Large Rainfall Events Research Articles

Rainfall characteristics determine respiration rate of biological soil crusts in drylands

Altering precipitation regimes are of particular concern in drylands, where isolated rainfall events often drive ecosystem structure and function. This study aims to explore the effects of varying individual rainfall amount on the release of CO2 by biological soil crusts (biocrusts), which are dominant biotic components and play key roles in drylands, in different climate zones. For a field experiment, we sourced algal crust (early succession) and moss crust (later succession) from sites across the main arid and semi-arid regions of northern China along a precipitation gradient ranging from 180 mm in Tengger Desert to 390 mm in Mu Us Sandland. Then we measured the post rainfall CO2 release rates in response to five rainfall magnitudes (0–2, 2–5, 5–10, 10–20, >20 mm individual rainfall amount) over two years (2011–2012) using a Li-6400-09 Soil Chamber in a uniform background environment. To evaluate the effect of a rainfall amount, a coefficient of variation was calculated the C release of both biocrust types from each location (CV) and among different locations (CVLocations). The results showed that algal and moss crusts among different locations had higher amounts of C release after larger rainfall events, compared to small events. However, CV of both biocrust types from each location was lower after larger rainfall events. The CVLocations of algal and moss crusts showed contrary tendencies after rainfall events of >20 mm. These results imply that an increase in small-sized rainfall events (<5 mm) will lead to an increase in C release from biocrusts, but an increase in larger rainfall events (>20 mm) may lead to less variation in C release from algal crust-dominated regions and to increasing heterogeneity in C release from moss crust-dominated regions. This indicates that C-release amount from biocrust-covered regions may be easily changed by altering the number of individual rainfall events, even if the total annual rainfall amount stays the same. Further, how biocrusts in different successional stages respond to changes in rainfall regimes will be an important determinant of future C release patterns in drylands. These changes may even result in changing the way biocrusts contribute to the function of desert ecosystems. The current analyses also have important implications regarding changes in rainfall regimes that in turn change C release patterns in biocrust-covered regions.

Precipitation Characteristics and Land Cover Control Wet Season Runoff Source and Rainfall Partitioning in Three Humid Tropical Catchments in Central Panama

AbstractMechanisms of runoff generation in the humid tropics are poorly understood, particularly in the context of land‐use/land cover change. This study analyzed the results of 124 storm hydrographs from three humid tropical catchments of markedly different vegetation cover and land‐use history in central Panama during the 2017 wet season: actively grazed pasture, young secondary succession, and near‐mature forest. We used electrical conductivity to separate baseflow (old water) from storm‐event water (new‐water). In all three land covers, new‐water dominated storm runoff generation in 44% of the sampled storm events, indicating the dominance of fast shallow flow paths in the landscape. Activation of these flow paths was found to depend on a combination of maximum rainfall intensity and total storm rainfall, which, in turn, relates to markedly contrasting hydrograph separation results among land covers. Relationships between these rainfall characteristics and storm runoff generation were nonlinear, producing a threshold response with the exceedance of specific rainfall volumes and/or intensities. The pastoral catchment delivered order of magnitude more new‐water during storm events than the two forested catchments. Although new‐water contributed minimally (&lt;10%) to total wet season runoff in the forested catchments, 43% of runoff generation in the pasture came from five large rainfall events where a threshold response produced substantial increases in total runoff and new‐runoff efficiency. Based on our results, we propose a conceptual model of hydrologic flow paths in humid tropical systems that can explain previously observed disparities in seasonal storage and runoff with respect to land use/land cover.

Sensitivity of productivity to precipitation amount and pattern varies by topographic position in a semiarid grassland

AbstractAboveground net primary productivity (ANPP) in grasslands is an important integrator of terrestrial ecosystem function, a key driver of global biogeochemical cycles, and a critical source of food for wild and domesticated herbivores. ANPP exhibits high spatial and temporal variability, driven by a suite of factors including precipitation amount and pattern, biotic and abiotic legacies, and topographic heterogeneity. Global climate models forecast an altered hydrological cycle due to climate change, including higher precipitation variability and more extreme events, which may further increase spatiotemporal variability in ANPP. Therefore, it is essential to understand the sensitivity of this central ecosystem function to various precipitation metrics, legacies, and topographic positions to better inform sustainable grassland management. In this study, we analyzed long‐term (36‐yr) ANPP data collected across a topographic sequence in the semiarid shortgrass steppe of North America to examine patterns and drivers of spatiotemporal variability in ANPP. We observed that (1) ANPP varied substantially by topographic position, with greater divergence during years with high production, (2) ANPP variability was higher temporally (16‐fold maximum difference across years) than spatially (4‐fold maximum difference across topographic positions), (3) warm‐season perennial grasses were the dominant plant functional type across all topographic positions and strongly influenced total ANPP dynamics, and (4) ANPP had strong sensitivities to current year precipitation amount and pattern that varied by plant functional type, as well as weaker sensitivities to precipitation and productivity legacies. Overall, the lowest topographic position had the highest sensitivity to precipitation, likely due to higher resource availability via the downhill movement of water and nutrients during years with high precipitation and large rainfall events. These results suggest that temporal and spatial ANPP variability in shortgrass steppe is primarily driven by the combined effects of precipitation amount and pattern during the current year, with the dominant warm‐season perennial grasses governing these responses.

Co-regulation of rainfall amount and timing on soil carbon mineralization in a typical salt marsh of the Yellow River Delta, China.

Studying the effects of rainfall regimes such as rainfall amount and timing on soil carbon mineralization is of great importance for our understanding the mechanisms underlying the stability and accumulation of soil carbon in coastal salt marshes. In this study, we examined the responses of soil carbon mineralization (CO2 and CH4 fluxes) from undisturbed soil columns to rainfall events in different seasons (dry and wet seasons) with filed experiments in a primary Suaeda salsa region in the Yellow River Delta salt-marsh wetland, which is far away from the coast and not affected by tides. The results showed that rainfall amount and timing had a significant interaction in affecting soil CO2 flux rates. During the dry season, large rainfall events significantly reduced soil CO2 flux rates but had no significant effect in the wet season, which might be closely related to the significant increase in soil water content and salinity. Rainfall amount, rainfall timing and their interactions had no significant effect on soil CH4 efflux rates. Rainfall timing and rainfall amount did not affect CH4/CO2. CH4/CO2 increased with increasing soil water content and salinity. Soil water content and soil salinity showed similar increases to increasing rainfall amount. Our results suggested that the changing rainfall regime under climate change in the future would have a great impact on soil carbon mineralization and carbon sink function by regulating soil water and salt migration in this region.

Soil Moisture Dynamics in Response to Precipitation and Thinning in a Semi-Dry Forest in Northern Mexico

Understanding soil moisture behavior in semi-dry forests is essential for evaluating the impact of forest management on water availability. The objective of the study was to analyze soil moisture based in storm observations in three micro-catchments (0.19, 0.20, and 0.27 ha) with similar tree densities, and subject to different thinning intensities in a semi-dry forest in Chihuahua, Mexico. Vegetation, soil characteristics, precipitation, and volumetric water content were measured before thinning (2018), and after 0%, 40%, and 80% thinning for each micro-catchment (2019). Soil moisture was low and relatively similar among the three micro-catchments in 2018 (mean = 8.5%), and only large rainfall events (&gt;30 mm) increased soil moisture significantly (29–52%). After thinning, soil moisture was higher and significantly different among the micro-catchments only during small rainfall events (&lt;10 mm), while a difference was not noted during large events. The difference before–after during small rainfall events was not significant for the control (0% thinning); whereas 40% and 80% thinning increased soil moisture significantly by 40% and 53%, respectively. Knowledge of the response of soil moisture as a result of thinning and rainfall characteristics has important implications, especially for evaluating the impact of forest management on water availability.

Nitrous Oxide and Methane Emissions from Beef Cattle Feedyard Pens Following Large Rainfall Events

HighlightsNitrous oxide and methane emissions were measured from a commercial beef feedyard following large rainfall events.Nitrous oxide emissions dropped below detection levels for ten days following a 77 mm rainfall event.Daily N2O and CH4 emissions followed a diel pattern, peaking at manure temperatures of 36°C to 38°C.Results will be used to refine empirical models for predicting GHG emissions from open-lot feedyards.Abstract. More than six million beef cattle are fed annually in feedyards on the semiarid Southern Great Plains (SGP). Manure deposited on the open-lot pen surfaces contributes to greenhouse gas (GHG) emissions. Nitrous oxide (N2O) and methane (CH4) are GHGs linked to climate change, and both have global warming potentials greater than carbon dioxide (CO2). Two sampling campaigns were conducted in 2019 to quantify N2O and CH4 emissions from open-lot pen surfaces. The occurrence of large, unforecast rainfall events during both campaigns provided an opportunity to compare GHG emissions from the dry manure before rainfall and from the wetted pen surface for one to two weeks following precipitation. Temporal variability was quantified by continuous sampling using six to eight automated flux chambers, a multiplexer system, and real-time analyzers. Spatial variability was quantified using a recirculating portable chamber on a 5 × 8 grid. Nitrous oxide emissions dropped below detection levels for ten days after the precipitation event. Nitrous oxide emissions were related to nitrification or other aerobic processes. Methane emissions dropped below detection levels for five days after the precipitation event and then increased to pre-rainfall levels by day 8. When present, N2O and CH4 emissions followed a diel pattern, with the highest emissions occurring during the afternoon when manure pack temperatures at the 25 mm depth were 36°C to 38°C and ambient temperatures were 31°C to 32°C. Average CH4 emissions from the feedyard pen surface were 96-fold lower than estimated enteric CH4 emissions. The results of this field research will be used to refine empirical models for predicting annual N2O and CH4 emissions from open-lot beef cattle feedyards on the semiarid SGP. Keywords: Beef cattle, Flux chamber, Greenhouse gas, Manure, Nitrous oxide, Rainfall.

Evaluating the effects of timber harvest on hydrologically sensitive areas and hydrologic response

Effects of forest treatments on watershed hydrology in terms of water yield and runoff processes is a primary concern. This paper evaluates the effects of long-term land cover change on hydrological processes in the Mica Creek Experimental Watershed (MCEW) in northern Idaho, USA. In the MCEW, effects of clearcut and partial cut harvest practices on streamflow were monitored and evaluated from 1991 to 2013. Firstly, snowpack dynamics in terms of snowmelt timing and average melt rate under different elevations, aspects, land covers, and climate conditions were analyzed at the point-scale with the snow accumulation and melt (SAM) model from the perspective of the energy balance. Then, the grid-based soil moisture routing (SMR) hydrology model was used to provide temporal and spatial hydrological changes in the MCEW. We assigned locations as hydrologically sensitive areas (HSAs) based on the probability of runoff generation (P(Ai = HS)) to capture potential downstream environmental effects of actual land cover change and optimal harvest patterns. The results highlight the strong impacts timber harvest can have on increasing streamflow and, in particular, peak flow. On average, the daily averaged degree of saturation increased by 20% after timber harvest resulting in higher risks of flooding from large rainfall events. Three logging scenarios including logging in areas with low P(Ai = HS), high P(Ai = HS), and in the entire watershed area, showed that logging areas had a positive relationship with water yield and that more extreme peak flow was likely to occur after clearcutting in high P(Ai = HS) areas (high elevation) under rainfall driven events or logging in low P(Ai = HS) areas (medium elevation) during snowmelt dominated events. Clearcutting on south-facing slopes at medium elevation strongly increased the average melt rate leading to potential flooding if a snowpack was present and temperatures increased. Scenario analysis suggests that partial cutting in areas with low P(Ai = HS) would reduce peak flow amount by as much as 40%. However, for watersheds to be logged entirely, choosing proper harvest locations such as clearcutting in high P(Ai = HS) areas having large snow events may effectively reduce extreme peak flow from spring snowmelt. Our findings inform forest management decisions favoring partial cutting over clearcutting, and how to avoid concentrating harvest practices in HSAs by adapting spatial distribution and timing of harvesting to climate conditions to minimize impacts on the water cycle.

Monitoring the Hydrological Balance of a Landslide-Prone Slope Covered by Pyroclastic Deposits over Limestone Fractured Bedrock

Many mountainous areas in Campania, Southern Italy, are characterized by steep slopes covered by loose unsaturated pyroclastic deposits laying upon fractured limestone bedrock. The soil covers are mainly constituted by layers of ashes and pumices. Large and intense rainfall events trigger shallow landslides, often turning into debris flows that cause huge damage and casualties. The slope of Cervinara, around 40 km Northeast of Naples, was involved in a catastrophic flowslide on 16 December 1999, triggered by a rainstorm of 325 mm in 48 h. To capture the main effects of precipitation on the slope stability, hydro-meteorological monitoring activities have been carried out at the slope to assess the water balance for three years (2017–2020). The field monitoring data allowed the identification of the complex hydrological processes involving the unsaturated pyroclastic soil and the shallow groundwater system developing in the limestone bedrock, which control the conditions that potentially predispose the slope to landslide triggering. Specifically, late autumn has been identified as the potentially most critical period, when slope drainage processes are not yet effective, and soil covers already receive large amounts of precipitation.

Leaf litter of two riparian tree species has contrasting effects on nutrients leaching from soil during large rainfall events

One goal of revegetating riparian zones is to mitigate nutrient movement into waterways, however release of dissolved nutrients and organic compounds from decaying leaf litter during rainfall may partially offset these benefits. We aim to understand how litter-derived nutrients and organics affect nutrient leaching from riparian soil, and how tree species affect these processes. In the laboratory we simulated large rainfall events through the leaf litter of two riparian woody tree species, Eucalyptus tereticornis and Casuarina cunninghamiana, with and without subsequent leaching through soil, as well as soil alone. We compared the forms and loads of nitrogen and phosphorus in leachate. Litter of both tree species stimulated additional nitrate release from soil (~100–200%) compared to bare soil. More ammonium and dissolved organic nitrogen also leached from soil with E. tereticornis litter, whereas less leached with C. cunninghamiana litter. More phosphate leached from soil with either species litter compared to bare soil. Increased nitrogen releases from soil with litter were greater than inputs from litter, suggesting they are driven by positive priming of soil microbial processes, whereas litter inputs increased phosphorus leaching. This information could be combined with rates of other riparian nutrient processes (e.g. plant uptake and denitrification) to quantify the net impact of trees on nutrient retention in riparian zones.

Assessing the significance of wet‐canopy evaporation from forests during extreme rainfall events for flood mitigation in mountainous regions of theUnited Kingdom

AbstractThere is increased interest in the potential of tree planting to help mitigate flooding usingnature‐based solutionsornatural flood management. However, many publications based upon catchment studies conclude that, as flood magnitude increases, benefit from forest cover declines and is insignificant for extreme flood events. These conclusions conflict with estimates of evaporation loss from forest plot observations of gross rainfall, through fall and stem flow. This study explores data from existing studies to assess the magnitudes of evaporation and attempts to identify the meteorological conditions under which they would be supported. This is achieved using rainfall event data collated from publications and data archives from studies undertaken in temperate environments around the world. The meteorological conditions required to drive the observed evaporation losses are explored theoretically using the Penman–Monteith equation. The results of this theoretical analysis are compared with the prevailing meteorological conditions during large and extreme rainfall events in mountainous regions of the United Kingdom to assess the likely significance of wet canopy evaporation loss. The collated dataset showed that eventEwclosses between approximately 2 and 38% of gross rainfall (1.5 to 39.4 mm day−1) have been observed during large rainfall events (up to 118 mm day−1) and that there are few data for extreme events (&gt;150 mm day−1). Event data greater than 150 mm (reported separately) included similarly high percentage evaporation losses. Theoretical estimates of wet‐canopy evaporation indicated that, to reproduce the losses towards the high end of these observations, relative humidity and the aerodynamic resistance for vapour transport needed to be lower than approximately 97.5% and 0.5 to 2 s m−1respectively. Surface meteorological data during large and extreme rainfall events in the United Kingdom suggest that conditions favourable for high wet‐canopy evaporation are not uncommon and indicate that significant evaporation losses during large and extreme events are possible but not for all events and not at all locations. Thus the disparity with the results from catchment studies remains.

Evaluation of sedimentation pond performance for a cleaner water production from an open pit mine at the edge of the Alto Tajo Natural Park

Controlling sediment produced by water erosion is the highest environmental challenge in steep, open pit sand mines located in erosive climates. Although restoration is impractical in active mine areas, sedimentation ponds are the Best Available Technique by the European Union to reduce sediment spillages from these environments. Few studies have described and supported such a solution with high resolution data. The María José mine is one of two active kaolin mines in the mining area of the Alto Tajo Natural Park, a highly erosive setting. It has a complex maintained pond system as a hydrologic and sedimentary control measure. In this landscape, mining can only be sustainable if clean water from production is ensured. The pond system retains sediment and water during a rain event, deposits the sediment, and eventually spills the water under controlled events. The María José spillages have been continuously monitored for suspended sediment concentration and water discharge at the mine outlet since 2012. During four years the efficiency of the pond system varied (96.7–99%), producing an average annual sediment yield of 5.6 Mg ha−1 y−1, a reduction of 98.4% compared with the sediment yield reported for similar local mines having no ponds. A quarter of this sediment was produced under controlled spillages allowing runoff management; the rest during large rainfall events when runoff decreased pond efficiency gives rise to an increase in suspended sediment concentration, as is typical of local natural rivers. Provided continuous maintenance, sediment ponds are shown to be a successful method to produce clean water. Successful pond efficiency implies that a mine produces water and sediment during baseflow conditions, allowing sufficient sediment volume to accumulate during rainstorms.

Seasonal variations in the response of soil respiration to rainfall events in a riparian poplar plantation

Rainfall events have profound influence on the soil carbon release in different forest ecosystems. However, seasonal variations in soil respiration (RS) response to rainfall events and associated regulatory processes are not well documented in riparian forest ecosystems to date. We continuously measured soil respiration in a riparian plantation ecosystem from 2015 to 2018 to explore the relationships between soil respiration and rainfall events. Across the 4 years, 83 individual rainfall events were identified for spring, summer and autumn. We found that mean RS rate after rain (post-RS) was significantly higher than that before rain (pre-RS) (p < 0.05) in spring, and the relative change in soil respiration (RSrc) increased against rainfall size due to the stimulation by the significant increases in soil moisture content (ΔSM). In contrast, mean post-RS was lower than pre-RS and RSrc was significantly decreased with the increasing rainfall size (p < 0.01) in summer and autumn. Reduced changes in soil temperature (ΔTS) and increased soil moisture content after rain (post-SM) contributed to the decreased RS due to frequently occurring heavy rain events in summer. Increased ΔSM following rainfall events coupled with groundwater level increase suppressed RSrc in autumn, even though increased ΔTS could offset the negative effects of SM on RS to some extent. In addition, we found that higher post-SM after large rainfall events (>10 mm day−1) changed the response of RS to soil temperature (TS) by reducing the temperature sensitivity (Q10) even in this riparian plantation ecosystem. Our study highlights the importance of integrating seasonal difference in soil respiration response to rainfall events and the impact of large rainfall events on soil C release for estimating forest soil carbon cycling at multiple scales.

Prediction of shallow landslides in pyroclastic-covered slopes by coupled modeling of unsaturated and saturated groundwater flow

Slopes covered with unsaturated shallow pyroclastic deposits, lying upon fractured limestone bedrock, are widespread in the mountains around Naples (southern Italy). Rainfall infiltration, reducing soil suction, eventually triggers shallow landslides. While drastic reduction of suction is unanimously recognized as the triggering mechanism, there is still debate about the hydrological processes controlling slope drainage and causing the establishment of landslide predisposing conditions. Field observations at the slope of Cervinara suggested that temporary storage of water in a perched aquifer, in the upper part of the fractured bedrock, may affect the leakage through the soil-bedrock interface. Hence, a physically based model, coupling flows in the unsaturated soil cover and in the perched aquifer, has been applied to three large rainfall events which occurred in December 1999 (when a landslide was triggered), January 2009, and November 2012. The results highlight that the different responses of soil and aquifer to precipitations, related not only to rainfall event characteristics (i.e., duration and mean intensity) but also to the initial conditions of the slope, determined by antecedent precipitations, can play a prominent role in the triggering of landslides. In fact, further simulations with synthetic rainfall events and different initial conditions provide a possible interpretation of the triggering of the landslide of December 1999, indicating that a soil profile with dry conditions at the base and a low level in the perched aquifer, typical of late autumn, can impede the drainage of infiltrating water through the soil-bedrock interface, thus favoring the build-up of pore pressure within the soil cover.

Drip water δ18O variability in the northeastern Yucatán Peninsula, Mexico: Implications for tropical cyclone detection and rainfall reconstruction from speleothems

This study examines the oxygen isotopic composition (δ18O values) of drip water, rainfall, and groundwater in the Río Secreto cave system, located in the Yucatán Peninsula, Mexico. The main motivation of this study was to determine the implications of drip water hydrology for the reconstruction of rainfall, droughts and tropical cyclone activity from stalagmite δ18O records. Monitoring of environmental and isotopic conditions was conducted for two years, from June 2017 to April 2019. This study provides the first instrumental evidence of an “amount effect” on interannual timescales in the Yucatán Peninsula. Observed bi-weekly to interannual variability in drip water δ18O values can be explained for individual drips by different integrations of rainfall amount in the time domain. Drip sites in two chambers (Stations A and B) integrate 4–15 months of rainfall accumulation. In a third chamber (Station LF) one drip site reflects the annual rainfall isotopic cycle with a positive offset and another, the largest rainfall events. During epikarst infiltration, the integration of rainfall amount by drip water source reservoirs determines the degree to which they “dilute” a tropical cyclone (TC) isotopic signature. TCs can be detected particularly when: (1) the water volume of the reservoir is low, such as during a persistent meteorological drought, and; (2) TCs have a sufficiently distinct isotopic signal relative to that of the reservoir prior to the event. TC isotopic signals can be masked or attenuated when drip water samples integrate more than a week and if significant rainfall events proceed the TC. In Río Secreto cave, reconstructing precipitation amount and detecting the TC isotopic signatures from stalagmite δ18O records is possible. Our analysis shows that stalagmite δ18O records are more likely to underestimate the magnitude of annual-scale droughts following normal hydroclimate conditions and more likely to record TCs during multiyear droughts than during normal or wet periods. Drip water monitoring results suggest that available stalagmite δ18O records from the Maya lowlands might be underestimating the intensity of paleo-drought events, such as the Terminal Classic droughts associated with the disintegration of the Maya civilization. This study complements the results from Lases-Hernandez et al. (2019) comparing two different sampling protocols of drip water collection. This study shows that a discrete sampling protocol is expected to approximate the amount-weighted isotopic composition of a drip, as long as it is conducted at a temporal resolution higher than the rainfall integration time by the drip reservoir. We highlight the importance of conducting multiyear monitoring of drip water and rainfall in order to interpret stalagmite δ18O as a paleoclimate proxy.

Evaluations and proposals for the debris flow hazard mapping method of the GIDES Project

On March 11 and 12, 2011, a large rainfall event caused floods and thousands of gravitational mass movements on the coast of the state of Parana, Brazil. This paper focuses on the large debris flows that reached the Jacarei river basin and uses them to test the new hazard mapping method proposed by the GIDES Project, a technology transfer partnership between Brazil and Japan. The method’s purpose is to be simple and fast, and, so, applicable in a developing country of continental dimension. Comparison of the maps generated by the GIDES methodology and the actual events that happened in the study area showed many discrepancies, that is, in its original form the methodology could not predict accurately the events. However, after adaptations to the studied case, major improvements were obtained. The adaptations aimed at testing morphometric parameters as the original technique to reach the best fit possible between the generated maps and the occurrence area of the studied event. For the debris flow transportation area, the parameters that produced better maps closer to the studied actual event was made with the relation between the maximum height reached by the debris flow and the maximum channel slope. No satisfactory morphometric relationship was found for the boulders’ deposition region. For the area of fine or less dense materials’ deposit, the most significant change was the incorporation of slopes from 0° to 2° in the mapping procedure. Finally, we found values and equations that could be used initially in the analysis of other sub-basins with some similarity with the studied area to map the debris flow hazard, although validation in other places is still needed. These different techniques adapted to the local reality can be used separately or together to create faster, simpler, cheaper, and reliable maps using relatively easy to find morphometric input data.

The hydrological function of a large chain-of-ponds: a wetland system with intermittent surface flows

Like many wetlands globally, the Mulwaree River chain-of-ponds system exists in two dichotomous states characterised by the presence or absence of surface flow connecting large, deep, permanently inundated ponds. We develop a conceptual model of hydrological function of this chain-of-ponds system combining surface and subsurface water levels, 2H and 18O stable isotopes and 222Rn as a groundwater tracer over a period of time that incorporated extended dry periods and large rainfall events. During high-flow or flood events, ponds are connected by flow along connecting channels and preferential flow paths. The water column is fully mixed to depths of up to 7 m. During high-flow, water level in the ponds can be greater than the water level in the surrounding floodplain aquifer, producing a hydraulic gradient away from the ponds, reflecting a losing wetland system. During no-flow periods, connecting channels and preferential flow paths are dry. A thermocline develops within the ponds and surface waters become enriched in 2H and 18O with evaporation losses. During periods of no-flow, increases in water level beyond atmospheric flux often occur during winter. Only small groundwater inflows enter the ponds from the floodplain aquifer. The hydrological function of this chain-of-ponds system is delicately balanced making it potentially sensitive to changes in climate that alter rainfall and evaporation rates, and any local-scale groundwater interference activities. Efforts to conserve and protect this system, and the aquatic ecosystems it supports, will be critical into the future.

Time‐intensive geoelectrical monitoring under winter wheat

ABSTRACTSeveral studies have explored the potential of electrical resistivity tomography to monitor changes in soil moisture associated with the root water uptake of different crops. Such studies usually use a set of limited below‐ground measurements throughout the growth season but are often unable to get a complete picture of the dynamics of the processes. With the development of high‐throughput phenotyping platforms, we now have the capability to collect more frequent above‐ground measurements, such as canopy cover, enabling the comparison with below‐ground data. In this study hourly direct‐current resistivity data were collected under the Field Scanalyzer platform at Rothamsted Research with different winter wheat varieties and nitrogen treatments in 2018 and 2019. Results from both years demonstrate the importance of applying the temperature correction to interpret hourly electrical conductivity data. Crops which received larger amounts of nitrogen showed larger canopy cover and more rapid changes in electrical conductivity, especially during large rainfall events. The varieties showed contrasted heights although this does not appear to have influenced electrical conductivity dynamics. The daily cyclic component of the electrical conductivity signal was extracted by decomposing the time series. A shift in this daily component was observed during the growth season. For crops with appreciable difference in canopy cover, high‐frequency direct‐current resistivity monitoring was able to distinguish the different below‐ground behaviours. The results also highlight how coarse temporal sampling may affect interpretation of resistivity data from crop monitoring studies.

Patterns and Drivers of Carbon Dioxide Concentrations in Aquatic Ecosystems of the Arctic Coastal Tundra

AbstractMultiple aquatic ecosystems (pond, lake, river, lagoon, and ocean) on the Arctic Coastal Plain near Utqiaġvik, Alaska, USA, were visited to determine their relative atmospheric CO2 flux and how this may have changed over time. The nearshore coastal waters and large freshwater lakes were small sinks of atmospheric CO2, whereas smaller waterbodies were substantial sources. pCO2 was linked to dissolved organic carbon concentrations across broad spatial and temporal scales, with greater concentrations found in smaller freshwater systems (i.e., ponds and rivers). On a day‐to‐day basis, water temperatures appeared to be the strongest driver of pCO2 levels in tundra ponds, where warmer temperatures likely stimulated microbial mineralization of carbon in both aquatic and hydrologically linked terrestrial environments. Large rainfall events, which may lead to inflow of carbon‐rich groundwater into these ponds, also were associated with increased daily average pCO2. Based on comparison to historical data, we estimate that CO2 concentrations in tundra ponds have increased more than 1.8 times over the past 40 years. Quantifying CO2 flux from these abundant aquatic ecosystems on the Arctic Coastal Plain and elsewhere in the high northern latitudes will likely have important implications for furthering understanding of landscape‐level and nearshore carbon dynamics in the Arctic.

Interaction of mangrove surface coverage and groundwater inputs on the temperature and water level near Tulum, Quintana Roo, Mexico: Observations and modelling

We report on a series of high resolution sensor measurements from within the Yax Chen cave system near the city of Tulum, Quintana Roo, Mexico and a box model of mangrove-groundwater interactions. The sensors were positioned in the cave following a transect moving inland. Conductivity, water pressure and temperature data were collected at 30 min intervals for a span of two years. Temperature, water level, and conductivity records showed a response to large rainfall events (Hurricane Nate in October 2017 and Topical Storm Philippe in November 2017) which coincided with differences in surficial vegetation. Groundwater with areas of mangrove coverage showed an input of warm mangrove water as the water level receded to pre-rainfall levels and, the temperature effect was not observed in areas dominated by an upland forested terrain. A model of the groundwater-mangrove interaction was developed with an on-off switch for the flow of mangrove water into the groundwater system when the rainfall is sufficiently large. The model reproduces the observed timing difference in the temperature and conductivity response, and matches the field data during rainfall events. This model shows the effectiveness of simple box models in understanding a complicated geophysical processes and provides quantitative support to this previously hypothesized groundwater interaction.

Hydrologic response in the karstic and basaltic hydro-geological units of Lake Kinneret watershed

The hydrologic responses of two similar in size watersheds in the Lake Kinneret basin are examined: Karstic Hermon watershed and basaltic Meshushim watershed. The streamflow properties at these watersheds are different in their surface flow to baseflow ratio, runoff coefficients and response to extreme rainfall events. The HYdrological Model for Karst Environment (HYMKE) model, developed to simulate daily flow in karst formation, was modified to address the basaltic formation at the Meshushim watershed. Water fluxes simulations were used to compare the hydrologic processes between the watersheds. The twice-higher annual precipitation in the Hermon watershed, generates annual streamflow that is five times more than in the Meshushim. This amplification of the rainfall-streamflow ratio between the watersheds is because larger fraction of the rainfall is lost to evapotranspiration at the basaltic Meshushim watershed and larger portion of the rainfall percolates to the karstic aquifer through preferential flow and appear as baseflow at the Hermon watershed. During large rainfall events when soil water content is near saturation, lower rainfall amount over the Meshushim watershed generates larger peak flow than the Hermon watershed. In both watersheds, surface flow was generated only when the soil water content is at or near saturation conditions. The streamflow dependency on soil water content, suggests high sensitivity of streamflow generation to the intra-annual variability of precipitation. Understanding the hydrologic response of the different sources of Lake Kinneret improves the ability to forecast its inflow.