Document Type

Article

Department/Program

Virginia Institute of Marine Science

Publication Date

2013

Journal

BIOGEOSCIENCES

Volume

10

Issue

8

First Page

5571

Last Page

5588

Abstract

Microphytobenthos and benthic macroalgae play an important role in system metabolism within shallow coastal bays. However, their independent and interactive influences on sediment organic matter (SOM) are not well understood. We investigated the influence of macroalgae and microphytobenthos on SOM quantity and quality in an experimental mesocosm system using bulk and molecular level (total hydrolyzable amino acids, THAA; phospholipid linked fatty acids, PLFA; pigment) analyses. Our experiment used an incomplete factorial design made up of two factors, each with two levels: (1) light (ambient vs. dark) and (2) macroalgae (presence vs. absence of live macroalgae). Over the course of the 42-day experiment, total organic carbon (TOC) and total nitrogen (TN) increased under ambient light by 173 +/- 14 and 141 +/- 7 %, respectively, compared to in the dark (78 +/- 29 and 39 +/- 22 %). THAA comprised a substantial fraction of SOM (similar to 16% of TOC, 35% of TN) and followed TOC and TN accumulation patterns. Mole percent composition of the THAA pool indicated that SOM was composed of more labile organic material (e. g., L-glutamic acid, phenylalanine) under ambient light conditions while SOM in dark treatments was more degraded, with higher proportions of glycine and D-alanine. PLFA content, which represents viable biomass, made up similar to 1% of TOC and contained high levels of algal fatty acids in the light, particularly PLFA derived from diatoms. In the presence of microphytobenthos (i.e., light and macroalgae treatments), SOM lability increased, resulting in the observed increases in bacterial PLFA concentrations. Macroalgae, which were added to half of the light treatments, decreased SOM accumulation compared to light treatments without macroalgae, with TOC and TN increasing by only 130 +/- 32 and 94 +/- 24 %, respectively. This decrease likely resulted from shading by macroalgae, which reduced production of microphytobenthos. The presence of macroalgae decreased SOM lability as well, which resulted in diminished buildup of bacterial biomass. By the final day of the experiment, principal component analysis revealed that sediment composition in treatments with macroalgae was more similar to dark treatments and less similar to light treatments without macroalgae. Overall, microphytobenthos and benthic macroalgae fundamentally altered SOM quality and quantity, which may have notable ecological consequences for shallow-water systems such as increased hypoxia/anoxia, sulfide accumulation, enhanced mineralization and/or stimulated denitrification.

DOI

10.5194/bg-10-5571-2013

Keywords

COUPLED NITRIFICATION-DENITRIFICATION; COASTAL MARINE-ENVIRONMENT; NITROGEN INCORPORATION; ESTUARINE SEDIMENTS; AMINO-ACIDS; NUTRIENT AVAILABILITY; MICROBIAL COMMUNITY; INTERTIDAL SEDIMENT; CHAETOMORPHA-LINUM; LIPID BIOMARKERS

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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