Modelling water discharges and nitrogen inputs into a Mediterranean lagoon - Impact on the primary production

Type Article
Date 2006-03
Language English
Author(s) Plus MartinORCID1, La Jeunesse I2, Bouraoui F3, Zaldivar J4, Chapelle Annie5, Lazure PascalORCID6
Affiliation(s) 1 : IFREMER, LERAR, F-33120 Arcachon, France.
2 : Univ Catholique Louvain, Dept Geog, B-1348 Louvain, Belgium.
3 : Commiss European Communities, Joint Res Ctr, IES Inland & Marine Waters Unit, I-21020 Ispra, VA, Italy.
4 : Commiss European Communities, Joint Res Ctr, IES Soil & Waste Unit, I-21020 Ispra, VA, Italy.
5 : IFREMER, Ctr Brest, DEL EC, F-29280 Plouzane, France.
6 : IFREMER, Ctr Brest, DEL AO, F-29280 Plouzane, France.
Source Ecological Modelling (0304-3800) (Elsevier), 2006-03 , Vol. 193 , N. 1-2 , P. 69-89
DOI 10.1016/j.ecolmodel.2005.07.037
WOS© Times Cited 55
Keyword(s) Thau lagoon, Primary production, Integrated modelling, Lagoon model, Watershed model
Abstract The Soil and Water Assessment Tool (SWAT model, 2001 Version) has been applied to the Than lagoon catchment area in order to simulate water discharges and nutrient inputs into the lagoon over a 10 years period (1989-1999), and to provide routing inflows to a previously developed lagoon ecosystem model. The watershed model has been calibrated and validated using measured data available for the two main rivers. The results indicate that the mean annual nitrogen inputs into the Thau lagoon is 117 +/- 57 tons y(-1), with the two main rivers, contributing for 80% of total annual nitrogen export. The variations of outputs to the lagoon are nonetheless important from 1 year to another. Due to the local agricultural practices and a reduced in-stream natural depuration, point sources seem to be the main factor affecting the fresh water quality.

The coupling with the lagoon model allowed to estimate the impact of those terrestrial inputs on the lagoon nitrogen cycling and primary productivity. Influence of river discharges makes itself felt essentially near the river outlets. The northern bordure of the lagoon is then characterised by highly variable dissolved inorganic nitrogen concentrations, especially during flood events, while more stable and lower concentrations were simulated in the southern part of the lagoon. Simulated chlorophyll a ranged 1-15 mu g l(-1), with maximums in March. Mean annual phytoplankton production was 364 +/- 142 gC m(-2). The simulations showed that maximum annual productions are due to macrophytes (up to 1300 gC m(-2) y(-1)), but at the whole lagoon scale, annual phytoplankton production resulted greater. From our results it also appeared that the greatest part of primary producers nitrogen requirements is satisfied by nutrient regeneration within the lagoon.
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