Characteristics of a Shallow River Plume: Observations from the Saco River Coastal Observing System

Estuaries and Coasts (Impact Factor: 2.54). 07/2011; 34(4):785-799. DOI: 10.1007/s12237-011-9401-y


Interest in the coastal dynamics of river plumes has mainly focused on large rivers, but plumes from the more numerous smaller
rivers have important local consequences and may, in aggregate, be significant contributors to coastal circulation. We studied
the dynamics of the plume from the Saco River in Saco Bay, Gulf of Maine, over a 3-year period. The transport and salinity
in the region are governed by river discharge, tides, winds, and interaction with the Western Maine Coastal Current. The dynamics
of the flow field vary with location within the plume and discharge. The far-field dynamics of the Saco River plume are dominated
by inertial processes (hence qualifying it as a small-scale river plume), during times of low discharge, with low salinity
water present both up and downstream of the river mouth, but are dominated by rotational processes during times of high discharge
(thus qualifying it as a large-scale river plume), with buoyant water primarily advected downshelf. Near-field dynamics are
governed by weak, subcritical flow during low discharge but strongly inertial, supercritical flow during high discharge. Offshore
movement of the plume is not governed by Ekman dynamics but is instead a result of discharge, wind-induced vertical mixing,
and the geography of the coastline and adjacent islands.

KeywordsRiver plumes–Winds–Tides–Discharge–Observations–Estuaries–Shelf dynamics

Download full-text


Available from: Stephan I. Zeeman,
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Continuing pressures from human activities have harmed the health of ocean ecosystems, particularly those near the coast. Current management practices that operate on one sector at a time have not resulted in healthy oceans that can sustainably provide the ecosystem services humans want and need. Now, adoption of ecosystem-based management (EBM) and coastal and marine spatial planning (CMSP) as foundational principles for ocean management in the United States should result in a more holistic approach. Recent marine biogeographical studies and benthic habitat mapping using satellite imagery, large-scale monitoring programs, ocean observation systems, acoustic and video techniques, landscape ecology, geographic information systems, integrated databases, and ecological modeling provide information that can support EBM, make CMSP ecologically meaningful, and contribute to planning for marine biodiversity conservation. Examples from coastal waters along the northeast coast of the United States from Delaware Bay to Passamaquoddy Bay, Maine, illustrate how benthic biogeography and bottom seascape diversity information is a useful lens through which to view EBM and CMSP in nearshore waters. The focus is on benthic communities, which are widely used in monitoring programs and are sensitive to many stresses from human activities.
    Environmental Management 12/2012; DOI:10.1007/s00267-012-9988-1 · 1.72 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The hydrodynamic response, in terms of the competitive stratification-destratification processes and the along- and cross-shore circulation in Thassos Passage, was studied. This passage is a narrow and shallow channel, located in the vicinity of Nestos River mouth, connecting the eastern and western Thracian Seas. Stratification-mixing conditions were studied in terms of the water column potential energy anomaly �, and the quantification of the along- and cross-channel dynamic equation terms, utilizing the results of a regional three-dimensional model. Circulation conditions were assessed by separating the tidal and non-tidal seasonal signals recorded from a bottom-mounted ADCP, and cross-correlating residual circulation to the meteorological influence. Results showed that short-term mixing events, produced under strong south-west winds (8-14 m s-1), and stratification incidents under high river discharge conditions (>100 m3 s-1), may alter the potential energy anomaly of the water column with a time-lag of 3-6 hrs. Such changes were attributed to the along- and cross-channel advective and straining terms, with significant spatial variability, due to the Thassos Island sheltering effect. The along-channel potential energy anomaly flux was computed heading westwards, having a mean value of 22.5 J m-2 s-1. North-northeast winds tend to increase the sub-tidal level in the channel, while south and south-west winds are responsible for its reduction. At the northern part of Thassos Passage, the development of an elongated sandbar enhances frictional effects, favoring the development of a clockwise rotation system, supported further by southern wind events. Cross-correlations of residual flows and wind effects indicated a wind transfer coefficient of 8%, rotating the wind-induced surface flow by 14o rightwards. Overall, the impact of seasonal water column stratification on the water flow of Thassos Passage was limited, due to the reduced Nestos River runoff after its damming.
    Continental Shelf Research 06/2013; DOI:10.1016/j.csr.2013.04.003 · 1.89 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Larvae of most coastal marine invertebrates develop through a series of pelagic stages in the inner shelf regions where they are subject to strong velocity fields, including buoyancy-driven flows from river plumes. Taxon-specific larval behavior can interact with flow fields to determine dispersal trajectories. In this study, we examined the hydrodynamic features of the Saco River plume (in the southwestern Gulf of Maine) from July to August and explored how larval behavior may alter the distribution of mytilid (i.e., Mytilus and Modiolus) bivalve larvae and three genera of brachyuran (Carcinus, Hemigrapsus, and Cancer) crab larvae in and around that plume. Hydrographic surveys (via conductivity-temperature-depth casts) and larval sampling (via plankton tows) were conducted to assess temporal and spatial variation in the horizontal and vertical distribution of larvae. The horizontal extent of the Saco River plume varied little during our study and was governed by both inertial and rotational effects. Late stage mytilid larvae were relatively homogeneously distributed in and out of the plume, while the distribution of brachyuran larvae varied among different locations, species, and larval stages. We conclude that mytilid larvae entered the plume through physical entrainment and/or upward swimming processes and could tolerate salinities associated with the plume (
    Estuaries and Coasts 03/2015; 38(6). DOI:10.1007/s12237-015-9951-5 · 2.54 Impact Factor
Show more