In this study, we quantified the relevance of natural controls (e.g., geology, catchment physiography) on suspended sediment yield (SSY) in headwater streams managed for timber harvest. We collected and analyzed six years of data from 10 sites (five headwater sub-catchments and five watershed outlets) in the Trask River Watershed (western Oregon, United States).
The scientists found that local variability in stream habitat, such as water depth and instream cover, play a greater role in reducing the effects of timber harvest and climate change on trout than previously realized. Instream cover and shade improve trout survival by providing a place to hide from predators.
The importance of multiple processes and instream factors to aquatic biota has been explored extensively, but questions remain about how local spatiotemporal variability of aquatic biota is tied to environmental regimes and the geophysical template of streams. We used an individual-based trout model to explore the relative role of the geophysical template versus environmental regimes on biomass of trout (Oncorhynchus clarkii clarkii). We parameterized the model with observed data from each of the four headwater streams (their local geophysical template and environmental regime) and then ran 12 simulations where we replaced environmental regimes (stream temperature, flow, turbidity) of a given stream with values from each neighboring stream while keeping the geophysical template fixed. We also performed single-parameter sensitivity analyses on the model results from each of the four streams. Although our modeled findings show that trout biomass is most responsive to changes in the geophysical template of streams, they also reveal that biomass is restricted by available habitat during seasonal low flow, which is a product of both the stream’s geophysical template and flow regime. Our modeled results suggest that differences in the geophysical template among streams render trout more or less sensitive to environmental change, emphasizing the importance of local fish–habitat relationships in streams.
Land use and climate change occur simultaneously around the globe. Fully understanding their separate and combined effects requires a mechanistic understanding at the local scale where their effects are ultimately realized. Here we applied an individual-based model of fish population dynamics to evaluate the role of local stream variability in modifying responses of Coastal Cutthroat Trout (Oncorhynchus clarkii clarkii) to scenarios simulating identical changes in temperature and stream flows linked to forest harvest, climate change, and their combined effects over six decades. We parameterized the model for four neighboring streams located in a forested headwater catchment in northwestern Oregon, USA with multi-year, daily measurements of stream temperature, flow, and turbidity (2007– 2011), and field measurements of both instream habitat structure and three years of annual trout population estimates. Model simulations revealed that variability in habitat conditions
among streams (depth, available habitat) mediated the effects of forest harvest and climate change. Net effects for most simulated trout responses were different from or less than the sum of their separate scenarios. In some cases, forest harvest countered the effects of climate change through increased summer flow. Climate change most strongly influenced trout (earlier fry emergence, reductions in biomass of older trout, increased biomass of young-of-year), but these changes did not consistently translate into reductions in biomass over time. Forest harvest, in contrast, produced fewer and less consistent responses in trout. Earlier fry emergence driven by climate change was the most consistent simulated response, whereas survival, growth, and biomass were inconsistent. Overall our findings indicate a host of local processes can strongly influence how populations respond to broad scale effects of land use and climate change.
Our studies of stream invertebrate responses to contemporary timber practices compared treated to control sites prior to and following harvest at Hinkle, Alsea and upper Trask watersheds. In each watershed the BACI study design and robust replication has been crucial in accounting for natural variations in macroinvertebrate distributions while examining patterns of change in response to harvest. As these basins vary physically in association with regional and geologic differences, initially we observed distinctive invertebrate assemblage composition for each watershed. In addition the proportion of chironomid midges and total benthic densities were higher at Alsea and Trask headwaters than at Hinkle. Our ability to detect responses to harvest within basins was enhanced when we found no pre-harvest differences in macroinvertebrate densities, percent chironomids, or taxa richness between control and treatment reaches of similar size at Hinkle and Trask watersheds. However significant invertebrate community differences were observed between the two Alsea tributaries, likely due to differences in tributary sizes or other physical and chemical differences. Though benthic invertebrate densities increased at headwater sites post-harvest, there were no detectable density differences at mainstem sites. Prey consumption by trout, whose densities at mainstem sites increased following harvest, possibly explained the lack of change observed for invertebrate densities.
Paired watershed studies provide valuable scientific understanding of the effects of disturbance on aquatic resources. Geographic information system (GIS) tools, combined with principal components and cluster analyses, were used to develop a landscape classification of forested headwater basins in order to support these paired watershed studies. Spatial and statistical analyses were applied to landform, geologic texture, forest cover, and climate variables that describe the biophysical and climatic setting of forested headwater catchments (300 – 58,000 km2) in western Oregon. Cluster analysis isolated 5 groups that account for major differences in environmental conditions across the landscape, but have a large ratio of among to within group dissimilarity. The first and second principal component axes correlate most strongly to differences in slope and elevation, and the percent coniferous tree cover and past harvest, respectively.
Little is known on the importance of riparian areas to birds near small headwater streams in mesic forests. Progress towards understanding limiting factors that affect bird populations has been difficult because of lack of information beyond the breeding period. I compared bird assemblages between headwater riparian and upland areas throughout the post-breeding period by capturing birds using mist-nets in six paired riparian and upland locations along six headwater streams of the Trask River in northwestern Oregon. In order to assess whether birds prefer headwater riparian areas, I also examined factors affecting habitat selection by juvenile Swainson's thrushes (n=37) using radio telemetry. While riparian and upland locations had similar coarse wood volume and fruiting and tall (> 1.3 m tall) shrub cover, riparian locations had less shrub cover (< 1.3 m tall) and different shrub composition than upland locations. Total capture rate was double that of upland in riparian locations, while bird species richness was similar. Similar numbers of birds were captured in mist-nets oriented perpendicular and parallel to the stream suggesting that birds were not using riparian areas as movement corridors. Adult capture rate was greater in riparian locations than adjacent uplands while results of juvenile capture rates were ambiguous. Riparian locations supported higher capture rates of Swainson's thrushes and winter wrens than adjacent uplands.
At the Sediment Symposium, researchers review and summarize our overall understanding of current scientific knowledge of in-stream sediment. The video archive of the presentations is available.
To view the presentations, please visit this website: http://oregonstate.edu/conferences/event/2013sedimentsummit/videoarchive...
This document presents brief portraits of various aspects of the Trask River study area. For each portrait, there is more information that can be derived from it however, in an effort to at least provide an initial look at the watershed the narrative was kept brief. For example, the section on geomorphology is evolving with the linkage of the terrain map with the channel gradient map to help us predict where we would expect to find more sediment accumulation. This contextual analysis is meant to help bound expected responses to management given the physical and biological template of the watershed. In the next installment I will look in more detail at the small catchments and how they vary. Some of the salient features of the physical and biological Trask Study landscape are summarized below with the more detailed sections following.
In this experimental study, we examined how small increases in summer water temperatures affected aquatic insect growth and autumn emergence. We maintained naturally fluctuating temperatures from 2 nearby streams and a 3rd regime, naturally fluctuating temperatures warmed by 3–5 degrees Celsius, in flow-through troughs from mid-summer until autumn. We added selected abundant Ephemeroptera, Plecoptera, and Trichoptera species to the 3 treatments in late July and observed emergence until early December. We described the taxon-specific responses of the caddisfly Psychoglypha bella and the mayfly Paraleptophlebia bicornuta, both of which survived well in the troughs (67–86%), and the stonefly Mesocapnia projecta, which we did not collect in mid-summer but had colonized all experimental troughs by October. We observed primarily phenological rather than morphological responses to higher water temperatures. The most synchronous emergence of male and female P. bella and P. bicornuta occurred in the trough with the coolest temperatures. Only P. bella emerged asynchronously from the trough with the warmest temperatures. The decreases in synchrony were largely the result of earlier emergence of males. Paraleptophlebia bicornuta were larger and tended towards asynchrony in the trough with water (and temperatures) from their natal stream. Individuals in the trough with the warmest temperature were smaller than individuals in other troughs, but did not but did not emerge earlier.