ALGAL GROWTH POTENTIAL
UPPER BIG THOMPSON RIVER, COLORADO
Environmental Protection Agency
National Field Investigations Center-Denver, Denver, Colorado
September, 1973

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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.

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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.

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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.

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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.

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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.

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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.

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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

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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

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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

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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

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