![[logo] US EPA](https://webarchive.library.unt.edu/eot2008/20081105200011im_/http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
2000 Progress Report: Watershed Response to Natural and Anthropogenic Stress: Lake Tahoe Nutrient Budget
EPA Grant Number: R825433C029Subproject: this is subproject number 029 , established and managed by the Center Director under grant R825433
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: EERC - Center for Ecological Health Research (Cal Davis)
Center Director: Rolston, Dennis E.
Title: Watershed Response to Natural and Anthropogenic Stress: Lake Tahoe Nutrient Budget
Investigators: Reuter, John E. , Goldman, Charles R. , Heyvaert , Alan C. , Jassby, Alan D.
Institution: University of California - Davis
EPA Project Officer: Levinson, Barbara
Project Period: October 1, 1996 through September 30, 2000
Project Period Covered by this Report: October 1, 1999 through September 30, 2000
RFA: Exploratory Environmental Research Centers (1992)
Research Category: Center for Ecological Health Research , Targeted Research
Description:
Objective:To provide estimates of loading by major category of input through the creation of a nutrient budget.
Progress Summary:Before nutrient reduction to Lake Tahoe can be significantly achieved, it is first necessary to quantify the sources of phosphorus and nitrogen.Last year we presented a review of our findings regarding a nutrient budget for Lake Tahoe. Five major sources of nutrients (including phosphorus and nitrogen) to Lake Tahoe were identified: (1) direct wet and dry atmospheric deposition, (2) stream discharge, (3) overland runoff directly to lake, (4) groundwater and (5) shoreline erosion.
Atmospheric deposition - Jassby et al. (1994) suggested that atmospheric deposition provides most of the dissolved inorganic nitrogen and over half of the total nitrogen to the loading budget of Lake Tahoe, and also contributes significant amounts of soluble reactive-P and total-P. Direct N-loading to the lake surface was recently estimated at 234 MT yr-1 and P contribution at 12.4 MT yr-1 (1 MT = 1,000 kg or 2,205 pounds).
Stream Loading - Using data of the Lake Tahoe Interagency Monitoring Program from the early 1980s to the early 1990s the Tahoe Research Group has calculated stream loads for N and P as part of two separate studies. The results for annual N-loading were 81.1 MT yr-1 and 55.2 MT yr-1 for the beginning and end of this period, respectively. Comparable loading values for total-P were 12.5 MT yr-1, and 11.2 MT yr-1 (Marjanovic 1989; Jassby et al. 1994). Differences from period-to-period reflect the variation in precipitation and runoff. Contributions for N and P in our budget were taken as the mean, or 68.2 MT yr-1 and 11.9 MT yr-1 , respectively. Thodal (1997) and Dugan and McGauhey (1974) also estimated streamflow nutrient loads; averaging their estimates with the more recent estimates produces loading estimates of 81.6 MT yr-1 and 13.3 MT yr-1 for total-N and total-P, respectively.
Direct Runoff - The Tahoe basin has 52 intervening zones which drain directly into the lake without first entering the streams. These intervening zones are generally found between the individual watersheds and as such are distributed around the entire lake. Based on a study of urban runoff at South Shore in 1983-84 by the Lahontan Regional Water Quality Control Board and a series of four runoff studies by the Tahoe Research Group between 1993 and 1998, we estimated the loading from direct non-stream runoff at 41.8 MT yr-1 for total N (10% of the total-N budget) and P-loading 15.5 MT yr-1 for total P (34% of the total-P budget). The observation regarding the high contribution of P-loading from direct runoff is particularly important since a significant portion of the urbanization at Tahoe is found in the intervening zones.
Groundwater - The most comprehensive, basin-wide groundwater study to date is that of Thodal (1997). He calculated "rounded estimates" of 60 MT yr-1 for N-loading and a 4 MT yr-1 for P-loading. This accounted for 14% of the TN budget and 9% of the TP budget.
Shoreline Erosion - The process of shoreline erosion and its quantitative importance to the nutrient and sediment budgets of Lake Tahoe have received very little attention. However, the importance of shoreline erosion has been highlighted in recent years when the combination of high lake levels and strong and sustained winds eroded areas of the western shoreline by many feet. A rough estimate based on rates of shoreline erosion and average nutrient concentrations in soils around the lake yields estimates of 0.5-1.0 MT yr-1 total N and 0.3-0.6 MT yr-1 for total P. Both values are less than the errors in the other estimates; however, more quantitative estimates of erosion loss are needed.
The budget clearly suggests the importance of direct runoff as an important P source from urban areas and highlights the need for additional study in this area. However, phosphorus reduction strategies at Lake Tahoe will have to address multiple sources including direct runoff, atmospheric deposition and stream loading. At the same time, the contribution of atmospheric deposition to the N budget clearly dominates other sources. Using the estimated loading of dissolved-P as a first approximation of biologically available-P (BAP), this budget further shows that BAP is on the order of 35-40 of total-P. This is not uncommon; however, the 17 MT value may underestimate true BAP. Research to investigate this further has been proposed. Looking at dissolved-P alone, the relative importance of the groundwater contribution increases.
Studies on the Tahoe nutrient budget have been classified by investigators as 'preliminary', i.e. these provide a first-approximation for establishing working hypotheses for further investigations. Since this preliminary budget was presented, a number of actions have been taken to improve our understanding this is important issue.
1. Additional sampling for direct runoff nutrient concentration was done in an 'urban' and 'non-urban' intervening zone along the west shore. An 'urban' intervening zone is one define as having greater than of equal to 25% of its area in a covered (C) or existing (E) state as defined by the Tahoe Regional Planning Agency. Intervening zone (IZ) 107 has a C+E value of 52% while IN 105 has a value of 10%.
For the 1999 data, the following mean concentrations (mg/L) were found:
| Total Suspended Sediment | Nitrate | Total-P | Soluble-P | |
| IZ 107 | 71 | 0.03 | 0.29 | 0.017 |
| IZ 105 | 23 | 0.004 | 0.14 | 0.008 |
As is evident, the more urban intervening zone (i.e. 107) showed higher nutrient
levels in surface runoff; TSS was 3-fold higher, nitrate was approximately an
order of magnitude higher, while both TP and soluble-P were elevated by a factor
of two. Currently we have data for surface runoff from 'urban' areas from three
studies at Lake Tahoe; these are denoted as follows (1) Lahontan (1984), (2)
Ski Run (1993) and (3) IZ 107 (1998-99; includes this study). It was very interesting
that the primary difference between these data sets lies in the soluble-P to
TP ratios. Soluble-P was elevated in the Lahontan (1984) and Ski Run (1993)
studies at 0.34 and 0.19, respectively. However, for the IZ 107 monitoring,
this ratio declined to 0.05. Indeed, soluble-P in IZ 107 was similar to the
'non-urban' areas (0.01-0.02 mg/L). This lowered the overall mean soluble-P
concentration from the 'urban' area and consequently lowered the estimated soluble-P
load from 5 to 3 metric tons (MT) per year. This lowered the total soluble-P
load from 17 MT to 15 MT with little affect on the other nutrient forms.
Based on available data at this time, the difference in mean nutrient concentrations between 'urban' and 'non-urban' intervening zones is approximated as follows (TSS = total suspended sediment and TKN = total Kjeldahl-N; all concentration expressed as mg/L):
| TSS | TKN | Nitrate | Total-P | Soluble-P | |
| 'Urban' | 231 | 1.01 | 0.04 | 0.41 | 0.08 |
| 'Non-urban' | 37 | 0.33 | 0.02 | 0.09 | 0.01 |
Clearly, and as repeatedly suggested, a more comprehensive monitoring program
for direct runoff is need. On the basis of these findings, the State of California
has allocated funding to accomplish this over the next 2-3 years.
2. In response to the preliminary nutrient budget, which called for a much more detailed investigation of shoreline erosion, the Desert Research Institute (University of Nevada), conducted a study on the historic change in shoreline at Lake Tahoe from 1938-1998. This study estimated total-N loading to Lake Tahoe from shoreline erosion to be 1 MT per year. This as virtually identical to our initial estimate of 0.75 MT, using very course assumptions. Similarly, our rough estimate for TP loading was 0.45 MT/yr with the DRI calculation at 1.6 MT/yr. We were pleased to se that both sets of projected loading values from shoreline erosion were similar, with very little change in our conclusions, vis-à-vis, management strategy
3. Below, we summarize the revised loading estimates expressed as metric tons per year, based on the changes presented above.
| Total N | Total P | Dissolved P | ||
| Atmospheric deposition | 234 (56%) | 12.4 (26%) | 5.6 (37%) | |
| Stream loading | 82 (20%) | 13.3 (28%) | 2.4 (16%) | |
| Direct runoff | 42 (10%) | 15.5 (33%) | 3 (20%) | |
| Groundwater | 60 (14%) | 4 (9%) | 4 (27%) | |
| Shoreline erosion | 1 (<1%) | 1.6 (3%) | No Data | |
| Total | 419 | 46.8 | 15.0 | |
Ecosystem Protection/Environmental Exposure & Risk, Water, INTERNATIONAL COOPERATION, Scientific Discipline, RFA, ECOSYSTEMS, Water & Watershed, Restoration, Aquatic Ecosystem Restoration, Aquatic Ecosystems & Estuarine Research, Terrestrial Ecosystems, Aquatic Ecosystem, Biochemistry, Environmental Microbiology, Watersheds, Ecology and Ecosystems, ecological impact, watershed management, watershed restoration, ecological research, ecology assessment models, aquatic habitat protection , land use, wetland restoration, Lake Tahoe, contaminant exposure, anthropogenic processes, aquatic ecosystems, environmental stress, watershed sustainablility, hydrology, nutrients, restoration strategies, ecosystem stress, biodiversity
Progress and Final Reports:
1999 Progress Report
Original Abstract
Final Report
Main Center Abstract and Reports:
R825433 EERC - Center for Ecological Health Research (Cal Davis)
Subprojects under this Center:
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R825433C001 Potential for Long-Term Degradation of Wetland Water Quality Due to Natural Discharge of Polluted Groundwater
R825433C002 Sacramento River Watershed
R825433C003 Endocrine Disruption in Fish and Birds
R825433C004 Biomarkers of Exposure and Deleterious Effect: A Laboratory and Field Investigation
R825433C005 Fish Developmental Toxicity/Recruitment
R825433C006 Resolving Multiple Stressors by Biochemical Indicator Patterns and their Linkages to Adverse Effects on Benthic Invertebrate Patterns
R825433C007 Environmental Chemistry of Bioavailability in Sediments and Water Column
R825433C008 Reproduction of Birds and mammals in a terrestrial-aquatic interface
R825433C009 Modeling Ecosystems Under Combined Stress
R825433C010 Mercury Uptake by Fish
R825433C011 Clear Lake Watershed
R825433C012 The Role of Fishes as Transporters of Mercury
R825433C013 Wetlands Restoration
R825433C014 Wildlife Bioaccumulation and Effects
R825433C015 Microbiology of Mercury Methylation in Sediments
R825433C016 Hg and Fe Biogeochemistry
R825433C017 Water Motions and Material Transport
R825433C018 Economic Impacts of Multiple Stresses
R825433C019 The History of Anthropogenic Effects
R825433C020 Wetland Restoration
R825433C021 Sierra Nevada Watershed Project
R825433C022 Regional Transport of Air Pollutants and Exposure of Sierra Nevada Forests to Ozone
R825433C023 Biomarkers of Ozone Damage to Sierra Nevada Vegetation
R825433C024 Effects of Air Pollution on Water Quality: Emission of MTBE and Other Pollutants From Motorized Watercraft
R825433C025 Regional Movement of Toxics
R825433C026 Effect of Photochemical Reactions in Fog Drops and Aerosol Particles on the Fate of Atmospheric Chemicals in the Central Valley
R825433C027 Source Load Modeling for Sediment in Mountainous Watersheds
R825433C028 Stress of Increased Sediment Loading on Lake and Stream Function
R825433C029 Watershed Response to Natural and Anthropogenic Stress: Lake Tahoe Nutrient Budget
R825433C030 Mercury Distribution and Cycling in Sierra Nevada Waterbodies
R825433C031 Pre-contact Forest Structure
R825433C032 Identification and distribution of pest complexes in relation to late seral/old growth forest structure in the Lake Tahoe watershed
R825433C033 Subalpine Marsh Plant Communities as Early Indicators of Ecosystem Stress
R825433C034 Regional Hydrogeology and Contaminant Transport in a Sierra Nevada Ecosystem
R825433C035 Border Rivers Watershed
R825433C036 Toxicity Studies
R825433C037 Watershed Assessment
R825433C038 Microbiological Processes in Sediments
R825433C039 Analytical and Biomarkers Core
R825433C040 Organic Analysis
R825433C041 Inorganic Analysis
R825433C042 Immunoassay and Serum Markers
R825433C043 Sensitive Biomarkers to Detect Biochemical Changes Indicating Multiple Stresses Including Chemically Induced Stresses
R825433C044 Molecular, Cellular and Animal Biomarkers of Exposure and Effect
R825433C045 Microbial Community Assays
R825433C046 Cumulative and Integrative Biochemical Indicators
R825433C047 Mercury and Iron Biogeochemistry
R825433C048 Transport and Fate Core
R825433C049 Role of Hydrogeologic Processes in Alpine Ecosystem Health
R825433C050 Regional Hydrologic Modeling With Emphasis on Watershed-Scale Environmental Stresses
R825433C051 Development of Pollutant Fate and Transport Models for Use in Terrestrial Ecosystem Exposure Assessment
R825433C052 Pesticide Transport in Subsurface and Surface Water Systems
R825433C053 Currents in Clear Lake
R825433C054 Data Integration and Decision Support Core
R825433C055 Spatial Patterns and Biodiversity
R825433C056 Modeling Transport in Aquatic Systems
R825433C057 Spatial and Temporal Trends in Water Quality
R825433C058 Time Series Analysis and Modeling Ecological Risk
R825433C059 WWW/Outreach
R825433C060 Economic Effects of Multiple Stresses
R825433C061 Effects of Nutrients on Algal Growth
R825433C062 Nutrient Loading
R825433C063 Subalpine Wetlands as Early Indicators of Ecosystem Stress
R825433C064 Chlorinated Hydrocarbons
R825433C065 Sierra Ozone Studies
R825433C066 Assessment of Multiple Stresses on Soil Microbial Communities
R825433C067 Terrestrial - Agriculture
R825433C069 Molecular Epidemiology Core
R825433C070 Serum Markers of Environmental Stress
R825433C071 Development of Sensitive Biomarkers Based on Chemically Induced Changes in Expressions of Oncogenes
R825433C072 Molecular Monitoring of Microbial Populations
R825433C073 Aquatic - Rivers and Estuaries
R825433C074 Border Rivers - Toxicity Studies