Effects of green macroalgal blooms on intertidal sediments: net metabolism and carbon and nitrogen contents

Abstract

Eutrophication in coastal areas promotes blooms of green macroalgae that accumulate on the sediment, affecting the exchange of mass and energy at the sediment -water interface. The effects of macroalgal blooms on the microbenthic net metabolism and on the carbon and nitrogen contents of the sediment were studied during an in situ experiment. Two sediment enclosures (with and without macroalgae) of 1.5 × 1. ). This relatively low macroalgal biomass always suppressed the photosynthetic activity of microphytobenthos, decreased the oxygen availability for the sediment and reduced the oxygen penetration depth in the light and in the dark. The microbenthic community metabolism clearly shifted to heterotrophic, while the photoautotrophic activity was located in the macroalgal canopy. This macroalgal mat was net autotrophic, and more productive than the microphytobenthic community inhabiting the bare sediment. Part of the macroalgal production was buried in the sediment, increasing its carbon and nitrogen contents with respect to bare sediment during all seasons except spring. Concentrations of inorganic nutrients in the sediment were always higher below the macroalgal mat than in bare sediment, likely due to a direct input of inorganic nitrogen and phosphate associated with macroalgal debris.

Freeze-lysable inorganic nutrients in intertidal sediments: dependence on microphytobenthos abundance

“…O 2 profiles (n = 3 to 4) were measured in the light (800 µmol photons m -2 s -1 ) and in the dark at the sediment -water interface in each of the 6 sediment cores using O 2 microelectrodes (Unisense A/S, Denmark). Net primary production (P n ) and dark respiration (R d ) rates were calculated from the O 2 gradient at the diffusive boundary layer of the light and dark profiles respectively (Kühl et al 1996, García-Robledo et al 2008, Corzo et al 2009). …”

“…Bacteria are able to store large amounts of PO 4 3 -as polyphosphate, and bacteria-associated PO 4 3 -represented a large fraction (up to 80%) of total P in lake sediments (Gachter et al 1988). Large vacuolated sulphuroxidising bacteria are absent in the typical intertidal sediments of Cádiz Bay, due to the relatively low organic matter content and the absence of free sulphide in the sediment (García-Robledo et al 2008, Corzo et al 2009). Therefore, a large contribution of bacteria to the FL-NO 3 -pool is unlikely.…”

“…FL-NH 4 + and FL-PO 4 3 -have also been interpreted as originating mainly from intracellular pools associated with microbial and meiofaunal biomass (Aller 1994, Ferguson et al 2004. High concentrations of FL inorganic nutrients (FL-IN) were found in intertidal sediments below macroalgal mats, released most likely from macroalgal detritus (Corzo et al 2009). However, so far, no specific studies have been carried out to quantify the contribution of the different components of the complex biological community inhabiting the marine sediment to the FL-IN pool.…”

Artificial Top Layer Sediment Resuspension To Counteract Chaetomorpha Linum (Muller) Kutz Blooms In A Eutrophic Lagoon. Three Years Full-Scale Experience

“…If the Chaetomorpha linum mat grows within about the first 20 cm, the underlying part does not carry out photosynthesis and is subject to bacterial attacks [35], to the point that the last decimeter of the mat thickness decays and produces organic mud on the bottom, enriching the sediment in carbon and nitrogen [36] and producing effects on microbial community and processes [37]. The anaerobic mineralization that occurs at the sedimentwater interface releases inorganic nutrients toward the water column [38], such as ammoniun (NH 4 + ) [39], and carbon dioxide (CO 2 ) and orthophosphate (PO 4 3-) [40].…”

Influence of outbreak of macroalgal blooms on phosphorus release from the sediments in Swan Lake Wetland, China

“…The excessive growth of filamentous algae can destroy P concentration equilibrium at the sedimentwater interface, which thus causes modification of P dynamics between the water and sediments (Lavery & McComb 1991;Gomez et al 1998;Corzo et al 2009;García-Robledo & Corzo 2011;Zhang et al 2012). It has been recognized that nutrient exchange between the sediments and macroalgae occurred, and the macroalgae could derive nutrients stored in the sediments to maintain growth in many estuaries (Liere et al 1982;Gomez et al 1998;Boyle et al 2004).…”