Above- and below-ground vertebrate herbivory may each favour a different subordinate species in an aquatic plant community

At least two distinct trade-offs are thought to facilitate higher diversity in productive plant communities under herbivory. Higher investment in defence and enhanced colonization potential may both correlate with decreased competitive ability in plants. Herbivory may thus promote coexistence of plant species exhibiting divergent life history strategies. How different seasonally tied herbivore assemblages simultaneously affect plant community composition and diversity is, however, largely unknown. Two contrasting types of herbivory can be distinguished in the aquatic vegetation of the shallow lake Lauwersmeer. In summer, predominantly above-ground tissues are eaten, whereas in winter, waterfowl forage on below-ground plant propagules. In a 4-year exclosure study we experimentally separated above-ground herbivory by waterfowl and large fish in summer from below-ground herbivory by Bewick’s swans in winter. We measured the individual and combined effects of both herbivory periods on the composition of the three-species aquatic plant community. Herbivory effect sizes varied considerably from year to year. In 2 years herbivore exclusion in summer reinforced dominance of Potamogeton pectinatus with a concomitant decrease in Potamogeton pusillus, whereas no strong, unequivocal effect was observed in the other 2 years. Winter exclusion, on the other hand, had a negative effect on Zannichellia palustris, but the effect size differed considerably between years. We suggest that the colonization ability of Z. palustris may have enabled this species to be more abundant after reduction of P. pectinatus tuber densities by swans. Evenness decreased due to herbivore exclusion in summer. We conclude that seasonally tied above- and below-ground herbivory may each stimulate different components of a macrophyte community as they each favoured a different subordinate plant species

Viability of meta-populations of wetland birds in a fragmented landscape: Testing the key-patch approach

The key patch approach assumes that metapopulations in fragmented landscapes are likely to be viable with at least one "key" sub-population that is sufficiently large to ensure re-colonization of surrounding minor habitat patches. It is based on a minimum viable number of breeding pairs and within-breeding season dispersal distance, linked to size of the animal and longevity. It was tested using census data of 15 wetland bird species (bearded tit, bluethroat, great reed warbler, sedge warbler, Savi's warbler, grasshopper warbler, spotted crake, water rail, common snipe, common teal, garganey, little bittern, night heron, great bittern and marsh harrier) in 14 wetland complexes of variable size (3-55 k

Environmental indicators for soil remediation and soil protection

Beschreven wordt welke indicatoren voor bodemsanering en bodembescherming van lokale bronnen in de Milieubalans/Milieuverkenningen opgenomen kunnen worden. Drie hoofdonderwerpen zijn behandeld: de omvang en ernst van de (water) bodemverontreiniging, (water) bodemsanering en tot slot bodembescherming. Per hoofdstuk wordt aangegeven: welke indicatoren zijn ontwikkeld ; op welke manier de onderscheiden indicatoren nader kunnen worden ingevuld ; welke informatie hiervoor ter beschikking staat (of komt) ; welke informatie benodigd is en welke knelpunten voorzien worden bij vergaren van de benodigde informatie. Op basis van het in het NMP2 geformuleerde bodembeschermingsbeleid zijn indicatoren ontwikkeld voor: de omvang van de bodemverontreiniging; de sanering of beveiliging van ernstig/urgente gevallen ; het voormalig, huidig en toekomstig gebruik van verontreinigde grond ; de geleverde en te leveren financiele inspannig door doelgroepen ; de geleverde financiele inspanning opgedeeld naar saneringsvorm; grondstromen als gevolg van de bodemsaneringsvorm; bodemkwaliteitsontwikkeling als gevolg van bodembelasting. Voor de "minimalisatie van de stagnatie van maatschappelijke processen" en optimale besteding van de financiele middelen" zullen nog indicatoren moeten worden vastgesteld en een gegevensinfrastructuur worden ontwikkeld. Ook is geconstateerd dat een indicator voor "beleidsmonitoring bodembescherming" verder uitgewerkt moet worden.For future versions of the integrated reports: Environmental Balance and Environmental Outlook, RIVM has chosen to present an overview of environmental issues, especially those related to actual and future environmental policies in the Netherlands. In terms of so-called target and related policy monitoring indicators. These environmental indicators are represented by a limited numbers of concise and appealing parameters to present the vast amount of information on environmental pressure and quality. This report defines Environmental indicators for the extent of soil pollution and the progress of soil remediation and of soil protection restricted to point sources. The most important gaps and discrepancies between definition of indicators and quantification (collecting data) are listed. It is concluded that for the present quantifying the majority of the listed indicators, for instance where information structures are lacking or relevant parameters are not collected, is not possible.RIV

[Levels of facultative anaerobic bacteria and relative weights of thymus, spleen and caecum in SPF N:NIH mice and Riv-TOX rats.]

This report describes variations in the levels of groups of facultatively anaerobic bacteria in the intestinal tract and the relative weights of caecum, thymus and spleen in N:NIH mice and Riv:TOX rats kept under SPF conditions. Considerable variation in the composition of the enteric bacterial flora of mice and rats was detected. The possible influence of a poor colonization resistant (strictly anaerobic) flora (mCRF) on levels of other enteric flora elements and on relative weights of lymphoid organs is discussed.RIV

Colonisation resistance and relative calcal weight in mice associated with different microflora

This report describes observations on colonization resistance to E.coli O90 K- and Enterobacteriaceae and relative caecal weight in mice associated with different enteric microflora. It is concluded that the colonization resistance of the enteric microflora in mCRF mice appears to be limited.VH

Inundation Frequency Determines the Post-Pioneer Successional Pathway in a Newly Created Salt Marsh

The effect of inundation frequency on plant community composition, species turnover, total and growth form cover, species richness, and abundance of individual species was investigated in a newly created salt marsh (Belgium) with a gradient of inundation frequencies from 0.01% to 100%. Cover of all plant species was estimated in 119 permanent 2 × 2 m plots along seven randomly chosen transects perpendicular to the main inundation gradient in 2003, 2005, and 2007. Plant composition change clearly varied along the inundation frequency gradient. The cover of annual species increased at a higher rate at higher inundation frequencies, while cover of perennials increased at higher rate at lower inundation frequencies. Species richness and the abundance of most species increased over time, indicating general absence of competitive exclusion among species. Conversely, the abundance and frequency of Atriplex spp., Chenopodium spp., and Salsola kali strongly decreased over time, indicating their early successional character. Frequent inundations hampered plant species turnover because of the low number of species which can tolerate that environmental condition. The appearance of communities dominated by Elymus athericus or Salicornia procumbens strongly increased over time, leading to a stronger separation of plant communities and an appearance of typical salt-marsh zonation

The mobile epifauna of the soft bottoms in the subtidal Oosterschelde estuary: structure, function and impact of the storm-surge barrier

Data on the mobile epifauna of the Oosterschelde estuary, collected by beam trawl, were compiled from several studies. Multivariate statistical techniques brought out the fact that the Oosterschelde, when compared with neighbouring areas, has a characteristic epibenthic fauna. Diversity as measured by Hill's diversity numbers N through N +infinite, is higher for the Oosterschelde (N1=4.5) than for the Voordelta (N1=3.5) and the Westerschelde (N1=2.2).Four epifaunal communities can be distinguished within the Oosterschelde, the two most seaward communities being the richest. Annual production is estimated at about 6 gADW m-2 yr-1, annual consumption is estimated at over 25 g ADW m-2 yr-1. These results are highly dependent on the assumptions. Over 85% of the epibenthic production and consumption in the Oosterschelde is accounted for by only six species: starfish Asterias rubens, plaice Pleuronectes platessa, bib Trisopterus luscus, brown shrimp Crangon crangon, shore crab Carcinus maenas and dab Limanda limanda. In spite of its abundance, the sand goby Pomatoschistus minutus contributes little to the production.From the available data it is difficult to assess the impact of the construction of the storm-surge barrier and the compartmentalization dams on the epibenthic fauna. The increase in flatfish in the Hammen area is probably linked to the decrease in current velocities in that area. On the other hand the increase in flatfish in the Hammen area is probably linked to the decrease in current velocities in that area. On the other hand the increase in the gadoids bib and whiting Merlangius merlangus is predominantly due to the stronger year classes in the post-barrier time period. Lower nutrient inputs through the Northern branch, in combination with the increase of the gadoids, may have caused the decline of the brown shrimp in the Oosterschelde. A decrease has also been observed in the sand eel Ammodytes tobianus and the hooknose Agonus cataphractus