WhatÕs in a Watershed: The Parameters
The majority of this information is available in the Environmental Protection AgencyÕs Volunteer Stream Monitoring: A Methods Manual, Available online at http://www.epa.gov/volunteer/stream/index.html
This handout is based on some of this information and made for a high school audience, and contains less of the field instruction that the original manual contains.
Biological Oxygen Demand (BOD) (Not testing)
Biological oxygen demand (BOD) is a measure of the oxygen the organisms (the big ones you see and the very small ones you need a microscope to see) living in a stream consume. Remember that in a stream, there are more tiny organisms than big ones, so most of the BOD will be due to them. BOD is also affected by other things happening in the stream – living things arenÕt the only things that require oxygen. Certain chemical reactions vital to stream health also require oxygen. Because of all of these things, there are many things that can affect the BOD, like temperature, pH (which youÕll learn about below), what microorganisms are present, and now many there are, and what kind of other material is present in the stream.
BOD directly affects dissolved oxygen, which youÕll read about momentarily. If a stream has a high BOD, dissolved oxygen will be low, and organisms in the water will not be able to breathe. Most animals will not survive well in a stream with high BOD.
The United States Environmental Protection Agency (1997) gives sources of increased BOD as leaves and plant debris; dead plants and animals; animal manure; paper mill waste, wastewater treatment plants, feedlots, and food-processing plants; failing septic systems; and urban stormwater runoff.
Streams produce and consume oxygen. As the stream runs over an uneven bottom, the surface mixes with the air, and oxygen gets mixed into the water. This means that faster moving streams with more rocks will mix in more oxygen than slow, smooth streams. Plants in the stream carry out photosynthesis and produce oxygen in the water. Oxygen is used up by animals and plants in respiration, and in decomposition of dead things, and in some chemical reactions.
All the living things in a stream need oxygen to survive, but since oxygen is a gas and water is a liquid, we have to be clever about how we can measure how much oxygen is in a stream. Scientists do this by measuring how much oxygen is dissolved in the water, and call it dissolved oxygen (DO). This is like measuring how much sugar is in your KoolAid after youÕve mixed it in and itÕs all dissolved.
Because all of the organisms in the stream need oxygen, lower levels of oxygen indicate less healthy streams. The US EPA (1997) lists some sources of decreased dissolved oxygen as wastewater from sewage treatment plants and stormwater runoff from farms, streets, and bad septic systems. Each of these contain material that gets decomposed by microorganisms that use a lot of oxygen when they do the decomposing. Oxygen gets taken out of the stream faster than it gets put back in, which means that organisms have a hard time breathing.
Dissolved oxygen levels vary in the same stream over time because colder water holds more oxygen. Warmer water, due to time of day, time of year, or human activities (such as water cooling machinery which heats water up a lot) holds less oxygen, which is bad for the aquatic organisms in the stream.
Scientists often use two types of bacteria, coliforms, and fecal streptococci, to indicate potential sewage contamination in water. These are good indicators because they themselves are generally not dangerous, but both can often found in the feces of humans and other animals, and so if they are present, it is a good sign that other, more risky pathogens (things that make us sick) may be present. If there is a high count of coliform bacteria, swimming may not be safe, and eating the animals in that watershed may be a bad idea, too.
Why not test for the disease-causing things directly? Mainly because there are a LOT of them. Things that can make us sick can be bacteria, viruses, or protozoans, another small kind of animal. And there are lots of types of each that can put us in the hospital – so if you were the one doing this stream monitoring, and you had only a small amount of time and money, would you choose to do a test for every single pathogen, or do you think you would look to something that will indicate that levels of other things are likely to be unsafe?
However, there is one other thing to keep in mind. Many science kits come with a test for total coliforms. This test is for a group of bacteria that are actually fairly common, and not just in feces. The members of this group occur in feces, but also in soil and wood, so their presence doesnÕt necessarily mean there is contamination – so a positive on this test has to be interpreted carefully. Remember that in the woods, the animals are going to do what they need to do where they need to do it, and with this test, you wonÕt be able to tell if you have some old tree dropping bacteria into your sample, some deer who just happened to pass by, or actual contamination with a positive sample. So in areas like this, total coliforms isnÕt really recommended as a good test. In urban areas, particularly in the water supply this is still considered a useful test.
How does fecal contamination get into a watershed? In some places, itÕs natural – in the deep woods, an animal defecates wherever is convenient with little regard to watersheds. In the city, like the middle of Los Angeles, bears defecating in the stream are less of a concern, and contamination is more likely to come from humans – septic systems which overflow, wastewater treatment facilities, or runoff from streets where owners may not properly clean up after pets. In agricultural areas, runoff from farms is a source.
Fecal contamination can also cause cloudy water (see turbidity below) and increase biological oxygen demand. It also often smells as you would expect it would.
Nitrogen is found in several forms in aquatic ecosystems and their terrestrial surroundings. These different forms, for example ammonia (NH3) and nitrite (NO2), together are called nitrates. Plants have to have nitrates to survive, but like most things, too much of a good thing is bad. When there is too much nitrogen and phosphorus (see below), plants change growth patterns, the plants that can grow change, the dissolved oxygen and temperature change, and the animals that can survive in the area change. Nitrates in particular are key in causing very low levels of dissolved oxygen, and can even kill warm blooded animals if their concentrations get high enough.
Nitrates come into watersheds from bad septic systems, fertilizer runoff from homes or agriculture, wastewater treatment sites, and industrial sources.
pH describes how acidic or alkaline something is. The scale goes from 1.0 to 14.0, with acids at the low end of the scale and bases (alkaline) at the high end. Pure water is neutral, with a pH of 7.0. pH is critical to every biochemical process that living things carry out.
Most aquatic organisms can only live in a narrow pH range of 6.5 – 8.0. While the pH of pure water is 7.0, streams, even clean ones, are far from pure, and they rarely have pHÕs right at 7.0. But a healthy stream should have a pH in the range where most aquatic organisms can survive. Once a streamÕs pH falls outside of that range, itÕs life starts to die off. The ones that do survive are not healthy. Also, some toxic elements just sit on the bottom of the stream not bothering any of the plants or animals, until the stream pH becomes low (acidic). Then these compounds and elements react with the water and plants and animals can take them in; some species can be particularly sensitive to this and do not survive ingesting these toxins.
Changes in pH can come from acid precipitation, wastewater being put into a watershed, and the natural weathering of rock along a stream.
Alkalinity is similar to pH, but is way to describe waterÕs ability to make acids become neutral. If alkaline compounds (like baking soda) are present in water, they will combine with H+ ions of things that would be an acid, and form new compounds. This switch-a-roo keeps the pH from becoming too acidic. In other words, if alkalinity is high, and you add an acid to your water (say, from acid rain), your pH wonÕt change much. If alkalinity is low, and you add an acid, your water becomes acidic. From what you read in the pH section, you could probably guess that a stream where any addition of acid immediately changes the pH is not a very healthy stream. Healthy streams can resist a bit of acid being put in without much pH change – after all, some acid being put into the system is natural!
Like nitrogen, phosphorous is a nutrient that plants and animals must have to survive. In aquatic ecosystems, however, phosphorous is very limited – thereÕs not very much of it. This means that when a bit is dropped into an ecosystem under the wrong circumstances, a lot of bad things can happen. In streams, algae blooms can happen, causing dissolved oxygen to decrease to very low levels, resulting in the death of many aquatic animals that rely on that oxygen to survive. Therefore, while we might think that adding phosphorous is good since most systems have so little, itÕs actually a very dangerous thing.
Phosphorous comes in several forms. ItÕs rare to find it as a plain old element (P), but normally, it is found as a phosphate (PO4). Phosphorous comes from a lot of places. Natural sources include natural weathering of soil and rocks, but most large phosphorous inputs are human-induced and come from fertilizer runoff from lawns or agriculture, water treatment plants, bad septic systems, wetlands that have been drained, and cleaners, like soaps. However, some places have enacted laws to ban soap with high phosphorus content: the Great Lakes states together have banned laundry soaps containing over 0.5% phosphorous to protect the Great Lakes from phosphorous-related problems.
Temperature (Not testing)
Like pH, every biochemical process every living thing carries out depends on temperature. Every species has a temperature range that is best for its survival; some species like colder weather, some like warmer. Some survive only in very narrow ranges, some can tolerate much wider ranges. Regardless, if an organism spends too long outside the range it can tolerate, it will get stressed, and it can die.
Temperature affects dissolved oxygen levels, photosynthesis rates, metabolic rates of aquatic organisms, and how sensitive organisms are to things that can make them sick like diseases, parasites, and poisons.
Temperature obviously changes seasonally in many places, but can also be changed by weather in general. Similarly, removal of vegetation shading streams will change temperature. Inflows into a stream, such as storm drains, groundwater inflows, and cooling water discharge will also affect stream temperature.
Total Dissolved Solids (TDS) (Not testing)
Total dissolved solids includes all the solids dissolved in the water column, and all the solids suspended (floating) that will settle out. In streams, TDS can be a variety of ions and other tiny particles, clay, dirt, silt, algae, organic debris, or plankton. The TDS level is actually very important to all the living things in the stream system and even affects cellular water balance! Suspended particles can also carry toxins, which can cling to them, particularly in areas like irrigation ditches.
From an ecological perspective, TDS, as you could imagine, can affect water clarity. High levels of TDS mean that light canÕt pass through the water; this means less photosynthesis occurs, less oxygen is produced. Water with high TDS also heats up faster and stays warmer longer. All of these effects have consequences for the organisms living in the ecosystem.
Dissolved solids come from industrial sources, sewage, agriculture (fertilizer, pesticide), soil erosion, septic systems, and storm drain run off.
The test for TDS is to weigh a beaker, collect water in it, and then evaporate the water out of the beaker in an oven. We will not be testing for TDS in class today.
Turbidity measures how clear the water is. Stream water has particles – microorganisms, dirt, plants, and other things floating in it. All of these things can make it hard to see through the water and can even affect the color of the water. Turbidity measures how far light passes through the water.
Turbidity can have big effects on a stream. High turbidity means there are a lot of particles in the stream. These particles tend to absorb more heat. This means the temperature increases in the stream. When temperature increases, the dissolved oxygen decreases. More particles also block the light, which means that plants at the bottom get less – and photosynthesis decreases. Dissolved oxygen decreases even more. Finally, if there are too many particles in the stream, fish will get their gills clogged. As particles settle on the bottom, invertebrates and larvae or eggs among the bottom may be smothered.
Turbidity often comes from natural sources, such as soil erosion, or bottom feeders stirring up bottom sediments (although human activity can lead to either of those happening with increased frequency). Turbidity can also come from runoff in cities and wastewater.
Benthic macroinvertebrates are animals which live on the bottom of streams. The prefix macro- means large, and macroinvertebrates are big enough to be seen without the help of a microscope. They live in all kinds of streams and rivers, in high mountains to urban streams, fast moving streams to rivers which move so slow you barely see them move. They are worms, clams, snails, insects, and crayfish, just to name a few. Most live at least part of their life attached to or under some form of cover underwater.
Once again, we could try to actually monitor every single organism in the stream, but a lot of organisms are hard to ever see. So we use benthic macroinvertebrates because they are easy to find, easy to catch, easy to identify, and they are good indicators. What makes them good indicators?
Invertebrates in streams are affected by the conditions of the stream, and so everything in the physical (like temperature, turbidity), chemical (like nitrates, phosphorous), or biological (like dissolved oxygen) environment will affect them, as it will affect all other living creatures. However, unlike those other critters which may be hard to find because they can move to other areas when they see a person coming, macroinvertebrates canÕt escape pollution, so they can tell us about pollution in the stream better than other species can – if we know how to ask. Another great thing about them is that some are very tolerant to pollution, and some are not – so we can learn a lot simply by looking at which species are present: for example, if a stream has only species which do not tolerate pollution, then a stream is likely to be in good health.
One disadvantage of this method, however, is that if we find only species which are pollution tolerant, we canÕt automatically assume that there is pollution in the stream and that is why the other species are not present. It is possible that that there is not enough oxygen in the stream to sustain the other species, or other biological parameters.