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Enhanced weathering of (ultra)basic silicate rocks such as olivine-rich dunite has been proposed as a large-scale climate engineering approach. When implemented in coastal environments, olivine weathering is expected to increase seawater alkalinity, thus resulting in additional CO2 uptake from the atmosphere. However, the mechanisms of marine olivine weathering and its effect on seawater–carbonate chemistry remain poorly understood. Here, we present results from batch reaction experiments, in which forsteritic olivine was subjected to rotational agitation in different seawater media for periods of days to months. Olivine dissolution caused a significant increase in alkalinity of the seawater with a consequent DIC increase due to CO2 invasion, thus confirming viability of the basic concept of enhanced silicate weathering. However, our experiments also identified several important challenges with respect to the detailed quantification of the CO2 sequestration efficiency under field conditions, which include nonstoichiometric dissolution, potential pore water saturation in the seabed, and the potential occurrence of secondary reactions. Before enhanced weathering of olivine in coastal environments can be considered an option for realizing negative CO2 emissions for climate mitigation purposes, these aspects need further experimental assessment.

Foundation species host diverse associated communities by ameliorating environmental stress. The strength of this facilitative effect can be highly dependent on the underlying biotic and abiotic context. We investigated community level patterns of macrofauna associated with and adjacent to the marine foundation species eelgrass (Zostera marina) along a hydrodynamic stress gradient. We could demonstrate that the relative importance of this foundation species for its infaunal community increases with environmental variables associated with increasing hydrodynamic stress (depth, sand ripples formation, sediment grain size and organic content). Faunal assemblages in proximity to the Zostera patch edges, however, showed no (infauna) or negative (epifauna) response to hydrodynamic stress. Our study highlights that the facilitative outcome of a foundation species is conditional to the faunal assemblage in question and can be highly variable even between positions within the habitat.

The Rio Grande Rise is an extensive seamount region in the South-western Atlantic, with potential for deep-sea mining activities in the future. Such activities pose significant long-term disturbances and potentially severe impacts to both ecosystem structure and functioning, as well as associated ecosystem services. The Rio Grande Rise presents a severely understudied area, with very little knowledge on either local and regional scales. Most detailed knowledge available is centered on highly localised geological information and interpolated and/or modelled environmental data, while high-resolution data on biogeography, ecosystem processes and functioning are lacking. The Rio Grande Rise is most likely a remnant of the Parana-Etendeka igneous province, and formed when the African and South-American plates separated to form the Southern Atlantic basin, about 75 million years ago. More recent cruises have generated very local and high-resolution acoustic impedance data on the substrate, showing extremely dense layers, likely to be cobalt-rich crusts and underlying bedrock, interspersed with thick sediment layers. Literature studies revealed that nowadays the Rise appears to be located within a relatively low-productivity oceanic region. Open-database mining yielded large-scale, extrapolated environmental data rasters, which show the Rise to be an oceanic region relatively free of pollution and anthropogenic disturbances, with high geomorphological heterogeneity and potential for high biodiversity. This image was confirmed in a small number of scientific submarine cruises, where a diverse range of seascapes was observed, from soft sediment to carbonate pavement and cobalt crust outcrops. Especially the latter substrata were found to be inhabited by diverse benthic communities, dominated by sessile organisms, presenting three-dimensional structural heterogeneity and with associated vertebrate and invertebrate animals. Cobalt-rich crusts appear to grow at an extremely slow rate of several mm per million years, in the deep ocean where biological and ecological processes such as reproduction, growth and recolonisation are characterised by slow dynamics. The main disturbances posed by deep-sea mining of cobalt-rich crusts on the Rio Grande Rise consist of (1) complete removal of substrate with its particular benthic communities, (2) strong localised increases in suspended particulate matter, causing smothering of breathing apparatus and dilution of food particles, (3) crushing by tailings and overburden and (4) toxicity effects by released metals and other toxic substances, likely to be increased under high pressure. These impacts will likely change the deep-sea ecosystem at the Rio Grande Rise and its functioning for time scales in the order of decades to centuries. State-of-the-art geological, environmental and ecological modelling, complemented with high-quality, fine-resolution data are needed to provide a detailed evaluation of the impacts of cobalt-rich ferromanganese crust mining in the Rio Grande Rise, with the goal to formulate strategic environmental management plans.

Porewater profiles and sediment-water fluxes of oxygen, nutrients, pH, calcium, alkalinity, and sulfide were measured in intertidal sandflat sediments from the Oosterschelde mesotidal lagoon (The Netherlands). The influence of bioturbation and bioirrigation by the deep-burrowing polychaete Arenicola marina on the rates and sources of benthic alkalinity generation was examined by comparing measurements in intact and defaunated sediment cores before and after the addition of A. marina in summer and fall 2011. Higher organic matter remineralization rates, shallower O2 penetration, and greater sediment-water solute fluxes were observed in summer, consistent with higher sediment community metabolic rates at a higher temperature. Lugworm activity stimulated porewater exchange (5.1 × in summer, 1.9 × in fall), organic matter remineralization (6.2 × in summer, 1.9 × in fall), aerobic respiration (2.4 × in summer, 2.1 × in fall), alkalinity release (4.7 × in summer, 4.0 × in fall), nutrient regeneration, and iron cycling. The effects of lugworm activity on net sediment-water fluxes were similar but more pronounced in summer than in fall. Alkalinity release in fall was entirely driven by metabolic carbonate dissolution, while this process explained between 22 and 69% of total alkalinity production in summer, indicating the importance of other processes in this season. By enhancing organic matter remineralization and the reoxidation of reduced metabolites by the sediment microbial community, lugworm activity stimulated the production of dissolved inorganic carbon and metabolic acidity, which in turn enhanced metabolic CaCO3 dissolution efficiency. In summer, evidence of microbial long distance electron transport (LDET) was observed in defaunated sediment. Thus, alkalinity production by net carbonate dissolution was likely supplemented by anaerobic respiration and LDET in summer., Highlights • High alkalinity (TA) production was measured in intertidal Oosterschelde sands. • Alkalinity release was enhanced by the activity of the lugworm Arenicola marina. • Lugworm activity stimulated porewater exchange, carbon, nutrient, and iron cycling. • Metabolic carbonate dissolution was the dominant benthic alkalinity source. • Anaerobic respiration and long distance electron transport produced TA in summer.

Negative emission technologies (NETs) target the removal of carbon dioxide (CO 2 ) from the atmosphere, and are being actively investigated as a strategy to limit global warming to within the 1.5–2°C targets of the 2015 UN climate agreement. Enhanced silicate weathering (ESW) proposes to exploit the natural process of mineral weathering for the removal of CO 2 from the atmosphere. Here, we discuss the potential of applying ESW in coastal environments as a climate change mitigation option. By deliberately introducing fast-weathering silicate minerals onto coastal sediments, alkalinity is released into the overlying waters, thus creating a coastal CO 2 sink. Compared with other NETs, coastal ESW has the advantage that it counteracts ocean acidification, does not interfere with terrestrial land use and can be directly integrated into existing coastal management programmes with existing (dredging) technology. Yet presently, the concept is still at an early stage, and so two major research challenges relate to the efficiency and environmental impact of ESW. Dedicated experiments are needed (i) to more precisely determine the weathering rate under in situ conditions within the seabed and (ii) to evaluate the ecosystem impacts—both positive and negative—from the released weathering products.

Benthic ecosystem engineering organisms attenuate hydrodynamic or biogeochemical stress to ameliorate living conditions. Bioturbating infauna, like the lugworm Arenicola marina, determine intertidal process dynamics by maintaining the sediment oxygenated and sandy. Maintaining the permeability of the surrounding sediment enables them to pump water through the interstitial spaces, greatly increasing the oxygen availability. In a field experiment, both lugworm presence and siltation regime were manipulated to investigate to what extent lugworms are able to cope with sedimentation of increasing mud percentage and how this would affect its ecosystem engineering. Fluorescent tracers were added to experimentally deposited mud to visualise bioturbation effects on fine sediment fractions. Lugworm densities were not affected by an increasing mud percentage in experimentally deposited sediment. Negative effects are expected to occur under deposition with significantly higher mud percentages. Surface chlorophyll a content was a function of experimental mud percentage, with no effect of lugworm bioturbation. Surface roughness and sediment permeability clearly increased by lugworm presence, whereas sediment erosion threshold was not significantly affected by lugworms. The general idea that A. marina removes fine sediment fractions from the bed could not be confirmed. Rather, the main ecosystem engineering effect of A. marina is hydraulic destabilisation of the sediment matrix.

In this study, we investigated the emergence of spatial self‐organized patterns on intertidal flats, resulting from the interaction between biological and geomorphological processes. Autocorrelation analysis of aerial photographs revealed that diatoms occur in regularly spaced patterns consisting of elevated hummocks alternating with water‐filled hollows. Hummocks were characterized by high diatom content and a high sediment erosion threshold, while both were low in hollows. These results highlight the interaction between diatom growth and sedimentary processes as a potential mechanism for spatial patterning. Several alternative mechanisms could be excluded as important mechanisms in the formation of spatial patterns. We developed a spatially explicit mathematical model that revealed that scale‐dependent interactions between sedimentation, diatom growth, and water redistribution explain the observed patterns. The model predicts that areas exhibiting spatially self‐organized patterns have increased sediment accretion and diatom biomass compared with areas lacking spatial patterns, a prediction confirmed by empirical evidence. Our study on intertidal mudflats provides a simple but clear‐cut example of how the interaction between biological and sedimentary processes, through the process of self‐organization, induces spatial patterns at a landscape level.

To assess the role of macrofauna-mediated sediment changes on nematode community recovery, we examined the temporal development of macrobenthos, nematode communities and sediment properties following hypoxia in 16 m2 replicated plots over a 6 mo period. Hypoxia drastically changed nematode community composition (i.e. reduced diversity and abundances of all dominant nematodes, except Odontophora spp.), but complete mortality, as was the case for the macrobenthos, did not occur. Macrofauna diversity recovered slowly, but community composition approached that of control communities after several months. In contrast, nematode diversity recovered to control values within 1 mo but, subsequently, decreased again; hence, no clear convergence towards the control community composition was apparent. This diversity decline and lack of community recovery was mainly attributed to abundance overshoots of the epistrate feeding nematodes Chromadora spp., Daptonema spp. and Ptycholaimellus ponticus in the treatments, which dominated the treatment community after 2 mo. Nematode community reassembling was strongly related to the coupled macrobenthos- environmental temporal development. The dynamics of 2 sediment characteristics, which were both mediated by the colonizing macrobenthos, are presented as possible determinant factors for this relationship: (1) low nematode post-settlement resuspension resulting from stable sediments at early macrofauna recovery stages and (2) enhanced nematode reproduction and settlement success in a dense microphytobenthos mat in relation to the temporal variation in macrobenthos grazing pressure and bioturbation. In conclusion, the strong relationships between macrobenthos recovery, environmental development and nematode community development after hypoxia highlight the importance of macrobenthos-sediment interactions in the recovery and structuring of nematode communities.

The selective processing of sediment fractions (sand and mud; >63 μm and ≤63 μm median grain size) by macrofauna was assessed using two size classes of inert, UV-fluorescent sediment fraction tracers (luminophores). The luminophores were applied to the sediment surface in 16 m2 replicated plots, defaunated and control, and left to be reworked by infauna for 32 days. As the macrofaunal assemblage in the ambient sediment and the control plots was dominated by the common cockle Cerastoderma edule, this species was used in an additional mesocosm experiment. The diversity, abundance and biomass of the defaunated macrobenthic assemblage did not return to control values within the experimental period. Both erosion threshold and bed elevation increased in the defaunated plots as a response to the absence of macrofauna and an increase in microphytobenthos growth. In the absence of macrobenthos, we observed an accretion of 7 mm sediment, containing ca. 60% mud. Image analysis of the vertical distribution of the different luminophore size classes showed that the cockles preferentially mobilised fine material from the sediment, thereby rendering it less muddy and effectively increasing the sand:mud ratio. Luminophore profiles and budgets of the mesocosm experiment under "no waves-no current" conditions support the field data very well. © 2009 Elsevier Ltd. All rights reserved.

Objetivo Realizar un estudio prospectivo multicentrico de seleccion alternante para valorar las perdidas hematicas postoperatorias de la protesis total de rodilla en relacion con el momento de soltar la isquemia, realizando o no hemostasia, y las posibles complicaciones locales y generales. Material y metodo Se analizan 194 pacientes (194 rodillas) distribuidos en dos grupos homogeneos: 1. Grupo I hemostasia (H): se libera el torniquete de isquemia despues de la colocacion de los implantes metalicos, realizando la hemostasia previa al cierre de la herida quirurgica. 2. Grupo II no hemostasia (NH): se coloca la protesis, se realiza el cierre de la herida quirurgica, se coloca vendaje compresivo y en este momento se afloja el manguito neumatico. Resultados El sangrado promedio total del grupo I (H) fue de 721cc. (30-2210) y el del grupo II (NH) fue de 625cc. (60-1540), no existiendo diferencias significativas entre ambos grupos (p = 0,3). No se encuentran tampoco diferencias significativas entre ambos grupos con respecto a las complicaciones locales o generales. Conclusion Las perdidas hematicas postoperatorias no se relacionan directamente con el momento de soltar la isquemia durante las protesis totales de rodilla.

Purpose We conducted a prospective multicenter study with alternate selection methodology in order to evaluate postoperative blood loss further to primary knee replacement at the time of tourniquet release, with or without hemostasis, as well as possible local and systemic complications. Materials and methods We studied 194 patients (194 knees) divided into two similar groups. Group I (Hemostasis - H) - the tourniquet was deflated intraoperatively after implantation of the metal components and hemostasis was achieved prior to wound closure. Group II (No Hemostasis - NH) - the tourniquet was released after the wound was closed and a compressive bandage applied. Results Mean bleeding was 721ml (30-1540) for group I and 625 ml (60-1540) for group II. No statistically significant differences were found (p = 0.3). No significant differences were found between the groups as regards general or local complications. Conclusions Postoperative blood loss is not related directly with the time of tourniquet release further to TKR. Our findings cast certain doubts on the efficacy of tourniquet release, which means that intraoperative hemostasis may not be necessary.

Objetivo Evaluar la incidencia y repercusion de las lesiones e intervenciones previas en la articulacion de la rodilla en pacientes operados de protesis de rodilla. Material y metodo Se registraron 474 pacientes diagnosticados de gonartrosis intervenidos con una protesis total de rodilla (PTR) primaria en 5 centros espanoles, durante 12 meses, analizando sus caracteristicas morfologicas y las lesiones e intervenciones previas sufridas en la articulacion de la rodilla comparado con una poblacion aleatoria de 129 pacientes intervenidos, en los mismos centros y en el mismo periodo de tiempo, de protesis total de cadera (PTC) primaria. En cada paciente analizamos la edad, el sexo, el lado intervenido, el peso, la talla y el indice de masa corporal (IMC: kg/m2), las protesis previas en la articulacion contralateral o en otras articulaciones y el ano de su colocacion. Los parametros evaluados fueron la alineacion de la rodilla, la actividad laboral desempenada previamente y en el momento de la intervencion, la actividad fisica, las enfermedades e intervenciones generales previas a la intervencion, los traumatismos padecidos, las intervenciones en la articulacion de la rodilla y el estado oseo. Resultados No hemos encontrado diferencias estadisticamente significativas entre el grupo PTR y PTC comparando los traumatismos previos, la actividad laboral, las intervenciones del sistema musculoesqueletico previas ni tampoco la alineacion de la rodilla. En el grupo de las PTR no encontramos diferencias estadisticamente significativas entre las lesiones de rodilla previas con la edad, el peso, la talla o el IMC ni entre la tecnica quirurgica previa de la articulacion de la rodilla con la edad, el peso, la talla o el IMC. Sin embargo, en el grupo PTR hubo un mayor numero de lesiones meniscales y un mayor IMC que entre los operados de PTC. Ademas, en las PTR las mujeres presentaron un IMC mayor (p Conclusiones Se constato una correlacion significativa entre artrosis de rodilla y obesidad, y tambien una correlacion baja entre meniscectomia previa y artrosis de rodilla. Por ello, el tratamiento de la obesidad debe ser una medida preventiva de la artrosis de rodilla, y por tanto de los PTR. Los pacientes operados de meniscectomia o rotura de ligamento cruzado anterior deben ser estudiados con mayor detenimiento.

Two species of the genus of large gastropods Cymbium were observed on the tidal flats of the Banc d'Arguin, Mauritania: C. pepo and C. tritonis. Average densities on a flat studied in detail were 0·0009 and 0·0014 individuals per m2, respectively. Both species leave the tidal flats in April and are absent until at least September. Their density on the tidal flats was maximal on sandy sediments. Probably the distribution of their prey species determines the distribution of Cymbium. Prey species observed were the bivalves Anadara senilis (97%), and an occasional Solen vagina and Venerupis sp. The annual predation pressure of Cymbium on intertidal Anadara was estimated to be

Hypoxia represents one of the major causes of biodiversity and ecosystem functioning loss for coastal waters. Since eutrophication-induced hypoxic events are becoming increasingly frequent and intense, understanding the response of ecosystems to hypoxia is of primary importance to understand and predict the stability of ecosystem functioning. Such ecological stability may greatly depend on the recovery patterns of communities and the return time of the system properties associated to these patterns. Here, we have examined how the reassembly of a benthic community contributed to the recovery of ecosystem functioning following experimentally-induced hypoxia in a tidal flat. We demonstrate that organism-sediment interactions that depend on organism size and relate to mobility traits and sediment reworking capacities are generally more important than recovering species richness to set the return time of the measured sediment processes and properties. Specifically, increasing macrofauna bioturbation potential during community reassembly significantly contributed to the recovery of sediment processes and properties such as denitrification, bedload sediment transport, primary production and deep pore water ammonium concentration. Such bioturbation potential was due to the replacement of the small-sized organisms that recolonised at early stages by large-sized bioturbating organisms, which had a disproportionately stronger influence on sediment. This study suggests that the complete recovery of organism-sediment interactions is a necessary condition for ecosystem functioning recovery, and that such process requires long periods after disturbance due to the slow growth of juveniles into adult stages involved in these interactions. Consequently, repeated episodes of disturbance at intervals smaller than the time needed for the system to fully recover organism-sediment interactions may greatly impair the resilience of ecosystem functioning.

Modeling the effect of biota on sediment dynamics is a difficult task. In this paper we re-analyze experimental results of Willows et al. (1998) on the effects of Macoma balthica on sediment erosion. A process-based framework is proposed, fully compatible with a physical description of erosion processes in case of no biogenic influences. The bed is represented by a fluff layer on top of a substrate. A characteristic feature of the framework is that the sediment is represented by a probability density distribution for the critical shear stress, allowing for Type I and Type II erosion. M. balthica increases the sediment mass in the fluff layer. This increase is determined by considering the action radius, the overlap of feeding areas, and the feeding rate per animal. The calibrated action radius and feeding rate were in the range as found in the literature. The distribution of sediment over the erodibility classes and the erosion rate parameter are hardly influenced at all. Due to overlapping feeding areas, the effect is non-linear with density of the animals. The model results are in close agreement with the measured results, suggesting that no further formulations of biological effects are needed to simulate the experiments of Willows et al. (1998) . In nature, other effects like disrupting the biofilm by grazing can be of importance and should be included in a later stage. This study emphasizes the crucial role of sediment availability and the effect of biota on it. This aspect needs more attention in future experiments. The proposed model turned out to work well for the effects of M. balthica and offers opportunities to include other biogenic effects in a process-based way as well.

Bioturbation is one of the major processes influencing ecosystem functioning. Population parameters such as species density, burrow density and species-specific life modes, determine the impact of bioturbation on the ecosystem. A laboratory experiment was developed, using microcosms mimicking a marine intertidal sediment–water interface which allowed for quantification of different population parameters. The vertical redistribution, bioturbation rate and maximum penetration depth of two sizes (41 and 129 µm) of luminophores were measured in five treatments (control, low density of burrows with and without Corophium (1989 ind./m2), and high density of burrows with and without Corophium (14,921 ind./m2)) after 1, 7 and 14 days. Results indicate that the behavioural activities of Corophium are of the utmost importance in sediment reworking, since they contributed to a five-fold increase in bioturbation rate compared to the passive transport induced by the static structure of the burrows. Furthermore, density is an important parameter because only high densities play a prominent role in particle transport and hence in organic matter processing, while the role of low Corophium densities is limited in sediment reworking. No evidence for differentiation in sediment size fractions was observed. Finally, bioturbation rates in this study were low compared to other studies, and these results suggest an influence of the tidal rhythmicity in the behavioural activity of Corophium on the bioturbation rate.

Juvenile growth rate and production of the bivalves Macoma balthica and Cerastoderma edule and the polychaeteNereis diversicolor were investigated on two contrasting tidal flat sediments that represented different recovery stages following disturbance. Juvenile M. balthica and N. diversicolor grew faster and yielded a higher production in the early succession community where fresh microalgal food supply was higher and physical stress was lower in comparison with the mature community, while C. edule recruitment success did not differ between recovery stages. Growth rate responses were positively related to the consumer specific microalgal dietary requirement suggesting the roles of microalgal food availability and interference within the mature community on juvenile feeding efficiency. In addition to the enhanced growth, lower post-settlement dispersal in the more stable sediments of the early succession community also contributed substantially to the higher cohort production ofM. balthica and N. diversicolor at early recovery stages. This study emphasises that the recruitment success of tidal flat macrobenthic juveniles is both context- and trait dependent (i.e. disturbance history and feeding trait). As recruitment is the foundation upon which all subsequent interactions within the community take place, our results illustrate the important role of biotic– physical interactions that affect food supply and sediment stability to tidal flat benthic community dynamics.

Macrobenthos recovery after hypoxia-induced mass mortality was assessed in an estuarine tidal mudflat during 3 years. During the first 2 years, a Pearson-Rosenberg type of community recovery took place along with the improving bottom water oxygen conditions. After 3 months, spionid polychaetes became superabundant (i.e. opportunistic peak), followed rapidly by a steep decline (i.e. ecotone point). Subsequently, a moderate increase in species richness and a steep increase in biomass, related to the growth of long-lived species occurred (i.e. transition region). Afterwards, however, the recovering community diverged again from the ambient, undisturbed, sediments due to enhanced recruitment success of long-lived species presumably resulting from the lowered interference from bioturbation during early recovery stages in the disturbed plots. Hence, despite early community recovery may be more or less deterministic, lagged divergent community reassembling may occur at the longer-term, thereby contributing to benthos patchiness in areas which are frequently subjected to disturbances.

Macrobenthic recolonisation patterns after complete defaunation resulting from experimentally induced hypoxia were investigated in a polyhaline, estuarine mudflat. Based on simultaneous sampling of biotic and environmental variables in replicated 16 m2 control and defaunated plots, with a high resolution in time during 6 mo, the ecological interactions related to the macrobenthos reassembly were elucidated. Colonisation was predominantly determined by juvenile recruitment, and 3 successional stages were identified, each characterised by different species assemblages and environmental characteristics. During recovery, a shift in functional group dominance from mobile surface deposit feeders to tube-dwelling surface deposit feeders to biodestabilising taxa occurred, while their proportional dominance remained quite stable in the control plots throughout the experiment. Species colonisation patterns of later colonists revealed positive interactions with early colonizing opportunistic tube-building polychaetes Pygospio elegans, while later successional species (Heteromastus filiformis, Macoma balthica) adversely affected the stable, favourable conditions created by the tube-building infauna. Transitions between different successional stages were related to recruitment of species, changes in environmental characteristics (oxygenation state of the sediment), direct and indirect ecological interactions (bio[de]stabilisation, exploitation competition for food). In general, our study suggests that macrobenthic reassembly after hypoxia is related to different types of interactions, all acting in a unique manner. Hence, macrobenthic successional dynamics in a tidal mudflat habitat should be considered as a dynamic process, related to resource availability, natural temporal variation, life history traits (e.g. opportunistic behaviour) and bio-engineering capacities of the colonising species.

We assessed the influence of benthic communities on sediment properties in large defaunation experiments in replicated 16 m2 plots on a tidal flat in the Westerschelde estuary (SW Netherlands). We compared microphytobenthos and benthic macrofauna recovery and recolonisation between control and defaunated sediments during 8 mo following the defaunation, focussing on how the temporal scale of biological responses interact with the temporal scale of sedimentological developments (grain size, bed level, erosion threshold). In the first month, microphytobenthos (surface chl a content) increased to >3 times the control values and remained elevated until 3 mo after the start of the experiment. Macrofaunal recovery started with mobile mudsnails after only a few days. Tube-building macrofauna dominated first, followed by surface-disrupting species. Both groups became much more dominant in defaunated than in control plots. Surface pelletisers almost recovered to control levels after 4 mo, while biodiffusing bivalves did not recover during the course of the experiment. Mud content of the sediment surface first increased with chl a, but started to decrease, concomitant with an over-representation of surface disruptors. A similar trend was observed for critical erosion threshold. Bed elevation of experimental plots exceeded controls by several cm after 1 mo, and remained higher through summer. The time scales of changes in microphytobenthos and in abiotic characteristics of the sediment were largely set by the time scale of macrofauna recovery. Macrobenthos plays a critical, but complex role in the dynamics of intertidal sediments.

Summary. — Probable maximal floods of the torrent del Paller (Eastern Pyrenees). Two methods were used to calculate the torrent floods generated by extraordinary rainfalls according to a known return period. The first one is based upon the calculation of the total precipitations in the considered basin. The second one is based upon the measurement of the river bed and hydraulic geometry., Estimació del probable cabal maxim en el « torrent del Paller » (Pirineu axial). La fí del present treball és la de calcular el cabal d'avinguda degut a unes précipiterions extraordinàries i per un période de retorn conegut. S'han utilitzat dos mètodes : un prèn com a dades de partida la quantitat d'aigua precipitada sobre la conca i l'altre es recolza en la geometría hidráulica. El Torrent del Paller que s'ha escollit per fer l'estudi té l'origen en el Puigllançada i desguassa a un tributari del Llobregat. Pel primer mètode s'han utilitzat les dades pluviomètriques de La Molina treballant amb un période de retorn de 50 anys. Es convenient la utilització de la intensitat de la precipitació caiguda en 10 minuts, o com a màxim, en un temps igual al temps de concentrado (de 30 minuts en el nostre cas). Utilitzant l'ajust de Gumbel s'ha obtingut una intensitat de pluja de 86,6 mm/h per un période de retorn de 50 anys. Calculant el cabal pel mètode racional hem obtingut un valor de 23 m3/s. Mitjançant la geometría hidráulica hem contrôlât 18 seccions del curs, en un recorregut de 1012,70 mm, assolint un cabal màxim de 6,56 m3/s, éssent el mitjà de 3 m3/s i a de 1,5 m3/s., Estimación del probable caudal máximo en el Torrent del Paller (Pirineo axial). La finalidad del presente trabajo consiste en calcular el caudal de avenida para precipitaciones extraordinarias con periodo de retorno conocido. Han sido utilizados dos métodos : uno toma como datos de partida la cantidad de agua precipitada sobre la cuenca y, el otro se basa en la geometría hidráulica. La cuenca objeto de estudio es la del Torrent del Paller, (contrafuertes del Pugllançada), vertiendo sus aguas en un afluente del Llobregat. Han sido utilizados datos pluviométricos de la estación de La Molina, trabajando con un período de retorno de 50 años ; es conveniente el uso de la intensidad de precipitación caída en 10 minutos o, como máximo, para un tiempo igual al tiempo de concentración (30 minutos en nuestro caso). Utilizando el ajuste de Gumbel, se ha obtenido una intensidad de lluvia de 86,6 mm/h para un tiempo de recurrencia de 50 años. Calculándose el caudal por el método racional nos da un valor de 23 m3/s. Mediante la geometría hidráulica, se controlan 18 sec- cinoes del cauce del torrente en un recorrido de 1 012,70 m, dándonos un caudal máximo de 6,56 m3/s, siendo el caudal medio de 3 m3/s y a de 1,4 m3/s., Montserrat Jardi F. Estimation du débit maximum probable dans le torrent del Paller (Pyrénées catalanes). In: Revue géographique des Pyrénées et du Sud-Ouest, tome 58, fascicule 1, 1987. Catastrophes. pp. 55-62.

The effect of physical disturbance in the form of trampling on the benthic environment of an intertidal mudflat was investigated. Intense trampling was created as unintended side-effect by benthic ecologists during field experiments in spring and summer 2005, when a mid-shore area of 25 × 25 m was visited twice per month by on average five researchers for a period of 8 months. At the putatively-impacted location (I) (25 × 25 m) and two nearby control locations (Cs) (25 × 25 m each), three sites (4 × 4 m) were randomly selected and at each site, three plots (50 × 50 cm) were sampled after 18 and 40 days from the end of the disturbance. Multivariate and univariate asymmetrical analyses tested for changes in the macrofaunal assemblage, biomass of microphytobenthos and various sediment properties (grain-size, water content, NH4 and NO3 concentrations in the pore water) between the two control locations (Cs) and the putatively-impacted location (I). There were no detectable changes in the sediment properties and microphytobenthos biomass, but was observed. Microphytobenthos and NH4 were correlated at I to the number of footprints, as estimated by the percentage cover of physical depressions. This indicated that trampling could have an impact at small scales, but more investigation is needed. Trampling, instead, clearly modified the abundance and population dynamics of the clam Macoma balthica (L.) and the cockle Cerastoderma edule (L.). There was a negative impact on adults of both species, probably because footsteps directly killed or buried the animals, provoking asphyxia. Conversely, trampling indirectly enhanced recruitment rate of M. balthica, while small-sized C. edule did not react to the trampling. It was likely that small animals could recover more quickly because trampling occurred during the growing season and there was a continuous supply of larvae and juveniles. In addition, trampling might have weakened negative adult-juvenile interactions between adult cockles and juvenile M. balthica, thus facilitating the recruitment. Our findings indicated that human trampling is a relevant source of disturbance for the conservation and management of mudflats. During the growing season recovery can be fast, but in the long-term it might lead towards the dominance of M. balthica to the cost of C. edule, thereby affecting ecosystem functioning.