Grantee Research Project Results
Final Report: An Integrated Watershed Approach to Evaluate and Model Ecosystem Effects of Erosion and Pollutant Transport in Urbanized Subalpine Landscapes
EPA Grant Number: R826282Title: An Integrated Watershed Approach to Evaluate and Model Ecosystem Effects of Erosion and Pollutant Transport in Urbanized Subalpine Landscapes
Investigators: Goldman, Charles R. , Heyvaert , Alan C. , Jassby, Alan D. , Reuter, John E. , Schladow, S. G. , Kavvas, M. Levant
Institution: University of California - Davis
EPA Project Officer: Packard, Benjamin H
Project Period: June 1, 1998 through May 31, 2001 (Extended to January 31, 2002)
Project Amount: $879,376
RFA: Water and Watersheds Research (1997) RFA Text | Recipients Lists
Research Category: Water , Watersheds
Objective:
This research project integrated the fields of biology, ecology, limnology, hydrology, geochemistry, engineering, and environmental modeling in a multi-disciplinary program designed to provide watershed managers and decisionmakers with a science-based understanding of, and innovative tools for, the development of environmental policy. This research was conducted in the Sierra Nevada at Lake Tahoe. The primary objectives were to: (1) apply new hydrologic model to describe dynamics of non-point source pollutants over complex landscapes; (2) use lake modeling techniques and field measurements to quantify the fate of biogenic and inorganic particulate matter in Lake Tahoe; (3) integrate watershed processes related to erosion and pollutant transport with lake and stream response; (4) employ paleolimnological techniques to reconstruct lake and watershed response to historical disturbance; and (5) work within the context of existing government agencies and non-profit conservation groups to develop a watershed-scale erosion control management plan.
The Tahoe Basin is a changing landscape; at present, significant portions of this once pristine region are urbanized. Studies from the early 1960s to today have shown that many factors such as land disturbance, increasing resident and tourist population, habitat destruction, air pollution, soil erosion, roads and road maintenance, loss of wetlands, and areas for natural infiltration of runoff have all interacted to degrade the basin's air quality, terrestrial landscape, and streams, as well as the lake itself. We now know that once nutrients enter the lake they remain in the water, and can be recycled for decades. As a consequence, these pollutants accumulate over time and contribute to Lake Tahoe's progressive decline. The ability of Lake Tahoe to dilute nutrient and fine-sediment loading to levels where they have no significant affect on lake water quality has been lost.
Cause for Concern. Continuous, long-term evaluation of Lake Tahoe's water quality since the early 1960's has shown that algal growth is increasing at a rate greater than 5 percent per year. Over this same period, there has been a decline of clarity at an alarming rate of nearly one foot per year. This long-term trend in loss of transparency is both statistically significant (p <0.001) and now perceptive to even the casual observer. If the loss of clarity continues at this rate, the resulting Secchi depth will be accompanied by a change of lake color and a change in trophic status. Fine-sediments and nutrients are the major constituents, which must be controlled to meet desired conditions for lake clarity and algal growth.
Science-Based Decisionmaking. The watershed approach used at Lake Tahoe recognizes that lake water quality is linked to upland watershed processes and air quality. This understanding precipitated the formulation of the Environmental Improvement Program (EIP) by the Tahoe Regional Planning Agency. The EIP is a regional document, which presents restoration projects considered necessary to achieve environmental restoration in the Tahoe basin.
To effect lake management, we investigated the following:
· What are the specific sources of sediment and nutrients to the lake
and what are their respective contributions?
· How much loading reduction is necessary to achieve the desired thresholds
and/or Total Daily Maximum Loads (TMDLs) for Lake Tahoe (i.e., lake response)?
· How will this reduction be achieved?
The Role of Adaptive Watershed Management. Coordinated efforts for natural resource management in the Tahoe Basin are being organized under the adaptive management framework. The adaptive management approach is designed to speed rates of development and implementation of appropriate resource management strategies through research and monitoring. A critical element of this process is the constant refinement of management strategies through an iterative process of monitoring, data evaluation, decisionmaking, and management action. It may take many years to see changes in Lake Tahoe's clarity, resulting from immediate reductions of nutrient input to the lake; hence the need for forecast modeling at both the watershed and lake scales.
TMDLs and Water Clarity Protection. Research has shown that it is the load of fine-sediment and nutrients and not simply their concentration that affects the long-term clarity trend. Consequently, a TMDL approach is well suited for Lake Tahoe and an ideal match for the EIP restoration approach. It is becoming more widely recognized at Lake Tahoe that solutions to the declining clarity require quantitative targets for load reduction. Historically, science has identified the need for sediment and nutrient reduction, but it has been largely silent on the required magnitude of reduction. Qualitative solutions/targets have been forwarded. Fertilizer use must be reduced, and erosion control projects must be installed. There needs to be an implementation of BMPs designed to treat surface runoff, environmentally sensitive lands need to be purchased, and building restrictions are necessary. Although these approaches have been beneficial, they provide little advice on the level of effort needed for implementation of restoration activities to achieve the desired level of water clarity, as expressed by the Tahoe Regional Planning Agency's Thresholds and the water quality standards for clarity as set forth by the States of California and Nevada.
Summary/Accomplishments (Outputs/Outcomes):
Algal Growth. The first measurements of phytoplankton growth in Lake Tahoe were completed by Charles Goldman in 1959. At that time, the annual rate was slightly less than 40 g C m-2 yr-1 and typical of an ultraoligotrophic lake. For the years prior to 1959, the average annual primary productivity was reconstructed from an analysis of sediment cores. Heyvaert (1998) concluded that the baseline pre-disturbance (prior to 1850) primary productivity was 28 g C m-2 yr-2. The calculated value for 1900-1970, the period between the effects of the Comstock logging era in the late 1800s when significant portions of the Basin's forests were clear cut and the onset of urbanization, was almost identical at 29 g C m-2 yr-2. The recovery of baseline conditions following the extensive timbering activities of the Comstock period provides evidence that Lake Tahoe can recover from watershed disturbance within decades.
The long-term increase in primary productivity in Lake Tahoe is attributed to increased nutrient loading acting in concert with the lake's long hydraulic retention time (approximately 650 years) and efficient recycling of nutrients. While year-to-year variability in primary productivity is directly related to the depth of mixing (Goldman, et al., 1989), the long-term trend results from the buildup of dissolved and fine particle size matter, which has a very slow sinking rate, reinforcing that the most efficient management strategy is the source control that keeps these materials out of the lake.
Results from long-term algal growth response bioassay experiments show a clear shift from co-limitation by both nitrogen (N) and phosphorus (P) to predominant P limitation (Goldman, et al., 1993). This shift began in the early to mid-1980s, and is attributed to the accumulation of anthropogenic nitrogen from atmospheric deposition directly on to the lake surface (Jassby, et al., 1994). These results confirm current efforts to reduce P-loading through erosion control, revegetation, land acquisition of environmentally sensitive parcels, and other similar projects.
Lake Water Clarity. Water clarity is an excellent indicator of lake response in Lake Tahoe and has been measured using a Secchi disk on a continuous basis since 1968. Jassby, et al. (1999), found lake clarity to be dominated by a long-term decreasing trend; this trend was highly significant (p <0.0025) with a slope of -0.25 m/yr. The long-term change in Secchi depth appears to be due to a long-term accumulation of particles in the lake. The mean seasonal pattern over the period of record has been bimodal, with a strong annual minimum Secchi depth in approximately June, and a weaker local minimum in December. These minimum periods were statistically modeled and found to be related to the melting of the seasonal snowpack and the mixing into the deep chlorophyll maxima, respectively. The overall maximum was in February with a secondary local maximum in October.
The first comprehensive study of particle number, size, and composition in Lake Tahoe was undertaken as part of this grant from 1999-2000 (Coker, 2000). The average depth-weighted particle concentration in the lake ranged from approximately 8,000 to 12,000 particles/ml. From 1999-2000, the relative contribution of organic particles (presumably mostly of a lake origin as either phytoplankton or bacteria) was 50-85 percent, while the mineral (terrestrial) suspensoids ranged from a 10-40 percent contribution. While the absolute number of mineral particles never exceeded the organic particles, the relative contribution of the former to light scattering is much greater.
Results from the University of California at Davis (UCD) Clarity Model for Lake Tahoe, constructed as part of this grant, further support the importance of the fine-grain size mineral suspensoids in affecting Secchi depth (Schladow, et al., 2001). Initial model runs suggest that the fine inorganic particles (mineral or soil origin) are exerting a major influence on water clarity at Lake Tahoe. A reduction in the lake particle inventory (not annual loading) by approximately 50 percent could return the lake to the clarity levels experienced 30 years ago. At the same time, continued buildup of mineral particles will further reduce clarity.
Nutrient and Sediment Loading Budget. Five major sources of nutrients to Lake Tahoe have been identified: (1) direct wet and dry atmospheric deposition; (2) stream discharge; (3) overland runoff directly to lake; (4) groundwater; and (5) shoreline erosion. The major losses include settling of material from the water column to the bottom, and to a much lesser extent, discharge to the Truckee River outflow. This initial budget was able to provide first estimates for phosphorus and nitrogen loading; however, to use this budget for TMDL purposes, a much more indepth analysis of the specific sources of N and P is needed. At the same time, lake-wide estimates for sediment and particle size loads are needed, especially given the potential importance of mineral suspensoids to lake clarity.
Total-N | Total-P | Dissolved-P | |
Atmospheric Deposition | 234 (59%) | 12.4 (28%) | 5.6 (39%) |
Stream loading | 82 (20%) | 13.3 (31%) | 2.4 (17%) |
Direct runoff | 23 (6%) | 12.3 (28%) | 2.4 (17%) |
Groundwater | 60 (15%) | 4 (9%) | 4 (27%) |
Shore erosion | 1 (<1%) | 1.6 (4%) | No Data |
Total | 400 | 43.6 | 14.4 |
(values as metric tons) |
This budget clearly suggests the importance of direct runoff as an important P source from urban areas, and highlights the need for additional study of loading from this source. At the same time, the contribution of atmospheric deposition to the N budget clearly dominates other sources. Heyvaert (unpublished data) found that nutrient sedimentation losses to the bottom of Lake Tahoe are 402 MT for total N and 53 MT for total P. These data are consistent with the independent loading estimates given above. This close consistency gives us increased confidence that the loading rates are representative.
Reconstruction of Lake and Watershed Response to Historical Disturbance Using Paleolimnological Techniques. We now have a relatively reliable geochronology for the Lake Tahoe sediments, constructed from 210Pb and 14C data. These data indicate that significant basin-wide changes have occurred in mass sedimentation rates over the last 150 years. Specifically, high sedimentation rates were associated with clear-cut logging in the Tahoe basin from 1860-1900, followed by a three-to-five-fold decrease in mass sedimentation rates during the early twentieth century. These lower rates persisted until urbanization began in the Tahoe basin after World War II. From 210Pb data, the average mass sedimentation rate (with a 90 percent confidence interval) during the Comstock logging era from 1860-1900 was 0.043 (± 0.011) g cm-2 yr-1. By comparison, the average mass sedimentation rate for the recent period from 1970 to 1990 was 0.027 (± 0.006) g cm-2 yr-1. These rates are significantly higher than the average sedimentation rate of 0.009 (±0.004) g cm-2 yr-1 that was determined for the intervening period from 1900 to 1970. Pre-disturbance sedimentation rates were estimated from 14C measurements in several deep sections of two cores. The long-term average rate was 0.006 (± 0.002) g cm-2 yr-1, which is slightly less than the sedimentation rate that was estimated for the intervening period between Comstock logging and urbanization. Because these rates are comparable, it appears that landscape recovery was rapid after clear-cut logging ended, and that sedimentation rates dropped to nearly pre-disturbance levels.
Lake Tahoe Clarity Model. Watershed mitigation at Tahoe may take 10-15 years to complete. Because the lake has a retention time of decades for nutrients, monitoring may not detect the direct effect of restoration on lake clarity for many years. Lake modeling provides a tool to overcome this time lag. To explore management options for loading reduction to the lake, a one-dimensional model was developed as a major deliverable from this grant (Schladow). The model, the UCD model, DLM-Tahoe Clarity, is driven by daily inputs of meteorological and hydrologic data. Water quality inputs are from streams, surface runoff, groundwater, and atmospheric loading. The model seeks to predict the distribution of nutrient concentration, algal concentration, and suspended particle concentration. Water clarity, a function of light absorption and scattering, can be calculated from algal concentration, size distribution, and concentration of particles. Intensive data collection has been initiated to provide sufficient calibration and validation data for the optical part of the model.
The model consists of three components: (1) hydrodynamics (physical processes), which includes water motions, mixing, waves, particle settling, etc. This portion of the model is largely driven by meteorological forcing factors and lake depth; (2) water quality (algal growth related)-includes nutrient uptake and cycling, dissolved oxygen, zooplankton, etc.; and (3) optical properties (Secchi depth), which include adsorption and scattering of light by organic and inorganic particles, and dissolved matter. The optical model calculates the scattering and absorption characteristics of the water constituents (particulate organic, particulate inorganic, and dissolved matter) based on particle size distribution, composition, and bulk concentration, then calculates the Secchi depth from the inherent optical properties.
The adopted one-dimensional approach adequately describes the changing conditions in the lake for two independent time periods of approximately one year's duration (Losada 2001). During 1999, actual measured clarity varied from a maximum of approximately 34 m to a minimum of approximately 13 m, and the model predictions captured this seasonality. The clarity model will serve as a management tool to allow for the prediction of allowable nutrient and sediment loads. TMDLs will be largely based on output from this model.
Sediment Transport Modeling-Nonpoint Source Pollution. The UCD Hydrologic Research Laboratory (Kavvas) developed a physically based, spatially distributed, watershed hydrologic model that employs six sub-models to represent the major hydrologic processes in a watershed: (1) snow accumulation and snowmelt model; (2) spatially averaged soil moisture flow model; (3) spatially averaged subsurface storm-flow model; (4) averaged overland flow model; (5) stream network flow model; and (6) groundwater model coupled with the stream network flow model.
The UCD Sediment Transport Model was applied to Lake Tahoe's Ward Creek Watershed to test its utility in modeling hydrology and related ecological problems. First, the watershed's hydrologic simulation is presented to demonstrate the strength of the physically based watershed hydrology model. Second, the impact of forest fire on the hydrologic response from the watershed is discussed. As a final example, erosion and sediment transport from the watershed is presented using the results from the coupled hydrology-erosion/sediment transport model.
Hydrologic simulation of the watershed is an essential first step that leads to any ecological application, such as erosion/sediment transport and nutrient transport as the hydrological processes are the driving mechanisms for all these transport processes. The Ward Creek Watershed is one of the 63 sub-basins in Lake Tahoe, and is located at the northwest region of the lake. The basin is 26 km2 and can be characterized as a natural alpine/subalpine watershed. Elevations vary from 1,907 m to 2,662 m with the mean elevation of 2,229 m above sea level. Slopes range from 0 to 100 percent with the mean slope of 25 percent. Soil types within the watershed vary from alluvium to rock outcrop, but mostly they are sandy loam. The main source of discharge comes from spring snowmelt: snowpack remains typically from November to May in the watershed. The model was run for the first week of September 1998 rain event to test its performance. Using the physically based model, UCD Hydrologic Research Laboratory delineated individual contribution from different hydrological processes. Groundwater components provided base-flow conditions for the event period. Also, the contribution from subsurface stormflow and overland flow that provided peak generation during the second and third rainfall event of the period was significant.
Application of the hydrologic model to study the impact of different fire scenarios on the hydrologic response of the watershed revealed that one of the major and obvious changes was the clearing of vegetation, which had an implication to interception and evapotranspiration. Another notable change was soil texture modification as attributed to high temperature during the fire. Whether the change occurs in either coarser or finer direction, it influenced the infiltration characteristics of the burned area.
As the final example, the model was applied to erosion and sediment transport in the Ward Creek Watershed. The model was successful in simulating the observed sediment load at the mouth of the watershed. In addition, the model provided spatial and temporal variations in sediment load within the watershed, and demonstrated its capability in identifying the source areas within the watershed that deserve higher priority in restoration consideration.
Journal Articles on this Report : 14 Displayed | Download in RIS Format
Other project views: | All 57 publications | 21 publications in selected types | All 15 journal articles |
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Type | Citation | ||
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Coats RN, Goldman CR. Patterns of nitrogen transport in streams of the Lake Tahoe Basin, California-Nevada. Water Resources Research 2001;37(2):405-415. |
R826282 (2000) R826282 (Final) |
Exit |
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Dogrul E, Kavvas ML, Chen ZQ. Prediction of subsurface storm flow in heterogeneous sloping aquifers. Journal of Hydrologic Engineering 1998;3(4):258-267. |
R826282 (1998) R826282 (2000) R826282 (Final) |
Exit |
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Goldman CR. Four decades of change in two subalpine lakes--Baldi Lecture. Verhandlungen der Internationalen Vereinigung Limnologie 2000;27(Pt 1):7-26. |
R826282 (1998) R826282 (1999) R826282 (2000) R826282 (Final) |
not available |
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Hatch LK, Reuter JE, Goldman CR. Daily phosphorus variation in a mountain stream. Water Resources Research 1999;35(12):3783-3791. |
R826282 (1999) R826282 (2000) R826282 (Final) R825433 (Final) |
Exit Exit |
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Hatch LK, Reuter JE, Goldman CR. Relative importance of stream-borne particulate and dissolved phosphorus fractions to Lake Tahoe phytoplankton. Canadian Journal of Fisheries and Aquatic Sciences 1999;56(12):2331-2339. |
R826282 (1999) R826282 (2000) R826282 (Final) R825433 (Final) |
Exit |
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Hatch LK, Reuter JE, Goldman CR. Stream phosphorus transport in the Lake Tahoe Basin, 1989-1996. Environmental Monitoring and Assessment 2001;69(1):63-83. |
R826282 (2000) R826282 (Final) R825433 (Final) |
Exit |
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Heyvaert AC, Reuter JE, Slotton DG, Goldman CR. Paleolimnological reconstruction of historical atmospheric lead and mercury deposition at Lake Tahoe, California-Nevada. Environmental Science & Technology 2000;34(17):3588-3597. |
R826282 (1999) R826282 (2000) R826282 (Final) R825433 (Final) |
Exit |
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Huovinen PS, Goldman CR. Inhibition of phytoplankton production by UV-B radiation in clear subalpine Lake Tahoe, California-Nevada. Verhandlungen der Internationalen Vereinigung Limnologie 2000;27(Pt 1):157-160. |
R826282 (1998) R826282 (1999) R826282 (2000) R826282 (Final) |
Exit |
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Jassby AD, Goldman CR, Reuter JE, Richards RC. Origins and scale dependence of temporal variability in the transparency of Lake Tahoe, California-Nevada. Limnology and Oceanography 1999;44(2):282-294. |
R826282 (1998) R826282 (1999) R826282 (2000) R826282 (Final) R825433 (Final) |
Exit Exit Exit |
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Jassby AD, Goldman CR, Reuter JE, Richards RC. Biostatistical evaluation of long-term lake clarity record. Verhandlungen der Internationalen Vereinigung Limnologie 2000;27:2634-2635. |
R826282 (1999) R826282 (2000) R826282 (Final) R825433 (Final) |
not available |
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Kavvas ML, Chen Z-Q, Tan L, Soong S-T, Terakawa A, Yoshitani J, Fukami K. A regional-scale land surface parameterization based on areally-averaged hydrological conservation equations. Hydrological Sciences Journal 1998;43(4):611-631. |
R826282 (1998) R826282 (2000) R826282 (Final) R825433 (Final) |
Exit Exit Exit |
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Rueda FJ, Schladow SG. Dynamics of large polymictic lake. II: Numerical simulations. Journal of Hydraulic Engineering 2003;129(2):92-101. |
R826282 (Final) R825428 (Final) R825433 (Final) |
Exit |
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Rueda FJ, Schladow SG, Palmarsson SO. Basin-scale internal wave dynamics during a winter cooling period in a large lake. Journal of Geophysical Research: Oceans 2003;108(C3):Art. No. 3097, doi:10.1029/2001JC000942. |
R826282 (Final) R825433 (Final) |
Exit Exit Exit |
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Tayfur G, Kavvas ML. Areally-averaged overland flow equations at hillslope scale. Hydrological Sciences Journal 1998;43(3):361-378. |
R826282 (1998) R826282 (Final) R825433 (Final) |
Exit Exit Exit |
Supplemental Keywords:
watershed, Lake Tahoe, nutrient, sediment, erosion, ecosystem protection, ecosystem assessment, ecology and ecosystems, aquatic ecosystems, ecosystem, ecosystem effects, ecosystem indicators, environmental exposure and risk, waste, water, biochemistry, chemical mixtures, environmental exposure and risk, contaminated sediments, ecological effects, ecological indicators, ecological effects, ecological exposure, ecological models, ecological response, human health, environmental chemistry, hydrology, limnology, nutrients, state, watershed, environmental biology, Nevada, NV, California, CA, biogeochemistry, biological integrity, contaminated sediment, environmental monitoring, erosion, fate, transport, hydrological stability, lake ecosystems, land use, nutrient supply, nutrient transport, phytoplankton dynamics, pollutant transport, sediment runoff, subalpine landscapes, suspended particulate matter, urban landscapes., RFA, Scientific Discipline, Water, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Nutrients, Hydrology, Water & Watershed, Environmental Chemistry, Ecosystem/Assessment/Indicators, Ecosystem Protection, State, Ecological Effects - Environmental Exposure & Risk, Ecology and Ecosystems, Watersheds, limnology, environmental monitoring, fate and transport, hydrological stability, nutrient supply, nutrient transport, ecological effects, ecological exposure, erosion, watershed management, urban landscapes, pollutant transport, ecosystem effects, subalpine landscapes, biological integrity, phytoplankton dynamics, Nevada (NV), ecosystem indicators, sediment runoff, aquatic ecosystems, ecosystem, water quality, biogeochemistry, ecological models, land use, lake ecosystems, suspended particulate matterProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.