TMDL Parameters

TMDL Parameters

Once the process is understood and stakeholders are involved, the focus of the TMDL process

turns to the mission at hand – understanding and establishing loads for the parameters for which a

water body is limited.

Total Maximum Daily Loads are measured in terms of quantities per unit of time entering an

aquatic ecosystem. On the other hand, there are many parameters that are directly related to

water quality but are not measured, typically, in terms of loads. Typical load-related parameters

include total phosphorus, orthophosphorus, total nitrogen, organic nitrogen, ammonia, chemical

oxygen demand (COD), biochemical oxygen demand (BOD), total suspended solids (TSS), total

dissolved solids (TDS), pathogens (e.g., bacteria and fecal coliform), pesticides, metals, and

sulfate. Nonload parameters include pH, dissolved oxygen (DO), turbidity, chlorophyll, and

habitat alteration or modification. Temperature can be considered as either a load (heat load) or a

nonload (temperature) parameter.

Often only one or two parameters are directly regulated through the TMDL process. However,

other parameters related to the health of the water body may be required as part of the monitoring

plan. For example, total phosphorus and ammonia may be regulated, but data on pH, dissolved

oxygen, turbidity, and temperature may also be collected and reported since these more directly

relate to the health of the ecosystem.

Intere st in a variety of parameters has created a significant demand for reliable, easy-to-use,

multi-parameter, water quality monitoring equipment which measures these parameters simulta-neously,

either continuously over time or discretely (at specific points in time), and can be ideal

for many nonload TMDL monitoring applications.

Let’s explore each of the commonly regulated or required parameters in a little more detail:

Load Parameters

These parameters can be measured in the field or in the laboratory, and can be defined in terms of

mass per period of time (such as pounds/day).

Phosphorus (P)

Phosphorus is essential to all life, as it is a component of DNA, RNA, membranes, and ATP (the

energy-transporting molecule inside living cells). In most fresh waters, concentrations of P

available for use by aquatic plants are so low that plants can’t grow at their maximum rates. But

the human activities frequently release more P into the environment – often in the forms of

industrial effluent, agricultural runoff and wastewater treatment. The introduced P encourages

more growth of algae.

Algae removes oxygen from the water at night when they respire and when they decompose after

they die. The net effect: substantial decreases in dissolved oxygen, which kills fish and other

aquatic organisms (see below). Algae also physically clog waterways, plug water intakes, and

release foul odors and bad taste compounds.

Total phosphorus includes particles of organic material or inorganic compounds like iron or

aluminum oxides that contain P. When these particles dissolve or break down, they release

orthophosphorus, which is the chemical form that algae can actually absorb. There are

generally enough other nutrients present in fresh water so algae can grow proportionate to

the concentration of orthophosphorus in the water, closely linking algal blooms and high

levels of orthophosphorus.

Because it builds up in sediments and then internally recycles, P is often a very important param-eter

in lakes. Phosphorus tends to accumulate in association with colloids and organic matter in

the bottom of the lake, and not be washed out as water flows out of the lake.

Ammonium- N (NH 4

+ ) and Nitrate-N (NO 3

- )

Ammonium – or its uncharged form, ammonia NH 3 – is a bioavailable form of nitrogen which

aquatic plants can absorb and incorporate into proteins, amino acids, nucleic acids, and other

essential molecules. Nitrate (NO 3

- ) is also bioavailable and forms when bacteria use dissolved

oxygen to oxidize ammonium. While ammonium rarely moves in groundwater, nitrate is very

mobile, and may seep into streams, lakes, and estuaries from groundwater enriched by animal or

human wastes and commercial fertilizers.

High concentrations of ammonium or nitrate can enhance the growth of algae and aquatic plants,

in a manner similar to enriched phosphorus. Although in most fresh water bodies phosphorus is the

most limiting nutrient for growth; nitrogen may be limiting in other cases where phosphorus is

naturally high, and in many estuaries.

A second effect of high ammonium occurs when bacteria convert NH 4

+ to NO 3

- , a process called

nitrification, which lowers dissolved oxygen (see below). In the course of this process – also

called oxidation – four atoms of oxygen are consumed for every individual N atom converted

from NH 4

+ to NO 3

- . In other words, about 4.5 mg of O 2 are consumed for every 1 mg of NH 4

oxidized in the water. For example, if 2 mg of NH 4

+ -N/L are oxidized, that consumes about 9.0 mg

of O 2 /L. Because water at typical field temperatures becomes "saturated" with oxygen at 8 to 9

mg O 2 /L, nitrification of just 2 mg/L of ammonium can use up all the dissolved oxygen in the water

(assuming there’s no reaeration). That leaves little or no dissolved oxygen for use by aquatic

organisms for respiration.

Wastewater treatment plants and confined animal feeding operations may release waters with 10

to 60 mg NH 4

+ -N/L. If these waters constitute a high fraction of the receiving water volume – for

example, during low flow conditions – serious deficiencies of dissolved oxygen can occur

downstream.

A third significant effect of NH 4

+ -N causes direct toxicity to aquatic life. At higher pH (typically

above pH 7.5 or 8.0), a significant fraction of the total ammonium in the water exists as the

uncharged, or "free," ammonia (NH 3 ) form. Because this form is readily taken up through

membranes and interferes with cell metabolism, it has a direct toxic effect. The toxicity of this

ammonia increases with increasing temperature. Simple chemical models are used to estimate

the amount of free NH 3 present.

Suspended Sediments/Turbidity

Particles of organic or inorganic material, such as soil, clay and silt, frequently enter streams

from disturbed sites, including agricultural lands, forestry roads or logging disturbance, and

building sites. Particles have several effects on water quality:

Nutrient and chemical pollutant enrichment: Sediments, especially fine sediments from

topsoils, often carry high concentrations of nutrients like P, N, and soil organic matter. They

can also contain pollutants such as heavy metals, pesticides, and other toxic organic com-pounds.

These pollutants may be released into the water directly, or if an animal directly

ingests the particles, the pollutants may dissolve in the digestive system of the animal and

toxify it.

Clogging spawning beds: Some game fish, such as steelhead and salmon, require clean gravel

beds in which to lay their eggs. The flow of oxygenated water through these gravels provides

oxygen to the eggs and to freshly hatched fish (called "fry"). Fine particles clog pores in the

gravel, greatly restricting the flow of water and oxygen to the eggs and fry; as a consequence,

they may suffocate and die.

Direct abrasion: Inorganic particles like silts and sands can scratch the gill tissues of aquatic

organisms, killing or weakening them. Weakened fish and other organisms are more susceptible

to disease and parasites.

Decreased light penetration: Suspended sediments cut down on the depth of light penetration

through water – they increase the turbidity of the water. In some cases this leads to direct danger

to humans: for instance, making it difficult or impossible to find drowning swimmers below the

water surface. High turbidity affects the type of vegetation that develops in a body of water.

With high turbidity in shallow water, suspended phytoplankton shade out rooted plants.

Turbidity can be measured in the field or in the laboratory. Turbidity is a measure of how far

light will penetrate into the water; (how "murky" the water is), and is closely related to total

suspended solids (TSS). TSS includes all the particles that are suspended in the water, including

silt, clay, organic material and algae. When the water is stagnant, some of these particles settle

out while others stay in suspension for long periods of time. [Total dissolved solids (TDS) are

mainly ions like sodium, calcium, chloride and sulfate that are actually dissolved in water and, in

most cases don’t absorb light and contribute to turbidity.]

To separate TSS from TDS a water sample is filtered through a glass fiber filter. The weight of

material that is filtered out is called the TSS. The material that passes through the filter is

considered TDS, although many very small particles (colloids) can actually pass through the

filter.

For long-term, in situ continuous monitoring of turbidity, a self-cleaning turbidity sensor is

usually necessary to avoid fouling of the sensor. Turbidity readings from continuous monitoring

devices that are not self-cleaning will generally yield significantly inaccurate readings.

Oxygen Demand - BOD and COD

The concentration of oxygen in the water is very important to the health of aquatic organisms. In

addition, a whole range of reactions that result in degradation of water quality occur when

oxygen is lost from the water column (e.g., see Sulfate below).

Oxygen in water is used by plants (at night) and animals. Microbes breaking down organic

matter or oxidizing ammonia also use up oxygen. Finally, some chemicals may react with

oxygen without requiring the activity of microbes. Biochemical oxygen demand (BOD) refers to

the decomposition or oxidation processes that microbes mediate, while Chemical Oxygen

Demand (COD) refers to the generally rapid chemical oxidation processes.

BOD is usually associated with sources of organic material that enter the stream. Many

point sources contain high concentrations of material that decomposes quickly: for ex-ample,

a food processing plant may release wastewater high in sugar. Manure also decom-poses

relatively quickly in streams, so releases from feedlots, chicken farms, and dairies add

to BOD. Many industries, wastewater treatment plants, and Confined Animal Feeding

Operations (CAFOs) release waters with high BOD or COD.

Nonpoint sources also contribute to BOD. Topsoil contains organic matter, which continues to

break down when it enters water bodies, so eroding topsoils are important contributors to BOD.

Plant residues like wheat straw or lawn grass clippings washing into streams also contribute to

BOD. Vegetation along the stream (riparian zone vegetation) may also contribute to BOD when

leaves fall in autumn, or plants die and wash or fall into the stream or lake. When any of these

materials settle to the bottom of the water body they continue decomposing in the bottom sedi-ments.

This is called sediment oxygen demand (SOD), which can also include some COD as

well as BOD.

Ammonia is a special case (see Ammonia section above). Although ammonia is a simple inor-ganic

molecule, it is oxidized by microbes to nitrate and uses substantial amounts of dissolved

oxygen in the process.

COD is associated with chemicals like reduced iron or manganese that chemically oxidize when

encountering oxygen. These chemicals may derive from natural sources such as some anaerobic

groundwater, or may be due to human activities. Both point sources and nonpoint sources can

contribute COD to surface water.

To measure BOD, field samples are collected and incubated in the laboratory to determine how

much oxygen they remove from the water over time (usually five days). In some cases, other

dissolved materials, like iron and manganese, may consume oxygen rapidly even without micro-bial

activity.

To measure COD the sample is brought into the laboratory and reacted with a mixture of chromic

and sulfuric acid. The acid oxidizes all organic matter in the sample. The sample is back-titrated

to determine how much oxidation potential is left in the system. The amount of chromic acid

broken down by organic matter in the sample is related to the total amount of oxidizable organic

matter in the sample.

Temperature/Thermal Loading

Many aquatic organisms are sensitive to high water temperatures. The solubility of oxygen is

lower in warm water, limiting oxygen supply (see "Dissolved oxygen" below). In some in-stances,

disease organisms and parasites thrive in warmer water and attack weakened aquatic life.

Temperature is a particular concern in areas that support cold water game fish such as trout,

salmon and steelhead. Their bodies burn energy more rapidly at high temperatures, so they don’t

use energy as efficiently.

Algae also grow more rapidly at higher temperatures when nutrients and light are abundant.

Temperature is related to heat "loadings" from a variety of nonpoint sources: direct sunlight on

water (e.g., in stream sections with inadequate riparian vegetation); inputs of warm surface water

from reservoirs or ponds; industrial effluents; and summer runoff from rooftops and paved

surfaces in urban areas. Expected heat loadings due to direct sunlight on water can be calculated

based on light intensity at full sunshine and percent shade in a given stream reach (Brian

Kaspar, Oregon Department of Environmental Quality, Personal Communication.).

Pathogens/Bacteria

Water quality is degraded by the presence of human pathogens in two primary ways: (1) humans

swimming in or drinking the water can directly ingest the pathogens; and (2) fish, shellfish, and

other aquatic organisms can accumulate the organisms either internally or externally and, if eaten

without proper preparation, may induce illness. In the US, human pathogens generally come

from leaking septic tanks or sanitary sewerage leaks or overflows.

Methods for measuring pathogens directly are costly and time-consuming. In most cases,

indicator organisms are used instead of analyzing for the pathogens themselves. These indicator

organisms are bacteria that also occur in human and animal waste, but are generally not patho-gens

themselves. They include coliforms (which are primarily non-toxic, naturally occurring

bacteria in human and animal digestive systems); sometimes one specific coliform, E. coli; or

enterococci, another class of human gut organisms. In contrast to the pathogens, the coliforms

are easy to collect and count, and often provide at least an indication of whether or not fecal

material has entered the water body. The downside of using indicator organisms like coliforms is

that the coliform tests are generally nonspecific: in other words, they don’t distinguish between

human coliforms and coliforms from other warm-blooded animals. High coliform numbers

could occur due to human sources or to domestic animals (e.g., livestock, dogs, cats) or even

wildlife such as raccoons, waterfowl and, in some cases, bears and other large animals that

directly contaminate water with their feces. Until better methods for distinguishing between

these forms become available, total coliform-type numbers will be used.

Loads are expressed in terms of cells per 100 ml of water in most cases, with a variety of thresh-old

values (for instance, 100 cells/100ml) as a guideline to distinguish between contaminated and

uncontaminated water.

Heavy Metals

Environments are enriched with heavy metals by a variety of human activities. Most of these

metals, like copper, zinc, lead and chromium are very insoluble in most waters. However, they

may be associated with particles that are suspended in the water and flow with the water. They

are especially associated with very small particles (generally smaller than 1 micron) called

colloids that settle out very slowly.

Many aquatic plants and animals are very sensitive to soluble metals, even at concentrations in

the range of parts per billion. However, because of their insolubility, high concentrations of

metals rarely occur unless the pH is very low (as in acid mine drainage) or an industrial source is

releasing high concentrations.

Metals are usually found in water at concentrations around the 1-100 part per billion range. Most

of the metals are naturally occurring, so there is a real background load that must be considered

(although without suspended solids these loads are normally very low).

Loads are expressed in terms of total metal concentrations. To obtain total metal concentrations,

strong acid is added to the water sample, which is then heated to dissolve all organic and mineral

solids that may contain metals. Allowable loads are expressed in terms of pounds of the

metal per day.

Trace Organics/Pesticides

Humans introduce a wide range of organic molecules into the environment. Many of these have

been found to be toxic. For example, the gasoline additive MTBE has just been banned from use

in California because of potential contamination. In many cases, pesticides are of high concern

in waters. These may originate from agriculture, forestry, urban, and rangeland control of weeds,

insects, fungal diseases, and other pests.

There are hundreds of these trace organics in the environment. Analysis is usually expensive and

tedious, and even now errors can enter into the analysis. Both in terms of cost-efficiency and

time, care must be taken to select the most important organic molecules to test for – those that are

most likely to occur in the watershed. For example, if corn is a dominant crop in the watershed,

it makes sense to analyze streams in the watershed for pesticides used on corn.

There is generally great uncertainty about the short-term and long-term toxic effects of these

chemicals in the environment, which makes setting concentration and load standards challenging.

Still, standards are set in some instances, and allowable loads can be calculated. In most cases

there is no background load because these chemicals do not occur in nature.

Sulfate

Sulfate is a byproduct of many human activities. It also occurs naturally in waters and reaches

moderate to high concentrations in many arid and semi-arid regions of the US like the Southwest.

Sulfate causes problems because in the absence of oxygen in the water, it can be converted to

sulfide, which is toxic to many forms of aquatic life. Hydrogen sulfide is the "rotten egg" smell

that often occurs in hot springs.

Sulfate is often not routinely analyzed in water, but under certain conditions it may be important.

For example, wastewater treatment plants that use alum (aluminum sulfate) treatments to remove

phosphorus will often release high concentrations of sulfate into the receiving water.

Nonload Parameters

These parameters are difficult or impossible to express in terms of load. They are often measured

directly in the field with a variety of single-parameter or multi-parameter instruments. Techno-logical

innovations over the last 10 years have yielded compact, easy-to-use, accurate multi-parameter

instruments which allow simultaneous readings of these nonload parameters.

Habitat Alterations or Modifications

Habitat alterations or modifications along water bodies are caused by dams, dredging,

channelization, ditching, housing developments, highway construction and maintenance, and

county operations. Many of the modifications involve stripping streams of their natural wooded

buffers, causing increased runoff and increased stream turbidity due to eroded soils and

streambanks. An indicator that some of the impacts of these modifications are being corrected

would be decreases in turbidity and suspended solids (including sedimentation and silt) brought

about by BMPs.

A report on Ohio EPA’s web site (http://chagrin.epa.state.oh.us/document_index/305b.html)

explains that the major reason nearly half of the state’s streams are not meeting federal Clean

Water Act standards is due to habitat modification – surpassing severe nutrient enrichment as

the leading cause of stream impairment in Ohio for the first time since the CWA was approved

in 1972.

While channel modifications cannot be associated with a load number per se, many states make a

connection between habitat and aquatic life because of the changes in sediment transport, flow, light,

temperature, bottom substrate, and other stream health factors associated with these modifications.

Specific biological standards based on biological indices such as IBI (Index of Biological Integrity)

and ICI (Invertebrate Community Index) are used as measurement tools. The IBI examines and

evaluates various aspects of the fish community; ICI examines the macroinvertebrates (aquatic

insects).

Corrective actions are essentially BMPs, including restoring riparian buffer zones and stream

habitat, stream reconstruction, riparian tree planting to stabilize shore erosion, and the introduction

of vegetation to provide habitat features that will restore stream habitat.

Some states try to locate unimpaired streams to use as a reference to measure their biological

composition, including fish and macroinvertebrates. The biological communities in these reference

streams then serve as target objectives

when improving the quality of the

modified streams. Natural geomorphol-ogy

(stream cross section, depth,

bottom substrate, meander pattern, and

other variables) can also be inferred

from the landscape properties, and

used to guide restoration efforts.

Dissolved Oxygen

Fish, invertebrates, and most aquatic

organisms need oxygen for their metabo-lism.

They obtain this oxygen from

dissolved oxygen gas held in the water.

When these DO levels get too low,

organisms are weakened and eventually

die. The young of any species are

especially susceptible because of their

high metabolism and limited mobility,

which doesn’t allow them to effectively

seek higher-oxygen waters.

Therefore, DO is one of the most critical

parameters that reflects the health of the

aquatic ecosystem. Dissolved oxygen

measurements provide a direct indication

of the ability of the water to support

aquatic life other than plants.

Stirring Independent

Dissolved Oxygen Measurements

When taking manual samples, agitating the

probe precludes the need for stirring. For long-term

deployments, stirring dependence is a

particular problem because of the power

required to operate an automatic stirrer. A new

approach – called Rapid-Pulse DO technology

– consumes far less oxygen and functions

accurately in all flow conditions including

minimal flow, high flow, and changing flow.

The Rapid-Pulse system measures the current

resulting from the reduction of oxygen diffusing

to the electrode. The current is still propor-tional

to the partial pressure of oxygen in the

solution. However, unlike standard polaro-graphic

DO sensors, which are constantly

polarized, the Rapid-Pulse DO sensor is rapidly

polarized and depolarized during a measure-ment

sequence. As a result, there is no need

for an energy-intensive stirring device with a

Rapid-Pulse DO sensor. Rapid-Pulse technol-ogy

is also less prone to passive fouling.

The maximum amount of oxygen (saturation concentration) that can be dissolved in

water decreases with increasing temperature. For example, air-saturated water at 15° C

contains 10.1 mg/L DO; at 25° C, the stream would be air-saturated at approximately

8.3 mg/L DO. It’s important to note that water can receive substantially more DO when

the gas source is pure oxygen, as from photosynthesis, instead of air, which is only 21%

oxygen. (For details, see YSI Technical Note titled, Environmental Dissolved Oxygen

Values Above 100% Air Saturation. To view this document, visit the YSI web site at http:/

/www.ysi.com/ysi/envweb.nsf; then click on technical support; then click on technical

notes).

Oxygen enters water from photosynthesis by algae and other submerged aquatic plants, and

from the atmosphere. Oxygen exchange between the stream and the atmosphere often occurs

most effectively where cascades, riffles or fast-moving water exist.

Oxygen is consumed by larger organisms, microbes breaking down organic matter from

sediments, manure, dead algae or other plant materials, microbes oxidizing ammonia to

nitrate, and chemicals that spontaneously oxidize. Living algae consume DO at night when

they are not photosynthesizing.

Dissolved oxygen must be determined in the field since sample handling can rapidly change

concentrations. Even short periods of low DO can kill organisms, so continuous monitoring

is especially important for this parameter. Oxygen electrodes have been developed which are

relatively stable and, with some maintenance, can provide continuous monitoring of this

parameter in water.

Although wet chemistry titration methods are still used to measure DO, electrode methods

are preferred in most cases. Industry standard polarographic DO monitoring technology for

lab and field measurements relies on a stirring attachment in low-flow situations to ensure a

fresh supply of water in front of the probe’s membrane. Because oxygen is depleted as the

molecules diffuse through the membrane to the cathode, a new supply of oxygen is needed to

prevent a decrease in signal.

The pH refers to the balance between acidity and alkalinity. A pH of 7.0 is neutral; values

below 7 are acidic, and above 7 are alkaline. Excessively high or low pH levels often are

associated with nutrient deficiencies, metal toxicities, and other problems for aquatic life.

High pH makes ammonia more toxic. Low pH increases the solubility of most heavy metals

like zinc and copper.

Natural waters reflect the pH of the soils they have moved across or through. Industrial,

municipal, and agricultural waters may be significantly higher or lower in pH.

During algal blooms, algal photosynthesis increases the water pH, especially in stagnant or

slow-moving water systems. This happens because algae absorb bicarbonate, use the CO 2 in

photosynthesis and then excrete the hydroxyl ion, which raises the pH. In extreme cases it

may exceed pH 10, causing a variety of chemical problems for aquatic life.

Total Dissolved Solids (TDS), Salinity, Electrical Conductivity

Water contains varying concentrations of dissolved ions. Sodium (Na + ) and chloride (Cl - )

dominate marine waters. Fresh waters, however, may be dominated by the cations Ca 2+ ,

Mg 2+ , Na + , or K + , and anions Cl - , SO 4

2- , CO 3

2- , and HCO 3

- . Because ions carry electrical

charges, water with high salt concentration will carry a greater current than water with a

lower concentration of salts. Excessive ionic content can also cause some fresh water

organisms to "dry out" physiologically.

Humans – through livestock and agricultural operations, septic tanks, swimming pools, and other

trappings of modern life – often make water saltier.

It’s important to note that ions are more "conservative" (less affected by the environment) than

pH, temperature and dissolved oxygen. For instance, DO can change because of atmospheric

inputs as well as uptake by plants, animals and microbes. In addition to the impact on DO from

algae, pH can also change due to algal activity. However, because ions do not change readily due

to environmental factors, the presence of a specific ion in a stream or other water body can be

used as a good screening tool, an effective "first cut" tracer to determine if other water sources –

and pollutants such as untreated waste – are entering the stream between two monitoring points.

Fresh water scientists typically measure this as specific conductance, which is an indicator of

salinity.

Total dissolved solids (TDS) are usually expressed in units of mg/L, or ppm. In marine or

estuarine waters, ionic content is usually reported as salinity in parts per thousand (ppt). Salinity

in fresh water is usually measured indirectly by measuring the specific conductance (temperature

and compensated conductivity) or electrical conductivity (EC) of the water. Units of EC are

milliSiemens/cm, deciSiemens/m, or microSiemens/cm. Depending upon the specific types of

salts present, multiplying the EC by a value between 0.55 and 0.9 can provide an estimate of

salinity in parts per million.

Modern conductivity meters automatically calculate salinity from conductivity and temperature.

With some multi-parameter equipment, TDS is also an automatically calculated measurement

derived from specific conductance and a constant that is empirically determined by the user for

the site in question.

Turbidity

High turbidity makes water appear "murky." In a water system, turbidity is often well correlated

with total suspended solids.

Turbidity probes measure the scattering of light caused by particles as the light passes through

water, expressing the value in nephelometric turbidity units (NTUs). Turbidity sensors can be

placed long-term in water, but they require self-cleaning capability or they will foul with organ-isms,

air bubbles, or sediments that can interfere with light readings. When selecting a turbidity

probe, pay close attention to whether the probe is at a 90° angle or 180° angle to the light source.

The international standard is a 90° angle. The ISO 7027 standard states that a 90° measurement

is a true nephelometric measurement.

Chlorophyll, Chlorophyll- a

The measurement of chlorophyll in surface water can be used to estimate nutrient loading.

Chlorophyll can be determined in two ways: 1) in situ; i.e., without disrupting the living cells,

and 2) by breaking the cells and extracting the discrete chlorophyll molecules into organic

solvent.

Algae contain a wide range of pigments, primarily chlorophyll- a. Field instruments can

measure the presence of chlorophyll by measuring the release of light energy at one

wavelength when the sample media is stimulated by light of another wavelength – a

phenomenon called fluorescence. More fluorescence usually indicates a larger presence

of chlorophyll in the sample.

Chlorophyll fluoresces when exposed to blue light. In in situ (in place; in the water in the

field) chlorophyll testing equipment the light source is usually a blue light emitting diode

(LED) and the detector has a filter in front of it to block out interference from other sources,

primarily turbidity in the water.

In situ testing equipment for chlorophyll is not as accurate as lab equipment. Most field

instruments that use fluorescence to analyze chlorophyll are really measuring everything that

fluoresces under the optical characteristics (source + filter) of the sensor. There are many

other pigments within an algal cell that can and will absorb blue light and fluoresce just as

chlorophyll does. However, depending upon the species, much of the fluorescing pigment

within an algal cell (about 90%) is chlorophyll- a. The delicate balance manufacturers walk is

narrowing the transmitted bandwidth enough to focus on algae, but not so much that it is too

species-specific to provide a good indicator of a variety of algae that could be present.

To actually determine levels of only chlorophyll- a, an extraction must be done and high-pressure

liquid chromatography (HPLC) must be performed on the extract. However, con-tinuous

in situ trend monitoring can help water quality monitors determine when a more

accurate – and costly – chlorophyll- a lab test is warranted. Exciting, new, self-cleaning

chlorophyll sensor technology – which can also be used for continuous monitoring or discrete

sampling – will allow an increasing number of environmental researchers to deploy long-term,

unattended chlorophyll monitors without unwieldy, power-consuming pump systems.

Summary of Parameters and Their Relationships

A summary of the parameters, their units of measurement, and their typical method of measure-ment

are presented in Table 1.

arameter P st ni U si analys of method Standard

bacteria indicator athogens, P lm ounts/100 C st coun plate Laboratory

Alterations abitat H tx te see - arious V tx te see - arious V

etals M L/ metal Mg ICP-AES OR absorption atomic flameless digestion, Acid

spectroscopy) emission atomic plasma coupled (inductively

oxygen Biochemical/chemical

demand

g/L M sy da 5 over loss Oxygen

etc. pesticides, organics, race T L/ icrograms M re spectromet gas Extraction/concentration,

Phosphorus otal T L/ TP mg

ppm

complex color blue colorimetric acid, in Dissolved Laboratory:

Orthophosphorus

PO 4 SRPs ,

OP/L mg

ppm

complex blue colorimetric Laboratory:

TKN nitrogen, kjeldahl otal T L/ TKN mg

ppm

determination colorimetric acid, in Dissolved Laboratory:

Ammonium-N

Ammonia-N

NH mg 4

+ -N/L

ppm

determination colorimetric Laboratory:

determination colorimetric electrode, selective ion Field:

Nitrate-N

Nitrate-nitrite-N

NO mg 3

- -N/L

ppm

colorimetric Laboratory:

colorimetric electrode, selective ion Field:

suspended Total

TSS solids,

TSS/L mg filter, oven-dry filter, glass micron 1.5 through filter Laboratory:

weigh

TDS, solids, dissolved Total

salinity

/L mg residue weigh above, method TSS from filtrate Dry Laboratory:

& TDS to conversion standard use and EC Determine Field:

measurement) (calculated electrodes

EC, conductivity, Electrical

conductance Specific

MicroSiemens/cm

milliSiemens/cm

conduct to water of ability Measure field: and Laboratory

electrodes - electricity

oxygen, Dissolved

O mg 2 L /ed electro DO titration, Wet Laboratory:

DO (Rapid-Pulse) Independent Stirring electrode, DO Field:

Electrode

urbidity T sU T N ro sens light-based - Nephelometer : Laboratory

nephelometer Field Field:

H p st uni H p ed electro Glass field: and Laboratory

hlorophyll-a C L/ icrograms M CL HP extraction, Solvent Laboratory:

chlorophyll otal T L/ icrograms M ec Fluorescen Laboratory:

Fluorescence Field:

emperature T Fr o C eg D re thermomet mercury or Thermistor Laboratory:

Thermistor Field:

Table 1: Major TMDL parameters, common units, and typical methods of measurement in the

laboratory or field. Note that many of the parameters listed in the table, including dissolved

oxygen, chlorophyll and turbidity, are electrode measurements that can be measured either in the

field or in the lab with one multi-parameter water quality monitoring instrument.

Parameter Interactions

Figure 1 summarizes the relationships among the parameters listed in Table 1. Parameters are

generally grouped into categories of nutrients (N and P in this case), sediments, carbon (organic

matter) and salts.

The arrows are meant to connect relationships, not always actual quantities. The example is A

à B, where A and B are both water quality conditions or parameters.

The (-) next to an arrow means that an increase in A results in a decrease in B. For example,

increasing temperature (A) generally causes a decrease in dissolved oxygen (B), because oxygen

is less soluble at higher temperatures. The (+) next to an arrow means that an increase in A

results in an increase in B. For example, higher total P generally results in higher

orthophosphorus because orthophosphorus can be released from particles containing P. (It’s

important to remember that these relationships are general rules rather than absolutes.)

The "Ind" next to an arrow indicates that A is an indicator, rather than a direct measurement, of

B. For example, electrical conductivity (EC) is an indicator of total dissolved salts. We deter-mine

EC because it is easier to measure than total dissolved salts directly. The amount of salts

can have a direct effect on the health of the organisms, but the EC generally doesn’t; its only use

is as a rapid, inexpensive, reliable indicator of the salt concentrations in the water.

Figure 1 also indicates which parameters are typically measured in the field, which are measured

in the laboratory, and which may be measured in either or sometimes both locations. Parameters

like temperature, pH and dissolved oxygen can change rapidly after sampling and may give

completely different values in the laboratory than in the field. On the other hand, there are no

good field methods for determining total suspended solids, so this must be done in the laboratory

unless correlations are worked out between TSS and field measurements such as turbidity.

FIGURE 1. Relationships among water quality parameters and their effects on aquatic life. The overall

form is A à àà ààB. If an increase in A increases B, a (+) symbol is found next to the line; if increases in A

lead to decreases in B, a (-) symbol is next to the arrow. "Ind" next to the arrow means that A is an

indicator of B, and is used because it is faster and more convenient in general. Shading in the boxes

indicates whether the parameter is measured in the field, in the laboratory, or in both.

Following are a few examples that may help you use figure 1.

Some monitoring measurements have direct adverse impacts on biological life, while others have

indirect effects. For example, algae modify pH and dissolved oxygen, which directly affect the

health of fish and other aquatic animals. Figure 1 was developed to demonstrate the relationships

between frequently measured parameters and how they reflect on the health of the aquatic

environment.

For example, if one were interested in the role of SEDIMENTS in the TMDL process, and how

related measurements affect aquatic health, the following information can be derived from Figure

1. Algae are generally counted as part of total suspended solids, and increasing algae

increases (+) both turbidity and total suspended solids.

2. Increasing turbidity has a direct adverse effect (-) on the health of aquatic organisms by

decreasing the depth of light penetration through the water column.

3. Turbidity measurements are an indicator (Ind) of TSS. In many cases, specific

correlations have to be developed for a given site to convert turbidity measurements to

TSS measurements.

4. Total suspended solids have an adverse (-) effect on the health of aquatic organisms

by silting up stream bottom organisms and eggs, bringing in metals, phosphorus and

organic material.

Temperature

Fish

Invertebrates

Shellfish

Orthophosphorus -PO

Chlorophyll a

Total chl/fluorescence

Total phosphorus

Total N - TKN

Nitrate - NO 3 -

Ammonium -NH 4 +

Dissolved

Oxygen

Algae

Interaction diagram for water quality parameters

Total dissolved solids

Total suspended

solids

Electrical conductivity

Turbidity

(-) (+)

(+)

(-)

(+)

(+) (+)

(+)

(+) As A increases, B INCREASES

(+)

(-)

(-) As A increases, B DECREASES

(-)

Laboratory

only

Laboratory

and field Field only

Ammonia - NH 3

Ind Indicator of

value in next box

Ind

Total organic

carbon

Biological O2

demand

(-)

Salts

Sediments

Nutrients

Ind

Carbon

A B

(+)

Using Flow Measurements to Determine Loads

As noted in the introduction to this paper, TMDLs are legally expressed in terms of loads, al-though

most monitoring produces results based on concentration. As a result, water quality

analysts have had to rely upon physical and mathematical approaches to bridge the span between

concentration and load. Loads have been set based on minimum flows in many cases.

Methods of measuring flows include specific flow/cross-section analysis using in-stream flow

meters; depth-flow relationships using weirs, flumes, or open-channel measurements; or an

ultrasonic Doppler flow device for in-channel or in-pipe measurements.

Flow/Cross-Section Analysis Using In-Stream Flow Meters

A standard USGS measurement method involves dividing the stream into ten or more subunits.

Flow and depth are measured in each subunit, and these data are used to estimate total flow

through the system. This method can be used in both open channel (e.g., natural stream) systems

or in fixed-dimension constructed systems like ditches or flumes. Normally a reference depth

site is selected which is convenient to read, never fully exposed out of the water, and not likely to

be swept away or otherwise lost from the site. A staff gauge may be installed at this point, which

gives depth in terms of either centimeters or tenths of a foot. The reading on the staff gauge is

read each time one visits the site.

Depth-Flow Relationships

After one season of regular measurements, it is possible to assemble a rating curve. The rating

curve is simply the relationship between the depth measured on the staff gauge and the corre-sponding

measured flow rate.

If desired, continuous flow rates can be collected in this site simply by installing a continuous

recording depth monitor and then converting the depth reading to flow. This is extremely valu-able

in determining typical ranges and time-related patterns of flow in the system.

Ultrasonic Doppler Flow Device

The Ultrasonic Doppler (USD) system can be installed in the stream bed or in the bottom of a

culvert or other channel, with regular or irregular cross-sections. A weighted average flow rate is

estimated by sending out sonic signals into the water column, which bounce off suspended

particles or bubbles. The frequency of the waves that return to the unit is related to the velocity

of the particle, based on the Doppler effect, which observes that fast-approaching particles

shorten the wavelength.

The entire field of particles in the water column is rapidly sampled with this method, and their

velocities are averaged to provide a mean velocity for the stream cross-section. The channel

cross-section can be entered into the software program that comes with the USD unit, and based

on the water depth (which provides a cross-sectional area), the product of mean velocity and total

cross section gives total flow rate. The advantage of the USD is that it does not require a rating

curve and fits in many channel types, including culverts.

The flow values obtained are entered into the equation for calculating total loads at that specific

point (see Sections I.B. and IV.A). Basically, the concentration of the regulated parameter at that

sampling point is multiplied by the flow rate at that point. The calculated loads are compared

with the regulated tolerable loads for that parameter to assess whether or not the water body

is in compliance with its TMDL.

Flows are critically important in determining TMDLs. For calculating the maximum allowable

loads from tributaries or point sources to a river, for example, one might base tolerable loads on

the load when flow is lowest: for example, lowest mean monthly flow. Since flow is low, these

will be conservatively low load numbers, and WLAs and LAs will also consequently be conserva-tively

low.

Good data over multiple years (preferably at least 10) are needed to obtain an adequate idea of

the lowest mean monthly flow rate for this calculation. On some larger streams, the U.S. Geo-logical

Survey has continuous flow monitors that can provide current and historical information

on flows. However, in many other instances, flows are poorly or incompletely known, and best

guesses based on modeling may be used to estimate lowest mean monthly flow rates.

Understanding flows is not just important for determining loads for TMDLs. The variation in

stream flow can provide insight into the health of the watershed. As watersheds urbanize, for

example, streams often become "flashy," with very rapid changes in flow rates due to rapid runoff

from rooftops, parking lots and streets. This increases the potential for streambank erosion,

flooding, and other problems downstream.

Flow measurements will continue to be an important part of water quality monitoring, and should

become more widespread as methods for continuous flow monitoring become more easily

applied and widely available.