Experimental Stream Facility (ESF)
- Experimental Stream Configuration
- Unique ESF Features
- Multiple Water Sources
- Variable Simulated Solar Irradiance
- Continuous Water Quality and Climate Monitoring
- Chemical Dosing System
- Supervisory Control and Data Acquisition
ESF is one of only a handful of research facilities in the U.S. designed to conduct small stream research. The facility has eight stream mesocosms that provide the benefits of both a controlled laboratory study and a field study. Mesocosm is an experimental system designed to simulate natural conditions and use naturally occurring organisms and artificial structures. Researchers study how pollutant loads interact with important characteristics of stream habitat. Changes to the stream ecosystem structure and function can be measured and observed in ways that are not possible in field or laboratory studies. The capabilities of the facility have been extended for research applications in the fields of ecohydrology, sedimentology, and biogeochemistry.
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.
The mesocosm is 39 feet long. The upper channel typically has a tile streambed while the lower channel has a gravel streambed. The channels are interchangeable. A small pool section can be added between the upper and lower channels. Plastic or stainless steel mesocosms are used, depending upon the properties of the contaminant under study. A removable baffle to subdivide the channel sections into like units may be used to increase statistical replication.
All source water, chemical dose, and recirculated water flows pass through an in-line mixer into the bottom of the 33 gallon head tank. Water flows over a rectangular barrier into the upper channel section. The head tank can be raised or lowered which changes the channel slope. This simulates different stream flow conditions.
The upper channel is usually configured to simulate large, flat rocks in a natural stream where periphyton (such as algae and small crustaceans) attach and grow. The channel is approximately 12 inches wide; 3.5 inches deep; and 14 feet 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 calm flow at a depth of 1 inch. The tiles are sampled randomly to get several measurements, such as algal biomass, stored nutrients, and periphyton community structure.
Gravel Tray Section
The lower channel is usually configured to simulate a stretch of choppy water caused by such a shoal or sandbar in a natural stream. It includes small rocks and gravel which provide shelter for water invertebrates. The channel is approximately 21 inches wide, 6.5 inches deep, and 14 feet 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 or fine silt/clays can be used depending on experimental objectives. Water moves through this section in a more turbulent flow at a2 inch depth. Water jets can be configured in this section to simulate peak flow speeds during storms. Gravel trays are 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.
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 organisms captured by the downstream net divided by their respective density counted in the gravel section.
A 59 gallon tail tank at the end of each mesocosm simulates conditions of a pool in a natural stream. The tail tanks have continuous clam-based behavioral biomonitoring and real-time water quality sensing equipment. It can be configured for exposing larger stream animal and plant life (i.e., fish). Side-streams are connected 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.
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. This allows residence time to be manipulated while maintaining speed rates and turbulent features for the biotic colonization sections. 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.
There are several unique features that make the ESF a one-of-a-kind facility for conducting controlled, flow-through, meso-scale simulation studies of stream ecosystems. The process flow diagram on the next page depicts the key components and linkages of the systems.
Water is pumped into four supply tanks from several sources. The water flows by gravity from the supply tanks to each mesocosm. Natural water flow can be supplied from two nearby sources:
- Heiserman Stream, a relatively unimpacted (70 % forested) 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.
Other sources include:
- Third level wastewater sewage from the adjacent Lower East Fork Wastewater Treatment Plant can be pumped to an ESF supply tank. The availability of wastewater allows the effects of emerging contaminants in wastewater to be studied alone or in combination with other variables.
- Carbon-treated tap water is also available for experiments.
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 photosynthetically active radiation (PAR). This is similar to that experienced by a forested stream where leaves in the tree canopy provide shade. EPA added more lights to two mesocosms to simulate a stream flowing through an agricultural field or developed area without a forest. The lights are programmed to run on a 24-hour cycle based on the ESF’s geographical location.
Each mesocosm has sensors in the tail tank that measure the surface water quality. The sensors continually transmit the water quality data for each mesocosm at five minute intervals. A complementary set of these sensors monitors the influent waters to the facility. There is an outdoor weather station and indoor sensors to continuously monitor PAR, air temperature, and humidity. Precipitation is tracked by the outdoor station as well.
Chemical doses of stressors/pollutants can be metered into the mesocosm head. The chemical feed pumps are accurate to within 0.5 milliliters/minute or 0.2 gallons per day. Pressure transducers 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).
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).
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.