Sea level rise increases the frequency and intensity of storm surges and extreme tidal events in coastal freshwater wetlands. Seawater affects soil biogeochemical processes by inducing osmotic stress and stimulating SO^^" reduction. The objective of this study was to determine the mechanism by which salinity alters C mineralization rates by quantifying the relative importance of ionic stress, compared with the addition of the SO^^" electron acceptor, on the production of CO2 and CH^. A batch incubation study measured potential anaerobic respiration and methanogenesis with time in a freshwater wetland soil exposed to varying concentrations (3.5,14, and 35 g kg" ) of seawater or salt (NaCI) solutions. Seawater addition induced a short-term (2-wk) stimulation of COj production (20-32% greater than the freshwater control) and a continuous suppression of CH^ production (up to 94% less than freshwater). Ionic stress (represented by NaCI) did not reduce CO2 production at all but did decrease CH. production for 2 wk in both the 14 and 35 g kg" NaCI treatments. Our results indicate that microbial populations rebound quickly from ionic stress. The intrusion of dilute seawater (3.5 g kg" ') to freshwater wedands can accelerate organic C mineralization through the short-term increase in SO^ "-induced respiration without inhibiting methanogenesis. Overall, the organic C mineralization rate was 17% higher for 3.5 g kg" ' seawater than the freshwater control. The temporary nature of the microbial response suggests that "pulses" of seawater may have a greater influence on the rate of C cycling in freshwater wetlands than a gradual sea level rise.Abbreviations: MBC, microbial biomass carbon; OC, extractable organic carbon; TOC, total extractable organic carbon.

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Organic matter decomposition regulates rates of carbon loss (CO 2 and CH 4 ) in wetlands and has implications for carbon sequestration in the context of changing global temperature. Here we determined the influence of temperature and vegetation type on both aerobic and anaerobic decomposition of organic matter in subtropical wetland soils. As in many other studies, increased temperature resulted in higher rates of respiration and methanogenesis under both aerobic and anaerobic conditions, and the positive effect of temperature depended on vegetation (source of carbon substrate to soil). Under anaerobic incubations, the proportion of gaseous C (CO 2 and CH 4 ) lost as CH 4 increased with temperature indicating a greater sensitivity of methanogenesis to temperature. This was further supported by a wider range of Q 10 values (1.4-3.6) for methane production as compared with anaerobic CO 2 (1.3-2.5) or aerobic CO 2 (1.4-2.1) production. The increasing strength of positive linear correlation between CO 2 :CH 4 ratio and the soil organic matter ligno-cellulose index at higher temperature indicated that the temperature sensitivity of methanogenesis was likely the result of increased C availability at higher temperature. This information adds to our basic understanding of decomposition in warmer subtropical and tropical wetland systems and has implications for C models in wetlands with different vegetation types.

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Restoration can be viewed as the process of reestablishing both exogenous drivers and internal feedbacks that maintain ecosystems in a desirable state. Correcting exogenous and abiotic drivers is clearlynecessary, but may be insufficient to achieve desired outcomes in systems with self-organizing biotic feedbacks that substantially influence ecological stability and timing of responses. Evidence from a broad suite of systems demonstrates the prevalence of biotic control over key ecosystem attributes such as hydroperiod, nutrient gradients, and landform that are most commonly conceived of as exogenously controlled. While a general theory to predict conditions under which biotic controls exert such strong feedbacks is still nascent, it appears clear that the Greater Everglades/South Florida landscape has a high density of such effects. The authors focus on three examples of biotic control over abiotic processes: hydroperiod and discharge controls exerted by peat accretion in the ridge-slough landscape; phosphorus (P) gradients that emerge, at least in part, from interactions between accelerated peat accretion rates, vegetation structure and fauna; and reinforcing feedbacks among land elevation, aquatic respiration, and carbonate dissolution that produce local and landscape basin structure. The authors propose that the unifying theme of biogeomorphic landforms in South Florida is low extant topographic variability, which allows reciprocal biotic 395 Downloaded by [UOV University of Oviedo] at 03:50 14 October 2014 396 M. J. Cohen et al.modification of local site conditions via mechanisms of peat accretion (including via effects of landscape P redistribution on primary production) or limestone dissolution. Coupling these local positive feedbacks, which drive patch expansion, with inhibitory or negative feedbacks on site suitability at distance, which serve to constrain patch expansion, provide the mechanistic basis for landscape pattern formation. The spatial attributes (range and isotropy) of the distal negative feedback, in particular, control pattern geometry; elucidating the mechanisms and properties of these distal feedbacks is critical to restoration planning.