to grazing pressure and changing climate. Monitoring carbon exchange is a crucial component for effective pasture management to promote sustainable pastureland management practices. We hypothesized that pasturelands, when intensively managed, would exhibit a small but important CO2 cumulative uptake year-round. We used the Eddy covariance method to measure the net ecosystem exchange of CO2 (NEE) and productivity of an intensively managed pastureland at Kentucky State University Research and Demonstration station from 2015 to 2020. The study has two objectives: to quantify interannual variability in net ecosystem exchange, and examine the controlling environmental factors, in particular temperature, sunlight, and precipitation of NEE. Diurnal and seasonal fluctuations followed typical patterns of carbon uptake and release. Overall, the pasture site consistently was carbon sink except for 2016, in part due to a warmer winter season than usual, sequestering 1394 gCm−2 over the study period. Precipitation and temperature were critical environmental factors underpinning seasonal CO2 uptake and release. Of critical importance was the net carbon uptake during the non-growing season.

Changes in evapotranspiration, transpiration and evaporation across natural and managed landscapes in the Amazon, Cerrado and Pantanal biomes

Land-use and land-cover change (LULCC) can dramatically affect the magnitude, seasonality and main drivers of evaporation (E) and transpiration (T), together as evapotranspiration (ET), with effects on overall ecosystem function, as well as both the hydrological cycle and climate system at multiple scales. Our understanding of tropical ecosystem responses to LULCC and global change processes is still limited, mainly due to a lack of ground-based observations that cover a variety of ecosystems, land-uses and land-covers. In this study, we used a network of nine eddy covariance flux towers installed in natural (forest, savanna, wetland) and managed systems (rainfed and irrigated cropland, pastureland) to explore how LULCC affects ET and its components in the Amazon, Cerrado and Pantanal biomes. At each site, tower-based ET measurements were partitioned into T and E to investigate how these fluxes varied between different land-uses and seasons. We found that ET, T and E decreased significantly during the dry season, except in Amazon forest ecosystems where T rates were maintained throughout the year. In contrast to Amazon forests, Cerrado and Pantanal ecosystems showed stronger stomatal control during the dry season. Cropland and pasture sites had lower ET and T compared to native vegetation in all biomes, but E was greater in Pantanal pasture when compared to Pantanal forest. The T fraction of ET was correlated with LAI and EVI, but relationships were weaker in Amazon forests. Our results highlight the importance of understanding the effects of LULCC on water fluxes in tropical ecosystems, and the implications for climate change mitigation policies and land management.

A microregional reindeer herding landscape in Yamal: patterns and dynamics of movements

Human and animal mobility lies at the core of any nomadic pastoralist system. Anthropological studies of migratory patterns of mobile pastoralists’ movements have revealed two universal sets of factors—ecological and non-ecological—that influence such movements differently. Our study focuses on the nomadic movement of the Yamal Nenets reindeer herders in the Russian Arctic using a microregional approach to study the indigenous communities on a large scale. The Nenets households of the Mordyyakha microregion in the northwest of the Yamal Peninsula have changed winter pasture sites several times over the past 15–20 years, while maintaining a stable summer route. Based on fieldwork among these people, we analyse how environmental and non-environmental factors influence the dynamics of their summer and winter meridional nomadic routes. We argue that long-term changes in their winter mobility are mainly related to the quality of pastures. Changing winter sites is a strategy that relates to ecological factors and still remains relevant for the households migrating via the meridional pastoral corridors of Yamal. In contrast, changing summer areas, as a rule, occurs in response to developing industry and, thus, relates to non-ecological factors.

ISOLATION AND IDENTIFICATION OF ACTINOMYCETES WITH ANTIBACTERIAL ACTIVITY FROM SOIL SAMPLES AROUND KANDY, SRI LANKA

Commercially exploited antibiotics are originally isolated from Actinomycetes. Even so, Actinomycetes are mostly underestimated for their antibacterial potential. This study aimed to isolate and identify Actinomycetes with antibacterial activity from soil samples around Kandy Sri Lanka. Soils were taken from five different habitats (waste disposal (WS), originally cultivated (OR), riverbanks (RB), pasture (PS), and rhizospheric (RH)). Serially diluted samples were grown on an Actinomycetes isolation agar medium and screened for antibacterial activity against Escherichia coli (ATCC25922), Staphylococcus aureus (ATCC25923), Pseudomonas aeruginosa (ATCC27853) and Klebsiella pneumoniae (ATCC13883) using perpendicular streak method. Isolates with inhibitory activity were subjected to secondary screening. 19 actinomycetes isolates were identified of which 10 isolates showed inhibitory activity during preliminary screening. During the secondary screening, two isolates from RB site and one isolate from OR site expressed broad-spectrum antibacterial activity while the other five isolates from RB, OR, WS, and PS sites inhibited either Escherichia coli or Staphylococcus aureus. The soil samples are a promising source of novel antibacterial compounds and thus these findings can be used for further investigations in developing broad-spectrum antibiotics for therapeutic targets in the future. KEYWORDS: Actinomycetes, soil, antibacterial activity, S. aureus, E. coli

Influence of antecedent soil moisture content and land use on the surface runoff response to heavy rainfall simulation experiments investigated in Alpine catchments

In small Alpine catchments, floods are mostly triggered by surface runoff generation during convective heavy precipitation events. Their magnitude also depends on the antecedent soil moisture content, which was shown in several previous studies. This study aims at understanding (a) which sites change their surface runoff response to rainfall events with high precipitation intensity under very moist pre-conditions to what extent and (b) on which site characteristics this depends on. Therefore, we conducted repeated rainfall simulation experiments (40–80 m2, 1 h, 100 mm h−1) at 20 sites in five Eastern Alpine areas and analyzed their results on the basis of soil-physical parameters derived from collected soil samples.The hay meadow sites reacted with a strong increase in surface runoff to reduced saturation deficits, the pasture sites showed a smaller but visible response. The forest sites had the highest water retention capacities. The change in the surface runoff response is a function of the saturation deficit at the beginning of the initial experiment (r = −0.58). The soil physical parameters, especially the fine pore fraction (r = 0.56), correlate with the difference of the total surface runoff coefficient between the initial and the repeated experiment. The fine pore fraction also shows a high correlation (r = −0.78) with the saturation deficit at the beginning of the initial experiment, although pores of this fraction were saturated during all experiments. (Non-quantifiable) Land use effects, which in turn influence the soil physical parameters, play an important role in explaining how the surface runoff response in the repeated rainfall simulation experiment differs from the initial experiment. The information on land use and soil characteristics allowed the sites to be categorized into four types in terms of surface runoff disposition and the increase in total surface runoff coefficient in the second rainfall simulation experiment.

Linking above and belowground carbon sequestration, soil organic matter properties, and soil health in Brazilian Atlantic Forest restoration

Forest restoration mitigates climate change by removing CO2 and storing C in terrestrial ecosystems. However, incomplete information on C storage in restored tropical forests often fails to capture the ecosystem's holistic C dynamics. This study provides an integrated assessment of C storage in above to belowground subsystems, its consequences for greenhouse gas (GHG) fluxes, and the quantity, quality, and origin of soil organic matter (SOM) in restored Atlantic forests in Brazil. Relations between SOM properties and soil health indicators were also explored. We examined two restorations using tree planting (‘active restoration’): an 8-year-old forest with green manure and native trees planted in two rounds, and a 15-year-old forest with native-planted trees in one round without green manure. Restorations were compared to reformed pasture and primary forest sites. We measured C storage in soil layers (0–10, 10–20, and 20–30 cm), litter, and plants. GHG emissions were assessed using CH4 and CO2 fluxes. SOM quantity was evaluated using C and N, quality using humification index (HLIFS), and origin using δ13C and δ15N. Nine soil health indicators were interrelated with SOM attributes. The primary forest presented the highest C stocks (107.7 Mg C ha−1), followed by 15- and 8-year-old restorations and pasture with 69.8, 55.5, and 41.8 Mg C ha−1, respectively. Soil C stocks from restorations and pasture were 20% lower than primary forest. However, 8- and 15-year-old restorations stored 12.3 and 28.3 Mg ha−1 more aboveground C than pasture. The younger forest had δ13C and δ15N values of 2.1 and 1.7‰, respectively, lower than the 15-year-old forest, indicating more C derived from C3 plants and biological N fixation. Both restorations and pasture had at least 34% higher HLIFS in deeper soil layers (10–30 cm) than primary forest, indicating a lack of labile SOM. Native and 15-year-old forests exhibited higher soil methane influx (141.1 and 61.9 μg m−2 h−1). Forests outperformed pasture in most soil health indicators, with 69% of their variance explained by SOM properties. However, SOM quantity and quality regeneration in both restorations approached the pristine forest state only in the top 10 cm layer, while deeper soil retained agricultural degradation legacies. In conclusion, active restoration of the Atlantic Forest is a superior approach compared to pasture reform for GHG mitigation. Nonetheless, the development of restoration techniques to facilitate labile C input into deeper soil layers (>10 cm) is needed to further improve soil multifunctionality and long-term C storage.

Evaluation of remotely sensed imagery to monitor temporal changes in soil organic carbon at a long-term grazed pasture trial

Temporal variation of soil organic carbon (SOC) is driven by land use/management practice, ecosystem conditions and climatic variation. Robust quantification of changes in SOC that is cost-effective and provides a statistical assessment of uncertainty is challenging, particularly in the face of large spatial variability and slow soil SOC changes. Remote-sensing indicators of above-ground vegetation provide some indication of the amount of fresh organic material being supplied to the soil. Although, because of the time taken for this organic material to decay and become incorporated into the soil, there will be a lag between the changes in the indicator of vegetation growth and the resulting changes in SOC. In this work, we investigate how a remotely sensed indicator of vegetation cover can be used with a lag period to predict or indicate changes in SOC for grazed pasture sites at a long-term monitoring study, which has been monitoring soil under different land uses for over forty years. We assessed how well this worked for indicating the SOC changes for different depths in the soil profile. Results suggested that a lagged remotely sensed vegetation cover—the average cover of the two preceding years—provides some indication of SOC changes for the 0–10 cm soil depth, but changes for deeper soil depths were not well predicted. Further, we investigated the potential of using soil data from a point-in-time spatial dataset (e.g. data from a baseline sampling round) to calibrate a relationship between the remotely sensed cover and SOC, which can then be applied to predict or indicate the temporal variation of SOC. Results showed this approach gave large prediction errors, likely because the temporal variation (at a fixed point in space) and spatial variation (for a fixed point in time) of SOC that is predictable by cover differences are not interchangeable.

Prior exposure of microbial communities to seawater reduces resilience but increases compositional and functional resistance to flooding events

Storm surges, flooding, and the encroachment of seawater onto agricultural land are predicted to increase with climate change. These flooding events fundamentally alter many soil properties and have knock-on effects on the microbial community composition and its functioning. The hypotheses tested in this study were (1) that the extent of change (resistance) of microbial community functioning and structure during seawater flooding is a factor of pre-adaptation to the stress, and (2) if structure and function are altered, the pre-adaptation will result in communities returning to previous state prior to flooding (resilience) faster than unexposed communities. We chose a naturally occurring saltmarsh-terrestrial pasture gradient from which three elevations were selected to create mesocosms. By selecting these sites, we were able to incorporate the legacy of differing levels of seawater ingress and exposure. Mesocosms were submerged in seawater for 0, 1, 96- and 192-h, with half of the mesocosms sacrificed immediately after flooding, and the other half taken after a 14 day “recovery” period. The following parameters were monitored: 1) changes in soil environmental parameters, 2) prokaryotic community composition, and 3) microbial functioning. Our results indicated that any length of seawater inundation significantly altered the physicochemical properties of all the soils, although a greater change is observed in the pasture site compared to the saltmarsh sites. These changes remained following a recovery period. Interestingly, our results indicated that for community composition, there was a high degree of resistance for the Saltmarsh mesocosms, with the Pasture mesocosm displaying higher resilience. Further, we observed a functional shift in the enzyme activities with labile hemicellulose being preferentially utilised over cellulose, with the effect increasing with longer floods. These results suggest that changing bacterial physiology is more critical to understanding the impact of storm surges on agricultural systems than bulk community change.

Co-planting of a fast-growing, nitrogen-fixing host tree facilitates regeneration of the root hemiparasitic ‘iliahi (Hawaiian sandalwood)

Root hemiparasitic trees can photosynthesize yet also acquire resources from host plants, which may benefit the long-term survival and growth of the hemiparasite. Experimental evaluation of planting distance between tree hemiparasites and their hosts can lead to biological insights and contribute to practitioner decision making. On an abandoned pasture site in a historically tropical dry forest in Hawai‘i, we studied the effects of two host species and four planting distances on the survival and growth of ‘iliahi (Hawaiian sandalwood, Santalum paniculatum), an endemic root hemiparasitic tree. Treatments included a control with no host or one of two native host species: ‘aʻaliʻi (Dodonaea viscosa), a fast-growing shrub, or koa (Acacia koa), a fast-growing nitrogen-fixing tree. ‘Iliahi and host seedlings were planted at a distance of <0.2, 0.5, 1.0, or 2.0 m from each other. After three years, survival of ‘iliahi seedlings was greatest for ‘iliahi paired with koa at 1.0 m (88 %) compared to the control with no host (53 %) and when paired with koa at 2.0 m (55 %). Height and ground line diameter of ‘iliahi seedlings were greater when paired with koa at closer distances than with ‘aʻaliʻi at any distance or the control with no host. Specifically, ʻiliahi growth was greatest when paired with koa at <0.2 m distance. Foliar nitrogen concentration was greater for ‘iliahi paired with koa at <0.2, 0.5, and 1.0 m distances, whereas the other foliar nutrient concentrations were typically greater for the ‘iliahi control with no host. For sites with few or no pre-established hosts, such as abandoned pastures, ‘iliahi growth can be greatly improved by co-planting in proximity to koa. As with other Santalum spp., early and abundant parasitic root connections with a host, especially a nitrogen-fixing host, are likely important for ‘iliahi establishment and early growth.

Interaction of site, spacing, weed control and fertiliser in Pinus radiata plantations in southeast New South Wales

ABSTRACT Two trials addressing soil preparation, weed control, fertiliser application and planting density were established on dry, high-elevation sites as part of a program to develop site-specific management. The sites differed in soils and the level of pasture improvement. The objectives included identifying treatment combinations that had greatest productivity and best stem and branch form, considering that poor stem form is an issue on pasture sites. The trials were assessed at 13 years of age. Volume production was high compared with a plantation established earlier on a native forest site, but it was not possible to determine whether this was a result of higher survival, higher nutrition, improved weed control or improved genetics. There was little difference in the effects of soil preparation treatments, and there was no effect at 13 years of the small early-fertiliser application. Weed control was important, with effects on volume production varying between sites and having a greater effect on the highly improved pasture site. Increasing stocking from 1000 stems ha−1 to 1500 stems ha−1 increased volume production by about 24% where weed control was applied. There were differences in stem and branch form between sites, and the highly improved pasture site had a higher level of multi-leaders, probably attributable to low boron. The study shows the value of small, standardised silvicultural trials in the development of site-specific management.

Estimating water fluxes in the critical zone using water stable isotope approaches in the Groundnut and Ferlo basins of Senegal

AbstractSustainable water management in semi‐arid agriculture practices requires quantitative knowledge of water fluxes within the soil‐vegetation‐atmosphere system. Therefore, we used stable‐isotope approaches to evaluate evaporation (Ea), transpiration (Ta), and groundwater recharge (R) at sites in Senegal's Groundnut basin and Ferlo Valley pasture region during the pre‐monsoon, monsoon, and post‐monsoon seasons of 2021. The approaches were based upon (i) the isothermal evaporation model (for quantifying Ea); (ii) water and isotope mass balances (to partition Ea and Ta for groundnut and pasture); and (iii) the piston displacement method (for estimating R). Ea losses derived from the isothermal evaporation model corresponded primarily to Stage II evaporation, and ranged from 0.02 to 0.09 mm d−1 in the Groundnut basin, versus 0.02–0.11 mm d−1 in Ferlo. At the groundnut site, Ea rates ranged from 0.01 to 0.69 mm d−1; Ta was in the range 0.55–2.29 mm d−1; and the Ta/ETa ratio was 74%–90%. At the pasture site, the ranges were 0.02–0.39 mm d−1 for Ea; 0.9–1.69 mm d−1 for Ta; and 62–90% for Ta/ETa. The ETa value derived for the groundnut site via the isotope approach was similar to those from eddy covariance measurements, and also to the results from the previous validated HYDRUS‐1D model. However, the HYDRUS‐1D model gave a lower Ta/ETa ratio (23.2%). The computed groundwater recharge for the groundnut site amounted to less than 2% of the local annual precipitation. Recommendations are made regarding protocols for preventing changes to isotopic compositions of water in samples that are collected in remote arid regions, but must be analysed days later. The article ends with suggestions for studies to follow up on evidence that local aquifers are being recharged via preferential pathways.

Leaf-litter frog abundance increases during succession of regenerating pastures

Abstract The extensive clearing and modification of forests by anthropogenic activities is a major driver of biodiversity loss. Declines of common species are especially concerning because of the potentially large cascading effects they might have on ecosystems. Regrowth of secondary forests may help reverse population declines by restoring habitats to similar conditions prior to land conversion but the value of these secondary forests to fauna is not well understood. We compared the abundance of a direct-developing terrestrial frog, Craugastor stejnegerianus, in riparian and upland habitats of pasture, secondary forest, and mature forest sites. Mean abundance per transect was lower in upland pasture compared to mature forest. Secondary forest had similar abundance to mature forest regardless of age. We show that conversion of forest habitat to pasture represents a conservation threat to this species. However, riparian buffers help mitigate the negative effect of conversion of forest to pasture, and regrowth of secondary forest is an effective management strategy for restoring the abundance of this common leaf-litter species.

Machine learning based estimation of field-scale daily, high resolution, multi-depth soil moisture for the Western and Midwestern United States.

High-resolution soil moisture estimates are critical for planning water management and assessing environmental quality. In-situ measurements alone are too costly to support the spatial and temporal resolutions needed for water management. Recent efforts have combined calibration data with machine learning algorithms to fill the gap where high resolution moisture estimates are lacking at the field scale. This study aimed to provide calibrated soil moisture models and methodology for generating gridded estimates of soil moisture at multiple depths, according to user-defined temporal periods, spatial resolution and extent. We applied nearly one million national library soil moisture records from over 100 sites, spanning the U.S. Midwest and West, to build Quantile Random Forest (QRF) calibration models. The QRF models were built on covariates including soil moisture estimates from North American Land Data Assimilation System (NLDAS), soil properties, climate variables, digital elevation models, and remote sensing-derived indices. We also explored an alternative approach that adopted a regionalized calibration dataset for the Western U.S. The broad-scale QRF models were independently validated according to sampling depths, land cover type, and observation period. We then explored the model performance improved with local samples used for spiking. Finally, the QRF models were applied to estimate soil moisture at the field scale where evaluation was carried out to check estimated temporal and spatial patterns. The broad-scale QRF model showed moderate performance (R2 = 0.53, RMSE = 0.078 m3/m3) when data points from all depth layers (up to 100 cm) were considered for an independent validation. Elevation, NLDAS-derived moisture, soil properties, and sampling depth were ranked as the most important covariates. The best model performance was observed for forest and pasture sites (R2 > 0.5; RMSE < 0.09 m3/m3), followed by grassland and cropland (R2 > 0.4; RMSE < 0.11 m3/m3). Model performance decreased with sampling depths and was slightly lower during the winter months. Spiking the national QRF model with local samples improved model performance by reducing the RMSE to less than 0.05 m3/m3 for grassland sites. At the field scale, model estimates illustrated more accurate temporal trends for surface than subsurface soil layers. Model estimated spatial patterns need to be further improved and validated with management data. The model accuracy for top 0-20 cm soil depth (R2 > 0.5, RMSE < 0.08 m3/m3) showed promise for adopting the methodology for soil moisture monitoring. The success of spiking the national model with local samples showed the need to collect multi-year high frequency (e.g., hourly) sensor-based field measurements to improve estimates of soil moisture for a longer time period. Future work should improve model performance for deeper depths with additional hydraulic properties and use of locally-selected calibration datasets.

Upscaling point-scale soil hydraulic properties for application in a catchment model using Bayesian calibration: An application in two agricultural regions of New Zealand

Hydrological modeling for landscape and catchment scale applications requires upscaling of soil hydraulic parameters which are generally only available at point scale. We present a case study where hourly root zone soil water content and drainage observations from nine flat, pastoral sites (Waikato and Canterbury regions in New Zealand) were used to develop an upscaling approach to parameterize the soil water balance module of the TopNet catchment model, based on scaling multi-layer soil profile information from the national soil data base, S-map, to the single-layer soil profile used in TopNet. Using a Bayesian calibration approach, the hydraulic behavioral parameters of TopNet's soil water balance module were identified. Of the eleven calibration parameters considered three were found to be insensitive to data (stress point, unsaturated hydraulic conductivity and infiltration rate); three were correlated and could be determined from specific soil water content observations (wilting point, field capacity and drainable water); and five were correlated and could be determined from combined specific soil water content and drainage observations (drainage rate, saturated hydraulic conductivity profile, effective soil depth, soil water holding capacity and wetting front suction). Based on the eight correlated parameters, upscaling functions were then developed to derive suitable model parameters from S-map-hydro for each site. The validity of the upscaling functions was verified at each site. The approach used in this research can be used to parameterize the TopNet model at other similar locations, and also provides a transferable framework to parameterize other catchment-scale hydrology models where point-scale soil hydraulic data available.