Burrowing beetles of the genus Bledius (Staphylinidae) as agents of bioturbation in the emergent areas and shores of an athalassic inland lake (Fuente de Piedra,southern of Spain)

Bledius (Elbidus) bicornis (Germ.) and B. (Eucerotobledius) furcatus (Oliv.) (Coleoptera: Staphylinidae) are the most important burrowing species in the emergent areas and shores in the athalassic lake of Fuente de Piedra (Málaga, S. of Spain). A first estimate of the importance of these organisms in this system is presented. These insects kick out sediment during their burrowing activity, which accumulates on the surface near the burrows as tumuli which can be easily eroded. The lake perimeter (17 km) is densely colonized (usual densities from 1700 to 2500 ind m⁻²). The amount of granulated material that can be potentially kicked out was 46.22 g dry wt m⁻² day⁻¹. At the same time, the material that constitutes the tumuli shows different characteristics from the compact ground below the surface. Thus, it is relatively enriched with organic matter (6.15 g per square meter), soluble phosphate (406.5 μg m⁻²) and ammonium (4856 μg m⁻²), whereas it lacks nitrate. Results of a transect from uninhabited areas to zones of maximum population density also show a similarity between the higher ground level of ammonium and phosphate concentrations and population density.     

Natural and man-caused factors affecting the abundance and cycling of dissolved organic substances in precambrian shield lakes

A study on nutrient regeneration processes and a measure of their fluxes at the sediment-water interface was carried out in two different stations of a shallow lagoon of the Po delta river (Italy). A few parameters on the solid fraction (grain-size, porosity, C, N) and pore water profiles of o-P, NH₃, NO _inf3 ^sup– , SiO₂, Tot-CO₂, SO _inf4 ^sup2– , Fe, Mn, Ca, Mg, pH, Eh were determined. At both stations the results were typical for fine sediments rich in organic matter. The ratio of variations of sulphate (SO _inf4 ^sup2– ) to total carbonate demonstrates the main role sulphate reduction plays on the organic matter decay. The use of the ratios of variations of sulphate (SO _inf4 ^sup2– ) to ammonia (NH₃) and of sulphate (SO _inf4 ^sup2– ) to phosphate (o-P) in pore waters enabled us to calculate the C/N/P of the decomposing organic matter. Obtained C/N/P indicated an enrichment of N and P with regard to C/N/P ratios of the solid fraction, due to the selective stripping of N and P during organic matter mineralization. This phenomenon decreases with depth, where organic matter becomes more refractory. Calculations on saturation degrees have shown the possibility of authigenic calcite, apatite and rhodochrosite precipitation in sediments. Nutrient fluxes were estimated for SiO₂, NH₃ and o-P by means of benthic chambers and modelling the pore water profiles. The model used for the calculation of fluxes allowed us to account for the bioturbation-irrigation influence near the interface, by means of a cumulative diffusion coefficient. Directly measured fluxes proved to be always significantly greater than the theoretical ones. These differences seem to be due to surface processes which do not affect pore water concentrations (degradation of fresh materials at the interface; micro-bioturbation by small gasteropoda such as Hydrobia ventrosa) and/or to the different concept of the two methods in time and space. Number, size and biomass of macrobenthic species living in the sediment underneath the benthic chambers were determined. The comparison between data on macrobenthic populations and flux values showed a good relationship between the number of organisms and benthic fluxes within each station. However, flux variations between stations are to be attributed mainly to the different arrangement of the tubes of the polychaetes Polydora ciliata in the sediment.     

The rates of sediment-water exchange of oxygen and sediment bioturbation in Lough Neagh,Northern Ireland

Oxygen is transported 30 mm into the sediment at an 8 m depth site in eutrophic Lough Neagh by the irrigational activities of the benthic fauna. Faunal activity also mixes the upper 20 mm of sediment. Sediment oxygen uptake rate, redox potential-depth profile and the chlorophylla concentration were measured in the upper sediment layers from February to November 1979. Chlorophylla input to the sediment, following the Spring phytoplankton maximum, remained in the 0–1 cm sediment layer but did cause the redox potential profile to change from one with potentials around 400 mV in the upper 50 mm to one with a strong gradient over the 0–30 mm region. The start of benthic faunal activity in May caused the chlorophylla to be mixed into the 1–2 cm layer and also caused oxygen to be transported into the sediment at a rate sufficient to change the redox potential back to its initial state. The biodiffusion coefficient for solids in the upper 20 mm was estimated to be 6 × 10⁻⁸ cm² s⁻¹. Oxygen transport in the pore, waters of the upper sediment layers was considered to be best described as advection, caused by the irrigational activities of the benthic fauna.     

High resolution vertical profiles of pH in recent sediments

High resolution (0.1 cm sampling interval) profiles of pH were obtained from some recent estuarine (Long Island Sound, Chesapeake Bay) and freshwater (Lake Erie) sediments and from laboratory microcosms containing homogenized Lake Erie sediment (both with and without tubificid oligochaetes) by incrementally precessing a micro-pH electrode downward through the sediment. These profiles revealed that hydrogen ion undergoes chemical reactions on a scale smaller than can be resolved using classic 1 cm sampling intervals, and that the vertical distribution of hydrogen ion is affected by bioturbation. In all sediments examined, a local pH minimum occurred immediately below the oxidized zone. In estuarine sediments, a second deeper pH minimum was observed. The presence of tubificids prevented profound pH changes from developing in microcosm sediments treated with a layer of activated sewage sludge and resulted in more modest alterations of pH profile in microcosm sediments lacking such a layer. The technique used in this study is by no means limited to pH. In principal, any chemical species that can be directly determined by electrodes (e.g. O₂, S^-2) may be studied. Microelectrode techniques could be especially useful in the study of chemical gradients around animal burrows and in time series studies of whole core diagenesis.     

The response of stream periphyton to Pacific salmon: using a model to understand the role of environmental context

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Experimental test of the ecosystem impacts of the keystone predator Triops cancriformis (Branchiopoda: Notostraca) in temporary ponds

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Restoration of an Ecosystem Function to Revegetation Communities: The Role of Invertebrate Macropores in Enhancing Soil Water Infiltration

Guidelines for revegetation in agricultural landscapes may not address restoration of ecosystem functions because management is focused on the replanting stage, although certain functions are delivered by organisms that colonize revegetation months or years later. We investigated the ecosystem function of water infiltration to tree root zones and channels, delivered by invertebrates that form soil macropores. We measured macropore density and infiltration rates at revegetation sites established on retired grazing land, in relation to site age, tree species composition, and geographical location, compared with adjacent matched pastures. Revegetated sites had significantly more macropores than pastures, and revegetation sites aged 11–20 years had more macropores than sites aged 3–5 and 6–10 years. Tree species had a marginal effect, with more macropores in sites with Acacia spp. and Eucalyptus spp. than those with Eucalyptus spp. only. Besides ants, the main groups of soil burrowers were mygalomorph and lycosid spiders and also ground‐nesting native bees. Infiltration rates in revegetation sites aged 11–20 years were double those of pastures and of 3–5 and 6–10 year sites. This is the first study to quantify the rate of recovery of an invertebrate‐driven soil hydrological ecosystem function following revegetation.     

大型底栖动物对河口沉积物的扰动作用

利用微宇宙示踪技术,定量研究了天津北塘河口地区的天津厚蟹、沙蚕、泥螺和青蛤4种底栖动物对沉积物的扰动作用.结果表明：生物扰动对沉积物的分布具有明显影响.不同底栖动物扰动能力不同,对表层沉积物的扰动强度（扩散系数,10^-3 cm²·d^-1）大小依次为：沙蚕（2.95）> 天津厚蟹（1.00）> 青蛤（0.78）> 泥螺（0.35）> 对照（0.05）;对深层沉积物则是天津厚蟹（3.10）>沙蚕（2.33）>青蛤（0.28）>泥螺（0.15）> 对照（0.05）.这种差异主要与不同底栖动物所属的功能群不同有关.底栖动物体积与表层沉积物扩散系数显著相关（P<0.05）,可采用底栖动物体积预测其对沉积物的扰动强度.     

生物扰动对沉积物中污染物环境行为的影响研究进展

生物扰动由于显著改变沉积物结构和性质,进而影响沉积物中污染物的环境行为。综述生物扰动对沉积物中氮、磷、重金属和疏水性有机污染物环境行为的影响。生物扰动促进这些污染物从沉积物向水体释放。生物扰动还对不同的污染物产生其它不同的影响。对于氮,生物扰动还影响其硝化与反硝化作用;对于磷,生物扰动不仅改变其化学形态,还提高有机磷降解。对于重金属,生物扰动还能改变其在沉积物中的分布及化学形态。对于疏水性有机污染物,生物扰动主要增强生物富集和代谢,以及提高生物降解。     

The response of meiofauna and microphytobenthos to engineering effects of fiddler crabs on a subtropical intertidal sandflat

Fiddler crabs are key bioturbators on tidal flats. During their intense bioturbation process, they manipulate large amounts of sediment, altering the physical state of existing materials. We investigated whether different types of sediment bioturbation produced by fiddler crabs modulate meiofaunal assemblages and microphytobenthic content. We hypothesized that sedimentary structures produced by burrowing (the burrow itself and the excavation pellets) and feeding (feeding pellets) generate different microenvironments compared with areas without apparent signs of fiddler crab disturbance, affecting both meiofauna and microphytobenthos, independent of the sampling period. Our results indicate that the engineering effects of burrow construction and maintenance and the engineering effects of fiddler crab foraging modulate meiofaunal assemblages in different ways. Overall, meiofauna from burrows and excavation pellets was more abundant and diverse than at control sites, whereas feeding pellets contained poor meiofaunal assemblages. By contrast, only foraging effects were detected on microphytobenthos; independent of the sampling period, Chl a and phaeopigment content were higher in the feeding pellets, but similar among burrows, excavation pellets and control sites. The present study demonstrates that the different engineering effects of fiddler crabs are an important source of habitat heterogeneity and a structuring agent of meiofaunal assemblages on subtropical tidal flats.