Sulfate Reduction and Sulfur Cycles at Two Seagrass Beds Inhabited by Cold Affinity Zostera marina and Warm Affinity Halophila nipponica in Temperate Coastal Waters

Bomina Kim,Ayeon Choi,Jung-Ho Hyun,Kun-Seop Lee,Chang-Keun Kang

doi:10.1007/s12237-017-0225-2

Abstract

To evaluate the impact of invading seagrass on biogeochemical processes associated with sulfur cycles, we investigated the geochemical properties and sulfate reduction rates (SRRs) in sediments inhabited by invasive warm affinity Halophila nipponica and indigenous cold affinity Zostera marina. A more positive relationship between SRR and below-ground biomass (BGB) was observed at the H. nipponica bed (SRR = 0.6809 × BGB − 4.3162, r2 = 0.9878, p = 0.0006) than at the Z. marina bed (SRR = 0.3470 × BGB − 4.0341, r2 = 0.7082, p = 0.0357). These results suggested that SR was more stimulated by the dissolved organic carbon (DOC) exuded from the roots of H. nipponica than by the DOC released from the roots of Z. marina. Despite the enhanced SR in spring-summer, the relatively lower proportion (average, 20%) of acid-volatile sulfur (AVS) in total reduced sulfur and the strong correlation between total oxalate-extractable Fe (Fe(oxal)) and chromium-reducible sulfur (CRS = 0.2321 × total Fe(oxal) + 1.8180, r2 = 0.3344, p = 0.0076) in the sediments suggested the rapid re-oxidation of sulfide and precipitation of sulfide with Fe. The turnover rate of the AVS at the H. nipponica bed (0.13 day−1) was 2.5 times lower than that at the Z. marina bed (0.33 day−1). Together with lower AVS turnover, the stronger correlation of SRR to BGB in the H. nipponica bed suggests that the extension of H. nipponica resulting from the warming of seawater might provoke more sulfide accumulation in coastal sediments.

Highlights

Seagrass is the most productive marine flowering plant (Hemminga and Duarte 2000) and is regarded as an ecosystem engineer due to its physical, chemical, and biological influences on coastal environments (Orth et al 2006; Waycott et al 2009; Connolly 2012; Fourqurean et al 2012; Kaldy 2012)
Because the inorganic N and P produced via benthic mineralization in the seagrass bed are a major nutrient source for plant growth (Shorts 1987), organic carbon (Corg) oxidation in seagrass bed plays an important role in carbon and nutrient cycling in coastal environments (Holmer et al 2001; Devereux 2005)
The positive correlations between sulfate reduction rates (SRRs) and belowground biomass (BGB) were stronger at the H. nipponica bed (y = 0.6809x − 4.3162, r2 = 0.9878, p = 0.0006) than at the Z. marina bed (y = 0.3470x − 4.0341, r2 = 0.7082, p = 0.0357) (Fig. 5c)

Summary

Introduction

Seagrass is the most productive marine flowering plant (Hemminga and Duarte 2000) and is regarded as an ecosystem engineer due to its physical, chemical, and biological influences on coastal environments (Orth et al 2006; Waycott et al 2009; Connolly 2012; Fourqurean et al 2012; Kaldy 2012). Because the inorganic N and P produced via benthic mineralization in the seagrass bed are a major nutrient source for plant growth (Shorts 1987), organic carbon (Corg) oxidation in seagrass bed plays an important role in carbon and nutrient cycling in coastal environments (Holmer et al 2001; Devereux 2005). Due to the high sulfate concentration (28 mM) in seawater, sulfate reduction is considered to be among the most important anaerobic Corg mineralization pathways in marine sediments (Blackburn et al 1994; Holmer and Nielsen 1997; Holmer et al 2001; Hyun et al 2007, 2009)

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