Microphytobenthos and benthic macroalgae determine sediment organic matter composition in shallow photic sediments
Virginia Institute of Marine Science
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.
COUPLED NITRIFICATION-DENITRIFICATION; COASTAL MARINE-ENVIRONMENT; NITROGEN INCORPORATION; ESTUARINE SEDIMENTS; AMINO-ACIDS; NUTRIENT AVAILABILITY; MICROBIAL COMMUNITY; INTERTIDAL SEDIMENT; CHAETOMORPHA-LINUM; LIPID BIOMARKERS
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This work would not have been possible without the help of M. Luckenbach, S. Fate, and R. Bonniwell at the Virginia Institute of Marine Science (VIMS) Eastern Shore Lab as well as R. Bushnell, J. Cope, E. Ferer, E. Lerberg, D. Maxey, L. Palomo, S. Salisbury, C. Smith, J. Stanhope, and H. Walker at VIMS. We are also grateful to J. Middelburg and M. Houtekamer at the Netherlands Institute for Sea Research (NIOZ). This research was supported by the National Science Foundation (Virginia Coast Reserve Long-Term Ecological Research project 0080381 and 0621014; Division of Environmental Biology (DEB) Ecosystems Program 0542645 to I. C. Anderson and E. A. Canuel and 0542635 to C. R. Tobias), the European Association of Organic Geochemists (Shell Travel Award to A. K. Hardison), the Environmental Protection Agency (EPA FP916722010 to A. K. Hardison), the Netherlands Organization for Scientific Research (Pionier 833.02.2002 to B. Veuger), and the Darwin Center for Biogeology (project 142.16.1052 to B. Veuger). The EPA has not officially endorsed this publication and the views expressed herein may not reflect the views of the EPA. This paper is Contribution No. 3298 of VIMS, The College of Willliam & Mary.
Hardison, A. K., Canuel, E. A., Anderson, I. C., Tobias, C. R., Veuger, B., and Waters, M. N.: Microphytobenthos and benthic macroalgae determine sediment organic matter composition in shallow photic sediments, Biogeosciences, 10, 5571-5588, https://doi.org/10.5194/bg-10-5571-2013, 2013.