Simulation des Nitratabbaus im Grundwasser

Ten reaction vessels containing 1 m³ were used as the experimental arrangement. They were filled with coarse sand or fine gravel and installed 60 cm below the floor. The pore volume (water saturation) was 227… 260 l. Anaerobic conditions were established by the addition of 6 g glucose at storage. The reactors were given tap water with 50 and 200 mg/l NO from KNO₃ in such a way that a volumetric rate of flow of 0.2, 0.4 and 0.8 l/d was created. The volumetric rates of flow corresponded to the natural recharge of groundwater, the recharge of groundwater under the conditions of irrigation and the conditions of an intensive wastewater ground treatment. In the effluent from the reaction vessels the nitrate concentration was determined every month. It was stationary from the 7th to the 55th month after the beginning of the experiment. The experiments are evaluated by means of a model which takes into account the diffusion, convection and kinetics of the nitrate degradation according to Michaelis-Menten. A simple method for solving homogeneous non-linear differential equations of the second order is proposed. The experimental and model results show a good agreement and prove the very slow nitrate degradation in the groundwater with k_M = 210 mg/l, v_max = 1.5 mg/l · d or k₁ = 0.005 d^?1.     

An experimental study on the speciation of dissolved zinc,cadmium, lead and copper in river rhine and north sea water,by differential pulsed anodic stripping voltammetry

Dissolved electroactive concentrations of zinc, cadmium, lead and copper in river Rhine and North Sea samples have been measured at natural and lower pH values by differential pulsed anodic stripping voltammetry using a Kemula-type hanging mercury drop electrode. Average concentrations detected in North Sea samples at salinities $\text{? 32‰ S}$ and their range are (in μgl^?1): 3.9 (2.0–7.5) for zinc, 0.23 (0.13–0.31) for cadmium, 0.3 (0.1–0.6) for lead and 0.3 (0.25–0.60) for copper (pH 8.1). The APDC-MIBK extracting/concentrating method, followed by AAS measurement applied to the same samples, resulted in 3.9 (2.0–7.5) for zinc, 0.11 (0.01–0.27) for cadmium, 0.5 (0.2–0.9) for lead and 1.6 (0.7–3.2) for copper. A fraction of the electroactive concentrations at pH 2.7 (6.1 for Zn) is electroactive at pH 8.1. The fractions are 100% for Cd, 20% for Cu, 13% for Pb and 40% for Zn. The remaining fractions are partly composed of organically bound species in solution. The low value for lead may be caused by the presence of particulate lead that is dissolved at low pH.Ionic copper and lead species, added separately to seawater at pH 8.1 are removed from the electroactive form, and taken up in (organic) complexes in the same ratio (at least for copper) as the species already present. Added ionic zinc is not removed within the time scale of the measurements (30 min). North Sea water at the natural pH has a complexing capacity, probably due to the presence of dissolved organic compounds, in a concentration equivalent to 3.10^?7M copper. The complexing capacity is zero at pH 2.7. The usual method of standard addition for the determination of electroactive copper and lead concentrations may lead to erroneous results in samples where complexation of this type occurs.     

Influence of atmospheric inputs on the iron distribution in the subtropical North-East Atlantic Ocean

Aerosol (soluble and total) iron and water-column dissolved (DFe, < 0.2 μm) and total dissolvable (TDFe, unfiltered) iron concentrations were determined in the Canary Basin and along a transect towards the Strait of Gibraltar, in order to sample across the Saharan dust plume. Cumulative dust deposition fluxes estimated from direct aerosol sampling during our one-month cruise are representative of the estimated deposition fluxes based on near surface water dissolved aluminium concentrations measured on board. Iron inventories in near surface waters combined with flux estimates confirmed the relatively short residence time of DFe in waters influenced by the Saharan dust plume (6–14 months). Enhanced near surface water concentrations of DFe (5.90–6.99 nM) were observed at the Strait of Gibraltar mainly due to inputs from metal-rich rivers. In the Canary Basin and the transect towards Gibraltar, DFe concentrations (0.07–0.76 nM) were typical of concentrations observed in the surface North Atlantic Waters, with the highest concentrations associated with higher atmospheric inputs in the Canary Basin. Depth profiles showed that DFe and TDFe were influenced by atmospheric inputs in this area with an accumulation of aeolian Fe in the surface waters. The sub-surface minimum of both DFe and TDFe suggests that a simple partitioning between dissolved and particulate Fe is not obvious there and that export may occur for both phases. At depths of around 1000–1300 m, both regeneration and Meddies may explain the observed maximum. Our data suggest that, in deep waters, higher particle concentrations likely due to dust storms may increase the scavenging flux and thus decrease DFe concentrations in deep waters.     

Long‐term growth of a valley‐bottom gully,western Iowa

Growth of a permanent, valley‐bottom gully from 1964 to 2000 was determined annually from survey and sediment‐discharge data and compared with runoff and base?ow discharges. Data were analysed to test the hypothesis that rates of gully growth decay exponentially with time in response to shrinking catchment area caused by gully enlargement. Also, monthly values of growth rates and runoff, averaged over the 36‐year record, were analysed with mass‐wasting data to determine the extent to which colluvium availability affected growth rates seasonally. From 1964 to 2000, the gully volume increased by 9200 m³, accounting for 34 per cent of sediment yield from the watershed. There were tight power‐law relationships between annual growth rates and annual runoff, with runoff exponents of 1·57 and 1·30 for headward and volumetric growth, respectively. Increases in gully length, area, and volume were ?tted successfully assuming an exponential decay in growth rate with time. Rather than being due to a decrease in catchment area, however, the decline in growth rate was caused by a 77 per cent decrease in the ratio of runoff to base?ow, which also widened the gully and reduced the mean slope of its banks. Order‐of‐magnitude seasonal changes in erosion ef?ciency, de?ned as the fraction of stream power used to evacuate sediment from the gully, were roughly correlated with colluvium availability, as indicated by seasonal changes in the number of bank mass‐wasting events. No more than 2·2 per cent of stream power was used to evacuate sediment during any month. This study demonstrates the danger of attributing declining rates of gully growth to a shrinking catchment area if corroborative runoff and base?ow data are not available. Moreover, it illustrates that stream power alone provides only a rough and physically indirect measure of erosion potential. Copyright © 2004 John Wiley & Sons, Ltd.     

Estimating fluvial wood discharge using time‐lapse photography with varying sampling intervals

Monitoring large wood (LW: width > 10 cm, length > 1 m) in transport within rivers is a necessary next step in the development and refinement of wood budgets and is essential to a better understanding of basin‐wide controls and patterns of LW flux and loads. Monitoring LW transport with coarse interval (≥ 1 min) time‐lapse photography enables the deployment of monitoring cameras at large spatial and long temporal scales. Although less precise than continuous sampling with video, it allows investigators to answer broad questions about basin connectivity, compare drainages and years,and identify transport relationships and thresholds. This paper describes methods to: (i) construct fluvial wood flux curves; (ii) analyze the effects of sample interval lengths on transport estimates; and (iii) estimate total wood loads within a specified time period using coarse‐interval time‐lapse photography. Applying these methods to the Slave River, a large‐volume (10³ m³ s^‐1), low‐gradient (10^{? 2} m km^{? 1}) river in the subarctic (60^° N), yielded the following results. A threshold relationship for wood mobility was located around 4500 m³ s^‐1. More wood is transported on the rising limb of the hydrograph because wood flux declines rapidly on the falling limb. Five‐ and ten‐minute sampling intervals provided unbiased equal variance estimates of 1 min sampling, whereas 15 min intervals were biased towards underestimation by 5–6%, possibly due to periodicity in wood flux. Total LW loads estimated from the 1 min dataset and adjusted for a 15% misdetection rate from 13 July to 13 August are: 1600 ± 200 # pieces, 600 ± 200 m³ and of the order of 1.3 × 10⁵ kg carbon. The total wood load for the entire summer season is probably at least double this estimate because only the second half of the summer was monitored and a large early summer peak freshet was missed. Copyright © 2014 John Wiley & Sons, Ltd.     

Changes in recreational shore anglers’ attitudes towards,and awareness of,linefish management along the KwaZulu-Natal coast,South Africa

Management of recreational fisheries cannot be based on biological and stock assessment data alone but needs to include appropriate social aspects (including knowledge, attitudes and behaviour) of anglers within the fishery. The primary purpose of this study was to evaluate and complement existing recreational fisheries research, through the analysis of demographic and psychographic angler attributes collected from two independent, shore-based snapshot monitoring surveys conducted on the KwaZulu-Natal (KZN) coastline of South Africa, in 1994–1996 and 2009–2010. Results show significant changes between the two survey events in the demographics of anglers (including ethnic composition, age distribution, years of fishing experience and employment status) participating in the KZN shore-based linefishery. Traditional management regulations (minimum size limits, daily bag limits and closed seasons), though appearing to have support, have had limited effectiveness, based on the increased levels of admitted non-compliance and poor knowledge of regulations for target species. Anglers in both surveys believed that catches had declined over the years, with overfishing being the most common reason given. The results are discussed in the context of changing management practices in the KZN recreational shore-based linefishery. The implications of changes in fisheries management policies and responsibilities along the KZN coast are highlighted.     

Regional Advection Perturbations in an Irrigated Desert (RAPID) experiment

Summary The RAPID field experiment took place in August–September 1999 at a site 25km south of Twin Falls, Idaho, USA. The experiment concerned micrometeorological observations over extensive, well-irrigated fields covered with the fast-growing crop alfalfa. During daytime, on a number of days the sensible heat flux was negative and the latent heat flux exceeded net radiation. The energy required for the latent heat flux to be larger than net radiation has to be advected from elsewhere. As the fields were large, we refer to this process as regional advection. Local advection, on the other hand, refers to advection effects, where the wet to dry transition is on a field scale. Evidence is presented that the RAPID data are subject to regional advection conditions.A simple model, based on Penman-Monteith, is derived that describes the regional-advection case rather well. The influence of wind speed under those conditions is illustrated using data and the model. The correlation coefficients between temperature and horizontal wind component appear to be good indicators for advection.     

Biological data from sharks landed within the United Arab Emirates artisanal fishery

Landing site and market surveys of sharks landed along the Arabian Gulf coast of the United Arab Emirates were undertaken between October 2010 and September 2012 to obtain biological data from this artisanal fishery. Data were collected on the size and sex of 12 482 individuals representing 30 species. Maximum sizes of Carcharhinus sorrah, C. amblyrhynchoides and Hemipristis elongata were extended by at least 300?mm total length (TL) compared with published global maxima. The size at 50% maturity was determined for males of five species and this indicated that the males of smaller shark species (<1 000 mm maximum TL) in the fishery were largely mature. For many species, including Loxodon macrorhinus and Mustelus mosis, overall sex ratios were male-biased, indicating that sexual segregation is likely in those species. Furthermore, sex ratios for several species, such as Rhizoprionodon acutus, showed differences across seasons. Overall, the landings contained a high proportion of juveniles, causing concerns about the sustainability of this fishery. Biological parameters of a number of species differed from those recorded earlier for the region, demonstrating a need for additional local data collection to support the development of management measures.