Effect of Sediment Manipulation on the Biogeochemistry of Experimental Sediment Systems

Abstract

Before biological or biogeochemical experimentation, sediments are often manipulated and defaunated witb tbe use of many different approaches and only modest consideration of treatment effects on sediment biogeochemistry and fluxes. Mesocosm experiments require large quantities of sediment and no standard protocol to defaunate and equilibrate muddy sediments before initiation of experiments has been determined.Using fine-grained sediments, we examined a number of treatments: H) intact witb macroinfauna; (2) intact, macroinfauna individually removed; (3) homogenized surface sediment witb macrofauna; (4) bomogenized deep sediment witbout macroinfauna; and (5) intact deep sediment witbout macroinfauna. In weekly batcb core flux incubations, we measured dissolved oxygen, dinitrogen gas, ammonium (NH,;), nitrate plus nitrite (NO^ f NO,;), silicate (Si), and soluble reactive phospborus (SRP) fluxes over a 5-week period. In addition, we determined porewater ammcmium concentrations over time.Different sediment preparation techniques, witb the same muddy sediment, significantly affected nutrient and gas fluxes, and tbe amount of nutrient and gas fluxes differed between sediment preparation tecbniques. Severely manipulated sediments, sucb as homogenized treatments, had high initial effluxes but eventually equilibrated to lower and more constant nutrient and gas fluxes. Moreover, biogeocbemical flux cbanges for all treatments became similar after about 2 to 3 weeks. Sieved sediments exbibited low fluxes over tbe entire 5-week period, and flux rates did not cbange over time. A feasible method for sediment preparation for mesocosm studies is to use bomogenized deep sediment equilibrated over an almost 2-week period. Overall, sediment preparation and tbe time after sediment manipulation affect sediment biogeochemical processes and must be considered before initiating experiments.

Species-specific effects of two bioturbating polychaetes on sediment chemoautotrophic bacteria

“…Nevertheless, sieving compared to freezing or asphyxiation has been found to be the least disruptive method in regard to the magnitude of the effect and recovery time, both of the microbial community and the geochemical conditions (Porter et al 2006, Stocum & Plante 2006. Manipulated sediments can, however, take between 5 d and 2 wk to reach a steady state or resemble natural biogeochemical conditions (Findlay et al 1990, Kristensen 2001, Porter et al 2006, Stocum & Plante 2006, which suggests that after a short acclimatization period, opportunistic, fast-growing bacteria may be favored in sediments. It is possible that the weeklong acclimatization of the microbial community in our incubations may not have allowed for the complete recovery of the slow-growing microbial community after the initial disturbance of the sediment (i.e.…”

Short-term effects of nereid polychaete size and density on sediment inorganic nitrogen cycling under varying oxygen conditions

“…All sediment samples were collected from a nearshore cove located in the mesohaline region of the Choptank estuary (salinity 8−10) in 1−2 m of water with soft, muddy sediment (Porter et al 2006).…”

“…Sample cores were then defaunated by capping the cores with rubber stoppers and placing them in the dark for 12 h to induce anoxia. After that time, the top 10 cm of sediment was removed from each core along with the macrofauna that had migrated toward the surface in response to low O 2 treatment (Porter et al 2006). In the second experiment, sediments were sieved using a 500-µm sieve to remove infauna and larger material; the sediment slurry was then allowed to settle in 6 buckets (20 l).…”

Effect of tidal resuspension on benthic–pelagic coupling in an experimental ecosystem study

“…The sediment was moved to an outdoor fiberglass tank and covered with black plastic. Sediment was defaunated and prepared using the techniques for large-scale sediment preparation developed by Porter et al (2006) and briefly described below.Mar Ecol Prog SerBefore the start of the experiment, we kept the sediment anaerobic for ≥4 d to remove macrofauna. Then we discarded the top 10 cm of the sediment layer and added the underlying sediment evenly to the 6 mesocosms to form a 10 cm bottom sediment layer.…”