SEDIMENTARY REGIME AND CHANNEL CONFINEMENT AS DRIVERS OF RIPARIAN ECOSYSTEM PATTERN AND PROCESS

We explore geomorphic and ecological diversity of riparian corridors in the glaciated surroundings of eastern Lake Erie, through the “process domains” framework (sensu Montgomery 1999), wherein geomorphic patterns are proposed to drive disturbance and succession processes that ultimately structure the ecosystem. The numerous middle-order streams here offer an ideal study system, because they are unified in latitude, elevation, climate, and regional forest ecotype, but vary markedly in local sedimentary and channel environments. Both coarse (massive outwash cobbles and local shale slabs), and fine sediments (cohesive silts and clays) are erosion resistant, and typically yield stable fluvial geomorphology. Conversely, sands and fine gravels are very erodible, and often unstable. Study corridors further present a wide range of confinement, from tightly constrained to broadly underfitted channels. Thus, the river reaches studied here (n = 10) potentially represent six sediment X channel-confinement process domains. Highly erodible fluvial sediments are not common in the old and non-mountainous terrain of the Lower Great Lakes and are typically too dynamic to support vegetational succession beyond pioneer communities. In contrast, coarse sediments dominate gorges draining the Allegheny Plateau (e.g. Zoar Valley Canyon and Chautauqua Gorge, NY), across a wide range of channel confinement. Where channels are confined there is effectively no truly riparian landscape; only gorge slopes and active channel. Where unconfined, however, temporally punctuated and spatially extensive lateral accretion fosters primary vegetational succession, eventually independent of the flood regime. Fine cohesive sediments similarly dominate the lake plains, also representing the full spectrum of confinement. Along unconfined channels (e.g. The Upper Cuyahoga River of NE Ohio) flood waters inundate the riparian zone, but with minimal physical damage, yielding riparian ecology structured by frequency and duration of inundation. Where confined (e.g. the Lake Erie Plain reach of Cattaraugus Creek NY), flood waters can instead produce extensive damage, with flood frequency and severity structuring the ecosystem through serial secondary succession (i.e. response to disturbance).