# Presentation: 939696

## Management of 

**Management of **
**Small  Docks and **
**Piers**

**Environmental**
**Impacts**

**Notes:**
1. Greeting.
2. The topic of this module is “Environmental Impacts of Small Docks”

## National Oceanic and Atmospheric Administration

**This presentation funded by the**
_**National Oceanic and Atmospheric Administration**_
**National Centers for Coastal Ocean Science**
- and
**The Office of Ocean and Coastal Resource Management**
**Materials prepared by Steve Bliven of Bliven & Sternack**

**Notes:**
This material was prepared, at the request of coastal managers, by two offices of the National Oceanic and Atmospheric Administration (NOAA); the National Centers for Coastal Ocean Science—a research branch—and the Office of Ocean and Coastal Resource Management—a management branch.

The slide show(s) and workbook were prepared by a contractor for these agencies–Steve Bliven of Bliven & Sternack in Massachusetts

## Environmental Impacts 

**Environmental Impacts **
**from Small Docks**

** ****Impacts to Vegetation**
** ****Impacts from Contaminants**
** ****Impacts from Associated Boat Use**
** ****Impacts on Sediments and Sedimentation**

**Notes:**
A review of the scientific literature and concerns of coastal managers suggests four principal areas for environmental impacts from small docks:
 Impacts to vegetation
 Impacts from contaminants
 Impacts from associated boat use
 Impacts on sediments and sedimentation 

## Impacts On Vegetation

**Impacts On Vegetation**

**Submerged Aquatic Vegetation and**
**Marsh Grasses**

** ****Form basis of marine  food web**
** ****Provide critical habitat**
** ****Filter nutrients and contaminants**
** ****Stabilize sediments**

**Notes:**
Beginning with the impacts to vegetation—
Submerged aquatic vegetation, or SAV, and marsh grasses provide several important environmental benefits:
They provide the plant material that forms the basis of the marine food web as it washes into estuaries. 
The vegetation also provides critical habitat for shellfish and fin fish, particularly in their critical juvenile stages.
The SAV beds and marsh grasses take up nutrients and contaminants from the water.
Finally, the vegetation also stabilizes sediments, lessening turbidity, shoreline erosion and channel infilling.

## Impacts On Vegetation

**Impacts On Vegetation**

**Four Principal Types:**

** ****Short-term construction impacts**
** ****Chronic impacts from shading**
** ****Chronic impacts from boat/float storage**
** ****Associated boat use**

**Notes:**
Our review will focus on four main sources of impacts to vegetation:
The short-term impacts produced by construction activities
Chronic, or long-term, impacts caused by docks shading SAV or marsh grasses
Chronic impacts from storage of floats or boats on the marsh face or allowing floats or boats to rest on SAV beds during low tide.
And finally, the impacts associated with boat use.  

## Impacts On Vegetation

**Impacts On Vegetation**

**Short-term Construction Impacts**

** ****Destruction of vegetation**
** ****Changes in elevations**
** ****Opportunities for regrowth**

**Notes:**
Dock construction can have several types of adverse impacts.
 As you can see in the picture, working along the marsh face can destroy the vegetation there.  Similarly, working in the water can disrupt SAV beds.
 A second, and less obvious impact is changing the elevations on the face of the marsh.  Marsh vegetation is strongly influenced by the amount of salt water it is exposed to.  If the marsh peat is compacted or the marsh surface dug away, salt water may stay longer on the marsh or pond there.  This will eventually lead to changes in vegetative species, not always for the better.
 Installation of pilings may affect SAV.  Research in Florida found bare areas up to 5 1/2 feet in diameter around pilings that had been jetted into place with a high pressure hose.  These “halos” may remain for up to 10 years, decreasing the size of the SAV beds and allowing scour of bottom sediments.
 The good news is that marshes can regenerate themselves—if the topography is not changed.  A survey of the South Carolina site in the picture done 15 months later showed that the marsh grass had recolonized the area and substantial recovery had occurred.  This is not, however,  to suggest that this sort of damage should be allowed to occur.

## Impacts On Vegetation

**Impacts On Vegetation**

**Shading is the obvious **
**impact of docks ...**

**Notes:**
The most visible long-term dock-related impact on vegetation is from chronic shading.  
Both marsh grasses and sea grasses have adapted to living in extended periods of light.  

## Impacts On Vegetation

**Impacts On Vegetation**

**Impacts include**
**Reduced shoot density**
**Reduced biomass**
**Reduced growth**
**Increased height (due to etiolation)**
**Increased erosion, undercutting of vegetation**
-          **Susceptibility varies by species:**
-  **Spartina patens                     Distichlis spicata                        S. alterniflora**
**  ****Min****	****	****	****	****	****	****	****	****         Max**

**—————————————————————————————**_**	**__**	**__**	**__**	**__**	**__**	**__**	**__**	**__**	**_

**Notes:**
Impacts from chronic shading can result in:
 Reduced density of the plant stems and shoots
 Reduced biomass—plants with stunted growth
 Increased height  
Occasionally plants will grow higher, probably due to  a condition called etiolation.  This occurs when plants try to “stretch out” toward the light.  It is characterized by long weak stems and small leaves. Although it is taller, it still has less plant material.
 Increased erosion and undercutting of vegetation
Once the vegetation is affected, the bare soils are subject to erosion or undercutting along the marsh edge or at the edges of SAV beds, resulting in additional losses of vegetative matter.
It is important to note that susceptibility to shading impacts varies with species.  In the marshes, Spartina alterniflora, which lives along the edges of creeks, is more susceptible than the grasses of the higher marsh like S. patens and  Distichlis.

## Impacts On Vegetation

**Impacts On Vegetation**

**Light Profile Under a Dock**

- Min for full growth

- Min for plant maintenance

**Notes:**
This graph shows the shading caused by a dock in an east-west orientation.  
The dots indicate the amount of light measured under the dock.  Note that they drop to almost zero under the dock.  
The upper horizontal line represents the amount of light needed by plants for full growth.  As you see, the amount of light present rapidly drops below that level on the south side of the dock (the left) and is below the “full growth level” even when not directly under the dock on the north side—due to the effects of the shadow on that side.
In most of the area under the dock, light is below the “maintenance” level.
This graph also illustrates an important point about dock orientation.  An east- west orientation, particularly in higher latitudes, produces shading on the north side of the dock.  A similar graph with the dock running north-south would not show this sort of offset.

## Impacts On Vegetation

**Impacts On Vegetation**

**Eelgrass Density Under and Adjacent to Docks**

**Notes:**
In this graph, produced by Fred Short and Dave Burdick in their work with eelgrass, we see how the density of plant stems is less under the dock (the left bar) than in a control area away from the dock (the right bar).  It is important to note that there are impacts even in areas near the dock, but not directly under it, as may be seen in the two middle bars.
It should be noted that this sort of shading impact also shows up in fresh waters.

## Impacts On Vegetation

**Impacts On Vegetation**

**Similar Impacts in**
**Fresh water**

** ****Significant shading**
** ****Reduced plant abundance**
** ****Fewer fish and invertebrates **
** ****Reduced species diversity**

**Notes:**
Similar impacts to vegetation are seen in fresh water setting.
In a study in Wisconsin, researchers noted that the presence of docks:
 Increased shading under the docks.
 There was a reduction in plant abundance and biomass.  This meant less food material and habitat for juvenile fish.  The median biomass under the docks was 5 grams—in control sites the median was 107 grams, reflecting, approximately, a 95% drop in biomass.
 There were fewer fish and macroinvertebrates. (The researchers did not sample for smaller invertebrates.)  The median number of macroinvertebrates under the docks was 23 compared with 61 in the control sites.
 In addition to there being  fewer fish and macroinvertebrates, there was also a reduction in species diversity.

## Impacts From Contaminants

**Impacts From Contaminants**

**Wood preservatives include:**
**	**

** ****Creosote**
** ****Pentachlorophenols**
** ****Chromated Copper Arsenate**

**Notes:**
The most common contaminant-related concern associated with small docks is leaching of wood preservatives.
Wood continuously exposed to water can decay rapidly.  Additionally, wooden pilings that are immersed in marine waters are subject to wood-boring and other fouling organisms.
For centuries, people have sought means to prevent the breakdown of wood materials in salt waters.
For the early part of the 20th century, the most common preservatives were oil-based: creosote and pentachlorophenols.  These were found to have wide-spread environmental and human health impacts.
Consequently, in the latter part of the 20th century wood began to be treated with metal-based compounds applied under pressure to get them deep into the wood.  Today the most common form of preservative is pressure-treated wood with Chromated Copper Arsenate or CCA.  
Each of the components of CCA is toxic at high enough levels.  A big question today is whether CCA-treated materials have impacts away from the surfaces they are designed to protect.

## Impacts From Contaminants

**Impacts From Contaminants**

| Retentions
(lbs./cu.ft.) | Uses/Exposures |
| --- | --- |
|    
    0.10 – 0.25
    0.21 – 0.41
    0.31– 0.61
              2.50 | 
Above ground
Soil & Freshwater use
Permanent Wood Foundation
Salt water use |

**Notes:**
As you will see in this table, the levels of CCA treatment for materials to be used in salt water is up to 10 times higher than what is recommended for above-ground and freshwater use. 

## Impacts From Contaminants

**Impacts From Contaminants**

**Metal Uptake in Algae**

**Digestive Gland**
**Metaplasia in Oysters**

**Notes:**
Laboratory research has found the the metals from CCA-treated wood do indeed leach out into the adjacent waters and can have toxic effects.  
Laboratory tanks containing CCA-treated wood were stocked with the alga Ulva lactuca and then snails were introduced.  The Ulva took up metals leached from the wood and when the snails fed on the alga, they became moribund and died within a 3–4 weeks  
The graph at the upper left shows elevated metal levels in algae living  on CCA-treated.pilings (right hand bars) when compared to a control setting (left hand bars).
It should be noted that in a confined laboratory setting, like the Ulva/ snail study, CCA most likely reached MUCH higher concentrations than would be found in the natural environment.  A field study of oysters living on CCA-treated bulkheads found they were smaller than those from control populations.  The direct impacts are to the digestive glands, reducing the oysters’ ability to feed.

## Impacts From Contaminants

**Impacts From Contaminants**

**Notes:**
The metals that leach from CCA-treated material can be noted in sediments away from the source. 
These metals attach most readily to fine grained sediments with high organic content.
As you can see in the graph above, concentrations of the metals drop off as you move further from the source.  In this case, they have almost reached background levels by 10 meters, with the sharpest drop being in first three meters 

## Creeks with vs. without docks:

**Creeks with vs. without docks:**
**Same sediment Cu, Cr and As concentrations.  **
**Oysters attached to pilings had > [Cu], but no physiological effects or acute toxicity.**
**Creeks with new docks (4-12 mo.) vs. creeks without docks:**
**Same percent survival of mummichogs, juvenile red drum, white shrimp, mud snails, and oysters.**
- Priscilla Wendt, Robert Van Dolah, South Carolina Dep’t Natural Resources, 2001 l

**Notes:**
But what does all this mean in the field?
The field studies mentioned previously all were done in areas of low flushing bounded by solid bulkheads treated with CCA materials.  They clearly show that with a significant source, low flushing rates and fine-grained sediments, there may be impacts away from the treated material.
Studies in South Carolina resulted in somewhat different findings.  One of the studies looked at creeks with docks and compared them to creeks without docks.  The results showed the same levels of copper, chromium and arsenic in the sediments of both.  Oysters attached to pilings showed no visible impacts, although they had higher copper levels than control individuals.  The second study compared creeks with new docks (4–12 months old—and that age range is important as we will discuss later) with creeks without docks and found no basic differences in populations of sampled species.

## Impacts From Contaminants

**Impacts From Contaminants**

** ****CCA Leaching Decreases with Age**
**	****99% leaching completed within 90 days**
**  ****CCA Impacts  Depend on Flow and **
**    ****Flushing**
**	****Measurable impacts in low flushing areas**
**	****No impact observed in high flushing areas**

**Notes:**
To all of these research results, we must add one additional fact.  Leaching of metals from CCA-treated materials decreases by about 50% daily once the wood is immersed in seawater and approximately 99% of the leaching occurs within the first 90 days in the marine environment.  Consequently, it is not surprising that the studies in South Carolina found no measurable impacts from docks that had been in the water longer than 90 days.
What we can take from all this is that:
 there appear to be measurable impacts in areas with low flushing, significant sources (bulkheads vs. pilings), and fine grained sediments.
 there have been no measurable impacts in areas with high flushing rates. 
We should also note that since 2004, pressure-treated wood intended for use in fresh water will no longer use CCA.  Other treatments have been developed for freshwater use.  CCA-treated materials will continue to be produced for use in marine waters.

## Impacts From Contaminants

**Impacts From Contaminants**

**Impacts From Other Contaminants**
** ****Fuel spills**
** ****Paints, stains and seasonal upkeep**
** ****Flotation materials**

**Notes:**
There are other contaminants of concern related  to docks.  These include:
 Fuel spills at docks.  Usually this is due to filling outboard engines while at the dock.  As we will discuss later, some petroleum products also enter the water from operation of these engines.
 Spillage from paints and stains used in seasonal upkeep, as well as paint scrapings, may enter the water.  
 In appropriate flotation materials, generally Styrofoam or “beadboard”, when not encapsulated, can break down and release small plastic pellets that have both environmental and visual impacts.

## Impacts to Sediments and 

**Impacts to Sediments and **
**	****Bottom Topography**

**Alteration of Flows and Deposition**

**Notes:**
Managers often hear that the installation of docks will cause changes in the makeup of sediments and bottom topography. 
Generally this is attributed to the docks changing long-shore flows of water. This is alleged to have two different possible impacts depending on the situation:
Either increasing the velocity of waters moving around pilings leading to erosion or scour
Slowing the movement of waters allowing sediments to settle out and increasing sedimentation rates.
There has been little research in this area that directly applies to small, pile supported docks.  However, solid fill cocks, as shown in the upper part of the photograph, will clearly change water flows, generally resulting in sedimentation on the up-drift side.

## Impacts to Sediments and 

**Impacts to Sediments and **
**	****Bottom Topography**

**Disruption During**
**Pile Installation**

**Notes:**
Changes in bottom topography have been clearly noted as a result of pile installation as we mentioned earlier.  Jetting as a means of installing piles will result in a ring of elevated sediments around the piling; areas that may take years to repair themselves.

## Impacts to Sediments and 

**Impacts to Sediments and **
**	****Bottom Topography**

**“****Pumping” by boats and floats**

**Notes:**
A third type of impact to bottom sediments is attributed to a “pumping” effect from boats or floats that sit on the bottom at low tide and bring fine sediments with them as they rise with the incoming tide.  There has been little, if any, quantifiable research done on this issue.  
There are clearly other issues related to boats and docks sitting on the bottom—disruption or shading of vegetation, damage to shellfish resources—but the impacts on sedimentation and bottom topography are not yet clearly understood.

## Impacts From Boating Use

**Impacts From Boating Use**

**Issues of Concern:**

** ****SAV Scarring and Blowouts**
** ****Fuel Discharges**
** ****Erosion**
** ****Resuspension of Sediments**

**Notes:**
Boating use associated with docks raises a number  of issues, although it is very difficult to separate out the impacts from boats associated with docks from general boating use.  The most prominent of these impacts are:
 SAV scarring and blowouts—physical damage to submerged plants
 Fuel discharges or spills
 Erosion along the shore
 Resuspension of sediments and the resultant turbidity.

## Prop Scarring

**Prop Scarring**

**Waquoit Bay, MA**

**Impacts From Boating Use**

**Notes:**
These photographs reflect damage done by engine propellers moving through vegetation beds.  In the upper left, you can clearly see the paths taken by boats to and from their docks—as well as circles around moorings produced as the bottom chain swings around the mooring as winds and currents move the attached boat.
In the second picture, we can see the development of a new channel as boats pass through the vegetation beds.
Not surprisingly, most of this sort of impact takes place when boats pass through shallow waters.  
The impacts can add up, however.  Researchers in Corpus Christi Bay in Texas found that almost 40% of the beds were moderately or heavily scarred.

## Impacts From Boating Use

**Impacts From Boating Use**

**Fuel Spills**

**Notes:**
As we mentioned earlier, fuel spills, generally far smaller than those shown in the graphics, come from two sources:
 fuel spillage at docks (clearly a dock-related activity) and 
 discharges from outboard engines.  Even with the improvements in levels of discharge with the advent of four-cycle engines, the four-cycle engines continue to discharge amounts of the toxic components of petroleum products as do two-cycle engines.
It is very difficult to ascribe outboard engine discharges to docks, however.  General boating, or even land-based runoff, may produce significantly higher amounts. 

## Impacts From Boating Use

**Impacts From Boating Use**

**Erosion and Slumping**

**Notes:**
Boat wakes can contribute to increased shoreline erosion.  This may lead to “slumping’ or breaking off of sections of the marsh as seen in the right-hand picture.  
The most significant surface wakes come from vessels moving at higher speeds.  It is not clear how great an impact boats moving slowly to and from a dock may have.

## Impacts From Boating Use

**Impacts From Boating Use**

**Resuspension of Sediments and**
**	****Turbidity**

**Notes:**
Running a boat through shallow waters produces a surface (or bow) wake mentioned in the prior slide.  It also will produce a secondary wake—sometimes referred to as prop wash— related to effects from the propeller.  This wake moves behind the boat in a downward direction where it can affect SAV and bottom sediments.
The secondary wake does not fan out like a surface wake and consequently has localized impacts.  
Bottom sediments that are continually resuspended by boat traffic will cloud the water (known scientifically as turbidity), reducing light levels necessary for plant maintenance and growth. Prop wash can also result in  changes in bottom topography—sometimes referred to as “prop dredging”.
A comparison between prop wash from propeller-driven boats and water-jet propelled craft showed no significant differences in the amount of resuspension of sediments.
Slow-moving, heavy, deep draft boats cause more turbidity than faster-moving, planning hulls that ride on the surface.
As mentioned earlier, it is difficult to clearly link these impacts directly to docks.  General boating may have a far greater contribution—but neither contribution has been quantified.

## Slide 27