Planktonic methane production and oxidation within the algal maximum of the pycnocline: seasonal fine-scale observations in an anoxic estuarine basin

Abstract

High resolution profiles of methane concentration and potential methane-oxidation rates were used to test the importance of in situ production and oxidation in controlling methane structure and dynamics in the southern anoxic basin of the Pettaquamscutt Estuary, Rhode Island, USA. Profiles conducted in both April and August showed low but increasing methane concentrations in the surface oxic layer, a minor maximum about 0.75 m above the Eh = 0 boundary, a methane minimum just above Eh = 0, and a rapid increase to a major maximum about 0.75 m below Eh = 0. Methane concentrations in both maxima increased between April and August while concentrations in the methane minimum decreased. This methane minimum in the suboxic zone was strongly associated with a minor oxygen maximum and a major peak in chlorophyll due to the oxygenic alga Euglena proxima. April incubations in the presence of added oxygen at 2°C supported oxidation rates as high as 9% d-' in and just below the methane minimum at the Eh = 0 boundary, due to psychrophilic methane-oxidation. Similar experiments conducted in August at 22°C showed a similar narrow peak in potential methaneoxidation rates in and just below the methane minimum at the Eh = 0 boundary, suggesting that the boundary was now dynamically controlled by rapid mesophilic methane-oxidation. Analysis of the August incubations at 2°C showed a decline in methane at the depths of the major methane maximum for 4 d, followed by a 4 d increase in methane concentration at the same depths, due presumably to the exhaustion of dissolved oxygen and the cessation of the masking oxidation. These results indicate that the seasonal increase in the major methane maximum is generated Ln situ by psychrophilic methaneproduction, a production that IS largely masked by a concomitant psychrophilic methane-oxidation. The shift from an initial dominance of methane-oxidation to a final dominance of methane-production in the same water sample bottles indicates just how sensitive the structure of the major methane maximum is to the bacterial processes of methanogenesis and methanotrophy, changes in water temperature, and oxygen inputs by in situ primary production and physical intrusions. Such processes have made it bfficult to document a major production of methane in the pycnocllne.

Layered organization in the coastal ocean: An introduction to planktonic thin layers and the LOCO project

“…For example, it has been shown that fish feed preferentially on intense zooplankton thin layers, affecting the depth distribution and behavior of fish in Monterey Bay (Benoit-Bird, in review). While interactions within thin layers are just beginning to be investi gated, thin layers are likely to be important for a variety of biological processes, including growth rates, reproductive success, grazing, predator-prey encounters, nutrient uptake and cycling rates, as well as toxin production (Lasker, 1975;Mullin and Brooks, 1976;Sieburth and Donaghay, 1993;Donaghay and Osborn, 1997;Cowles et al, 1998;Hanson and Donaghay, 1998;Dekshenieks et al, 2001;Rines et al, 2002;McManus et al, 2008). In addition, the layering of the ocean and its plankton species into persistent thin structures acts to diversify and expand available ecological niche space.…”

Dissolved Methane Distribution in the Reloncaví Fjord and Adjacent Marine System During Austral Winter (41°–43° S)

“…3a and 4) is consistently observed to coincide with increased particle accumulation at pycnoclines (Sieburth and Donaghay 1993). Thus, it is believed that these particles may act as anoxic microenvironments, as they are chemical hotspots providing both organic and inorganic substrates to sustain the anaerobic metabolism of pelagic microbiota (Ploug et al 1997).…”

“…Indeed, both autochthonous (plankton) and/or allochthonous (seston) particles can be colonized by decomposers (heterotrophs), which include a proportion of methanogens. Sieburth and Donaghay (1993) reported the existence of methanogenic bacterial consortia that can use methylated amines to create reduced micro-niches in oxygenated seawater and produce both CH 4 and HS − in the u p p e r o c e a n . M e th a n o g e n ic s u b s t r a t e s s u c h a s monomethylamine and trimethylamine, which are constituents of diatoms, dinoflagellates, and flagellate phytoplankton species, could be involved in CH 4 production during grazing by copepods (De Angelis and Lee 1994).…”

Global annual methane emission rate derived from its current atmospheric mixing ratio and estimated lifetime

“…Sieburth and Donaghay, 1993;Zindler et al, 2013), permafrost soil, and wild animals), the difference should have anthropogenic sources such as livestock, rice cultivation, coaling mining, oil and gas, landfills, biomass burning, waste water, and others. However, natural sources have also been influenced by anthropogenic activities like the reduction of the area of natural wetlands or the impact on the permafrost soil.…”

“…Prather et al (2012) estimated for τ CH 4 -OH = 11.2 ± 1.3 years, for τ CH 4 -bacteria = 120 years, for τ CH 4 -strat = 150 years, and for a possible oxidation by atomic chlorine in the marine atmospheric boundary layer 200 years (according to Allan et al, 2007). For the period 1979-1993Dentener et al (2003 calculated for τ CH 4 -OH = 9.0±1.3 years. For the period 1978-2004Prinn et al (2005 estimated a lifetime of 10.2 (+0.9, −0.7) years.…”