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2000 Progress 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. , Jassby, Alan D. , Kavvas, M. Levant , Reuter, John E. , Schladow, S. G.
Current Investigators: Goldman, Charles R. , Heyvaert , Alan C. , Jassby, Alan D. , Kavvas, M. Levant , Reuter, John E. , Schladow, S. G.
Institution: University of California - Davis
EPA Project Officer: Perovich, Gina
Project Period: June 1, 1998 through May 31, 2001 (Extended to January 31, 2002)
Project Period Covered by this Report: June 1, 2000 through May 31, 2001
Project Amount: $879,376
RFA: Water and Watersheds (1997)
Research Category: Water and Watersheds
Description:
Objective:This project integrates the fields of biological and ecological research, limnology, hydrology, geochemistry, engineering, and environmental modeling in a multi-disciplinary program designed to provide watershed managers and decision makers with a science-based understanding of, and innovative tools for, the development of environmental policy. This research is being conducted in the Sierra Nevada at Lake Tahoe. The primary objectives are to: (1) apply a 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.
Progress Summary:Deteriorating environmental conditions at Lake Tahoe have been documented since the 1960s, and include loss in transparency of 0.3 meters annually, increased algal growth at 5 percent per year, changes in biodiversity, increased loading of nutrients and fine sediment, wetland loss, invasion of non-native biota, air pollution, and decline in forest health. Data suggest that if degradation continues, the remarkable clarity of Tahoe will be lost in 30 years. This precipitated the Presidential Forum in 1997, and necessitated a more rapid conversion of basic limnological studies into management decisions. A primary goal is for science (monitoring, research, and modeling) to assist in the restoration of water quality and ecosystem health at Lake Tahoe. Reduction in phosphorus and fine-sediment loading is considered critical to reduce the accelerated decline in water clarity.
Our approach can be summarized in a series of three questions that need to be understood to achieve effective management of lake clarity:
(1) What are the sources and relative contributions of nutrients and fine sediments?
(2) How much of a reduction in this material is needed to attain desired water
clarity?
(3) How will this reduction be achieved?
A critical component for long-term planning at Lake Tahoe is a water clarity model, based on the lake's capacity to receive and process sediment and nutrients. By knowing the level of loading required to attain the desired lake conditions (total maximum daily load [TMDL] approach), responsible agencies will be better able to plan in a more quantitative and progressive manner. Based on research from Years 1-3, along with our other extensive research and monitoring database, we have been developing such a model as the focal point of this grant. The clarity model also provides the structure for future water quality research and monitoring. The model will be used in a predictive fashion, allowing agencies to assess lake response based on various levels and stages of watershed management. Information obtained with this grant originally served as the building blocks to construct the clarity model. However, because of the pressing need for this type of management tool at Lake Tahoe, we will end this grant on an accelerated schedule with a first-generation version of a clarity model. Ultimately, the clarity model should be able to identify the total amount of nutrient loading per year required to achieve the Secchi depth threshold standard. Coupled with a nutrient budget, regulators would then establish targets for reduction, i.e., expectation of a TMDL program. Planning documents, proposed projects, Best Management Practices (BMPs), and restoration/erosion control work then could be assessed on the basis of their ability to meet these target loads.
Sediment Transport Model
Erosion and sediment transport take place by hydrologic flow processes within watersheds. It is necessary to have a physically based hydrologic watershed model to predict erosion/sediment transport from Lake Tahoe's multiple watersheds. When complete, the model will be utilized for the following purposes: (1) quantifying the effect of changes to land surface/vegetation (e.g., road cuts, urbanization, forest practices) on the water, sediment, and nutrient balances in Lake Tahoe watersheds; (2) flood forecasting; and (3) assessing long term water balances at Lake Tahoe under various scenarios of future climate change. The watershed hydrologic model includes the following processes: overland flow, interception, evapotranspiration, soil unsaturated flow, subsurface stormflow, rapid saturated flow (above an impeding soil layer below the plant root zone), deep unconfined groundwater aquifer flow, and stream network flow routing.
With the completion of the calibration and verification of the hydrology model, the foundation for modeling erosion/sediment transport has now been built. The development of the transport models was the focus for research during 2000. The erosion process was modeled mainly in two components, upland and in-stream erosion. In the upland erosion component, rill and interrill interaction was considered. The 2-D continuity equation was used together with kinematic wave approximation. By performing local scale averaging in the perpendicular direction to the flow, the continuity equation became a 1-D equation, which is easier to solve. The source term of the equation comes from rain splash erosion, which is considered proportional to the square of rainfall intensity. In the rill part of the model, the 1-D continuity equation was used. The source term of this equation comes from the solution of the interrill erosion equation as lateral sediment input plus erosion taking place in the rill bed. The unique data used for this study were taken from previous field experiments on erosion performed in northern California. The interrill and rill components of the model were calibrated using these data.
Channel erosion was modeled in a similar manner; however, the cross section of the channel was taken as trapezoidal. This makes the model more general. Both in rills and in the channel it is assumed that flow should have a shear stress higher than the critical shear stress required for initiation of the sediment particles. Once shear stress of the flow exceeds the critical value, sediment starts to erode. It does necessarily mean that eroded sediment is transported downstream. Once the concentration exceeds the transport capacity, eroded sediment is deposited. Although we attempted to obtain a fully physically based erosion and sediment transport model, it will still contain some empiricism due to the lack of field sediment data. All of the existing physically based models use empirical relationships based on some limited laboratory or field data for the source term of the continuity equation. The most important factors in such a problem are determination, calibration, and validation of the empirical parameters. For further study of channel erosion processes, a 2-D channel flow model also was developed as an independent module, so that it can be switched with the existing 1-D channel flow model if additional details on channel hydraulics are required. The 2-D channel flow model will allow us to identify the source of erosion in a stream by distinguishing the main portion and bank portion of the stream separately.
In addition to the modeling work in the Ward Creek watershed, the intervening zone (runoff directly to lake) in the Kings Beach area of north Lake Tahoe was studied to assess the transport of sediment. The intervening zone has the added complexity of an urban component that provides a modeling challenge, and a model considering the effect of urbanization should be used. Due to the presence of multiple components within the watershed, different models were proposed to deal with those components. The rural portion of the intervening zone can be modeled by the same hydrologic model used for the Ward Creek watershed, and will provide necessary hydrologic inputs to urban components. For modeling of the urban component of the watershed, the Storm Water Management Model (SWMM), an urban model developed for water quantity and quality simulations by the Environmental Protection Agency (EPA) was proposed, as it has been widely used and tested for many urban applications. The SWMM has been successfully installed and tested for a hypothetical urban watershed, and it is ready to be used in modeling the runoff and transport processes in the intervening zone. We currently are in the process of finalizing the Geographic Information Systems (GIS) analysis, which will provide various model parameters for the modeling of both rural and urban components.
Water 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 1-D modeling approach has been adopted as a primary focus of this grant. The 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 in turn be calculated from the algal concentration and the 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)-includes water motions, mixing, waves, particle settling, etc. (this portion of the model is complete and 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. (work is near completion on this component); and (3) optical properties (Secchi depth)-includes adsorption and scattering of light by organic and inorganic particles, and dissolved matter. Work is near completion on this component. The model is being run using data collected during 2 years-1992, at the end of a drought, and 1999, a wet El Niño year.
For the first time, we now have data on the characterization of particulate matter in Lake Tahoe; this material largely determines clarity. Key findings include: (1) the majority of particles in Lake Tahoe were smaller than 2 µm; (2) average, depth-weighted particle concentrations ranged from 8,000-12,000 particles/mL; and (3) the contribution of organic versus inorganic particles were in the range of 35-75 percent depending on the season.
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. This year's research progress has clarified the relationships between the water constituents and the optical characteristics. We have found good correlations between Kd, the diffuse attenuation coefficient, and Secchi depth, and between particulate absorption and chlorophyll-a concentration, which link the water quality model to the clarity model. Preliminary calculations spanning the range of conditions observed at Lake Tahoe show a very good agreement between observed and predicted Secchi depth.
At this stage, we believe this model includes all major water constituents needed to support a predictive model of water clarity. In principle, this model should be generally applicable to a wide range of aquatic settings, and would provide a tool for other EPA projects concerned with eutrophication. Because it is based on physical principles of light scattering and absorption, rather than on correlative regressions, it will be useful without extensive recalibration or "localization."
Future Activities:We applied for and received a no-cost extension for 2001. This was requested because: (1) work on the clarity model was proceeding further than originally proposed, and (2) most of our effort to date has been in construction, calibration and verification of models, and collecting input data. We have not had sufficient time to report preparation.
During the project year 2001, the following work is planned for the sediment transport model: (1) the newly developed snowmelt component will be applied to some historical snowmelt-runoff events to validate the model for the snowmelt-induced runoff events; (2) the developed overland rill flow-sheet flow erosion/sediment transport/nutrient transport model will be incorporated into the watershed hydrology model and will be applied to the Ward Creek watershed for calibration and validation; and (3) field observation of flow/sediment transport processes will be continued.
All three components of the DLM-Tahoe Clarity model are nearly completed. This year, they will be incorporated into the final clarity model; we anticipate completion within 3 months. Once finalized, the model will be validated and run on test scenarios. This currently is being conducted in collaboration with Xavier Casamitjana and Joaquim Losada from the University of Girona. Co-Principal Investigator Schladow is on sabbatical leave in Spain overseeing this effort.
Journal Articles on this Report: 15 Displayed | Download in RIS Format
| Other project views: | All 56 publications | 26 publications in selected types | All 20 journal articles |
| 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 2000;37(2):405-415. |
R826282 (2000) R826282 (Final) |
not available |
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Dogrul E, Kavvas ML, Chen ZQ. Prediction of subsurface stormflow in heterogeneous sloping aquifers. Journal of Hydrologic Engineering 1998;3(4):258-267. |
R826282 (1998) R826282 (2000) R826282 (Final) |
not available |
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Goldman CR. Four decades of change in two subalpine lakes. Baldi Lecture. Verhandlungen IVL 2000;27(Pt 1):7-26 |
R826282 (1998) R826282 (1999) R826282 (2000) R826282 (Final) |
not available |
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Goldman CR. Management-driven limnological research. Archives of Hydrobiology, Special Issues Advanced Limnology 2000;55:257-269. |
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) |
not available |
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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) |
not available |
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Hatch L, 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) |
not available |
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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 and Technology 2000;34(17):3588-3597. |
R826282 (1999) R826282 (2000) R826282 (Final) R825433 (Final) |
not available |
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Huovinen PS, Goldman CR. Inhibition of phytoplankton production by UV-B radiation in clear subalpine Lake Tahoe, California-Nevada. Verhundlungen der Internationale Vereinigung Limnologie 2000;27(Part 1):157-160. |
R826282 (1998) R826282 (1999) R826282 (2000) R826282 (Final) |
not available |
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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) |
not available |
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Jassby AD, Goldman CR, Reuter JE, Richards RC. Biostatistical evaluation of long-term lake clarity record. Verhundlungen der Internationale Vereinigung Limnologie, Volume 27. |
R826282 (1999) R826282 (2000) R826282 (Final) R825433 (Final) |
not available |
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Kavvas ML, Chen ZQ, Tan L, Soong ST, 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) |
not available |
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Rueda FJ, Schladow SG, Palmarsson FJ. Wind-driven basin-scale internal waves in a deep monomictic alpine lake: theory, observations, and 3-D numerical simulations. Journal of Hydraulic Engineering 2003;129(2):92-101 |
R826282 (2000) |
not available |
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Schladow SG, Thompson KL. Winter thermal structure of Lake Tahoe. Limnology and Oceanography 2001;40(2):359-373. |
R826282 (2000) R826282 (Final) R825428 (Final) |
not available |
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Thompson KL, Schladow SG. Deep winter mixing due to seasonal differential cooling in Lake Tahoe. Limnology and Oceanography 2000. |
R826282 (2000) R826282 (Final) R825428 (Final) |
not available |
limnology, water clarity, watershed management, adaptive management, best management practices, ecological restoration, eutrophication, watershed disturbance, urbanization, subalpine, lake hydrodynamics, erosion, runoff, modeling. , Ecosystem Protection/Environmental Exposure & Risk, Water, Geographic Area, Scientific Discipline, RFA, Ecosystem/Assessment/Indicators, Water & Watershed, Nutrients, Hydrology, Watersheds, Environmental Chemistry, Ecological Effects - Environmental Exposure & Risk, Ecosystem Protection, Ecology and Ecosystems, State, phytoplankton dynamics, water quality, hydrological stability, ecosystem effects, ecological response, fate and transport, watershed management, ecosystem indicators, limnology, biological integrity, sediment runoff, lake ecosystems, land use, urban landscapes, environmental monitoring, ecological exposure, aquatic ecosystems, erosion, nutrient transport, biogeochemistry, Nevada (NV), ecosystem, nutrient supply, suspended particulate matter, ecological models, ecological effects, pollutant transport
Relevant Websites:
Progress and Final Reports:
1998 Progress Report
1999 Progress Report
Original Abstract
Final Report