Arne E. Skaugset

Local variability mediates vulnerability of trout populations to land use and climate change

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.

Corrected prediction intervals for change detection in paired watershed studies

Abstract Hydrological data may be temporally autocorrelated requiring autoregressive process parameters to be estimated. Current statistical methods for hydrological change detection in paired watershed studies rely on prediction intervals, but the current form of prediction intervals does not include all appropriate sources of variation. Corrected prediction intervals for the analysis of paired watershed study data that include variation associated with covariance and linear model parameter estimation are presented. We provide an example of their application to data from the Hinkle Creek Paired Watershed Study located in the western Cascade foothills of Southern Oregon, USA. Research implications of using the correct prediction limits and incorporating the estimation uncertainty of autoregressive process parameters are discussed. Editor D. Koutsoyiannis Citation Som, N.A., Zégre, N.P., Ganio, L.M. and Skaugset, A.E., 2012. Corrected prediction intervals for change detection in paired watershed studies. Hydrological Sciences Journal, 57 (1), 134–143.

Reducing Sediment Production from Forest Roads During Wet-Weather Hauling

Forest roads produce fine sediment with traffic during wet weather. If the forest road is connected to a stream, it can be a source of turbidity and fine sediment, which may be detrimental to aquatic organisms, especially salmonids. The goal of this work was to investigate turbid runoff during wet-weather use from the pavement of forest roads designed to reduce sediment production. This research tested alternatives for road pavements that were designed specifically to minimize turbid runoff caused by subgrade mixing during wet-weather hauling. Alternative designs of the pavement for unbound aggregate roads influenced the production of sediment, but results were not consistent; the pavement treatments produced different results across different research locations. There was no statistically significant treatment effect. This factor suggested that fine sediment in surface runoff did not originate from the subgrade but rather from the surface aggregate. Road managers who want to minimize the production of sediment from forest roads should be concerned with the unbound aggregate pavement rather than the subgrade. Road segments that developed ruts produced considerably more sediment than road segments where ruts did not form. Thus, to minimize sediment production during wet-weather hauling, managers should design the aggregate pavement to resist rut formation and with consideration of the availability of fine sediment in the aggregate.

Evaluation of Erosion Prediction Models for Forest Roads

Forest roads can be a source of accelerated erosion, which can be detrimental to aquatic habitat, fish, and other aquatic biota. Erosion models are increasingly used to quantify sediment production from forest roads. This project evaluated the efficacy of these models to predict erosion from forest roads. Sediment production was measured from 44 road segments in the humid, temperate rain forests of Oregon and California. Sediment production from these road segments was estimated with four contemporary erosion models: the Washington Road Surface Erosion Model (WARSEM); Sediment Model 2 (SEDMODL2); WEPP:Road, an interface for the Water Erosion Prediction Project Model; and the revised universal soil loss equation (RUSLE). The erosion models consistently overestimated the amount of sediment produced by the road segments by 2 to 8 times. The results were highly variable, and there were considerable differences in erosion estimated by the four models, even for the same road segment. Further, the erosion models could not consistently identify the road segments that were the top sediment producers. It is hypothesized that the regionalized parameters used as inputs for the models do not adequately characterize the hydrology of the individual road segments. In the humid, temperate rain forests of the Pacific Northwest, surface erosion from forest roads is best predicted by the amount of runoff from the road during storms. Thus, research that will better quantify the hydrology of forest roads will provide better information to predict surface erosion from forest roads.

Suspended sediment and turbidity after road construction/improvement and forest harvest in streams of the Trask River Watershed Study, Oregon

Transport of fine-grained sediment from unpaved forest roads into streams is a concern due to the potential negative effects of additional suspended sediment on aquatic ecosystems. Here we compared turbidity and suspended sediment concentration (SSC) dynamics in five nonfish bearing coastal Oregon streams above and below road crossings, during three consecutive time periods (“before”, “after road construction/improvement”, and “after forest harvest and hauling”). We hypothesized that the combined effects of road construction/improvement and the hauling following forest harvest would increase turbidity and SSC in these streams. We tested whether the differences between paired samples from above and below road crossing exceeded various biological thresholds, using literature values of biological responses to increases in SSC and turbidity. Overall, we found minimal increases of both turbidity and SSC after road improvement, forest harvest, and hauling. Because flow is often used as a surrogate for turbidity or SSC we examined these relationships using data from locations above road crossings that were unaffected by roads or forest harvest and hauling. In addition, we examined the association between turbidity and SSC for these background locations. We found a positive, but in some cases weak association between flow and turbidity, and between flow and SSC; the relationship between turbidity and SSC was more robust, but also inconsistent among sites over time. In these low order streams, the concentrations and transport of suspended sediment seems to be highly influenced by the variability of local conditions. Our study provides an expanded understanding of current forest road management practice effects on fine-grained sediment in streams and introduces alternative metrics using multiple thresholds to evaluate potential indicators of biological relevance.

Calculating Discharge from Culverts under Inlet Control Using Stage at the Inlet

Discharge through circular culverts under inlet control can be calculated using several empirical and theoretical methods; however, most methods require knowledge of site-specific characteristics, and some may even require that a rating curve be developed for each individual culvert. This process is onerous and often too time-consuming for land managers. The objective of this study was to identify a simple and accurate method to determine discharge at culverts. In this study, discharge at culverts was measured in forested watersheds using trapezoidal flumes and salt tracer tests and compared to discharge estimated using theoretical and empirically derived equations. The equation that best estimated culvert discharge was determined. This equation requires two variables: the diameter of the culvert and the height of the water at the culvert inlet. While this study used capacitance devices to measure and record stage at the culvert inlet, simple staff gauges or crest gauges could be used to measure water height adequately and subsequently calculate discharge from culverts.

Designing Forest Roads to Minimize Turbid Runoff during Wet Weather Use

Wet weather use on forest roads can be a significant source of turbidity and fine sediment in streams that in turn may be detrimental to aquatic organisms including salmonids. Regulations governing traffic use during wet weather in the Pacific Northwest have become increasingly restrictive with water quality in mind. Current methods of design for forest roads do not consider the environmental performance of roads and little research has been conducted on design methods to minimize sediment production from forest roads.

An Analysis of Opportunity Costs with Wet-Weather Timber Hauling

Abstract Hauling logs during wet weather on low-volume roads can be a significant source of chronic turbidity and fine sediments that maybe detrimental to aquatic organisms including salmonids in streams. As a result, regulations governing wet-weather hauling in the western timber-producing states and British Columbia have become increasingly restrictive. A potential result of the changes in regulations is limited access to an increasing proportion of commercial forestland during the winter months. The cost of restricted hauling and harvesting is potentially a resource that could be made available to improve aggregate road surfaces to minimize hauling restrictions during wet weather. The objective of this research was to investigate the opportunity costs associated with regulatory restrictions for hauling timber on a forest road during wet weather. The regulatory restrictions set forth in the California Forest Practice Rules of 2004 were applied to the MacDonald-Dunn Research Forest at Oregon State University. Historic rainfall data were applied randomly over twenty 20-year simulation periods and harvesting and hauling activities were restricted accordingly. The estimated costs and revenue for a 20-year simulation period without wet-weather restrictions were compared to three management scenarios for harvesting and hauling with wet-weather restrictions to determine the opportunity costs associated with wet-weather restrictions. Dependent on the management scenario, wet-weather restrictions decreased total net revenue for the McDonald-Dunn Research Forest from 1.7 to 18 percent. From this analysis, opportunity costs (and total net revenue decreases) were smallest with the management alternative that involved the overtime use of equipment during periods when hauling and harvesting activities were not restricted.

CHANGES IN STREAM TEMPERATURE AND CANOPY COVER FOLLOWING TIMBER HARVESTING ADJACENT TO NON-FISH BEARING HEADWATER STREAMS

Summer stream temperatures were measured for four years in six headwater streams before four of the streams were clearcut without buffers according to modern forest practice rules. Stream temperatures were monitored for one additional year following the harvest treatment. Percent cover was sampled along the streams before and following harvest and measurements taken after harvest measured shade provided by understory vegetation and logging debris as well as overstory vegetation. Stream temperatures in the four treatment streams responded variably to treatment as compared to the unharvested control streams. Two streams warmed significantly, one stream cooled significantly, and the fourth stream showed no significant change. Before and after stream cover comparisons that considered only overstory vegetation indicated mean changes in cover ranging from 81 to 94% in treatment streams and 3 to 5% in control streams whereas surveys that incorporated cover from understory vegetation and logging slash quantified mean changes in cover ranging from 17 to 42% in treatment streams and 11 to 15% in control streams.

Hydrologic Influences On The Relationship Between Suspended Sediment Concentration and Turbidity

Establishment of total maximum daily loads (TMDLs) in water-bodies is required under the Federal Clean Water Act to meet water quality criteria. Turbidity can be used as a surrogate for suspended sediment concentrations (SSC) to predict sediment load in streams. Real time in situ measurements of turbidity were collected at a stream gauging location in the Coast Range of Oregon from October 2005-June 2006 in conjunction with the collection of individual discrete water samples. The water samples were subsequently analyzed for SSC and turbidity in a laboratory.