Surficial Layer Research Articles

Factors affecting methylmercury distribution in surficial, acidic, base-metal mine tailings

The most toxic form of Hg commonly of concern in the environment is methylmercury (MeHg), as it accumulates in living tissues and bioconcentrates in food webs. Sulfide-rich metal ores are often enriched in Hg, but little is known regarding the potential for Hg methylation in acidic tailings produced from these ores. This study examined acidic tailings from four mines in northern Ontario, Canada, to determine whether they could be an important source of MeHg to downstream environments. Where sulfate reducing bacteria (SRB) were abundant and active in pH-circumneutral, unoxidized layers (Potter mine), negligible MeHg was detected. By contrast, a zone of active sulfate reduction found in the acidic, oxidizing, surficial layers of tailings from the Kidd Metsite contained the highest concentrations of MeHg in bulk tailings (12.1 nmol kg − 1 dry wt. of sediment) and porewaters (88 pM) measured in this study. Cell count estimates of SRB by the “most-probable-number” (MPN) method were low in these surficial tailings, suggesting that sulfate reducers from this environment were acidophilic and did not thrive under the pH-neutral conditions of the MPN incubations. A later study of bacterial DNA from these tailings produced evidence of a novel Deltaproteobacterium which has only previously been detected in acid mine drainage environments. Further research will be necessary to determine whether this Deltaproteobacterium is a sulfate reducer and/or an efficient Hg methylator. Surface water concentrations of MeHg did not exceed Canadian water quality guidelines at any of the sites sampled, but one site (Broulan) featured total Hg (Hg T) concentrations of 838 pM in filtered samples, far in excess of recommended levels. Trends in surface water MeHg and Hg T reflected corresponding values in porewaters from the same sites, indicating that concentrations of these substances in tailings influence surface water concentrations.

Formation of De Geer Moraines Deposited Subglacially, Central Québec

This paper presents a model for the genesis of De Geer moraines in the Chapais and Radisson areas, Québec. The model is mainly based on faciès and deformation structure analysis. Three facies associations have been identified: (1) sorted sediments that form foreset laminations dipping downglacier. Till lenses or glacial diamictons are found within the sorted sediments or form a surficial layer on the proximal side of the sections; (2) a non-fissile and poorly compacted till overlies and deforms sorted sediments. Laminae of finely sorted sediments may be incorporated in the till; (3) a fissile and compact till commonly lies on the basal till sheet. All three facies associations feature deformation structures (faults, folds, load and drag structures) which indicate an upglacier origin. The model proposed is an emplacement of De Geer moraines in bottom crevasses by an active glacier. In areas where meltwaters were channelized, sediments accumulated in the crevasses as foreset laminations. Till filled the crevasses in areas remote from meltwater flow. Glacial activity remobilized the basal till locally and pushed it toward bottom crevasses located downglacier, or overturned large layers of till. Finally, in areas located even further laterally, meltwaters had almost no effect and the moraines were formed by plastering of till in the crevasses. The three faciès associations are part of a continuum beginning with the moraines composed of sorted sediments and grading laterally into the moraines formed of fissile and compact till. This continuum is described for the first time.

Solving the mystery of booming sand dunes

Desert booming can be heard after a natural slumping event or during a sand avalanche generated by humans sliding down the slip face of a large dune. The sound is remarkable because it is composed of one dominant audible frequency (70 to 105 Hz) plus several higher harmonics. This study challenges earlier reports that the dunes' frequency is a function of average grain size by demonstrating through extensive field measurements that the booming frequency results from a natural waveguide associated with the dune. The booming frequency is fixed by the depth of the surficial layer of dry loose sand that is sandwiched between two regions of higher compressional body wave velocity. This letter presents measurements of the booming frequencies, compressional wave velocities, depth of surficial layer, along with an analytical prediction of the frequency based on constructive interference of propagating waves generated by avalanching along the dune surface.

Nature and rates of fine-sedimentation on a mid-shelf: “La Grande Vasière” (Bay of Biscay, France)

The study area, “La Grande Vasière” (LGV), stretches out on the French Atlantic continental shelf (at ca. 100 m water depth), along 250 km from the Glénan Islands at the north to the southwest of Rochebonne at the south. Box-cores were sampled in this mid-shelf area during four cruises in June 1995, and in April, June and September 2002. They were investigated using sedimentological approaches (X-radiographs and grain-size analyses) and radionuclide studies ( 210Pb geochronology and excess 234Th). The main results are: (1) the surficial sediments are generally organized into a decimetre-scale fining up sequence which can be the result of extreme storms; (2) an upper mixing layer of 7–20 cm reflects an important biological benthic activity and/or the impact of fishing (i.e. trawlers); (3) a thin (i.e. a few mm) surficial mud-rich layer is the result of the present-day sedimentation; (4) an apparent annual sedimentation rate of 1–3 mm is recorded in several loci of the study area. Some seasonal variations appear, corresponding to the deposition of fine material from April to September, and to the reworking and the re-suspension during the winter. This fine material is the result of the decantation of estuarine plumes, mainly the Loire and the Vilaine rivers, over the study area. LGV lies (1) under the influence of a winter-to-spring thermo-haline wedge that acts as a filter for the transfer of fine river-borne material to the slope and the open sea, and (2) below water depths where the mean swell action permits sedimentation, mainly in summer. From the point of view of the nature of its sediments, LGV is not a mud-belt, but a heterolithic and patchy sandy area that is submitted to increasing silting with environmental changes, on a seasonal-time scale.

A Preliminary Study on Electrical Structure and Dynamics of the Ultra‐High Pressure Metamorphic Belt Beneath the Dabie Mountains

AbstractMagnetotelluric data along a profile in the East Dabie Mountains was collected, which is across the ultra‐high pressure metamorphic belt, in NNE direction. By data‐analysis and interpretation, the two‐dimensional electrical structure of crust‐upper mantle of Dabie orogen is obtained, indicating that the North Huaiyang Tectonic Belt and Dabie Block are different tectonic units. They are separated by the Xiaotian‐Mozitan fault, which is dipping north and probably decoupled in the mid‐lower crust. Four electrical layers can be identified from surface to depth, which are the surficial weathering layer, the high resistivity layer in mid‐upper crust, the relatively high conductive layer in the crust and the mantle layer. In the Dabie Block, the mid‐upper crust is mainly of high resistivity, and corresponding with the distribution area of ultra‐high pressure metamorphic rock, of which the thickest portion is below Yuexi‐Yingshan. In the Dabie Block, there maybe exist channels of granitic magma activity of the Yanshan Period (205~66Ma), which make further uplift of the ultra‐high pressure metamorphic rocks and affect the distribution of inner‐crust high conductive layers and cause great difference in depth of the high conductive layer.

A Transient Model of Vadose Zone Reaction Rates Using Oxygen Isotopes and Carbon Dioxide

The importance of identifying and quantifying subsurface geochemical reaction rates and processes by monitoring and modeling CO2 and O2 concentrations is well established. These parameters, however, are typically studied independently under presumed steady‐state conditions. Here we present models of seasonally variable vadose zone CO2 and O2 concentrations that use δ18O of O2 as a constraint to create a dynamic link between these three parameters under transient conditions. The gas transport modeling was used to quantify the controls of biogeochemical processes and parameters (i.e., temperature and moisture content) on vadose zone distributions of CO2 and O2 gas concentrations. The investigation was conducted on a 3‐m‐thick, unvegetated, fine‐sand vadose zone located in northern Alberta, Canada (56°40′N, 111°07′W). Using the modeled molar ratio of surface fluxes for O2 and CO2, the change in reaction rate for a temperature change of 10°C (Q10), moisture content at maximum reaction rates, and biogeochemical discrimination against consumption of 18O16O (αk), we determined that organic C oxidation by microbial respiration was the predominant mechanism consuming O2 and producing CO2 The mean αk was determined to be 0.973, suggesting that subsurface respiration was via the alternative oxidase pathway, which may be common in cold climates. Modeling revealed that the moisture content of a moist, surficial clayey sand layer (0.1–0.3 m thick) had a dramatic effect on pore‐gas CO2 and O2 concentrations and on δ18OO2 The vadose zone in this study was at an unvegetated site to simplify the model application; however, it can be modified to include root respiration and applied to natural vadose zones to help quantify the role of subsurface respiration in global O2 and C budgets.

Sedimentary Development of Coral Bay, St. John, USVI: A Shift From Natural to Anthropogenic Influences

Analyses of sediment cores and surface samples collected in Coral Bay, St. John, USVI, reveal four sedimentary facies. The bottom three reflect the natural transgressive evolution of the bay during the Holocene sea-level rise. The surficial facies represents a dramatic increase in terrigenous sediment input since the 1950's. This surficial layer is defined by a decrease in grain size, increase in organic content, increase in terrigenous constituents, and subtle decrease in calcium carbonate content compared to underlying sediments. Based upon 210Pb and 14C dating, accumulation rates have increased by roughly one order-of--magnitude since the 1950's as a result of this increase in terrigenous sediment input. The surficial sediment layer likely represents an anthropogenic signal reflecting the dramatic increase in island development over the past few decades. The surficial “impacted” layer is most pronounced (i.e., exhibits the greatest deviation from underlying sediments) adjacent to the most heavily developed areas, and in protected, low energy regions. It becomes less pronounced in the more open and seaward portions of the bay. This pattern suggests proximity to input and energy level are the dominant controls governing where terrigenous sediments ultimately accumulate. Comparisons with anthropogenically-impacted estuaries along the U.S. Atlantic and Gulf coasts show that, although there are substantial differences in scale and watershed character, all have experienced recent dramatic increases in sediment accumulation. Unlike Coral Bay, however, there is no anthropogenic signal in sediment texture and composition. This may be a reflection of St. John's high-relief terrain, high erodibility of rocks/soils, and intense weathering associated with tropical volcanic island settings.

The effects of layering on reflection coefficient and transmission measurements from a sand/water interface at the Sediment Acoustics Experiment 2004 (SAX04)

During the Sediment Acoustics Experiment 2004 (SAX04), transmission measurements from 4.5 to 50 kHz were taken on an eight-transducer array buried at an angle of 15 deg using a source mounted on a remotely operated vehicle (ROV). Simultaneously, the reflection coefficient was measured using a three-receiver vertical line array (VLA). Reflection coefficient measurements at angles from 10 to 70 deg were obtained. Environmental characterization of the area has revealed layering effects such as a surficial mud layer, mud inclusions, and depth-dependent sediment properties such as porosity. The consequence of this layering on the variability of the amplitude of reflection coefficient measurements and the time of arrival of transmission measurements will be investigated. [Work supported by ONR, Ocean Acoustics.]

Lithological mapping of the unsaturated zone of a porous media aquifer to delineate hydrogeological characteristic areas: Application to Israel's coastal aquifer

With water quality steadily decreasing, decision-making with regard to water supply must improve aquifer management models, which are based upon various assumptions. Amongst these are assumptions concerning subsurface aquifer lithology. The objective of this study is to present a means of improving information and assumptions, as well as providing guidelines to characterise the unsaturated zone media. This media integrates soils and the parental material of soils, which results in a more realistic picture of the surficial layers of the aquifer. This is a key factor for understanding the behavior of the upper border of coastal aquifers and simulation of their hydrogeological models. Developing a digital GIS unsaturated zone map enables 3-dimensional depiction by illustrating the varying permeability characteristics of the stratigraphic layers. The resultant map conveys information about areas having low to high permeability and areas in which perched aquifers might be found. This can consequently contribute to better understanding of the recharge process, and of the reasons for deterioration of groundwater quality in the aquifer. In the case of aquifers prone to stress from significant anthropogenic land-use, the map highlights areas whose vadose zone has the ability to convey liquids and pollutants to the aquifer below. The focus of this study is Israel 's Coastal aquifer, a resource of critical significance to the country's water supply, which underlies the most populated areas of the country. This aquifer has been chosen because of its variegated lithology and water quality, the quantities of water being pumped from it, the large amount of existing data, and the potential of water which can be readily stored in it. This aquifer would appear to be an appropriate example of coastal aquifers around the world, to demonstrate the utility of such unsaturated zone mapping. This mapping can prove a tool for developing recommendations with regard to irrigation, land-use planning, and aquifer management. Key words: GIS mapping, Unsaturated zone/vadose zone, lithology, confined aquifer, phreatic aquifer, Coastal aquifer,

Earthquake ground motion in Mexico City: An analysis of data recorded at Roma array

We analysed in detail three earthquakes recorded in a small-aperture accelerometric array in Mexico City, using the correlation of the records as a function of time along the accelerogram and frequency. Ground response is strongly conditioned by the fundamental period of the soft soils at the site of the array ( T 0). Energy at periods longer than 2 T 0 is guided by the crustal structure (with a thickness of 45 km). The wave field at periods between T 0 and 2 T 0 also consists of surface waves but guided by the upper 2–3 km of volcanic sediments in central Mexico. For periods smaller than T 0, ground motion is uncorrelated among the stations. Our results indicate that seismic response of Mexico City, including its very long duration, results from deeply guided surface waves (between 2 and 45 km depth) interacting with the very local response of the soft surficial clay layer.

Growth of c-GaN films on the nitridated β-Ga2O3 substrates using RF-MBE

Cubic GaN is successfully grown on β-Ga2O3 by molecular beam epitaxy for the first time. Prior nitridation of the (100) β-Ga2O3 single-crystal substrate by exposure to electron cyclotron resonance nitrogen plasma causes the formation of a surficial (001) c-GaN layer, upon which homo-epitaxial growth of c-GaN can be achieved by radio-frequency molecular beam epitaxy. The epitaxial relationship is confirmed by electron microscopy to be (001) c-GaN // (100) β-Ga2O3, [110] c-GaN // [010] β-Ga2O3, and [1-10] c-GaN // [001] β-Ga2O3.

Natural and anthropogenic geochemical signatures of floodplain and deltaic sedimentary strata, Sacramento–San Joaquin Delta, California, USA

The geochemical history of an upper deltaic plain pending tidal wetland restoration was reconstructed to assess remobilization of redox-sensitive constituents in sediment, identify depositional processes promoting geochemical retention, and determine the extent of contamination with Hg, As, Pb, Cu, and Zn. Three 12–14-m sediment cores were analyzed for bulk sediment geochemistry using ICP-AES. Rather than showing similar stratigraphic and geochemical down-core trends, cores had a unique record indicative of strong spatial gradients in deposition processes. Each strata type (e.g. basal clay, sand channel, distal floodplain, and agriculturally impacted surficial horizon) had a unique geochemical “fingerprint”. The agriculturally impacted surficial layer showed high [Hg], [As], and [Pb]. The significance is that a restored upper delta will have a complex geomorphology defying conventional criteria of “success” in a restoration framework. Also, there is a significant risk of generating toxic, bio-available CH 3Hg + that would be hazardous to fish.

Unusual long‐period Rayleigh wave radiation from a vertical dip‐slip source: The 7 May 2001 North Sea earthquake

Crustal structures with a thick, surficial sediment layer with low seismic wave speeds produce a reversal in the polarity of the shear stress eigenfunctions of long‐period Rayleigh waves at shallow depth. Consequently, seismic disturbances with a strong vertical dip‐slip component that are within or just below the sediment layer should generate Rayleigh waves that show a polarity reversal when compared with Rayleigh waves from the same source in a more typical crustal structure. Here the first observation of this unusual behavior is presented by modeling surface waves from the 7 May 2001 North Sea earthquake. A previous study finds a focal mechanism close to vertical dip slip for this earthquake, and suggests that the source is within the 6 km thick sediment layer found in this region. An appropriate structural model is used to generate synthetic seismograms and estimate a double‐couple focal mechanism for the source. The orientation of the fault plane determined here is similar to that found by the previous study; however, the slip direction is opposite, demonstrating that the use of an incorrect structural model has a profound effect on focal mechanism determination for this type of seismic source.

Characteristics of Surface Waves in Media with Significant Vertical Variations in Elasto-Dynamic Properties

In media with strong vertical variations in elasto-dynamic properties, the characteristics of surface waves may deviate significantly from their typical appearance in media with small contrasts. Different numerical examples suggest that ignoring this behavior may lead to poor results in surface wave analysis. The cases analysed are: (1) Neighboring surface wave modes which exchange their major characteristics at osculation points of their dispersion curves; (2) Quasi-channel waves propagating inside a buried low velocity channel; (3) Surface waves in the presence of a low-velocity layer at the very surface; and (4) Rayleigh surface waves in the presence of a very high velocity contrast allowing normal quasi-compressional pseudo-modes. Amplitude-depth functions are used to analyze the physical cause of the unusual characteristics. One important result is a vanishing vertical displacement of the fundamental mode and dominance of the first higher Rayleigh mode at low frequency for cases with a large elastic contrast at shallow depth (increase in Vs approaching 300% at [Formula: see text]). If the displacement is treated as the fundamental mode, a systematic overestimate of deeper shear wave velocity will arise in the inversion, since higher modes have higher phase velocity. A second result is from a profile with a very thin, surficial low-velocity layer, where higher modes dominating the response might prevent fundamental mode detection and inversion. Finally, if shear wave velocity of the half-space exceeds the compressional wave velocity of an overlying layer, quasi-compressional waves (or guided P-waves) come into the velocity range of normal modes. This may lead to surface wave mode-misidentification.

Prehistoric mega-tsunami in the eastern Mediterranean and its sedimentary response

The volcanic island of Santorini that belongs to the trench-arc-backarc Aegean system of the eastern Mediterranean underwent a catastrophic eruption in the Bronze age (circa 3500 y BP), with caldera collapse and creation of a tsunami wave that was funnelled westward. The sedimentary response to this exceptional event in the deep sea was the deposition of resediments called Homogenites. The data set available after almost thirty years of active research consists of 60 sediment cores, including several giant piston cores up to 30 meters long, raised from water depths ranging from 4100 to 2500 m in discrete parts of the Ionian Sea. Two types of Homogenite are recognized. Type A Homogenite consists of pelagic turbidites typically recorded in the Calabrian Ridge and in the western Mediterranean Ridge accretionary prisms, characterized by the «cobblestone topography», only in lows or basinal settings. Their stratigraphic position consistently above the Holocene sapropel S-1 and the depositional base are interpreted as the result of liquefaction of the unconsolidated pelagic sediments draping the nearby slopes caused by the tsunami waves, followed by downslope movement and settling. Type B Homogenite is a megaturbidite of African provenance that expanded throughout the Messina and Sirte abyssal plains originating an up to 24 m thick surficial acoustically-transparent layer calibrated by coring. Type B Homogenite has a coarse and thick sandy base consisting of bioclasts deriving from the continental shelf of North Africa and is interpreted as triggered by the tsunami wave reaching the Sirte Gulf. The Dec. 26, 2004 megatsunami that hit the coastlines of SE Asia provides a real world example of how sediment dispersal can be triggered by a series of gigantic waves. Megaturbidites similar in thickness to Type B Homogenite have been recorded in all the abyssal plains of the Mediterranean, both west and east of the Ionian basin, but their age is older (late Pleistocene) and their emplacement occurred during low sea-level stands corresponding to the last glaciation. The occurrence of a Holocene megabed, postdating the Climatic Optimum, is a paradox in a paleoclimatic scenario. An exceptional event, as the megatsunami originated by the collapse of the Santorini caldera is required.

Transitional carbonate-terrigenous shelf sub-environments inferred from textural characteristics of surficial sediments in the Southern Gulf of Mexico

The present study describes the spatial and temporal patterns of surficial sediments within the transition zone of the terrigenous and carbonate (CO) provinces in the Southern Gulf of Mexico after flood events during the rainy season of 1999. The sampling design consisted of two across-shelf (A, B) and two along-shelf (C, D) transects that followed depth and sediment gradients. Twelve stations, approximately 7–8 km apart, were allocated to each transect. PVC cores of 10 cm in diameter were taken to a depth of 5 cm for organic matter (OM), CO content and grain-size analysis after recording relevant information such as corer penetration, characteristics of the surficial layer of sediment and depth of the soft “liquefied” layer if present. OM was determined by combustion and CO content was analysed by acid digestion and titration. Size-frequency distributions (SFDs) were measured using a Malvern Mastersizer X laser particle sizer into 15 whole phi size intervals. A multivariate approach was chosen to look in detail at the derived sediment SFDs and pick up depth-related sub-environments that would help to construct a conceptual model of sediment movement. Additionally, OM and CO content were used to identify the relative influences of river input and CO sediment, together with the bulk sediment surface area/OM relationship to strengthen the interpretation of sediment sources. Three sub-environments were qualitatively identified within the Southern Gulf of Mexico and validated using a multivariate approach, which reflect the across-shelf topography and depth gradient. The spatial pattern was temporally maintained in relation to sediment size distribution and CO content. OM and CO content showed an inverse association in response to the effect of fine sediment of terrigenous origin carrying adsorbed OM. In contrast, CO content seems to be related to coarser material with less surface area and organic content. A number of differences were found between the present and previous studies carried out on the transitional area of the southern Gulf in relation to sediment size and CO content. It is considered that these differences are mainly the consequence of local hydrology, which makes transitional environments highly variable. As in other CO–siliclastic transitions, climate and hydrological setting are the main controls of the dispersion and deposition of fine materials on the Southern Gulf of Mexico shelf.

Temporal trends in the sources of PCDD/Fs to and around the Venice Lagoon

Two salt marsh cores were collected from the Venice Lagoon, Italy, and analysed for PCDD/Fs. The samples were undisturbed and had an approximately constant accumulation rate. Radiochemical chronologies were established for the different core sections. The PCDD/F pattern in the surficial layers was very similar to that of atmospheric deposition measured in the same area. However, the pattern changed with increasing depth and was very different in the deeper sections, where the highest PCDD/F concentrations were measured. This layer was dated around the 1950s. Deeper layers have a profile similar to the surficial one. Undisturbed salt marsh cores appear to be a reliable tool for the reconstruction of temporal trends in the atmospheric deposition of persistent organic pollutants. It is proposed that the trends in the core reflect atmospheric deposition that probably results from the sum of two different contributions: emissions of the industrial district of Porto Marghera on the edge of the lagoon and the regional background.

Assessment of soil particle redistribution on two contrasting cultivated hillslopes

The particle size distributions of surface soils from two cultivated silty fields (Moorfield and Railway South) in Herefordshire, UK, were assessed by sampling on 20-m grids across the fields. Moorfield (8 ha) had a uniform landscape sloping mainly in a North–South direction while Railway South (12 ha) had complex undulating landscape characteristics. Samples from 3 surficial layers were also taken at 3 landscape positions at Moorfield to investigate recent (within-season) soil particle redistribution. Size fractions were determined using chemical dispersion, wet sieving (to separate the sand fractions) and laser granulometry (for the finer fractions). The distribution of various fractions and the relationships between elevation and the various fractions suggest preferential detachment and movement of coarse to very coarse silt fractions (16–63 μm), which were found mostly at downslope or depositional areas. Upper slope samples had higher clay to fine silt (< 16 μm) contents than bottom slope samples. The upslope–downslope patterns of size fractions, particularly on uniformly sloping areas, of the 2 fields were similar and their deposited sediments were dominated by coarse silt fractions. Samples from 3 landscape positions at Moorfield became coarser from the less eroded summit, through the eroding side-slope to the bottom-slope depositional area. Within each of these landscape positions the top 0–2.5 cm layers were more enriched in coarse silt fractions than the bottom layers. The spatial patterns of soil particle size distributions in the 2 fields may be a result of sediment detachment and deposition caused by water erosion and tillage operations.

Joint Interpretation of Geophysical Data for Archaeology: A Case Study

Interpret-joints within geophysical data recorded in a complex area where ruins do not outcrop and only earthenware remains within the surficial layer are present. The study area, located in central Italy, consists of Roman, medieval and modern ruins that are included in reworked sediments. The geology is formed by inhomogeneous alluvial sediments (sand and gravel) several meters thick with diamagnetic character. To reduce the ambiguity in the subsurface reconstruction, a joint interpretation of georadar, magnetic and electrical tomography data was performed. The georadar was chosen to reconstruct detailed subsurface features, the electrical tomography to distinguish resistive bodies (stones, voids, etc.) from conductive (cavities filled by clay) and, because of the diamagnetic character of in situ sediments, the magnetic method was chosen to detect the earthenware ruins. The geophysical data were controlled by excavation, which detected silos of 1 m in diameter and a concrete layer at a few centimeters from the topographic surface. Time slices in the georadar data allowed us to detect the silos and to define the lateral edge of the concrete layer. Silos were also indirectly detected by the magnetic data because of the earthenware present in the filling sediments. Electrical tomography detected the concrete layer and an ancient anthropogenic surface of few centimeter depths. The study demonstrates that, because the geophysical methods are based on different physical characteristics, they can have different resolution and therefore detect different bodies.

Heterogeneity in soil nitrogen within first-order forested catchments at the Turkey Lakes Watershed

Topographic positional regulation of nitrogen (N) dynamics in soil within Canadian Shield headwaters, located in calibrated catchments containing mature, tolerant hardwood forest, was examined to determine how N pools, mineralization, nitrification, and leaching in soil relate to N export in drainage waters. A uniformly high net N mineralization and nitrification potential for surficial soil layers rich in organic N was demonstrated for ridge, upper-middle slope, and lower slope – footslope topographic positions. Results from plot-scale studies revealed that NO3– concentrations in soil water from well-drained soils were very highly variable throughout the catchments, ranging from 25 to 175 µmol·L–1, with a median of 80 µmol·L–1. The isotopic effects of denitrification were not detected in soil water collected from lower slope – footslopes, and in situ rates of N2O production from soils on lower slope – footslopes and valley bottoms were very low and highly variable. Higher N exports from soils than from streams were not explained by differences in soil water N with topographic position or denitrification in lower landscape topographic positions. Using an average soil water N value, based on the replicated plots within catchments, did not reduce the calculated substantial differences in N export between soils and streams.