Optimized acid rain abatement strategies using ecological goals

This article addresses the use of critical loads in optimized emission abatement strategies. Critical loads represent the maximum tolerable deposition possible without adverse impacts, a limit that is highly spatially variable. As deposition targets, critical loads cannot be satisfied at all receptors in Europe. Consequently, there is a need for alternative criteria that still relate to ecological indicators, yet that are feasible, consistent, and equitable. Two criteria are suggested: the relative critical load coverage and the relative deposition reduction. Deposition goals based on these criteria will guarantee that a specified fraction of ecosystems will attain target loads and thus will be protected from adverse environmental impacts. In areas that cannot achieve target loads with the best available control measures, deposition can be reduced to a specified fraction of the unabated level. Examples are presented that demonstrate their derivation and application of the two criteria. The criteria have been implemented in the European-scale Regional Acidification Information and Simulation (RAINS) model. Results obtained indicate that optimized emission strategies based on critical loads may be similar to emission strategies based on deposition reductions at certain levels of the two criteria. This suggests that it may not be necessary to utilize critical loads to formulate deposition targets. A second example shows the effect of excluding countries from European cost minimization. A country's participation can save costs with moderate deposition targets; however, significant costs can be imposed with low (stringent) deposition targets. These preliminary results have significant implications for multilateral negotiations.     

ENVIRONMENTAL AUDITING: Exceedance of Critical Loads for Lakes in Finland,Norway, and Sweden: Reduction Requirements for Acidifying Nitrogen and Sulfur Deposition

/ The main objectives of this study were to identify the regions inFennoscandia where the critical loads of sulfur (S) and acidifying nitrogen(N) for lakes are exceeded and to investigate the consequences for depositionreductions, with special emphasis on the possible trade-offs between S and Ndeposition in order to achieve nonexceedance. In the steady-state model forcalculating critical loads and their exceedances, all relevant processesacting assinks for N and S are considered. The critical loads of N and S areinterrelated (defining the so-called critical load function), and therefore asingle critical load for one pollutant cannot be defined without makingassumptions about the other. Comparing the present N and S deposition withthe critical load function for each lake allows determination of thepercentage of lakes in the different regions of Fennoscandia where: (1) Sreductions alone can achieve nonexceedance, (2) N reductions alone aresufficient, and (3) both N and S reductions are required but to a certaindegree interchangeable. Secondly, deposition reduction requirements wereassessed by fixing the N deposition to the present level, in this wayanalyzing the reductions required for S, and by computing the percentage oflakes exceeded in Finland, Norway and Sweden for every possible percentdeposition reduction in S and N, in this way showing the (relative)effectiveness of reducing S and/or N deposition. The results showed clearregional patterns in the S and N reduction requirements. In practically thewhole of Finland and the northern parts of Scandinavia man-made acidificationof surface waters could be avoided by reducing S deposition alone. In thesouthern parts of Sweden some reductions in N deposition are clearly neededin addition to those for S. In southern Norway strong reductions are requiredfor both N and S deposition.KEY WORDS: Acidification; Critical load; Exceedance; Sulfur; Nitrogen;Deposition; Lake     

Computing Atmospheric Nutrient Loads to the Chesapeake Bay Watershed and Tidal Waters

Application of integrated Chesapeake Bay models of the airshed, watershed, and estuary support air and water nitrogen controls in the Chesapeake. The models include an airshed model of the Mid‐Atlantic region which tracks the estimated atmospheric deposition loads of nitrogen to the watershed, tidal Bay, and adjacent coastal ocean. The three integrated models allow tracking of the transport and fate of nitrogen air emissions, including deposition in the Chesapeake watershed, the subsequent uptake, transformation, and transport to Bay tidal waters, and their ultimate influence on Chesapeake water quality. This article describes the development of the airshed model, its application to scenarios supporting the Chesapeake Total Maximum Daily Load (TMDL), and key findings from the scenarios. Key findings are that the atmospheric deposition loads are among the largest input loads of nitrogen in the watershed, and that the indirect nitrogen deposition loads to the watershed, which are subsequently delivered to the Bay are larger than the direct loads of atmospheric nitrogen deposition to Chesapeake tidal waters. Atmospheric deposition loads of nitrogen deposited in coastal waters, which are exchanged with the Chesapeake, are also estimated. About half the atmospheric deposition loads of nitrogen originate from outside the Chesapeake watershed. For the first time in a TMDL, the loads of atmospheric nitrogen deposition are an explicit part of the TMDL load reductions.     

Model Calculations of Total Maximum Daily Loads of Mercury for Drainage Lakes1

Abstract: The Watershed Analysis Risk Management Framework watershed model was enhanced to simulate the transport and fate of mercury and to calculate the fish mercury concentrations (FMC) attained by fish through the food web. The model was applied to Western Lake Superior Basin of Minnesota, which has many peat lands and lakes. Topographic, land use, and soil data were used to set up the model. Meteorology and precipitation chemistry data from nearby monitoring stations were compiled to drive the model. Simulated flow and mercury concentrations for several stream stations were comparable to available data. The model was used to perform mercury total maximum daily load calculations for two contrasting drainage lakes (Wild Rice Lake and Whiteface Reservoir). The model results for wet deposition, dry deposition, evasion, watershed yield, and soil sequestration of mercury were comparable with available actual data. The model predicted lake ice cover from November to April and weak stratification in summer, typical of shallow lakes in cold regions. The simulated sulfate decrease and methylmercury increase near the lake bottom in late summer are caused by sulfate reduction and mercury methylation that occur in the surficial sediment. Simulated FMC were within the range of observed values and the R² of correlation between the simulated and observed FMC was 0.77. Under the 1989‐2004 base condition, the average simulated FMC of four‐year‐old walleye was 0.31 μg/g for Whiteface Reservoir and 0.15 μg/g for Wild Rice Lake. The FMC criterion in Minnesota is 0.2 μg/g. Wild Rice Lake already meets this criterion without any load reduction. The model showed that a 65% reduction in atmospheric mercury deposition will not, by itself, allow Whiteface Reservoir to meet the criterion in 15 years. Additional best management practices will be needed to reduce 50% of the watershed input.     

Mobilization and Toxicity Potential of Aluminum from Alum Floc Deposits in Kensico Reservoir,New York

There is detailed literature on the mobilization of aluminum (Al) from soil to surface waters as a result of elevated acidic deposition to base‐poor forest watersheds. There is considerably less information on the mobilization and effects of Al from the application of alum that is used in some water supplies to control turbidity during high‐flow events. We report on the results of field measurements, laboratory sediment release experiments, and chemical equilibrium calculations conducted to evaluate the potential for the mobilization of Al from alum floc deposits in sediments of Kensico Reservoir, New York. Under ambient water quality conditions, mobilization of sediment Al is not a noteworthy concern at Kensico Reservoir. However, under experimental conditions of low pH, low acid neutralizing capacity (ANC), and low temperature, the inorganic fraction of monomeric Al can be mobilized from Kensico sediments to concentrations that would likely impair the health of aquatic organisms (>2 μmol/l). Elevated concentrations of monomeric Al were observed only when ANC decreased below 50 μeq/l, which is outside the range of values observed in Kensico during the 1997‐2007 interval (120‐460 μeq/l). Concentrations of complexing ligands are relatively low in Kensico waters (i.e., fluoride, naturally occurring organic solutes) and do not appear to substantially contribute to potential Al mobilization. For other water supplies with low ANC, the potential for sediment release of Al may exist.     

STREAM CHEMISTRY IN THE SOUTHERN BLUE RIDGE: FEASIBILITY OF A REGIONAL SYNOPTIC SAMPLING APPROACH1

ABSTRACT: A pilot study, which was conducted in the Southern Blue Ridge geographical province of the Southeastern U.S., demonstrated the feasibility of a probability-based regional synoptic design for the National Stream Survey, which is a project aimed at estimating the number and percentage of streams in various regions of the U.S. that are acidic or at risk from acid deposition. Estimated population distributions for key chemical variables were not appreciably affected by week-to-week variability in stream chemistry during the spring index period chosen for the study. Differences were observed in estimated acid neutralizing capacity (ANC), nitrate, and pH frequency distributions between spring and summer. Observations made at the downstream node did not represent the chemistry of the entire reach for some variables (ANC and nitrate) as indicated by differences in chemical concentrations between upstream and downstream sampling locations. Coefficients of variation in chemical species were low enough to provide a reasonably stable classification of streams based on ANC. Although median ANC, sulfate, and nitrate concentrations were quite low in the region, the probability of finding streams with ph < 6.3 is less than 1.3 percent at the α= 0.05 confidence level.     

Use of stream chemistry for monitoring acidic deposition effects in the Adirondack region of New York

Acid-neutralizing capacity (ANC) and pH were measured weekly from October 1991 through September 2001 in three streams in the western Adirondack Mountain region of New York to identify trends in stream chemistry that might be related to changes in acidic deposition. A decreasing trend in atmospheric deposition of SO4/2- was observed within the region over the 10-yr period, although most of the decrease occurred between 1991 and 1995. Both ANC and pH were inversely related to flow in all streams; therefore, a trend analysis was conducted on (i) the measured values of ANC and pH and (ii) the residuals of the concentration-discharge relations. In Buck Creek, ANC increased significantly (p < 0.05) over the 10 yr, but the residuals of ANC showed no trend (p > 0.10). In Bald Mountain Brook, ANC and residuals of ANC increased significantly (p < 0.01), although the trend was diatonic-a distinct decrease from 1991 to 1996 was followed by a distinct increase from 1996 to 2001. In Fly Pond outlet, ANC and residuals of ANC increased over the study period (p < 0.01), although the trend of the residuals resulted largely from an abrupt increase in 1997. In general, the trends observed in the three streams are similar to results presented for Adirondack lakes in a previous study, and are consistent with the declining trend in atmospheric deposition for this region, although the observed trends in ANC and pH in streams could not be directly attributed to the trends in acidic deposition.     

Development of the Chesapeake Bay Watershed Total Maximum Daily Load Allocation

Nutrient load allocations and subsequent reductions in total nitrogen and phosphorus have been applied in the Chesapeake watershed since 1992 to reduce hypoxia and to restore living resources. In 2010, sediment allocations were established to augment nutrient allocations supporting the submerged aquatic vegetation resource. From the initial introduction of nutrient allocations in 1992 to the present, the allocations have become more completely applied to all areas and loads in the watershed and have also become more rigorously assessed and tracked. The latest 2010 application of nutrient and sediment allocations were made as part of the Chesapeake Bay total maximum daily load and covered all six states of the Chesapeake watershed. A quantitative allocation process was developed that applied principles of equity and efficiency in the watershed, while achieving all tidal water quality standards through an assessment of equitable levels of effort in reducing nutrients and sediments. The level of effort was determined through application of two key watershed scenarios: one where no action was taken in nutrient control and one where maximum nutrient control efforts were applied. Once the level of effort was determined for different jurisdictions, the overall load reduction was set watershed‐wide to achieve dissolved oxygen water quality standards. Further adjustments were made to the allocation to achieve the James River chlorophyll‐a standard.     

EFFECTS OF URBANIZATION ON CHANNEL INSTABILITY1

ABSTRACT: Channel instability and aquatic ecosystem degradation have been linked to watershed imperviousness in humid regions of the U.S. In an effort to provide a more process‐based linkage between observed thresholds of aquatic ecosystem degradation and urbanization, standard single event approaches (U.S. Geological Survey Flood Regression Equations and rational) and continuous hydrologic models (HSPF and CASC2D) were used to examine potential changes in flow regime associated with varying levels of watershed imperviousness. The predicted changes in flow parameters were then interpreted in concert with risk‐based models of channel form and instability. Although low levels of imperviousness (10 to 20 percent) clearly have the potential to destabilize streams, changes in discharge, and thus stream power, associated with increased impervious area are highly variable and dependent upon watershed‐specific conditions. In addition to the storage characteristics of the pre‐development watershed, the magnitude of change is sensitive to the connectivity and conveyance of impervious areas as well as the specific characteristics of the receiving channels. Different stream types are likely to exhibit varying degrees and types of instability, depending on entrenchment, relative erodibility of bed and banks, riparian condition, mode of sediment transport (bedload versus suspended load), and proximity to geomorphic thresholds. Nonetheless, simple risk‐based analyses of the potential impacts of land use change on aquatic ecosystems have the potential to redirect and improve the effectiveness of watershed management strategies by facilitating the identification of channels that may be most sensitive to changes in stream power.     

URBANIZATION OF AQUATIC SYSTEMS: DEGRADATION THRESHOLDS,STORMWATER DETECTION,AND THE LIMITS OF MITIGATION1

ABSTRACT: Urbanization of a watershed degrades both the form and the function of the downstream aquatic system, causing changes that can occur rapidly and are very difficult to avoid or correct. A variety of physical data from lowland streams in western Washington displays the onset of readily observable aquatic-system degradation at a remarkably consistent level of development, typically about ten percent effective impervious area in a watershed. Even lower levels of urban development cause significant degradation in sensitive water bodies and a reduced, but less well quantified, level of function throughout the system as a whole. Unfortunately, established methods of mitigating the downstream impacts of urban development may have only limited effectiveness. Using continuous hydrologic modeling we have evaluated detention ponds designed by conventional event methodologies, and our findings demonstrate serious deficiencies in actual pond performance when compared to their design goals. Even with best efforts at mitigation, the sheer magnitude of development activities falling below a level of regulatory concern suggests that increased resource loss will invariably accompany development of a watershed. Without a better understanding of the critical processes that lead to degradation, some downstream aquatic-system damage is probably inevitable without limiting the extent of watershed development itself.     

ESTIMATING NUTRIENT AND SEDIMENT THRESHOLD CRITERIA FOR BIOLOGICAL IMPAIRMENT IN PENNSYLVANIA WATERSHEDS1

ABSTRACT: This study employs a simple nonlinear statistical approach to establish nitrogen, phosphorus, and sediment concentration and unit area load thresholds to aid in the evaluation of aquatic biological health of watersheds within the state of Pennsylvania. Flow, nitrogen and phosphorus species, sediment, basin area, land cover, and biological assessment data were assembled for 29 Pennsylvania watersheds. For each watershed, rating curves depicting flow versus load relationships were developed using the U.S. Environmental Protection Agency's (USEPA's) storage and retrieval database (STORET) flow and concentration data, then applied to daily flow data obtained from U.S. Geological Survey (USGS) daily flow gauging stations to estimate daily load between 1989 and 1999. The load estimates and concentration data were then sorted into six sets of data: mean annual unit area nitrogen, phosphorus, and sediment loads; and average nitrogen, phosphorus, and sediment concentrations. Results of Mann‐Whitney tests conducted on each of the six datasets indicate that there is a statistically significant difference between the concentrations and unit area loads of nitrogen, phosphorus, and sediment in impaired and unimpaired watersheds. Concentration thresholds, calculated as the midpoint between the impaired and unimpaired watersheds’ 95 percent confidence interval for the median, were estimated to be 2.01 mg/L, 0.07 mg/L, and 197.27 mg/L for nitrogen, phosphorus, and sediment, respectively. Annual unit area load thresholds were estimated to be equal to 8.64 kg/ha, 0.30 kg/ha, and 785.29 kg/ha, respectively, for nitrogen, phosphorus, and sediment species.     

IMPACT OF COAL SURFACE MINING AND RECLAMATION ON SUSPENDED SEDIMENT IN THREE OHIO WATERSHEDS1

ABSTRACT: Prior to PL95–87 little research had been conducted to determine the impacts of mining and reclamation practices on sediment concentrations and yields on a watershed scale. Furthermore, it was unknown whether sediment yield and other variables would return to undisturbed levels after reclamation. Therefore, three small watersheds, with differing lithologies and soils, were monitored for runoff and suspended sediment concentrations during three phases of watershed disturbances: undisturbed watershed condition, mining and reclamation disturbances, and post‐reclaimed condition. Profound increases in suspended‐sediment concentrations, load rates, and yields due to mining and reclamation activities, and subsequent drastic decreases after reclamation were documented. Even with increases in runoff potential, reductions in suspended‐sediment concentrations and load rates to below or near undisturbed‐watershed levels is possible by using the mulch‐crimping technique and by removing diversions. Maximum concentrations and load rates occurred during times of active disturbances that exposed loose soil and spoil to high‐intensity rains. Sediment concentrations remained elevated compared with the undisturbed watershed when diversions were not well maintained and overtopped, and when they were not removed for final reclamation. Diversions are useful for vegetation establishment, but should be maintained until they are removed for final reclamation after good vegetative cover is established.     

EFFECTIVENESS OF BIOPHYSICAL CRITERIA IN THE HIERARCHICAL CLASSIFICATION OF DRMNAGE BASINS1

ABSTRACT: A subwatershed base map of 84 hydrologic subregions within the Columbia River Basin (approximately 58,361,000 ha) was developed following hierarchical principles of ecological unit mapping. Our primary objectives were to inspect the relations between direct and indirect biophysical variables in the prediction of valley bottom and stream type patterns, and to identify hydrologic subregions (based on these results) that had similar aquatic patterns for which consistent management practices could be applied. Realization of these objectives required: (1) stratified subsampling of valley bottom and stream type composition within selected sub‐watersheds, (2) identification of direct and indirect biophysical variables that were mappable across the basin and that exerted primary control on the distribution of sampled aquatic patterns, and (3) development of hydrologic subregion maps based on the primary biophysical variables identified. Canonical correspondence analysis indicated that a core set of 15 direct variables (e.g., average watershed slope, drainage density, ten‐year peak flow) and 19 indirect variables (i.e., nine subsection groups, four lithology groups, and six potential vegetation settings) accounted for 31 and 30 percent (respectively) of valley bottom/stream type composition variability and 84 and 80 percent (respectively) of valley bottom/stream type environmental variability within subsamples. The 19 indirect biophysical variables identified were used to produce an ecological unit classification of 7,462 subwatersheds within the basin by a hierarchical agglomerative clustering technique (i.e., hydrologic subregions were identified). Discriminant analysis indicated that 13 direct biophysical variables could correctly assign 80 percent of the subwatersheds to their indirect biophysical classification, thus demonstrating the strong relation that exists between indirect biophysical based classifications (ecological units) and the direct biophysical variables that determine finer‐level aquatic patterns. Our hydrologic subregion classifications were also effective in explaining observed differences in management hazard ratings across all subwatersheds of the basin. Results of this research indicate that ecological units can be effectively used to produce watershed classifications that integrate the effects of direct biophysical variables on finer‐level aquatic patterns, and predict opportunities and limitations for management.     

Atmospheric deposition of pesticides to an agricultural watershed of the Chesapeake Bay

The Choptank River watershed, located on the Delmarva Peninsula of the Chesapeake Bay, is dominated by agricultural land use, which makes it vulnerable to runoff and atmospheric deposition of pesticides. Agricultural and wildlife areas are in close proximity and off-site losses of pesticides may contribute to toxic effects on sensitive species of plants and animals. High-volume air samples (n = 31) and event-based rain samples (n = 71) were collected from a single location in the watershed representing regional background conditions. Surface water samples were collected from eight stations in the tidal portion of the river on five occasions during 2000. Chlorothalonil, metolachlor, atrazine, simazine, endosulfan, and chlorpyrifos were frequently detected in the air and rain, with maximal concentrations during the period when local or regional crops were planted. The wet deposition load to the watershed was estimated at 150 +/- 16, 61 +/- 7, and 51 +/- 6 kg yr(-1) for chlorothalonil, metolachlor, and atrazine, respectively. The high wet deposition load compared with the estimated annual usage for chlorothalonil (13%) and endosulfan (14-90%) suggests an atmospheric source from outside the watershed. Net air-water gas exchange fluxes for metolachlor varied from -44 +/- 19 to 9.3 +/- 4.1 ng m(-2) d(-1) with negative values indicating net deposition. Wet deposition accounted for 3 to 20% of the total metolachlor mass in the Choptank River and was a more important source to the river than gas exchange. Estimates of herbicide flux presented here are probably a low estimate and actual rates may be significantly higher in areas closer to pesticide application.     

Long Profile Evolution of a Mountain Stream in Relation to Gravel Load Management: Example of the Middle Giffre River (French Alps)

6 m³) following extensive gravel extraction from the channel, this evolution appears to be reversed today, showing that this river is capable of rehabilitating itself. The watershed supplies the river with 50,000 m³/yr of material and part of this load (30,000 m³/yr) is extracted. Although it is theoretically possible to reverse this phenomenon, it is unacceptable for the local economy as man-made installations unadapted to flooding were developed along the river during the period of incision. Today, the development policy is in conflict with the maintenance and the preservation of natural sediment transport and deposition.     

Evaluation of Three Watershed‐Scale Pesticide Environmental Transport and Fate Models1

Abstract: The U.S. Environmental Protection Agency (USEPA) Office of Pesticide Programs (OPP) has completed an evaluation of three watershed‐scale simulation models for potential use in Food Quality Protection Act pesticide drinking water exposure assessments. The evaluation may also guide OPP in identifying computer simulation tools that can be used in performing aquatic ecological exposure assessments. Models selected for evaluation were the Soil Water Assessment Tool (SWAT), the Nonpoint Source Model (NPSM), a modified version of the Hydrologic Simulation Program‐Fortran (HSPF), and the Pesticide Root Zone Model‐Riverine Water Quality (PRZM‐RIVWQ) model. Simulated concentrations of the pesticides atrazine, metolachlor, and trifluralin in surface water were compared with field data monitored in the Sugar Creek watershed of Indiana’s White River basin by the National Water Quality Assessment (NAWQA) program. The evaluation not only provided USEPA with experience in using watershed models for estimating pesticide concentration in flowing water but also led to the development of improved statistical techniques for assessing model accuracy. Further, it demonstrated the difficulty of representing spatially and temporally variable soil, weather, and pesticide applications with relatively infrequent, spatially fixed, point estimates. It also demonstrated the value of using monitoring and modeling as mutually supporting tools and pointed to the need to design monitoring programs that support modeling.     

Modeling atmospheric nitrogen deposition and transport in the Chesapeake Bay watershed

Atmospheric deposition of nitrate nitrogen and ammonium nitrogen has been identified as a major factor in the decline of water quality in the Chesapeake Bay. Reports have indicated that atmospheric deposition may account for 25 to 80% of the total nitrogen load entering the bay. However, uncertainties exist regarding the accuracy of the atmospheric deposition inputs, nitrogen retention coefficients, and in-stream nutrient uptake rates used in these studies. This project was designed to reassess the potential inputs of atmospheric nitrogen deposition to the bay through the use of a high-resolution wet deposition model, improved wet and dry deposition and nutrient retention estimates, existing soils and land use data, and geographic information systems software. Model results indicate that the methods used in previous studies may overestimate the contribution of atmospheric nitrate and ammonium deposition to the Chesapeake Bay watershed (CBW). Wet and dry atmospheric nitrate and ammonium nitrogen deposition estimates to the CBW ranged from 52.7 to 141.9 and 41.9 to 60.1 million kg/yr, respectively, between 1984 and 1996. Dry and total atmospheric deposition loads to the watershed are substantially less than previous estimates. Estimates of the percent contribution of atmospherically deposited nitrogen to the Chesapeake Bay represent between 20 and 32% of the total nitrate and ammonium nitrogen load to the watershed from all nitrogen sources. While these estimates are lower than many other published estimates, regression analysis of model parameters, nitrogen retention coefficients, output, and measured in-stream nitrogen loads indicate that the calculated nitrogen loads may still be too high.     

Herbicide Transport in Goodwater Creek ExperimentalWatershed: I. Long‐Term Research on Atrazine1

Lerch, R.N., E.J. Sadler, K.A. Sudduth, C. Baffaut, and N.R. Kitchen, 2010. Herbicide Transport in Goodwater Creek Experimental Watershed: I. Long‐Term Research on Atrazine. Journal of the American Water Resources Association (JAWRA) 1‐15. DOI: 10.1111/j.1752‐1688.2010.00503.x Abstract: Atrazine continues to be the herbicide of greatest concern relative to contamination of surface waters in the United States (U.S.). The objectives of this study were to analyze trends in atrazine concentration and load in Goodwater Creek Experimental Watershed (GCEW) from 1992 to 2006, and to conduct a retrospective assessment of the potential aquatic ecosystem impacts caused by atrazine contamination. Located within the Central Claypan Region of northeastern Missouri, GCEW encompasses 72.5 km² of predominantly agricultural land uses, with an average of 21% of the watershed in corn and sorghum. Flow‐weighted runoff and weekly base‐flow grab samples were collected at the outlet to GCEW and analyzed for atrazine. Cumulative frequency diagrams and linear regression analyses generally showed no significant time trends for atrazine concentration or load. Relative annual loads varied from 0.56 to 14% of the applied atrazine, with a median of 5.9%. A cumulative vulnerability index, which takes into account the interactions between herbicide application, surface runoff events, and atrazine dissipation kinetics, explained 63% of the variation in annual atrazine loads. Based on criteria established by the U.S. Environmental Protection Agency, atrazine reached concentrations considered harmful to aquatic ecosystems in 10 of 15 years. Because of its vulnerability, atrazine registrants will be required to work with farmers in GCEW to implement practices that reduce atrazine transport.     

Analyzing the Impacts of Off-Road Vehicle (ORV) Trails on Watershed Processes in Wrangell-St. Elias National Park and Preserve,Alaska

Trails created by off-road vehicles (ORV) in boreal lowlands are known to cause local impacts, such as denuded vegetation, soil erosion, and permafrost thaw, but impacts on stream and watershed processes are less certain. In Wrangell-St. Elias National Park and Preserve (WRST), Alaska, ORV trails have caused local resource damage in intermountain lowlands with permafrost soils and abundant wetlands and there is a need to know whether these impacts are more extensive. Comparison of aerial photography from 1957, 1981, and 2004 coupled with ground surveys in 2009 reveal an increase in trail length and number and show an upslope expansion of a trail system around points of stream channel initiation. We hypothesized that these impacts could also cause premature initiation and headward expansion of channels because of lowered soil resistance and greater runoff accumulation as trails migrate upslope. Soil monitoring showed earlier and deeper thaw of the active layer in and adjacent to trails compared to reference sites. Several rainfall-runoff events during the summer of 2009 showed increased and sustained flow accumulation below trail crossings and channel shear forces sufficient to cause headward erosion of silt and peat soils. These observations of trail evolution relative to stream and wetland crossings together with process studies suggest that ORV trails are altering watershed processes. These changes in watershed processes appear to result in increasing drainage density and may also alter downstream flow regimes, water quality, and aquatic habitat. Addressing local land-use disturbances in boreal and arctic parklands with permafrost soils, such as WRST, where responses to climate change may be causing concurrent shifts in watershed processes, represents an important challenge facing resource managers.     

Influences on Wood Load in Mountain Streams of the Bighorn National Forest,Wyoming, USA

We documented valley and channel characteristics and wood loads in 19 reaches of forested headwater mountain streams in the Bighorn National Forest of northern Wyoming. Ten of these reaches were in the Upper Tongue River watershed, which has a history of management including timber harvest, tie floating, and road construction. Nine reaches were in the North Rock Creek watershed, which has little history of management activities. We used these data to test hypotheses that (i) valley geometry correlates with wood load, (ii) stream gradient correlates with wood load, and (iii) wood loads are significantly lower in managed watersheds than in otherwise similar unmanaged watersheds. Statistical analyses of the data support the first and third hypotheses. Stream reaches with steeper valley side slopes tend to have higher wood loads, and reaches in managed watersheds tend to have lower wood loads than reaches in unmanaged watersheds. Results do not support the second hypothesis. Shear stress correlated more strongly with wood load than did stream gradient, but statistical models with valley-scale variables had greater explanatory power than statistical models with channel-scale variables. Wood loads in stream reaches within managed watersheds in the Bighorn National Forest tend to be two to three times lower than wood loads in unmanaged watersheds.