ISSN:
1573-5117
Keywords:
wetlands
;
lake
;
water quality
;
sediment
;
nitrogen
;
phosphorus
;
macrophytes
;
nutrient retention
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract The role of wetland on water quality of rivers was estimated in a natural lake, Grand-Lieu (5600 ha), discharging to the Loire estuary. Inputs of its two tributaries, budgets and retention within the lake for particulate matter (PM), nitrogen (N) and phosphorus (P) were compared during the inflow period (Oct–May), by an input-output study, in two hydrologically contrasted years, 1993–94 with high inflow (292 106 m3), and 1995–96 with low inflow (76 106 m3). Globally the loads per ha were similar for the two tributaries for the same year, with higher values at the beginning of the flows, and total inputs markedly higher in 1993–94. During this year, average loads for the main tributary were 154 kg ha-1 PM, 40 kg ha-1 total N and 1.35 kg ha-1 total P. In the two tributaries, NO3 represented 80% of total N for the two years, and PO4 65% and 44% of total P. Total inputs, total outputs and storages are highly related to annual inflow, with large differences between elements. The highest change of inputs occur for NO2, PO4 and PM, and the lowest for NH4. Storage and outputs of the lake were also much higher in 1993–94, the most important annual differences concerning P storage, and outputs of PM and all forms of nitrogen except NH4. However, only the retention rate of total P doubled with the high outflow of 1993–94 (40% against 18%), while those of PO4 and NH4 were equivalent (79–72% and 72–66% respectively). In contrast the retention rate of all the other elements was lower with the large flow of 1993–94: 61 against 86% for NO3, 85–90% for NO2, 32–60% for total N, and 14–20% for PM. Globally, this wetland received important discharge of inorganic nitrogen from its catchment area, trapping or converting most of it (62–85%) into organic matter, while it exported a large amount of dissolved and particulate organic nitrogen (16 g m-2 y-1 in 1993–94 and 4.5 in 1995–96), 2.6 and 1.9 times more than it received. The exportation of organic N per m2 and retention of total N (9.9–14.5 g m-2 y-1) represent record values. This seems mainly due to the importance of water flow, juxtaposition of habitats with different degree of closure, plant biomass and resuspended endogenous, organic sediments in exportation. The lake is not able to counterbalance the dramatic increase of agricultural and sewage inputs, that induce its eutrophication and silting up.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1017014027788
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