ALGAL GROWTH POTENTIAL UPPER BIG THOMPSON RIVER, COLORADO Environmental Protection Agency National Field Investigations Center-Denver, Denver, Colorado September, 1973 ------- INTRODUCTION An environmental impact statement1 reported that development in the vicinity of Estes Park, Colorado will increase nutrient (N and P) levels in the Big Thompson River and in certain reservoirs. Subsequently, objectionable algal growths could be stimulated in the nutrient-rich waters. To evaluate existing and potential algal problems, biostimula- tion and nutrient characteristics were determined for waters from the Big Thompson River, major tributaries, Lake Estes and the Estes Park wastewater treatment plant (WWTP). METHODS Stream and effluent samples (Table 1) were collected July 23-25, 1973. All samples were collected by grab sampling, labeled, chilled in an ice chest, and transported to Denver for analyses. Nutrient samples were preserved with mercuric chloride (40 mg/1 HgC^) • Samples were collected both upstream of and at several locations downstream from the Estes Park WWTP to determine the nutrient assimila- tion capacity of the Big Thompson River. Algal growth potential tests were performed as outlined in "Algal Assay Procedure - Bottle Test," August, 1971.2 Effluent 1Draft Environmental Impact Statement, "Upper Thompson Sanitation District, Estes Park, Colorado, Project //C 080322," EPA, Region VIII. 1973, 130 pp. 2"Algal Assay Procedure - Bottle Test." National Eutrophication Research Program, Environmental Protection Agency, Corvallis, Oregon (1971), 82 pp. ------- -2- and stream samples were autoclaved and mixed in duplicate serial decimal dilutions (0.1, 1.0, 10.0, 50.0%) to simulate a wide range of flows. River water without effluent additions was tested to serve as a control. Duplicate nitrogen and phosphorus spikes in combined serial decimal dilutions (.01, .1, 1.0 mg/1 P; 0.1, 1.0, 10 mg/1 N) were added to river water to determine the algal growth limiting nutrient. An incoulum of algae, Selenastrum oapvioomutum (standard test organisms obtained from the EPA Water Laboratory, Corvallis, Oregon) was added to each test bottle. Test conditions (100 ml in 250 ml Erlenmeyer flasks; 400 ft-c of continuous light at mid-flask; 24°C water bath; 88 oscillations per minute shaking; 7 day incubation) remained constant for all tests. Algal growth was measured by initial and daily in vivo fluorescence readings using a high-sensitivity Turner fluorometer. Fluorescence readings were empirically converted to dry weights. Nutrient concentrations (TKN, NH3-N, Organic N, NO2+NO3-N, Ortho- and Total P) were measured on all samples before and after autoclaving, using a Technicon Autoanalyzer. Nutrient analyses were performed according to standardized EPA methods.^ DISCUSSION Nutrient levels varied greatly among the sampling locations (Table 2). Total P ranged from <'.005 to .12 mg/1, and inorganic N ranged from <.02 to .28 mg/1. While surface algal blooms4 were 3"Methods for Chemical Analysis of Water and Wastes - 1971," Water Quality Office, Analytical Quality Control Laboratory, Environmental Protection Agency, Cincinnati, Ohio (1971), 312 pp. ^A concentrated growth or aggregation of algae sufficiently dense as to be readily visible. ------- -3- not observed, nutrient levels were sufficient to support abundant periphyton. The cool, fast-moving water precludes gross densities of plankton. The highest stream temperature observed was 16°C. Higher water temperatures and impoundment of the water with the present nutrient levels could create suitable conditions for algal blooms. Test water from the Estes Park WWTP effluent contained 9.2 mg/1 total P and 13.0 mg/1 inorganic N. A twelve-fold increase in total P (.01 to .12 mg/1) and a three-fold (.06 to .18 mg/1) increase in inorganic N was noted from immediately upstream to 400 meters downstream from the Estes Park WWTP outfall. Further downstream in Lake Estes nutrient levels decreased. Inorganic N and total P were .04 and .02 mg/1 respectively both upstream and downstream from the dam, indicating that Lake Estes did not act as a settling basin where nutrient levels decreased. Although nutrient levels declined down- stream from the Estes Park WWTP, total P never decreased to upstream levels. Phosphorus levels, for example, in the river near Drake, Colorado (13 miles downstream) remained twice those upstream of the Estes Park WWTP, indicating the Big Thompson River did not assimilate this nutrient. Other nutrient sources included the water from the Alva Adams Tunnel and Fish Creek. These sources had total P levels of up to .04 mg/1. The volume of water coming from the tunnel (72 percent of the inflow to Lake Estes) makes this an important source. ------- -4- Laboratory algal growth potential (AGP) tests demonstrated the potential of stream water to grow algae (Table 3). While none of the stream water tested stimulated an algal bloom, water from the Alva Adams Tunnel and Lake Estes at the Dam grew almost 1 1/2 times (2.3 and 2.2 mg/1 versus 1.5 mg/1) as much algae as water from the Big Thompson River upstream of the Estes Park WWTP. Effluent spikes to stream water demonstrated biostimulation characteristics of the waste from the Estes Park WWTP (Table 3). A 10 percent effluent addition stimulated bloom conditions in every case. Lesser effluent additions stimulated algal growth but no blooms. Nutrient spikes demonstrated that at all stations tested algal growth was limited by the amount of phosphorus present. Stream levels of phosphorus are increased by the Estes Park WWTP and the proposed plant would add still more phosphorus. Additions to tunnel water as low as .01 mg/1 P stimulated algal growth and additions of .1 mg/1 P stimulated bloom conditions. These additions represent total P concentrations of .02 and .11 mg/1 respectively. Additions greater than .1 mg/1 P caused no further increases in algal growth. Similar results were obtained for the other stations tested. Laboratory-tested treatment procedures have removed greater than 90 percent of the total P from sewage effluents.5 Chemical 5Effluents from Sioux Falls, South Dakota and Pocatello, Idaho waste- water treatment plants have been tested in 1973 at this lab. ------- -5- precipitation by lime (Ca(0H)2) provided practical and efficient removal of phosphorus. Similar treatment at the proposed Estes Park sewage facilities would help lower stream phosphorus levels and also reduce algal problems. Results of laboratory AGP tests indicate that any increase in phosphorus levels up to 0.1 mg/1 would cause more algal growth. At 0.1 mg/1 P algal blooms occurred in the laboratory. Algal growths are already being stimulated at present levels (.01-.04 mg/1 P) . To eliminate further problems stream phosphorus levels should not be allowed to increase over the .01 mg/1 level found upstream of the Estes Park WWTP. Significant sources of phosphorus noted in this study were Fish Creek, the Estes Park WWTP effluent, and the Alva Adams Tunnel water. Fish Creek (1.8 mgd) constitutes a minor source of phosphorus (0.4 percent of the load) among the sources investigated (Table 4). Although most of the flow (72 percent) into Lake Estes is by way of the Alva Adams Tunnel, only 26.6 percent of the total phosphorus load was from this source. The present Estes Park WWTP with less than 1 percent of the flow into the lake, contributes 2/3 of the phosphorus load (Table 4). Thus, if the effluent from the present WWTP were diverted to the proposed new tertiary WWTP and nutrient stripping were then practiced, problems of excessive algal growths in the receiving waters would be alleviated. ------- SUMMARY 1. Algal growth potential tests showed that phosphorus was the nutrient limiting to algal growth. Concentrations of phosphorus ranging from 0.01 to 0.10 mg/1 stimulated additional algal growth in Big Thompson River water. 2. Phosphorus concentrations in the Big Thompson River increased from 0.01 mg/1 upstream of the Estes Park WWTP to 0.02 mg/1 in Estes Lake. In the thirteen-mile reach from Estes Lake to Drake, phosphorus was not assimilated; the concentration of this nutrient remained at 0.02 mg/1. This concentration is sufficient to support algal growth. 3. The Estes Park WWTP contributed 67 percent of the phosphorus load in the Big Thompson River. Nutrient stripping could remove more than 90 percent of this phosphorus. CONCLUSIONS Treated effluents from the existing Estes Park WWTP and from a proposed new tertiary WWTP have the potential of stimulating excessive algal growths in the Big Thompson River and downstream reservoirs, unless nutrient (phosphorus) stripping is provided. If nutrient stripping is applied to the wastes from both plants, excessive algal growths can be alleviated. ------- -7- TABLE 1 SAMPLING STATIONS ESTES PARK/BIG THOMPSON RIVER STUDY Station Description Big Thompson River 10 meters upstream of the Estes Park STP Outfall Estes Park STP Effluent before chlorination Big Thompson River 400 meters downstream of the Estes Park STP Outfall. Alva Adams Tunnel at Estes Park Hydroelectric plant. Fish Creek near Mouth. Lake Estes at Dam. Big Thompson River 1000 meters downstream from Olympus Dam. Big Thompson River at First Diversion downstream from Drake, Colorado. Big Thompson River at First Diversion downstream from Loveland Hydroelectric Plant. River Mile 58.5 58.4 58.2 57.9 57.7/0.1 57.4 56.8 36.9 33.1 ------- -8- TABLE 2 NUTRIENT ANALYSIS OF AGP SAMPLES ESTES PARK/BIG THOMPSON RIVER STUDY Total Inorganic N (mg/1) Total P (mg/1) Station Description Initial Autoelaved Initial Autoclayed Big Thompson River 10 meters upstream of the Estes Park STP. 0.06 0.06 0.01 0.01 Estes Park STP Effluent. 13.0 8.3 9.2 9.1 Big Thompson River 400 meters downstream from the Estes Park STP. 0.18 0.12 Alva Adams Tunnel at Hydro- electric Plant. <0.02 0.02 0.04 0.01 Fish Creek near Mouth 0.28 0.04 Lake Estes at Dam 0.04 0.04 0.02 0.02 Big Thompson River 1000 meters downstream from Olympus Dam. 0.04 0.04 0.02 0.02 Big Thompson River at First Diversion downstream from Drake, Colorado. 0.03 0.02 Big Thompson River at First Diversion downstream from Loveland Hydroelectric plant. 0.03 0.02 ------- TABLE 3 ALGAL GROWTH POTENTIAL RESULTS MAXIMUM STANDING CROP ESTES PARK/BIG THOMPSON RIVER STUDY mg/1 Algae (dry weight) Station Description Control (100% River Water) 1% Sewage 10% Sewage Growth Limiting Nutrient Big Thompson River upstream of Estes Park STP. 1.5 4.6 67.6 P Alva Adams Tunnel 2.3 4.5 49.0 P Lake Estes at Dam 2.2 5.5 51.0 no i Big Thompson River downstream from Olympus Dam. 1.0 6.0 60.0 P ------- Source Flow (MGD) TABLE 4 TOTAL P LOADINGS ESTES PARK/BIG THOMPSON RIVER STUDY Total P Load (mg/gal) (Kg /day) (lb/day)" % Contribution Big Thompson River upstream of Estes Park STP 85-0 Estes Park STP 1.5 Alva Adams Tunnel 225.0 Fish Creek 1.8 0.04 26.60 0.07 0.12 3.40 39.90 15.80 0.22 7.5 87.8 34.6 0.5 6.0 67.0 26.6 0.4 ------- |