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Microphytobenthos and chironomid larvae attenuate nutrient recycling in shallow‐water sediments
Author(s) -
Benelli Sara,
Bartoli Marco,
Zilius Mindaugas,
VybernaiteLubiene Irma,
Ruginis Tomas,
Petkuviene Jolita,
Fano Elisa Anna
Publication year - 2018
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/fwb.13052
Subject(s) - benthic zone , nutrient , sink (geography) , diel vertical migration , sediment , environmental chemistry , nutrient cycle , pelagic zone , environmental science , ecology , biology , chemistry , paleontology , cartography , geography
In shallow‐water sediments, the combined action of microphytobenthos and bioturbating fauna may differentially affect benthic nutrient fluxes and exert a bottom‐up control of pelagic primary production. In many cases, the effects of microphytobenthos and macrofauna on nutrient cycling were studied separately, ignoring potential synergistic effects. We measured the combined effects of microphytobenthos and chironomid larvae on sediment–water fluxes of gas (O 2 , TCO 2 and N 2 ) and nutrients (NH 4 + , NO 3 − , NO 2 − , PO 4 3 −and SiO 2 ) in shallow‐water sediments of a hypertrophic freshwater lagoon. Fluxes were measured in the light and in the dark in reconstructed sediments with low (L = 600 ind/m 2 ), high (H = 1,800 ind/m 2 ) and no (C) addition of chironomid larvae, after 3 weeks of pre‐incubation under light/dark regime to allow for microalgal growth. Besides flux measurements, pore water nutrient (NH 4 + , PO 4 3 −and SiO 2 ) and dissolved metal concentrations (Fe 2+ and Mn 2+ ) were analysed and diffusive fluxes were calculated. Chironomid larvae increased sediment heterotrophy, by augmenting benthic O 2 demand and TCO 2 and N 2 dark production. However, on a daily basis, treatments C and L were net O 2 producing and N 2 sinks while treatment H was net O 2 consuming and N 2 producing. All treatments were net C sink regardless of chironomid density. Microphytobenthos always affected benthic nutrient exchange, as significantly higher uptake or lower efflux was measured in the light compared with dark incubations. Theoretical inorganic N, P and Si demand by benthic microalgae largely exceeded both dark effluxes of NH 4 + , PO 4 3 −and SiO 2 and their net uptake in the light, suggesting the relevance of N‐fixation, water column NO 3 − and solid‐phase associated P and Si as nutrient sources to benthic algae. Chironomid larvae had a minor effect on inorganic N and P fluxes while they significantly stimulated inorganic Si regeneration. Their bioturbation activity significantly altered pore water chemistry, with a major reduction in nutrient (highest for NH 4 + and lowest for SiO 2 ) and metal concentration. Underlying mechanisms are combinations of burrow ventilation and bioirrigation with stimulation of element‐specific processes as coupled nitrification–denitrification, co‐precipitation and inhibition of anaerobic paths such as Fe 3+ or Mn 4+ reduction or re‐oxidation of their end products. The combined activity of benthic algae and chironomid larvae may significantly attenuate internal nutrient recycling in shallow eutrophic ecosystems, and contribute to the control of pelagic primary production.