Effects Of Infauna Research Articles

Direct measurements of acoustic and physical properties in mud and comparison to sediment acoustics models

Sediment acoustics models relate seabed physical properties to acoustic wave speed and attenuation, and direct measurements of sediment acoustic and physical properties provide a means to test such models. We examine direct measurements from two field experiment sites with muddy sediments that contain different ratios of clay, silt, sand, and organic components, comparing the acoustic data with sediment acoustic model predictions using parameters obtained from cores as model inputs. In the New England Mud Patch, sediment sound speed profiles up to several meters below the seabed surface were measured using in situ acoustic probes mounted to a gravity corer. At a second site near Mobile Bay, in situ probe measurements of sound speed, attenuation, and shear speed were obtained in the upper 20 cm of sediment, and diver cores were collected and scanned with an acoustic core logger. Sediments from both sites were analyzed for porosity and grain size distribution. The applicability of various models to the mud found at each site will be discussed, as well as effects of infauna and organic matter, which were also measured, but are not explicitly included in the models. [Work sponsored by ONR.]

Comparison between infauna abundance and seabed geoacoustic properties

To investigate the effects of infauna on seabed geoacoustic properties, a field experiment was conducted during May 2017 in Petit Bois Pass, near the mouth of Mobile Bay, Alabama. In situ measurements of seabed geoacoustic properties were collected using hydrophones to generate and receive compressional waves from 5 kHz to 100 kHz and bimorph transducers to measure shear waves from 300 Hz to 1.5 kHz. The measurement system was deployed multiple times at three distinct sites within the pass, and acoustic measurements were conducted at depths ranging from 5 cm to 20 cm into the sediment. For each deployment of the acoustic system, diver cores were collected. A subset of the cores were sieved on site to collect infauna, and the remaining cores were taken back to the laboratory where they were sectioned and analyzed for porosity and grain size distribution. Comparison between compressional and shear wave speed and attenuation, the sediment geotechnical properties, and the distribution and abundance of infauna...

Biogeochemical heterogeneity and suboxic diagenesis in hemipelagic sediments of the Panama Basin

Early diagenetic processes in hemipelagic sediments of the Panama Basin (∼3900 m) are strongly influenced by an active benthic community and intense bioturbation comparable to organic-rich, shallow water deposits. Rapid reworking enhances the role of suboxic decomposition, particularly Mn cycling, and burrow formation increases biogeochemical heterogeneity as reflected in pore-water profiles. Apparent regular patterns in the distribution of some solutes, such as NH + 4 and Mn 2+, around identifiable burrow structures are consistent with the active irrigation of burrows and a biogenic origin for heterogeneity. The effects of infauna are sufficiently pervasive, relative to the size of normal samples, that similar variations in solute patterns between cores can be observed when samples are separated over wide-ranging spatial scales, from a few centimeters to hundreds of meters. The spatial variation in pore-water solute distributions in samples (cores, passive-equilibration “peepers”) taken during a single cruise is comparable to the interannual variability observed between cruises over a 4 yr period. Mineralized tubes and associated burrow complexes are direct visual evidence for biogenic heterogeneity in these deposits and for a significant interaction between macroinfauna and suboxic microbial communities. Comparison of in situ peeper arrays with cores processed on board ship confirms a variety of retrieval and handling artifacts also inferred in other studies. These appear to be largely related to core warming, promoting lysis of biomass, dissolution of biogenic debris, and irreversibly producing subsurface NH + 4 maxima and increasing concentration gradients of NO - 3, NO - 2, and Si(OH) 4. Agreements and mismatches between solute fluxes predicted from cores, in situ peeper arrays, and a benthic flux incubation chamber are consistent with various retrieval artifacts and with the enhancement of NO - 3 (nitrification) and Si(OH) 4 fluxes by burrow irrigation. Unlike organic-poor, deep-sea deposits from oligotrophic regions, where the sediment–water interface can be the site of most benthic decomposition, subsurface processes are significant in the Panama Basin, and average reaction rate attenuation with sediment depth, is similar to that in bioturbated shallow-water deposits.

Recolonization of sediment-associated microalgae and effects of estuarine infauna on microalgal production

Experiments were performed to determine the rate of recolonization of sediment-associated microalgae and effects of infauna on microalgal biomass and production. Estuarine sediment was defaunated and transplanted to the field and the laboratory. Recolonization of sediment by flora and fauna, relative to control sediment, was measured by chlorophyll a, gross primary production, community Oo uptake and infaunal abundance, sampled at Days 1, 10, and 40. Microalgal colonization in the field was, rapid, with chlorophyll a returning to control levels by Day 10. Infaunal density returned to control levels within 40 d. In the field experiment, the effects of the infauna on the microalgae may have been confounded both by the rapid rate of infaunal recolomzation and by the import of microalgae. The laboratory experiment reduced these problems. Removal of infauna in the laboratory, primarily tanaids, increased sediment-associated microalgal growth. After 40 d, chlorophyll a was 4 times greater and gross primary production 2 times greater in the defaunated sediment than in the controls. Grazing of microalgae by infauna appeared to be the mechanism of control. Patterns of community 0, uptake were difficult to interpret and showed no simple relationship with infaunal density. These experiments indicate that estuarine infauna is one of the factors controlling sedimentassociated microalgal biomass and production.

Effects of infauna on the sediment and seston of a subtidal environment : Young, D. K., 1968/71. Vie Milieu, Suppl. 22: 557–571

Effects of infauna on the sediment and seston of a subtidal environment : Young, D. K., 1968/71. Vie Milieu, Suppl. 22: 557–571