LONG-TERM PATTERNS OF WATER QUALITY IN A MANAGED WATERSHED IN OREGON: 1. SUSPENDED SEDIMENT1

The cumulative effects of forest management activities on water quality at a downstream point were monitored from 1972-1980 during development of a watershed for timber resources. Suspended sediment concentration and turbidity were measured at two hydrologic stations which bracketed a 10-km reach of the Middle Santiam River in the Western Cascades of Oregon as it flowed through an 8000-ha block of intensively managed forest land. Slope failures often accompany road building and harvesting in steep forested watersheds and pose the most serious threat to water quality. Although 180 km of road were constructed and 3400 ha of old-growth forests were harvested from slopes averaging over 60 percent, long-term changes in sediment yields remained undetectable during the period of measurement. The geologic characteristics of the basin and the road construction and maintenance techniques as prescribed by Oregon's forest practice regulations helped to minimize the occurrence of slope failures so that long-term changes in suspended sediment export rates did not occur. Throughout the nine-year measurement period, seven slope failures which added sediment directly to streams produced measurable short-term responses at the downstream sampling location, but these erosion events were too small and too infrequent to produce long-term changes in sediment yield from the watershed.     

Direct and Indirect Effects of Forest Harvesting on Sediment Yield in Forested Watersheds of the United States

Managed forests generally produce high water quality, but degradation is possible via sedimentation if proper management is not implemented during forest harvesting. To mitigate harvesting effects on total watershed sediment yield, it is necessary to understand all processes that contribute to these effects. Forest harvesting best management practices (BMPs) focus almost exclusively on overland sediment sources, whereas in‐and‐near stream sources go unaddressed although they can contribute substantially to sediment yield. Thus, we propose a new framework to classify forest harvesting effects on stream sediment yield according to their direct and indirect processes. Direct effects are those caused by erosion and sediment delivery to surface water from overland sources (e.g., forest roads). Indirect effects are those caused by a shift in hydrologic processes due to tree removal that accounts for increases in subsurface and surface flows to the stream such that alterations in water quality are not predicated upon overland sediment delivery to the stream, but rather in‐stream processes. Although the direct/indirect distinction is often implicit in forest hydrology studies, we have formalized it as a conceptual model to help identify primary drivers of sediment yield after forest harvesting in different landscapes. Based on a literature review, we identify drivers of these effects in five regions of the United States, discuss current forest management BMPs, and identify research needs.     

A Depth‐Proportional Intake Device for Automatic Water Samplers1

Abstract: This paper describes the construction and testing of a device for pumping water samplers that collects suspended sediment samples by moving the intake vertically to keep it at the same proportion of flow depth. The device uses a simple sprocket mechanism that can be mounted vertically on the downstream side of culverts and bridge pilings to protect against damage from floating debris during storms. Suspended sediment samples collected from an urban stream with the depth‐proportional device were compared with manual samples taken with a depth‐integrated sampler. Scatter in the relationship between pumped and manual samples (R² = 0.76) are probably explained by horizontal variability in concentrations, poor mixing associated with lateral sediment inputs from construction site erosion, the downstream orientation of the intake, and the failure of the concentration at 60% of the flow depth to match the average vertical concentration.     

Research Gaps Related to Forest Management and Stream Sediment in the United States

Water quality from forested landscapes tends to be very high but can deteriorate during and after silvicultural activities. Practices such as forest harvesting, site preparation, road construction/use, and stream crossings have been shown to contribute sediment, nutrients, and other pollutants to adjacent streams. Although advances in forest management accompanied with Best Management Practices (BMPs) have been very effective at reducing water quality impacts from forest operations, projected increases in demand for forest products may result in unintended environmental degradation. Through a review of the pertinent literature, we identified several research gaps related to water yield, aquatic habitat, sediment source and delivery, and BMP effectiveness that should be addressed for streams in the United States to better understand and address the environmental ramifications of current and future levels of timber production. We explored the current understanding of these topics based on relevant literature and the possible implications of increased demand for forest products in the United States.     

EVALUATION OF HYDROLOGIC MODELING TECHNIQUES FOR FOREST LAND MANAGEMENT PLANNING1

ABSTRACT: A growing concern for environmental quality paralleled with increasing demands on our forest resources has prompted the Washington State Department of Natural Resources to evaluate simulation modeling as a technique for analyzing management decisions in terms of their environmental effects. The evaluation focused on a system of integrated models developed at the University of Washington which simulate processes and activities within the forest ecosystem. A major part of the system is a hydrologic model which predicts changes in discharge, stream temperature, and concentrations of suspended sediment and dissolved oxygen based on information generated by other models representing intensive management practices. The evaluation consisted of applying the system to a 72,000 acre tract of forest land, validating the models with two years of discharge and water quality data from a 93,000 acre watershed, and determining the pertinence of hydrologic modeling for management purposes. Results show several potential uses of hydrologic modeling for forest management planning, especially for analyzing the effects of timber harvesting strategies on water quality.     

Temporal and Spatial Turbidity Patterns Over 30 Years in a Managed Forest of Western Washington1

Abstract: Forest practices have progressively changed over the last 30 years in the Pacific Northwest to address water quality concerns. There have been some assessments of these new management practices made at a site scale but very few studies have attempted to evaluate their efficacy at reducing cumulative sediment production at a watershed scale. Such an evaluation is difficult due to the spatial and temporal variability in sediment delivery and transport processes. Due to this inherent variability, detecting a response to management changes requires a long‐term data record. We utilized a water quality dataset collected over 30 years at four locations in the Deschutes River watershed (western Washington) to assess trends in turbidity and whether sediment control procedures implemented over this time period had any detectable influence. The sample sites ranged from small headwater streams (2.4 and 3.0 km²) to the mainstem of the Deschutes River (150 km²). Declining trends in turbidity were detected at all the permanently monitored sites. The mainstem Deschutes River site, which integrates sediment processes from the entire study watershed, showed dramatic declines in turbidity even with continued active forest management. For the small basins, logging and road construction occurred in the 1970s and 1980s and turbidity declined thereafter, achieving prelogging levels by 2000. There are no temporal trends in flow that could be responsible for the observed trends in turbidity. Our results suggest that increased attention to reducing sediment production from roads and minimizing the amount of road runoff reaching stream channels has been the primary cause of the declining turbidity levels observed in this study.     

Estimating bulk density in vertically exposed stoney alluvium using a modified excavation method

Despite many decades of education and refining land-use practices, accelerated stream bank erosion is still prevalent in the United States. Eroding stream banks produce a sediment load to the riverine system and can cause reduced water quality as a result of increased suspended sediment. As total maximum daily loads (TMDLs) for water bodies impaired by turbidity or suspended sediments become more numerous, a simple, in situ field technique will be needed to estimate the bulk density of readily erodible stream bank material so that reasonably accurate sediment loading rates can be estimated. In this study, the excavation/polyurethane-foam technique for estimating total bulk density was applied to vertically exposed alluvium with high coarse-fragment content. Though not previously attempted in vertically exposed alluvium with high coarse-fragment content, the excavation/polyurethane-foam technique appears to provide a reasonably accurate estimate of the total and soil (<2-mm size fraction) bulk density from vertically exposed, alluvial deposits with high coarse-fragment content (i.e., >70%) along eroding stream banks. Obtaining bulk density estimates using this method would facilitate calculation of sediment loading rates to riverine systems with actual field data.     

FOREST PRACTICES AS NONPOINT SOURCES OF POLLUTION IN NORTH AMERICA1

ABSTRACT: Forest management activities may substantially alter the quality of water draining forests, and are regulated as nonpoint sources of pollution. Important impacts have been documented, in some cases, for undesirable changes in stream temperature and concentrations of dissolved oxygen, nitrate-N, and suspended sediments. We present a comprehensive summary of North American studies that have examined the impacts of forest practices on each of these parameters of water quality. In most cases, retention of forested buffer strips along streams prevents unacceptable increases in stream temperatures. Current practices do not typically involve addition of large quantities of fine organic material to streams, and depletion of streamwater oxygen is not a problem; however, sedimentation of gravel streambeds may reduce oxygen diffusion into spawning beds in some cases. Concentrations of nitrate-N typically increase substantially after forest harvesting and fertilization, but only a few cases have resulted in concentrations approaching the drinking-water standard of 10 mg of nitrate-NIL. Road construction and harvesting increase suspended sediment concentrations in streamwater, with highly variable results among regions in North America. The use of best management practices usually prevents unacceptable increases in sediment concentrations, but exceptionally large responses (especially in relation to intense storms) are not unusual.     

Using turbidity and acoustic backscatter intensity as surrogate measures of suspended sediment concentration in a small subtropical estuary

The suspended sediment concentration is a key element in stream monitoring, although the turbidity and acoustic Doppler backscattering may be suitable surrogate measures. Herein a series of new experiments were conducted in laboratory under controlled conditions using water and mud samples collected in a small subtropical estuary of Eastern Australia. The relationship between suspended sediment concentration and turbidity exhibited a linear relationship, while the relationships between suspended sediment concentration and acoustic backscatter intensity showed a monotonic increase. The calibration curves were affected by both sediment material characteristics and water quality properties, implying that the calibration of an acoustic Doppler system must be performed with the waters and soil materials of the natural system. The results were applied to some field studies in the estuary during which the acoustic Doppler velocimeter was sampled continuously at high frequency. The data yielded the instantaneous suspended sediment flux per unit area in the estuarine zone. They showed some significant fluctuations in instantaneous suspended mass flux, with a net upstream-suspended mass flux during flood tide and net downstream sediment flux during ebb tide. For each tidal cycle, the integration of the suspended sediment flux per unit area data with respect of time yielded some net upstream sediment flux in average.     

BIOECONOMIC ANALYSIS OF SELECTED CONSERVATION PRACTICES ON SOIL EROSION AND FRESHWATER FISHERIES1

ABSTRACT: Farmers can generate environmental benefits (improved water quality and fisheries and wildlife habitat), but they may not be able to quantify them. Furthermore, farmers may reduce their incomes from managing lands to produce these positive externalities but receive little monetary compensation in return. This study simulated the relationship between agricultural practices, water quality, fish responses to suspended sediment and farm income within two small watersheds, one of a cool water stream and one of a warm water stream. Using the Agricultural Drainage and Pesticide Transport (ADAPT) model, this study related best management practices (BMPs) to calculated instream suspended sediment concentrations by estimating sediment delivery, runoff, base flow, and streambank erosion to quantify the effects of suspended sediment exposure on fish communities. By implementing selected BMPs in each watershed, annual net farm income declined $18,000 to $28,000 (1 to 3 percent) from previous levels. “Lethal” fish events from suspended sediments in the cool water watershed decreased by 60 percent as conservation tillage and riparian buffers increased. Despite reducing suspended sediments by 25 percent, BMPs in the warm water watershed did not reduce the negative response of the fisheries. Differences in responses (physical and biological) between watersheds highlight potential gains in economic efficiency by targeting BMPs or by offering performance based “green payments.”     

SUSPENDED SEDIMENT DYNAMICS IN SMALL FOREST STREAMS OF THE PACIFIC NORTHWEST1

This paper reviews suspended sediment sources and transport in small forest streams in the Pacific Northwest region of North America, particularly in relation to riparian management. Mass movements, reading and yarding practices, and burning can increase the supply of suspended sediment. Sediment yields recovered to pre‐harvest levels within one to six years in several paired catchment studies. However, delayed mass movements related to roads and harvesting may produce elevated suspended sediment yield one or more decades after logging. There is mixed evidence for the role of streamside tree throw in riparian buffers in supplying sediment to streams. Harvesting within the riparian zone may not increase suspended sediment yield if near stream soils are not disturbed. Key knowledge gaps relate to the relative roles of increased transport capacity versus sediment supply, the dynamics of fine sediment penetration into bed sediments, and the effects of forest harvesting on suspended sediment at different scales. Future research should involve nested catchments to examine suspended sediment response to forest practices at multiple spatial scales, in combination with process‐based field studies.     

EFFECTIVENESS OF TIMBER HARVEST PRACTICES FOR CONTROLLING SEDIMENT RELATED WATER QUALITY IMPACTS1

ABSTRACT: Timber harvest best management practices (BMPs) in Washington State were evaluated to determine their effectiveness at achieving water quality standards pertaining to sediment related effects. A weight‐of‐evidence approach was used to determine BMP effectiveness based on assessment of erosion with sediment delivery to streams, physical disturbance of stream channels, and aquatic habitat conditions during the first two years following harvest. Stream buffers were effective at preventing chronic sediment delivery to streams and physical disturbance of stream channels. Practices for ground‐based harvest and cable yarding in the vicinity of small streams without buffers were ineffective or only partially effective at preventing water quality impacts. The primary operational factors influencing BMP effectiveness were: the proximity of ground disturbing activities to streams; presence or absence of designated stream buffers; the use of special timber falling and yarding practices intended to minimize physical disturbance of stream channels; and timing of harvest to occur during snow cover or frozen ground conditions. Important site factors included the density of small streams at harvest sites and the steepness of inner stream valley slopes. Recommendations are given for practices that provide a high confidence of achieving water quality standards by preventing chronic sediment delivery and avoiding direct stream channel disturbance.     

Best Management Practices Influence Modeled Erosion Rates at Forest Haul Road Stream Crossings in Virginia

Forestry best management practices (BMPs) reduce sedimentation by minimizing soil erosion and trapping sediment. These practices are particularly important in relation to road construction and use due to the heightened potential for sediment delivery at stream crossings. This study quantifies the implementation and effectiveness of BMPs at 75 randomly selected forest road stream crossings on recent timber harvests in the Mountains, Piedmont, and Coastal Plain regions of Virginia. Road characteristics at stream crossings were used to estimate erosion using the Universal Soil Loss Equation for Forests and the Water Erosion Prediction Project for Roads. Stream crossings were evaluated based on the Virginia Department of Forestry (VDOF) BMP manual guidelines and categorized as BMP?, BMP‐standard, or BMP+ based on the quality of road template, drainage, ground cover, and stream crossing structure. BMP implementation scores were calculated for each stream crossing using VDOF audit questions. Potential erosion effects due to upgrading crossings were estimated by adjusting ground cover percentage and approach length parameters in the erosion models. Results indicate that erosion rates decrease as BMP implementation scores increase (p < 0.05). BMP‐standard and BMP+ ratings made up 83% of crossings sampled, with an average erosion rate of 6.8 Mg/ha/yr. Hypothetical improvements beyond standard BMP recommendations provided minimal additional erosion prevention.     

DECISION FRAMEWORK FOR SEDIMENT CONTROL IN MUDDY CREEK WATERSHED1

ABSTRACT: The tailwater of Bridgewater Dam, below Lake James, North Carolina, is a designated trout stream. It has environmental attributes for a good cold water fishery with the exception of high suspended sediments. Muddy Creek, a tributary about 1.5 km downstream of the dam, is a major source of sediments. The Muddy Creek Watershed Restoration Initiative was established to develop and implement a sediment control plan. The Watershed Analysis Risk Management Framework was applied to simulate soil erosion and sedimentation and to help determine appropriate action. The simulated sediment concentrations of the river were comparable to observed data from November 1994 to November 2001. For the base condition, the sediment load was 135,000 kg/d from surface erosion and 1,300,000 kg/d from bank erosion. Increasing the buffer strip from existing 50 to 80 percent to 100 percent of stream segments would only reduce surface erosion to 70,400 kg/d with little change in sediment concentrations. Eliminating riverbank erosion would reduce the sediment load from 920,000 to 87,700 kg/d. The bank stabilization project would not only lower suspended sediment concentrations for Muddy Creek, but also reduce the lake sediment accumulation in the downstream Lake Rhodhiss by approximately 13 percent.     

Nitrate and sediment fluxes from a California rangeland watershed

Long-term water quality records for assessing natural variability, impact of management, and that guide regulatory processes to safeguard water resources are rare for California oak woodland rangelands. This study presents a 20-yr record (1981-2000) of nitrate-nitrogen (NO(3)-N) and suspended sediment export from a typical, grazed oak woodland watershed (103 ha) in the northern Sierra Nevada foothills of California. Mean annual precipitation over the 20-yr period was 734 mm yr(-1) (range 366-1205 mm yr(-1)). Mean annual stream flow was 353 mm y(-1) (range 87-848 mm yr(-1)). Average annual stream flow was 48.1 +/- 16% of precipitation. Mean annual NO(3)-N export was 1.6 kg ha(-1) yr(-1) (range 0.18-3.6 kg ha(-1) yr(-1)). Annual NO(3)-N export significantly (P < 0.05) increased with increasing annual stream flow and precipitation. Mean daily NO(3)-N export was 0.004 kg ha(-1) d(-1) (range 10(-5) to 0.55 kg ha(-1) d(-1)). Mean annual suspended sediment export was 198 kg ha(-1) yr(-1) (range 23-479 kg ha(-1) yr(-1)). There was a positive relationship (P < 0.05) between annual suspended sediment export, annual stream flow and precipitation. Mean daily suspended sediment export was 0.54 kg ha(-1) d(-1) (range 10(-4) to 155 kg ha(-1) d(-1)). Virtually no sediment was exported during the dry season. The large variation in daily and annual fluxes highlights the necessity of using long-term records to establish quantitative water quality targets for rangelands and demonstrates the difficulty of designing a water quality monitoring program for these ecosystems.     

LAND USE AND AQUATIC BIOINTEGRITY IN THE BLACKFOOT RWER WATERSHED,MONTANA1

ABSTRACT: Benthic macroinvertebrate samples representing 151 taxa were collected in August 1995 to examine the linkage between land use, water quality, and aquatic biointegrity in seven tributaries of the Blackfoot River watershed, Montana. The tributaries represent silvicultural (timber harvesting), agricultural (irrigated alfalfa and hay and livestock grazing), and wilderness land uses. A 2.4 km (1.5 mile) reach of a recently restored tributary also was sampled for comparison with the other six sites. A geographic information system (GIS) was used to characterize the seven subwatersheds and estimate soil erosion, using the Modified Universal Soil Loss Equation, and sediment delivery. The wilderness stream had the highest aquatic biointegrity. Two agricultural streams had the largest estimated soil erosion and sediment delivery rates, the greatest habitat impairment from nonpoint source pollution, and the most impoverished macroinvertebrate communities. The silvicultural subwatersheds had greater rates of estimated soil erosion and sediment delivery and lower aquatic biointegrity than the wilderness reference site but evinced better conditions than the agricultural sites. A multiple-use (forestry, grazing, and wildlife management) watershed and the restored site ranked between the silvicultural and agricultural sites. This spectrum of land use and aquatic biointegrity illustrates both the challenges and opportunities that define watershed management.     

Recreational Stream Crossing Effects on Sediment Delivery and Macroinvertebrates in Southwestern Virginia,USA

Trail-based recreation has increased over recent decades, raising the environmental management issue of soil erosion that originates from unsurfaced, recreational trail systems. Trail-based soil erosion that occurs near stream crossings represents a non-point source of pollution to streams. We modeled soil erosion rates along multiple-use (hiking, mountain biking, and horseback riding) recreational trails that approach culvert and ford stream crossings as potential sources of sediment input and evaluated whether recreational stream crossings were impacting water quality based on downstream changes in macroinvertebrate-based indices within the Poverty Creek Trail System of the George Washington and Jefferson National Forest in southwestern Virginia, USA. We found modeled soil erosion rates for non-motorized recreational approaches that were lower than published estimates for an off-road vehicle approach, bare horse trails, and bare forest operational skid trail and road approaches, but were 13 times greater than estimated rates for undisturbed forests and 2.4 times greater than a 2-year old clearcut in this region. Estimated soil erosion rates were similar to rates for skid trails and horse trails where best management practices (BMPs) had been implemented. Downstream changes in macroinvertebrate-based indices indicated water quality was lower downstream from crossings than in upstream reference reaches. Our modeled soil erosion rates illustrate recreational stream crossing approaches have the potential to deliver sediment into adjacent streams, particularly where BMPs are not being implemented or where approaches are not properly managed, and as a result can negatively impact water quality below stream crossings.     

Historical Land-Use Influences the Long-Term Stream Turbidity Response to a Wildfire

Wildfires commonly result in an increase in stream turbidity. However, the influence of pre-fire land-use practices on post-fire stream turbidity is not well understood. The Lower Cotter Catchment (LCC) in south-eastern Australia is part of the main water supply catchment for Canberra with land in the catchment historically managed for a mix of conservation (native eucalypt forest) and pine (Pinus radiata) plantation. In January 2003, wildfires burned almost all of the native and pine forests in the LCC. A study was established in 2005 to determine stream post-fire turbidity recovery within the native and pine forest areas of the catchment. Turbidity data loggers were deployed in two creeks within burned native forest and burned pine forest areas to determine turbidity response to fire in these areas. As a part of the study, we also determined changes in bare soil in the native and pine forest areas since the fire. The results suggest that the time, it takes turbidity levels to decrease following wildfire, is dependent upon the preceding land-use. In the LCC, turbidity levels decreased more rapidly in areas previously with native vegetation compared to areas which were previously used for pine forestry. This is likely because of a higher percentage of bare soil areas for a longer period of time in the ex-pine forest estate and instream stores of fine sediment from catchment erosion during post-fire storm events. The results of our study show that the previous land-use may exert considerable control over on-going turbidity levels following a wildfire.     

Test of APEX for nine forested watersheds in East Texas

Hydrologic/water quality models are increasingly used to explore management and policy alternatives for managing water quality and quantity from intensive silvicultural practices with best management practices (BMPs) in forested watersheds due to the limited number of and cost of conducting watershed monitoring. The Agricultural Policy/Environmental eXtender (APEX) model was field-tested using 6 yr of data for flow, sediment, nutrient, and herbicide losses collected from nine small (2.58 to 2.74 ha) forested watersheds located in southwest Cherokee County in East Texas. Simulated annual average stream flow for each of the nine watersheds was within +/- 7% of the corresponding observed values; simulated annual average sediment losses were within +/- 8% of measured values for eight out of nine watersheds. Nash-Sutcliffe efficiency (EF) values ranged from 0.68 to 0.94 based on annual stream flow comparison and from 0.60 to 0.99 based on annual sediment comparison. Similar to what was observed, simulated flow, sediment, organic N, and P were significantly increased on clear-cut watersheds compared with the control watersheds. APEX reasonably simulated herbicide losses, with an EF of 0.73 and R(2) of 0.74 for imazapyr, and EF of 0.65 and R(2) of 0.68 for hexazinone based on annual values. Overall, the results show that APEX was able to predict the effects of silvicultural practices with BMPs on water quantity and quality and that the model is a useful tool for simulating a variety of responses to forest conditions.     

EVALUATION OF BEST MANAGEMENT PRACTICES FOR CONTROLLING NONPOINT POLLUTION FROM SILVICULTURAL OPERATIONS1

ABSTRACT: Fifteen years of streamflow and water quality data were evaluated to determine the effectiveness of Best Management Practices (BMP's) in controlling nonpoint source pollution from an 110. acre commercial clearcut located in the Ridge and Valley Province of central Pennsylvania. The analyses addressed both short- and long-term changes in the physical and chemical properties and the hydro-logic regime of the stream draining this 257-acre watershed. Overall, the BMP's employed on this commercial clearcut were very effective in preventing serious deterioration of stream quality as a result of forest harvesting. Although statistically significant increases in nitrate and potassium concentrations and temperature and turbidity levels were measured the first two years following harvesting, the increases were relatively small and, with the exception of turbidity, within drinking water standards. Nevertheless, such increases may violate EPA's anti-degradation policy. Nitrate and potassium concentrations and turbidity levels remained above pre-harvesting levels for as long as nine years following harvesting. Clearcutting also significantly increased water yield, which in turn initially lowered the concentrations of most solutes because of dilution. Increased water yields returned to pro-harvesting levels within four years as a result of rapid regrowth. The export of some ions increased; however, the increased export appeared to be insufficient to affect site fertility. Implementation of periodic post-harvest inspections of harvested areas, increasing the width of the buffer zone, and utilizing buffer zones on all perennial and intermittent channels would reduce further impacts of silvi-cultural activities on water quality.