Causal Analysis/Diagnosis Decision Information System (CADDIS)

• Common Candidate Causes
• Interactive Conceptual Models

CC.2. Sediments

This section deals with the physical effects of both inorganic and organic particles as candidate causes:

• excessive levels of suspended sediment,
• excessive levels of deposited & bedded sediment, and
• insufficient levels of sediment.

Although sediment is a natural part of aquatic habitats, the quantity and characteristics of sediments can affect the physical, chemical, and biological integrity of streams, lakes, rivers, estuaries, wetlands, and coastal waters (US EPA, 2006a; Wood and Armitage, 1997; Waters, 1995).

Excessive suspended sediment (Image CC.2-1), excessive deposited and bedded sediment (Image CC.2-2), and insufficient sediment (Image CC.2-3) have different modes of action that cause different biological effects. For this reason, we encourage you to consider these as separate candidate causes. Accordingly, we have divided most of the material on this page into three subsections — one for each aspect of sediment.

A generic conceptual model (Figure CC.2-1) has been developed that shows how sources and activities lead to excessive or insufficient sediment and subsequently to biological effects. If you are still deciding what aspects of sediments are of greatest interest, we recommend reading through the conceptual model and this entire page. If you already know the attribute of interest, you can use the right navigation bar to skip immediately to the relevant subsection.

 

Each subsection includes:

• A checklist of relevant observations,
• Sources and activities for including sediment,
• Site evidence for including sediment,
• Biological effects for including sediment,
• Site observations for deferring sediment, and
• Ways to measure sediment.

 

In addition, we have included a section of available literature reviews for all types of sediment-response relationships at the end of this module. These reviews contain useful information from laboratory and field studies, should you choose to include excess or insufficient sediments on your list of candidate causes.

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CC.2.1. Suspended Sediment

Suspended sediment (SS) is primarily fine inorganic particles of clay and silt (typically < 0.063mm) but also includes fine sand (0.63-0.250 mm) and particulate organic matter suspended in the water column.

CC.2.1.1. What to Consider When Determining if Suspended Sediment (SS) Should be Included as a Candidate Cause

Excessive suspended sediment should be included as a candidate cause when potential human sources and activities, site evidence, or observed effects support portions of the source-to-impairment pathways in the conceptual model for sediment (Figure CC.2-1).

Checklist of Sources, Site Evidence, and Biological Effects

A checklist is provided below to help you identify key data and information useful for determining whether to include SS among your candidate causes; the title for each column is linked to more detailed descriptions. The checklist is also intended to guide you in developing evidence to refute, weaken, or enhance support for SS as a cause during the analysis phase. You may be aware of other situations when SS should be eliminated or included as a candidate cause; please send us your insights using the comment section.

Consider including SS as a candidate cause based on the presence of sources and activities, site evidence, or biological effects.

Consider contributing, modifying, and related factors as candidate causes when SS is included as a candidate cause:

• Deposited and bedded sediment
• Flow alteration
• Pathogens
• Insufficient light for photosynthesis
• Nutrient enrichment
• Altered habitat
• Low dissolved oxygen
• Excess plant growth
• Specified and unspecified toxic chemicals

Consider deferring (defer) SS as a candidate cause when, at the site of the impairment:

• The water is clear and periods of SS have not occurred based on continuous, long term monitoring.

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Sources and Activities that Suggest Including SS as a Candidate Cause

Recorded or direct observations of increased supply or delivery of suspended particles indicate that SS should be included as a potential candidate cause. These sources and activities may occur at or upstream from the impaired site. Sources that increase SS also influence other stressors. Therefore, when considering SS also consider: excess deposited and bedded sediment, insufficient light for photosynthesis, candidate causes associated with nutrient enrichment, altered habitat, and flow alteration. If nutrients or organic matter are parts of the causal pathway leading to SS, excess plant growth, ammonia, pathogens, and low dissolved oxygen may also be of concern.

Increased SS can result from any activity or land use that:

• Loosens soil or leaves bare ground, especially during rainy or windy seasons, thereby increasing the readily available supply of sediment,
• Increases the force of flowing water over the landscape or in the stream, thus increasing the delivery of particles into water bodies or maintaining them in suspension, or
• Increases sediment resuspension or erosion of the beds, banks, or shores of water bodies

EXPOSED SOIL — Bare ground is susceptible to erosion. Some specific activities that expose soil and make it more erodible are listed below:

Autumn plowing — Tilling soil in the autumn tends to leave fields bare longer and during seasons with greater rainfall, thus increasing soil erosion.

Livestock grazing — Livestock trample banks, shores, and beds and can remove or disturb vegetation (Image CC.2-4).

Devegetated banks or shores — Devegetated banks or shores expose erodible materials that can enter the water body (Image CC.2-4).

Logging roads and trails — Exposed erodible materials can enter streams with runoff. Logging can make soil susceptible to erosion.

Construction — Erodible materials that can enter streams with runoff are exposed during construction. In addition, compacted earth is less permeable, increasing delivery of storm water (Image CC.2-5).

Road maintenance — Grading of dirt roads, application of crushed limestone, and application of ash and sand to icy roads provide material that may wash into streams during snowmelt or storms.

Land slides — Land slides can deliver sediment directly to streams. Also, erosion can carry material from land slides to water bodies.

Burned forest — Fires destroy trees, undergrowth, and leaf litter that normally stabilize soils.

Gullies — Gullies indicate removal of soil by erosion that may carry sediment to a water body (Images CC.2-4 and CC.2-5).

Stored soil or waste — Soil or organic wastes stored in outdoor piles may be washed into water bodies.

IN-STREAM PROCESSES — Some processes or conditions in streams or other water bodies that generate or resuspend sediment are listed below:

In-stream gravel mining — Gravel mining exposes and suspends sediment.

Vehicle traffic in stream — Vehicles fording streams erode banks and suspend sediment (Image CC.2-6).

Boat traffic — The force from props or dragging of anchors can resuspend sediment from the river or lake bottom and wakes erode banks and shores.

Dredging — The process of dredging resuspends some of the material being dredged.

Trawling — Dragging equipment and nets along the bottom of water bodies resuspends sediment.

Breached impoundment — Upstream impoundments normally enhance settling and thus decrease sediment delivered downstream. However, if the impoundment is breached, large amounts of sediment can be rapidly released downstream.

Incised or widened stream channels — This is indicative of flow conditions that are eroding the stream bed and transporting sediment from the streambed or bank downstream.

Channel modification — Installation of culverts or bridge pilings, as well as deepening, straightening, or redirecting channels can disturb deposited and bedded sediment, disrupt stream banks, and alter flow regimes.

Eroding and collapsing stream banks — These are sources of sediment which may arise due to undercut or unstable banks (Image CC.2-7).

Shallow or poorly developed root systems — Stream banks erode due to a number of factors, but the lack of stabilizing structures such as complex, interwoven roots commonly contribute to bank erosion and increased sediment supply (Image CC.2-6 and CC.2-7).

Impoundments — Downstream dams create impoundments that increase deposition but also can favor production of algae which act as suspended particles.

Fish activity — Some bottom feeding fish such as carp stir up sediments to find food, resuspending fine materials in the process.

ALTERED FLOW — Hydrologic processes in the watershed or waterbody may increase the delivery of sediment. Some specific situations that alter flow are listed below:

Upstream scoured stream beds — If the diverse sizes of sediment that would normally be present are absent from upstream locations, then the material has been suspended and carried downstream. It also suggests that hydrologic forces are strong and that there may be other erosive forces that would act as sources of sediment.

Impervious surfaces — Impervious surfaces in the watershed may increase the magnitude and frequency of high flow events, thereby increasing resuspension and bed and bank erosion (Image CC.2-8).

Lack of connectivity with flood plain — Suspended material remains longer in suspension rather than being deposited in flood plains where velocity is slowed compared to the torrent of the flooding waterway. Furthermore, deepened channels or intermittent barriers to flood plains can cause streams to cut down into the stream bed, eroding bed material and deepening the channel. Ultimately, banks are undercut and collapse, hillsides collapse, and the overall stream is widened. During these processes, new sediment is suspended in the stream.

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Site Evidence that Suggests Including SS as a Candidate Cause

In addition to observations of sources discussed above, direct observation of increased SS (especially at impaired sites) may be used as evidence of either spatial or temporal co-occurrence. Observations at the site suggesting that conditions are conducive for the occurrence of SS may be used as evidence of a complete causal pathway. Some examples include:

Muddy or turbid water — Unlike chemical contaminants, we can see SS. If the water is cloudy or muddy, that is, not transparent for any reason, there is an excess of some sort of material suspended in the water (Image CC.2-9). If water is tinged with green, golden, or brown coloration, there may be phytoplankton that may act as particles similar to clay. One caution, colored substances dissolved in water (e.g., humic acid) can be mistaken for SS (Image CC.2-10).

Visible plumes — Discontinuous color between the water in the channel and another source (e.g., tributary, outfall, ditch) suggests that SS should be considered. Spectral imagery of plumes or suspended material from aerial photography (Image CC.2-11) and hyperspectral imagery can document location of plumes and concentrations of suspended material in deeper waterbodies.

Deposited sediment — Sediment on substrates or aquatic plants, or a muddy bottom suggests that SS was present but has since been deposited.

Embedded substrate — An embedded substrate suggests that SS was present but has since been deposited.

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Biological Effects that Suggest Including SS as a Candidate Cause

Biological effects depend on the natural history of the species in your region. Therefore, our advice is general and is intended to encourage consideration of local fauna and flora.

In general, biological effects due to sediment and related stress are not sufficiently specific to be considered symptomatic of sediment.

Changes in composition of fish assemblages — Fish that rely on sight to locate and pursue prey may be less successful in turbid water (e.g., salmonids, cyprinids, and centrarchids). Others, like catfish and suckers, are tolerant because they hunt using olfactory or tactile sensations. Reduced feeding may result in reduced growth and local extirpation. Suspended particles can damaged gills resulting in increased susceptibility to low dissolved oxygen or to pathogens and in extreme cases may cause death. However, relative sensitivities to this mechanism are unknown.

Changes in composition of invertebrate assemblages — Filter-feeding invertebrates (e.g., net-spinning caddisfly larvae) and species with gills (e.g., mayflies) are particularly sensitive to SS. However, if the suspended sediments consist primarily of algae or other organic particles, filter feeders may thrive.

Changes in submerged aquatic vegetation — Submerged aquatic vegetation may die out due to reduced light penetration and scouring from suspended sediments.

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Site Evidence that Supports Excluding SS as a Candidate Cause

General advice on excluding candidate causes from the list is provided in Step 2.2 of the Step-by-Guide and in Tips for Listing Candidate Causes and includes the use of high quality in-stream measurements and the absence sources or activities that may increase SS.

Additional site observations can support deferring analysis of SS as a candidate cause. When the water is clear, the rocky substrates are consistently bare and not more embedded than unimpaired sites, and these conditions have persisted for more than a year, you may choose to defer analyzing SS as a candidate cause.

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CC.2.1.2. Ways To Measure Suspended Sediment

You may encounter a variety of existing sediment-related data expressed in units or types of measurements listed below [see Edwards and Glysson (1998) for field methods for measurement of fluvial sediment]. In addition, measures of channel structure are included here because they can be informative regarding sources and mechanisms that alter sediment supply. For measures of phytoplankton concentration, see Nutrients.

Turbidity — The amount of light transmission due to absorption and scattering as affected by suspended sediments [nephelometric turbidity units (NTU)].

Total suspended solids (TSS, also termed total filterable solids) — Suspended organic and inorganic solids that are not in solution and which can be removed by filtration (mg/L).

Suspended sediment concentration (SSC) — Dry weight of sediment from a known volume of water-sediment mixture (clay, silt, sand, and organic matter) (mg/L).

Light penetration — Amount of light that can reach various depths of water due to attenuation [Secchi depth (m) or extinction coefficient (L/mg cm^-1)].

Water clarity — Qualitatively reported observations of transparency of water.

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CC.2.2. Deposited and Bedded Sediment

Deposited and bedded sediments (DBS) are mineral and organic particles that settle out of the water column and collect on the bed of a water body, or that travel primarily by rolling along a stream bed rather than moving in the water column. It includes surficial and deeper deposits and bedded layers within the depths used by organisms.

Other terms commonly used to describe DBS include: bedded sediment, clean sediment, bedload, fines, deposits, soils, and eroded materials. The organic components include organic solids such as soil organic matter, algal cells, particulate detritus, and anthropogenic materials such as organic flocs.

Changes in the composition, distribution, or quantity of deposited and bedded sediment can alter the behavior, health, or survival of biota by altering benthic habitat quality or availability.

CC.2.2.1. What to Consider When Determining if Excessive Deposited and Bedded Sediment (DBS) Should be Included as a Candidate Cause

Excessive DBS deposited and bedded sediment should be included as a candidate cause when potential human sources and activities, site observations, or observed effects support portions of the source-to-impairment pathways in the conceptual model for sediment (Figure CC.2-1).

Checklist of Sources, Site Evidence, and Biological Effects

A checklist is provided below to help you identify key data and information useful for determining whether to include or to exclude DBS among your candidate causes; the title for each column is linked to more detailed descriptions. The checklist also is intended to guide you in developing evidence to refute, weaken, or enhance support as a candidate cause. You may be aware of other situations when DBS could be eliminated, deferred, or included as a candidate cause; please send us your insights using the comment section.

Consider including DBS as a candidate cause based on the presence of sources and activities, site evidence, or biological effects.

Consider contributing, modifying, and related factors as candidate causes when DBS is included as a candidate cause:

• Excess suspended sediment
• Insufficient light for photosynthesis
• Nutrient enrichment
• Invasive macrophytes
• Low dissolved oxygen
• Pathogens
• Ammonia
• Specified and unspecified toxic chemicals
• Altered habitat
• Flow alteration

Consider deferring (eliminate or defer) low DBS as a candidate cause when, at the site of the impairment:

• The water is clear, the geologic substrate is bare and not embedded, and it has been this way for more than a year, or
• The substrate is composed of only boulders or bedrock.

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Sources and Activities that Suggest Including DBS as a Candidate Cause

Nearly all DBS begins as suspended sediment. Therefore, all sources of suspended sediment and activities that suspend sediment are indirect sources of deposited and bedded sediment. They are listed in Sources and Activities that Suggest Including SS as a Candidate Cause. This section is limited to sources of deposition.

Downstream dams — Impoundments can reduce water velocity in upstream reaches, resulting in settling and accumulation of sediment.

Channel modification — Installation of culverts or bridge pilings, or straightening and redirection of channels can increase local deposition of sediment (Image CC.2-12).

Water withdrawal — Reduction of the volume of water in a flowing system reduces the velocity, thus increasing settling of sediment.

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Site Evidence that Suggests Including DBS as a Candidate Cause

Since suspended sediment may be deposited, Site Evidence that Suggests Including SS as a Candidate Cause are also suggestive of DBS. Observations at the site suggesting that conditions are conducive for the occurrence of DBS may be used as evidence of a complete causal pathway. In addition, direct observation of increased DBS, especially at the impaired site, may be used as evidence of spatial or temporal co-occurrence. Some examples include:

Silt — Fine sediment on aquatic plants and rocks suggests that sediment has been deposited (Image CC.2-13).

Embedded substrate — This suggests that sediment has been deposited, bedded, and retained at the site.

Discolored underside of rocks — Cobble or rocks with a black rim indicates that the substrate is sufficiently embedded to cause anoxic conditions.

Deposits of sediment — Sediment bars of mud, muck, or sand, and filling of pools with sediment are direct evidence of DBS (Image CC.2-14).

Slow moving water — When the force of water is slight, particles settle and substrates may not be periodically cleared of excess DBS.

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Biological Effects that Suggest Including DBS as a Candidate Cause

Biological effects of DBS depend on the natural history of species in your region. Therefore, our advice is general and is intended to encourage consideration of local fauna and flora. However, some biological effects may suggest DBS as a candidate cause.

Biological effects of DBS are in general not sufficiently specific to be considered symptomatic. Therefore, when considering DBS also consider: SS, other types of habitat alterations, flow alteration, insufficient light for photosynthesis, nutrients, pathogens and contaminants that migrate with particles, excess growth of plants that root in the deposited and bedded sediments, ammonia that forms in anoxic sediments, and low dissolved oxygen in poorly aerated sediments.

Changes in composition of fish assemblages — Populations of salmonids and other lithophilic species may decline when spawning substrates are embedded or buried in sediment (Image CC.2-15). Filled interstitial spaces of gravel can prevent gas exchange and asphyxiate embryos or trap sac fry. Other species, such as darters require coarse gravels as habitat for all stages of life.

Changes in composition of invertebrate assemblages — Organisms that prefer coarse gravel are reduced [e.g., EPT (Ephemeroptera, Plecoptera, Tricoptera)  (Image CC.2-16)], whereas some burrowing species increase in response to sediment deposits. Other burrowing organisms, such as threatened and endangered Unionid mussels, live in deeper gravels and cannot survive in embedded substrates.

Changes in submerged aquatic vegetation — Submerged aquatic vegetation may die out due to reduced light when they are covered with sediment. Alternatively, DBS may provide a suitable habitat for rooting of pioneering species that would not normally occur in a particular aquatic system.

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Site Evidence that Supports Excluding DBS as a Candidate Cause

General advice on excluding candidate causes from your initial list of candidate causes is provided in Step 2.2 of the Step-by-Guide and in Tips for Listing Candidate Causes, and includes the use of high quality in-stream measurements and the absence of evidence of sources or activities that may increase DBS.

Additional site observations can support excluding DBS as a candidate cause. When the water is clear, the rocky substrates are consistently bare, and these conditions have persisted for more than a year, you may choose to defer analysis DBS. Further, when the substrate is composed of boulders or bedrock that suggests that insufficient sediment is a candidate cause, rather than excess, you may choose not to list DBS.

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CC.2.2.2. Ways to Measure Deposited and Bedded Sediment

You may encounter a variety of existing sediment-related data [see Edwards and Glysson (1998) for field methods for measurement of fluvial sediment]. In addition, measures of channel structure are included here because they can be informative regarding sources and mechanisms that alter sediment supply.

Definitions of Measures of DBS:

Bedload sediment/bedload transport — Proportion of total sediment rolling, sliding, and bouncing along the stream bottom and being transported downstream. The proportion of bottom sediments moving as bedload will depend on, at a minimum, stream power, the sizes and size distribution of the available bottom sediment particles, the size and quantity of woody debris in the streambed, and the riffle/pool structure of the stream. Bedload is measured several ways and is usually expressed in kg/day (see US EPA, 2006b).

Percent fine sediment at surface — Proportion of fine sediment on substrate surface (percent fines at surface, % fines).

Percent fine sediment at depth — Proportion of fine sediment to a certain depth of substrate (percent fines at x cm of depth).

Sedimentation rate — Amount of suspended sediment that settles onto substrate per unit time, typically reported as grams per square meter of substrate per day (g/m²/d).

Embeddedness — Degree to which interstitial spaces between particles in coarse substrates are filled by finer particles (% embeddedness).

Suspendable solids — Amount of fine sediment re-suspended upon disturbance of streambed, usually described in grams per square meter of substrate (g/m²).

Settleable solids — Essentially the same as suspendable solids, equal to amount of fine sediment suspended during disturbance of streambed (typically during periods of increased stream discharge) and subsequently re-settling onto streambed as disturbance subsides or high discharges return to baseflow. Often reported as grams of sediment per square meter of substrate (g/m²).

Particle size distribution — Relative proportion of different particle sizes comprising the stream bed, often summarized as the fraction of the substrate in boulders, cobbles, gravel, sands, and silt/clay (e.g., % silt, % cobble).

Particle size geometric mean — Geometric mean of the particle sizes (mm, as measured from intermediate or median particle axis diameters).

Median particle size — Commonly know as D₅₀, particle size at the 50th percentile of bed material size distribution (mm, as measured from intermediate or median particle axis diameters).

Substrate stability — Ease with which deposited sediments may become re-suspended, often described as grams of sediment re-suspended within a unit area (m²) of the streambed at a given level of stream power (in watts), (g/m²/W).

Relative bed stability — Index of substrate mobility, equal to the ratio of the particle size of observed sediments to the size of sediments that each stream can move or scour during its flood or bankfull stage (mm/mm ratio).

Bottom deposit depth — Depth of fine sediments covering the streambed (mm or cm).

Pebble count — A description of the particle size distribution of the streambed sediment particles obtained by measuring the length of the intermediate/median axis of approximately 100 randomly-chosen streambed particles. Particle selection is typically done while walking in the stream in multiple cross-sectional transects or while crossing the stream and moving upstream in a zig-zag pattern. Once 100 particles have been measured, a cumulative particle size distribution is graphed to determine median substrate particle size, as well as other percentiles in the substrate particle size distribution. See Wolman (1954) for further details.

Definitions of Measures of Channel Structure Related to Sources and Indirect Measures of Sediment:

Residual pool volume — The volume of water in pools at low flow.

Bank stability — A measure of the susceptibility of a stream bank to erosion.

Waterbody dimensions — Measurements of width, mean depth, and depth at thalweg.

Bathymetry — Spatial variation in water depth (i.e., underwater topography).

Riffle/pool ratio — Proportion of stream channel length in riffles versus pools.

Gradient — Slope over which a stream flows, or the change in elevation (“rise”, in meters) divided by the distance over which this change in elevation occurs (“run”, also in meters); no units in calculated slope as they cancel out.

Sinuosity — Degree to which a stream meanders, measured as actual stream channel length divided by the straight-line distance between the starting and ending points (m/m or km/km).

Incision Downcutting of a stream bed, usually measured as the increase in depth over time (e.g., m/y).

Bank erosion — Visible loss of soil and vegetation from stream banks may be measured as horizontal bank loss over time (e.g., cm/y).

Channel braiding — Extent to which a streambed is divided into multiple channels. The term “anastomosing channels” usually refers to reaches with relatively long major and minor channels branching and rejoining in a complex network. Stream reaches classified as “braided channels” also have multiple branching and rejoining channels, but these sub-channels are generally smaller, shorter, and more numerous, often with no obvious dominant channel(s).

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CC.2.3. Insufficient Sediment

Insufficient sediment (IS) refers to a reduction of the amount of sediment relative to similar streams.

When sediment resuspension exceeds deposition through an entire stream reach, streambed scour and downcutting can occur (Image CC.2-3). Streambed scour can be observed downstream of many dams. Many organisms require sediment or a mixture of substrates as habitat to spawn, to avoid being displaced by the force of the water, to position themselves, to avoid predators, or to capture prey. Insufficient habitat can lead to an environment which supports few organisms.

CC.2.3.1. What to Consider When Determining if Insufficient Sediment (IS) Should Be Included as a Candidate Cause

IS should be included as a candidate cause when potential human sources and activities, site evidence, or observed effects support portions of the source-to-impairment pathways in the conceptual model for sediment (Figure CC.2-1).

Checklist of Sources, Site Evidence, and Biological Effects

A checklist is provided below to help you identify key data and information useful for determining whether to include IS among your candidate causes; the title for each column is linked to more detailed descriptions. Also, the checklist is intended to guide you in developing evidence to refute, weaken, or enhance support for IS as a candidate cause during the analysis phase. You may be aware of other situations when IS should be eliminated or included as a candidate cause; please send us your insights using the comment section.

Consider including IS as a candidate cause based on the presence of sources and activities, site evidence, and biological effects.

Consider contributing, modifying, and related factors as potential candidate causes when including IS as a candidate cause:

• Flow alteration
• Altered habitat

Consider deferring (eliminate) IS as a candidate cause at the impaired site when:

• The stream bed is embedded or the substrate is composed of mostly small sized particles.

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Sources and Activities that Suggest Including IS as a Candidate Cause

Recorded or direct observations of decreased supply, delivery, or retention of sediment indicate that IS should be included as a potential candidate cause. These sources and activities may occur at or upstream from the impaired site thereby removing or interfering with sources that would normally supply sediment. Situations that restrict settling of sediment or remove sediment by forceful scouring can also lead to IS, sometimes referred to as “sediment starvation.” When IS is suspect, the flow of water is usually strong and may be a direct cause or may modify the habitat in other ways. So, when including IS, also consider including flow alteration and habitat structure as candidate causes.

Upstream dam — Sediment settles out of suspension in the low velocity pool upstream of dams and is not transported downstream creating a sediment deficit. Forceful release from dams can also scour sediments.

Impervious surfaces — During storms, water is delivered to streams more quickly and with greater force when it runs off impervious surfaces. The force of the water may be sufficient to scour sections of stream bed and interfere with settling of particles.

Channel modification — Some channel modifications, particularly channel straightening, can alter hydrology and geomorphology of streams resulting in areas of scour.

Incised stream channels — This is indicative of flow conditions that are eroding the stream bed.

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Site Evidence that Suggests Including IS as a Candidate Cause

In addition to observations of sources discussed above, direct observation of IS at the impaired site may be used as evidence of either spatial or temporal co-occurrence. Insufficient sediment should be listed as a candidate cause if:

• The substrate is composed of only boulders or bedrock (Image CC.2-17), or
• The streambed is lined with bare concrete or riprap.

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Biological Effects that Suggest Including IS as a Candidate Cause

Biological effects depend on the natural history of species from a geographical region. Therefore, our advice is general and is intended to encourage consideration of local fauna and flora.

In general, biological effects due to insufficient sediment and related stress are not sufficiently specific to be considered either symptomatic or more suggestive of sediment over other causes. Therefore, when there are very low abundance and diversity of species, you should also consider exposures to toxic substances, extremes of temperature, low dissolved oxygen, or flows that dislodge organisms.

Low abundance or diversity of fish species, invertebrate species, and submerged aquatic vegetation may occur when IS is a cause, because there is no suitable substrate habitat for shelter or reproduction, few prey, or no rooting substrate.

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Site Evidence that Supports Excluding IS as a Candidate Cause

Insufficient sediment is a relatively rare cause and is more likely to be overlooked than to be included without reason.

The presence of abundant sediment over a long period of time would support deferring insufficient sediment as a candidate cause. Additional discussion of excluding candidate causes is provided in Step 2.2 of the Step-by-Step Guide and in Tips for Listing Candidate Causes.

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CC.2.3.2. Ways to Measure Insufficient Sediment

Ways to measure deposited and bedded sediment would also be used to measure insufficient sediment.

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CC.2.4. Literature Reviews of Stressor-Response Information for Suspended and Bedded Sediment

Berry, W; Rubenstein, N; Melzion, B; Hill, B. (2003) The biological effects of suspended and bedded sediment (SABS) in aquatic systems: A review (PDF) (58 pp, 285K, About PDF). Internal Report of the USEPA Office of Research and Development, Narragansett, RI.

This review summarizes literature and models of the direct and indirect biological effects of suspended and bedded sediments on a wide range of organisms from various habitats. The review focuses on studies that describe quantitative dose-response relationships of aquatic organisms exposed to suspended and bedded sediments and provides a simple, practical compilation of referenced sediment-effects information that may be useful for developing sediment total maximum daily loads and water quality criteria for suspended and bedded sediments. Also provided are summaries of existing models for the biological effects of suspended and bedded sediments, tables of data on the biological effects of suspended sediment, and current criteria and standards for both suspended and bedded sediment.

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Chapman, DW. (1988) Critical review of variables used to define effects of fines in redds of large salmonids. Trans Am Fish Soc 117:1-21.

This study critically reviews the variates used to evaluate the effects of fine sediment on the survival and emergence from redds of salmonid alevins. Survival to alevin emergence usually regresses positively on geometric mean particle size, mean particle diameter, fredle index, permeability, and dissolved oxygen. It relates negatively to percentages of small fines.

Doisy, KE; Rabeni, CF. (2004) Effects of suspended sediment on native Missouri fishes: a literature review and synthesis. University of Missouri - Columbia, Columbia, Missouri 65211-7240.

Reviews were conducted of the literature and databases pertaining to the harmful effects of suspended sediments on freshwater fishes of Missouri. Known concentrations of suspended sediment found in streams within different ecoregions of the state were compared to known responses from several fish species. This information was used to model the susceptibility of native fish to various suspended sediment events. The authors recommend how to acquire sufficient information on which to base decisions for managing suspended sediments.

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Gray, JR; Glysson, GD; Turcios, LM; and Schwarz, GE. (2000) Comparability of suspended-sediment concentration and total suspended solids data (PDF) (20 pp, 572K, About PDF). U.S. Geological Survey, Water Resource Investigations Report 00-4191, Reston, VA.

This report outlines why, in natural waters, suspended sediment concentration (SSC) is a more accurate and precise measurement of suspended sediment than total suspended solids (TSS). While SSC measurements are done on an entire field-collected water/sediment sample, TSS laboratory techniques often involve sub-sampling which introduces error, particularly if sand-sized material exceed one-quarter of the sediment dry weight. As percentages of sand-size suspended sediment increases SSC tend to exceed TSS values. Additionally, between-sample variance for TSS is greater than between-sample variance for SSC. The USGS concludes that SSC is a more reliable measure of suspended sediment in natural waters, and that SSC and TSS data should not be used interchangeably.

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Newcombe, CP; Jensen, JOT. (1996) Channel suspended sediment and fisheries: a synthesis for quantitative assessment of risk and impact. N Amer J Fish Manag 16:693-727.

This study synthesizes dose-response data for different groups of fishes. The synthesis is based on data for suspended sediment concentration, duration of exposure, and severity of ill effects for both non-salmonid and salmonid fishes. Dose-response models are also presented and relate to taxonomic group, species of fish, natural history, life history phase, and sediment particle size range.

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Rosetta, T. (2005) Draft technical basis for revising turbidity criteria (PDF) (129 pp, 2MB, About PDF). Oregon Department of Environmental Quality (DEQ), Water Quality Division, Salem, OR. October 2005.

Although written to provide the technical basis for revising turbidity criteria for the state of Oregon, the document contains a review of published effect levels. Information was obtained using available DEQ materials, state library resources, and computer database searches, as well by contacting representatives from other states regarding their approaches to developing turbidity criteria. Primary references published as journal articles were used to evaluate aquatic life effects as well as human-related visual and aesthetic effects. Qualifying studies for this evaluation included turbidity effects relative to control or background levels and those that identified statistically significant effects of turbidity (light and visual) influences. Endpoints used in this evaluation include biological and behavioral responses to turbidity by aquatic organisms in both laboratory and field tests. These effects were organized into three categories: (1) impacts on aquatic life, (2) impacts on treatment processes such as drinking water treatment or industrial-use treatment, and (3) aesthetic and safety considerations.

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Waters, TF. (1995) Sediment in streams - sources, biological effects and control. Amer Fish Soc Monogr 7, Amer Fish Soc, Bethesda, MD.

This study identifies causes or sources of anthropogenic inorganic sediment, summarizes the results of research on the effects of sediment on stream biota (e.g., primary producers, invertebrates and fish), and describes sediment control measures used to preserve various stream communities and freshwater fisheries.

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Wilbur, DH; Clarke, DG. (2001) Biological effects of suspended sediments: a review of suspended sediment impacts on fish and shellfish with relation to dredging activities in estuaries. N Amer J Fish Manag 21:855-875.

In this study, the authors assess the effects of increased concentrations of suspended sediment caused by human activities, such as navigational dredging, on estuarine fish and shellfish. The review synthesizes the results of studies that report biological responses to known suspended sediment concentrations and exposure durations and relates these findings to suspended sediment conditions associated with dredging projects. Biological responses of various taxonomic groups and life history stages are graphed as a function of concentration and exposure duration and compared with the expected concentrations and durations from anthropogenic activities that resuspend sediments.

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Wood, PJ; Armitage, PD. (1997) Biological effects of fine sediment in the lotic environment. Environ Manag 21(2):203-217.

This publication reviews information on the causes and extent of sedimentation in the lotic environment. The nature and origins of fine sediment, sediment suspension and deposition, and the effects of sediments on biota are outlined with respect to sources and impacts of human activity, variations in streamflow and particle size characteristics, and deleterious impacts associated with fine sediments on riverine habitats, primary producers, macroinvertebrates and fisheries. Multiple causes and adverse effects are identified and reviewed to provide river managers with a guide to source material.

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U.S. EPA (Environmental Protection Agency). (2006) Framework for developing suspended and bedded sediments (SABS) water quality criteria. U.S. EPA, Washington DC; EPA-822-R-06-001.

This document outlines a stepwise process for criteria development which includes gathering information, synthesizing the state of knowledge, analyzing available data, gathering more data if needed, and selecting SABS criteria values. The process is designed to engage stakeholders, develop several lines of scientific evidence, and document the decision analysis process while accommodating regional differences. The report also includes a description of technical methods for measuring, classifying, and associating various levels of SABS with designated uses. Methods include those for selecting appropriate indicators of water resource impairment due to SABS imbalances. Several statistical methods are described for developing associations that can be used to support decision-making. Also reviewed are impacts of SABS in aquatic systems, current state SABS criteria, and conceptual models of SABS sources and effects.

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Dong, A; Simsiman, GV; Chesters, G. (1983) Particle-size distributions and phosphorus levels in soil, sediment, and urban dust and dirt samples from the Menominee River watershed, Wisconsin, USA. Water Res 17(5): 569-577.

Edwards, TK; Glysson, GD. (1998) Field methods for measurement of fluvial sediment. Available at http://water.usgs.gov/osw/techniques/Edwards-TWRI.pdf.

US EPA (Environmental Protection Agency). (2006a) Framework for developing suspended and bedded sediments (SABS) water quality criteria. U.S. Environmental Protection Agency, Office of Water, Washington, DC; EPA-822-R-06-001.

US EPA (Environmental Protection Agency). (2006b) Watershed assessment of river stability & sediment supply (WARSSS) version 10. Available at http://www.epa.gov/WARSSS/.

Waters, TF. (1995) Sediment in streams: sources, biological effects and control. American Fisheries Society Monograph 7. Bethesda, MD: American Fisheries Society.

Wolman, MG. (1954) A method for sampling coarse river-bed material. Trans Amer Geophys Union 35(6):951-956.

Wood, PJ; Armitage, PD. (1997) Biological effects of fine sediment in the lotic environment. Environ Manage 21(2):203-217.

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