Modeling effects of patchiness and biological variability on transport rates within bioturbated sediments

Bioturbation models are typically one-dimensional, with the underlying assumption that tracer gradients are predominantly vertical, and that sediment reworking is laterally homogeneous. These models implicitly assume that bioturbation activity does not vary with horizontal location on the sediment surface. Benthic organisms, however, are often patchily distributed. Moreover, due to natural variability, bioturbation activity varies among individuals within a population, and hence, among bioturbated patches. Here we analyze a 1D model formulation that explicitly includes patchiness, exemplified by conveyor-belt transport. The patchiness is represented with one coefficient αb, as the fraction of bioturbated areas of the total area. First, all the mixed patches are considered to feature the same bioturbation rates. Then variability of these rates among patches is introduced in the model. The model is analyzed through different scenarios to assess the influence of patchiness and biological variability on the resulting tracer profiles (luminophores, 234Th and 210Pb). With patchiness, the principal feature of the resulting profiles is exponential decrease of tracer concentrations near the SWI, due to the accumulation of particles in the nonbioturbated patches, and the presence of subsurface peaks or anomalous concentrations at depth, as the result of particle transport in the bioturbated patches. This pattern is unusual compared to published patterns for conveyor-belt transport. Adding intra-population variability in bioturbation rates induces biodiffusive-like transport, especially with luminophores. This theoretical work provides new insights about the influence of patch structure on particle dispersion within sediments and proposes a new applicable approach to model various bioturbation processes (type and rates of transport) that can be horizontally distributed in sediments

Elaboration of a biotic index of pollution using macroinvertebrates for the monitoring of Lake Nokoué in Benin

A study on the relationships between the physicochemical parameters and of the macroinvertebrates of the Lake Nokoué was carried out for the purpose of developing a biotic index of pollution. A total of 96 stations were prospected twice during the flooding and the dry seasons from September 2004 to February 2006. At each station, seven physicochemical parameters were measured and macroinvertebrates were collected. Canonical analyses of correspondence were used to show the relations between the parameters of the environment and the macroinvertebrates. A self-organizing map (SOM) of Kohonen allows the categorization of the studied stations into four groups according to different degrees of pollution. Rough scores were allotted to each taxon according to its abundance in the various groups of stations determined by the SOM for each campaign. A synthesis of the data obtained from the four field surveys allows the assignment of a score to each taxon according to its abundance in the different groups of stations. A biotic index was developed and used for the evaluation of the level of pollution of the stations studied. It then emerged that the borders of the lake present a «poor quality» of water; however, during the dry season there is slight improvement.© 2015 International Formulae Group. All rights reserved.Keywords: Biotic index, pollution, invertebrates, lagoons, Benin, West Afric

Effects of wastewater treatment plant pollution on in-stream ecosystems functions in an agricultural watershed

We studied the effect of point-source and non-point-source pollution on the retention capacity of the stream and its link with the metabolic state (primary production and respiration) and invertebrates assemblages in a third order Mediterranean stream. Two experimental sites were chosen: one in the upper part of the catchment (Monte´gut site) characterized by low concentrations in nitrate and phosphate and one in the lower part of the catchment (Le´zat site) characterized by high nitrate and phosphorus concentrations. Both experimental sites were located on reaches that included a Waste Water Treatment Plant (WWTP) point nutrient source allowing discussion of the relative effects of point-source and non-point-source nutrients loads on ecosystem function (respiration and uptake rates) and aquatic organism assemblages. NH4 +-N, and PO43x-P uptake rates were determined using solute additions conducted at constant rates (short-term nutrient addition procedure) and NO3 x-N uptake rates were determined using instantaneous solute addition (slug addition procedure). Rates of gross primary production (GPP) and ecosystem respiration were determined using the open system, two-stations diurnal oxygen change method. Benthic invertebrate communities were investigated for species and functional feeding groups diversities measurements. Results show that autotrophy in the river results from nutrients of two distinct origins: point sources for phosphorus (urban area and WWTP) and non-point sources for nitrogen (agricultural zones) with local additions from WWTP inputs. Comparison between the two sites shows that the WWTP did not affect uptake rates, respiration or primary production of the ecosystem in the low-nutrient Monte´gut reach despite increase of invertebrates communities biomass density. Inputs from the WWTP, in the high nitrate and phosphate Le´zat reach, increased respiration, lower benthic biomass and led to changes in the species composition and did not affect uptake rates

Bioturbation effects on bioaccumulation of cadmium in the wetland plant Typha latifolia: A nature-based experiment

The development of efficient bioremediation techniques to reduce aquatic pollutant load in natural sediment is one of the current challenges in ecological engineering. A nature-based solution for metal bioremediation is proposed through a combination of bioturbation and phytoremediation processes in experimental indoor microcosms. The invertebrates Tubifex tubifex (Oligochaeta Tubificidae) was used as an active ecological engineer for bioturbation enhancement. The riparian plant species Typha latifolia was selected for its efficiency in phytoaccumulating pollutants from sediment. Phytoremediation efficiency was estimated by using cadmium as a conservative pollutant known to bioaccumulate in plants, and in itially introduced in the overlying water (20 μg Cd/L of cadmium nitrate – Cd(NO3)2· 4H2O). Biological sedim ent reworking by invertebrates' activity was quantified using luminophores(inert particulates). Our results showed that bioturbation caused by tubificid worms' activity followed the bio-conveying transport model with a downward vertical velocity (V) of luminophores ranging from 16.7 ± 4.5 to 18.5 ± 3.9 cm· year− 1. The biotransport changed the granulometric properties of the surface sediments, and this natural process was still efficient under cadmium contamination. The highest value of Cd enrichment coefficient for plant roots was observed in subsurface sediment layer (below 1 cm to 5 cm depth) with tubificids addition. We demonstrated that biotransport changed the distribution of cadmium across the sediment column as well as it enhanced the pumping of this metal from the surface to the anoxic sediment layers, thereby increasing the bioaccumulation of cadmium in the root system of Typha latifolia. This therefore highlights the potential of bioturbation as a tool to be considered in future as integrated bioremediation strategies of metallic polluted sediment in aquatic ecosystems

Macroinvertebrate community traits and nitrate removal in stream sediments

1. In-stream nitrate removal capacity may be used as a proxy for the ecosystem service of water quality regulation. It is well known that this natural function is driven by abiotic and biotic factors in running water environments. With regard to biotic drivers, most of the literature focuses on the microbial community influences, but there has been very little emphasis on the relationship with the benthic macroinvertebrate community. Since this community feeds on microbial assemblages (autotrophic and/or heterotrophic biofilms) that live on the streambed and in the hyporheic zone of the river, macroinvertebrates also have the potential to influence nitrate removal via its influences on microbiological processes.2. The objective of this study was to examine the potential relationship between the macroinvertebrate communities and nitrate removal. A dataset of in-stream nitrate removal rates measured in nine-third-order streams was analysed. The simultaneous influences of abiotic (hydromorphological, physical and chemical characteristics) and biotic (biofilm and macroinvertebrate) drivers were examined and together explained 56% of the in-stream nitrate removal variance. An analysis of the independent contributions of each driver showed that abiotic drivers (e.g. ammonium, dissolved organic carbon, temperature and transient zone) contributed 40% of this nitrate removal variance, whereas the macroinvertebrate community contributed 39%.3. The potential relationship between macroinvertebrates and nitrate removal was subsequently explored using trait-based approaches of the macroinvertebrate community. This method allows for the selection of trait modalities assuming a top-down control of microbial communities by macroinvertebrates, with in-stream abiotic conditions correlated with nitrate removal (assuming that environmental conditions affect macroinvertebrate community composition).4. The main trait modalities positively correlated with nitrate removal were scraper (feeding habit), flagstones/boulders/cobbles/pebbles (substrate preference), crawler and interstitial (locomotion) and detritus (food). The main modalities negatively correlated with nitrate removal were silt and mud with microphytes (as substrate preference), and with fine sediment with microorganisms, and dead animals (as food sources). These results agreed with the hypothesis of top-down control and enhanced understanding of the influence of hydromorphological factors on nitrate removal.5. This study highlights the involvement of the macroinvertebrate community in in-stream nitrate processing, and demonstrates the usefulness of applying a functional approach to explain relationships between biodiversity and ecosystem function

17. La remédiation naturelle et l’autoépuration des milieux aquatiques

Selon la Directive-cadre sur l'eau (DCE*, 2000), les hydrosystèmes européens doivent avoir atteint le bon état chimique et écologique des masses d’eaux d’ici 2015 et 2027, respectivement. Actuellement, les actions de gestion préconisées en faveur d’une meilleure qualité de l’eau dépassent rarement le niveau de diagnostic et la mise en place des redevances. Mieux comprendre le fonctionnement de la biodiversité de ces hydrosystèmes et leur géomorphologie peut permettre de définir des plans de r..

Rôle de la bioturbation dans le fonctionnement biogéochimique de l'interface eau-sédiment (modélisation de la diversité des transports biologiques et effets sur la diagenèse précoce des sédiments d'une retenue)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF