ASTM D6146-97(2018)

Standard Guide for Monitoring Aqueous Nutrients in Watersheds

SIGNIFICANCE AND USE
4.1 The user of this guide is not assumed to be a trained technical practitioner in the water quality field. The guide is an assembly of the components common to all aspect of watershed nutrient monitoring and fulfills a need in the development of a common framework for a better coordinated and a more unified approach to nutrient monitoring in watersheds.  
4.2 Limitations—This guide does not establish a standard procedure to follow in all situations and it does not cover the detail necessary to meet all of the needs of a particular monitoring objective. Other standards and guides included in the references describe the detail of the procedures.
SCOPE
1.1 Purpose—This guide is intended to provide general guidance on a watershed monitoring program directed toward the plant nutrients nitrogen and phosphorus. The guide offers a series of general steps without setting forth a specific course of action. It gives assistance for developing a monitoring program but not a program for implementing measures to improve water quality.  
1.2 This guide applies to waters found in streams and rivers; lakes, ponds, and reservoirs; estuaries; wetlands; the atmosphere; and the vadose and subsurface saturated zones (including aquifers). This guide does not apply to nutrients found in soils, plants, or animals.  
1.3 Nutrients as used in this guide are intended to include nitrogen and phosphorus in dissolved, gaseous, and particulate forms. Specific species of nitrogen include: nitrate, nitrite, ammonia, organic, total Kjeldahl, and nitrous oxide. The species of phosphorus include total, total dissolved, organic, acid-hydrolyzable, and reactive phosphorus as described in Ref (2).  
1.4 Safety—Health and safety practices developed for a project may need to consider the following:  
1.4.1 During the construction of sampling stations:
1.4.1.1 Drilling practices during monitoring well installations,
1.4.1.2 Overhead and underground utilities during monitoring well drilling,
1.4.1.3 Traffic patterns/concerns during sampling station installation,
1.4.1.4 Traffic patterns/concerns during surveying sampling station locations and elevations,
1.4.1.5 Drilling through materials highly contaminated with fertilizers, and
1.4.1.6 Installing monitoring equipment below the soil surface.  
1.4.2 During the collection of water samples:
1.4.2.1 Using acids for sample preservation,
1.4.2.2 Sampling during flooding events and ice conditions,
1.4.2.3 Traffic on bridges,
1.4.2.4 Condition of sampling stations following flood events,
1.4.2.5 Sampling of water or soils, or both, highly contaminated with fertilizers,
1.4.2.6 Conditions of sampling stations resulting from vandalism,
1.4.2.7 Adverse weather conditions, and
1.4.2.8 Transporting liquid samples.  
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Jul-2018
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: D19 - Water
• Drafting Committee: D19.02 - Quality Systems, Specification, and Statistics

Relations

• Replaces: ASTM D6146-97(2012) - Standard Guide for Monitoring Aqueous Nutrients in Watersheds
• Effective Date: 01-Aug-2018
• Refers: ASTM D1129-13(2020)e2 - Standard Terminology Relating to Water
• Effective Date: 01-May-2020
• Refers: ASTM D1357-95(2019) - Standard Practice for Planning the Sampling of the Ambient Atmosphere
• Effective Date: 01-Aug-2019
• Refers: ASTM D4448-01(2019) - Standard Guide for Sampling Ground-Water Monitoring Wells
• Effective Date: 01-Feb-2019
• Refers: ASTM D4696-18 - Standard Guide for Pore-Liquid Sampling from the Vadose Zone
• Effective Date: 15-Nov-2018
• Refers: ASTM D6145-97(2018) - Standard Guide for Monitoring Sediment in Watersheds
• Effective Date: 01-Aug-2018
• Refers: ASTM D3590-17 - Standard Test Methods for Total Kjeldahl Nitrogen in Water
• Effective Date: 01-Jun-2017
• Refers: ASTM D1739-98(2017) - Standard Test Method for Collection and Measurement of Dustfall (Settleable Particulate Matter)
• Effective Date: 01-Mar-2017
• Refers: ASTM D4410-16 - Terminology for Fluvial Sediment
• Effective Date: 01-Jan-2016
• Refers: ASTM D4700-15 - Standard Guide for Soil Sampling from the Vadose Zone (Withdrawn 2024)
• Effective Date: 01-Feb-2015
• Refers: ASTM D653-14 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Aug-2014
• Refers: ASTM D4448-01(2013) - Standard Guide for Sampling Ground-Water Monitoring Wells
• Effective Date: 01-Apr-2013
• Refers: ASTM D6145-97(2012) - Standard Guide for Monitoring Sediment in Watersheds
• Effective Date: 15-Jun-2012
• Refers: ASTM D3856-11 - Standard Guide for Management Systems in Laboratories Engaged in Analysis of Water
• Effective Date: 15-Nov-2011
• Refers: ASTM D1357-95(2011) - Standard Practice for Planning the Sampling of the Ambient Atmosphere
• Effective Date: 01-Oct-2011

Overview

ASTM D6146-97(2018): Standard Guide for Monitoring Aqueous Nutrients in Watersheds establishes a general, practical framework for developing watershed monitoring programs focused on plant nutrients, specifically nitrogen and phosphorus. Developed by ASTM International, this standard addresses the need for a unified approach to nutrient monitoring in various aquatic environments, including streams, rivers, lakes, ponds, reservoirs, estuaries, wetlands, atmospheric water, and subsurface zones such as aquifers and the vadose zone.

The guide is suitable for non-experts and technical professionals alike, providing foundational steps for designing water quality monitoring programs. It emphasizes general principles rather than specific procedures, helping users establish effective strategies without prescribing detailed methods.

Key Topics

• Target Nutrients: The standard focuses on nitrogen (including nitrate, nitrite, ammonia, organic nitrogen, total Kjeldahl nitrogen, nitrous oxide) and phosphorus (including total, total dissolved, organic, acid-hydrolyzable, and reactive phosphorus) in dissolved, gaseous, and particulate forms.
• Applicability: Relevant for surface and ground waters, excluding nutrients in soils, plants, or animals.
• Monitoring Objectives: Guidance is provided on identifying monitoring needs, setting clear scientific objectives, and selecting relevant water quality variables.
• Design and Scale: Outlines methods for selecting study areas, such as points, plots, fields, and whole watersheds, and provides insights for both trend and targeted monitoring.
• Sampling and Analysis: Discusses sampling types (grab, composite, integrated, continuous), site selection, sampling frequency, and duration appropriate for different water bodies and objectives.
• Quality Assurance: Emphasizes the importance of quality control in sample collection, handling, analysis, and data management to ensure reliability and comparability.
• Safety Considerations: Addresses field safety, handling hazardous materials, sample preservation, and working in diverse weather and hydrologic conditions.

Applications

ASTM D6146-97(2018) has broad value across sectors and projects, supporting efforts to:

• Identify Water Quality Issues: Recognize and assess nutrient-related problems such as eutrophication, algal blooms, or compliance with regulatory standards.
• Study Trends: Establish baseline conditions and track changes in water quality over time, including the impact of land use or management practices.
• Allocate Nutrient Loads: Provide data for decision-making on point and nonpoint source pollution, critical for regulatory and remediation initiatives.
• Support Research and Modeling: Supply foundational data to calibrate, test, and refine water quality models and answer research questions about nutrient behavior.
• Evaluate Management Practices: Measure effectiveness of agricultural practices, wastewater management, or land use changes aimed at reducing nutrient pollution.
• Guide Resource Protection: Assist local governments, watershed groups, and non-profits in managing and protecting surface water, groundwater, and associated ecosystems.

The standard is regularly referenced by environmental professionals, water utilities, regulators, consultants, and organizations engaged in watershed management.

Related Standards

To ensure comprehensive nutrient monitoring in watersheds, consult these related ASTM and industry standards:

• ASTM D5851 - Guide for Planning and Implementing a Water Monitoring Program
• ASTM D4448 - Guide for Sampling Ground-Water Monitoring Wells
• ASTM D1426 - Test Methods for Ammonia Nitrogen in Water
• ASTM D3867 - Test Methods for Nitrite-Nitrate in Water
• ASTM D3590 - Test Methods for Total Kjeldahl Nitrogen in Water
• Standard Methods for the Examination of Water and Wastewater (APHA)
• EPA Methods for Chemical Analysis of Water and Wastes

Using ASTM D6146-97(2018) in conjunction with these standards ensures high-quality, actionable data for monitoring nutrients in a variety of water resources and supporting effective watershed management programs.

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Keywords: watershed monitoring, nutrient monitoring, water quality, nitrogen, phosphorus, ASTM D6146, surface water, ground water, water sampling, nonpoint source pollution, point source pollution, quality assurance, environmental indicators.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D6146 − 97 (Reapproved 2018)
Standard Guide for
Monitoring Aqueous Nutrients in Watersheds
This standard is issued under the fixed designation D6146; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Various forms of nitrogen and phosphorus are plant nutrients, both naturally occurring and
manmade, that can threaten water resources. Nutrients that run off or infiltrate through the soil profile
canresultinunfishableandunswimmablestreams,lakes,andestuaries,andunsafesurfaceandground
water used for drinking. High concentrations of nitrate in drinking water are a threat to young infants,
and surface waters can suffer from algal blooms, fish kills, and unpalatable and unsafe water for
swimming and drinking. Nutrients are also added to watersheds by means of chemigation.
This guide recommends a process for developing and implementing monitoring projects for
nutrients in a watershed. It follows Guide D5851 with more specifics applicable to watersheds and
nutrients. These guidelines are presented for use in the nationwide strategy for monitoring developed
by the Intergovernmental Task Force on Monitoring (ITFM). The nationwide monitoring strategy is
an effort to improve the technical aspects of water monitoring to support sound water quality
decision-making. It is needed to integrate monitoring activities more effectively and economically to
achieve a better return of investments in monitoring projects (1).
Guide D6145 is offered as a guide for monitoring actual and potential nonpoint and point source
pollution within a watershed. The guide is applicable to surface water and ground water resources,
recognizing the need for a comprehensive understanding of naturally occurring and manmade impacts
to the entire watershed hydrologic system.
1. Scope forms. Specific species of nitrogen include: nitrate, nitrite,
ammonia, organic, total Kjeldahl, and nitrous oxide. The
1.1 Purpose—This guide is intended to provide general
species of phosphorus include total, total dissolved, organic,
guidance on a watershed monitoring program directed toward
acid-hydrolyzable,andreactivephosphorusasdescribedinRef
the plant nutrients nitrogen and phosphorus. The guide offers a
(2).
series of general steps without setting forth a specific course of
action.Itgivesassistancefordevelopingamonitoringprogram 1.4 Safety—Health and safety practices developed for a
butnotaprogramforimplementingmeasurestoimprovewater project may need to consider the following:
quality. 1.4.1 During the construction of sampling stations:
1.4.1.1 Drilling practices during monitoring well
1.2 Thisguideappliestowatersfoundinstreamsandrivers;
installations,
lakes, ponds, and reservoirs; estuaries; wetlands; the atmo-
1.4.1.2 Overhead and underground utilities during monitor-
sphere; and the vadose and subsurface saturated zones (includ-
ing well drilling,
ing aquifers). This guide does not apply to nutrients found in
1.4.1.3 Traffic patterns/concerns during sampling station
soils, plants, or animals.
installation,
1.3 Nutrients as used in this guide are intended to include
1.4.1.4 Traffic patterns/concerns during surveying sampling
nitrogen and phosphorus in dissolved, gaseous, and particulate
station locations and elevations,
1.4.1.5 Drilling through materials highly contaminated with
fertilizers, and
This guide is under the jurisdiction ofASTM Committee D19 on Water and is
1.4.1.6 Installing monitoring equipment below the soil sur-
thedirectresponsibilityofSubcommitteeD19.02onQualitySystems,Specification,
face.
and Statistics.
Current edition approved Aug. 1, 2018. Published September 2018. Originally
1.4.2 During the collection of water samples:
approved in 1997. Last previous edition approved in 2012 as D6146 – 97 (2012).
1.4.2.1 Using acids for sample preservation,
DOI: 10.1520/D6146-97R18.
1.4.2.2 Sampling during flooding events and ice conditions,
The boldface numbers given in parentheses refer to a list of references at the
end of this standard. 1.4.2.3 Traffic on bridges,
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6146 − 97 (2018)
1.4.2.4 Condition of sampling stations following flood D6145 Guide for Monitoring Sediment in Watersheds
events,
3. Terminology
1.4.2.5 Sampling of water or soils, or both, highly contami-
nated with fertilizers, 3.1 Definitions:
1.4.2.6 Conditions of sampling stations resulting from
3.1.1 For definitions of terms used in this standard, refer to
vandalism, Terminology D1129 and Guide D5851.
1.4.2.7 Adverse weather conditions, and
3.2 Definitions of Terms Specific to This Standard:
1.4.2.8 Transporting liquid samples.
3.2.1 aquifer, n—a geologic formation containing water,
1.5 The values stated in SI units are to be regarded as
usually able to yield appreciable water.
standard. No other units of measurement are included in this
3.2.2 ground water, n—that part of the subsurface water that
standard.
is the saturated zone. (D653, D18)
1.6 This standard does not purport to address all of the
3.2.3 nonpoint pollution, n—a condition of water within a
safety concerns, if any, associated with its use. It is the
water body caused by the presence of undesirable materials
responsibility of the user of this standard to establish appro-
from diffuse locations with no particular point of origin.
priate safety, health, and environmental practices and deter-
3.2.4 vandose zone, n—the zone of soil located between the
mine the applicability of regulatory limitations prior to use.
surface and the water table that is not saturated.
1.7 This international standard was developed in accor-
3.2.5 watershed, n—all lands enclosed by a continuous
dance with internationally recognized principles on standard-
hydrologic surface drainage divide and lying upslope from a
ization established in the Decision on Principles for the
specified point on a stream. (D4410, D19)
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
4. Significance and Use
Barriers to Trade (TBT) Committee.
4.1 The user of this guide is not assumed to be a trained
2. Referenced Documents technical practitioner in the water quality field.The guide is an
assembly of the components common to all aspect of water-
2.1 ASTM Standards:
shed nutrient monitoring and fulfills a need in the development
D515 Test Method for Phosphorus In Water (Withdrawn
of a common framework for a better coordinated and a more
1997)
unified approach to nutrient monitoring in watersheds.
D653 Terminology Relating to Soil, Rock, and Contained
4.2 Limitations—This guide does not establish a standard
Fluids
procedure to follow in all situations and it does not cover the
D1129 Terminology Relating to Water
detail necessary to meet all of the needs of a particular
D1357 Practice for Planning the Sampling of the Ambient
monitoring objective. Other standards and guides included in
Atmosphere
the references describe the detail of the procedures.
D1426 Test Methods for Ammonia Nitrogen In Water
D1739 Test Method for Collection and Measurement of
5. Monitoring Components
Dustfall (Settleable Particulate Matter)
D3370 Practices for Sampling Water from Closed Conduits 5.1 A watershed monitoring program of nutrients is com-
prised of a series of steps designed to collect nutrient data to
D3590 Test Methods for Total Kjeldahl Nitrogen in Water
D3856 Guide for Management Systems in Laboratories achieve a stated objective. The purposes of monitoring may be
several and include: analyzing trends, studying the fate and
Engaged in Analysis of Water
D3858 Test Method for Open-Channel Flow Measurement transport of nutrients, defining critical areas, assessing
of Water by Velocity-Area Method compliance, measuring the effectiveness of management
D3867 Test Methods for Nitrite-Nitrate in Water practices, testing for sufficient levels, making wasteload
D4410 Terminology for Fluvial Sediment allocations, testing models, defining a water quality problem,
D4448 Guide for Sampling Ground-Water MonitoringWells and conducting research (3).
D4696 Guide for Pore-Liquid Sampling from the Vadose 5.1.1 Monitoringtoanalyzetrendsisusedtodeterminehow
water quality is changing over time. In some cases baseline
Zone (Withdrawn 2017)
D4700 Guide for Soil Sampling from the Vadose Zone monitoring is included as the early stage of trend monitoring.
5.1.2 Fate and transport monitoring is conducted to deter-
D5092 Practice for Design and Installation of Groundwater
Monitoring Wells mine whether pollutants move and where they may go.
5.1.3 Water quality monitoring can be used to locate critical
D5851 Guide for Planning and Implementing aWater Moni-
toring Program areas within watersheds exhibiting greater pollution loading
than other areas.
5.1.4 Nutrient monitoring may also be used to assess
compliance with water quality plans or standards.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
5.1.5 Nutrient monitoring may assess the effectiveness of
Standards volume information, refer to the standard’s Document Summary page on
individual management practices in improving water quality
the ASTM website.
or, in some cases, may be used to evaluate the effect of an
The last approved version of this historical standard is referenced on
www.astm.org. entire nutrient management program in a watershed.
D6146 − 97 (2018)
5.1.6 The testing of nutrient levels in water bodies may be attributes for nutrient monitoring objectives are often binary;
used to see if sufficient amounts are present to support certain that is, either the objective is accomplished or not.
aquatic organisms.
5.4 Step 3: Statistical Design—A statistical experimental
5.1.7 Monitoring of receiving water bodies may be used to
design should be stated that is consistent with the objectives of
determine wasteload allocations between point and nonpoint
the monitoring program. Appropriate experimental designs
sources. Such allocations require a thorough knowledge of the
could include: reconnaissance, plot, single watershed, above-
individual contributions from each source.
and-below, two watersheds, paired watershed, multiple
5.1.8 Nutrient monitoring may be used to fit, calibrate, or
watersheds, and trend stations (3). The design selected will
test a model for local conditions.
dictate most other aspects of the monitoring project including
5.1.9 Nutrient monitoring may be used for research ques-
thestudyscale,thenumberofsamplinglocations,thesampling
tions such as the accuracy of different types of samplers in
frequency, and the station type.
collecting a representative sample.
5.4.1 Reconnaissance or synoptic designs may be used as a
5.1.10 Finally, nutrient monitoring may be used to give
preliminary survey where no data exist or to assess the
adequate definition to a water quality problem or determine
magnitude and extent of a problem. This type of sampling
whether a problem exists. Guide D5851 provides overall
could be used to identify critical areas as well. A critical area
guidance on water monitoring.
is one that is contributing a significant amount of nutrients to
5.1.11 Thisguidesuggestsanddiscussesthefollowingsteps
the water body of interest. Randomization in sampling loca-
in designing a watershed monitoring program for nutrients.
tions may be important for reconnaissance monitoring. Recon-
More detail on each step may be found in Ref (3).
naissance monitoring could be used in a “whole aquifer” study
with well placement located randomly or on a grid basis.
5.2 Step 1: Water Quality Need—The first step is to define
5.4.2 Plot designs have been commonly used in agricultural
the need for nutrient monitoring. The need statement should
experiments for 100 years (4). Plots are generally small areas
include several components: the potential or real water quality
that can be replicated on the land or waterscape. Plots allow
issue requiring attention (for example, eutrophication), the
replication and control of certain variables, such as soil type.
potential water resource use impairment (for example,
Plot designs are analyzed using Analysis of Variance (3).
recreation),thenameoftheactualwaterresource(forexample,
Long Lake), the potential threats or causes (for example,
5.4.3 The single watershed before-and-after approach has
phosphorus), and the potential sources that may cause a
been sometimes used to compare water quality conditions
problem (for example, agriculture) (3). Very often the need is
before a watershed treatment to after. Generally, this technique
toidentifyawaterqualityproblem,butinsomecases,theneed
is not recommended, since the results are confounded with
may be to assess the existing water quality whether a problem
time and climate variables, and should be avoided. For
exists or not. An example of a need statement might be: “The
example, the water quality differences from year-to-year may
lack of recreation in Long Lake is due to excessive eutrophi-
be caused by climate differences not the watershed activity.
cation caused by excessive phosphorus loading possibly from
5.4.4 The above-and-below design is used after a watershed
agricultural sources.”
practice is in place. Sampling is conducted both upstream and
downstream, or in the case of ground water monitoring,
5.3 Step 2: Objectives—The second step in developing a
up-gradient and down-gradient from the activity of interest.
nutrient monitoring program is to define the monitoring objec-
Although this design is not as susceptible to the effect of
tives. The objectives of the monitoring study should address
climate as the single watershed design, the differences in water
the water quality need or problem. An objective statement
quality between the two stations may be partly due to inherent
should include an infinitive verb, an object word or phrase, and
watershed differences such as soils or geology. If monitoring is
some limits on the objective such as the surface or ground
conducted before and after the practice in installed, the design
water resource or watershed boundaries and variables to
would follow the paired watershed approach described below.
monitor. An example of a monitoring objective might be: “To
5.4.5 Ground water monitoring using this approach is re-
determine the effect of implementing agricultural management
practices on phosphorus concentrations in Long Lake.” When ferred to as up-gradient versus down-gradient monitoring.This
is probably the most commonly used strategy in ground water
severalobjectivesareused,ahierarchialapproachmaybeused
to determine higher priority objectives. An objective tree can studies and is appropriate for most designs. Placement of the
wells is important because ground water sites are three
be used to distinguish among several objectives. To determine
how several objectives can be linked, the following question dimensional. Gradients may occur in both vertical as well as
horizontal directions. Also due to heterogeneity at some sites,
can be asked: “Does the achievement of objectiveAcontribute
directly to the achievement of objective B?” If it does then gradient directions may change over time.
objective A feeds into objective B and a diagram can be built
5.4.6 The paired watershed approach uses a minimum of
showing all possible objectives and their linkages.
two watersheds — control and treatment — and two periods of
5.3.1 To assess whether objectives are being achieved, study — calibration and treatment (5). The control watershed
objective attributes could be determined. Attributes define the serves as a check for year-to-year climate variations and
level of achievement for each objective. They answer the receives no changes in land uses or activities during the
question of how close are we to achieving our goals? For monitoring study. During calibration, the two watersheds are
example, are we 50 % of the way to achievement? These treated identically and paired water quality data are collected.
D6146 − 97 (2018)
During the treatment period, one watershed is treated with a 5.6.1 Water quality variable selection depends on the moni-
practice while management in the control watershed remains toring objectives, water body type, the use of the water, the
unchanged. land activity being investigated, the cost or difficulty in
5.4.7 For ground water monitoring, an above-and-below analysis, and any known or suspected nutrient issue associated
approach to the paired watershed design is recommended. with the water body. To assist in the selection of water quality
During the calibration period, monitoring would take place variables, activity matrices have been developed (3). Other
up-gradient and down-gradient for both the control and treat-
techniques for selection include ranking the variables of
ment portions of the ground water formation being studied. interest, developing correlations between variables, and deter-
During the treatment period, one of the areas bounded by wells
mining the probability of exceeding a water quality standard
would receive a practice while the other control area would
(3).
remain as before.
5.7 Step 6: Sample Type—Nutrients in watersheds may be
5.4.8 The multiple watershed approach involves more than
collected as grab, composite, integrated, or continuous
two watersheds. Watersheds with treatments already in place
samples. The type of sample collected is a function of the
are selected from across the region of interest. Sampling from
purpose in monitoring, the variables to sample, and whether
these watersheds is conducted over a period of time. Groups of
concentration or mass is the desired outcome.Agrab sample is
similar watersheds are tested against each other to determine
a discrete sample that is taken at a specific point and time. A
water quality differences (3).
series of grab samples, usually collected at different times and
5.4.9 Trend stations are single watersheds monitored over
combined together in one sample, are considered composite
time. A trend is a persistent change in the water quality
samples. Composite samples may be either time-weighted or
variables of interest over time. It is important while using most
flow-weighted. A specific type of a surface water grab sample
forms of trend analysis that there not be gaps in the data set,
is a depth-integrated sample. Such samples account for veloc-
that water quality analysis methods not change, that the
ity or stratification induced differences in water quality. Con-
hydrological control is stable, and a casual link can be made
tinuous sampling is rare because the technology is limited, but
between the water quality and watershed activities. A control
usually involves water quality variables measured using elec-
trend station is highly recommended where no changes in
trometric methods, such as specific ion electrodes for ammonia
watershed activities occur during the trend investigation (3).
and nitrate nitrogen.
5.5 Step 4: Scale of Study—The size or scale of the
5.8 Step 7: Sampling Location—The location of sampling
m
...