Factors controlling nitrogen release from two forested catchments with contrasting hydrochemical responses

Quantifying biogeochemical cycles of nitrogen (N) and the associated fluxes to surface waters remains challenging, given the need to deal with spatial and temporal variability and to characterize complex and heterogeneous landscapes. We focused our study on catchments S14 and S15 located in the Adirondack Mountains of New York, USA, which have similar topographic and hydrologic characteristics but contrasting stream nitrate ( ) concentrations. We characterized the mechanisms by which reaches the streams during hydrological events in these catchments, aiming to reconcile our field data with our conceptual model of factors that regulate nutrient exports from forested catchments. Combined hydrometric, chemical and isotopic (δ ) data showed that the relative contributions of both soil and ground water sources were similar between the two catchments. Temporal patterns of stream chemistry were markedly different between S14 and S15, however, because the water sources in the two catchments have different solute concentrations. During late summer/fall, the largest source of in S14 was till groundwater, whereas shallow soil was the largest source in S15. concentrations in surface water decreased in S14, whereas they increased in S15 because an increasing proportion of stream flow was derived from shallow soil sources. During snowmelt, the largest sources of were in the near‐surface soil in both catchments. Concentrations of increased as stream discharge increased and usually peaked before peak discharge, when shallow soil water sources made the largest contribution to stream discharge. The timing of peaks in stream concentrations was affected by antecedent moisture conditions. By elucidating the factors that affect sources and transport of N, including differences in the soil nutrient cycling and hydrological characteristics of S14 and S15, this study contributes to the overall conceptualization of release from temperate forested catchments. Copyright © 2007 John Wiley & Sons, Ltd.     

The role of the atmosphere in coastal ecosystem decline—future research directions

Current assessments of the role of atmospheric deposition in the declining health of aquatic ecosystems indicate that the atmosphere could account for as much as 30% to 40% of total external nitrogen loading to some coastal waters. All such assessments are uncertain and need to be refined. To focus attention on the problem as it affect eastern North American coastal waters, a series of interdisciplinary workshops has been conducted, bringing together scientists and regulators. The series started with a meeting at Mt. Washington, Maryland in 1994, with subsequent meetings at Warrenton, Virginia in 1995, and Raleigh, North Carolina in 1997. Although the workshops considered all nitrogen species, toxic chemicals, trace metals, precipitation chemistry, airborne aerosols, and supporting meteorological investigation, most of the discussion centered around the issue of nitrogen-species deposition. It was concluded that work is urgently needed to establish integrated monitoring stations to provide high quality deposition and watershed retention data within the catchment area to take spatial and temporal variability into account in atmospheric deposition models, to improve biogeochemical watershed models, especially from the perspective of biological utilization and cycling of deposited materials, to refine emissions inventories and projections on which scenario investigations are based, to enhance all ongoing data collection efforts, especially those related to specific process studies, and to improve spatial resolution by increasing the number of deposition measurement sites. An overall conclusion was that there must be a strong effort to include considerations of air pollution and atmospheric deposition in the water quality regulatory process. It was repeatedly emphasized that any new efforts should build on existing programs rather than risk new starts that compete with ongoing and already productive work.     

Hyperscale terrain modelling of braided rivers: fusing mobile terrestrial laser scanning and optical bathymetric mapping

Quantifying the morphology of braided rivers is a key task for understanding braided river behaviour. In the last decade, developments in geomatics technologies and associated data processing methods have transformed the production of precise, reach‐scale topographic datasets. Nevertheless, generating accurate Digital Elevation Models (DEMs) remains a demanding task, particularly in fluvial systems. This paper identifies a threefold set of challenges associated with surveying these dynamic landforms: complex relief, inundated shallow channels and high rates of sediment transport, and terms these challenges the ‘morphological’, ‘wetted channel’ and ‘mobility’ problems, respectively. In an attempt to confront these issues directly, this paper presents a novel survey methodology that combines mobile terrestrial laser scanning and non‐metric aerial photography with data reduction and surface modelling techniques to render DEMs from the resulting very high resolution datasets. The approach is used to generate and model a precise, dense topographic dataset for a 2.5 km reach of the braided Rees River, New Zealand. Data were acquired rapidly between high flow events and incorporate over 5 x 10⁹ raw survey observations with point densities of 1600 pts m^‐2 on exposed bar and channel surfaces. A detailed error analysis of the resulting sub‐metre resolution is described to quantify DEM quality across the entire surface model. This reveals unparalleled low vertical errors for such a large and complex surface model; between 0.03 and 0.12 m in exposed and inundated areas of the model, respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

Monica—A computer algorithm for solving boundary value problems using the double-hardening constitutive law Monot: II. Algorithm validation

The computer algorithm MONICA¹, which incorporates the double-hardening constitutive law Monot², has been tested on a large number of numerical examples. This paper summarizes the validation process, which has included consideration of both single element stress paths and multi-element boundary value problems. These results show MONICA to be effective for analysing practical problems using a soil model of the double-hardening type. They also demonstrate the ability of Monot to model a wide range of material responses. Problems involving pore pressure changes are identified as an area in which this form of analysis is of particular use^3,4.     

Chemistry of acid production in black coal mine washery wastes

Column leaching tests on black coal mine washery wastes were performed, to determine the chemistry of acid generation. Coal mine coarse rejects and tailings were subjected to wet and dry cycle dissolution and subsequently column leached. The rates of iron sulphide oxidation and carbonate mineral dissolution were determined based on the drainage chemistry. The kinetic data from column leach experiments are used to predict the time required to deplete the acid producing and acid consuming minerals in the mine wastes. The acid production in the mine rejects was found to depend upon iron chemistry, carbonate chemistry, diffusion of oxygen, and permeability. The chemistry of the drainage from two different coal mines is compared.     

Reconstruction of Late Paleozoic heat flows and burial histories at the Rhenohercynian-Subvariscan boundary, Germany

The thermal and burial history of the Herzkamp syncline, located in the transition zone between the Variscan Rhenish Massif and the Ruhr foreland basin (western Germany), was reconstructed using PDI/PC-1D-basin modelling software (IES). The models were calibrated with new vitrinite reflectance data measured on Palaeozoic outcrop samples. High sample density and quality of the calibration data allowed a 3D reconstruction of the heat flow as well as of burial and erosion history. Vitrinite reflectance values range from 0.8 to 4.9%R_r and generally increase with increasing stratigraphic age. The coalification pattern confirms pre-tectonic maturation, especially in the western part of the study area. A "low-coalification zone" showing stagnating/decreasing coalification with increasing stratigraphic age exists, however, northeast of the Ennepe thrust, indicating synorogenic coalification. This anomaly is explained by early thrusting in the northern Rhenish Massif resulting in restricted burial/early uplift and thus lower thermal maturity. One result of numerical modelling is that palaeo-heat flows during maximum burial (Westphalian or post-Westphalian) decreased southwards from approximately 65 to less than 50 mW/m². Maximum burial depths for the base and top of the Namurian also decrease southwards from 7000 to 3600 m and 4600 to 1800 m, respectively, resulting in southwards-decreasing coalification of the respective stratigraphic horizon. Eroded overburden increases southwards (3100-5700 m), with the exception of the low-coalification zone, which is characterised by lower amounts of eroded overburden (1300-2900 m) and an earlier onset of erosion, i.e. in the Westphalian B rather than Westphalian D or post-Westphalian.     

A phase-sensitive acoustic sounder for the detection of atmospheric temperature

An acoustic interferometer was built and operated during nocturnal temperature inversions to detect atmospheric temperature differences between the surface air and that at 50 m above the ground. The system departs from earlier succesful designs by using a time-multiplexed two-sided approach to attempt to correct for phase fluctuations caused by wind. Preliminary results from the apparatus indicate that the signals lack the necessary phase stability to permit calculation of temperature, even when subjected to averaging over 20-min intervals. It is concluded that simultaneous insonification of the scattering volume is a requisite for stable phase measurements in such a system.     

Nematode/copepod ratios for monitoring pollution: A rebuttal

The nematode/copepod ratio recently proposed by Raffaelli & Mason is not a valid tool for assessing pollution. We found many discrepancies in the original paper and felt obliged to point them out. There was no quantitative assessment of contagion; and seasonal variation was great, two factors which could alter the ratio. We partitioned the original data into Raffaelli & Mason's and others and found that the ratio was not significantly correlated with grainsize when using the literature values. There are several exceptions to their statement that nematodes dominate in organically enriched sites and that there are not copepods in deep water samples. We do not believe that reducing the very complex meiofaunal community structure to a single ratio is appropriate and are concerned that those not familiar with the meiofaunal literature will try to use this ratio method as a panacea for assessing pollution before its validity is fully known.     

Strong correlation between summer temperature and pollen accumulation rates for Pinus sylvestris,Picea abies and Betula spp. in a high‐resolution record from northern Sweden

Highly resolved pollen spectra analysed from a 47 cm peat monolith recovered from a mire in northern Sweden exhibit climatic sensitivity in the pollen accumulation rates (PAR) of boreal treeline species. Robust temporal control, afforded through multiple AMS radiocarbon dating of the post‐atomic‐bomb‐test period (AD 1961–2002), provides a unique opportunity to compare pollen accumulation rates with the instrumental meteorological record. Strong correlations are observed between summer temperature and PAR for Pinus sylvestris, Picea abies and Betula spp. (excluding B. nana). Despite well constrained, contiguous (‘annual’) sampling, the temporal resolution of the pollen signal preserved within each sample appears to be degraded to ca. 3–5 year resolution. This is likely to reflect processes occurring during peat accumulation and pollen deposition, as well as dating uncertainties and the effects of subsampling. These findings identify limitations to the maximum resolution that may realistically be recovered from the peat archive using high‐resolution sampling protocols and AMS ¹⁴C dating. We also identify the need for additional work to quantify the role of climate on peat accumulation and the resultant impact on assemblage‐based palaeoenvironmental reconstructions within mire sequences. The strongest climate association observed for Picea abies (r = 0.53; n = 36) was extended through the monolith beyond the 42 year period of ‘annual’ sampling and the response successfully correlated with the Bottenviken historical instrumental record to AD 1860. Although only presenting data from a single site, and requiring wider replication, we conclude that for sites close to the ecological limits of tree species, where levels of anthropogenic/non‐climatic forcing on pollen production are low, well‐dated records of PAR may potentially provide a proxy for reconstructing past summer temperature variability. Copyright © 2007 John Wiley & Sons, Ltd.     

Hydraulic modelling of subglacial tunnel channels,south‐east Alberta,Canada

One of the key issues associated with the hypothesis of catastrophic subglacial drainage of the Livingstone Lake event is whether flows of such large magnitudes are physically feasible. To explore this issue, a one‐dimensional hydraulic network flow model was developed to investigate the range of peak discharges and associated flow parameters that may have been carried by a tunnel channel network in south‐east Alberta, Canada. This tunnel channel network has been interpreted elsewhere to carry large discharges associated with subglacial meltwater flows because of the convex longitudinal profiles of individual channels. This computational modelling effort draws upon established and verified engineering principles and methods in its application to the hydraulics of this problem. Consequently, it represents a unique and independent approach to investigating the subglacial meltwater hypothesis. Based on the modelling results, it was determined that energy losses resulting from friction limit the maximum peak discharge that can be transported through the tunnel channel network to 10⁷ m³ s⁻¹, which is in reasonable agreement with previous estimates of flood discharges for proposed megafloods. Results show that flow through channels with convex longitudinal profiles occurs when hydraulic head exceeds 910 m (Lost River) and 950 m (Sage Creek) , respectively. These are considerably below the maximum head capable of driving flow through the system of 1360 m, beyond which ice is decoupled from the bed across the pre‐glacial drainage divide. Therefore, it is concluded that these model results support the hypothesis of catastrophic subglacial drainage during the Livingstone Lake event. Copyright © 2000 John Wiley & Sons, Ltd.