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Effects of light on sediment nutrient flux and water column nutrient stoichiometry in a shallow lake

Spears, Bryan M.; Carvalho, Laurence; Perkins, Rupert; Paterson, David M.. 2008 Effects of light on sediment nutrient flux and water column nutrient stoichiometry in a shallow lake. Water Research, 42 (4-5). 977-986. 10.1016/j.watres.2007.09.012

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Abstract/Summary

The effects of light and temperature on nutrient cycling (silica (Si), nitrogen (N) and phosphorus (P)) between sediments and water and consequent water-column nutrient stoichiometry were assessed in a shallow lake (Loch Leven, Scotland) using a series of intact sediment core incubation experiments. Estimates of actual seasonal dark and light P-fluxes were assessed using 24-hour incubations. Sediment-P uptake was observed in spring (7oC) and release in autumn (12oC) and summer (17oC), with the highest release rates (~17 mg PO4-P m-2 sediment surface area d-1) occurring in summer. In a longer (21 day) experiment in which the effects of light (light (n=6) and dark (n=6)) and temperature (five 4-day cycles to represent: 7oC=>13oC=>23oC=>13oC=>7oC) on water-column nutrient concentrations were assessed, PO4-P, TP, SiO2 and TSi concentrations in the water column were all significantly higher under dark conditions (ANOVA, α = 0.05). NH4-N (ammonium nitrogen) water-column concentrations were observed to be higher under dark conditions at low temperatures and higher under light conditions following a high temperature (23oC) treatment. No significant light effects were observed for water-column total nitrogen (TN) concentration. Flux estimates for all nutrients measured are given. In terms of water-column nutrient stoichiometry, TN:TP ratio was significantly higher under light conditions, TSi:TN was significantly lower under light conditions, and TSi:TP did not vary significantly between the dark and light treatments. The main processes acting to regulate diffusive nutrient release appeared to be photosynthetic elevation of bottom water pH and dissolved oxygen concentration (both significantly higher under light conditions) and possibly also direct microalgal sequestration. This work highlights a feedback mechanism in recovering shallow lakes in which benthic microalgae affect the stoichiometry (to favour P/Si limitation) of the plankton, and also, therefore, of the main source of nutrients to the sediments via disproportionate regulation of sediment P, Si, and N release.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1016/j.watres.2007.09.012
Programmes: CEH Programmes pre-2009 publications > Water
CEH Sections: Watt
ISSN: 0043-1354
Additional Keywords: sediment, phosphorus, nitrogen, silica, flux, lake, light, water column, loch leven
NORA Subject Terms: Agriculture and Soil Science
Biology and Microbiology
Ecology and Environment
Earth Sciences
Chemistry
Date made live: 17 Apr 2008 14:42
URI: http://nora.nerc.ac.uk/id/eprint/2535

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