Pesticides and heavy metals in Danish streambed sediment

The role of streambed sediment as a sink for pesticides and heavy metals was investigated in 30 Danish lowland streams. The investigated streams drain catchments varying in hydrology, topography, soil type and land use. The <250 m newly accumulated fraction of the uppermost 1–2 cm layer of streambed sediment was analysed for 19 old and modern pesticides and 9 heavy metals. DDE was present in the sediment of all the streams. Of the herbicides, fungicides and insecticides currently in use, the most frequently detected was diuron (50.0%), fenpropimorph (66.7%) and lambda-cyhalothrin (6.7%), respectively. The pesticides detected in the highest concentration were fenpropimorph (1700 ng g^–1), propiconazole (130 ng g^–1) and isoproturon (110 ng g^–1). The heavy metals are listed in order of increasing median concentration: Cd (0.80 g g^–1), Co (9.1 g g^–1), As (12.0 g g^–1), Ni (19.0 g g^–1), Cr (19.2 g g^–1), Pb (19.7 g g^–1), Cu (20.1 g g^–1), V (28.5 g g^–1), Zn (103 g g^–1). The average number of pesticides detected in the 27 streams draining predominantly agricultural catchments was (3.7±2.0) being higher (p=0.077) than in the three streams draining non-agricultural catchments (1.7±0.6). Pesticides were significantly related to catchment size, soil type and hydrological regime. Several heavy metals (Cr, Cu, Pb, V and Zn) were related to urban activity and soil type.     

A mathematical model for the leukocyte filtration process

Leukocyte filters are applied clinically to remove leukocytes from blood. In order to optimize leukocyte filters, a mathematical model to describe the leukocyte filtration process was developed by modification of a general theoretical model for depth filtration. The model presented here can be used to predict the time-dependent leukocyte filtration as a function of cell-cell interaction in the filter, filter efficiency, filter capacity, filter dimensions, and leukocyte concentration in the suspension applied to the filter. The results of different leukocyte filtration experiments previously reported in the literature could be well described by the present model. (c) 1995 John Wiley & Sons, Inc.     

Mechanistic evaluation of virus clearance by depth filtration

Virus clearance by depth filtration has not been well‐understood mechanistically due to lack of quantitative data on filter charge characteristics and absence of systematic studies. It is generally believed that both electrostatic interactions and sized based mechanical entrapment contribute to virus clearance by depth filtration. In order to establish whether the effectiveness of virus clearance correlates with the charge characteristics of a given depth filter, a counter‐ion displacement technique was employed to determine the ionic capacity for several depth filters. Two depth filters (Millipore B1HC and X0HC) with significant differences in ionic capacities were selected and evaluated for their ability to eliminate viruses. The high ionic capacity X0HC filter showed complete porcine parvovirus (PPV) clearance (eliminating the spiked viruses to below the limit of detection) under low conductivity conditions (≤2.5 mS/cm), achieving a log₁₀ reduction factor (LRF) of > 4.8. On the other hand, the low ionic capacity B1HC filter achieved only ～2.1–3.0 LRF of PPV clearance under the same conditions. These results indicate that parvovirus clearance by these two depth filters are mainly achieved via electrostatic interactions between the filters and PPV. When much larger xenotropic murine leukemia virus (XMuLV) was used as the model virus, complete retrovirus clearance was obtained under all conditions evaluated for both depth filters, suggesting the involvement of mechanisms other than just electrostatic interactions in XMuLV clearance. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 31:431–437, 2015     

From Demographic Strategies to Mathematical Models: Trends in Population Dynamics Studies of Aquatic Oligochaeta

The existence of a negative relationship between fine sediment infiltration during the incubation period and salmonid embryo survival has often been discussed in the literature. However, few studies have specifically addressed this relationship in the field. We conducted a field experiment to examine the relationship between survival of Atlantic salmon (Salmo salar) embryos contained in incubation baskets and the patterns of fine sediment infiltration into the baskets during the incubation period. The results indicate that survival to pre-eyed (STPE), eyed (STE) and hatched (STH) stages of development were all negatively correlated with the percentage of fine sediment entering the baskets. STPE and STE were most strongly affected by silts and clays (<0.063 mm) although this size class represented only a small fraction of the grain size distribution inside the incubation baskets (0.03–0.41%). STH was most strongly correlated with the infiltration of medium sand (0.25–0.50 mm) material. On average, 66% of the implanted embryos survived to the pre-eyed stage of development compared to 63% for the eyed and 48% for the hatched stages of development.     

Influence of streambed sediment clogging on microbial processes in the hyporheic zone

1. The hyporheic zone plays a key role in hydrological exchange and biogeochemical processes in streambed sediments. The clogging of sediments caused by the deposition of particles in the bed of streams and rivers can decrease sediment permeability and hence greatly affect hyporheic microbial processes. 2. The main objective of this study was to determine the influence of sediment clogging on hyporheic microbial processes in three French rivers (the Usses, Drôme and Isère). In each river, microbial abundance and activity were studied at three depths (10, 30 and 50 cm) in the sediment at one unclogged (high porosity) and one clogged site (low porosity). 3. The results showed that the sediment clogging had inconsistent effects on microbial processes in the three rivers. Increases (Usses) or decreases (Drôme and Isère) in both aerobic and anaerobic processes were detected at the clogged sites compared to unclogged sites. These results suggest that microbial changes because of the sediment clogging are mainly mediated by the residence time of water within the hyporheic sediments. 4. A single model predicting the effect of clogging on hyporheic microbial processes cannot be applied generally to all rivers because the degree of clogging creates heterogeneous effects on flow rates between surface and interstitial waters. As a consequence, the influence of heterogeneous clogging on surface water–hyporheic exchanges needs to be evaluated by water tracing and hydraulic modelling to determine the links between microbial processes and hydraulic heterogeneity induced by clogging in hyporheic sediments.     

Effects of Particle Size and Redox Potential on Arsenic Fractionation in Soils Irrigated with Arsenate-rich Water

Aging affects arsenic (As) bioaccessibility in soils. This study focuses on the influences of particle size and redox potential on As(V) aging in irrigated soils. The results showed that variation of As fractions in fine particles, except the loosely adsorbed fraction, was larger than that in coarse particles over time. Anoxic conditions decreased the change in As fractions, with the exception of the exchangeable fraction in soils over time, in comparison to the aerobic condition. The aging processes of As(V) in different particle sizes and soils at different redox potentials exhibited several stages. The only significant difference in the aging process of As(V) in different particle sizes was the longer transformation period of the water-soluble fraction into the Fe/Mn/Al oxides-bound fraction in fine particles than in coarse particles. The redox potential had a significant influence on the aging process of As(V) in soils after 10 days of incubation. In terms of As bioaccessibility, anoxic conditions shortened the aging process of As(V) in soils. During the aging process, fine particles and aerobic conditions intensified the decrease in As(V) bioaccessibility in soils in comparison to the coarse particles and anoxic condition.     

Spheroidal carbonaceous particles as a marker for recent sediment distribution

We have tested the hypothesis that spheroidal carbonaceous particles (SCP), emitted from oil and coal combustion, can be used as a marker for recent sediment distribution in lake basins. Sediment traps have been used to study when and how the particles are introduced into a lake, a laboratory experiment has been made to study the depositional behaviour of the particles in relation to other sedimentary constituents, and spatial SCP distributions have been surveyed in three lakes. The results support the hypothesis that SCP can be used as a marker, and also indicate that acidification can change sediment distribution in lakes.     

Spatial and temporal variation in dissolved oxygen in natural egg pockets of chum salmon, in Kennedy Creek, Washington

The effects of dissolved oxygen (DO) on incubating salmonid embryos have been studied extensively in the laboratory but there is little information on levels experienced by salmon embryos in complex natural channels. We monitored 33 natural egg pockets of chum salmon Oncorhynchus keta , from shortly after spawning until emergence, and found that DO levels varied considerably among and within egg pockets over time. Egg pocket DO levels varied from 2–10 mg l⁻¹ at the time of spawning and generally declined during incubation but the declines did not occur in all pockets and were not always steady. Much of the variability may be attributed to local channel topography. Pool tailouts had the highest and least variable DO levels whereas levels in lateral bars were generally lower and more variable. Levels in glides and riffles tended to be intermediate between those in pool tailouts and lateral bars. In spite of the variation in DO levels and habitats used by chum salmon, DO levels were not correlated with egg pocket sediment composition (per cent of the sample<1.0 or 4.0 mm diameter) or with the egg pocket's depth.