ZOOGEOMORPHIC AGENTS IN MID-ATLANTIC FLUVIAL, AEOLIAN, AND COASTAL BIOTOPES

Along with the growing role of humans as geomorphic agents, native or introduced animals exert varying degrees of impact on ground vegetation, sediment cohesion, slope stability, water infiltration, and related critical-zone processes. The historic role of beavers as landscape engineers in fluvial and lacustrine settings often masks the cumulative impact of other animals. Stream bank bioturbation has been the focus of levee protection efforts, but requires more attention by fluvial geomorphologists along sites inhabited by semiaquatic rodents, birds (e.g., bank swallows), and fish (catfish). Along small streams with habitual deer fording sites, hoof penetration may exceed 5 cm, leading to accelerated bank erosion through slumping and focused runoff. Georadar imaging is being increasingly applied as an effective means of non-invasive 2D and 3D characterization of large animal burrows, including northern pine snakes in paraglacial aeolian plains of New Jersey and large (>0.5 m³) rodent burrow complexes in the bluffs of the lower Delaware River. The latter tend to increase the vulnerability of outer terrace segments to storm-induced erosion, mass wasting, and treethrow. On coastal barriers inhabited by ungulates, vegetation removal through natural grazing is compounded by edge-loading action of artiodactyls (deer, boar). At Assateague Island (MD/VA), pediturbation by herds of feral horses results in surface reworking (sediment advection, compaction) that may exceed10,000 m³/hour of activity. Rooting and wallowing produce lasting deflation basins with potential for aeolian reactivation, whereas shallow excavations and burrowing (e.g., nesting estuarine and sea turtles) introduce microtopographic anomalies along intertidal and berm regions. In the supratidal zone, foxes, rodents, and ghost crabs are responsible for extensive excavations (>5,000 cm³/burrow) that may induce localized surface lowering through enlargement and collapse. Although often seasonal and site-specific, the impact of a particular species may leave a long-term legacy, including formation of secondary drainage pathways, erosional reactivation corridors, and biomantles. Therefore, recognition, mapping, and quantification of the rates and extent of biogenic activity must be incorporated into morphodynamic models.