Systematics, ecology and feeding biology of estuarine nematodes

As part of extensive biological and chemical investigations in the Ems estuary, the nematode fauna of this area (mainly located in the sediments of tidal flats) was studied.First, a new method of isolating nematodes was developed, as none of the existing methods appeared to be quantitatively reliable for the isolation of organisms from silty sediments. The new method is based on differences in specific weight between nematodes (and other meiobenthos),and sediment particles: sediment samples are suspended in Ludox-TM, a colloidal silica, and, whereas organisms float to the surface of this suspension, sediment particles sink to the bottom. The isolation method can be used for either preserved or fresh sediment samples.In a survey of the estuary 121 nematode species were identified and during subsequent investigations 12 other species were noticed: thus, in all 133 species were identified, 4 of which were new to science. The distribution of species over the estuary was studied and the genesis of species associations was related to environmental conditions. Two main faunas were distinguished: one in the Wadden Sea part of the estuary, the other in the Dollart, both extending into the middle reaches of the estuary. In the lower sediment layers a characteristic nematode fauna was found that consisted of species that were mainly absent from the upper sediment layers It was concluded that faunal associations from the lower sediment layers originate from marine subtidal locations, whereas the associations from the upper sediment layers of tidal flats are specific to estuarine tidal environments.Several nematode species were cultured in agar in the laboratory and their feeding-biology was studied. From these investigations it appeared that nematodes, specific to the surface of littoral macrophytes 3 use non-selective feeding methods, consuming large amounts of bacteria, and, when their buccal cavity is large enough, also diatoms and other algae; the food organisms are ingested by means of continuous oesophageal pulsations. The interstitial nematodes, on the other hand, probably all feed selectively, oesophageal pulsations only being triggered off when a useful food organism is sensed among an overwhelming majority of similarly sized inedible particles. The larger food organisms, diatoms and other algae, protozoa, and small metazoans (including prey-nematodes) may be ingested whole or punctured and subsequently sucked out; specific buccal structures determine which consumption technique is used: when armature is absent food items are ingested whole, when armature is present food items are attacked and sucked out. Individual bacteria are probably too small for most interstitial nematodes and consequently are ignored as food.Special attention was focused on the ecosystem of the tidal flats close to the outfall in the southeast Dollart. It appeared that in that area the benthic ecosystem was dominated by a herbivorous food-chain, comprising diatoms and diatomconsuming nematodes (throughout the year) and oligochaetes (only in the warmer part of the year).It is concluded that the success of nematodes in colonizing almost all estuarine biotopes is due to their size, their sophisticated methods of food acquisition and their tolerance of environmental stress. The discharge of organic waste enhances the effects of natural gradients occurring in the estuary. The main effect is the overall decrease of species diversity and the indirect promotion of a herbivorous foodchain in which nematodes predominate the grazing fauna.<p/

Model-predicted ammonia emission from two broiler houses with different rearing systems

Ammonia (NH3) emissions from broiler production can affect human and animal health and may cause acidification and eutrophication of the surrounding environment. This study aimed to estimate ammonia emissions from broiler litter in two systems of forced ventilation, the tunnel ventilation (TV) and the dark house (DH). The experiment was carried out on eight commercial broiler houses, and the age of the birds (day, d), pH and litter temperature were recorded. Broilers were reared on built-up wood shaving litter using an average flock density of 14 bird m–2. Temperature and relative humidity inside the broiler houses were recorded in the morning during the grow-out period. A factorial experimental design was adopted, with two types of houses, four replicates and two flocks with two replicates each. A deterministic model was used to predict ammonia emissions using the litter pH and temperature, and the day of grow-out. The highest litter temperature and pH were found at 42 d of growth in both housing systems. Mean ambient air temperature and relative humidity did not differ in either system. Mean model predicted ammonia emission was higher in the DH rearing system (5200 mg NH3 m−2h−1 at 42 d) than in the TV system (2700 mg NH3m−2 h−1 at 42 d). TV presented the lowest mean litter temperature and pH at 42 d of growth. In the last week of the broilers’ grow-out cycle, estimated ammonia emissions inside DH reached 5700 mg m−2h−1 in one of the flocks. Ammonia emissions were higher inside DH, and they did not differ between flocks. Assuming a broiler market weight in Brazil of close to 2 kg, ammonia emissions were equivalent to 12 g NH3 bird-marketed−1. Model-predicted ammonia emissions provided comprehensible estimations and might be used in abatement strategies for NH3 emission

Rehabilitation of the nematode fauna in a phytostabilized, heavily zinc-contaminated, sandy soil

Background, Aim and Scope. The Maatheide in Lommel, Belgium, is an extremely metal contaminated, sandy area where vegetation has disappeared over ca. 130 hectares due to the activities of a former pyrometallurgical zinc smelter. To reduce the environmental impact of this area a rehabilitation strategy had to be developed. Therefore, in the centre of this area, an experimental phytostabilization (grass) field of three hectares had been installed in 1990. After a grass cover had been established, the development of the nematode fauna in the phytostabilized soil was studied. Nematodes act at various levels in soil ecosystems: herbivorous species extract their food from plant roots, bacterivorous and fungivorous species feed on microbes, predatory species consume other nematodes, and omnivorous species have mixed diets. In a mature soil ecosystem that normally exercises its manifold functions, a diverse nematode fauna occurs, reflecting the intactness of the ecosystem. As such, this fauna is indicative of crop growth, vegetative diversity, organic matter decomposition, microbial activity and diversity, and the maturity of the soil ecosystem. Methods. A metal immobilizing soil amendment (beringite) and municipal waste compost (to improve the nutrient status and water-retaining capacity) were incorporated in the soil and metal tolerant ecotypes of grasses were sown. Soil samples for nematode analyses were taken four times. Results. As a result of the treatment, pH of the soil increased and the water extractable amount of Zn was strongly reduced. Grass growth revitalized the impoverished soil ecosystem, organisms as well as metabolic processes. The nematode fauna of the experimental field in the Maatheide has been studied since 1997 and the recovery of the various feeding guilds and taxa was checked again in 2002. Nematode densities and feeding guilds have normalized, with omnivores and predators as the last guilds to reappear. Up to 27 species with a current diversity were observed in the grass-covered experimental plot, but a number of ubiquitous species, present at a comparable site at some distance, remained absent. Conclusion. It can thus be concluded that rehabilitation of an impoverished soil ecosystem is possible in heavily contaminated soils by means of phytostabilization, but there are some limitations on rehabilitation, since a number of common nematode species remained absent. Further research should indicate if this absence is indicative of a loss of essential processes in the soil. Recommendation and Perspective. Phytostabilization of heavily zinc-contaminated, sandy soil also remediates impoverished soil ecosystems. In particular, the recovery of nematode feeding categories is indicative for the normalization of soil life. The absence/presence of a number of ubiquitous taxa should be checked again after some time to verify if recovery is completed

Effects of soil compaction on the relationships between nematodes, grass production and soil physical properties

As farm machinery has become heavier, concern has grown about its direct effects on soil physical conditions and its indirect effects on crop yields and soil biota. To study the relationships between these parameters, non-grazed temporary grassland plots on a loamy sand soil were subjected to full-width load traffic with widely different loads (0, 4.5, 8.5 and 14.5t) one to four times per year for a period of 5 years. Soil bulk density was monitored as an indicator of soil compaction. Grass yield was measured throughout the experimental period. Root distribution over the soil profile and nematodes populations were assessed during the final year of the experiment. Results indicate that a moderate degree of compaction (~4.5t load) gave the highest crop yield and that at higher degrees of compaction roots failed to penetrate into the deeper soil layers (>20cm depth). Total numbers of nematodes were not affected by compaction, but their distribution over the various feeding types shifted towards a population with increased numbers of herbivores and decreased numbers of bacterivores and omnivores/predators. This change in the structure of the nematode assemblage is associated with poorer conditions for crop growth