RESTORATION AND MANAGEMENT OF LAKES AND RESERVOIRS - CHAPTER 12 docx

12 Plant Community Restoration12.1 INTRODUCTION Because of the vital role plants play in the aquatic ecosystem there is a growing interest in restoringaquatic plant communities.. Aquatic

12 Plant Community Restoration

12.1 INTRODUCTION

Because of the vital role plants play in the aquatic ecosystem there is a growing interest in restoringaquatic plant communities Aquatic plant restoration may: (1) improve fish and wildlife habitat;(2) reduce shoreline erosion and bottom turbulence; (3) buffer nutrient fluxes; (4) shade shorelines;(5) reduce nuisance macrophyte and algae growth; (6) treat stormwater and wastewater effluent;(7) replace exotic invaders with native species; (8) improve aesthetics; and (9) generally moderateenvironmental disturbance Although there is some debate about the proper term(s) — enhance,restore, rehabilitate, develop, restructure — for these efforts (Haslam, 1996; Moss et al., 1996;Munrow, 1999) the essence is to return aquatic plants to areas where they were previously found,

to develop areas where they should be found, or to restructure present plant populations to providethe ecological assets of a healthy macrophyte community For purposes of this discussion, resto-ration is broadly and loosely defined It can mean planting a single species where plants werepreviously extirpated It can mean changing habitat conditions so revegetation occurs naturally Itcan mean restoring diversity to a monotypic, exotic plant community It can mean doing nothingand letting nature take its course In few, if any, cases is an aquatic plant community restored orrehabilitated in the strictest, ecological definition of the terms (Haslam, 1996; Moss et al., 1996;Munrow, 1999; Chapter 1)

Various techniques have been used to restore saline and fresh water marshes, swamps, grasses, and fresh water plants in lakes and streams (Kadlec and Wentz, 1974; Johnston et al.,1983; Orth and Moore, 1983; Marshall, 1986; Storch et al., 1986; Moss et al., 1996) The technologyfor aquatic plant community restoration is quickly developing but presently it is still as much of

sea-an art as it is a science Much more is known about restoring wetlsea-ands, which includes shorelineemergent plants, than is known about restoring submergent communities

Table 12.1 lists decision items for estimating the potential for success or the amount of workinvolved in a plant restoration If the habitat for restoration has most of the items in the right or

“increase success” side of the table, little or nothing other than patience may be needed to restoreplants If most items are in the “decrease success” column, anticipate more work, expense, andpotential for failure The suggested remedies are broad categories They may not be suitable because

of cost, physical limitations, environmental impact, or regulatory or political realities at any specificlocation For instance, drawdown may be physically impossible, prohibitively expensive, or notapproved by regulatory agencies on a natural lake without a control structure Some techniques areuntested Would algicide treatments, a selective plant management technique, temporarily increasewater clarity for macrophyte establishment? Most restoration areas need some remediation or adesirable plant community would be present Remediation and restoration should not be viewed

as a single effort For example, after macrophytes are planted, they may need protection frompredators and waves before they become successfully established and spread Careful selection ofplant material can overcome some habitat limitations Some species are more tolerant of turbidity

or fluctuating water levels, or are able to grow in deeper water than are other species Many of thesuggested remedies are discussed in other sections of this book (e.g., nutrient limitation andinactivation to increase water clarity, drawdown, dredging) or are discussed more thoroughly inthe following sections and in the case histories

Some tests needed to enhance restoration success are simple Secchi depths explain a lot aboutwater clarity and whether algal blooms, benthivorous fish, wind and waves, or heavy powerboatuse causes turbidity Aquarium tests determine sediment seed banks, sediment suitability for plantgrowth, and propagule viability Wind and wave impacts are estimated from local weather summa-ries, a lake map, and observation of plant distribution Simple observation is used to determine

animal and human use (e.g., carp (Cyprinus carpio) spawning, powerboating, bank fishing) Plant

collections determine species occurrence and distribution These tests may not be all that are neededbut they will answer some of the basic questions needed for a successful restoration

Aquatic plant restoration is discussed based on the level of effort needed to complete a project.The least effort method is “doing nothing,” followed by habitat protection and alteration, and finally

by active establishment In reality all three might be needed in a single project Habitat may need

to be altered before any plants will grow After alteration, doing nothing for a growing season ortwo determines if natural revegetation will occur If natural revegetation occurs, the additional costand time-consuming effort of planting may not be needed If this is not the case, planting is needed

to increase desirable species, diversity, or to revegetate difficult areas Even after successful plantestablishment, further efforts are usually needed to protect the plant community For instance,herbivory may be a problem or other aquatic plant management techniques may be needed tocontrol nuisance macrophytes

12.2 THE “DO NOTHING” APPROACH

There is evidence that aquatic plant management techniques such as harvesting and herbicidaltreatment favor rapidly reproducing, aggressively growing species — the weeds (Cottam andNichols, 1970; Nicholson, 1981; Bowman and Mantai, 1993; Doyle and Smart, 1993; Nichols and

TABLE 12.1

Decision Items for Assessing Plant Restoration Potential and Suggested

Remediation Techniques

Factors for Assessing Plant Restoration

Potential Decrease Success Increase Success Remedies a

Water clarity Turbid water Clear water during most of

growing season

1, 2, 3, 4, 12 Sediment characteristics

Density Low density Moderate to high density 2, 6, 7

Organic matter content High Moderate to low 2, 6, 7

Environmental energy (current, waves, etc.) High Low 4, 9

Water

Plant population

Non-desirable species Abundant Few or none 11, 12, 13

a Types of remedies: (1) nutrient limitation, (2) drawdown, (3) fish population manipulation, (4) physical barriers, (5) aeration, (6) shallow dredging, (7) sand blanket, (8) predator population control, (9) slow-no-wake or no-motor regulations, (10) stabilize water level, (11) macrophyte planting, (12) selective plant management, (13) do nothing.

Lathrop, 1994) Plant succession is continually “set back.” So what can be done? — “do nothing”and hope that natural successional trends will re-establish a diverse community of non-weedy,native species The advantages of doing nothing are that the developing plants are from local sourcesand they are adapted to local conditions so they may have the best chance for survival The technique

is inexpensive and plant succession is not continually “set back” so the community that developsmay be the most stable for existing conditions The disadvantages are that it may take a long timefor a plant community to develop or change, especially if the area was not previously vegetatedand/or if there is no natural source of propagules in the area (Smart and Dick, 1999; Nichols, 2001).Little is known about the dynamics of aquatic plant community change so the results are unpre-dictable and doing nothing may be politically unpalatable There is also evidence that plantcommunities can change from a diverse native community to one dominated by exotics withoutcause or manipulation For example, the plant community in the Cassadaga Lakes, New York, withlittle or no management, changed from one dominated primarily by native pondweeds to onedominated by curly-leaf pondweed and Eurasian watermilfoil — an obvious case where doingnothing did not work (Bowman and Mantai, 1993) In some locations the “do nothing” approach

is codified by designating areas as critical habitat, which is a regulatory approach to protect areas

so restoration is not needed or can occur naturally

12.2.1 CASE HISTORY: LAKE WINGRA, “DOING NOTHING”

Lake Wingra is a 137-ha, shallow (mean depth of 2.4 m), urban lake located in Madison, Wisconsin.The University of Wisconsin Arboretum and city parkland surrounds it so, unlike many urban lakes,

the shoreline is not heavily developed Around 1900, Equisetum spp., Zizania sp., Typha latifolia,

T angustifolia, and Scirpus validus were common species of the broad marshes surrounding the lake Dense growths of Chara spp were interspersed between the emergents Wild celery (Vallis- neria americana) was particularly abundant There were at least 34 species of aquatic plants in

Lake Wingra at this time and the lake bottom was completely vegetated (Bauman et al., 1974).During the first half of the 20th century dredging, filling, water-level fluctuation, and the introduc-tion of carp decimated the aquatic vegetation Macrophytes were sparse from the late 1920s through

1955 (Bauman et al., 1974) Eurasian watermilfoil (Myriophyllum spicatum) invaded Lake Wingra

in the early 1960s and by 1966 it was dominant and replaced the remaining native species From

the mid-1960s to the early 1970s M spicatum was present in dense stands in shallow areas of the

lake The milfoil stands declined in 1977 (Carpenter, 1980) Except for some minor plant harvestingaround a public boat livery and a swimming beach, there was little or no management on LakeWingra after the early 1950s when carp were seined to low levels

The reason for the milfoil decline was never adequately determined Between 1969 and 1996species number increased slightly, Simpson’s (1949) diversity increased dramatically from 0.52 to

0.88, the relative frequency of exotic species (M spicatum and Potamogeton crispus) dropped from

68.9% to 35.9%, and the relative frequency of species sensitive to disturbance (Nichols et al., 2000)increased from 0.1% to 19.1% (Table 12.2) The maximum depth of plant growth increased from

2.7 m to 3.5 m Wild celery and Potamogeton illinoensis returned — they were last reported in the

lake in 1929 The vegetation recovery in Lake Wingra was more dramatic than in the other Madison,Wisconsin area lakes that had a similar history of an Eurasian watermilfoil invasion (Nichols andLathrop, 1994) but are more heavily managed

The vegetation recovery in Lake Wingra was neither planned nor predicted so why did thevegetation recover? No reason can be given with absolute certainty because the results are obser-vational and were not part of an experimental program Historically Lake Wingra had a rich aquaticflora and even at the height of the milfoil invasion there were more than 15 species of plants inthe lake Dane County, Wisconsin also has 24 lakes greater than 30 ha in size so there is an abundantsupply of aquatic plant propagules in the vicinity for invasion and there is probably a seed(propagule) bank in the sediment, although this was never tested After the abundant carp population

was seined to low levels in the early 1950s they never regained their former abundance The lake

is shallow, with fine, moderately organic, and moderately nutrient rich sediments There has been

no major disturbance of the plant beds due to management activities and there is a “slow-no-wake”boating ordinance on the lake In total, Lake Wingra is an ideal location for aquatic plant growthand given the chance, they returned Eurasian watermilfoil declines occurred in other lakes andnative species are returning (Smith and Barko, 1992; Nichols, 1994; Helsel et al., 1999;) so theLake Wingra experience is not unusual

12.3 THE HABITAT ALTERATION APPROACH

The degradation or decimation of aquatic plant communities often resulted from major habitatalterations Plant communities were lost because of water level increases; wind and wave erosion;actions of benthivorous fish or plant predators; and cultural eutrophication, aquatic plant manage-ment, or other human activities Often a combination of these factors led to the demise of macrophytecommunities (Nichols and Lathrop, 1994) The end result is turbid water and/or high-energyenvironments that are unsuitable for aquatic plant growth Reversing unsuitable habitat conditionsallows vegetation to return Both regulatory and more active approaches involving engineering orbiomanipulation are used to alter habitat The disadvantages to these approaches are that there is

no way of predicting the results and they may be politically unpalatable, especially regulatoryapproaches Restoration may take a long time but experience indicates that revegetation occurs

TABLE 12.2 Comparison of Species Relative Frequencies in Lake Wingra, Wisconsin between 1969 and 1996 a

Plant Species Rel Freq (%) 1969 b Rel Freq (%) 1996

a Does not include emergent species.

bAfter Nichols, S.A and S Mori 1971 Trans Wis Acad Sci Art Lett 59:

107–119.

c Probably Potamogeton illinoensis.

d Species with less than 1.0% relative frequency in either or both sampling periods;

includes Elodea canadensis, Zosterella dubia, and Ranunculus longirostris.

e A modification of Simpson, W 1949 Nature 163: 688.

rapidly once limiting habitat factors are removed An advantage is the plant community that develops

is from local sources so it should be adapted to local conditions Costs and environmental impactsare highly variable, depending on the technique Regulatory approaches like establishing no-motor

or slow-no-wake zones are inexpensive and environmentally benign or beneficial Fencing

“founder” colonies of remaining plants to protect them from predation is of moderate cost structing islands and breakwalls to protect plants from wind and waves, large-scale fish removalprojects, and nutrient reduction techniques are expensive, some costing in the millions of dollars;and they may have moderate to severe environmental impacts, at least over the short-term

Con-12.3.1 CASE HISTORY: NO-MOTOR, SLOW-NO-WAKE REGULATIONS

12.3.1.1 Long and Big Green Lakes: Heavily Used Recreational Lakes in

Southeastern Wisconsin

12.3.1.1.1 Long Lake

Long Lake has a surface area of 169 ha and a maximum depth of 14.3 m A dam installed in 1855raised the natural level of this glacial lake by 2 m This created an extensive littoral zone extendingfrom shore by as much as 120 m before dropping sharply into deep water The Long Lake StateRecreation Area occupies the east shore of the lake and the west shore is developed with permanentand seasonal homes A 1989 survey found that Long Lake had 7,088 boating days of annual use,which corresponds to 41 boating days per hectare per year (Asplund and Cook, 1999) Peak boatingactivity occurs in July, with as many as 60 boats present on some weekends The lake is long andnarrow in a north-south direction, which makes it ideal for water-skiing and inner tubing The lake

has at least 22 species of floating and submerged plants with Chara sp being the most abundant

In May 1997 the Long Lake Fishing Club placed slow-no-wake buoys for approximately 1,500

m along the east shore of the lake The buoys were placed approximately 120 m out from the shore

so the slow-no-wake zone extended from the buoys into the shoreline Two no-motor zones ofabout 125 m each were placed within the slow-no-wake zone Although the restrictions weretechnically voluntary, a concerted effort was made to educate lake users about the importance ofrespecting the special boat-use zones

Asplund and Cook (1999) assessed the submerged macrophyte community in late August of

1997 They found that the large scour (non-vegetated) areas seen in 1995 were almost completely

covered with Chara Scour areas were reduced to as little as 1.5% of the area (Table 12.3) Boattracks were still evident in the no-wake area, but at a much lower frequency This suggests thatboats still uproot plants or cut off stems at no-wake speeds Alternative explanations are thatboaters occasionally traveled through the area at faster speeds or anchors were dragged alongthe bottom No boat tracks were observed in the no-motor plots Sampling found very littlevegetational difference between management areas in terms of overall stand density and canopyheight One can only speculate on the reason, but unprotected comparison areas may havehistorically received less boat use and were in fact protected because boaters avoided the eastside of the lake that was largely a no-wake zone In 1998 the local town board permanentlyestablished a no-wake zone along the eastern side of the lake, but the buoys were placed closer

to the shoreline so that about one-third to one-half the area protected in 1997 was outside theno-wake zone Aerial photography revealed that boat scour and tracks eliminated much of the

Chara that grew in 1997 in this newly unprotected area.

12.3.1.1.2 Big Green Lake

Big Green Lake is large (surface area 2,974 ha) and deep (maximum depth 72 m) However, it has

shallow bays where hardstem bulrush (Scirpus acutus) was an important part of the emergent

vegetation Historical accounts identified five bulrush stands in the lake ranging in size from 3,500

to 255,000 m2 (Asplund and Cook, 1999) The largest remaining stand was about 1,840 m2 in size

in 1997 and appeared to be shrinking

Motorboat activity was thought to be a major factor in the decline of this remaining stand Thesandbar area adjacent to the stand is a popular place for mooring boats and wading To addressthis concern the local town board enacted an ordinance in 1997 to place no-motor buoys aroundthe stand The extent of the stand was divided into three sections and mapped in 1997, 1998, and

2002 using GPS Stem densities were also determined for those years In 1998 the stand size andstem densities appeared to be somewhat greater or at least not shrinking (Table 12.4; Asplund andCook, 1999) By 2002 stand size and stem densities have not increased and may have decreasedslightly (Table 12.4) After 5 years of protection, it appears, at best, that restricting motorboat traffichas slowed the decline of the bulrush bed

12.3.1.2 Active Habitat Manipulation: Engineering and Biomanipulation

Case Studies

12.3.1.2.1 Lake Ripley, Wisconsin: Boat Exclosures

Lake Ripley has a surface area of 169 ha, a maximum depth of 13.4 m, and an extensive littoralarea less than 2 m deep Littoral sediments are very flocculent and easily resuspended due to ahigh percentage of marl Homes ring the lake, there are more than 300 boats docked around the

TABLE 12.3

Comparison of the Percentage of Unvegetated Area in

Protected and Unprotected Areas of Long Lake, Wisconsin

a Vegetation consisted primarily of Chara sp and native milfoils.

Source: After Asplund, T and C.E Cook 1999 LakeLine 19(1): 16.

lake, and on weekends boat use approaches 50 boats on the lake at one time (Asplund and Cook,1997) Historically, Lake Ripley had a diverse plant community dominated by wild celery, pond-

weeds (primarily P illinoensis and P pectinatus), and water lilies (Nuphar variegata and Nymphaea odorata) Eurasian watermilfoil dominated the vegetation in the 1980s but has since declined.

Native species were slow to recolonize areas suitable for plant growth

Motorboats had a major impact on aquatic plants Boat “tracks” or scour lines through theremaining plant beds were visible from aerial photos in areas of high boat traffic (Asplund andCook, 1997) It was not known whether the impact was due to increased turbidity caused byresuspension of bottom sediments, turbulence from boat wakes and prop wash, direct scouring ofthe sediment, direct cutting by motor propellers, or breakage from contact with boat hulls.Asplund and Cook (1997) examined the impact of motorboating on the aquatic plant community

by constructing two solid plastic and two mesh fencing exclosures in the lake that excluded boataccess After a single growing season, species composition was similar between the plots with

Chara sp and Najas marina being the predominant species However, plant growth between the

areas varied considerably The plant growth in the protected areas was not significantly differentbetween those areas protected with mesh or solid fencing The protected areas had about one andone-half times as much area covered, about one and one-half to two times the maximum plantheight, and two to two and one-half times the biomass as the unprotected areas (Table 12.5).Through additional water chemistry testing they concluded that motorboats reduced plant biomass

by sediment scouring and direct cutting of the plants, but not by turbidity generation

Similar exclosures of varying sizes and designs were needed to protect remaining plants fromherbivorous fish, wading or aquatic mammals, and waterfowl in other restoration efforts (Moss et

al, 1996; van Donk and Otte, 1996)

12.3.1.2.2 Big Muskego and Delavan Lakes, Wisconsin: Drawdown,

Benthivorous Fish Removal, and Nutrient Reduction

Big Muskego Lake has a surface area of 840 ha and is very shallow (mean depth is 0.75 m) Adam built in the 1800s flooded this former deep-water marsh The lake is eutrophic and drains apredominantly agricultural watershed of 7,600 ha Before the treatment the submersed plant com-munity was dominated by Eurasian watermilfoil and common carp dominated the fishery Althoughthe lake was well vegetated, with approximately 95% of the area containing vegetation; soft,flocculent and highly organic sediments, carp, wind and wave action, and turbidity limited thegrowth of desirable, native aquatic plants Besides increasing plant diversity, wildlife managerswere interested in increasing the extent of the emergent zone Before treatment cattails were found

at 9.9% of the sampling points and all other emergent species were found at less than 1% of thesampling points

Drawdown (Chapter 13) of Big Muskego Lake started in October 1995 and the water level waslowered by about 0.5 m between December 1995 and July 1996 A channel was excavated topromote further drawdown in mid-July 1996 This caused an additional 0.5 to 0.6 m drawdown

Source: After Asplund, T and C.E Cook 1997 Lake and Reservoir Manage 13: 1–12.

between July 1996 and January 1997 The lake was allowed to refill during late winter and earlyspring 1997 Normal water levels returned by April 1997 Overall, about 13% of the sediment areawas exposed for approximately 1 year, while over 80% of the sediment area was exposed for about

6 months (James et al., 2001a, b) In addition, drawdown concentrated undesirable fish so theywere more easily removed with a piscicide

Prior to drawdown Muskego Lake sediments were very fluid Surface sediments were over90% water, sediment density was low, and organic content of the sediment was very high (morethan 40%) (James et al., 2001a, b) Hopefully, desiccation would consolidate sediments, reducingresuspension potential and turbidity A concern was the effect oxidation of aerially exposed sedi-ments might have on mobilizing sediment organic nitrogen and phosphorus Internal nutrient loadingafter reflooding exposed sediments could stimulate excessive algal blooms that would be counter-productive to macrophyte growth

Lake drawdown effectively consolidated sediments (e.g., increased sediment density) anddecreased organic matter content Mean porewater concentrations of soluble reactive phosphorusand NH4–N initially increased after reflooding but declined markedly 1 year later (James et al.,2001a, b) Macrophyte growth responded to the new habitat conditions Mean macrophyte biomassincreased from pretreatment levels of 150 g/m2 in 1995 to post-treatment levels of 1,400 g/m2 in

1998 This high biomass may have played a role in depleting sediment phosphorus reserves (James

et al., 2001a, b)

The plant community also changed dramatically (Table 12.6) Species number increased from

18 to 25 taxa The relative frequency of emergent species increased from 14.2% to 35.3% The

a Other species include: Carex spp., Ceratophyllum echinatum, Elodea canadensis, Zosterella

dubia, Najas flexilis, Potamogeton nodosus, P pusillus, Sagittaria latifolia, and Zizania aquatica.

They had a relative frequency of less than 1% in both sampling periods.

Source: Data from John Madsen, Department of Biology, Minnesota State University, Mankato.

Personal communications, 2002.

relative frequency of exotic species decreased from 70% to 17% Simpson’s (1949) diversityincreased from 0.61 to 0.88.

The areal extent of the plant community changed very little between pre- and post-treatment.This was not surprising since there was little room for plant community expansion Before treatmentonly about 1% of the area was not vegetated After treatment only about 0.5% was not vegetated.From a wildlife management perspective the treatment was very successful The desired increase

in emergent coverage was achieved and there was a substantial increase in sago pondweed mogeton pectinatus), a prime waterfowl food.

(Pota-Success needs to be carefully defined when planning restorations since results are unpredictableand riparian property owners may not appreciate increased aquatic vegetation An example isDelavan Lake in southeastern Wisconsin It has a surface area of 725 ha, a maximum depth of 16.5

m, and a mean depth of 7.6 m A major rehabilitation in the late 1980s and early 1990s includedefforts to reduce internal and external phosphorus loading; eradicate benthivorous fish, primarily

carp and buffalo (Ictiobus cyprinellus); restock predatory game fish; and temporarily draw down

lake levels Historically Delavan Lake had a rich aquatic flora Surveys done between 1948 and

1975 identified 25 macrophyte taxa (not all in the same survey), but vegetation was declining bythe 1950s In 1955, the Izaak Walton League planted a number of desirable species in the southwestend of the lake because of a concern over the loss of aquatic vegetation In the early 1960s onlyseven species were reported and by 1968 only four species remained The aquatic vegetation for

several years before rehabilitation consisted of a single pondweed species (Potamogeton sp.) and white water lily (N odorata) As expected the diversity and abundance of aquatic plants increased

because of rehabilitation The number of species increased to six in 1990 and 20 in 1993 By 1998,

however, species number decreased to 13 and Eurasian watermilfoil, curly-leaf pondweed (P crispus), and coontail (Ceratophyllum demersum) reached nuisance levels in parts of the lake,

especially in areas less than 3 m deep in the northern and southern ends of the lake and near theinlet and outlet (Robertson et al., 2000) Additional plant management was anticipated and mac-rophyte harvesting and chemical treatment were part of the original rehabilitation plan; but mac-rophyte growth was much greater than expected A total of 5,376 m3 of plant material was harvestedduring the 1997, 1998, and 1999 growing season Heavy macrophyte growth near the inlet waspartially blamed for remobilizing sediment phosphorus that reduced the success of phosphoruslimitation efforts (Robertson et al., 2000) By 2001, 12 submergent or free floating species werefound but the relative frequency of exotic species was 36.7% (Table 12.7)

12.3.1.2.3 Breakwaters of All Sizes

Breakwaters are used to reduce the impact of wind and wave erosion on aquatic plants (Chapter

5) They are used to protect established plants, new plantings, or to make suitable habitat for plantinvasion or community expansion

The simplest breakwaters are wave breaks; V-shaped wave deflectors constructed out of twohalf-sheets of plywood or other suitably sturdy material (approximately 1.2 m by 1.2 m in size).They are joined at an approximately 90° angle and staked to the bottom on the lakeward side ofremaining plants or new plantings (Bartodziej, 1999)

Sandbags containing sediment and rhizomes of reeds (Phragmites australis) and burlap bags

containing sediment and rhizomes of reeds placed inside old tires filled with sand were used to try

to stabilize sediments on Lake Poygan, Wisconsin These plantings eventually failed (Kahl, 1993).Coir (coconut fiber) geotextile rolls, plant rolls, geotextile mats, branch box breakwaters, brushmattresses, and wattling bundles were used as wave breaks and erosions control devises in someMissouri impoundments (Fischer et al., 1999) Coir rolls were 0.4 m in diameter and placed inshallow trenches Emergent species were planted on 0.5-m centers on the shoreward side of theroll A plant roll is similar to a coir roll It is a cylinder of plant clumps and soil wrapped in burlapand placed in a trench The ones used in Missouri were 3 m long Coir geotextile non-woven mats,placed flat and anchored on the reservoir bottom, with emergents planted on 0.3-m centers through-

out the mat was another technique used Brush mattresses and wattling bundles consisted of young

willow (Salix sp.) shoots tied in bundles or in a long roll and staked to the bottom Brush boxes

were similar except the willow shoots were woven between and wired to posts driven into thebottom These techniques are most easily installed in reservoirs under drawdown conditions.The Missouri impoundments project is very recent so the results are inconclusive (Fischer etal., 1999) The Missouri researchers learned that patience is the key Do not expect lush aquaticvegetation covering the entire littoral zone after one year unless you have a small pond and plenty

of time and money Wave action appeared to be the primary limiting factor to initial plant survivaland dispersion The growth of thick algal mats in the protected areas; fluctuating water levels,especially during cold weather; herbivory; and drifting logs and debris that knocked down protectivedevises were also problems

Floating booms of logs or old tires have been used to dampen wave action (see Chapter 5).Probably the most interesting floating devises are the Schwimmkampen (Germany) or Ukishima(Japan) — artificially constructed floating wetlands (Hoeger, 1988; Mueller et al., 1996) They areconstructed on floating platforms that support wetland vegetation They move up and down withfluctuating water levels and improve water quality primarily by dissipating wave action thusreducing shoreline and bottom erosion They provide nursery areas for small fish and crustaceansand in urban areas they have been used for aesthetics by enhancing privacy and dissipating noise.Depending on size, they can be towed to different areas of the lake as needed

One of the larger projects was the Terrell’s Island breakwall constructed on Lake Butte desMorts, Wisconsin Lake Butte des Morts is a 3,587-ha lake with a mean depth of 1.8 m and amaximum depth of 2.7 m Originally Lake Butte des Morts and other upriver lakes of the WinnebagoPool were large riverine marshes Dams constructed in the 1850s raised water levels by about 1 m.Initially they were rich in aquatic vegetation but vegetation decline accelerated from the 1930sthrough the present because of high water levels, extreme flooding, erosion of shorelines and bottomsediments, lake shore development, plant removal, carp, and accelerated nutrient inputs (WisconsinDepartment of Natural Resources (WDNR), 1991) Between 1994 and 1998, 3,245 m of breakwallwas constructed connecting the mainland to a series of small islands and enclosing around 243 ha

TABLE 12.7 Relative Frequency (%) of Aquatic Plants

in Delavan Lake, Wisconsin for 2001 Species Rel Freq (%)

a Other species were Lemna minor and Chara sp.

Source: Data from Kevin MacKinnon, District

Admin-istrator, Delavan Lake Sanitary District, Delavan, WI.

Personal communications, 2002.

of water (Arthur Techlow, WDNR, Oshkosh, Wisconsin, personal communication, 2002) Thebreakwall was constructed of limestone with a planned 3.7 m wide top, 3 to 1 side slopes, and aheight of 0.9 m above the ordinary summer water level It was constructed with only one gap toallow boater access This gap was gated to prevent access by large carp (Figure 12.1) but to allowother fish access for spawning The gap was also built with sufficient overlap to reduce waves.Small islands were also constructed to reduce wind fetch inside the breakwater Waterfowl foodand habitat and a fish spawning area were the main reasons for restoring vegetation to the area.The total cost for everything including feasibility studies, engineering, administration, and construc-tion was approximately 1.7 million (not adjusted to current prices) U.S dollars (Arthur Techlow,WDNR, Oshkosh, Wisconsin, personal communications, 2002).

Vegetation in the area was sampled pre-construction from 1988 to 1994 and after constructionfrom 1999 to 2001(Tim Asplund, Mark Sessing, and Chad Cook, WDNR, Madison, Wisconsin,personal communications, 2002) In 1999 and 2000 other water quality parameters were comparedbetween the area enclosed by the breakwall and open water areas The percent frequency ofvegetated sampling points increased from 15% before construction to 39%, then 55%, then 99%from 1999 to 2001 (Figure 12.2); species numbers also increased The plant community compositionchanged dramatically (Table 12.8) Sago pondweed and wild celery were the dominant pre-con-

struction species making up over 60% of the relative frequency After construction elodea (Elodea canadensis) was the dominant species with a relative frequency varying from 34% to 52%, while

the combined relative frequency of sago pondweed and wild celery varied from 11.6% to 17%.For plant restoration the breakwall is working Although the importance of sago pondweed andwild celery, very desirable waterfowl food plants, declined in the plant community their abundanceincreased on an absolute basis During 1999, the overall water clarity improved inside the breakwallbut it was lower than mid-lake sites during the end of July and into early August (Tim Asplund,WDNR, personal communication, 2002) In the fall, turbidity and suspended solids declined, greatlyimproving water clarity and light penetration inside the breakwall It appeared that the quiescentenvironment created by the breakwall resulted in greater algae blooms during the summer compared

to the rest of the lake, but lower inorganic sediment resuspension throughout the year (Tim Asplund,WDNR, personal communication, 2002) Water quality data for 2000 show higher water clarity,

FIGURE 12.1 Carp exclusion gate at Terrell’s Island restoration area The center of the gate is spring loaded

so that a boat pushes it down when entering or leaving the area

FIGURE 12.2 Aquatic plants growing behind the breakwater at the Terrell’s Island restoration area, August

2002

TABLE 12.8

Comparison of Species Relative Frequencies at Terrell’s Island Area before

and after Breakwall Construction

Species

Average Rel Freq (%), 1988–1994, Before Construction

Rel Freq (%), After Construction

a Other species were Nitella sp., P natans, P nodosus, and unidentified species.

Source: Data from Tim Asplund, Mark Sessing, and Chad Cook, WDNR, personal communications,

2002.

lower fertility, and fewer algae at stations within the breakwater when compared to stations in theopen lake The suspended solids within the breakwater come primarily from algae while those inthe open lake are mostly non-organic (Mark Sessing, WDNR, personal communication, 2002).Wind and wave action inside the breakwater are still sufficient that erosion of the constructedislands is a problem.

Artificial islands were constructed in pools of the upper Mississippi River between Wisconsinand Minnesota The objective for island construction was to improve habitat conditions for aquaticplants by reducing wave resuspension of fine materials, thereby improving light penetration inlocalized areas Aquatic vegetation, mainly wild celery, became established on the down-streamside of the islands but detailed results are not available (Janvrin and Langreher, 1999)

12.4 AQUASCAPING

Aquascaping — a term describing the planting of aquatic and wetland plants — is landscaping inand around water (see Chapter 5 for additional discussion) The vision of landscaping may notseem appropriately applied to lakes or reservoirs but natural landscaping is a term that has beenused for many years in terrestrial systems, which is applied to planning, restoring, and managingextensive areas such as prairies, savannahs, and woodlands Admittedly, aquascaping is oftenapplied to small projects like water gardens and sedimentation ponds but good planning, cultural,and management principles are needed regardless of the size of the project

The advantage of aquascaping is that with success, you get what you want where you want it

In many areas, such as the southeastern and western United States, active revegetation may be theonly option Reservoirs in these regions are often constructed in areas that lack natural lakes andthey may be remote from any aquatic plant populations that could serve as a propagule source As

a result these reservoirs have no aquatic plant seed bank and receive only limited inputs of seed

or other plant propagules If they are colonized it is often with nuisance species that are adaptedfor exploiting disturbed conditions (Smart and Dick, 1999) The disadvantages of active revegetationare that it is expensive, labor intensive, and can easily fail Plant restoration makes a good volunteerproject so some of the expense for plant material and labor can be minimized (Figure 12.3).Aquascaping matches plant material with the habitat at specific locations within the restorationarea Water chemistry, water depth, substrate, turbidity, wave action, and human or animal uses areimportant considerations when developing an aquascaping plan and selecting plant material Alsoimportant is selecting plants that provide the desired function Is the restoration being done toprevent shoreline erosion, to provide fish or wildlife habitat, to intercept nutrients, to be aestheticallypleasing, or for some other reason? A final plan should include a map(s) showing habitat charac-teristics, species locations, plant densities, planting methods, and protective measures Specificquestions to ask include:

1 What are the habitat limitations of the site(s) within the restoration area?

2 What plant species have the desired properties needed for the restoration? Will theythrive in the physical and chemical habitat? Are they able to withstand wind, waves,turbidity, human and animal traffic, or drawdown? Are the plants good waterfowl food,fish or waterfowl habitat, aesthetically pleasing, or whatever functional characteristicsare wanted?

3 Are the desired species readily and locally available at a reasonable price?

4 What is the best way to propagate the plants for existing conditions?

5 Do the selected species have good reproductive potential? Once established can the plantsgrow and reproduce well enough to maintain and increase the population?

6 Are the selected species native to the region?

7 Do the selected species have weedy tendencies? Will any become a nuisance in the future?

8 How large a population is needed to ensure a viable stand despite losses from herbivores,pathogens, poor reproductive success, wind, waves, turbidity, competition with otherspecies, and climatic conditions?

9 Where will each species be located and in what densities?

10 What habitat remediation techniques are needed?

11 What cultural and protective measures are needed?

The answers to these questions are not simple Many introductions, reintroductions, and transplants

of species fail because innate species characteristics, interactions between species, or habitatcharacteristics are not considered (Botkin, 1975)

Even if a species formerly grew in an area, the habitat might be altered so that it is no longersuitable for that species or for plants in general As discussed earlier (Table 12.1), habitat remedi-ation may be needed for any plants to grow However, careful selection of plant material canovercome some habitat limitations As an aid to plant selection, Table 12.9 provides information

on median depth, substrate preference, and turbidity tolerance for a number of species Table 13.1

(Chapter 13) of this volume shows how selected aquatic plants respond to drawdown Consult thistable if water level fluctuation is a concern in the rehabilitation area

Although many aquatic plants are broadly tolerant of water chemistry conditions, this is notalways the case The more information that is known about the plant material, the better the potentialfor a successful restoration There are regional studies for North America, Europe, Japan, andprobably other areas that provide aquatic plant distribution with regard to a variety of chemicalparameters (Moyle, 1945; Seddon, 1972 Hutchinson, 1975; Beal, 1977; Pip, 1979, 1988; Hellquist

FIGURE 12.3 Volunteer planting emergent plants around constructed islands behind the Terrell’s Island

breakwater Twine will be strung between stakes to prevent predation of new planting by large waterfowl likegeese and swans

TABLE 12.9

Habitat Preferences of Selected Lake Plants a

Species Median Growth Depth b Substrate Preference c Turbidity Tolerance d