Wet Summer Research Articles

The Effect of Clearing Diseased Wood on the Soil’s Physicochemical Properties in Black Pine Forests

Clearing diseased wood is a common measure used to reduce the continued spread of pine wilt disease and prevent infecting other pines. However, the impact of clearing diseased wood on the physicochemical properties of the soil is still unclear. To elucidate this matter, we conducted a series of soil experiments and observations in Changdao, mainly focused on uncut black pine, cut black pine, and the inter-forest zone. The results showed the following. (1) The soil beneath the forest underwent a transition towards the characteristics of forest and grassland after clearing diseased wood, which indicated a potential shift in the ecosystem’s structure and function. (2) Clearing diseased wood led to an increase in the soil pH of 0.15, indicating that it facilitated the recovery of acidic soil. (3) The clearing of diseased wood can coarsen the soil’s texture. Moreover, it effectively reduced the surface soil temperature (0–20 cm) in summer by 1.52 °C, as well as significantly decreasing the surface (0–20 cm) soil moisture in spring and summer by 1.3% and 2.43%, respectively. (4) Clearing diseased wood clearing can effectively modify the content of essential nutrients in the soil. It reduced the available nitrogen by 26.86 mg·kg−1, increased the available phosphorus by 0.57 mg·kg−1, and decreased the available potassium by 1.68 mg·kg−1. Meanwhile, clearing diseased wood exacerbated soil salinization and increased the soil’s salt content by 0.70 g·kg−1. The findings of this study provide scientific solutions for the sustainable ecological development of black pine forests in Changdao.

Variation of material fluxes in a large heterogenic subtropical river: A combination of climate change and human damming influences

Study regionThe West River, the main tributary of the Pearl River, China Study focusA hydrological model of the West River was successfully established and used to quantify the role of basin-wide spatiotemporal change of the impacts of climate change and human damming activities in the variation of material fluxes (water discharge and sediment load) at the river outlet at both interannual and seasonal time scales of the period from 1975 to 2017. New hydrological insights for the regionThe interannual variations of water discharge and sediment load were controlled by a single factor locally: runoff variation was positively correlated with the ENSO index (r = 0.56, p < 0.001) and the dams caused a 75.1% reduction of the annual sediment load in the post-dam period (2009–2017). Seasonally, climate change can alter the monthly water discharge by − 12–23% in the latter half of an abnormal year, while the dams caused a 4.6% reduction and a 12.4% increase in the summer and winter sediment load, respectively. There was a strong interaction between the two influencing factors seasonally, particularly during the wetter summer or drier winter, wherein the dominant driving mechanism in the monthly variation of material fluxes can switch. For the river basin, the impacts of climate change and dams are spatially variable. The basin-wide spatiotemporal change of the impacts of climate change and human damming activities can complicate the hydrological signal at the river outlet.

Hydrological and Biogeochemical Controls of the Seasonality of Particulate and Dissolved Nitrogen Exports During Rainfall Events From a Forested Watershed in Monsoon Asia, Japan

AbstractFew studies have investigated the effects of hydrological conditions such as rainfall magnitude and soil nitrogen dynamics on nitrogen export from forests during rainfall events. In this study, the seasonal export of particulate and dissolved nitrogen during 24 rainfall events (range: 3.0–417 mm) in a temperate monsoon forest watershed in Japan was measured along with the seasonality of the soil nitrate () pool size and the nitrification rate. The increase in nitrogen export with increasing streamflow was larger for particulate nitrogen than for and dissolved organic nitrogen, but was always the most abundant nitrogen component exported, even during extreme rainfall. For all rainfall events in summer, measured exports were higher than the averaged exports, regardless of rainfall magnitude or preceding rainfall. Nitrification activity in the soil was high in summer because of the high temperature and wet conditions of the soil. Nitrification also occurred in the upper slope in summer, whereas during other seasons it is hindered by dry conditions. These results indicate that nitrogen dynamics in the soil also affect export during rainfall. Comparisons with previous studies suggested that the effects of soil nitrogen dynamics on concentrations in stream water may be stronger during rainfall than during base flow conditions. They also showed that regions with wet summers due to rainfall are more sensitive to export, compared with other regions, and that increased summer rainfall can have a particularly large impact on nitrogen export from forest watersheds.

Latewood intra-annual density fluctuations indicate wet summer conditions and enhanced canopy activity in a Mediterranean ring-porous oak

Summary The climatic significance and ecosystem implications of latewood intra-annual density fluctuations (IADFs) are still not fully understood in Mediterranean ring-porous oak species. To solve this issue, we investigated: (i) the climate drivers of radial growth and latewood IADFs in the Mediterranean oak Quercus faginea, and (ii) whether they were correlated to increased canopy cover and greenness as recorded by the Normalized Difference Vegetation Index (NDVI). IADFs were formed in the mid to late latewood and they were characterized by rows of parenchyma cells. Such IADFs were uncommon and only present in 30–50% of sampled trees during 1999 and 2014, both years characterized by high precipitation in late July and early August. This relationship between IADFs formation and summer wet conditions differed from the conditions that enhance Q. faginea annual growth, wet winter-spring conditions, and low summer temperatures. Furthermore, IADFs formation showed a positive relationship with August NDVI values, indicating a correspondence of canopy greenness with secondary growth reactivation. We conclude that latewood IADFs in Q. faginea are a robust proxy of rare late-summer wet conditions and enhanced canopy activity as reflected by increased August NDVI values. Further monitoring of xylogenesis in other Mediterranean hardwoods along climatic gradients is suggested to mechanistically explain IADF production in seasonally dry biomes.

Assessment of isoprene and near-surface ozone sensitivities to water stress over the Euro-Mediterranean region

Abstract. Plants emit biogenic volatile organic compounds (BVOCs) in response to changes in environmental conditions (e.g. temperature, radiation, soil moisture). In the large family of BVOCs, isoprene is by far the strongest emitted compound and plays an important role in ozone chemistry, thus affecting both air quality and climate. In turn, climate change may alter isoprene emissions by increasing temperature as well as the occurrence and intensity of severe water stresses that alter plant functioning. The Model of Emissions of Gases and Aerosols from Nature (MEGAN) provides different parameterizations to account for the impact of water stress on isoprene emissions, which essentially reduces emissions in response to the effect of soil moisture deficit on plant productivity. By applying the regional climate–chemistry model RegCM4chem coupled to the Community Land Model CLM4.5 and MEGAN2.1, we thus performed sensitivity simulations to assess the effects of water stress on isoprene emissions and near-surface ozone levels over the Euro-Mediterranean region and across the drier and wetter summers over the 1992–2016 period using two different parameterizations of the impact of water stress implemented in the MEGAN model. Over the Euro-Mediterranean region and across the simulated summers, water stress reduces isoprene emissions on average by nearly 6 %. However, during the warmest and driest selected summers (e.g. 2003, 2010, 2015) and over large isoprene-source areas (e.g. the Balkans), decreases in isoprene emissions range from −20 % to −60 % and co-occur with negative anomalies in precipitation, soil moisture and plant productivity. Sustained decreases in isoprene emissions also occur after prolonged or repeated dry anomalies, as observed for the summers of 2010 and 2012. Although the decrease in isoprene emissions due to water stress may be important, it only reduces near-surface ozone levels by a few percent due to a dominant VOC-limited regime over southern Europe and the Mediterranean Basin. Overall, over the selected analysis region, compared to the old MEGAN parameterization, the new one leads to localized and 25 %–50 % smaller decreases in isoprene emissions and 3 %–8 % smaller reductions in near-surface ozone levels.

Palynological Evidence From the Altai Mountains for the Links Between the Asian Westerly Jet Streams and Monsoon System During the Holocene

AbstractThe Asian westerly jet streams in the upper troposphere play a pivotal role in shaping precipitation patterns, sustaining the diverse but fragile ecosystems in arid Central Asia. Despite their significance, the evolution history of these jet streams and their synergistic effects with the monsoon systems on regional climate change in Asia during the Holocene remain poorly understood. To address this gap, we present a continuous pollen record since 8.6 cal ka BP from Lake Shuang in the Altai Mountains. The first two principal components of the pollen data are employed to track regional changes in vegetation, summer moisture, and winter temperature. Meanwhile, the pollen data and the TraCE‐21ka simulation results were compared to reveal the dynamic mechanism of regional climate change. Results indicate a humid phase spanning the interval ∼8 to 5 cal ka BP in this region, which broadly coincides with the intensification of the Indian Summer Monsoon. This temporal correlation is potentially linked to the poleward shift of the Asian jet, as suggested by simulation results. Furthermore, our data show a consistent winter warming trend throughout the Holocene, indicated by changes in the dominant tree pollen taxa and a reduction of cold‐resistant‐taxa. This trend is associated with the weakening of the East Asian Winter Monsoon, influenced by increasing winter solar insolation and atmospheric CO2 concentration. Overall, our research provides strong paleoclimatological evidence highlighting the interconnected meteorological roles of the Asian jet and monsoon systems in shaping regional climates.

A Case Study of Drought during Summer 2022: A Large-Scale Analyzed Comparison of Dry and Moist Summers in the Midwest USA

The summer of 2022 was very dry across Missouri and the surrounding regions including much of the Great Lakes, Midwest, and southern plains of the USA. A comparison of this summer to the dry summer of 2012 and the relatively wet summers of 2018 and 2021 was carried out using the National Centers for Environmental Prediction/National Centers for Atmospheric Research reanalysis, the Climate Prediction Center teleconnection indexes, and the blocking archive at the University of Missouri. The summer of 2022 was like that of 2012 which was characterized by a strong 500 hPa height anomaly centered over the western US and plains as well as very little blocking in the East Pacific. The summers of 2018 and 2021 were characterized by more zonal flow over the USA and more blocking in the East Pacific, similarly to the results of an earlier study. The teleconnection indexes for the prior spring and summer were largely similar for the two drier years and opposite for the wetter years. The surface conditions for the drier years were more similar while these were opposite for the wetter years. The integrated enstrophy (IE) used in earlier studies identified a change in the large-scale flow regime in early June 2022, which coincided with a decrease in the precipitation over the study region. However, one key difference was that the spring of 2022 was characterized by blocking more consistent with a wetter summer. This would have made the predictability of the drought of summer 2022 less certain.

Optimum Time of Insemination after Onset of Oestrus in Holstein – Friesian Dairy Cows in the Peri-urban Khartoum (Sudan)

The aim of this study was to determine the optimum time of insemination after onset of oestrus in Holstein-Friesian dairy cows. 146 and 92 Cows were randomly assigned to the control and prostaglandin F2α treated groups respectively. The experimental animals were then visually observed for oestrus for a period of twelve months. 188 and 99 inseminations were given to the control and prostaglandin F2α treated groups respectively. The inseminations were given at time intervals of 1-6, 7-12, 13-18, and 19-24 hours after onset of oestrus during winter, hot dry summer and hot wet summer. During the three seasons, inseminations were carried out in cows at postpartum interval of 41-60, 61-80, 81-100, 101-120, 121 and over days. The trial was conducted in Cows at parities 1 and 2 as a group, and parities 3 and over as a separate group. The optimum time of insemination to achieve the highest conception rates was at 13-18 hours in the control group of Cows. Winter had the highest conception rates compared to other seasons. Cows at postpartum intervals of 121 and over days had the highest conception rates. Conception rates in cows at parities 1 and 2 had the highest conception rate compared to other parities. The present study revealed that the control group of cows had the highest conception rates when inseminations were at 13 – 18 hours after onset of oestrus compared to prostaglandin F2α treated cows.

The extreme wet and large precipitation size increase carbon uptake in Eurasian meadow steppes: Evidence from natural and manipulated precipitation experiments

The distribution of seasonal precipitation would profoundly affect the dynamics of carbon fluxes in terrestrial ecosystems. However, little is known about the impacts of extreme precipitation and size events on ecosystem carbon cycle when compared to the effects of average precipitation amount. The study involved an analysis of carbon fluxes and water exchange using the eddy covariance and chamber based techniques during the growing seasons of 2015–2017 in Bayan, Mongolia and 2019–2021 in Hulunbuir, Inner Mongolia, respectively. The components of carbon fluxes and water exchange at each site were normalized to evaluate of relative response among carbon fluxes and water exchange. The investigation delved into the relationship between carbon fluxes and extreme precipitation over five gradients (control, dry spring, dry summer, wet spring and wet summer) in Hulunbuir meadow steppe and distinct four precipitation sizes (0.1–2, 2–5, 5–10, and 10–25 mm d−1) in Bayan meadow steppe. The wet spring and summer showed the greatest ecosystem respiration (ER) relative response values, 76.2% and 73.5%, respectively, while the dry spring (−16.7%) and dry summer (14.2%) showed the lowest values. Gross primary production (GPP) relative response improved with wet precipitation gradients, and declined with dry precipitation gradients in Hulunbuir meadow steppe. The least value in net ecosystem CO2 exchange (NEE) was found at 10–25 mm d−1 precipitation size in Bayan meadow steppe. Similarly, the ER and GPP increased with size of precipitation events. The structural equation models (SEM) satisfactorily fitted the data (χ2 = 43.03, d.f. = 11, p = 0.215), with interactive linkages among soil microclimate, water exchange and carbon fluxes components regulating NEE. Overall, this study highlighted the importance of extreme precipitation and event size in influencing ecosystem carbon exchange, which is decisive to further understand the carbon cycle in meadow steppes.

Contour marks as potential indicators of evaporation rates in the early Permian continental vertebrate site Bromacker (Thuringia, Central Germany)

Reconstructing the climate of the past requires archives that bear proxy information on temperature, precipitation, or atmospheric composition, for example. In this study we use contour marks as potential water level marks in mud sediments to reconstruct local evaporation rates at the Bromacker lagerstaette site in the Early Permian. The measured values indicate a daily evaporation of 1.5–3.75 mm with a median value of 2.25 mm/day. The calculated evaporation rates are compared with modern ones to estimating moisture, precipitation and seasonal climate. For evaluating reconstructed precipitation and evapotranspiration rates, values simulated by global climate models and calculated from geochemical datasets are furthermore incorporated. For the first time, quantitative data and models elucidate the climate of the Tambach Formation and Bromacker lagerstaette against the background of the pivotal transition from the Carboniferous Ice House to the Permian Hothouse climate. Our results suggest a strongly seasonal climate with wet summers and dry winters in a mountainous region based on unexpectedly low temperatures (10.9–15.0 °C) considering the palaeo-location of the site in the tropical belt during the Early Permian. According to the modern vegetation model by Holdridge a moist forest biome is suggested for the Bromacker lagerstaette.

Spatiotemporal variability in precipitation‐growth association of Betula nana in the Siberian lowland tundra

Abstract Shrubs are expanding across a warming Arctic, evident from range expansion and increases in biomass, stature and cover. This influences numerous aspects of Arctic ecosystems. While shrub growth is generally positively associated with summer temperature, tundra ecosystems are characterised by abiotic gradients on small spatial scales (metres), and the Arctic climate and its year‐to‐year variability are changing rapidly. Hence, it is often unclear to what extent climate‐growth associations are scalable to future climate scenarios and across environmental gradients within ecosystems. Here, we investigate the stability of climate–growth associations of Arctic dwarf shrubs across small‐scale (metre to kilometre) topographic gradients and decadal timescales. We constructed ring width series (1974–2018) for a common Arctic dwarf shrub (Betula nana) for three representative types of subsites in the Siberian lowland tundra: higher elevation, lower elevation and thermokarst‐affected (thaw ponds) terrain. We quantified decadal variability in climate–growth associations across subsites using partial least squares regression and a moving window approach. We found consistently positive association of shrub radial growth with summer temperature, but substantial spatial and temporal variability in precipitation response. Association of shrub growth with summer rainfall increased in recent decades. Shrubs on elevated sites showed particularly strong response to rainfall following drier periods, and a negative association with recent snowfall extremes. Shrubs sampled from thaw ponds showed strong positive association with rainfall, followed by high shrub mortality after an extremely wet summer. This likely resulted from waterlogging due to thermokarst. Synthesis. Our findings imply that the response of shrub growth to changes in Arctic precipitation regimes is regulated by (i) macro‐ (kilometre‐scale) and micro‐topographical (metre‐scale) gradients, (ii) colimitation between temperature and moisture and (iii) potentially nonlinear responses to precipitation extremes. This suggests that the scalability of precipitation‐growth relationships for Arctic shrubs across dynamic tundra landscapes and future climate scenarios is limited. We recommend that future climate–growth studies on Arctic tundra shrubs simulate future precipitation changes across spatial gradients and include detailed microsite and shrub physiological monitoring.

Central European Agroclimate over the Past 2000 Years

Abstract Central Europe has experienced a sequence of unprecedented summer droughts since 2015, which had considerable effects on the functioning and productivity of natural and agricultural systems. Placing these recent extremes in a long-term context of natural climate variability is, however, constrained by the limited length of observational records. Here, we use tree-ring stable oxygen and carbon isotopes to develop annually resolved reconstructions of growing season temperature and summer moisture variability for central Europe during the past 2000 years. Both records are independently interpolated across the southern Czech Republic and northeastern Austria to produce explicit estimates of the optimum agroclimatic zones, based on modern references of climatic forcing. Historical documentation of agricultural productivity and climate variability since 1090 CE provides strong quantitative verification of our new reconstructions. Our isotope records not only contain clear expressions of the medieval (920–1000 CE) and Renaissance (early sixteenth century) droughts, but also the relative influence of temperature and moisture on hydroclimatic conditions during the first millennium (including previously reported pluvials during the early third, fifth, and seventh centuries of the Common Era). We conclude that Czech agricultural production has experienced significant extremes over the past 2000 years, which includes periods for which there are no modern analogs. Significance Statement As temperatures increase, droughts are becoming a growing concern for European agriculture. Our study allows recent extremes to be contextualized and helps to better the understanding of potential drivers. Stable carbon and oxygen isotopes in oak tree rings were analyzed to reconstruct year-to-year and longer-term changes in both temperature and moisture over central Europe and the past 2000 years. We combine these proxy-based climate reconstructions to model how well crops were growing in the past. The early fifth and the early sixteenth centuries of the Common Era were most likely characterized by extreme conditions beyond what has been experienced in recent decades. Our reconstructions of natural variability might be used as a baseline in projections of future conditions.

Interannual variability of spring and summer monsoon growing season carbon exchange at a semiarid savanna over nearly two decades

Eddy covariance measurements of land-atmosphere energy, carbon, and water exchange now span multiple decades at some sites, supporting an improved understanding of flux interannual variability (IAV) and its ecophysiological and physical controls. Most eddy covariance IAV studies have focused on temperate forest ecosystems, where carbon fluxes are large and flux records are longest – but also where IAV is much lower than in dryland regions, which have been identified as an essential driver of the trend and variability in the global terrestrial carbon sink. In this study, we leveraged 19 years of continuous micrometeorological measurements at the AmeriFlux US-SRM mesquite savanna site in southern Arizona, USA to quantify the IAV, trends, and drivers of carbon fluxes during the distinct spring and summer growing seasons. We also assessed the ability of modern satellite and land surface models to capture the IAV of seasonal water and carbon fluxes. Annual net ecosystem production (NEP) was small and highly variable (23 +/- 64 gC m − 2 yr−1). Precipitation and associated measures of water availability determined most of the variability in NEP, largely through their influence on annual and seasonal gross ecosystem productivity (GEP) as opposed to ecosystem respiration (ER). Root-zone soil moisture captured between 73% (spring) and 85% (summer) of GEP variability and between 73% (spring) and 58% (summer) of ER variability. Throughout the study period, soil moisture and greenness increased with associated increases in GEP, ER and NEP. These trends were strongly influenced by very productive and wet summer growing seasons during the last two years, which were characterized by abundant understory grass cover. Typically, less than half of the variability in growing season GEP and evapotranspiration was captured by satellite-based estimates and land surface model simulations with local site forcing and calibration, highlighting the ongoing utility of long-term datasets to support careful model testing and improvement.

Local drying climate magnified by urbanization in West Africa

AbstractUrbanization often increases surface runoff and land surface temperature due to loss of land cover. However, the effect of urbanization on local atmospheric humidity remains understudied despite the disastrous effects it can have on human health and water‐food‐energy‐ecosystem nexus. Here, we examined changes in atmospheric humidity in the West Africa (WA) region between 1985 and 2018. There was an increase in vapour pressure and decrease in atmospheric humidity in urban areas suggesting intensified urban drying island (UDI) effects. Rapid urban expansion has aggravated UDI effect in recent years, particularly during the hot, wet summer but mild during the cold, and dry winter. In future climate, the impacts of the UDI effect in the region may be enormous considering the increasing rate of urbanization in the region. To achieve a sustainable future, city planners and policymakers should consider the UDI effect by promoting developments that increase green land cover. Overall, this study provides a detailed understanding of the urban ecosystem's environmental change, which is helpful for local climate change adaptation and mitigation.

On the reliability of composite analysis: an example of wet summers in North China

The validity of composite analysis is seldom discussed despite the fact that it can yield conflicting results. Our study confirms its validity by adding a reliability analysis to the classical composite analysis. Based on the signals extracted from composite analysis, 10 of the 14 wet summers in North China (1951–2020) can be “predicted” retrospectively. This study suggested the cyclonic anomaly over Mongolia at 500- and 850-hPa is closely associated with wet summers in North China. Interestingly, we found the most profound effects come from the Southern Hemisphere, with high confidence levels and large magnitude of the composite anomalies. These composite results are further cross-validated. We show that, based on the signals extracted from composite analysis, previously unseen wet summers in North China can be predicted with the mean absolute percentage error (MAPE) around 6%.

Holocene relationships between climate, waterfowl, and lacustrine nutrient cycling at Kettle Lake, North Dakota, USA

Avian populations can substantially influence lacustrine nutrient loading and biogeochemical cycling through guano deposition. Here, we examine the influence of climate-forced avian migration throughout the Holocene on Kettle Lake, North Dakota, using stable nitrogen and carbon isotope values (δ15N, δ13C) of lake sediment organic matter. Carbon content and δ13C values are negatively correlated with δ15N and appear to be driven by changes in charcoal abundance and watershed vegetation, respectively. We find enriched δ15N values when the guano mineral struvite is present in the lake sediment core in the early to Mid-Holocene. A strong δ15N-percent Nitrogen content relationship during periods with struvite, relative to periods without struvite, indicates that guano deposition from mass bird visitations altered past nitrogen cycle processes, likely through enhanced denitrification. These results attest to the ability of waterfowl to alter lacustrine N-cycling in a mid-continental North American lake, and indicate that paleo-N data in this particular lake are recording a unique history that does not necessarily represent regional paleoenvironmental conditions. However, a significant, positive relationship between δ15N and Ambrosia and Amaranthaceae pollen abundance suggests avian visitation and its impacts on the N-cycle occurred during periods of anomalously wet summers superimposed on the background conditions of early to Mid-Holocene drought.

Why a large‐scale monsoon does not exist in North America: Orographic effects

AbstractTo understand why a large‐scale monsoon does not exist in North America, we performed a series of sensitivity simulations to investigate orographic effects of the Rocky Mountains (RMs) using the Community Atmosphere Model version 5.1. Results show that the height of the RMs plays a fundamental role in shaping the monsoon over North America that is confined to a small area from northwestern Mexico to the southwestern United States. When the RMs' height is increased by five times their actual height, a larger part of the non‐monsoon region over North America becomes a monsoon region. The mechanical effects of the RMs uplift dominate in winter, while thermal effects dominate in summer. During winter the mechanical effects induce an equivalent barotropic atmospheric response in the troposphere. With the uplift of the RMs, the ridge and trough located on the western and eastern sides of Canada are strengthened. Most areas of North America are influenced by the northerlies during winter such that enhanced descending motion over the eastern RMs favours a dry winter climate. However, thermal effects dominate during summer through enhanced baroclinic atmospheric responses. The Mexico high and lower‐level cyclonic circulation are strengthened with the RMs uplift, triggering large‐scale ascending motion. Eastern North America is mainly controlled by the enhanced southerly wind along the western flank of the North Atlantic subtropical high. Thus, the enhanced water‐vapour transport and upward motion on the eastern side of the RMs increase summer precipitation. As a result, an obvious seasonal variation with the feature of ‘dry winter and wet summer’ finally develops, indicating that the height of the RMs plays a crucial role in shaping the monsoon over the central United States. Additional experiments show that the base area of the RMs has little effect on the large‐scale monsoon formation over North America.

Paleohydrologic history of pluvial lake San Agustin, New Mexico: Tracking changing effective moisture in southwest North America through the last glacial transition

Paleoclimate records across the Intermountain West region of North America show significant regional variation in timing and magnitude of wet conditions that accompanied the last glacial-interglacial transition. To understand the climate controls on paleohydrologic change, well-dated records are needed across the region. The Plains of San Agustin (New Mexico, USA) is a closed-basin watershed of the American Southwest influenced by both winter westerly and summer North American Monsoon precipitation. The flat valley floors of the Plains contain lake and groundwater discharge deposits that record multiple periods of past wet climate. We present a record of hydroclimate for the past 26,000 years based on radiocarbon, U–Th series, and OSL dating of these deposits and stratigraphic correlation across the three sub-basins of the lake system. We find that two major lake oscillations occurred, coincident with the global Last Glacial Maximum (∼23–18 ka) and with Heinrich Stadial 1 (∼17–14 ka). The LGM lake cycle created a deep lake in the lowermost sub-basin, fed by marsh/lake overflow in the upper sub-basins. The Heinrich Stadial 1 wet interval attained the highest recorded lake level between ∼17.0 and 15.3 ka, merging the lower two sub-basins into one lake. Both lake cycles agree well in timing and magnitude with other lake-based records from the southwestern U.S., supporting previous interpretations that a south-shifted cool season storm track brought a dipole-like pattern of enhanced moisture to the southwest at the expense of drier conditions in the northwest during the LGM and deglaciation. A transition from lake to groundwater discharge conditions followed during the Bølling-Allerød (14.7–12.9 ka) across the study area. Wet meadows prevailed in the lower sub-basin during the Younger Dryas (12.9–11.7 ka), with marsh and open lake conditions in the upper and middle sub-basins, respectively. During the early Holocene, discrete wet intervals are recorded by ages for wet meadow deposits in all sub-basins with centennial-millennial frequency at 9.9, 8.8, 8.2 ka. These events agree well with other Intermountain West records showing wetter-than-present conditions prior to 8 ka. Two additional wet periods, centered at 6.8 and 5.4 ka, occurred during the driest known interval of the middle Holocene, and likely were partly supported in the Plains of San Agustin by summer moisture associated with the peak strength of the North American Monsoon. Our record highlights that both winter and summer moisture support water resources in New Mexico watersheds.

Physical and biogeochemical drivers of solute mobilization and flux through the critical zone after wildfire

A nine-year time series of nutrient cation and anion concentration and efflux from three forested catchments in the Jemez River Basin Critical Zone Observatory (JRB-CZO) in northern New Mexico was used to quantify the pulse of chemical denudation resulting from varying levels stand-replacing wildfire intensity in May-June of 2013. The 3 years of pre-fire and 6 years of postfire data were also probed to shed light on the mechanisms underlying the pulsed release and the subsequent recovery. The initial large solute pulse released to the streams—K+, Ca2+, Mg2+, SO42-, Cl−, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and total dissolved nitrogen (TDN)—was caused by leaching of hillslope ash deposits during the first monsoon storms post-fire. Debris flow following the wildfire likely redistributed much of the ash-containing sediments along streams and valley bottoms. Sustained elevated solute concentrations observed in the surface waters throughout the post-fire period relative to pre-fire baselines is consistent with these soluble materials being periodically flushed from the soils during wet seasons, i.e., snowmelt and summer monsoons. As microbial mediated reactions and biotic uptake—due to plant regrowth—recover after fire, nutrient ion export (e.g., NO3-, Cl− and SO42-) steadily decreased toward the end of the post fire period, but remained above pre-fire levels, particularly for NO3- and SO42-. Surface water concentrations of polyvalent cations (e.g., Al and Fe) decreased significantly after the fire. Our observations suggest that changes in organic matter composition after fire (e.g., increased humification index—HIX) and the presence of pyrogenic carbon may not favor organo-metal complexation and transport. Finally, differences in burn severity among the three watersheds presented in this study, provide insights of the relative impact of solute exports and resilience. The catchments that experienced high burn severity exhibited greater solute fluxes than the less severely burn. Moreover, despite these differences, toward the end of the post-fire period these surface waters presented low and similar solute effluxes, indicating system recovery. Nonetheless, magnitudes and rebounds were solute and process specific. The results of this study highlight the importance of surface and near surface physical and biogeochemical processes on the long-lasting geochemical denudation of forested catchments following wildfires of varying intensities.

Ecological factors related to seed germination and early seedling establishment inUlmus minorMill., an endangered riparian tree species

AbstractNatural populations of Ulmus minor Mill., an outstanding component of European riparian forests, are endangered due to Dutch elm disease, which has led to the development of several breeding programs throughout Europe. However, the reproductive ecology of this species is scarcely known even though sexual regeneration is an essential factor that must be understood before implementing elm stand restoration. In this paper, the main ecological factors affecting seed germination and early seedling establishment in U. minor are studied through a factorial design with five different factors: Light (levels: Full-sun, Shade), Initial water (levels: Initially-flooded, Initially-irrigated), Subsequent water (levels: Semi-submerged, Later-irrigated), Soil cover (levels: Bare-soil, Litter) and Substrate (levels: Silty-clay, Sandy-loam). Seed germination and seedling survival were monitored for 7 weeks. All factors except Initial water and Substrate turned out to be highly significant. Shade increased seed germination and seedling survival. Response to Initial water fluctuated, with an early higher percentage of germinated seeds in Initially-flooded but a higher seedling survival in Initially-irrigated. Subsequent water did not affect seedling establishment and survival, but Semi-submerged treatments increased seed germination. Bare-soilincreased seed germination too, whereas, in the medium term, Litter affected positively seedling survival. Sandy-loam substrates favoured seed germination, but Silty-claysubstrates favoured seedling survival. Together, these results suggest that the most favourable scenario for U. minor sexual regeneration may be a combination of a not-too-severe late-winter or early-spring flood followed by a wet spring and summer, probably with a higher establishment in heavy-textured substrates located in small gaps and forest edges where the overstorey provides some protection against strong sunlight.