Importance of bank erosion for sediment input, storage and export at the catchment scale

Purpose

The importance of bank erosion was quantified during three periods (October 2006–April 2007, May 2007–April 2008 and May 2008–April 2009) in the 486 km² catchment area of River Odense, Denmark. A catchment sediment budget was established including other sediment sources such as tile drains and surface runoff, in-channel and overbank sinks and storage and the resulting bed load and suspended sediment load exported from the catchment.

Material and methods

Bank erosion and sedimentation were measured using ca. 3,000 erosion pins established in 180 pin plots, each consisting of three vertical lines of pins. Thirty-six representative reaches, each with a length of 100 m, were selected by a stratified random procedure in GIS. Bed load and suspended sediment export from the catchment were measured using a bed load sampler and from continuous measurements of turbidity at the outlet gauging station.

Results and discussion

The gross sediment input from bank erosion during the three study periods amounted to 21,100–25,200 t in the River Odense catchment, which is considerably higher than the estimated input of sediment from tile drains and surface runoff, which amounted to 220–500 t and 0–100 t, respectively. The measured bed load (20–490 t) was five to 60 times lower than the suspended sediment export from the catchment (1,240–2,620 t) during the three study periods, with the largest difference occurring in the driest year. Sediment sinks and storage were of high importance for the catchment sediment budget as the measured in-channel storage of sediment on stream banks was as high as 16,200–20,100 t, and the overbank sediment sink was estimated at 360–3,100 t.

Conclusions

Bank erosion was the dominant sediment source (90–94 %) in the River Odense catchment during the three study years. In-channel and overbank sediment sinks and storage dominated the sediment budget as 79–94 % of the sediment input from all sources was not exported from the catchment during the three study years. Such a large attenuation of sediment in river channels and on floodplains is extremely important for fluvial habitats and ecology. Moreover, it has strong implications for attempts to document changes in sediment export following implementation of mitigation measures.     

High prevalence of mycoplasmas in the genital tract of asymptomatic stallions in Austria

Mycoplasma equigenitalium and M. subdolum have been implicated in genital disorders and infertility of horses. The reported cytopathic effects of M. equigenitalium observed in vitro underscore its potential pathogenic role in reproductive dysfunction in mares. This study was initiated to determine the prevalence of mycoplasmas in the genital tract of stallions in relationship to age, clinical signs, geographic location and semen quality. For this purpose the mycoplasma flora of the genital tract of 116 stallions of the Noric breed was determined by isolation and colony immunoblotting and by polymerase chain reaction (PCR) assays. Of 438 swabs from the genital tract, pre-ejaculatory fluid and semen samples, 352 (80%) samples were positive by PCR and 125 (29%) were positive by culture. Mycoplasmas were isolated predominantly from the fossa glandis and urethra and less frequently from the penis shaft and from semen. M. equigenitalium (89 isolates) and M. subdolum (70 isolates) were the predominant species identified. M. equirhinis and M. felis were detected in 27 and 8 samples, respectively. Comparison of these isolations with clinical signs, semen quality, and age of the stallions revealed no significant correlation. However, geographical location of the stallion significantly correlated with mycoplasma detection. These results suggest that mycoplasmas are present as commensals in the genital tract of stallions. Thus, clinically healthy stallions may present a permanent reservoir for infection of mares via venereal transmission.     

Environmental threats and conservation implications for Atlantic salmon and brown trout during their critical freshwater phases of spawning,egg development and juvenile emergence

Atlantic salmon Salmo salar L. and brown trout Salmo trutta fario L. are species of high socio-economic and ecological value. Declining populations make them target species of fisheries management. This paper reviews the direct effects of deficient longitudinal connectivity, changes in discharge, high water temperatures, oxygen depletion, changes in water chemistry and increasing loads of fine sediment on the critical life stages of spawning, egg incubation and emergence. It further provides an overview about the basic autecological requirements of Atlantic salmon and brown trout and summarises important thresholds of physico-chemical tolerances. This collection of information provides important baselines for assessing historical, ongoing and new threats relevant for the management of both species in fresh waters. Critical early-life stages of both species are almost identical, creating synergies in conservation and restoration. Seaward-migrating forms are exposed to further stressors, but improving starting conditions can also greatly improve their resilience.     

Satellite-based stand-wise forest cover type mapping using a spatially adaptive classification approach

Due to high variation in forest communities, forest structure and the fragmentation of the forested area in Central Europe, satellite-based forest inventory methods have to meet particularly high-quality requirements. This study presents an innovative method to combine official forest inventory information at stand level with multidate satellite imagery using a spatially adaptive classification approach for producing wall-to-wall forest cover maps of important tree species and management classes across multiple ownership regions in a heterogeneous low mountain range in Germany. The classification approach was applied to a 5,200-km² area (about 2,080?km² of forest land, mostly mixed forests) located in the Eifel mountain range in Central Europe. In comparison with conventional classifiers, our results demonstrate a significant increase in classification accuracy in the order of 12%. The method was tested with ASTER images but holds the potential to be used for regular state forest inventories based on standard and novel earth observation data supplied for instance from the SPOT-5 and RapidEye sensors.     

Impact of the earthworm Lumbricus terrestris on the degradation of Fusarium-infected and deoxynivalenol-contaminated wheat straw

When conservation tillage is practised in agriculture, plant residues remain on the soil surface for soil protection purposes. These residues should be widely decomposed within the following vegetation period as microbial plant pathogens surviving on plant litter may endanger the currently cultivated crop. Important soil-borne fungal pathogens that preferably infect small grain cereals belong to the genus Fusarium. These pathogens produce the mycotoxin deoxynivalenol (DON), a cytotoxic agent, in infected cereal organs. This toxin frequently occurs in cereal residues like straw. So far it is unclear if DON degradation is affected by members of the soil food web within decomposing processes in the soil system. For this purpose, a microcosm study was conducted under controlled laboratory conditions to investigate the degradation activity of the earthworm species Lumbricus terrestris when exposed to Fusarium-infected wheat straw being contaminated with DON.Highly Fusarium-infected and DON-contaminated straw seemed to be more attractive to L. terrestris because it was incorporated faster into the soil compared with straw infected and contaminated at low levels. This is supported by a greater body weight gain (exposure time 5 weeks) and smaller body weight loss (exposure time 11 weeks) of L. terrestris, respectively, when highly contaminated straw was offered for different time periods.Furthermore, L. terrestris takes part in the efficient degradation of both Fusarium biomass and DON occurring in straw in close interaction with soil microorganisms. Consequently, earthworm activity contributes to the elimination of potentially infectious plant material from the soil surface.     

Dynamics of litter carbon turnover and microbial abundance in a rye detritusphere

Factors determining C turnover and microbial succession at the small scale are crucial for understanding C cycling in soils. We performed a microcosm experiment to study how soil moisture affects temporal patterns of C turnover in the detritusphere. Four treatments were applied to small soil cores with two different water contents (matric potential of ?0.0063 and ?0.0316 MPa) and with or without addition of ¹³C labelled rye residues (δ¹³C=299‰), which were placed on top. Microcosms were sampled after 3, 7, 14, 28, 56 and 84 days and soil cores were separated into layers with increasing distance to the litter. Gradients in soil organic carbon, dissolved organic carbon, extracellular enzyme activity and microbial biomass were detected over a distance of 3 mm from the litter layer. At the end of the incubation, 35.6% of litter C remained on the surface of soils at ?0.0063 MPa, whereas 41.7% remained on soils at ?0.0316 MPa. Most of the lost litter C was mineralised to CO₂, with 47.9% and 43.4% at ?0.0063 and ?0.0316 MPa, respectively. In both treatments about 6% were detected as newly formed soil organic carbon. During the initial phase of litter decomposition, bacteria dominated the mineralisation of easily available litter substrates. After 14 days fungi depolymerised more complex litter compounds, thereby producing new soluble substrates, which diffused into the soil. This pattern of differential substrate usage was paralleled by a lag phase of 3 days and a subsequent increase in enzyme activities. Increased soil water content accelerated the transport of soluble substrates, which influenced the temporal patterns of microbial growth and activity. Our results underline the importance of considering the interaction of soil microorganisms and physical processes at the small scale for the understanding of C cycling in soils.     

Susceptibility of cocooned pupae and adults of the parasitoid <Emphasis Type="Italic">Microplitis mediator</Emphasis> to selected insecticides

The braconid parasitoid Microplitis mediator (Haliday) is a key natural enemy of the cabbage moth, Mamestra brassicae (L.), in Europe. In the context of an Integrated Pest Management approach, the use of selective insecticides is essential for the conservation of naturally occurring beneficial arthropods. The present laboratory study investigated the side effects of six insecticides applied at recommended field rates on adults and cocooned pupae of M. mediator. Male and female parasitoids were paired in drum cells contaminated with dry residues of insecticides. Besides lethal effects after 24 h, parasitization capacity and longevity of the surviving parasitoids was evaluated. Lethal effects on cocooned pupae were also investigated by assessing adult emergence from treated cocoons. Pirimicarb caused 100% adult mortality after 24 h, whereas the other tested insecticides caused no direct toxic effects. However, sub-lethal effects in terms of reduced parasitization activity, percentage of parasitism or female longevity were found for flonicamid, pymetrozine, spinosad and thiacloprid. Spirotetramat shortened only male longevity. Adult emergence from treated cocoons was reduced only by flonicamid and pymetrozine.     

Carbon isotope constraints on the deglacial CO₂ rise from ice cores

The stable carbon isotope ratio of atmospheric CO(2) (δ(13)C(atm)) is a key parameter in deciphering past carbon cycle changes. Here we present δ(13)C(atm) data for the past 24,000 years derived from three independent records from two Antarctic ice cores. We conclude that a pronounced 0.3 per mil decrease in δ(13)C(atm) during the early deglaciation can be best explained by upwelling of old, carbon-enriched waters in the Southern Ocean. Later in the deglaciation, regrowth of the terrestrial biosphere, changes in sea surface temperature, and ocean circulation governed the δ(13)C(atm) evolution. During the Last Glacial Maximum, δ(13)C(atm) and atmospheric CO(2) concentration were essentially constant, which suggests that the carbon cycle was in dynamic equilibrium and that the net transfer of carbon to the deep ocean had occurred before then.     

The additional costs of segregated transport to slaughter to decrease Salmonella prevalence in pork--a simulation study

A stochastic simulation model was used to assess the additional costs related to segregated transport to slaughter. This control measure was assumed to be implemented within a producers' association to decrease Salmonella prevalence in pork. Calculations were based on the additional shipments caused by the separate transport of low- and high-prevalence herds and on the additional transport distance caused by changed routing. The results showed that there is not necessarily a considerable increase in the number of shipments due to herd status separation for transport. The percentage of shipments changed due to segregated transport varied between 43% and 69% depending on the threshold prevalence. The additional costs per slaughtered pig varied between 0.07€/pig and 0.58€/pig under the given assumptions. Costs were governed by the percentage of changed shipments and the additional distance of a changed shipment. Due to the fact that the percentage of changed shipments is related to the distribution of herd prevalence within the producers' association, there is no cost-effective threshold in general. Different producers' associations incur different costs caused by segregated transport to slaughter at the same threshold prevalence. The current study supports producers' associations in evaluating the additional costs of segregated transport for their members.