Office of Research and Development

National Risk Management Research Laboratory

Cincinnati, Ohio 45268

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The Experimental Stream Facility 1

Background

The Experimental Stream Facility (ESF) is a valuable research 

tool for the U.S. Environmental Protection Agency’s (EPA) 

Office of Research and Development’s (ORD) laboratories in 

Cincinnati, Ohio. This brochure describes the ESF, which is 

one of only a handful of research facilities in the United States 

designed to conduct small stream research.

The Need for Small Stream Research

Small stream ecosystems comprise over 72% of the river miles 

in the U. S.; yet, the role they play in managing watershedlevel water quality is uncertain. While the potential impact of 

naturally occurring biogeochemical functions within an individual 

small stream may seem minimal, the accumulated impact of the many small streams within a watershed may be 

significant. Small streams are largely unmapped, unregulated, overlooked in watershed models, and generally not 

considered in the total maximum daily load (TMDL) process or in land use regulations. As such, they are often 

ignored in land development plans, and are often replaced with culverts, storm sewers, or lined ditches, which 

eliminates any role they may play in maintaining water quality. Research is needed to increase our understanding 

of the relative importance of small stream ecosystems and the services they provide for effective watershed 

management. 

In addition to watershed management research, there is a continual need to better characterize how streams and 

rivers, in general, react to and process emerging contaminants and stressful mixtures. The numerous physical, 

chemical, and biological variables interacting under natural conditions, as aquatic ecosystems are exposed 

to contaminants of concern, confound the interpretation of effects on aquatic biology in receiving streams. 

Mesoscale studies are needed to gain a better understanding of the impact of contaminant stressors on multiple 

trophic levels and the levels which are the most sensitive to stress.

As a final point, biotic indicators form the basis for stream 

condition assessment in this Nation, but current design criteria 

for watershed best management practices (BMPs) are based 

largely on peak flow control and sediment removal. Research 

is needed to begin to bridge the gap between physical-based 

engineering design and biological-based assessment criteria.

The Need for the Stream Facility

The facility has eight stream mesocosms; a mesocosm is an 

experimental system designed to simulate natural conditions, 

often by using naturally occurring organisms and artificial Experimental stream mesocosms
The Experimental Stream Facility

2 

structures that simulate nature as closely as possible. Mesocosm design 

provides a balance between the benefits of a controlled laboratory study 

(e.g. controlled flow rates, solar irradiance and streambed type) and the 

benefits of a field study (e.g. continuous biota for colonization, and 

natural variability of biota and water quality). This allows researchers 

to study how pollutant loads interact with important characteristics of 

stream habitat that may or may not change as a result of anthropogenic 

stress. Changes to the stream ecosystem structure and function can be 

measured and observed in ways that are not possible in field or laboratory 

studies. Well designed and controlled experimental stream mesocosm 

studies can represent a primary tool for providing the process-level 

understanding necessary to move basic research and development from 

the laboratory bench-top to field applications.

Research Approach

ESF studies are designed to obtain information on both watershed 

management and the impact of contaminants of concern.

Watershed Perspective

The ESF sits at the downstream end of the watershed of the East Fork 

of the Little Miami River (1295 km2 / 500 mi2), and experiments are 

designed with watershed scale management as one focus of the studies. 

Studies at the ESF afford EPA the opportunity to collect and analyze 

data on in-stream process-level biological, chemical, and physical 

interactions. Each ESF study is designed to provide information on 

small stream ecosystem structure and function that can be used for the 

development and testing of: new indicators of ecological stress; water 

quality monitoring technologies; watershed monitoring strategies; and 

water quality management methods and models. Characteristics of small 

stream sub-watersheds in the East Fork watershed provide information 

for the design of ESF experiments, and the results of ESF experiments are 

subsequently incorporated into a multi-spatial scale watershed research 

plan designed to characterize, track, and model changes to water quality 
The Experimental Stream Facility 3

associated with the National Pollutant Discharge Elimination System (NPDES) and the Safe Drinking Water Act 

-associated BMP implementation projects. Hence, an overarching goal is to develop numerical descriptions of 

these stressor-biotic linkages for watershed models used as decision support in TMDL and TMDL-like analyses of 

watershed management.

Contaminant Perspective

The ESF mesocosms are especially useful for studying the impacts of contaminants of concern (e.g. endocrine 

disruptors, pharmaceuticals, pesticides) on the natural stream biota. Contaminants can be added at 

environmentally relevant levels; levels observed in natural ecosystems and reported in the literature. Exposure 

at these levels lets researchers observe more subtle changes (e.g. gene and protein expression) in stream biota as 

well as changes in biotic communities and ecosystem structure and function. This approach provides additional 

information to laboratory studies which commonly use lethal effects (e.g. LC50) as the endpoint. The postdose recovery period built into each experiment provides additional information on the ability of the biota to 

recover when the contaminant is removed from the ecosystem. The relative importance of specific changes in 

stream habitat (e.g. sediment load, flow rates) on contaminant impact can be simulated and are often included 

as interacting variables. Additional biotic indicators can be studied through the use of emergent traps, fish 

deployments, in-stream invertebrate exposures, and real time biomonitoring. Interactions and effects observed in 

the ESF setting help identify important assessment endpoints, and inclusion functions for field-scale models of the 

fate and transport.

Experimental Framework

Natural river water flows through the ESF, which allows studies to be conducted when stream biota are most 

abundant and active, approximately mid-March through late October. Typically two experiments are conducted 

per year, with each experiment running for about 12-15 weeks: 4-6 weeks for colonization of the streams by 

natural biota; 4-6 for applying a stressor(s) such as a chemical dose or flow manipulation; and 3-4 weeks for stream 

recovery after the stressor period ends.

Base Analytical Endpoints

The baseline analytical endpoints for each 

experiment include: sediment size fractions; 

carbon, nitrogen, and phosphorus in 

sediments; inter-gravel water nutrient species 

concentrations; surface water temperature, 

conductivity, pH, dissolved oxygen, oxidation/

reduction potential, and turbidity; stored 

organic matter; invertebrate community 

structure; periphyton (a gelatinous matrix, 

also known as a biofilm, that may consist 

of attached algae, bacteria, fungi, trapped 

fine sediment and deterital material, and 
The Experimental Stream Facility

4 

microinvertebrates that use it both as a food source and habitat); per capita invertebrate drift emigration rates; 

periphyton chlorophyll-a concentrations; carbon, nitrogen, and phosphorus in periphyton; surface water nutrient 

species concentrations; and algal community structure. These data are acquired and managed across all ESF 

studies, and are likewise a part of the associated field research. They 

serve as a basis for meta-analyses, scaling ESF results to the field, or 

comparing against novel indicators of exposure and stress.

The Research Team

National Risk Management Research Laboratory (NRMRL) is 

responsible for the operation, maintenance, and facilitation of the 

experiments at the ESF. However, the experimental designs are 

developed and implemented by a multi-disciplinary team of research 

scientists and engineers, and technical support personnel from across 

EPA’s ORD laboratories. The lead for each experiment can be a 

researcher from any of the EPA laboratories. Using the combined 

expertise of the multi-disciplinary team members optimizes 

coordination, leverages resources, and encourages collegiality in the 

integration of both risk assessment and risk management objectives 

into novel experiments.

The Experimental Stream Facility

The facility, located in Milford, Ohio, was originally built by the 

Proctor & Gamble Company, and was well known as a premier 

laboratory in the area of mesocosm research in ecotoxicology and risk 

assessment. The facility is currently owned by Clermont County, 

and became available to EPA in 2005, through a lease with the 

County (some lab and office space is used by the Clermont County 

Sewer District Water Quality Testing Laboratory). Since taking 

occupancy, EPA has made several modifications to the facility which 

make it a unique small stream research laboratory. The capabilities of the facility have been extended for research 

applications in the fields of ecohydrology/sedimentology, biogeochemistry, and risk management.

Experimental Stream Configuration

Each stream mesocosm includes a head tank, an upper biotic colonization channel, a lower biotic colonization 

channel, a tail tank, and a water recirculation system (see figure, page 4), and is 12 meters (m) long, or 39 feet (ft). 

The upper channel typically has a tile streambed, and the lower channel usually has a gravel streambed, but the 

channels can be interchanged. A small pool section can be added between the upper and lower channels. Plastic 

or stainless steel mesocosms are available, depending upon the physiochemical properties of the contaminant 

under study. A removable baffle to subdivide the channel sections into like units is optional for increasing 

statistical replication.

Scientist and engineers
The Experimental Stream Facility 5

Head Tank

All source water, chemical dose, and 

recirculated water flows pass through an in-line 

mixer into the bottom of the 126 liter (L), or 

33 gallon (gal), head tank. Water flows over a 

rectangular weir into the upper channel section. 

The head tank is mounted on a jacking system 

which can raise or lower the head tank, which 

allows the channel slope to be varied between 

0 and 4.3% to simulate different stream flow 

conditions.

Tile Section

The upper channel is usually configured to simulate large, flat rocks in a 

glide reach of a natural stream where periphyton attach and grow. The 

channel is approximately 30 centimeters (cm), or 12 inches (in), wide; 9 

cm (3.5 in) deep; and 4.5 m (14 ft) long. It is usually lined with 47 rows 

of unglazed ceramic tiles, with 3 tiles per row. The tiles provide a defined 

surface area, as well as a removable substrate for the growth of periphyton. 

Water moves through this section in a more laminar flow at a depth of 

2.5 cm (1 in). The tiles are sampled randomly during an experiment to 

derive several measurements, such as algal biomass, stored nutrients, and 

periphyton community structure.

Head Works 

1) Head Tank

2) Main River Water Influent

3) Alternate Water Source 

Influent

4) Flow Meter-Transmitter

5) Actuator

6) Chemical Dose Influent

7) Scissor Jack-Slope Control

1. Tiled sampled in low light channel 2. Tiled sampled in highlight channel 3. Cyanobacteria in 

tile section

1 2

3
The Experimental Stream Facility

6 

Gravel Tray Section

The lower channel is usually configured to simulate a riffle in a natural stream where small rocks and gravel 

provide both substrate for periphyton and shelter for aquatic invertebrates. The channel is approximately 50 cm 

(21 in) wide, 17 cm (6.5 in) deep, and 4.5 m (14 ft) long. It contains an array of gravel-filled plastic trays in 15 

rows, with 3 trays per row (mesh baskets can be used instead of plastic trays to allow interflow between sampling 

units.). Gravel (small river rock) ranging in size from 1.5 to 4 cm (0.6 to 1.6 in) diameter has been used to date, 

but substrates ranging from fine silt/clays to smaller gravel could be used depending on experimental objectives. 

Each gravel tray provides a removable substrate of defined volume and area, which can be used to quantify many 

of the base analytical endpoints. 

Water moves through this section 

in a more turbulent flow at a depth 

of 5 cm (2 in), and water jets 

can be configured in this section 

to simulate peak flow velocities 

during storm events. Gravel 

trays are also sampled randomly 

during an experiment. Similar 

gravel trays are used at several field 

sampling locations in the East 

Fork Watershed, and provide the 

same base analytical endpoint data. 

Standard operating procedures 

have been written for sampling, 

processing, and analyzing all 

variables obtained from the gravel 

trays and the tiles.

1. Trays at the start of experiment 2. Trays with accumulation & recently replaced trays 

3a-c. Gravel biota 4. Samplers are buried in gravel 5. Sampled tray
The Experimental Stream Facility 7

Drift Measurements

Invertebrate drift responses can be measured by 

positioning drift nets to isolate the gravel section. 

The upstream net secludes influent drift, while the 

downstream net catches all organisms drifting from 

the gravel during the measurement period. Per capita 

emigration is determined as the number of individuals 

captured by the downstream net divided by their 

respective density counted in the gravel section. 

Tail Tank

A 222 L (59 gal) tail tank at the end of each mesocosm 

simulates conditions of a pool in a natural stream 

channel. The tail tanks house continuous clam-based 

behavioral biomonitoring and real-time water quality 

sensing equipment, and can be configured for exposing 

larger stream biota (i.e., fish). Side-streams are plumbed 

in-line with the discharge from each mesocosm to supply 

flow to additional small tanks for other biotic exposure 

options. The biomonitors allow behavioral responses to 

be tracked in relation to the measured changes in stream 

structure and function. Outflow from the tail tank can 

be discharged under an NPDES permit or sent to the 

neighboring wastewater treatment plant. A new version 

of clam biomonitors is currently being tested.

Clam biomonitor housing in tail 

tank Tail tank with exposure cage Clams in biomonitor; plunger moves 

proportional to shell gape

Upstream Drift Net

1. Electronics

2. Plunger

3. Clam

4. Adhesive

5. Pedestal

6. Adjustable Height
The Experimental Stream Facility

8 

Recirculation System

Recirculation loops with pumps can return water at a constant pre-set flow rate from the tail tank to the head tank 

for each mesocosm, which allows residence time to be manipulated while maintaining velocities and turbulent 

features for the biotic colonization sections. This can be important for studies considering the fate and transport 

of stream solutes. The recirculation flow can also be diverted to the head tank of an adjacent mesocosm so that the 

effluent of one mesocosm can serve as influent to another, allowing up to eight streams to be studied in series.

Unique ESF Features

There are several unique features that make the ESF a one-of-a-kind facility for conducting controlled, flowthrough, meso-scale simulation studies of stream ecosystems. The process flow diagram below depicts the key 

components and linkages of the process-controlled systems.

Multiple Water Sources

Water is pumped into four ESF 

supply tanks from several sources, 

and flows by gravity from the 

supply tanks to each mesocosm. 

Each mesocosm has two sets of 

piping, flow meters, and computercontrolled valves to allow water 

from two supply tanks to flow to the 

head tank of each mesocosm. Flow 

through one set can be controlled 

within 0.38 liters/minute (L/min), 

or 0.1 gallons per minute (gpm), in 

the range of 19 to 190 L/min (5 to 

50 gpm). Flow though the other set 

can be controlled within the range of 

1. Tail tanks 2. Recirculation line from tail tank to pump 3. Flow meter on recirculation loop
The Experimental Stream Facility 9

 High light channel

East Fork River intakes East Fork River main channel ESF water supply tanks

0 to 57 L/min (0 to 15 gpm). This flow control, along with the ability to adjust the mesocosm slopes, allows for a 

range of controllable in-stream velocities.

Natural water flow can be supplied from two nearby sources: Heiserman Stream, a relatively unimpacted 

headwater stream, or the East Fork, a 6th order river channel. The East Fork water has two to three times the 

carbon and nutrient concentration of the Heiserman water. The availability of water from such different stream 

sources expands the natural simulation horizon of ESF experiments.

Tertiary wastewater effluent (oxidation ditches followed by 

clarification and sand filtration) from the adjacent Lower East Fork 

Wastewater Treatment Plant (WWTP) is pumped to an ESF supply 

tank which can be aerated to avoid stagnation. Excess wastewater is 

routed back to the WWTP. The availability of wastewater allows the 

effects of emerging contaminants in wastewater to be studied alone or 

in combination with other variables. Finally, carbon-treated tap water 

is also available for experiments.

Variable Simulated Solar Irradiance

High intensity grow lights provide simulated sunlight to fuel primary 

production in ESF mesocosms. The ceiling mounted lights provide 

daily-integrated irradiance of approximately 12% of unshaded (openfield) photosynthetically active radiation (PAR), which is similar to 

that experienced by a forested stream where leaves in the tree canopy 

shade the channel. Additional lights can be configured to provide 

daily-integrated irradiance of approximately 100% of unshaded 

(open-field) PAR to simulate a stream flowing through an agricultural 

field or developed area without a forested riparian buffer. The lights 

are programmed to run on a 24-hour cycle based on the ESF’s 

geographical location.

Grow lights - low light channels
The Experimental Stream Facility

10 

Continuous Water Quality and Climate Monitoring

Each mesocosm has sensors in the tail tank that measure the 

surface water quality base analytical endpoints listed previously. 

The sensors continually transmit the water quality data for each 

mesocosm at five minute intervals to the data acquisition system. 

A complementary set of these sensors monitors the influent waters 

to the facility. The ESF has an outdoor weather station and 

indoor sensors to continuously monitor PAR, air temperature, and 

humidity. Precipitation is continuously tracked by the outdoor 

station as well.

Chemical Dosing System

Chemical doses of stressors/pollutants can be metered into the 

head of each mesocosm from the chemical delivery system. Doses 

are continuously mixed in 570 L (150 gal) stainless steel tanks. 

The chemical feed pumps are accurate to within 0.5 milliliters/

minute (ml/min), or 0.2 gallons per day (gpd), within the range of 

25 to 150 ml/min (9.5 to 57 gpd), and are integrated with pressure 

transducers to ensure even pumping and fail safe operation. They 

work together with meters and valves on the river flow lines to 

provide constant in-stream dose concentration over extended 

dosing periods (e.g. 30 days, typically).

Chemical dosing tanks 

Continuous water quality monitoring equipment
The Experimental Stream Facility 11

Supervisory Control and Data Acquisition 

A supervisory control and data acquisition (SCADA) system 

performs several functions:

•	 monitors/controls natural river, wastewater, and 

recirculation flows;

•	 activates/controls the timing of the simulated solar 

irradiance;

•	 monitors/controls the chemical delivery system;

•	 acquires data from all the continuous water quality and 

behavioral monitoring sensors; and

•	 initiates phone calls to the operators in case of any system 

failure (e.g. low water flow).

Data files generated within the SCADA system are transferred to a data storage device, in which data management 

functions are housed. An effort is underway to make data accessible to all collaborators via email or the web.

Programmable Environmental Triggers

Logic control algorithms can be written for the SCADA system that trigger changes in flow rate, chemical dosing, 

or flow distribution (river inflow vs. recirculation) in response to natural changes in climate or water quality. 

Some examples include mesocosm flow regimes that can be programmed to change at the onset of a rain event, as 

detected by the weather station, or a change in water quality, as detected by one of the real-time sensors in the tail 

tank. The timing and proportion of flow that is recirculated can be used to manipulate sediment accumulation, 

colonization rates, and/or discharge rate from each mesocosm. Contaminant dosing can be programmed to be 

continuous or intermittent and triggered by a rain event.

Significance

Understanding the impact of contaminants on small streams, and reducing the loading of stressors to watersheds, 

is of concern to environmental stakeholders, including local and state governments, utilities, developers, and 

homeowners. Knowing how contaminants of concern affect aquatic biota will help determine which stressors 

are most important for the consideration of environmental regulators. Adoption of the watershed approach and 

best management practices to control both urban and rural sources of waterborne pollutants is helping to reduce 

contaminants at the watershed level. The chief beneficiaries are the environmental decision makers who will use 

the ESF data in watershed models to better characterize how streams react to, and process, emerging contaminants 

and stressful mixtures, and to quantitatively link known stressors in stream flow with the structure and function of 

stream ecosystems.

Screenshot of SCADA System
The Experimental Stream Facility

12 

Contacts

Technical Contact

Christopher Nietch PhD

Systems Ecologist

U.S. Environmental Protection Agency

Office of Research & Development

National Risk Management Research Laboratory

Water Suppy & Water Resources Division

(513) 569-7460 nietch.christopher@epa.gov

Communications

Michelle Latham

Biologist/Communications Specialist

U.S. Environmental Protection Agency

Office of Research & Development

National Risk Management Research Laboratory

Water Supply & Water Resources Division

(513) 569-7601 latham.michelle@epa.gov

Resources

Website

Experimental Stream Facility

http://www.epa/nrmrl/wswrd/wqm/esf/esf.html

Video

U.S. EPA (2009) Experimental Stream Facility - 

Design and Research 

http://www.youtube.com/user/USEPAgov#play/

uploads/5/jwOlYv7heE4

Fact Sheet

Experimental Stream Facility

(EPA/600/F-08/006)

http://www.epa.gov/ord/NRMRL/pubs/

facilities/600f08006.pdf

EPA Scientist leading a tour 

at the Experimental 

Stream Facility.

12
Office of Research and Development

National Risk Management Research Laboratory

Cincinnati, Ohio 45268

Official Business

Penalty for Private Use

$300

PRESORTED S

POSTAGE & 

EPA

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