To investigate the relationship between biological and physical mixing in forming strata, two systems have been used for comparison, the lower mainstem of Chesapeake Bay and the York River Subestuary. Within the lower Chesapeake Bay two sites were selected as biologically dominated, both are located within the bay stem plains and are characterized by muddy sand and an abundance of large, deep-dwelling organisms. X-radiographs indicate extensive biological reworking of sediments, with no long-term preservation of physical stratification. 210Pb profiles reveal low sediment accumulation rates within the mainstem sites (<0. 1 cm y-1), but significant differences in biological mixing depths (25 vs 40 cm) and biodiffusivity (>80 vs 6-30 cm3 y-1). Within the upper York River, transient, longitudinal sedimentary furrows regularly form within a broad flat portion of the river which comprises a secondary channel. Varying furrow morphologies were observed depending on tidal flow, ranging from: 1) no furrows during the higher flow conditions of spring tide; to 2) large patches of meandering furrows as the mean flow decreases; to 3) large, widely spaced (5-7 m), linear furrows with smaller furrows filling the space between the larger furrows, within a day of neap tide; to 4) uniform, linear, closely spaced (~0.7 m) furrows during the lowest mean current conditions of neap tide. A 35 month time series using kasten cores reveals that although the furrows produce mixing on the 25 cm depth scale on a fortnightly time frame, a signal of mixing exists on the 100 cm depth scale on the annual to interannual time frame which is unrelated to the formation of sedimentary furrows. The seabed throughout most of the energetic, microtidal York River is characterized by deep mixing with depths ranging from 25-200 cm. Throughout the entire river, one side, including the channel, flank and shoal, is dominated by high rates of short-term deposition and physical mixing, the other flank and shoal is dominated by biological mixing and is primarily either non-depositional or erosional. Below Gloucester Point, the north side of the river is dominated by physical processes, above Gloucester Point, the south side is physically dominated. Within the physically dominated side of the river, the mixed layer is characterized by 210Pb profiles with one or more segments of nearly uniform excess activity. X-radiographs reveal that although bioturbation exists, much of the mixed layer is comprised of centimeter to decimeter-scale units of finely to coarsely laminated strata bounded by hiatal surfaces, demonstrating that mixing results primarily from erosion, resuspension and deposition. The benthos in the York River are generally comprised of a depauperate community of small opportunistic species, there is a paucity of larger macrofauna. As a result, mixing in the biologically dominated side of the river is generally restricted to depths <40 cm, 210Pb geochronologies yield low biodiffusion rates (1-3 cm2 y-1) and x-radiographs reveal the presence of some laminations suggesting that although the mixing is controlled by biological process the mixing intensity is low relative to the lower Bay sites. Based on 210Pb geochronologies, residence time estimates for particles within the York River mixed layer are on the order of centuries. The volume and mass of sediments in the physically mixed layer is equivalent to 70 years of river sediment yield. This is consistent with the century scale residence times from core data, suggesting that the sediment within the upper seabed are cycled through the environment on the century time frame.