Evolution of N-balance with qualitative expert evaluation approach.

Pollution of rivers by nitrate is a major issue. Many land use units are considered as net nitrate producers when the input dominates the uptake (e.g. agricultural areas), or in the opposite, net consumers (e.g. wetlands), but the role of their spatial organization and temporal dynamics together across the watershed is unclear. Here, we used a Nitrate-related Ecological Functions (NEF) concept, together with an expert-based analysis in a Geographical Information System, to investigate the role of two opposite landscape types in the nitrate regulation across the Garonne river watershed (France). At any point in a watershed, there is nitrate production (NP) and nitrate removal (NR). The nitrate net balance (NNB) between NP and NR functions can be neutral (NB, Neutral Balance) when nitrate fluxes balance over space and time. The first landscape type, called Actual, was obtained using a set of 7 actual environmental variables, as land cover types, soil organic matter content and wetlands presence. The second landscape type, called Natural, described a non-anthropized landscape, using the same layer types as the Actual landscape. Potentials in NP and NR for each class in each map layer were rated by a set of experts according to their scientific knowledge. NP, NR and by difference, NNB maps were obtained, overlaid and compared to provide an evaluation of the potential for each landscape. In both landscapes, NNB were largely balanced (Actual = 48% and Natural = 67%). In the Actual landscape, NNB were secondly dominated by an imbalance toward NP (43%) and in the Natural landscape secondly imbalanced toward NR (32%). We constructed 'maps of disagreement' between both landscapes to provide a spatially explicit assessment of NNB evolution caused by changing land cover. We found that 67% of the agricultural areas and 60% of the artificial areas of the watershed had been subjected to a loss of nitrate ecological functions from Natural to Actual landscapes. Some management practices able to modify these factors may improve ecological functions and diminish the NEF disagreement of the watershed.

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 phyto-accumulating pollutants from sediment. Phytoremediation efficiency was estimated by using cadmium as a conservative pollutant known to bio-accumulate in plants, and initially introduced in the overlying water (20µg Cd/L of cadmium nitrate - Cd(NO3)2·4H2O). Biological sediment 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±3.9cm·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 1cm to 5cm 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.

Drug residues in urban water: A database for ecotoxicological risk management.

Human-use drug residues (DR) are only partially eliminated by waste water treatment plants (WWTPs), so that residual amounts can reach natural waters and cause environmental hazards. In order to properly manage these hazards in the aquatic environment, a database is made available that integrates the concentration ranges for DR, which cause adverse effects for aquatic organisms, and the temporal variations of the ecotoxicological risks. To implement this database for the ecotoxicological risk assessment (ERA database), the required information for each DR is the predicted no effect concentrations (PNECs), along with the predicted environmental concentrations (PECs). The risk assessment is based on the ratio between the PNECs and the PECs. Adverse effect data or PNECs have been found in the publicly available literature for 45 substances. These ecotoxicity test data have been extracted from 125 different sources. This ERA database contains 1157 adverse effect data and 287 PNECs. The efficiency of this ERA database was tested with a data set coming from a simultaneous survey of WWTPs and the natural environment. In this data set, 26 DR were searched for in two WWTPs and in the river. On five sampling dates, concentrations measured in the river for 10 DR could pose environmental problems of which 7 were measured only downstream of WWTP outlets. From scientific literature and measurements, data implementation with unit homogenisation in a single database facilitates the actual ecotoxicological risk assessment, and may be useful for further risk coming from data arising from the future field survey. Moreover, the accumulation of a large ecotoxicity data set in a single database should not only improve knowledge of higher risk molecules but also supply an objective tool to help the rapid and efficient evaluation of the risk.

Influence of in situ biological activity on the vertical profile of pre-emergence herbicides in sediment.

The in situ effect of biological activity on herbicide degradation was studied in sediment. Early diagenesis indicators of organic matter (OM) was selected to provide information on the presence and the kinetics of the various biotic and abiotic processes involved in the degradation of fresh organic matter, the vector of herbicides in sediment. Two tandem-coring samples were taken in the Malause reservoir, one in the hyperoxic zone (Tarn confluence, MT core) and the other in the central part, under the exclusive influence of the Garonne River (MG core), after having crossed a zone where the high intensity of abiotic processes is proven. At each site, analysis of the vertical profile of the herbicides was coupled with compounds associated with early diagenesis of OM. The MT core proved nearly seven times more contaminated than the MG core. DEA played a minor role in sediment contamination. Biological activity only seems to influence herbicide degradation indirectly. Neither oxygen concentration nor the level of labile carbon indicated any correlation between the consumption of fresh organic matter and substrate degradation. Herbicide transformation thus does not seem to depend on the consortia studied but on physicochemical parameters such as hydrolysis, leading to the long half-life of herbicides in sediment and hence their long-term presence in the aquatic environment.

Herbicide accumulation and evolution in reservoir sediments.

The aim of the present study was to understand the effect of reservoir configurations on sediment pesticide fate. Two dams were selected on the River Garonne, in southwest France: Carbonne and Golfech, both with reservoirs subject to accumulation of herbicide-contaminated sediment. They are situated upstream and downstream respectively of an agricultural and urban area: the Mid-Garonne. The results presented include pesticide concentrations and C/N ratios in the smaller sediment particles (<2 mm) and values of oxygenation and herbicide concentrations in the water. The dynamic behaviour of sediment in the reservoirs is discussed. The present study shows that the theoretical lifespan (weak remanence in vitro) and the results actually observed in the sediment are conflicting. Pesticide contamination in Carbonne indicates conservation, even accumulation, of herbicide molecules while in Golfech transformation processes clearly dominate. The hydromorphological position of Golfech reservoir, i.e. located at the junction of two rivers with contrasting hydrological regimes and very different oxygenation conditions, leads to accelerated pesticide desorption or degradation. Unfortunately, this configuration is rare.

Remobilization and bioavailability of cadmium from historically contaminated sediments: influence of bioturbation by tubificids.

The effects of bioturbation by tubificids on cadmium (Cd) remobilization and bioavailability from sediment were studied throughout two experiments. With bioturbation, particulate Cd was transitorily released into the overlying water, in correlation with sediment resuspension (maximum of 6.1+/-0.1 microg L(-1) after 6 days). Cd bioaccumulation by the bivalve Corbicula fluminea was very limited (maximum of 1.73+/-0.34 microg g(-1), dw), and independent of the algae diet. In contrast, without bioturbation, the release of dissolved Cd increased with the duration of the experiments (maximum of 9.9+/-0.8 microg L(-1) after 36 days). Cd bioaccumulation by C. fluminea varied according to their diet: low bioaccumulation when no algae were added (2.18+/-0.29 microg g(-1), dw), higher bioaccumulation when algae were added throughout the experiment (8.52+/-1.61 microg g(-1), dw), and the highest bioaccumulation when algae were added only during the last 10 days of the experiment (19.66+/-4.63 microg g(-1), dw).

Effects of bioturbation on cadmium transfer and distribution into freshwater sediments.

To investigate bioturbation effects on cadmium (Cd) fluxes from overlying water to sediments, indoor microcosms were developed. The bioturbating organisms were freshwater tubificid worms. Three experimental conditions were studied during 56 d. The three conditions were contaminated water column ([Cd]: 20 microg/L) with or without worms and uncontaminated water column with worms. Cadmium vertical profiles were determined in the pore water and in the sediments, based on six layers (0-0.5, 0.51, 1-2, 2-3, 3-5, 5-12 cm). Dissolved oxygen, manganese, sulfate, and particulate manganese were measured. Bioturbation was analyzed using conservative fluorescent particulate tracers. Bioturbation increased Cd flux into the sediments by close to a factor of two. Scavenging of Cd was more efficient in the bioturbated sediments because particles and adsorption sites for Cd were renewed at the sediment-water interface. Tubificids also increased the thickness of the Cd-enriched layer. Metals adsorbed on particles at the sediment surface were distributed by bioadvection, which predominated the mixing processes. Bioturbation also modified the vertical profiles of dissolved and particulate manganese and dissolved sulfate but not the profiles of dissolved oxygen. These results indicate that the advective transport of particles by bioturbation and their subsequent modification by redox reactions accelerates the trapping of metals in sediments.

Cadmium bioaccumulation in Tubificidae from the overlying water source and effects on bioturbation.

Cadmium bioaccumulation in tubificid oligochaetes in relation to metal vertical distribution in sediment and bioturbation intensity was studied during a 56-day experiment with a constant contamination source in the overlying water (20 microg L(-1)). The indoor microcosms simulate a two-compartment biotope with three experimental treatments based on metal exposure and faunal composition: contaminated water column with or without worms and uncontaminated water column with worms. Cadmium bioaccumulation in worms was studied after 7, 14, 21, 28, and 56 days. Bioturbation was analyzed as a functional parameter representative of organisms' activity and using conservative particulate tracers: luminophores (phi = 63-100 microm and 100-315 microm) and microspheres (phi = 1 microm). The results show no significant effects of cadmium exposure on bioturbation, despite high bioaccumulation levels in worms (50 microg g(-1) dry wt.), suggesting the existence of detoxification/sequestration processes.