Dynamic patch mosaics and channel movement in an unconfined river valley of the Olympic Mountains

Abstract

SUMMARY1. River valleys resemble dynamic mosaics, composed of patches which are natural, transient features of the land surface produced by the joint action of a river and successional processes over years to centuries. They simultaneously regulate and reflect the distribution of stream energy and exchanges of sediment, wood and particulate organic matter between riparian and aquatic environments. 2. We determined the structure, composition, dynamics and origin of seven patch types at the reach scale in the Queets River valley in the temperate coastal forests of the Olympic Mountains, Washington (U.S.A.). Patch types included: (1) primary and (2) secondary channels; (3) pioneer bars; (4) developing and (5) established floodplains; and (6) transitional and (7) mature fluvial terraces. 3. Lateral channel movements strongly shape patch distribution, structure and dynamics. The primary channel moved laterally 13 m year )1 , on average from 1939 to 2002, but was highly variable among locations and over time. Mean lateral movement rates ranged from 1 to 59 m year )1 and moving averages (2 km) ranged from 3 to 28 m year )1 throughout the valley. 4. Each patch type exhibited characteristic vegetation, soil and accumulations of large wood. Pioneer bars contained peak stem density (69 778 stems ha )1 ) and volume of large wood (289 m 3 ha )1 ). Mature fluvial terraces contained the highest mean stem (1739 m 3 ha )1 ) and canopy volume (158 587 m 3 ha )1 ). These patches also contained the most soil nitrogen (537 kg ha )1 ) and carbon (5972 kg ha )1 ). 5. Patch half-life (the time required for half of the existing patches to be eroded) ranged from 21 to 401 years among forested patch types. Erosion rates were highest in pioneer bars (2.3% year )1 ) and developing floodplains (3.3% year )1 ), compared with only 0.17% year )1 in mature fluvial terraces. New forests formed continually, as pioneering vegetation colonised 50% of the channel system within 18 years, often unsuccessfully. 6. In the Queets River, the structure, composition, and dynamics of the patchy riparian forest depends on the interplay between channel movements and biophysical feedbacks between large wood, living vegetation and geomorphic processes. The cycle of patch development perpetuates a shifting-mosaic of habitats within the river valley capable of supporting diverse biotic assemblages.

Flood Hydraulics and Impacts on Invasive Vegetation in a Braided River Floodplain, New Zealand

“…However, different vegetation types shifted spatially in the floodplain over time, with some areas losing vegetation cover and other areas gaining vegetation. This is consistent with the shifting-mosaic steady state model, which describes how river valleys resemble 'dynamic mosaics', with many 'patches' at different stages of development (Latterell et al, 2006). These patches are 'transient features' which are formed by the river and by patterns of vegetation succession which may occur over long time periods.…”

“…3, No. 1; by 1.4% gain per year, which is consistent with erosion rates of between 0.17% and 3.3% per year calculated by Latterell et al (2006) in their study of the Queets River in the Olympic Mountains of Washington, U.S.A. Few studies have evaluated vegetation removal by large floods in braided river floodplains, particularly impacts on invasive vegetation in these environments. Hickin and Sichingabula (1988) found significant geomorphic changes in a braided reach of the Squamish River (Canada) after a 30-year recurrence interval flood.…”

Pattern, process, and function in landscape ecology and catchment hydrology – how can quantitative landscape ecology support predictions in ungauged basins?

“…Olff et al, 1999;Remmert, 1991;Watt, 1947). Unsurprisingly, this kind of shifting landscape mosaics is also found in hydrologically controlled systems (Bornette and Amoros, 1996;Malard et al, 1999;Latterell et al, 2006).…”

Scaling down hyporheic exchange flows: from catchments to reaches

“…Wood also interacts with groundwater dynamics: debris dams positioned along gaining stream segments have an effect comparable to tight meander bends, driving water into the subsurface, where it travels along short hyporheic flow paths (Lautz et al, 2006;Boano et al, 2006). Interactions between flow and wood also produce spatial heterogeneity in deposits of sediments and organic matter (Gregory et al, 1991;Naiman et al, 2005;Latterell et al, 2006, Sear et al, 2010Osei et al, 2015). Fines and organic rich sediments are retained, eventually driving higher spatial 20 heterogeneity in HEF (Section 5.2 and 6).…”