Viz-WEPPcloud- A Web-based, Interactive, Hillslope Scale BMP Guiding Tool for the Water Erosion Prediction Project (WEPP) Model

Hillslope or watershed scale process-based hydrology and water quality simulation models are commonly employed to investigate the potential effects of land management and climate scenarios on water quality. Because of their complexity, such models are not always useful for planners and this limits their usability as planning tools. The Water Erosion Prediction Project (WEPP) model is a process-based hydrology and erosion model, which has been wildly applied to a multitude of land uses and management scenarios across the US. WEPPcloud is a watershed-scale interface for the WEPP model that can be applied anywhere in the US. Users only need a computer connected to the internet to run the model and all the data inputs and outputs are processed on servers, therefore making WEPP more accessible even to land managers that might not be adequately trained with the model. Land managers can use the interface to run and compare scenarios for selection of Best Management Practices (BMP). Our objective was to further aid managers in the decision-making process by developing a post-processing, interactive tool (Viz-WEPPcloud) that can be used to identify erosion hotspots and hillslopes suitable for targeted management. Detailed hillslope and scenario results from the WEPPcloud interface can be imported in Viz-WEPPcloud and displayed interactively. We demonstrate the usability of the Viz-WEPPcloud interface for erosion management with outputs from 20 watersheds in Lake Tahoe basin simulated for 11 different scenarios that include fuel treatments, prescribed fires, and wildfires of varying severities. We also exemplify the use of Viz-WEPPcloud to identify, quantify, and visualize hillslopes that are most susceptible to disturbance under different scenarios based on constraints such as land use, soil type, and slope steepness. This approach guides planners in targeting the hillslopes that provide the greatest reduction in sediment load by treating the least amount of area.

Retention and release of phosphorus in Forest-Meadow Systems of Lake Tahoe, California

Forests are important non-point sources for phosphorus (P) release to surface waters. Almost a century of fire suppression in lake Tahoe basin has resulted in excessive accumulation of forest litter layer containing large pool of phosphorus. Leachate from such forest floor can potentially act as a long-term source of biologically available phosphorus which can be transported via either leaching, litter flow or by surface runoff to the nearby surface waters. This premise is supported by recent studies that have reported high inorganic phosphorus concentration (25 mg/L P) in overland/litter interflow (Miller et al., 2005) derived from the forest floor O horizons (Loupe et al., 2007). Due to the downstream risk of excessive nutrient load on water clarity in Lake Tahoe the objective of this study was to characterize the fate and transport of P in the upland volcanic and granitic forest-meadow systems. Nine intact soil cores (7.6 cm diameter) representing the top 15 cm of mineral soil were collected from both a volcanic and granitic forest-meadow system. Duplicate air-dried soil samples were used to understand the P adsorption potential using the batch isotherm method. Intact cores were subjected to four flow experiments to characterize the effect of P type (organic vs inorganic) and direction of flow (infiltration and exfiltration) on transport of P. In the experiment 6.6 cm of DI water/spiking solutions (at pH ~ 6.5) were applied to the cores mimicking typical spring precipitation totals. The experiments were completed in the following specific order – (i) rainwater infiltration, (ii) Infiltration with inorganic P, (iii) Infiltration with an organic P solution, (iv) and rainwater exfiltration. The study provides important insights on P fate and transport from forest-meadow systems and have important implications of management on downstream water quality.

Multi-Decadal Response of Stream Water Quality to Commercial Forest Management Operations in a Mountainous Watershed

Concerns pertaining to the commercial forest management and consequent nutrient losses exist. Forest management activities can potentially alter the soil nutrient stores and the stream water quality. We investigated the impact of contemporary forest management activities on the stream nitrogen and phosphorus dynamics in a two-and-a-half decade-long (1992-2016) paired and nested watershed study in the Pacific Northwest. Monthly grab water samples were collected and analyzed for total Kjeldhal nitrogen (TKN), total available nitrogen (TAN), Nitrate + Nitrite (NO3+NO2), total phosphorus (TP) and Orthophosphate (OP) concentrations throughout the study period. Five years of calibration data, 4 years of post-road construction, 6 years of post-harvest and 9 years of post-harvest data (phase-II) were analyzed using the Before-After-Control-Impact-Paired (BACIP) design. We found statistically significant (α <0.05) increase in NO3+NO2 and OP concentrations following timber harvest. Downstream cumulative watersheds displayed relatively smaller increase in the stream NO3+NO2 and OP concentrations likely due to the dilution and attenuation effects. NO3+NO2 and OP exports also increased from all watersheds following the treatments. More interestingly the undisturbed watershed displayed similar increasing trends in concentrations and export of NO3+NO2 and OP. This increase was, however, smaller in magnitude compared to the disturbed watersheds. In summary, we found that the contemporary forest management activities altered the stream water quality by significantly increasing the stream NO3+NO2 and OP concentrations as well as export from the paired and nested watershed.