•High temporal resolution data was used to study stemflow dynamics.•Stemflow is affected by a complex interaction of biotic and abiotic factors.•During some events, stemflow represented a significant ...input of water at the base of the tree.•Stemflow dynamics were explained by the interaction of rainfall intensity with tree size.•Stemflow dynamics for pines and oaks differed but total stemflow volumes were similar.
Stemflow, despite being a small proportion of gross rainfall, is an important and understudied flux of water in forested areas. Recent studies have highlighted its complexity and relative importance for understanding soil and groundwater recharge. Stemflow dynamics offer an insight into how rain water is stored and released from the stems of trees to the soil. Past attempts have been made to understand the variability of stemflow under different types of vegetation, but rather few studies have focused on the combined influence of biotic and abiotic factors on inter and intra-storm stemflow variability, and none in Mediterranean climates. This study presents stemflow data collected at high temporal resolution for two species with contrasting canopies and bark characteristics: Quercus pubescens Willd. (downy oak) and Pinus sylvestris L. (Scots pine) in the Vallcebre research catchments (NE of Spain, 42° 12′N, 1° 49′E). The main objective was to understand how the interaction of biotic and abiotic factors affected stemflow dynamics. Mean stemflow production was low for both species (∼1% of incident rainfall) and increased with rainfall amount. However, the magnitude of the response depended on the combination of multiple biotic and abiotic factors. Both species produced similar stemflow volumes and the largest differences were found among trees of the same species. The combined analysis of biotic and abiotic factors showed that funneling ratios and stemflow dynamics were highly influenced by the interaction of rainfall intensity and tree size.
Fallout radionuclides (FRNs) and their ratios, such as Beryllium‐7 (7Be) and excess Lead‐210 (210Pbxs), have been used to determine suspended sediment source and age in catchments. These models are ...based on numerous assumptions, for example, that channel deposition of FRNs from precipitation is negligible in comparison to their delivery to the channel from land surface erosion during individual storm events. We test this assumption using a mass balance approach during eight storms from summer 2011 to fall 2012 in a mid‐Atlantic United States piedmont region watershed with mixed land use. Event peak discharge and storm type corresponded to the importance of direct channel FRN deposition from precipitation. During relatively low discharge summer thunderstorms, with minimal overland flow, less than 1% of 7Be and 210Pbxs flux deposited on the watershed exits the watershed associated with suspended sediment. The majority but not all deposited on the stream channel exits the watershed associated with suspended sediment (60% of 7Be and 80% of 210Pbxs). Here precipitation and throughfall onto the wetted channel area can be responsible for any FRN newly associated with suspended sediment, as opposed to landscape surface erosion. Furthermore, FRNs can be stored with sediments in the channel between events. Events with higher discharges, including hurricanes, show the opposite pattern—FRN flux associated with suspended sediment exported from the reach is greater than channel FRN wet deposition, suggesting net erosion from the watershed landscape and/or stored material during these types of storms.
Key Points
Radionuclides used in short‐term sediment age and source evaluation can enter streams by channel interception and landscape erosion
Channel interception can provide all of the 7Be and 210Pbxs delivered to the channel during low‐discharge thunderstorms
Efforts to age or source sediment using fallout radionuclides must consider stream channel interception under low runoff conditions
•Small-scale variability in topography affects throughfall via species composition.•Steeper slopes with overlapping canopies intercept the most rainfall.•Steeper slopes also result in greater spatial ...variability in throughfall flux.•Local features as determinants of water fluxes are important at longer time scales.
At very large spatial scales, the impacts of topography, elevation, and aspect on throughfall variability are apparent. However, within relatively small catchments (<50ha), differences in species composition induced by slight changes in elevation coupled with slope orientation, could result in sufficient canopy variability whereby throughfall hydrology would be definitively different across small gradients. This study aims to (1) quantify the differences in throughfall hydrology across small topographic gradients, (2) determine the variability of throughfall across such gradients, and (3) determine the seasonal effects on throughfall hydrology resulting from differences in species composition and growing niches.
Throughfall partitioning was measured during 15 sampling periods at 4 landscape positions including 3 hillslopes with aspects facing north (NF), west (WF), and south (SF) in addition to a flat area (F) situated in the center of a 12ha deciduous catchment. Throughfall partitioning was significantly lower on the steepest SF plot (TF=75.0%) than on the moderately sloping NF (TF=83.9%, p=0.001) and F (TF=81.7%, p=0.037) plots. SF also had the largest degree of throughfall variability (CV=20.1), resulting from overlapping canopies, which led to higher rates of canopy interception. NF and WF plots exhibited the largest inter-seasonal differences with decreases in throughfall partitioning of 13.2% (p=0.013) and 12.1% (p=0.052), respectively, and corresponded to the largest differences in plant canopy indices (PAI) between seasons. Although slope and aspect were found to be distinguishing variables in our study, it was the influence of these variables on species composition that led to differences in throughfall quantity. Our study illustrates the systematic distribution of water resources across topographic positions within a relatively small forested catchment and highlights the need for additional consideration of topography-induced controls on microclimate and growing space, which ultimately influence water quality and quantity for effective management strategies.
The aim of this study was to assess the factors that account for the geographical variation in soil organic carbon stocks at the 0–30‐cm depth (SOC30) of forests in Japan. Boosted regression tree ...analysis was applied to 2157 points throughout Japan and to four regional geographical subdivisions with 16 environmental variables. The rank of predictor variables was different for Japan as a whole and among the regions. For Japan as a whole, soil group, air temperature, slope inclination, altitude and organic carbon stocks of litter were the most important factors that affected SOC30 stocks. Overall, SOC30 stocks decreased with air temperature, which was attributed to the decomposability of organic carbon. In addition, SOC30 stocks decreased with slope inclination because of instability of the topsoil on slopes, which, in turn, is related to the increase in rock fragment content and decrease in soil bulk density. The distribution of volcanic soil resulted in larger SOC30 stocks than was expected from climatic conditions. Precipitation was not important because of conflicting effects between the increase in soil organic carbon content with increasing net primary production and the decrease in mineral soil mass by the loss in topsoil. The regional analyses provide insight into the factors that cause variation in SOC30 stocks, which were obscured by the macroscale analysis of Japan as a whole, thereby illustrating the power of regional geographical analyses. Our results provide an improved basis for soil, forestry and biogeochemical models that require accurate estimates of SOC30 stocks.
Highlights
We assessed factors that account for geographic variation in soil organic carbon (SOC) stocks.
Effect and dependence of factors were estimated by a machine learning approach.
SOC stocks were affected by soil type, climate, site‐specific location and organic matter input.
Volcanic soil distribution, climate, slope steepness and historical overuse of forest affected SOC stocks.
Individual tree-ring width chronologies and mean chronologies from Pinus tabuliformis Carr. (Chinese pine) and Sabina przewalskii Kom. (Qilian juniper) tree cores were collected and analyzed from two ...sites in the eastern Qilian Mountains of China. The chronologies were used to analyze individual and time-varying tree-ring growth to climate sensitivity with monthly mean air temperature and total precipitation data for the period 1958–2008. Climate–growth relationships were assessed with correlation functions and their stationarity and consistency over time were measured using moving correlation analysis. Individuals’ growth–climate correlations suggested increased percentages of individuals are correlated with certain variables (e.g., current June temperature at the P. tabuliformis site; previous June, December and current May temperature and May precipitation at the S. przewalskii site). These same climatic variables also correspond to the mean chronology correlations. A decreased percentage of individuals correlated with these climatic variables indicates a reduced sensitivity of the mean chronology. Moving correlation analysis indicated a significant change over time in the sensitivity of trees to climatic variability. Our results suggested: (1) that individual tree analysis might be a worthwhile tool to improve the quality and reliability of the climate signal from tree-ring series for dendroclimatology research; and (2) time-dependent fluctuations of climate growth relationships should be taken into account when assessing the quality and reliability of reconstructed climate signals.
Plant invasions are a current threat to biodiversity conservation, second only to habitat loss and fragmentation. Density and heights of three invasive plants,
Rosa multiflora,
Lonicera japonica, and
...Elaeagnus umbellata, were examined between edges and adjacent interiors of forest sites in southern Illinois. Density (stems
m
−2) and heights (cm) of invasive plants were obtained in plots along transects at edge and interior sampling locations within forest sites. The effect of species, sampling location, and site shape index on invasive plant density was investigated, as well as differences in heights of invasive plants in edge vs. interior sampling locations.
Species, sampling location, and fragment shape index were significant factors influencing invasive plant density at study sites. Density for all three species ranged from 0 to 18
stems
m
−2. All three species invaded interiors of sites, however,
R. multiflora and
L. japonica had significantly greater densities in edge as opposed to interior transects. These two species also had significant differences in density among site shape indices. Density of
E. umbellata was not significantly different between edge and interior sampling locations or among site shape indices. Mean heights of all three invasive plants were higher in edge transects, however, this relationship was only significant for
L. japonica.
These findings suggest that (1) preservation of tracts of forest with less edge can minimize invasion by these three plants in this area. Interiors of forest sites can be protected from invasion by having less edge habitat for invasive species to enter and become established; and (2)
E. umbellata, unlike the other two species, is established in both interior and edges of study sites. Therefore,
E. umbellata may pose the most ecological damage because it is well established throughout sites, and should be given a high priority when implementing management and control efforts in southern Illinois forest ecosystems.
Changes in anthropogenic activities have altered the speciation and concentration of inorganic reactive nitrogen (Nr) delivered to coastal and oceanic waters with precipitation. Less is known about ...rainwater dissolved organic nitrogen (DON) despite its quantitative importance (>20% of Nr) and potential contributions to primary and secondary production. We document decreases in rainwater nitrogen and carbon amounts between 1994 and 2019 in Delaware, USA with the major reduction observed for nitrate (64%) reflecting emissions technology improvements. DON in 2019 was 55% that of 1994, though only 2 years of data are available precluding any assessment of trends. Season, airmass back trajectory (AMBT), rainfall amount, and meteorology influenced Nr amounts in 2018–2019 rain. DON, which peaked in Summer, had different seasonal patterns than inorganic Nr and dissolved organic carbon, suggesting a biological source. Marine AMBT events showed the lowest Nr abundances. AMBTs from the southwest had the highest concentrations of Nr and DOC partially due to low rainfall amounts. Characterization of the oxidized fraction of DON revealed abundant highly unsaturated aliphatic and peptide‐like formulas suggesting a combination of secondary organic, biomass burning, and biological sources. The large changes in Nr and DOC loads emphasize the dynamic nature of atmosphere to land/water fluxes due to the influence of anthropogenic processes with potential implications for coastal and oceanic water quality and ecology. Models of atmospheric deposition to watersheds and the ocean should be frequently reevaluated with current data to accurately assess inputs from changing atmospheric sources.
Plain Language Summary
Despite its quantitative importance (>20% of rainwater reactive nitrogen (Nr)) and contributions to primary and secondary production in coastal and oceanic waters, temporal variability in dissolved organic nitrogen (DON) amounts and characteristics remains understudied. Here, we document reductions in rainwater nitrate (64%) and DON (55%) amounts in 2019 relative to 1994 in Delaware, USA. The nitrate reductions likely reflect improvements in anthropogenic emissions technologies. Only 2 years of DON data are available, unfortunately, precluding assessment of long‐term trends. Season, airmass back trajectory (AMBT), rainfall amount, and meteorology influenced Nr amounts in 2018‐2019 rain events. DON concentrations peaked in summer while inorganic Nr and dissolved organic carbon were highest in spring, suggesting a distinct biological source for DON. Marine AMBT events showed the lowest Nr abundances, and southwest AMBTs had the highest concentrations of Nr and DOC partially due to low rainfall amounts. Molecular analyses show DON to be primarily composed of compounds suggestive of biomass sources though Northwest AMBT rainwater showed evidence for the influence of anthropogenic inorganic sulfur co‐emissions. These results demonstrate the need to reevaluate Nr (and DON in particular) amounts and characteristics as the patterns of anthropogenic emissions change locally, regionally, and globally.
Key Points
Mid‐Atlantic rainwater reactive nitrogen and dissolved organic carbon fluxes are significantly reduced over the last 25 years
Rainwater dissolved organic nitrogen abundances are uncoupled from inorganic nitrogen and dissolved organic carbon
Dissolved organic nitrogen compositional data and peak Summer abundance suggests a biological origin
PDF
