Chapter 3:  Water Quality

Define Components of a Healthy Stream, Lake and Estuary:

Each of these water bodies is an ecosystem comprised of the aquatic flora and fauna, the medium in which they live (the water) and the surrounding landscape such as the channel, the riparian area and adjacent land.  Keeping each of these components healthy and functioning in the ecosystem may sometimes be very difficult.   As certain aspects of the system are altered, others may have to compensate for the unbalance.  In developing watersheds, there are continual influences on the aquatic ecosystems, some of which may be very harmful.  Over time, if the area is allowed to reestablish itself, stability may eventually return.  Through monitoring water quality in impaired watersheds, we may determine what is disturbing the system, and we may alleviate this stress through pollution prevention and best management practices.   Monitoring of healthy watersheds is also valuable information, and may be used to compare with impaired areas or serve as baseline data before a watershed is disturbed.   Knowing what to look for and understanding what you are monitoring for helps to put the pieces of the puzzle together, and results in a clearer picture of the lake, stream, or estuary as a whole aquatic ecosystem.


Some Acceptable Limits of Common Parameters   (NC DENR):

In order to know whether or not your water quality has been compromised due to input of contaminants and pollutants, you must first understand the components of a healthy water resource. Depending on whether or not you are monitoring a stream, lake, or estuary, the values you would consider acceptable may vary. The Division of Water Quality has set water quality standards for various water uses. Drinking water receives the most stringent of standards, and they progressively relax with level of human contact. Appendix A provides the detailed state standards for various parameters for surface water of a particular designation.

Here is a quick reference to common parameters sampled by volunteer groups:

pH: 6-9    Dissolved Oxygen: >5 ppm     Turbidity: <30 ntu    Fecal Coliform: <200 cfu    Nitrogen:      Phosphorus:

Parameters to measure and what they mean:


Measurements of various chemical constituents may vary depending on the materials suspended and dissolved in the water.  The land uses, soils, geology, and precipitation in the watershed affect these measurements.  When measuring chemical constituents, the elements or compounds are expressed as a concentration (mg/L or ppm).   PPM is parts per million and 1 ppm means that there is one part of what you are measuring per one million parts of water. 


Dissolved Oxygen (d.o.):   measure of the concentration of oxygen in the water; required for respiration of aquatic organisms as well as decomposition; the concentration may be influenced by several factors including temperature, salinity, atmospheric pressure and the amount of oxygen demand in the water;  measured in units of parts per million (ppm)


Biochemical Oxygen Demand (BOD):  occurs when bacteria in the water use up the available oxygen as they break down organic matter or nutrients (aerobic decomposition); higher levels of decomposition result in a higher stream BOD


Chemical Oxygen Demand (COD):   refers to the oxygen depletion by oxygen using chemicals


pH:  measure of the hydrogen or hydroxyl ion concentration of the water   (acidic or basic/alkaline) and is plotted on a logarithmic scale from 1 to 14;   pH<1 is battery acid, pH = 3 is vinegar, pH = 11.5 is ammonia; rainwater has a pH around 6.5; pH affects fish respiration rates, solubility of many chemicals and metals, and acidic water may liberate harmful metals such as aluminum that is naturally present in the soil


Hardness:  measures the concentration of calcium and magnesium ions in the water; when total hardness exceeds alkalinity, chloride and sulfide ions are present and may harm aquatic life


Phosphates and Nitrates: plant nutrients; may enter the water in excessive amounts through runoff (picked up from fertilizers used on lawns, agricultural fields, and detergents); excessive nutrients may cause prolific algae growth which may deplete dissolved oxygen in a lake or stream; measured in units of parts per million (ppm) or milligrams per liter (mg/L).


Temperature:  directly affects the chemical concentrations and fish species within a stream; the higher the temperature, the less dissolved oxygen the water can hold; low dissolved oxygen may inhibit feeding, growth and reproduction of fish; when temperatures exceed normal levels for a stream, it is considered "thermal pollution", this can be caused upstream by dams, removing of streambank shade trees (riparian areas), heated discharge from industry, and inflow of stormwater from urban areas; this parameter is of particular concern in terms of fish habitat – certain species are unable to tolerate high water temperatures.  The table below shows maximum weekly average temperature for growth and short-term maximum temperature for selected fish (degrees F) Source: Brungs & Jones, 1977

Diagram from the USDA Stream Corridor Resotration Manual, 1998

Turbidity:  caused by the number of suspended solids in the water (sediment, minerals, or other particulate matter); too many solids in the stream may impede light penetration, clog fish gills and bury fish spawning beds; other pollutants may also attach to the soil particles entering the water; turbidity is measured by a nephelometer or turbidimeter in units known as Nephelometric Turbidity Units (NTU), by a Secchi disk in still, deep water, or in Jackson Turbidity Units in waters with relatively high levels.


Total Suspended Solids (TSS):   amount of suspended solids in a liter of water; measured in mg/L; similar measurement as turbidity


Total Dissolved Solids (TDS):   materials left behind after a water sample is filtered and evaporated; this may be measured using conductivity; rainwater typically has a TDS measurement of 10 ppm; the amount of dissolved material transported by a water body varies according to local geology, acidity of rainfall, non-point source runoff, etc.


Color:  affected by the presence of dissolved substances and suspended matter in the water (color change may indicate discharges from industry) and may block the sunlight from aquatic plants; some color may occur naturally (i.e. the tea color from the presence of tannic acids released by the decay of organic matter)


Pathogens:  (disease-causing organisms) detection of fecal coliform bacteria may indicate the presence of contamination by human waste from failing septic systems or wastewater treatment plants; measured by the number of colony forming units (cfu)per 100 mL of water


The aquatic life present within a stream is a good indicator as to the stream health  

Macroinvertebrates (aquatic insect larvae) are large organisms that can be seen without a microscope and have no backbone

Macroinvertebrates help determine if a stream is in excellent, good, fair, or poor health according to the type and number of organisms present in the stream

Fish population, algae, and submerged aquatic vegetation studies also help do the same

More information in Chapter 4: Benthic/Macroinvertebrate Sampling


Streams channels, drainage patterns, floodplains, terraces and other watershed and stream corridor features are dynamic systems with various geomorphic processes contributing to their development.  Geomorphology is the study of the processes that form the Earth.  You may record geomorphic descriptions of the reach you are monitoring over time. This allows for your program to consider erosion, transport, and deposition of sediment as well as chemical and biological parameters. Photograph points at your sample location are an effective tool to document changes in the streambanks over time.

Some important geomorphic processes include:


Erosion:  detachment of soil particles


Sediment Transport:  movement of eroded soil particles in flowing water.  

All sediment in a stream (boulders to clay) is subject to transport downslope or downstream.  The largest particle a stream can move under certain conditions determines the stream competence.  A related term, tactive stress, is what lifts and drags (also known as shear stress).  It varies as a function of flow depth and slope.   The sediment is set into motion by the effect of faster water moving over slower water which causes the slower water to "roll up" in a spiral motion - shear stress.

Moving particles along the bottom of a stream (rolling, skipping and sliding) are considered bed load.  Due to their weight relative to the flow velocity, these particles essentially remain in contact with the bed while being transported.

The total sediment load in a stream at any given time is divided up as either: wash load or bed load.  The primary source of wash load is the watershed (sheet, rill gully and/or streambank erosion).  Wash load concentration is usually determined by supply.


Sediment Deposition:  settling of eroded soil particles to the bottom of a water body or left behind as the water recedes.

As you move across a stream corridor these processes occur a various rates and magnitudes dependent on several variables.  These variables include human action as well as natural occurrences.   Certain factors attribute to this variability such as changing temperature, soil moisture content, amount of vegetation, and human alteration of the soil.

As you move along the stream corridor erosion, transport and deposition are responsible for the creation of features such as the channel, floodplain, and terraces.

More information in Ch. 2:  Stream Processes/Morphology


Non-Point Source vs. Point Source Pollution:  Point source pollution is just that, pollution entering the water body from a point source such as a discharge pipe.   The National Pollutant Discharge Elimination System (NPDES) federal permitting program regulates this type of pollution.  The public has access to this information, and you can find out, in your watershed, which industries have such permits and what and how much they are discharging.   Non-point source pollution is a bit more complicated.  This type of pollution is transported to the water body through overland flow or surface runoff.  Although there may be fairly concentrated areas, this type of pollution is more difficult to monitor and regulate.  Most of what you may deal with in your watershed could result from non-point source pollution. Table ? offers some common sources of point and non-point sources and concentrations of nutrients.

Diagram from the USDA Stream Corridor Resotration Manual, 1998


Go to Chapter 4: Macroinvertebrate Sampling                                            Back to Table of Contents