Biological and water quality responses to hydrologic disturbances in third‐order forested streams

Abstract

We compared stream ecosystem responses to two types of disturbances: flood and debris flows. A large storm in February 1996 disturbed four similarly sized sub‐watersheds of the Calapooia River, in the Cascade Mountains of Oregon, USA. All sub‐watersheds had flood and in two, 31 and 81% of the perennial channel, a debris flow affected the channel. For 8 years, we used a suite of approaches: stream temperature, nutrient regime, periphyton and macroinvertebrate assemblages, and resident trout abundance and habitat to evaluate the persistence of instream impacts. Differences in stream temperatures and nitrate‐nitrogen concentrations were evident, probably, due to the removal of vegetation and modification of riparian soils at the debris flow sites. Instream biological responses varied. After the event, fish, including trout, were rare with no fish at the debris flow sites. Within 6 years, trout densities (Oncorhynchus mykiss and Oncorhynchus clarki) were similar and young‐of‐the‐year trouts were common. In contrast, periphyton and macroinvertebrate assemblages differed. Periphyton biomass was lower and nitrogen‐fixing periphyton was more abundant at the debris flow sites. Macroinvertebrate assemblage diversity was higher at the debris flow sites due to fewer dominant taxa. Macroinvertebrate functional feeding groups also differed with fewer gatherers and more scrapers at the debris flow sites. Debris flow impacts related to loss of riparian canopy will probably persist until mature red alder stands are re‐established along stream‐reaches affected by debris flows to provide nitrogen input and shade. Copyright © 2011 John Wiley & Sons, Ltd.

Natural and Anthropogenic Disturbance Influences on Aquatic Biological Diversity in the Pacific Northwest

“…Clearcuts lost canopy, debris flows lost channel roughness and canopy, and high flow disturbances had at least a rearrangement of the substrate. In both clearcuts and debris flows the loss of canopy results in immediate increases in insolation and therefore probably increases stream temperature [15,24] and overall instream production [25]. The change in insolation benefits any taxa better suited to warmer conditions and influences metabolism, including the rate of maturation of instream biota.…”

“…The three studies were: (1) an Oregon Coast Range study focused on impacts of timber harvest (18 sites) [18]; (2) a debris flow study in third-order streams of the Calapooia River (4 sites) where all sites were disturbed by either high flow or debris flow [15]; and (3) a debris flow study in the Chehalis watershed (11 sites) in southwestern Washington following a large storm. From those studies we selected four sites for each disturbance category: mature (M; >50 yrs since harvest); clearcut (CC; mean 2.5 yrs post harvest) from the Coast Range study; and high flow (HF) and debris flow (DF) sites from the Calapooia and Chehalis watersheds (8 yrs and 2 yrs post disturbance).…”

“…We hypothesize that four disturbance treatments will evidence increasing severity in the following order: (1) mature (M) sites were forests more than 50 years of age and neither physical habitat nor thermal conditions were changed; (2) clearcuts (CC) had the entire canopy removed (no remaining shady corridor, but stream bed was not disturbed), changes in thermal conditions have been reported in similar conditions [13,14]; (3) high flow (HF) sites had bed material extensively rearranged and flooded banks, while riparian vegetation remained largely intact [15]; and (4) debris flow (DF) sites had bed, banks, and much of the canopy removed with a subsequent partial deposition of new bed material, but with about 25% bare bedrock as well, extensive changes in both physical habitat and thermal conditions occurred [15]. All of the disturbed treatments had intact forest remnants situated upstream from the disturbance, which we assumed would provide sources for subsequent colonists.…”

The effects of severe flooding on native masu salmon and nonnative rainbow trout in the Atsuta River, Hokkaido, Japan

“…Some limitations of this study involved the luck of the control sites, including the reach-specific variability that was related to the timing of the investigation, and the habitat condition and the underestimation of the effects on environmental factors. In addition, the impacts from debris flow vary depending on the populations, species and environmental characteristics (Detenbeck et al 1992;Swanson et al 1998;Cover et al 2010;Danehy et al 2012). Further studies that are focused on these points should contribute substantially to our understanding of stream habitats and population persistence.…”

“…Debris flow may cause severe reductions in fish populations, alterations of water quality and long-term changes in habitat structure (Carline & McCullough 2003;Cover et al 2010;Danehy et al 2012). In addition, debris flow displaces stream substrates and large woody debris (LWD) that are important for the incubation and survival of eggs and fish as well as alters population age structures.…”