Regards croisés sur l'état de la Loire Moyenne : potamoplancton et qualité de l'eau, quel enseignement tirer de 20 années d'études ?

Lair, Nicole

doi:10.1051/hydro:2001002

Cited by 7 publications

(5 citation statements)

References 38 publications

(50 reference statements)

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“…The worsening eutrophication in the VB was the consequence of increasing DIN inputs from the Loire. A similar observation was reported in other coastal ecosystems, such as the Neuse River Estuary (Paerl et al, 2004), Belgian coastal waters (Lancelot et al, 2007) and the Seine Bay (Romero et al, 2013), where decreasing upstream Chl a, due to DIP input reduction, was accompanied by the increase in downstream Chl a, as a result of increasing DIN input. The seasonal change in annual Chl a peak in the VB also resulted from the conjunction of decreasing DIP loads and increasing summer DIN loads from the Loire.…”

Section: Link Between Eutrophication Trajectories In Rivers and In Thsupporting

confidence: 87%

“…This increase in summer DIN is the result of a delayed response due to the long transit time of DIN through soils and aquifers in the Loire catchment (up to 14 years; Bouraoui and Grizzetti, 2011). The decreasing DIN uptake by phytoplankton in the Loire may have also contributed to the increase in summer DIN (Lair, 2001;Floury et al, 2012). Concerning the Vilaine, the slight decrease in DIN from the early 1990s reflects the decrease in N fertilizer application in the Vilaine catchment (Bouraoui and Grizzetti, 2011;Aquilina et al, 2012), which is facilitated by a relatively short transit time of DIN in the Vilaine watershed (∼ 5-6 years; Molenat and Gascuel-Odoux, 2002;Aquilina et al, 2012).…”

Section: Eutrophication Trajectories At the River Basin Outletmentioning

confidence: 99%

“…Despite significant P input reduction, eutrophication persists in some rivers (Bowes et al, 2012;Jarvie et al, 2013), and particularly in downstream coastal ecosystems, where the primary productivity is often limited by N (Ryther and Dunstan, 1971;Paerl, 2018). As freshwater systems drain into coastal waters (Vannote et al, 1980;Bouwman et al, 2013), the efficient P reduction without simultaneous N abatement may result in more N being transported downstream, where it can exacerbate eutrophication problems in coastal ecosystems, delaying recovery (Paerl et al, 2004), for example, the Neuse River Estuary (Paerl et al, 2004), Belgian coastal waters (Lancelot et al, 2007) and the Seine Bay (Romero et al, 2013). Despite more than 20 years of nutrient reduction implementation in European freshwater ecosystems, including rivers (e.g., Nitrates Directive, 91/676/EEC, 1991;Urban Waste Water Treatment Directive, 91/271/EEC, 1991), little measurable progress has been observed in many European coastal waters (EEA, 2017;OSPAR, 2017).…”

Section: Introductionmentioning

confidence: 99%

“…Increased inputs in N and P (and not Si) in aquatic ecosystems can lead to limitation in diatom biomass due to a lack of dissolved silicate (Conley et al, 1993). Therefore, increasing eutrophication may favor the development of non-siliceous algae, such as dinoflagellates and harmful species Lancelot et al, 2007;Howarth et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

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Reduced phosphorus loads from the Loire and Vilaine rivers were accompanied by increasing eutrophication in the Vilaine Bay (south Brittany, France)

et al. 2019

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Abstract. The evolution of eutrophication parameters (i.e., nutrients and phytoplankton biomass) during recent decades was examined in coastal waters of the Vilaine Bay (VB, France) in relation to changes in the Loire and Vilaine rivers. Dynamic linear models were used to study long-term trends and seasonality of dissolved inorganic nutrient and chlorophyll a concentrations (Chl a) in rivers and coastal waters. For the period 1997–2013, the reduction in dissolved riverine inorganic phosphorus (DIP) concentrations led to the decrease in their Chl a levels. However, while dissolved inorganic nitrogen (DIN) concentrations decreased only slightly in the Vilaine, they increased in the Loire, specifically in summer. Simultaneously, phytoplankton in the VB underwent profound changes with increase in biomass and change in the timing of the annual peak from spring to summer. The increase in phytoplankton biomass in the VB, manifested particularly by increased summer diatom abundances, was due to enhanced summer DIN loads from the Loire, sustained by internal regeneration of DIP and dissolved silicate (DSi) from sediments. The long-term trajectories of this case study evidence that significant reduction of P inputs without simultaneous N abatement was not yet sufficient to control eutrophication all along the Loire–Vilaine–VB continuum. Upstream rivers reveal indices of recoveries following the significant diminution of P, while eutrophication continues to increase downstream, especially when N is the limiting factor. More N input reduction, paying particular attention to diffuse N sources, is required to control eutrophication in receiving VB coastal waters. Internal benthic DIP and DSi recycling appears to have contributed to the worsening of summer VB water quality, augmenting the effects of anthropogenic DIN inputs. For this coastal ecosystem, nutrient management strategies should consider the role played by internal nutrient loads to tackle eutrophication processes.

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Section: Link Between Eutrophication Trajectories In Rivers and In Thsupporting

confidence: 87%

Section: Eutrophication Trajectories At the River Basin Outletmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Reduced phosphorus loads from the Loire and Vilaine rivers were accompanied by increasing eutrophication in the Vilaine Bay (south Brittany, France)

et al. 2019

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“…This process, which generally follows a decrease in numbers of algae (Lair et al, 1999), has been shown to be also typical of several other temperate European rivers: the Mosel (Gosselain et al, 1998;Garnier et al, 1999), Rhine (Admiraal et al, , 1994de Ruyter van Steveninck et al, 1992), Seine (Garnier et al, 1995) and the Spree (Ko¨hler, 1993). In the Middle Loire, the appearance of this oxygen deficit was linked to the decrease of the algal density (associated with the increasing flow and the temperature drop) and the maintainence of abundant bacteria, which confirms the responsibility of the primary producers on the water oxygenation during the low water period (Lair & Reyes-Marchant, 2000;Lair, 2002). At the level of 4Ch, the oxygen deficit appeared two weeks later than at the three upstream sites, owing to tributaries fertilizer inputs and higher water temperature (20°C), which would preserve the algal development.…”

Section: Water Composition and Potamoplanktonmentioning

confidence: 63%

Spatio-temporal Investigations on the Planktonic Organisms of the Middle Loire (France), During the Low Water Period: Biodiversity and Community Dynamics

Picard

Lair

2005

Hydrobiologia

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The objective of this work was to analyse the distribution of the planktonic communities involved in the functioning of a 255-km river stretch and to get a better understanding of the influence of the river morphology on the diversity and dynamics of the micro-organisms. The planktonic communities (phytoplankton, bacterioplankton, proto-and metazooplankton) scarcely considered together in fluvial systems, were analysed at four sites of the Middle Loire during the low water period, in parallel to physical and chemical analyses. Physical and chemical variables such as turbidity, pH, suspended matter and chlorophyll a concentration were high, illustrating the classical, productive summer period. The algae played a major role in the water oxygenation until end-summer, then the algal drop concomitant to the bacterial sustained abundance appeared responsible for oxygen depletion. The downstream site enriched by nutrients inputs of two tributaries, carried the highest algal and bacterial densities. Situated in a meanders zone, the Middle Loire is characterised by a high habitat heterogeneity, the up-and downstream sites were wide and spread of vast standing zones and vegetated islands, whereas the two intermediate ones were narrower and more uniform. This morphological variability strongly impacted the micro-organisms diversity and distribution. Indeed, the algae and zooplankton composition were clearly influenced by the physical habitats of the river, the Cyanophyta were favoured by the lentic conditions and the Bacillariophyta by the turbulent ones, while the young stage of copepod and the large rotifer predators were indicator of a lentic origin. Thereafter, the river heterogeneity interfered with the zooplankton dynamics, the standing conditions enhancing the rotifer predation. In that way, we hypothesise that two opposite patterns characterised the wide sites spread of lentic water and the more uniform channels. In the first case, the zooplankton could prey on the ciliates protozoan, which in return favoured the flagellate ones; conversely in the second situation the zooplankton limited by the physical constraints did not impact the ciliates which could depress the flagellates. Thus, the similar geomorphology of the distant upstream and downstream sites (255-km apart) induced relatively close organisms distribution. Hence, disagreeing with the river continuum concept, this assertion shows the strong influence played by the local morphological characteristics of the Middle Loire in potamoplankton composition and dynamics.

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Continental Atlantic Rivers

Descy¹

2009

Rivers of Europe

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Regards croisés sur l'état de la Loire Moyenne : potamoplancton et qualité de l'eau, quel enseignement tirer de 20 années d'études ?

Cited by 7 publications

References 38 publications

Reduced phosphorus loads from the Loire and Vilaine rivers were accompanied by increasing eutrophication in the Vilaine Bay (south Brittany, France)

Reduced phosphorus loads from the Loire and Vilaine rivers were accompanied by increasing eutrophication in the Vilaine Bay (south Brittany, France)

Spatio-temporal Investigations on the Planktonic Organisms of the Middle Loire (France), During the Low Water Period: Biodiversity and Community Dynamics

Continental Atlantic Rivers

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