Distinguishing natural evolution and human impact on estuarine morpho-sedimentary development: A case study from the Vilaine Estuary, France

Abstract

Estuaries are coastal areas controlled by hydrodynamic factors such as sea-level changes, waves and tidal currents, and river discharge. This study focuses on the Vilaine Estuary which M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT27/06/2015, page 2/38 is strongly impacted by human activity after construction of Arzal dam in 1970. The purpose of this research is to differentiate the role of natural from anthropogenic factors on sediment dynamics within the Vilaine Estuary. We are proposing a hypothetical model based on the hydrodynamic modification and morpho-sedimentary development by analyzing the natural estuarine evolution and the impact of human alteration to the natural system by utilizing datasets including river discharge, tidal currents, winds and wave activities to further combine with photographic, bathymetric, topographic and sedimentary surveys.Results show that waves carry sediment from the sea and rework local sediments. The river damming is reducing the tidal prims and leads to the fall of tidal currents. This new situation supports the sediment deposition and reduces at the same time the accommodation space which decrease tidal currents in feed-back. The Vilaine Estuary is therefore coming close to a bay-type functioning which leads to a channel narrowing, a drastic increase of the tidal flat zone, an acceleration of erosional processes affecting the main channel, salt marsh and all associated depositional systems. We propose a hypothetical model showing that this evolution took place in two steps and we show that the dam has an effect to accelerate a natural infilling of the estuary.

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

“…Their catchment areas are dominated by agricultural activity, sustaining two-thirds of the national livestock and half the cereal production (Bouraoui and Grizzetti, 2008;Aquilina et al, 2012). The Arzal dam, 8 km from the mouth of the Vilaine, was constructed in 1970 to regulate freshwater discharge and prevent saltwater intrusion (Traini et al, 2015). The two studied rivers, especially the Loire, are the main nutrient sources in the northern Bay of Biscay, which includes the VB (Guillaud et al, 2008;Ménesguen et al, 2018a).…”

“…Chl a concentrations were measured with either spectrophotometry or fluorimetry. Microscopic quantitative micro-phytoplankton analyses in coastal waters were conducted on Lugol-fixed samples and counted according to Utermöhl (1958). Phytoplankton identification and counts were carried out for organisms whose size is > 20 µm (i.e., micro-phytoplankton) and smaller species with chain structure.…”

Seasonal and Intra-Annual Patterns of Sedimentary Evolution in Tidal Flats Impacted by Laver Cultivation along the Central Jiangsu Coast, China

“…Presently, studies relating to the impact of human activities on the sediment, hydrodynamics and ecological environment of tidal flats have concentrated on (1) artificial reclamation [16][17][18][19][20][21][22], (2) artificial introduction of plants [23][24][25][26], (3) seawall construction and repair [27][28][29] and (4) harbor and wind farm construction [30,31]. Despite significant interest, the effect of artificial seafood cultivation on the geomorphic evolution process has not been sufficiently studied and lacks thorough analysis due to the difficulty of data acquisition.…”

Evolução sedimentar do estuário do rio Capibaribe (Recife-PE) nos últimos 200 anos e suas relações com a atividade antrópica e processo de urbanização

“…Impactos antrópicos modificam o equilíbrio ambiental natural de várias maneiras como o desenvolvimento urbano, a agricultura e as mudanças hidrológicas que causam alterações na composição sedimentar e na introdução de poluentes (ZOURARAH et al, 2007;TRAINI et al, 2015). Estas interferências antrópicas são registradas durante os processos de sedimentação nos ambientes costeiros (JHA et al, 2003;SWARZENSKI et al, 2008, DÍAZ-ASENCIO et al, 2009).…”