Large wood in central Appalachian headwater streams: controls on and potential changes to wood loads from infestation of hemlock woolly adelgid

Large wood (LW) is an important component of forested headwater streams. The character of LW loads reflects a balance between adjacent valley processes that deliver LW to the channel (herein recruitment processes) and stream channel processes that either retain or transport LW through the reach (herein retention processes). In the central Appalachian Mountains, USA, LW characteristics in headwater streams located in eastern hemlocks (Tsuga candensis) forests are expected to change because of infestation of hemlock woolly adelgid (Adelges tsugae, HWA), an exotic, invasive insect. We examined LW characteristics in 24 headwater streams ranging from un‐infested to severe infestation, as determined by hemlock canopy health. The objectives of this work were to: (i) quantify wood loads; (ii) assess the relative importance of valley recruitment and in‐stream retention mechanisms in controlling reach‐scale wood loads; and (iii) assess if there was a detectable influence of HWA on LW loads. We hypothesized that LW loads would be similar to other forested streams in eastern USA and dominated by recruitment processes. In addition, higher LW loads would correspond with advanced HWA infestation. Mean wood frequency was 38 pieces/100 m ± 17 (standard deviation); mean wood volume was 3.69 m³/100 m ± 2.76. In general, LW load characteristics were influenced by both recruitment and retention parameters; jam (accumulations ≥ 3 pieces) characteristics were dominated by retention parameters. Results suggest that adjacent stand basal area influences LW loads and once LW is recruited to the channel, streams lack sufficient hydraulic driving forces, despite having lower resistance structures, to transport LW out of the reach. Sites in moderate decline had higher proportions of short (1–2 m and 1–4 m) and very long (>10 m) LW with higher frequency of jams that were low in volume. We present a hypothesized conceptual model of expected changes to LW loads associated with HWA infestation and hemlock mortality. Copyright © 2015 John Wiley & Sons, Ltd.     

Floodplain downed wood volumes: a comparison across three biomes

Downed large wood (LW) in floodplains provides habitat and nutrients for diverse organisms, influences hydraulics and sedimentation during overbank flows, and affects channel form and lateral migration. Very few studies, however, have quantified LW volumes in floodplains that are unaltered by human disturbance. We compare LW volumes in relatively unaltered floodplains of semiarid boreal lowland, subtropical lowland, and semiarid temperate mountain rivers in the United States. Average volumes of downed LW are 42.3 m³ ha^?1, 50.4 m³ ha^?1, and 116.3 m³ ha^?1 in the semiarid boreal, subtropical, and semiarid temperate sites, respectively. Observed patterns support the hypothesis that the largest downed LW volumes occur in the semiarid temperate mountain sites, which is likely linked to a combination of moderate‐to‐high net primary productivity, temperature‐limited decomposition rates, and resulting slow wood turnover time. Floodplain LW volumes differ among vegetation types within the semiarid boreal and semiarid temperate mountain regions, reflecting differences in species composition. Lateral channel migration and flooding influence vegetation communities in the semiarid boreal sites, which in turn influences floodplain LW loads. Other forms of disturbance such as fires, insect infestations, and blowdowns can increase LW volumes in the semiarid boreal and semiarid temperate mountain sites, where rates of wood decay are relatively slow compared with the subtropical lowland sites. Although sediment is the largest floodplain carbon reservoir, floodplain LW stores substantial amounts of organic carbon and can influence floodplain sediment storage. In our study sites, floodplain LW volumes are lower than those in adjacent channels, but are higher than those in upland (i.e. non‐floodplain) forests. Given the important ecological and physical effects of floodplain LW, efforts to add LW to river corridors as part of restoration activities, and the need to quantify carbon stocks within river corridors, we urge others to quantify floodplain and instream LW volumes in diverse environments. Copyright © 2016 John Wiley & Sons, Ltd.     

Wood storage in three mountain streams of the Southern Andes and its hydro‐morphological effects

This study analyses large wood (LW) storage and the associated effects on channel morphology and flow hydraulics in three third‐order mountain basins (drainage area 9–12 km²) covered in old‐growth Nothofagus forests, ranging from the temperate warm Chilean Andean Cordillera to the sub‐Antarctic Tierra del Fuego (Argentina). Amount, characteristics and dimensions of large wood (>10 cm diameter, >1 m long) were recorded, as well as their effects on stream morphology, hydraulics and sediment storage. Results show that major differences in LW abundance exist even between adjacent basins, as a result of different disturbance histories and basin dissection. Massive LW volumes (i.e. >1000 m³ ha^?1) can be reached in basins disturbed by fires followed by mass movements and debris flows. Potential energy dissipation resulting from wood dams is about a quarter of the total elevation drop in two streams, with a gross sediment volume stored behind wood dams of around 1000 m³ km^?1, which appears to be of the same order as the annual sediment yield. Finally, the presence of wood dams may increase flow resistance by up to one order of magnitude. Copyright © 2007 John Wiley & Sons, Ltd.     

Large wood distribution,mobility, and recruitment in an inter‐dam river reach: A comparison with geomorphic process on the Garrison Reach of the Missouri River pre and post the historical 2011 flood

This study assessed the effect of the largest flood since dam regulation on geomorphic and large wood (LW) trends using LW distributions at three time periods on the 150 km long Garrison Reach of the Missouri River. In 2011, a flood exceeded 4390 m³/s for a two‐week period (705% above mean flow; 500 year flood). LW was measured using high resolution satellite imagery in summer 2010 and 2012. Ancillary data including forest character, vegetation cover, lateral bank retreat, and channel capacity. Lateral bank erosion removed approximately 7400 standing trees during the flood. Other mechanisms, that could account for the other two‐thirds of the measured in‐channel LW, include overland flow through floodplains and islands. LW transport was commonly near or over 100 km as indicated by longitudinal forest and bank loss and post‐flood LW distribution. LW concentrations shift at several locations along the river, both pre‐ and post‐flood, and correspond to geomorphic river regions created by the interaction of the Garrison Dam upstream and the Oahe Dam downstream. Areas near the upstream dam experienced proportionally higher rates of bank erosion and forest loss but in‐channel LW decreased, likely due to scouring. A large amount of LW moved during this flood, the chief anchoring mechanism was not bridges or narrow channel reaches but the channel complexity of the river delta created by the downstream reservoir. Areas near the downstream dam experienced bank accretion and large amounts of LW deposition. This study confirms the results of similar work in the Reach: despite a historic flood longitudinal LW and channel trends remain the same. Dam regulation has created a geomorphic and LW pattern that is largely uninterrupted by an unprecedented dam regulation era flood. River managers may require other tools than infrequent high intensity floods to restore geomorphic and LW patterns. Copyright © 2018 John Wiley & Sons, Ltd.     

Long-term large wood load fluctuations in two low-order streams in Southern Chile

The eco-hydrogeomorphic significance of large wood (LW) and its potential for increasing downstream hazards during extreme floods have been widely recognized. We used LW data collected for a 10-year period from the two low-order streams of Pichún (Pi) and Vuelta de Zorra (VZ) in Southern Chile to (a) determine if the abundance and dimensions of individual LW pieces change with time, (b) quantify wood load fluctuations during the 10-year period, and (c) assess the role of LW recruitment from the riparian forests to explain wood load fluctuations during the study period. Nine years after the first survey, the number of LW pieces in Pi and VZ diminished by 60 and 40%, respectively. Despite the reduction in these numbers, in Pi, the LW dimensions did not change significantly during the study. In VZ, the dimensions exhibited statistically significant differences, despite being within the same class. In both catchments, the LW load fluctuated during a 10-year period, but the drivers of change differed. Although tree toppling was the recruitment mechanism responsible for LW in both stream cases, the high wood load measured in Pi at the beginning of the study suggested massive tree recruitments before the first survey, followed by wood exports which were higher than inputs in the subsequent 10-year period. In VZ, LW load decreased during the first 9 years (mean annual rate of ~9.2 m³ year⁻¹) and then increased by ~12.1 m³ year⁻¹ in year 10. At VZ, the inputs consisted of single trees that were recruited from the riparian area and by upstream flotation, while exports occurred by downstream fluvial transport. Wood inputs and exports occurred asynchronously and led to LW load fluctuations at decadal and annual intervals. Land management and tree species thus exert a major influence on wood inventory and budget in streams. © 2020 John Wiley & Sons, Ltd.     

Wood distribution in neotropical forested headwater streams of La Selva,Costa Rica

Surveys of wood along 30 forested headwater stream reaches in La Selva Biological Station in north‐eastern Costa Rica represent the first systematic data reported on wood loads in neotropical streams. For streams with drainage areas of 0·1–8·5 km² and gradients of 0·2–8%, wood load ranged from 3 to 34·7 m³ wood/100 m channel and 41–612 m³ wood/ha channel. These values are within the range reported for temperate streams. The variables wood diameter/flow depth, stream power, the presence of backflooding, and channel width/depth are consistently selected as significant predictors by statistical models for wood load. These variables explain half to two‐thirds of the variability in wood load. These results, along with the spatial distribution of wood with respect to the thalweg, suggest that transport processes exert a greater influence on wood loads than recruitment processes. Wood appears to be more geomorphically effective in altering bed elevations in gravel‐bed reaches than in reaches with coarser or finer substrate. Copyright © 2009 John Wiley & Sons, Ltd.     

Sensitivity analysis of temperature‐index melt simulations to near‐surface lapse rates and degree‐day factors at Vestari‐Hagafellsjökull,Langjökull,Iceland

The performance of temperature‐index melt models is particularly affected by the choice of near‐surface lapse rate used to determine the sum of positive daily temperatures at different elevations, and by the choice of factor used to relate this sum to the rate of melting. Data from the Langjökull ice cap are used in this study to quantify the influence of lapse‐rate and degree‐day factor variation on temperature‐index melt simulations. The lapse rate was significantly lower during summer than in spring or autumn, as a result of diabatic cooling, reducing boundary‐layer sensitivity to free‐air temperature change. The summer lapse rate was also significantly lower than the saturated adiabatic lapse rate. A sensitivity of approximately 600 mm water equivalent (w.e.) cumulative June–August melt per 0.1 °C 100 m^–1 change in lapse rate was found across a 500‐m altitude range. The sensitivity to a 1‐mm w.e. °C^–1 day^–1 change in degree‐day factors varied more: from approximately 500 mm w.e. cumulative summer melt at low elevation to approximately 200 mm w.e. at high elevation, reflecting the decline in melt rates associated with the greater persistence of snow with increasing altitude. The determination of a degree‐day factor for snow is complicated by the densification of the ageing snowpack, but the application of a parameterization for near‐surface density on the basis of albedo helped account for the development of snow water equivalence. Lapse rate was parameterized as a function of standardized anomalies in 750 hPa reanalysis temperature and significantly improved the simulation of cumulative summer melt compared with models applying the saturated adiabatic lapse rate. Copyright © 2012 John Wiley & Sons, Ltd.     

Bed‐material transport estimated from channel morphodynamics: Chilliwack River,British Columbia

This study investigates the relation between channel changes, as mapped from aerial photography, and bed‐material transport along Chilliwack River, British Columbia. Detailed mapping of channel features was completed for five dates between 1952 and 1991 using an analytical stereoplotter. Data were transferred to a geographic information system (GIS) to analyse changes during four consecutive periods. Erosion and deposition volumes along channel reaches were estimated by multiplying measured areal changes by the bed‐material depth along each reach. Bed‐material transport rates are related to morphologic changes using a sediment budget approach. The highest rate of transport for the four study periods is estimated as 55 000 ± 10 000 m³ a⁻¹ between 1983 and 1991. These rates are compared with estimates from short‐term (1–2 year) changes along the lower reach to investigate variations in sediment flux that may otherwise remain undetected. Significant morphologic change occurs roughly once every 5 years when flows are large enough to erode and entrain large volumes of bed material stored within the contemporary floodplain. In the absence of large floods, transport rates decline and vegetation begins to establish new floodplain. Copyright © 2000 John Wiley & Sons, Ltd.     

Drivers of variability in large wood loads along the fluvial continuum of a Mediterranean intermittent river

Although in-channel and floodplain large wood (LW) has been recognized as an important component of lotic ecosystems, there is still limited knowledge on the recruitment, mobility and retention of LW in rivers with an intermittent hydrological regime. In this study, we analysed the LW characteristics and related reach-scale variables of 22 reaches in a Mediterranean intermittent river (Evrotas, Greece) in order to identify predictors of in-channel and floodplain LW distribution. Our results indicated high downstream variation in LW volumes in the fluvial corridor (0.05–25.51 m³/ha for in-channel LW and 0–30.88 m³/ha for floodplain LW). In-channel and floodplain LW retention was primarily driven by the hydrological regime of the studied reaches (i.e. perennial or non-perennial) with higher volumes of LW observed in perennial sections. The width of the riparian corridor was an important predictor of LW storage at the reach scale. Non-perennial reaches had a disproportionally larger number of relatively small-diameter living trees at the expense of mature trees with larger diameters typical for riparian stands functioning as LW recruitment areas in perennial reaches. The smaller dimensions of in-channel LW in non-perennial reaches, coupled with the dominance of loose LW pieces, implies frequent LW transport during ordinary flood events. Nevertheless, overall low LW retention in the fluvial corridor under non-perennial flow regime predicts low volumes of mobilized LW. In contrast, the recruitment of relatively long and large-diameter LW from mature riparian stands in perennial reaches, together with additional LW stabilization by banks, bed sediments, living trees or other LW pieces decreases the potential for further LW transport. © 2020 John Wiley & Sons, Ltd.     

Reconstruction of a flash flood with large wood transport and its influence on hazard patterns in an ungauged mountain basin

The reconstruction of past flash floods in ungauged basins leads to a high level of uncertainty, which increases if other processes are involved such as the transport of large wood material. An important flash flood occurred in 1997 in Venero Claro (Central Spain), causing significant economic losses. The wood material clogged bridge sections, raising the water level upstream. The aim of this study was to reconstruct this event, analysing the influence of woody debris transport on the flood hazard pattern. Because the reach in question was affected by backwater effects due to bridge clogging, using only high water mark or palaeostage indicators may overestimate discharges, and so other methods are required to estimate peak flows. Therefore, the peak discharge was estimated (123 ± 18 m³ s^–1) using indirect methods, but one‐dimensional hydraulic simulation was also used to validate these indirect estimates through an iterative process (127 ± 33 m³ s^–1) and reconstruct the bridge obstruction to obtain the blockage ratio during the 1997 event (~48%) and the bridge clogging curves. Rainfall–Runoff modelling with stochastic simulation of different rainfall field configurations also helped to confirm that a peak discharge greater than 150 m³ s^–1 is very unlikely to occur and that the estimated discharge range is consistent with the estimated rainfall amount (233 ± 27 mm). It was observed that the backwater effect due to the obstruction (water level ~7 m) made the 1997 flood (~35‐year return period) equivalent to the 50‐year flood. This allowed the equivalent return period to be defined as the recurrence interval of an event of specified magnitude, which, where large woody debris is present, is equivalent in water depth and extent of flooded area to a more extreme event of greater magnitude. These results highlight the need to include obstruction phenomena in flood hazard analysis. Copyright © 2012 John Wiley & Sons, Ltd.     

The effects of longitudinal variations in valley geometry and wood load on flood response

We use field measurements and airborne LiDAR data to quantify the potential effects of valley geometry and large wood on channel erosional and depositional response to a large flood (estimated 150-year recurrence interval) in 2011 along a mountain stream. Topographic data along 3 km of Biscuit Brook in the Catskill Mountains, New York, USA reveal repeated downstream alternations between steep, narrow bedrock reaches and alluvial reaches that retain large wood, with wood loads as high as 1261 m³ ha⁻¹. We hypothesized that, within alluvial reaches, geomorphic response to the flood, in the form of changes in bed elevation, net volume of sediment eroded or aggraded, and grain size, correlates with wood load. We hypothesized that greater wood load corresponds to lower modelled average velocity and less channel-bed erosion during the flood, and finer median bed grain size and a lower gradation coefficient of bed sediment. The results partly support this hypothesis. Wood results in lower reach-average modelled velocity for the 2011 flood, but the magnitude of change in channel-bed elevation after the 2011 flood among alluvial and bedrock reaches does not correlate with wood load. Wood load does correlate with changes in sediment volume and bed substrate, with finer grain size and smaller sediment gradation in reaches with more wood. The proportion of wood in jams is a stronger predictor of bed grain-size characteristics than is total wood load. We also see evidence of a threshold: greater wood load correlates with channel aggradation at wood loads exceeding approximately 200 m³ ha⁻¹. In this mountain stream, abundant large wood in channel reaches with alluvial substrate creates lower velocity that results in finer bed material and, when wood load exceeds a threshold, reach scale increases in aggradation. This suggests that reintroducing small amounts of wood or one logjam for river restoration will have limited geomorphic effects. © 2020 John Wiley & Sons, Ltd.     

Rediscovering wood-laden debris flow studies: A perspective from Japan

Debris flow is one of the dominant processes distributing large wood (LW) within mountainous catchments. However, little has been reviewed on wood-laden debris flow (WLDF), presumably owing to limited reviewable works. This article, therefore, navigates the international readers through 40 years of WLDF studies, most of which have been published only in Japanese. Firstly, we reviewed the historical development of Japanese WLDF particularly focusing on the 1980s and the 1990s. A series of post-disaster fieldworks from the July 1982 Nagasaki flood to the July 1990 Kumamoto flood provided 32 catchment-scale wood budgeting data; empirical relationships among drainage area, dominant tree species, sediment yield, and wood loads associated with single debris flow disasters were illustrated. Secondly, the characteristics of WLDF were summarized based on relevant previous studies on the recruitment, transport, and deposition processes of LW during debris flows. Thirdly, we discussed the connectivity between those Japanese WLDF studies and international LW studies by relating/contrasting their research approaches and spatiotemporal scales. In contrast to global LW research trends, Japanese WLDF studies have almost exclusively regarded LW as hazardous materials (i.e., “driftwood” or “woody debris”) that need to be retained upstream of the inhabited areas. Those practice-oriented WLDF studies were concentrated on drainage areas of 10⁻² to 10⁰ km², representing 1–6 orders of magnitude smaller spatial scales than those generally covered by existing international LW studies. Strongly motivated by engineering requirements, “dynamic” interactions between debris flows and LW during floods have also been physically presented, mainly based on unique laboratory experiments involving steep flume (> 0.05) and mobile bed conditions. Finally, some future works for WLDF were briefly stated from practical and scientific perspectives. By “rediscovering” those WLDF studies domestically developed in Japanese debris flow channels since the 1980s, a more comprehensive understanding of LW dynamics in the river system may be achieved.     

Bioturbation on a south‐east Australian hillslope: estimating contributions to soil flux

The contribution of bioturbation to downslope soil transport is significant in many situations, particularly in the context of soil formation, erosion and creep. This study explored the direct flux of soil caused by Aphaenogaster ant mounding, vertebrate scraping and tree‐throw on a wildfire‐affected hillslope in south‐east Australia. This included the development of methods previously applied to Californian gopher bioturbation, and an evaluation of methods for estimating the volume of soil displaced by tree‐throw events. All three bioturbation types resulted in a net downslope flux, but any influence of hillslope angle on flux rates appeared to be overshadowed by environmental controls over the spatial extent of bioturbation. As a result, the highest flux rates occurred on the footslope and lower slope. The overall contribution of vertebrate scraping (57.0 ± 89.4 g m^?1 yr^?1) exceeded that of ant mounding (36.4 ± 66.0 g m^?1 yr^?1), although mean rates were subject to considerable uncertainty. Tree‐throw events, which individually cause major disturbance, were limited in their importance by their scarcity relative to faunalturbation. However, tree‐throw might be the dominant mechanism of biotic soil flux on the mid‐slope provided that it occurs at a frequency of at least 2–3 events ha^?1 yr^?1. Although direct biotic soil flux appears to be geomorphologically significant on this hillslope, such transport processes are probably subordinate to other impacts of bioturbation at this site such as the enhancement of infiltration following wildfire. Copyright © 2011 John Wiley & Sons, Ltd.     

Wood export prediction at the watershed scale

Wood export from a watershed is a function of peak annual discharge, but one hydrologic relationship alone does not fully explain observed variability. Consideration of physical processes that influence the amount of wood available for transport is needed. However, wood recruitment, storage, mobilization, breakage, and transport rates and processes remain difficult to quantify. A theoretical wood transport equation focused on variations in discharge was the motivation for investigation into watershed‐specific wood export rates. Herein, multiplicative coefficients categorized by water year type are developed, paired with the equation, and validated to provide a new method for prediction of wood export at the watershed scale. The coefficients are defined as representing a broad suite of watershed processes that encompass spatio‐temporally variable scales. Two complementary datasets from the 1097 km² mountainous North Yuba River, California watershed were used. Wood surveys above New Bullards Bar Reservoir yielded a wood availability estimate of 250 000–300 000 m³ along the channel network. Annual wood export into the reservoir was field‐surveyed in 2010, 2012 and 2013, and estimated in seven years via remotely sensed images over the 30 year study period of water years 1985–2014. Empirical, watershed‐scale wood export rates ranged from 0.3–5.6%. Comparison of predicted quantities using the new DVWP (discharge variations modified by watershed processes) wood export equation to observed wood export quantities resulted in an aggregate error rate of ±10%. When individual wood export quantities were compared, predicted to observed varied by 0.5–3.0 times. Total wood export of 59 000–71 000 m³ was estimated over the 30 year period, yielding a rate of 1.8 to 2.2 m³/year/km². Wood export predictive capabilities at the watershed scale may help water resource and regulatory agencies plan for wood transfers to augment downstream ecosystems. Copyright © 2017 John Wiley & Sons, Ltd.     

Seasonal variations between sampling and classical mean turbulent heat flux estimates in the eastern North Atlantic

The two commonly used statistical measures of the air-sea heat flux, the sampling and classical means, have been compared using hourly reports over a 7-year-period from a weather ship stationed in the NE Atlantic. The sampling mean is the average over all flux estimates in a given period, where individual flux estimates are determined from ship reports of meteorological variables using the well-known bulk formulae. The classical mean is the flux derived by substituting period-averaged values for each of the meteorological variables into the bulk formula (where the averaging period employed is the same as that over which the fluxes are to be determined). Monthly sampling and classical means are calculated for the latent and sensible heat fluxes. The monthly classical mean latent heat flux is found to overestimate the sampling mean by an amount which increases from 1–2 W m⁻² in summer to 7 W m⁻² in winter, on average, over the 7-year-period. In a given winter month, the excess may be as great as 15 W m⁻², which represents about 10% of the latent heat flux. For the sensible heat flux, any seasonal variation between the two means is of the order of 1 W m⁻² and is not significant compared to the interannual variation. The discrepancy between the two means for the latent heat flux is shown to arise primarily from a negative correlation between the wind speed and sea-air humidity difference, the effects of which are implicitly included in the sampling method but not in the classical. The influence of the dominant weather conditions on the sign and magnitude of this correlation are explored, and the large negative values that it takes in winter are found to depend on the typical track of the mid-latitude depressions with respect to the position sampled. In conclusion, it is suggested that sampling means should be employed where possible in future climatological studies.     

Effect of variable‐density groundwater flow on nitrate flux to coastal waters

A two‐dimensional variable‐density groundwater flow and transport model was developed to provide a conceptual understanding of past and future conditions of nitrate (NO₃) transport and estimate groundwater nitrate flux to the Gulf of Mexico. Simulation results show that contaminant discharge to the coast decreases as the extent of saltwater intrusion increases. Other natural and/or artificial surface waters such as navigation channels may serve as major sinks for contaminant loading and act to alter expected transport pathways discharging contaminants to other areas. Concentrations of NO₃ in the saturated zone were estimated to range between 30 and 160 mg?L^?1 as NO₃. Relatively high hydraulic vertical gradients and mixing likely play a significant role in the transport processes, enhancing dilution and contaminant migration to depth. Residence times of NO₃ in the deeper aquifers vary from 100 (locally) to about 300 years through the investigated aquifer system. NO₃ mass fluxes from the shallow aquifers (0 to 5.7 × 10⁴ mg?m^?2?day^?1) were primarily directed towards the navigation channel, which intersects and captures a portion of the shallow groundwater flow/discharge. Direct NO₃ discharge to the sea (i.e. Gulf of Mexico) from the shallow aquifer was very low (0 to 9.0 × 10¹ mg · m^?2?day^?1) compared with discharge from the deeper aquifer system (0 to 8.2 × 10³ mg?m^?2?day^?1). Both model‐calibrated and radiocarbon tracer‐determined contaminant flux estimates reveal similar discharge trends, validating the use of the model for density‐dependent flow conditions. The modelling approach shows promise to evaluate contaminant and nutrient loading for similar coastal regions worldwide. Copyright © 2015 John Wiley & Sons, Ltd.     

Spatial Distribution of SO2, NO2, and O3 Concentrations in an Industrial City of Turkey Using a Passive Sampling Method

Ambient concentrations of sulfur dioxide (SO₂), nitrogen dioxide (NO₂), and ozone (O₃) were measured at 51 sampling points by passive sampling technique in Kocaeli, an important industrial city in Turkey. Samples were analyzed by UV‐spectrophotometry for NO₂ and O₃ and by ion chromatography for SO₂, respectively. Concentrations of SO₂, NO₂, and O₃ were determined to investigate their spatial distribution and source characterization. The sampling campaigns revealed an average concentration of 8 µg/m³ (max. 82 µg/m³) for SO₂, and 14 µg/m³ (max. 40 µg/m³) for NO₂, in summer; while average winter concentrations were 25 µg/m³ (max. 61 µg/m³) for SO₂, and 50 µg/m³ (max. 100 µg/m³) for NO₂. The maximum ozone concentrations were determined to be 86 µg/m³ in summer and 61 µg/m³ in winter downwind of the source areas of the precursor pollutant emissions. The results showed that NO₂ and SO₂ concentrations in industrial and urban areas were two to four times higher compared with rural areas in the summer and winter. In the light of the information obtained from the spatial interpolation of the pollutant concentrations, a selection of appropriate locations for continuous monitoring was suggested according to the European Community (EU) directives.     

Seasonal controls on DOC dynamics in nested upland catchments in NE Scotland

Spatial and temporal variability of hydrological responses affecting surface water dissolved organic carbon (DOC) concentrations are important for determining upscaling patterns of DOC export within larger catchments. Annual and intra‐annual variations in DOC concentrations and fluxes were assessed over 2 years at 12 sites (3·40–1837 km²) within the River Dee basin in NE Scotland. Mean annual DOC fluxes, primarily correlated with catchment soil coverage, ranged from 3·41 to 9·48 g m^?2 yr^?1. Periods of seasonal (summer–autumn and winter–spring) DOC concentrations (production) were delineated and related to discharge. Although antecedent temperature mainly determined the timing of switchover between periods of high DOC in the summer‐autumn and low DOC in winter‐spring, inter‐annual variability of export within the same season was largely dependent on its associated water flux. DOC fluxes ranged from 1·39 to 4·80 g m^?2 season^?1 during summer–autumn and 1·43 to 4·15 g m^?2 season^?1 in winter–spring.Relationships between DOC areal fluxes and catchment scale indicated that mainstem fluxes reflect the averaging of highly heterogeneous inputs from contrasting headwater catchments, leading to convergent DOC fluxes at catchment sizes of ca 100 km². However, during summer–autumn periods, in contrast to winter–spring, longitudinal mainstem DOC fluxes continue to decrease, most likely because of increasing biological processes. This highlights the importance of considering seasonal as well as annual changes in DOC fluxes with catchment scale. This study increases our understanding of the temporal variability of DOC upscaling patterns reflecting cumulative changes across different catchment scales and aids modelling of carbon budgets at different stages of riverine systems. Copyright © 2010 John Wiley & Sons, Ltd.     

Distribution and characterization of in‐channel large wood in relation to geomorphic patterns on a low‐gradient river

A 177 river km georeferenced aerial survey of in‐channel large wood (LW) on the lower Roanoke River, NC was conducted to determine LW dynamics and distributions on an eastern USA low‐gradient large river. Results indicate a system with approximately 75% of the LW available for transport either as detached individual LW or as LW in log jams. There were approximately 55 individual LW per river km and another 59 pieces in log jams per river km. Individual LW is a product of bank erosion (73% is produced through erosion) and is isolated on the mid and upper banks at low flow. This LW does not appear to be important for either aquatic habitat or as a human risk. Log jams rest near or at water level making them a factor in bank complexity in an otherwise homogenous fine‐grained channel. A segmentation test was performed using LW frequency by river km to detect breaks in longitudinal distribution and to define homogeneous reaches of LW frequency. Homogeneous reaches were then analyzed to determine their relationship to bank height, channel width/depth, sinuosity, and gradient. Results show that log jams are a product of LW transport and occur more frequently in areas with high snag concentrations, low to intermediate bank heights, high sinuosity, high local LW recruitment rates, and narrow channel widths. The largest concentration of log jams (21.5 log jams/km) occurs in an actively eroding reach. Log jam concentrations downstream of this reach are lower due to a loss of river competency as the channel reaches sea level and the concurrent development of unvegetated mudflats separating the active channel from the floodplain forest. Substantial LW transport occurs on this low‐gradient, dam‐regulated large river; this study, paired with future research on transport mechanisms should provide resource managers and policymakers with options to better manage aquatic habitat while mitigating possible negative impacts to human interests. Copyright © 2011 John Wiley & Sons, Ltd.     

How Does Subsurface Characterization Affect Simulations of Hyporheic Exchange?

We investigated the role of increasingly well‐constrained geologic structures in the subsurface (i.e., subsurface architecture) in predicting streambed flux and hyporheic residence time distribution (RTD) for a headwater stream. Five subsurface realizations with increasingly resolved lithological boundaries were simulated in which model geometries were based on increasing information about flow and transport using soil and geologic maps, surface observations, probing to depth to refusal, seismic refraction, electrical resistivity (ER) imaging of subsurface architecture, and time‐lapse ER imaging during a solute tracer study. Particle tracking was used to generate RTDs for each model run. We demonstrate how improved characterization of complex lithological boundaries and calibration of porosity and hydraulic conductivity affect model prediction of hyporheic flow and transport. Models using hydraulic conductivity calibrated using transient ER data yield estimates of streambed flux that are three orders of magnitude larger than uncalibrated models using estimated values for hydraulic conductivity based on values published for nearby hillslopes (10^?4 vs. 10^?7 m²/s, respectively). Median residence times for uncalibrated and calibrated models are 10³ and 10⁰ h, respectively. Increasingly well‐resolved subsurface architectures yield wider hyporheic RTDs, indicative of more complex hyporheic flowpath networks and potentially important to biogeochemical cycling. The use of ER imaging to monitor solute tracers informs subsurface structure not apparent from other techniques, and helps to define transport properties of the subsurface (i.e., hydraulic conductivity). Results of this study demonstrate the value of geophysical measurements to more realistically simulate flow and transport along hyporheic flowpaths.