Summary Review of
Shoreland Management Science
Welcome. This an outline of a presentation made at the workshop ‘ How to Avoid Drowning in
Lakeshore Development’ , sponsored by the Minnesota Lakes Association and Government
Training Services, by P aul Radomski, on April 21, 2005, in Alexandria at the Arrowwood Resort.
1
“Science cannot tell us what is right or
wrong when there is a tradeoff involving a
hardship for people today versus a possible
gain for people in the future.”
Walters and Martell 2004
It is impossible to accurately predict parameters of lake ecosystems without some potential bias and with
high precision. However, modeling lake ecosystems aids in making choices. Management needs to make
choices, and science is about making predictions.
Management often needs to be able to predict if one policy is better than other. For example, is ‘ P olicy A’
better for a wide range of future conditions than ‘ P olicy B’ . Science can provide predictions through
mathematical models and thus aid in decision-making without precise estimates that are bound to be wrong
to some degree. We need to find strategies for management that do not depend on accurate (non-biased and
precise) predictions.
Science can also identify potential problem areas of existing policy, through research on the consequences of
shoreland development. P ertinent research in the area of shoreland development is summarized.
2
Objectives
•
•
•
•
•
Reason for Modernization of Rules
Science of Runoff
Science of Vegetative Buffers
Science of Boating Capacity
Science of Land Management
Statewide minimum shoreline standards affect nearly all of Minnesota's lakes and rivers. These
standards set guidelines for the use and development of shoreland property, including a sanitary code,
minimum lot size, minimum water frontage, building setbacks, building heights, and subdivision
regulations. Local units of government with priority shorelands are required to adopt these or stricter
standards into their zoning ordinances.Increasing development pressure around lakes has raised
concerns about water quality and impacts on lake use. The state's shoreland rules could be updated to
provide better tools to address those concerns based on local resource conditions and needs.
The Governor's Clean Water Initiative pilot project in the north-central lakes area aims to support,
coordinate, and enhance existing and future efforts so that critical threats to the health of those lakes are
reduced or eliminated. Stakeholders involved in designing the pilot project have voiced a strong
interest in updating these standards within the pilot project area: Aitkin, Cass, Crow Wing, Hubbard,
and Itasca counties.
I will talk about the need to modernize the shoreland rules and summarize the science of rainwater
runoff, vegetative buffers, boating capacity, and if time the science of land management.
3
Areas of Concern
• Loss of fish and wildlife
The shoreland standards are intended to preserve and enhance the quality of surface waters, conserve the
economic and natural environmental values of shorelands, and provide for the wise use of water and
related land resources of the state (6120.2600).
However, current state shoreland standards results in a substantial reduction in fish and wildlife habitat.
4
The nearshore area is valuable habitat for many species of wildlife, including these loons.
5
Comparison of Undeveloped
and Developed Shoreline
Recently, Tim Goeman and I studied the consequences of shoreline development. We
randomly selected 44 lakes of the 531 sunfish-walleye lakes in the state. We used color
infrared photography. The scale was 8” to the mile. Photos were scanned at high resolution
(1000 dpi). For each lake, we randomly selected 12 31-m (100 ft) square plots from both
developed and undeveloped shoreline plots. So we had a total of 1056 shoreline plots that we
analyzed. Color infrared photography allowed us to quantify emergent and floating-leaf
vegetation, shown here as the darker pink.
6
Radomski and Goeman 2001
Even though fish surveys have considerable measurement uncertainty and the correlations were
low, this comparative analysis suggests that declines in emergent and floating-leaf vegetation due
to development may result in lower fish production. (And analysis by other investigators support
this).
North American Journal of Fisheries Management 21:46–61, 2001Consequences Of Human
Lakeshore Development on Emergent and Floating-Leaf Vegetation Abundance
P AUL RADOMSKI AND TIMOTHY J. GOEMAN Minnesota Department of Natural Resources,
Division of Fisheries, 1601 Minnesota Drive, Brainerd, Minnesota 56401, USA
Abstract
Vegetation abundance along undeveloped and developed shorelines of Minnesota lakes was
compared to test the hypothesis that development has not altered the abundance of emergent and
floating-leaf vegetation. Aerial photographs of clear-water lakes dominated by centrarchids and
walleyes Stizostedion vitreum were analyzed for vegetation. Vegetative coverage was estimated in
12 randomly selected 935-m 2 digitized photograph plots for both developed and undeveloped
shorelines of 44 lakes representing a gradient of development. Vegetative cover in littoral areas
adjacent to developed shores was less abundant than along undeveloped shorelines. On average,
there was a 66% reduction in vegetation coverage with development. The estimated loss of emergent
and floating-leaf coverage from human development for all Minnesota’ s clearwater
centrarchid–walleye lakes was 20–28%. Significant correlations were detected between occurrence
of emergent and floating-leaf plant species and relative biomass and mean size of northern pike Esox
lucius, bluegill Lepomis macrochirus, and pumpkinseed Lepomis gibbosus (Spearman’ s rank
correlation, P < 0.05). Current shoreline regulatory policies and landowner education programs may
need to be changed to address the cumulative impacts to North American lakes.
7
Summary
• For each lake lot, 2/3rds of the
emergent and floating-leaf
vegetation was lost.
• MN has lost 20-28% of this
vegetation.
• Losses may result in lower fish
production.
Radomski and Goeman 2001
To conclude, we found:
8
From an airplane over a lake with high housing densities, it looks like some shorelines are
more like boat parking areas.
9
2004 Seining Survey Results from 13 SE Lakes
Fish Species
20
R2 =0.3113
15
10
R2 =0.5634
5
0
0 spp
Intol-rare
Nativespecies
20
40
60
80
Piers/mile
Garrison et al. 2005, Lyons and Marshalll 2005
Effects of pier shading on littoral zone habitat and communities in lakes Ripley and Rock, Jefferson
County, Wisconsin. By Paul J. Garrison, David W. Marshall, Laura Stremick-Thompson, Patricia L.
Cicero, and Paul D. Dearlove, March 2005. PUB-SS-1006 2005
Abstract
The direct and indirect ecological effects of pier shading were evaluated on two calcareous lakes in
southeast Wisconsin. Sunlight availability and the response of macrophytes, macroinvertebrates, and
both juvenile and small non-game fishes were evaluated under piers and within nearby control sites.
Findings revealed significant shading under piers with a corresponding reduction in aquatic plant
abundance, as well as a shift in community composition to one dominated by shade-tolerant species.
The median biomass under the piers was 5 grams compared with 107 grams in the control sites. The
resulting loss of macrophyte habitat under piers translated into a reduction in macroinvertebrate
numbers. The median number of macroinvertebrates under the piers was 23 compared with 61 in the
control sites. Juvenile Centrarchid fishes showed preference for abundant macrophyte cover found in
control areas. Mean fish catch rates under piers (11.2) were statistically lower than catch rates within
plant beds (38.7). Results suggest that the proliferation of piers and other near-shore structures are
contributing to the degradation of littoral zone habitat and biological diversity.
10
Juvenile Sunfish Habitat Preference
Fish Catch Rates
100
80
60
40
20
0
11.2 fish/pier
minnow trap sites
38.7
fish/plant
beds
(P<.01)
Garrison et al. 2005, Lyons and Marshalll 2005
Pier
Control
Effects of pier shading on littoral zone habitat and communities in lakes Ripley and Rock, Jefferson
County, Wisconsin. By Paul J. Garrison, David W. Marshall, Laura Stremick-Thompson, Patricia L.
Cicero, and Paul D. Dearlove, March 2005. PUB-SS-1006 2005
Abstract
The direct and indirect ecological effects of pier shading were evaluated on two calcareous lakes in
southeast Wisconsin. Sunlight availability and the response of macrophytes, macroinvertebrates, and
both juvenile and small non-game fishes were evaluated under piers and within nearby control sites.
Findings revealed significant shading under piers with a corresponding reduction in aquatic plant
abundance, as well as a shift in community composition to one dominated by shade-tolerant species.
The median biomass under the piers was 5 grams compared with 107 grams in the control sites. The
resulting loss of macrophyte habitat under piers translated into a reduction in macroinvertebrate
numbers. The median number of macroinvertebrates under the piers was 23 compared with 61 in the
control sites. Juvenile Centrarchid fishes showed preference for abundant macrophyte cover found in
control areas. Mean fish catch rates under piers (11.2) were statistically lower than catch rates within
plant beds (38.7). Results suggest that the proliferation of piers and other near-shore structures are
contributing to the degradation of littoral zone habitat and biological diversity.
11
Fallen Trees
• Significantly less trees in
water along developed
compared to
undeveloped shorelines
• Will affect littoral
communities for about 2
centuries
Christensen et al. 1996
A study of Wisconsin and Michigan lakes found that the loss of trees along shore due to
development will negatively affect fish for centuries. Shoreline trees often fall in the water and
create excellent fish habitat, so the loss of these trees along shore has long-term consequences.
Ecological Applications: Vol. 6, No. 4, pp. 1143–1149. Impacts of Lakeshore Residential
Development on Coarse Woody Debris in North Temperate Lakes
By David L. Christensen, Brian R. Herwig, Daniel E. Schindler, and Stephen R. Carpenter
Abstract.Coarse woody debris (CWD) is a critical input from forested watersheds into aquatic
ecosystems. Human activities often reduce the abundance of CWD in fluvial systems, but
little is known about human impacts on CWD in lakes. We surveyed 16 north temperate
lakes to assess relationships among CWD, riparian vegetation, and shoreline residential
development. We found strong positive correlation between CWD density and riparian tree
density (r2 = 0.78), and strong negative correlation between CWD density and shoreline cabin
density (r2 = 0.71) at the whole-lake scale. At finer spatial scales (e.g., between sampling
plots), correlations between CWD and riparian vegetation were weaker. The strength of
relationships between CWD and riparian vegetation was also negatively influenced by the
extent of cabin development. Overall, there was significantly more CWD in undeveloped lakes
(mean of 555 logs/km of shoreline) than in developed lakes. Within developed lakes, CWD
density differed between forested sites (mean of 379 logs/km of shoreline) and cabin-occupied
sites (mean of 57 logs/km of shoreline). These losses of CWD will affect littoral communities
in developed north temperate lakes for about two centuries. Because CWD is important
littoral habitat for many aquatic organisms, zoning and lake management should aim to
minimize further reductions of aquatic CWD and woody vegetation from lakeshore residences.
12
Fewer Green Frogs per Mile
What’s Happened to Frogs?
80
60
40
20
0
0
10
20
30
More Homes per Mile
Meyer et al. 1997, Wisconsin DNR, Woodford and Meyer 2003
30 homes per mile is equivalent to about 180’ lots
Development can bring with it dramatic change in shoreland plants. Biologists have set out to
measure changes in the number and kind of wildlife species. They found fewer loons, fewer
green frogs, and changes in the songbirds populations. Green frogs are often found along
shorelands. Males establish breeding territories within two feet of the lake’s edge. Biologists
conducted surveys of toads and frogs on 24 undeveloped lakes in Vilas and Oneida Counties.
Their results show that as homes become more dense green frog numbers decline.
Biological Conservation 110 (2003) 277–284. Impact of lakeshore development on green frog
abundance by James E. Woodford, Michael W. Meyer
Abstract
Many amphibian species exhibit metapopulation spatial dynamics and temporally are faced
with local population extinction and re-colonization. These natural population fluctuations can
exhibit stochastic effects when human-caused alteration and fragmentation of habitats occur
during sensitive life-cycle events. In this study, we explored the effects of shoreline
development on adult green frogs Rana clamitans melanota on lakes (n=24) of northern
Wisconsin. We estimated green frog abundance using both auditory and direct observation
surveys. The immediate shoreline habitat was mapped and placed into a Geographical
Information System (GIS) for analysis. Adult green frog populations were significantly lower
on lakes with varying degrees of shoreline house and cottage development than lakes with
little or no development. A negative linear relationship existed between shoreline
development densities and the number of adult green frogs. However, house and cottage
densities alone did not directly explain this reduction. Analysis of variance (ANOVA)
identified that the amount of suitable habitat, not development density, significantly affected
green frog abundance. Therefore, greater development densities significantly decrease breeding
habitat quality, resulting in lower adult frog abundance. These and other findings suggest that
lakeshore development regulations are not protecting sensitive amphibian species.
13
What are the consequences to fish habitat, where habitat is composed not only the water but the
sediment, the woody structure from trees falling into the lake, and aquatic vegetation.
Fish habitat is analogous to bird habitat (go into some detail here).
14
Damages the shore ecology
200,000 to 225,000 private lakeshore homes in the state of Minnesota, and about 181,000 on
fisheries lakes.
A Study on Landowner P erceptions and Opinions of Aquatic P lant Management in Minnesota
Lakes
P ayton and Fulton 2004.
Property characteristics:
Median length of property ownership was 15 years.
Almost all property was used as a primary residence (50%) or as a seasonal/recreational residence
(49%).
Seventy-five percent of respondents owned less than 200 feet of shoreline, with a median of 130 feet.
While natural vegetation was the most common shoreline type, more than 25% of property owners
indicated that sandy beach, rip rap, and mowed turf grass represented at least 40% of their shoreline.
On average, properties in the Metro Twin Cities area had larger percentages of their shoreline in rip
rap, seawall, and mowed turf grass.
15
Areas of Concern
• Loss of fish and wildlife habitat
• 25% of area lakes do not fully meet full
aquatic recreational use criteria
Minnesota PCA 2004, EPA 2000
PCA report: Minnesota Lake Water Quality Assessment Data: 2004.
Of the total of 2,790 assessed lakes 53 percent fully supported aquatic recreational use while 37 percent
did not. The remainder partially supported uses. In terms of lake acres 50 percent fully supported while
only 16 percent did not. The primary reason for the difference between these figures (number of lakes
vs. lake acres) is that the larger lakes tend to drive the acreage-based assessment and many of these
large lakes (e.g. Lake Mille Lacs, Leech, Lake of the Woods) tend to fully or partially support uses. In
contrast there are numerous small lakes that do not fully support aquatic recreational uses.
The examination of use support by ecoregion may provide more insight, since the thresholds used in
the assessment are ecoregion-based and the underlying characteristics that comprise the ecoregions: land
use, soil type, potential natural vegetation and landform can strongly influence the delivery of nutrients
to the lake. The majority of the assessed lakes of the NLF and NMW ecoregions either fully or
partially support aquatic recreation uses (25% do not). These two ecoregions are characterized by
moderately deep lakes and watersheds dominated by forest and wetland uses. In contrast the majority of
the lakes in the CHF, WCP and NGP ecoregions are non supporting of aquatic recreational uses. The
reasons for non-support of swimmable use vary between regions. NLF ecoregion lakes which do not
support swimmable use are often smaller and shallower than the norm and often have some past or
present source of excess P loading in their watershed such as a wastewater treatment plant discharge.
CHF ecoregion lakes that do not support swimmable use are often shallower than the norm. Also they
often have a source (or multiple sources) of excessive P loading such as: wastewater treatment plant
discharge, numerous feedlots, excessive land application of bio-solids, high percentage of agricultural
land use, or high percentage of impervious area (receive large amounts of storm water runoff) in their
watershed. All of these sources can contribute high P loading to a lake. In the WCP and NGP
ecoregions the vast majority of lakes are quite shallow and have highly agricultural watersheds. Runoff
from these agricultural lands is typically very high in P. This high P loading from the watershed and
shallowness of the lakes (which promotes poor retention of P by lake sediments and internal recycling
of P) typically lead to high in-lake P concentrations and subsequently nuisance algal blooms and low
transparency. The combination of high watershed P loading and the limited assimilative capacity of
shallow lakes often limit the degree to which water quality of these lakes might be improved.
16
Water Clarity vs TP Based on Ecoregion Reference Lakes
35.0
30.0
-0.8211
y = 118.83x
Clarity (Feet)
2
R = 0.7648
25.0
20.0
15.0
10.0
5.0
0.0
0
30
60
90
120
150
180
210
240
270
300
TP ppb
Example: Total Phosphorus Change from 15-25 ppb
Results in About a 4.5’ Clarity Reduction
12.5’
8.0’
Minnesota PCA
Many of the lakes in northcentral Minnesota have good water clarity (lakes in red oval). However,
small changes in the amount of total phosphorus in the water (TP, parts per billion) can produce large
reductions in clarity. And once a lake has an excess of phosphorus, water clarity becomes poor and it
is difficult in many cases for it to fully recover (lakes in the pink oval).
17
Paleolimnology:
development effects detected
Garrison and W akeman 2000
Because sediment naturally builds up on a lake bottom over time, an accurate record of environmental
change can be found in the lake’s sediment layers. Divers drive a plastic tube into bottom sediments
and bring a core up to be analyzed in a science called paleolimnology. Researchers have found that
certain tiny algae called diatoms live under very narrow environmental conditions. If the water quality
is poor, all types of diatoms cannot exist there, so diatoms are good indicators of past water quality.
18
20th Century Lake Trends
Ramstack et al. 2004
Lakes in the Metro and central Minnesota have seen declined in water quality. Lakes in Itasca County (NLF,
northern lakes and forest ecoregion) appear not to have been degraded yet.
Canadian Journal of Fisheries and Aquatic Sciences 61: 561–576 (2004)
Twentieth century water quality trends in Minnesota lakes compared with presettlement variability
Joy M. Ramstack, Sherilyn C. Fritz, and Daniel R. Engstrom
Abstract: A diatom-based transfer function was used to reconstruct water chemistry before European
settlement in 55 Minnesota lakes. The lakes span three natural ecoregions, which differ in their history
of land use, as well as in surficial geology, climate, and vegetation. Postsettlement trends were
compared with water chemistry change reconstructed from two presettlement core sections (circa 1750
and 1800) as a measure of natural variability. Presettlement water quality changes were generally small
and nondirectional in all three ecoregions. In contrast, half of the urban lakes showed a statistically
significant increase in chloride, whereas 30% of urban and 30% of agricultural region lakes record a
statistically significant increase in total phosphorus between 1800 and the present. These changes,
which are attributed to road salt and nutrient runoff, are strongly correlated with the percentage of
watershed area that is developed (residential or urban) in the case of chloride increases and the
percentage of developed (metropolitan areas) or agricultural (agricultural areas) land in the case of
nutrient increases. Water quality has changed little since 1800 for lakes in the forested regions of
northeastern Minnesota. The few changes that are seen in this region are likely related to natural
variations in climate or catchment soils.
19
Conservation Agenda: Waters and Watersheds
Challenges: Lake Development
Increased
Sedimentation
Increased Erosion
Red areas: >500 % change (1980-2000)
in seasonal housing density
With development, come management challenges. The lakes region has been growing at a very fast
rate. Some people are concerned about the consequences of this development on water quality and fish
and wildlife. They should be.
20
Areas of Concern
• Loss of fish and wildlife habitat
• 25% of area lakes do not fully meet full
aquatic recreational use criteria
• Nationally, poorly managed rainwater is
responsible for 15% of lake impairment
Minnesota PCA 2004, EPA 2000
It is important to manage our rainwater to reduce pollutants and excessive nutrients entering our lakes.
In an undisturbed environment, about 50% of the water soaks into the ground and about 10% runs over
the surface of the land and enters the lake. The rest of the water evaporates or is used by plants.
As we change the land by farming, logging, or adding buildings and roads, less water flows into the
ground, and more water runs off. Finally, in an urbanized area, we have the original relationship now
being essentially reversed: only 20% of the water soaks into the ground, and 50% becomes runoff.
{note that the totals (runoff + infiltration) go from 50-60% up to 70% in the urbanized environment.
This is because there is less vegetation for evapotranspiration}
This increased volume of runoff leads to increased flooding and erosion, and it means that less water is
going into the ground to recharge aquifers and to provide baseflow for wetlands and streams. In an
undisturbed environment, water falls to the ground, either hitting the surface and running off or
percolating through the soil into the groundwater. Through both routes, water makes its way to our
streams, ponds, wetlands, rivers, lakes and oceans.
As we develop and alter the landscape, however, this natural cycle is disturbed, impacting both water
quantity and water quality.
- increased runoff, more frequent flooding, more severe flooding
- decreased infiltration, less groundwater recharge, decrease in base flow to streams
- more pollution generated from our uses of the land and delivered to our waterways
21
Need Modern Rules
Shoreland Rules Don’t
Adequately Protect Water Quality
and Fish and Wildlife Habitat
One can conclude, based on the research conducted, that the existing shoreland rules do not adequately
protect water quality, and fish and wildlife habitat.
22
Runoff
Runoff (red arrows) originates from our highways, roads, parking lots, roofs, and lawns.
Rainwater that does not infiltrate into the ground or evaporate, runs directly into the lake or
into small rivers and then into the lake. Runoff carries pollutants, like oil, pesticides,
suspended solids, and the nutrient phosphorus.
23
Runoff
To understand runoff, which brings pollutants to our lakes, you need to understand rain drops. So one
needs to think small or on a small scale. Lay on the ground in the rain and watch where the rain goes.
Runoff is not only occurring when streams and rivers are full after a rain, but it is also the small sheets
of water that leave our lawns and heads down to the lake.
25
Rainwater Management
Two Paradigms
• Move water off fast
• Get water into
ground near where it
falls
Infiltration basins
Rain gardens
Less imperviousness
The first paradigm does not scale well, and the shift to include the second paradigm is accelerating.
26
Rainwater Management
• Amount of Rain
• Soil Permeability, &
Porosity
• Soil Moisture
• Slope
• Exposed Ground
• Impervious Surfaces
It is important to manage our rainwater to reduce pollutants and excessive nutrients entering our lakes.
The factors listed in this slide, along with others, determine the amount of runoff.
27
Impervious Surfaces
Materials like cement, asphalt, roofing, and
compacted soil that prevent percolation of runoff
into the ground.
Total Phosphorus in water from these sources:
Low traffic street: 1.31 ppm
Rooftop: 0.15 ppm
Driveway: 1.16 ppm
Lawn: 2.67 ppm
(Bannerman et al. 1993, Schueler 2003)
Phosphorus loading increases with intensity of land use. One indicator of intense development,
especially in urban areas, is impervious surface. Impervious surfaces are materials like cement, asphalt,
roofing and compacted soil that prevent percolation of runoff into the ground. We are concerned about
impervious surfaces because they: inhibit recharge of groundwater, prevent natural processing of
pollutants in soil and plants, they provide a surface for accumulation of pollutants, and they provide an
express route for pollutants to waterways. Even in lake country, there are lots of sources of
imperviousness, both on the lakeshore, and of course, within the watershed. Some examples from this
lakeshore home include sidewalks, roof, and even lawns, which can be nearly impervious because the
soil is compacted by heavy equipment during the construction process or regular foot traffic.
28
Runoff from a 1” Rain
This graph shows the difference between runoff from a meadow compared to an impervious
surface like a driveway.
29
Picture: Toxins-Oil into storm
drain
With the water comes pollutants like heavy metals, toxic organic chemicals, and nutrients.
30
Cumulative Impacts of
Impervious Cover
Schueler 2003, Wang et al. 2001, adapted from NEMO
The amount of impervious cover is a key indicator of the quality of the water flowing into our lakes.
Research consistently shows that as the amount of impervious surface increases in the watershed, the
health of the inlets decreases. Streams draining watersheds with more than 12% imperviousness have
shown to be consistently in poor condition, indexed by poor fish communities (Wang et al. 2001).
Average % of Impervious Cover by Land Use:
2-acre Residence: 12
1-acre Residence: 20
0.5-acre Residence: 25
0.33-acre Residence: 30
0.25-acre Residence: 38
0.125-acre Residence: 65
Industrial: 75
Commercial: 85
Shopping Center: 95
Studies have shown that 55-75% of impervious surfaces are for vehicles, 35% for human habitat. As
impervious cover increases, runoff increases linearly.
31
Phosphorus Pollution increases
with % Impervious Cover
Scheuler and Caraco 2001
The predicted benefits in this example watershed show that stormwater treatment practices (STP) with
better site design (BSD; or low-impact development) can reduce phosphorus loading to lakes.
The practices include infiltration basins, bioretention systems, and low impact designs such as rain
gardens.
32
Allowed Under Shoreland Rules
Draft proposal
Assumption: 2750 sq ft dwelling, 100% buildable
A 25% impervious cover cap standard is in the existing state shoreland rules. It is proposed that this
standard be reduced for residential (Res) lots and planned unit developments (R-PUD, C-PUD), and
remain at 25% for resorts.
33
Phosphorus (lbs. per acre)
Annual Phosphorus Loading
Atm
Forest
Ag
Res
Urban
Paterson et al. 2004, Corsi et al. 1997, Panuska and Lillie 1995, Wilson and Heiskary 1994
Although each type of land use in the watershed contributes some amount of phosphorus to the lake, the more
intense land uses tend to contribute more phosphorus per acre of land.
{Note: phosphorus load from urban development can vary greatly, depending on the intensity of
development – and impervious surface is a good indicator}.
34
Total Phosphorus (ppm)
Lakeshore Lawns
0.2 lbs TP/lots X No. of lots =
Pounds of Phosphorus per year
Graczyk et al. 2003, USGS
These graphics show the difference between phosphorus concentrations of runoff and yields to lakes
from lawns compared to woods. Phosphorus concentration in runoff is higher from wood sites than
lawn sites (left graphic), however, lawns lead to more phosphorus running into lakes than wood sites
due to higher runoff rates for lawns (right graphic). An average of 0.2 pounds of phosphorus enters the
lake from typical lakeshore lots with lawns.
Hydrology, Nutrient Concentrations, and Nutrient Yields in Nearshore Areas of Four Lakes in Northern
Wisconsin, 1999–2001
By David J. Graczyk, Randall J. Hunt, Steven R. Greb, Cheryl A. Buchwald, and James T. Krohelski
35
Potential environmental pollutants
from septics
• Excess
nutrients
– nitrogen and
phosphorus
• Solids
– organic
matter
• Sediment
– installation
•http://www.febconstruction.com/Slide%2014.htm
Septic systems, while generally good a slowing down the migration of phosphorus to the lake, do
create environmental problems.
36
Septic Systems
Phosphorus reaching the lake
1.7 lbs TP/person per year
X
Mean No. of People per Residence
X
No. of Residences
X
(1-Soil Retention Probability)
=
Pounds of Phosphorus per year
Phosphorus can also reach the lake from lakehome septic systems. Some septic systems may not be
effective in trapping phosphorus in the drainfield soil. Soil retention of phosphorus is dependent on
soil type, depth, and chemistry. Research has found that both fine-grained non-calcareous sediments
and coarse-grained calcareous sand have a high ability to retain phosphorus. The PCA has found that
elevated phosphorus concentrations rarely exceed 50 feet in length within the septic plume. Migration
rates of phosphorus through the soil from a septic system can be slow with soils with high potential for
phosphorus adsorption or mineralization.
For a 2 person household with a soil retention probability of 75%, the average amount of phosphorus
entering lakes from septic systems is estimated to be 0.85 pounds per year.
Particularly for lakes, there is concern about the impacts of poorly functioning septic systems. There are
many things you can do to protect your septic system, and there’s also assistance available from
Extension Service and PCA. According to the EPA, regular pumping of the tanks is necessary (every
3-5 years).
P articularly for lakes, we are very concerned about the impacts of failing septic systems. There are many
things you can do to protect your septic system, and there’ s also assistance available from MN Extension
Service among other sources if you need more information.
37
Septic System Setback
Rs = retention capacity of the sewage disposal system
Rs = 0.5- 0.95 for conventional septic tank/tile field systems
(Rechkow and Simpson)
Ontario Ministry of the Environment takes a graduated approach. In areas with poor soil, it is assumed
that soil retention is zero. In areas with good soil, retention is related to distance from shore with no
export at distances greater than 1000 feet.
38
Build-out Predictions
Itasca County Lake Sensitivity Project, Rian Reed, Minnesota DNR
Scientific models used to estimate water clarity and phosphorus levels for our lakes can be used to
predict the consequences of development build-out with our existing shoreland rules. This prediction
for a lake in Itasca County shows that as more development occurs around the lake, water clarity
declines.
39
Design Principles
Retain, Restore
the
Natural
Landscape
10%
50%
The key principle here is to keep the drop of water as close to where it fell in the watershed so
it can soak into the ground, getting us back closer to the 50%/10% scenario discussed earlier.
Any kind of development or alteration of the landscape should work with the natural
vegetation and contours, preserving the natural landscape and drainage patterns.
40
Review of Studies: WI DNR, US Army Engineer Research and Development Center 2000
Several scientific review papers have looked at recommended shoreline buffer widths. The width of the
vegetative buffer depends on the management objectives.
41
Vegetative Buffers
Desbonnte et al. 1994; 82 feet most efficient width for sediment removal and 197 for TSS
There is a positive correlation between a vegetative buffer’s width and its ability to trap sediments.
According to the review conducted by Desbonnet et al (1994), the most efficient width for sediment
removal is 82 feet and 197 feet for total suspended solids.
42
Vegetative Buffers
Desbonnte et al. 1995
Although buffers can effectively trap phosphorus in runoff, they do not provide long-term storage and
are not effective at filtering soluble phosphate. Phosphorus trapped in a buffer may gradually reach the
lake, especially one the buffer becomes phosphorus saturated.
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Desbonnte et al. 1995
Native vegetative buffer widths required for wildlife habitat are considerably larger than those required
for many water quality objectives.
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Vegetative Buffers
Vegetative buffer strips along lakes is critical. This thin green line protects lake water quality and
houses many animals.
http://mnlakes.org/main_dev/News/PDF/Apr04_1_6-8.pdf
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Experimental Design
•
•
•
•
100 northcentral MN lakes
Stratified by shoreland development class
Existing aerial photos
8 time periods (most: 1939, 1955, 1960,
1969, 1978, 1989, 1996, 2003)
• Image analysis (n=729)
I have recently completed a study on the historical changes in abundance of floating-leaf and emergent
vegetation in Minnesota lakes. Here is the experimental design.
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Boat
Survey 2003
ISODATA 2003 FSA
Photo
Boat surveys of this critical fish and wildlife habitat were similar to computer image analysis
techniques. Here is an example.
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Historical Changes
1939, …
2003
So for 100 lakes I compared the abundance of this habitat from 1939 to 2003.
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Shoreline Development
Development has varied by shoreland development class. Natural environmental (NE) lakes remain
lightly developed compared to recreational (RD) and general development (GD) lakes.
18 dock sites per mile approximates to an average lot size of about 290’ (maximum observed was 24.5
dock sites/mile or an average lot size of 215’)
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25
20
Natural
Environment
15
Plant cover lost (%)
10
5
0
25
20
Recreational
Development
15
10
5
0
25
20
General
Development
15
10
5
0
1939 1955 1960 1969 1978 1989 1996 2003
Time period
The estimated mean loss of critical fish and wildlife habitat for northcentral Minnesota lakes for 2003
was 6% for natural environment lakes, 14% for recreational development, and 17% for general
development.
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RD: Build-out Scenario
Full development of recreational development lakes at the shoreland standard lot width of 150 feet was
predicted to result in a 26% reduction in this critical fish and wildlife habitat.
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Summary
• Northcentral MN has lost 15% of
this vegetation.
• For 2003, 6% loss for NE, 14% for
RD, and 17% for GD lakes.
• Full build-out predicted >20%
loss.
To conclude, I found:
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53
54
Beachler and Hill 2003
Resuspension of sediment is a function of boat size, power, and sediment conditions. At near-plane
speeds, the minimum depth needed for little impact was 6 feet for coarse sand substrates, 9 feet for fine
sand, and 15 feet for silt. No wake zones are likely to be superior to speed limits, in terms of
mitigating the effects of both sediment resuspension and wake impacts on the shoreline.
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Asplund 1996
Average change from weekday to weekend for shallow and deep lakes studied in Wisconsin by Tim
Asplund. Boat density increased on weekends, and water clarity decreased by about 16 inches in the
shallow lakes and about 8 inches in the near-shore areas of all lakes.
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Watercraft and Waterfowl
• Loss of feeding time
• Energy loss
• Reduced breeding
success
• Reduced survival of
chicks
Korschgen and Dahlgren 1992, Cywinski 2004
1.
Kahl (1991) found that disturbance in a Wisconsin lake resulted in about a 50% reduction in
feeding time for canvasbacks.
2.
Knapton (2000) found that disturbance lead canvasbacks, redheads, and scaup to feed in less
productive areas.
3.
Belanger and Bedard (1990) found for snow geese that disturbance caused a 5.3% increase in
hourly energy expenditure.
4.
Disturbance can cause female nesting ducks to take flight, leaving eggs exposed. And chicks are
more prone to predation after disturbance.
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Special Protection Class
Proposal
•
•
•
•
1/3 of shoreline is wetland
Shallow lake
Significant wild rice present or historically
Documented rare, endangered or SC
species
• Special or unique fish and wildlife habitat
• Low development level, and others
Within the Shoreland Rules Revision, we are proposing a new class of lakes. These lakes would be a
subset of the natural environment lakes; those ones with these attributes.
Shallow lake-max depth of 15’ or 80% littoral area or more.
Others:
% public ownership
% hydric soils in shoreland area
% highly erodible land in shoreland area
Known problems or impairments
Lake size
Special consideration for lake sensitivity
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Existing Boat Densities
High HP
boat
Standard
20 acres/boat
Kelly and Sushak 1996: North-Central lakes, 90 acres/boat; Metro lakes, 19 acres/boat
Using data from the study just reviewed, I estimated the median (lines in the boxes) acres per boat for
northcentral lakes [number of developments x 10% / lake size in acres; where 10% is the estimated
probability of use of boats by riparian residents on a summer weekend afternoon based on boating use
surveys completed by the DNR]
20 acres/boat is one standard boat density based on boating safety; it is the common standard for lakes
with high horsepower boat use. 9 acres/boat is often used for low horsepower boat use (e.g., small
urban lakes with boating dominated by small craft).
Most lakes do not exceed the standard (i.e., the medians values are larger than standard).
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Residential Full Build-out
Using GIS tools, I did a full build-out of every lake in the state using state shoreland standard lot
widths for general development (large lakes: GD-L; small lakes: GD-S), natural environment (NE), and
recreational development lakes (RD). I then calculated the riparian residential use (graphs do not
include boat activity from public accesses, or the fact that some lakes are already developed at higher
densities).
A considerable number of lakes, when fully developed, will exceed safe boating capacities.
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Residential Full Build-out
With full residential buildout, 33% of the large general development lakes (GD-L) will exceed safe
boating capacity, 57% of small general development lakes, 30% of recreational development lakes, and
5% of natural environment lakes will exceed safe boating capacity.
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Residential Lot Widths for 90th Percentile of the
Lakes above Standards for Boating Safety
140 feet
240 feet
175 feet
190 feet
If the management objective was that only 10% of the lakes should exceed safe boating standards, then
standard lot widths would be:
140 feet for large general development lakes
175 feet for small general development lakes
190 feet for natural environment lakes
240 feet for recreational development lakes.
The end.
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