Temporal and Spatial Trends in Nutrient and Sediment Loading to Lake Tahoe, California‐Nevada, USA

Abstract

Since 1980, the Lake Tahoe Interagency Monitoring Program (LTIMP) has provided stream‐discharge and water quality data—nitrogen (N), phosphorus (P), and suspended sediment—at more than 20 stations in Lake Tahoe Basin streams. To characterize the temporal and spatial patterns in nutrient and sediment loading to the lake, and improve the usefulness of the program and the existing database, we have (1) identified and corrected for sources of bias in the water quality database; (2) generated synthetic datasets for sediments and nutrients, and resampled to compare the accuracy and precision of different load calculation models; (3) using the best models, recalculated total annual loads over the period of record; (4) regressed total loads against total annual and annual maximum daily discharge, and tested for time trends in the residuals; (5) compared loads for different forms of N and P; and (6) tested constituent loads against land use‐land cover (LULC) variables using multiple regression. The results show (1) N and P loads are dominated by organic N and particulate P; (2) there are significant long‐term downward trends in some constituent loads of some streams; and (3) anthropogenic impervious surface is the most important LULC variable influencing water quality in basin streams. Many of our recommendations for changes in water quality monitoring and load calculation methods have been adopted by the LTIMP.

Satellite remote sensing to assess cyanobacterial bloom frequency across the United States at multiple spatial scales

“…Field observations support the presence of cyanobacteria in Lake Meredith and Grapevine Lake ( Trevino and Petersen, 2020 ). Lake Tahoe, a highly studied ultra- oligotrophic lake in California known for its water clarity (e.g., Beutel and Horne, 2018 ; Coats et al, 2016 ), had no detectable cyanobacteria in any resolvable weekly composites across the lake as demonstrated through an average annual lake-scale bloom frequency of 0%.…”

Water quality and forest restoration in the Lake Tahoe basin: impacts of future management options

“…The Blackwood watershed has https://www.ecologyandsociety.org/vol27/iss2/art6/ a long history of soil erosion caused by both natural characteristics and anthropogenic disturbances (historical excessive grazing, road construction, forest harvest) and has been the target of several stream channel restoration projects (Oehrli 2013, Norman et al 2014. Other studies, including those used to develop a total maximum daily load program, also identified Blackwood Creek and Ward Creek as the greatest sources of sediment and phosphorus pollutants in the Lake Tahoe basin (Tetra Tech 2007, Coats et al 2016, along with Upper Truckee River and Trout Creek watersheds on the south side of the basin, which are outside the study area that we examined.…”

WEPPcloud hydrologic and erosion simulation datasets from 28 watersheds in US Pacific Northwest and calibrating model parameters for undisturbed and disturbed forest management conditions

“…The model runs are also archived in the HydroShare repository and contain both the input and the output data from the model, among other useful information. The watershed names reflect the watershed names used in other studies, which provided the observed water quality data for model assessment [3] . The streamflow for Mica Creek watersheds, MC3 and MC6, were recorded with flumes.…”

“…Modeled streamflow was compared to data from the USGS gauging stations for watersheds in the Lake Tahoe basin, Bull Run, and Cedar River watersheds, and data measured with flumes in the Mica Creek Experimental Watersheds, Idaho. Modeled sediment and phosphorus yield was compared to flow-weighted annual observations processed by [3] . Figs.…”