Model Application


The calibrated models were used to run a set of scenarios to examine the water-quality changes that might occur in this reach if inputs from the three point sources (Klamath Falls WWTP, South Suburban WWTP, Columbia Forest Products) and two tributaries (Lost River Diversion Channel, Klamath Straits Drain) were altered so that they were in compliance with the Klamath River TMDL (Oregon Department of Environmental Quality, 2010). The effect of altering the Link River input to meet Upper Klamath Lake TMDL in-lake phosphorus targets (Oregon Department of Environmental Quality, 2002) also was examined. The following four scenarios were run for calendar years 2006–09: 


1a. Base case; Link River, point sources, and tributaries at existing conditions.


1b. Link River at existing conditions; point sources and tributaries in compliance with TMDL.


2a. Link River at TMDL targets; point sources and tributaries at existing conditions.


2b. Link River at TMDL targets; point sources and tributaries in compliance with TMDL.


Scenario Setup


Point Sources and Tributaries


Wasteload allocations from the Klamath River TMDL (table 8; Oregon Department of Environmental Quality, 2010) were used to adjust the model input files for Klamath Falls WWTP, South Suburban WWTP, Lost River Diversion Channel, and Klamath Straits Drain. ODEQ staff were consulted to determine how to most appropriately adjust the source loadings in light of the TMDL allocations. The first two source loadings are considered point sources, with allocations regulated as monthly medians. The last two source loadings are considered nonpoint sources in the TMDL, and those allocations were considered as yearly averages. Columbia Forest Products met all TMDL allocations under existing conditions, so this input was unaltered in the scenarios. In adjusting the input files, constituents that contributed to total phosphorus (orthophosphorus, dissolved organic matter, particulate organic matter, and the three algae groups) were first decreased to meet the phosphorus loading criteria, which required the largest reductions (table 9). The percent reduction required to meet the allocations were held constant through each year, thus maintaining seasonal patterns, but allowing variation between years. It was assumed that DOM would be more difficult to remove, so for the Lost River Diversion Channel and Klamath Straits Drain, which have wetlands and associated DOM from their tributaries, model DOM concentrations were not reduced as much as the other constituents. Their reduction value was usually 10 percent lower than reductions for other phosphorus-containing constituents.


Because organic matter and algae contain nitrogen as well as phosphorus, reductions to meet the phosphorus allocations also reduced inputs of nitrogen. If further reductions to meet nitrogen loading criteria were needed, then nitrate and ammonia concentrations were decreased. The TMDL BOD5 allocations (table 8) were met after phosphorus reductions and did not require additional reductions in input concentrations. The model that was used to set TMDL allocations (Tetra Tech, 2009) considered all organic matter in the inputs to be labile, resulting in a higher oxygen demand over short periods compared to the model described herein, which divides the input organic matter into labile and refractory groups based on more recent information on the nature of organic matter in this system.


Link River


In-lake phosphorus target criteria from the Upper Klamath Lake TMDL (Oregon Department of Environmental Quality, 2002) were used to produce a TMDL compliant Link River input. These target phosphorus concentrations were 30 ppb (μg/L) from March to May and 110 ppb from June to July. Although the TMDL describes the 110 ppb level as an annual lake target, it was considered herein as a summer target (Daniel Turner, Oregon Department of Environmental Quality, oral commun., December 10, 2010). Constituents that contributed to phosphorus in the Link River input (orthophosphorus, dissolved organic matter, particulate organic matter, the three algae groups) were decreased in concentration until the phosphorus concentration targets were met (table 9). Dissolved organic matter was reduced less than other constituents because Upper Klamath Lake has extensive wetlands in its drainage; those reduction values were 10 percent lower than for other phosphorus-containing constituents. The reduction factors were held constant throughout the year to retain a seasonal pattern that was similar to existing conditions. Because the seasonal pattern was retained, the 30 ppb criterion was more restrictive than the 110 ppb criterion.


Scenario Results


Dissolved Oxygen


Reducing concentrations of Link River inputs to reflect attainment of Upper Klamath Lake TMDL in-lake phosphorus targets (scenario 2a) was highly effective in increasing dissolved-oxygen concentrations in the Klamath River upstream of Keno Dam (table 10 summarizes all years; figure 21A shows 2007 as a representative year). This scenario resulted in average increases of 1.9 to 3.2 mg/L dissolved oxygen for the June through October period compared to the base case (scenario 1a, Link River, point sources, and tributaries at existing conditions), but far more than that at certain locations when hypoxia occurred in the base case. In large part, this was caused by the large load reduction of blue-green algae and LPOM flowing into the reach from Link River and the resultant decrease in first-order SOD (fig. 21B–D). Blue-green algae concentrations decreased an average of 0.9–1.9 mg/L from June through October in scenario 2a compared to the base case (scenario 1a). Concentrations of other algae groups also decreased in the Link River inflow, but the algae were dominated by blue-greens in summer. Dead and decomposing blue-green algae and LPOM exerted a substantial oxygen demand in the water column and in the first-order sediment compartment after that material settles to the river bottom. Although the overall result was an increase in dissolved oxygen, an examination of spatial and temporal trends (fig. 21A) also showed a minor decrease in dissolved-oxygen concentration in late June and early July. That was a period when the blue-green algae were producing a substantial amount of oxygen through photosynthesis under existing conditions, so the simulated decrease occurred when oxygen was relatively abundant.


Reducing other tributary inputs to be compliant with the Klamath River TMDL (scenario 1b) also improved dissolved-oxygen concentrations in the reach, but to a lesser extent. This scenario increased dissolved oxygen for the June through October period by 0.0–0.2 mg/L, depending on the year. The combined effect of reducing concentrations from Link River and in-reach tributaries (scenario 2b) increased the reach-averaged dissolved-oxygen concentration by 2.0–3.2 mg/L for the June through October period.


Ammonia


Among the tested scenarios, reducing concentrations of Link River inputs to be compliant with Upper Klamath Lake TMDL requirements (scenario 2a) also was most effective in decreasing ammonia concentrations (table 10 summarizes all years, fig. 22A shows 2007 as a representative year). The June through October average decrease in ammonia concentration ranged from 0.20 to 0.34 mg/L depending on year for scenario 2a compared to the base case (scenario 1a). A minor increase in nitrate concentrations resulted for the same time period (fig. 22B), due to a decrease in anoxic conditions that then allowed for some ammonia nitrification. Reductions of concentrations in the point and nonpoint sources (scenario 1b) had a more limited effect on ammonia concentrations, with average June to October decreases between 0.01 and 0.03 mg/L. Only minor decreases in nitrate concentrations occurred for that scenario. None of the scenarios had much of an effect on the high concentrations of ammonia that occurred during some years in winter.


Orthophosphorus


The scenarios that reduced inflow concentrations at Link River (2a and 2b) and the scenarios that reduced inflow concentrations for the in-reach tributaries (1b and 2b) produced substantial decreases in orthophosphorus concentrations through the system (table 10 summarizes all years, fig. 23 shows a representative year). Scenario 2a reduced orthophosphate concentrations between 0.04 and 0.06 mg/L for the June through October period compared to the base case, depending on year; scenario 1b reduced orthophosphate concentrations between 0.02 and 0.04 mg/L.


Scenarios Summary


This set of scenarios demonstrated that hypoxic and anoxic conditions in this reach of the Klamath River were largely a result of organic matter and algae imported from Upper Klamath Lake through Link River. If improvements in Upper Klamath Lake and Link River water quality are not possible over the short term, then the Link River to Keno reach of the Klamath River will continue to have high levels of seasonal water-quality impairment in response to large organic loads emanating from Upper Klamath Lake. Near-term management strategies focused on improving water quality within the Link–Keno reach may reduce the impacts of these loads and may result in water-quality improvements not only in the Link–Keno reach but also in the lower Klamath River below Keno Dam. Although improvements in Upper Klamath Lake and Link River will have the largest influence on the presence and magnitude of anoxia in the Link–Keno reach, opportunities to decrease concentrations of nutrients, algae, particulate organic matter, and(or) algae in other tributary inputs could result in water-quality improvements as well. 


Rather than retaining the current seasonal patterns of nutrients and organic matter, reduction factors could be adjusted on a daily or monthly basis for each tributary input for future model scenarios. Other management or restoration options, such as different methods of managing streamflow, treatment for point and nonpoint sources, treatment wetlands, and other prescriptions, could be examined. Future uses of the model could include connecting water-quality results to the water-quality requirements of fish, testing the potential effects of the removal of the four dams downstream of Keno Dam, assessing the effects of climate change and future water allocations, and examining downstream effects of potential changes to the Upper Klamath Lake TMDL.


First posted July 14, 2011