Educational Programs | Workshops
Water Quality (Chemistry)
River Continuum Concept & Nutrient Cycling (phosphorus, nitrogen)
. Understand the properties of a natural system
. Break down a river system into its primary components
. Discuss the importance of feedback loops and dynamic equilibrium
. To develop the concept of systems as a way to analyze and understand the form, function, and interconnectedness of nature.
. To examine a river as a system balanced by interactions among its main components
. White boards and dry-erase markers
Our planet consists of many complex, large-scale, interacting systems. A system is a network of relationships among a group of parts, elements, or components that interact with and influence one another through the exchange of energy, matter, and/or information. A system receives input (energy, matter, info), processes or interact with this input and responds with an output. This exchange drives a feedback loop, or circular process whereby a system's output serves as input to that same system. The components in a system interact with each other within feedback loops.
In a negative feedback loop, the output acts as an input that moves the system in the opposite direction. This compensation stabilizes the system. For example, when your brain processes an input that you are too warm, its output is too get cooler by removing a jacket or turning on the air conditioner. As you get cooler, you brain processes this new input and outputs a response to turn off the air conditioner. As a result of this opposite input vs. output, or negative feedback loop, your body system stays at a stable temperature. This alternating give-and-take cycle, or dynamic equilibrium, functions to keep a system within a healthy range. Processes in the system move in opposite directions at equivalent rates so their effects balance out. The progression of dynamic equilibrium acts to stabilize a system when it is disturbed by external forces.
In a positive feedback loop, the output acts as an input that moves the system further in the same direction as the initial input. This magnification of effects destabilizes the system. For example, a desert environment can act as a system. The system's components in this case are the living organisms. If there are no predators in this desert, such as coyotes and mountain lions, then jackrabbits can reproduce and there is no stopping their increase in population. The input to the desert system is more jackrabbits. Each new generation of jackrabbits can then reproduce again, increasing the overall population because the desert system void of predators responds to the new generation by allowing even more jackrabbits to survive. As a result, the number of jackrabbits will increase until another component of the desert system breaks down, such as rabbit food sources, preventing other animals to eat and survive, at which time the desert system is destabilized. The predator component had been altered in this desert system leading to a breakdown of the system as a whole. Predominantly, natural systems experience a positive feedback loop due to human impacts, including over-hunting of predator species.
It is important to note that humans define system boundaries for simplicity and understanding. In reality, there are no boundaries defining systems; all systems serve as components in another larger system. In our case, we will look at the Beaver Creek watershed as a system, however we must keep in mind that inputs from outside the watershed such as precipitation and solar radiation affect the components of the system.
The River Continuum Concept was developed by Robin Vannote et al. in 1980. The concept was revolutionary in aquatic ecology because it was the first time biologists stepped back from studying a tiny portion of a river or creek and looked at rivers as a watershed-scale system. This new perspective allowed Vannote and his fellow researchers to see new patterns and connections between the various components of a river system. These components include the chemical, biological, and physical or geologic/geomorphic elements of a watershed. In the past, each of these components was studied independently. Now, studying the interactions among these components reveals properties of watersheds that were previously unknown. Such properties, referred to as emergent properties, are evident at the system level, but remain elusive when investigating individual components of a system. Today, scientists are discovering emergent properties that explain how aquatic organisms respond to changes in the physical and chemicaal components of a watershed. These discoveries answer questions about how and why aquatic organisms disperse themselves in creeks and rivers.
The main functions of a river system include transporting sediment, dissolved solids and gasses (e.g. Mg, Ca, Na, O2, CO2), organic matter, and nutrients. Sediment weathers out of the watershed geology. Dissolved solids come from the watershed geology, groundwater, and human activities. Dissolved gasses are produced by aquatic photosynthesis (O2) and respiration (CO2). Organic matter is created within a river by photosynthetic organisms (e.g. algae, water lilies) and enters from outside the river (e.g. fallen leaves). Nutrients, specifically nitrogen and phosphorus, are contained within organic matter and dissolved in the water.
(Unique to Water Chemistry Module) Nitrogen and phosphorus each enter river systems through unique, naturally controlled cycles. Phosphorus slowly weathers out of rocks into the soil and water. Organisms living in the soil and water absorb the phosphorus. Waste from organisms as well as dead organic matter contains phosphorus and settles onto lake beds and ocean floors where it eventually becomes incorporated into rock again, completing the cycle. Similarly, nitrogen slowly becomes available to living organisms as soil bacteria or lightning strikes chemically alter N2 from the atmosphere into NH4+ (ammonia) and NO3- (nitrate), the only forms of nitrogen plants can absorb. Then when animals eat plants, they absorb the nitrogen. Nitrogen can then move to predators as they eat herbivores. When plants and animals die, the nitrogen returns to the soil where different bacteria convert it back to N2, releasing it to the atmosphere and completing the cycle. Both cycles naturally release a limited amount into the biosphere. Organisms require these nutrients to survive so they compete for the limited amount of nutrients as they would food, water, and space. Consequently, this competition sets a limit on the number of organisms that can live in an area.
A river's biological community adjusts to changes in form (primarily controlled by sediment transport) and function of the river system in order to effectively use the energy (organic matter/nutrients) provided by the watershed. Organisms process the organic matter, utilizing a certain amount and passing the remainder downstream where other organisms repeat the cycle. Thus, the biological component adapts to changes in the chemical and physical components to maintain a dynamic equilibrium within a river system. For example, if a large flood travels through a watershed, river channels may change shape and orientation as sediment is eroded from some areas and deposited in others. In addition, organic matter and dissolved nutrients will be carried to various locations downstream. As a result, aquatic organisms will move to new habitats that have formed in the modified river channel in order to fulfill their niches - an organism's functional role in a system. In this way, changes in the physical and chemical components of the river caused by the flood lead to adjustments by the biological component, preserving the equilibrium of the river system.
Key characteristics of systems:
. Systems consist of interacting components.
. Synergies among system components create a whole that is more than the sum of its parts (emergent properties) - a key reason the river continuum concept was revolutionary.
. System boundaries are artificial: systems are components of another larger system.
. Systems have inputs, processes/interactions, outputs, and feedback loops.
Write down an example of a negative and a positive feedback loop system.
- What are the components?
- What is the output?
- What is the outcome of the loop?
Create a flow chart: Make a chart based on the example of a natural system with a feedback loop:
Feedback systems in science. Choose one of the following to draw a flowchart on a poster board or come up with your own negative feedback system in science. Be prepared to explain the benefits of having negative feedback systems.
o Feeling of hunger or thirst
o Human body temperature
o The regulation of glucose in our bodies (Diabetes is a disease in which part of
the feedback loop doesn't function properly due to a lack of the hormone
1. Mr. Carter is a butcher. He has sliced off the end of his finger. As blood poured out of the finger, his blood pressure dropped. His heart pumped faster to restore normal blood pressure. What effect would this response have on Mr. Carter's stability? How would this be an example of a negative feedback loop?
2. At a town meeting in Alaska, a biologist explained the population growth of wolves as follows: "Like all species, the population growth of wolves is regulated by positive and negative feedback loops. When the wolves were re-introduced, a positive feedback loop was present. Over time, the population stabilized due to a negative feedback loop." What is this biologist talking about? In addition to the wolves' population, think about changes in the populations of their prey.
Water Quality and Eutrophication
. Understand the character of vital water quality parameters (hardness, pH, DO, silica, nitrate, phosphate)
. Discover certain effects of water pollution
. Examine the process of eutrophication that disrupts dynamic equilibrium in aquatic systems
. To establish the role that water chemistry plays in the River Continuum Concept
. Understand what affects water chemistry in river systems
. Notebooks and pencil
There are a number of parameters that can be used to assess the quality of water
These include hardness, nitrate content, phosphate content, silica content, pH, dissolved oxygen content (DO), and biochemical oxygen demand (BOD).
Hardness is the measurement of the amount of dissolved minerals, usually Calcium and to a lesser extent Magnesium, in water. These elements are no longer solid, but have been dissolved into the water. Calcium and magnesium may be added to a natural water system as it passes through soil and rock containing large amounts of these elements. Limestone, a common rock in northern Arizona, is composed of calcium carbonate and can be readily dissolved into the region's water, making the water "hard". Hard water can be a problem when distributed in a municipal water system as it can precipitate out and leave a hard deposit which can clog pipes or leave a residue film on pots, glassware, hair, fabrics, etc.
Silica (Si02) occurs in all natural waters in varying degrees, but again in excessive quantities can be harmful. The basalt lava rocks in northern Arizona are relatively high in silica content and some of this silica dissolves into the regions ground and surface water. Silica is most problematic when water with a high silica content is used in industrial boiler feed operations. It can vaporize onto turbine blades greatly decreasing efficiency.
The pH is a measurement of the concentration of hydrogen (H) ions found in a liquid or substrate. The pH of a system is important because it has a strong effect on what kind of organisms can live there. The pH scale ranges from 0, which is the most acidic, to 14, which is the most basic (see scale below). Many organisms have an ecological tolerance to pH. For instance, a fish might be able to live in a lake where the pH ranges from 6-9. If the lake becomes more acidic, say down to a pH of 4, or more basic, up to a pH of 10, the fish will likely die. Thus the pH level of water is an important
indicator of its quality.
0 Acidic More free H
1 battery acid
3 vinegar, soft drinks, beer
5 coffee, normal rain
7 milk, pure water Neutral
9 baking soda
11 household ammonia
13 oven cleaner
14 Basic Less free H
The more free H, the lower the pH, and the less free H, the higher the pH. The relationship between the amount of free H and pH is an inverse relationship.
Nitrogen, commonly in nitrate compounds, is essential for plant growth, but the presence of excessive amounts in water supplies presents a major pollution problem. Nitrogen compounds may enter water as nitrates or be converted to nitrates from agricultural fertilizers, sewage, and drainage from livestock feeding area. Nitrates in conjunction with phosphates stimulate the growth of algae in water bodies, with all of the related difficulties associated with excessive algae growth which can include fish kills and foul odors. Phosphorus (commonly in phosphates), like nitrogen, is an important nutrient for aquatic plants.
Aquatic life depends on dissolved oxygen to survive. Organic pollutants such as agricultural fertilizers rich in nitrogen and phosphorus can lead to conditions of low dissolved oxygen in aquatic systems through a process called eutrophication. Organic pollutants also act as fertilizers for algae that respond to increased nutrients by overpopulating an aquatic ecosystem. Algae expel dissolved oxygen during photosynthesis, but as algae populations die, bacteria feeding on the excess algae explode in population. The elevated bacteria populations use up all the dissolved oxygen during respiration, leaving little for the remaining aquatic species. In addition, organic pollutants from animal and human waste often contain disease causing bacteria.
Measuring the biochemical oxygen demand can reveal the amount of pollution affecting an aquatic ecosystem. BOD measures the amount of oxygen consumed by bacteria in the water. High BOD indicates the presence of large populations of bacteria which can lead to eutrophic conditions characterized by little available DO due to substantial organic pollution.
Scenario: The Illinois River begins in the northeast region of the state and flows west and south, draining parts of Indiana and Wisconsin (see map below). From Chicago's Lake Michigan, which is connected to the river by a canal, to the confluence with the Mississippi River is a distance of 137 miles. The surrounding floodplains, once a mixture of prairie and oak-hickory forests, are now primarily used for raising crops. Formerly, the river was highly productive, especially in the lower 20 miles. It produced 10% of the U.S. freshwater fish catch in 1908 (24 million pounds, or 178 lb/acre). But by the 1970s, this same stretch of river produced a mere 0.32% of the total freshwater fish harvest in the U.S. (4 lb/acre). Two major factors are responsible for the change in productivity of the Illinois River: diversion of Chicago's sewage from Lake Michigan to the canal; and increased intensive agriculture. Both sewage and fertilizer contain high concentrations of nitrogen and phosphorus.
Year Critical Event Environmental Impact
1854-55 Heavy rains resulted in untreated sewage from Chicago entering Lake Michigan and then the city's drinking water Cholera and typhoid epidemic in Chicago
1900 Chicago Sanitary and Ship Canal built to convey sewage away from Lake Michigan and into Illinois River Waste entered Illinois River; commercial fish yield from the river reached a peak in 1908
1920 Fish populations declined in river
1920-1940 Most cities along river built sewage treatment plants Some recovery in fish population
1940-1960 Rapid population growth in Chicago and other cities along the river; increase in agricultural acreage Lower oxygen levels in river; further declines in fish populations; sport fish and ducks declined in backwaters and lakes of the river
1977-1979 Construction of Chicago Tunnel and Reservoir Plan (TARP) to capture and treat sewage overflows Some improvement in water quality by 1990, but no change in turbidity or total phosphorus; sodium increased
1. Develop a detailed hypothesis to explain why the fish population peaked in 1908, after the construction of the canal, and declined after that. Your hypothesis should also be able to explain the recovery of the fish in the late 1920s and the causes of environmental problems of the 1940s and 1950s.
2. The most important variables affecting life of a river or stream are the amount of organic material entering the stream from outside sources, water quality, habitat quality, water flow and interaction among living things. Identify these variables in the case of the Illinois River that are affected by the human activities discussed. Then, list the specific activities affecting each variable and the environmental effects/consequences of these activities.
3. You are an Environmental Protection Agency field researcher. What factors would you measure in the Illinois River to determine the level of pollution. Explain why for each factor you decide to measure.
Measuring Water Quality
. Generate hypotheses based on observations in the field
. Measure water quality parameters from several diverse sites along Beaver Creek
. Decipher patterns from differences in water quality among sites
. Guided observations and questions
o What are the sources of each water quality parameter?
o What rock types underlie the Beaver Creek Watershed?
o Are there possible inputs of nitrogen and phosphorus in the watershed?
o Which sites will be interesting for measuring water quality? Why?
o What water quality parameters will be found at each site? Why?
. Hypothesize answers
o Which water quality levels will be high and low at each site? Why?
o Does Beaver Creek harbor significant water pollution? Why?
o How may water quality affect the river continuum in Beaver Creek?
o Measure water quality parameters at each site.
o Compare the measurements for each site.
. Limnology kits
. Geologic map (http://www.mpcer.nau.edu/beavercreek/)
. Table of healthy water quality parameter ranges:
Temp pH Total hard Ca hard Mg hard Phosphate Nitrate Silica DO BOD
Healthy Range 0-24 oC 6.5-8.5 20-60 mg/L 10-30 mg/L 10-30 mg/L <0.1 mg/L <10 mg/L <100 mg/L 5-20 mg/L 0-30 mg/L
. Sample and test water (following limnology kit instructions) from several diverse locations along the creek including shady and exposed sites, the pool upstream of the campground, the spring near this pool, and Montezuma's Well
o pH, temperature, total hardness, calcium hardness, magnesium hardness, phosphate, nitrate, silica, dissolved oxygen.
. Hardness, Nitrate content, and Phosphate content are measured using titration methods as described in LaMotte water analysis kits. Silica content is measured using a colorimetric comparison test, methods described in the LaMotte water analysis kit. pH is measured using an electronic pH probe or LaMotte water analysis kit.
. BOD was determined by measuring the initial DO with an oxygen meter or LaMotte water analysis kit three times after sample collection and three times following eight days in an dark, cool place at ~25 oC. The average of the three measurements for each sample was used to calculate the BOD using the equation BOD = DO1 - DO8 = mg DO/L H2O/8 days. If your meter gives DO in ppm the conversion is simple: 1 mg/L = 1 ppm for dilute aqueous solutions.
. Enter measurement into tables, graph data.
. Compare water quality parameters to table of healthy ranges.
. If you sampled aquatic invertebrates in the last module, then your sampled invertebrates can reveal pollution levels. Pollution tolerant invertebrates are midges, black flies, and worms. Pollution intolerant invertebrates are mayflies, stoneflies, and caddis flies.
SOURCES Temp pH T hard Ca hard Mg hard Phosphate Nitrate Silica
SOURCES DO Day 1: trials 1, 2, 3 average DO Day 8: trials 1, 2, 3 average
DO1 = average X 0.02 = __________ mg DO/L H2O
DO8 = average X 0.02 = __________ mg DO/L H2O
BOD = (DO1 - DO8) = __________ mg DO/L H2O/8 days
SOURCES DO1 DO8 BOD