Investigating Peatland Stratigraphy and Hydrogeology Using Integrated Electrical Geophysics

Hydrology has been suggested as the mechanism controlling vegetation and related surficial pore-water chemistry in large peatlands. Peatland hydrology influences the carbon dynamics within these large carbon reservoirs and will influence their response to global warming. A geophysical survey was completed in Caribou Bog, a large peatland in Maine, to evaluate peatland stratigraphy and hydrology. Geophysical measurements were integrated with direct measurements of peat stratigraphy from probing, fluid chemistry, and vegetation patterns in the peatland. Consistent with previous field studies, ground-penetrating radar (GPR) was an excellent method for delineating peatland stratigraphy. Prominent reflectors from the peat-lake sediment and lake sediment-mineral soil contacts were precisely recorded up to 8 m deep. Two-dimensional resistivity and induced polarization imaging were used to investigate stratigraphy beneath the mineral soil, beyond the range of GPR. We observe that the peat is chargeable, and that IP imaging is an alternative method for defining peat thickness. The chargeability of peat is attributed to the high surface-charge density on partially decomposed organic matter. The electrical conductivity imaging resolved glaciomarine sediment thickness (a confining layer) and its variability across the basin. Comparison of the bulk conductivity images with peatland vegetation revealed a correlation between confining layer thickness and dominant vegetation type, suggesting that stratigraphy exerts a control on hydrogeology and vegetation distribution within this peatland. Terrain conductivity measured with a Geonics EM31 meter correlated with confining glaciomarine sediment thickness and was an effective method for estimating variability in glaciomarine sediment thickness over approximately 18 km(2). Our understanding of the hydrogeology, stratigraphy, and controls on vegetation growth in this peatland was much enhanced from the geophysical study.

Partners for Life: A Brittle Star and Its Octocoral Host

Throughout the New England and Corner Rise seamounts of the western North Atlantic Ocean, several ophiuroid species are conspicuously epizoic on octocorals. One species, Ophiocreas oedipus, was found only on the chrysogorgiid octocoral Metallogorgia melanotrichos. Colonies of M. melanotrichos were collected from 11 seamounts during expeditions in 2003, 2004, and 2005 at depths between 1300 and 2200 m. O. oedipus is obligately associated with M. melanotrichos, leading a solitary existence on all octocorals observed. Evidence suggests that a young brittle star settles directly on a young octocoral and the 2 species then grow, mature, and senesce together. The brittle star benefits directly by being above the bottom for suspension feeding and is passively protected by the octocoral, but the latter, as far as we have been able to determine, Seems neither to benefit nor be disadvantaged by the relationship.

Early Life History and a Modeling Framework for Lobster (Homarus Americanus) Populations in the Gulf of Maine

Beginning in the late 1980s, lobster (Homarus americanus) landings for the state of Maine and the Bay of Fundy increased to levels more than three times their previous 20-year means. Reduced predation may have permitted the expansion of lobsters into previously inhospitable territory, but we argue that in this region the spatial patterns of recruitment and the abundance of lobsters are substantially driven by events governing the earliest life history stages, including the abundance and distribution of planktonic stages and their initial settlement as Young-of-Year (YOY) lobsters. Settlement densities appear to be strongly driven by abundance of the pelagic postlarvae. Postlarvae and YOY show large-scale spatial patterns commensurate with coastal circulation, but also multi-year trends in abundance and abrupt shifts in abundance and spatial patterns that signal strong environmental forcing. The extent of the coastal shelf that defines the initial settlement grounds for lobsters is important to future population modeling. We address one part of this definition by examining patterns of settlement with depth, and discuss a modeling framework for the full life history of lobsters in the Gulf of Maine.