Management of Aquatıc Plants

Transcription

1 Management of Aquatıc Plants College of Agricultural Sciences 1

2 Under ideal conditions, limited amounts of aquatic vegetation add to the aesthetic beauty of the pond and the ecosystem balance among the pond s aquatic life.

3 Introduction If you build it, they will come. That can be said of ponds and aquatic plants. Just as grass and weeds will grow quickly on exposed soil, aquatic plants and algae will colonize new ponds in short order. While these plants and algae can grow abundantly and interfere with various pond uses, they also provide many benefits to the pond if their growth is limited. The first step in assessing the importance of aquatic plants to your pond is to determine your intended primary use(s) for the pond. Ponds are frequently used in several ways to satisfy more than one objective. For example, having water available in the pond for fire protection may satisfy one objective without interfering or conflicting with other objectives such as swimming or fishing. Multiple-use ponds are fine as long as the uses are compatible. When conflicting or incompatible uses are desired, it is necessary to assign priorities to the owner s objectives. For example, the objective of providing an area for swimming may conflict directly with the objective of having water available for If you build it, they will come. irrigation. Irrigation needs may lower the water level to a point where swimming is not possible at a time when swimming is most wanted. For this reason, you should list and prioritize specific objectives for your pond. This publication is intended to help pond owners understand the importance and benefits of aquatic plants and algae. When plant and algae growth reach nuisance levels, pond owners have many options to restore balance to the pond ecosystem. Too often, pond owners reach for quick fixes like aquatic herbicides. If not used properly, herbicides may eliminate too much vegetation or beneficial plants along with the targeted weeds. Herbicides are just one method of controlling unwanted plants and algae. Nonchemical methods may provide longer and more permanent control and should be considered when developing a pond vegetation management strategy. Information in this publication will help pond owners properly identify aquatic plants, understand their benefits, and choose appropriate control strategies (where necessary) to minimize damage to the pond ecosystem. 1

4 The Role of Aquatic Plants in Natural Pond Ecology Ponds are most healthy when there is a balanced ecosystem of insects, plants, fish, and animals otherwise known as a food web. A balanced food web includes some planktonic algae and aquatic plants at the top, which serve as a food source for small zooplankton and aquatic insects. The zooplankton and insects in turn provide food for the smallest fish in the pond. These then become prey for larger fish, which finally may be taken by raccoons, bears, or fishermen. Under ideal conditions, pond plants also provide oxygen to the water during the day as a result of photosynthesis. Some of this oxygen is then used to support the same plants during nighttime respiration. In the winter, water temperatures get much colder and ice may cover the top of the pond for an extended period of time. Most aquatic plants become dormant or produce seeds and die before winter, but a few plants are capable of remaining green and growing all winter long. These plants are usually able to get enough light through Aquatic plants serve as important habitat for insects and other pond life. the ice to cause some photosynthesis and help support pond life during the harsh winter conditions. The optimum amount of aquatic vegetation for a given pond is difficult to identify because it depends on the preferred use of the pond. Generally, aquatic vegetation should cover 20 to 40 percent of the pond area (bottom and top) to provide a healthy pond ecosystem. The smaller percentage is preferable for boating, irrigation, and swimming, while the larger percentages are best for ponds intended primarily for fishing recreation. Benefits of Plants and Algae A recent survey of Pennsylvania pond owners found that nearly two-thirds felt that aesthetic beauty was the main reason for building a pond on their property. Part of the picturesque view of a pond includes at least some aquatic vegetation and the beauty it can impart. The aesthetic beauty of water features with aquatic plants is one of the main reasons backyard ponds have become so popular in the last decade. Besides their aesthetic beauty, plants and algae provide many benefits to the pond ecosystem. Both the roots and leaves of aquatic plants can reduce muddy water conditions. The roots of submerged and floating plants stabilize the bottom sediments while the dense leaves of submerged plants trap floating debris and sediment. The plants also remove nutrients from the water column, thereby reducing the availability of nutrients to cause nuisance algae blooms. The nutrients are stored in the plants until fall when much of the nutrient load falls to the pond sediments as the plants die. Around the edge of the pond, the roots of emergent plants also stabilize the pond banks and reduce erosion. Under the water surface, the dense stems, roots, and leaves of aquatic plants serve as excellent habitat for insects and invertebrates including snails, leeches, and crayfish. The plant structure traps organic material and promotes the growth of periphyton (attached algae) and attracts zooplankton (barely visible aquatic animals) that serve as important food sources for 2

5 these scavengers. Aquatic insects also perch on aquatic plants and filter the surrounding water for food. The benefit of aquatic algae and plants to the pond fishery cannot be overestimated, especially since more than 50 percent of pond owners in Pennsylvania consider fishing recreation a major use of their ponds. A healthy and well-balanced fish population is more attainable if significant aquatic plant beds exist in the pond. Many pond fish use weed areas as nesting beds to provide cover for their young. Some feed directly on the plant leaves or the insects resting on the leaves. All fish use the cover provided by vegetation to stalk prey. Small fish hide from larger fish in underwater plants to prevent predation. As a result, the amount and type of vegetation will affect the fish population structures. Too much vegetation will allow many young fish to survive, making it difficult for larger fish to grow. Too little vegetation allows predator fish to easily capture smaller fish. In this case, fish may grow quickly until they consume all the smaller fish in the pond. In addition to fish, other types of wildlife thrive in the pond environment. In fact, pond owners are often surprised at the number and diversity of wildlife that is attracted to a pond, especially if the pond is constructed in an area that is otherwise lacking water resources. Part of this attraction is the type of aquatic plants present in the pond. Various aquatic plants are a vital component in the diet of ducks and geese. They not only eat the plants themselves but also devour the insects that live on the plant surfaces. Emergent plants around the pond edge also serve as important nesting areas that provide dense cover for waterfowl. Various mammals also use aquatic plants. For example, muskrats prefer ponds with cattail beds for food and cover. Many pond owners are also surprised to see whitetail deer occasionally feeding on various pondweed species in and around the pond. Last but not least, amphibians and reptiles such as turtles, salamanders, and snakes rely on pond plants for food and shelter. Overabundant Aquatic Plant Growth Many of the same benefits provided to ponds by optimum levels of plant growth can be taken away by overabundant plant growth. Nuisance plant and algae growth can ruin the aesthetic appeal of the pond, degrade water quality, and even kill aquatic life. Unfortunately, nuisance plant growth is a common complaint among pond owners in Pennsylvania (Figure 1). Pond Owners (Percent) Healthy pond fish populations depend on aquatic vegetation for food, cover, and reproduction. Plants/ Nuisance Leaks Water Fish algae wildlife quality kills Figure 1. The prevalence of various pond problems based on a survey of Pennsylvania pond owners. 3

6 Overabundant plant and algae growth ruin the aesthetic beauty of the pond. Aquatic plants and algae grow abundantly in certain settings for many reasons. The simplest explanation is an overabundance of nutrients, primarily phosphorus and nitrogen. A pond begins with mostly water, few nutrients, and little aquatic life. As a result, a newly created, deep, springfed pond may have little life of any kind because of the lack of nutrients available to support pond life. Over time, the pond accumulates nutrients in a process known as eutrophication. The addition of nutrients stimulates increased growth of algae, plankton, and aquatic plants, which grow, mature, and die. Their remains decay and the nutrients are released back into the water of the pond to keep the cycle going. A shallow, nutrient-rich pond exposed to sunlight with little water flowing through it will be teeming with algae and aquatic plants. Eventually, though, material that resists decay will accumulate and the pond will fill up and become a bog or wetland. This process of conversion to a bog or wetland can happen in a decade or may take centuries. Humans greatly accelerate the eutrophication process through landuse activities. Nearby fertilizer applications, septic systems, urban runoff, animal manure, erosion, and waterfowl can all add significant amounts of nutrients to a pond. Too many plants are discouraging to the pond owner and are also detrimental to the pond ecosystem. For example, a pond completely covered with water lilies will shade the pond enough to prevent other vegetation from growing under the water. The shade will also be sufficient to reduce the growth of planktonic algae that serve as the base of the pond food web. The resulting situation is a pond that is very unproductive for anything besides water lilies. Similarly, a pond covered with duckweed or watermeal will also shade out any life beneath the surface. In some cases, duckweed and watermeal may grow so quickly that they cause submerged plants to die prematurely due to shading. The decay of the dead submerged plants can result in reduced dissolved oxygen and the death of fish and other pond life. Complete coverage of the pond by floating plants can also eliminate oxygenation of the water and kill pond life by maintaining a complete separation of the water surface from the atmosphere. Important Pond Measures and Features Related to Aquatic Plants Strategies to manage aquatic plants and algae require an understanding of several features related to the pond structure. Some of these are basic measurements or observations that are rarely done by pond owners but can be easily accomplished. You might be surprised what you learn about your pond in the process. Watershed and Water Source The pond watershed is an important concept that must be understood to determine the sources of nutrients that may be causing excessive plant growth. The watershed includes the area of land surrounding the pond that contributes water to it. Identifying the pond watershed is important because anything that occurs within this area can impact the pond. Locating a pond in an undisturbed area and minimizing disturbance and land-use changes within the 4

7 pond watershed are important components of protecting a pond. A pond s watershed is determined by the source of water feeding the pond. Ponds that collect surface drainage will have a simple watershed boundary that includes all the land that drains surface water toward the pond. Ponds that collect stream or spring water will have more complex and larger watershed boundaries that include all the area that drains into the respective stream or spring that feeds the pond. The source of water feeding the pond can be important to the resulting growth of plants and algae in the pond. A pond with a continuous supply of water is almost always going to be a more satisfactory pond than one with an intermittent water supply. The nutrient conditions in a pond with a continuous overflow are likely to be better because excess nutrients will leave with the overflow water. In contrast, a pond having intermittent flows only has a chance to purge excess nutrients during storm events. Such ponds are prone to accumulate nutrients resulting in excessive plant growth much more rapidly than their overflowing cousins. Pond water can be tested for nutrients like nitrate and phosphate to determine if excessive levels are accumulating in the pond. Land-use activities that occur near the pond or within the watershed of the pond source (spring, stream, etc.) will largely determine the amount of nutrients that enter the pond and the resulting amount of plant and algae growth. Identify and protect the land areas directly adjacent to the pond and the land areas surrounding the water sources that feed the pond. Special care should be taken to avoid polluting activities such as applying fertilizers and animal manures or placing septic systems around the pond and its water sources. Pond Surface Area The importance of getting an accurate measurement of your pond surface area cannot be overestimated. The majority of pond owners visually estimate their pond area, which usually results in an overestimate of the true pond surface area. Rather, the pond area should be calculated based on some simple measurements. The effort necessary to estimate pond surface area is directly related to your pond s shape and uniformity. The simplest method using basic equations for common shapes can be applied if your pond closely resembles a circle, square, or rectangle in shape. The area of a circular pond can be estimated by measuring the distance around the pond shoreline in feet. Square the shoreline distance and divide by 547,390 to get the pond area in acres. For example, a pond that is 450 feet around the shoreline would have an area of 0.37 acres [(450 feet) 2 547,390 = 0.37 acres]. The area of a rectangular or square pond is estimated by simply measuring the length and width of the pond sides in feet. Multiply the length by the width to get the square feet of surface area. This value can be converted to acres by dividing by 43,560 square feet per acre. So, a pond that measures 150 feet long and 100 feet wide would have an area of 0.34 acres (150 feet x 100 feet = 15,000 ft 2 or 0.34 acres). Most ponds have an irregular shape for which the surface area cannot be adequately estimated using the formulas for common geometric shapes. Three methods can be used in this case depending on the degree of accuracy you desire. Keep in mind that the accuracy of your pond surface area estimate may be very important, especially for the safe use of aquatic herbicides. The three methods are described in order from least to most accurate. You should strive to use the most accurate method that you can reasonably accomplish. Nutrient levels in pond water can be easily determined using test kits available at most pet stores. Land uses near the pond and within the pond watershed can cause excessive aquatic plant growth. 5

8 80' 20' 108' 48' 88' 46' 134' 163' 137' Figure 2. An irregular-shaped pond broken into six trapezoids for estimation of pond surface area. Handheld GPS units are one method to measure pond area. 43' 70' 42' 159' Average Length and Width Method Take numerous measurements to determine the average length and width. Make certain you get both the longest and shortest distances in calculating the average length, as well as the widest and narrowest distances for determining the average width. The more measurements you make, the more accurate your result will be. The area is then calculated by multiplying the average width by the average length. If you do your measurements in feet, your result will be in square feet. You can convert square feet into acres by dividing it by 43,560 square feet per acre. Depending on the number of width and length measurements you make, the final area will probably be within about ±20 percent of the actual pond surface area. Multiple Trapezoids Method A more accurate method to determine the area of an odd-shaped pond is to divide the pond into multiple trapezoid shapes. A new trapezoid is defined anywhere the shoreline makes a rapid change in direction. Figure 2 shows an irregular pond shape divided into six trapezoids (shown in dotted lines). Note that instead of horizontal transects, this method requires measuring the distance between each vertical transect. This is most easily done during winter when the pond is frozen and the transects can be easily laid out and measured. This method requires more measurement and effort, but the final area estimate will probably be within about ±5 to 10 percent of the actual pond area. For the pond in Figure 2, multiplying the length and width of each trapezoid and then summing the area for all six trapezoids results in a pond area of 34,792 square feet, or about 0.80 acres. Global Positioning Systems (GPS) Handheld GPS systems have become quite common over the past five years as they have become more affordable. They are now routinely used for outdoor recreation (hunting, hiking, camping, etc.) and navigation. GPS units allow you to determine your exact location on Earth using multiple satellites in space. Various locations, or waypoints, can be stored in the GPS unit for use with mapping software that either accompanies the unit or can be purchased separately. The software can connect the waypoints and calculate the area inside the resulting shape. You can estimate pond surface area by walking the perimeter of the pond and stopping at various waypoint locations along the pond shoreline. If waypoints are stored at each location where the pond shape changes, the resulting area will be extremely accurate, probably within 1 percent of the actual pond area. Even if you do not own a GPS system, friends or family members that enjoy outdoor recreation may own a unit that you can use to estimate your pond surface area. Pond Volume The volume of water in ponds is often expressed in units called acre-feet. An acrefoot represents one surface acre that is one foot deep. To calculate the acre-feet of water in a pond, you ll need the surface area in acres as calculated above and an average depth of water in the pond. For a typical bowl-shaped pond, the average depth can be estimated as 0.4 times the maximum depth. So, a pond with a maximum depth of 12 feet would have an average depth of about 4.8 feet. A more accurate method for calculating average depth is to make many measurements and calculate an average. This is most often done by measuring the pond depth along two transects one along the width and one along the length. Make sure to pick transects that represent the shallow and deep portions of the pond. Depths can be measured easily from a canoe or boat using a weight and a string marked in feet. The more depth measures you make, the more accurate your final average will be. An even better way to calculate an average pond depth is to divide the pond into numerous (at least four) subareas (much as we did in the trapezoid method). Take at least one depth within each of the subareas and use these to calculate the overall average pond depth. This method is especially good if the pond bottom is irregular rather than bowl shaped. For the pond example 6

9 given in Figure 2, water depths measured in each of the six trapezoids resulted in an average pond depth of 4.5 feet. Multiplying this depth by the area of the pond in acres provides the pond water volume in acrefeet (4.5 feet x 0.80 acres = 3.6 acre-feet). Residence Time The residence time of a pond measures the average length of time it takes for a molecule of water to pass through the pond from its entry to the overflow pipe. Knowing this characteristic of your pond may be critical, especially for the use of some herbicides. In some cases, herbicides will not be effective unless they are present in the pond water for some period of time. For example, some herbicides suggest thirty days of contact time with the targeted plant to achieve effective control. If the residence time of a pond is only seven days, using this herbicide would not be successful in achieving control. The residence time is easy to calculate. Simply calculate the pond volume in acrefeet as described above and measure the rate that water leaves the pond in gallons per minute (gpm). The outflow can be estimated using a simple bucket and stopwatch to catch water leaving the pond through the outlet of the overflow pipe. The residence time in days can be calculated as follows: residence time = 226 x [pond volume] overflow rate For example, a one-acre pond with an average depth of 5 feet and an overflow rate of 10 gallons per minute would have a residence time of 113 days [226 x (5 acre-feet) 10 gpm = 113 days]. Other Pond Characteristics That Affect Plant Growth Numerous physical features of the pond are important in affecting the amount and diversity of aquatic plant and algae growth. You should inspect each of these pond features annually to determine if changes are needed before resorting to other plantcontrol strategies. Pond Depth and Slope Most plant and algae growth begins in less than 3 feet of water. This water depth allows sufficient sunlight to penetrate to the pond bottom to allow plant growth to begin from the sediment. This is true of all kinds of aquatic plants, including submerged, emergent, floating, and algae. Minimizing the area of the pond that has less than 3 feet of water will minimize the area that can be colonized by plants and algae. This is most easily done during pond construction by shaping pond banks to have a 1:3 bank slope or greater (i.e., a water depth of at least 3 feet at a point 9 feet from the shoreline). As the pond fills in over time, pond depths will decrease, leading to greater plant growth. Dredging can be used to restore deeper water and reduce plant growth. Overflow and Drain Pipes Most ponds have a vertical overflow drain pipe that controls the level of the pond water. This L-shaped pipe moves water and associated nutrients under the dam and out of the pond to a receiving stream. The overflow pipe is sized based on the pond s drainage area, inflow, and water-storage characteristics. It is especially important to inspect the overflow pipe and remove debris in or near the pipe. Obstructions of this pipe may result in increased retention of water in the pond and greater sediment buildup on the pond bottom. Blockage of the overflow pipe may also cause increased erosion and sedimentation from bank sediments. Depending on the construction, a drainpipe may also be installed in the pond to allow for easy manipulation of the pond water level (called drawdown ), which can be helpful in controlling plant growth around the edges of the pond. Steep slopes along pond banks will prevent most aquatic plant growth. An annual pond inspection might reveal structural problems (such as a clogged overflow pipe in this picture) that can be quickly fixed before they cause serious problems. 7

10 Plankton algae Filamentous algae Chara Nitella Leafy pondweed Types of Aquatic Plants and Algae Successful control of aquatic plants and algae always begins with accurate identification of the plants that exist in the pond or lake. Dozens of aquatic plant and algae species occur in Pennsylvania some are unique and easy to identify, while others are very difficult to accurately identify. They may change their appearance at different times of the year and many do not have conspicuous flowers or seeds to assist with identification. All aquatic plants can be separated into one of four categories: algae, submerged aquatic vegetation, floating plants, and emergent plants. Algae Algae occur in all ponds and frequently grow to nuisance levels due to excessive amounts of phosphorus and nitrogen in the pond water. In fact, surveys of pond and lake owners in Pennsylvania have found that algae are the most common nuisance aquatic plant. Algae are important to the pond ecosystem, providing food for insects that are fed upon by fish and other pond wildlife. However, excessive growth of algae can ruin the aesthetic appeal of the pond and also have devastating effects on pond life when it dies in the fall of the year. Algae occur in three different types plankton, filamentous, and an attached branched form. Plankton algae (phytoplankton) are the minute, single-celled suspended types that usually make the water pea-soup green, reddish, or brown. Ponds with excessive plankton algae will usually have clear water during the cold, winter months, but the water will quickly cloud up during spring and summer as plankton algae grow in response to warm water. The exact species of plankton algae in a pond can only be identified using a microscope. Filamentous algae are the most common algae complaint among pond and lake owners. These algae begin to grow on the bottom of the pond, usually in shallow water less than 3 feet deep. As the algae grow, they produce oxygen, which becomes trapped in the filaments, causing the algae to float toward the pond surface. Once enough oxygen becomes trapped in the algae, a large mat will break loose and spread across the surface. Although all filamentous algae begin to grow in shallow water, they can quickly cover the entire pond surface as mats break loose and become free floating. Filamentous algae are easily distinguished from all other plants and algae, but a microscope is usually necessary to identify the exact species. Attached branched algae look very much like a plant. They are anchored to the bottom just like a submerged plant, but they have no true root system. Two common attached branched algae are Chara and Nitella. Chara usually grows in ponds and lakes with hard water in areas underlain by limestone. It is gritty to touch and has a skunklike odor when crushed. Nitella is soft and usually found in higher elevation ponds and lakes with soft water. It is difficult to distinguish from several rooted, submerged aquatic plants. Submerged Aquatic Vegetation Submerged plants are the most diverse group of aquatic plants with many special features. They generally have submerged leaves that are flexible and small to reduce drag from underwater currents. The leaves tend to be buoyant with air vacuoles that allow them to capture the maximum light in the water column. The leaf surface is usually thin and without a waxy surface to allow for gas exchange from the surrounding water. Many submerged plants have multiple types and shapes of leaves (submersed and floating) to maximize their ability to capture energy from sunlight, making them difficult to identify. The stems of these plants are flexible and buoyant to allow the plant to float well within the water column. Stems also often contain chlorophyll to assist the plant in capturing the limited sunlight under the water. Most submerged aquatic plants grow in shallow water less than 3 feet deep where sunlight penetrates to the bottom of the pond. A few plants have the ability to grow in dimmer light conditions in very deep water. 8

11 Submerged plants have very diverse roots that allow them to grow among other aquatic plants, maximizing diversity. Some submerged plants prefer thick muck layers, while others prefer a sandy or gravel bottom. They also have a wide variety of reproduction methods. Some are annuals that die each year and regrow by seeds the following year, but most rely on continual, spreading growth from rhizomes or roots. A few even remain green all year long in a reduced growth state. In most cases, the flowers and seeds of submerged plants reach the surface of the pond or even grow on stems above the pond surface. Pictured on these pages are some of the most common submerged plants found in Pennsylvania ponds and lakes. See the invasive plants section on page 10 for information on other submerged plants that are not native to Pennsylvania. Pondweeds There are more than two dozen species of pondweeds in Pennsylvania. Most are native aquatic plants that are beneficial to the pond ecosystem, especially serving as habitat for fish and other aquatic life. A few, such as leafy pondweed (left), can grow abundantly and interfere with pond uses. Elodea This common aquarium plant is usually dark green and grows densely with whorls of two or three leaves that become more crowded near the tips of the stems. This plant prefers to grow in clear, spring-fed ponds with fine, organic sediment. It is one of the few aquatic plants that remain green during the winter. Elodea spreads primarily through stem fragments. Coontail Named because of its similarity to a raccoon s tail, coontail has whorls of many fine leaves. It often grows to nuisance levels because it can tolerate low light levels in deeper portions of the pond. It does not have true roots, so it is often free floating or loosely attached to bottom sediments. As does elodea, coontail can also overwinter as a green plant and reproduces mostly through stem fragments. Naiad Also known as bushy pondweed, naiad has fine leaves that are arranged in whorls around the stem. The leaves are brittle and will often fall from the stem if the plant is handled. This plant usually prefers sandy or gravel substrate and can grow in very deep water. Naiad produces seeds and dies each fall with growth the following year coming entirely from the deposited seeds. During the summer, naiad can spread quickly from stem fragments. Bladderwort This dense-growing plant has fine leaves arranged around stems that end with a small bladder, which makes this plant easy to identify. Bladderwort is most common in northeast Pennsylvania in acidic ponds and lakes, where it often occurs as a freefloating plant. Floating Aquatic Plants As the name implies, floating aquatic plants have most or all their leaves floating freely on the pond surface. Some floating plants (such as water lilies) get their nutrients through stems that extend to roots in the pond bottom. Other free-floating plants (such as duckweed) get all their nutrients from the water itself through roots that extend into the water beneath the floating leaf. All floating aquatic plants prefer quiescent water. Water lilies The classic pond plant, native water lilies have leathery leaves with air spaces that allow it to float. Water lilies are slow growing and usually grow in relatively shallow water less than 5 feet deep. The leaf stalks and stems are often flexible to allow leaves to move up and down with the water level. They use stored energy in their extensive roots to grow leaves rapidly to the surface in the spring. Native water lilies have large, white flowers, while nonnative tropical varieties have different-colored flowers. Water lilies provide excellent habitat for fish and other aquatic life. Elodea Coontail Naiad Bladderwort Water lily 9

12 Duckweed Watermeal Watershield Cattail Bulrush Duckweed This plant is easy to identify by its small, floating leaf with a tiny root extending from the bottom of the leaf. In the fall, duckweed produces winter buds that sink to the pond bottom. As the water warms in the spring, these buds float to the surface to start another colony of duckweed plants. Duckweed is spread between ponds by waterfowl and can grow very quickly, ultimately covering the entire water surface in stagnant ponds. Watermeal With very small, round leaves that are pale green or yellowish without any obvious root, watermeal appears more like grass seed than an actual plant. Watermeal often occurs with duckweed on stagnant ponds. Watershield This plant has a 2- to 4-inch elliptical or football-shaped floating leaf that is purple underneath. The underside of the leaves and elastic stems are covered with a characteristic gelatinous coating. Purple flowers are produced on stems above the water surface during summer. Watershield prefers clear, acidic ponds with a thick, organic muck layer on the bottom. Emergent Plants Emergent plants often look very much like terrestrial plants because most of the plant is above the water line. These plants like to have their feet (roots) wet but like to have their stems and leaves dry. Emergent plants can withstand changing water levels in the pond and some even thrive under these conditions. Their leaves are spongy with numerous air spaces and most have extensive roots that grow horizontal in pond sediments providing stability and preventing erosion along the pond edge. Most emergent plants grow slowly and provide excellent fish and wildlife habitat. Many pond insects, including beautiful dragonflies and damselflies, will use stems of emergent plants for perching areas. Emergent plants tend to cause fewer problems for pond owners than other aquatic plants. Cattail The most common of the emergent plants, cattails often colonize shallow water areas, especially in older ponds. Cattails are slow growing and limited to shallow water, so their growth rarely reaches nuisance levels. Muskrats like to eat cattails and are often attracted to ponds with significant cattail growth. Bulrush This plant has unique stems that are triangular in shape when cross-sectioned. They usually grow 2 to 3 feet tall with flowers on spikes near the tip. They may form very dense stands after being established for several years and can grow in water up to 3 feet in depth. Bulrush sprouts each spring from buds on rhizomes in the pond sediment. Invasive Aquatic Plants Watch Out for These! Nonnative aquatic plants are increasingly becoming a problem in private ponds and lakes throughout Pennsylvania. Some of these plants have occurred in the state for many years and are slowly spreading, while others have only recently appeared and are spreading rapidly. Listed below are some of the most troublesome invasive plants in Pennsylvania ponds. Hydrilla A submerged aquatic plant that resembles native elodea, hydrilla has finely toothed leaves coming off stems in whorls of three to eight. This aggressive plant roots in the bottom of ponds, lakes, and canals and outcompetes native aquatic plants. Stems grow to the surface, where they can branch and extend horizontally. This nonnative plant is extremely prolific in the warmer ponds of southern Pennsylvania. Hydrilla can also be spread into ponds as a hitchhiker on some potted aquatic plants. 10

13 Curly Leaf Pondweed Curly leaf pondweed is a European plant that is quite common in ponds throughout Pennsylvania, especially those with fertile and hard water. It has a very distinctive appearance with crinkled, finely toothed leaves that occur alternately along the stem. The flower spikes often stick up above the water surface during spring. It can tolerate low light and may grow in deep water. Curly leaf pondweed grows abundantly until late summer when it dies back to form winter foliage that remains green throughout the winter. Eurasian Milfoil Unlike native watermilfoil, which is usually found in acidic ponds and lakes in northern Pennsylvania, Eurasian watermilfoil is an invasive nonnative plant that quickly grows to nuisance levels. The leaves are green with a fine, feather-like appearance growing on long, reddish-colored stems (native milfoil species look very similar but usually have more delicate leaf structures). Flowers develop on a terminal spike with very short leaves surrounding them; however, it usually reproduces through fragmentation. It entered Pennsylvania from the Great Lakes drainage and quickly spread into all major watersheds in the state. It grows in a variety of conditions and often outcompetes and replaces native pond plants. Parrot Feather This is another submerged, rooted plant closely related to Eurasian milfoil. Parrot feather is popular among backyard pond owners, leading to its spread into larger ponds throughout the state. It has green, featherlike leaves that often grow above the water surface for up to 12 inches. It reproduces mostly through stem fragments and can quickly take over a pond. Purple Loosestrife An exotic, emergent plant from Europe and Asia that quickly spreads and outcompetes native plants. It should be removed as soon as it first appears. It has long, square stems with opposite leaves in whorls of about three. The narrow leaves are about 1 to 4 inches long and end in a point. It produces clusters of purple flowers on a terminal spike. Purple loosestrife often first appears in disturbed areas around the pond from seed germination. Many pond owners have been tempted by the beautiful purple flowers on this plant and have unknowingly planted loosestrife around their pond only to regret this decision in a few years when the plant takes over the entire pond edge. Yellow Floating Heart A relative newcomer to Pennsylvania, this floating plant is becoming widespread due to its popularity among backyard pond enthusiasts. This plant has a similar appearance to water lily, but its leaves are slightly more heart shaped and the flowers are yellow. This plant will grow more quickly than water lily and can reach nuisance levels. Additional Sources of Help for Aquatic Plant Identification The following Web sites provide pictures and descriptions of aquatic plants: Aquaplant from Texas A&M University: aquaplant.tamu.edu Center for Aquatic and Invasive Plants from the University of Florida: plants.ifas.ufl.edu Penn State Cooperative Extension Water Resources: water.cas.psu.edu/ponds.htm Other Web sites can be found by typing aquatic plant identification into any Web search engine. Several excellent field guides and books on aquatic plant identification are available through the North American Lake Management Society (phone ; For more help with identifying aquatic plants, digital photos of aquatic plants to Bryan Swistock at brs@psu.edu. Hydrilla Curly leaf pondweed Eurasian milfoil Parrot feather Purple loosestrife Floating heart 11

14 Aquatic Plant Growth Prevention and Control Preventing Aquatic Plant and Algae Growth The old saying an ounce of prevention is worth a pound of cure also applies to controlling aquatic plants and algae in ponds and lakes. Reacting to overabundant growth, once it has occurred, is simply a band-aid approach that often involves perpetual treatment to control the plant. But several strategies can be used to prevent plant and algae growth before it occurs. A simple strip of unmowed grass around the pond edge, like this buffer around a golf course pond, can reduce aquatic plant and algae growth in the pond by reducing nutrients delivered to the pond. Pond Construction Features Most plant and algae growth begins in shallow water less than 3 feet deep where sunlight can reach the pond bottom. Therefore, limiting the amount of shallow water in the pond will control the amount of plants and algae that can grow. As was mentioned earlier, this can be achieved by constructing the pond so the water is at least 3 feet deep at a point 9 feet from the shoreline (a 1:3 bank slope). If the pond will be used for swimming, you may wish to construct a small area with a gentler slope to allow for easy and safe entry into the pond. For existing ponds with gentle bank slopes and extensive shallow water, dredging can be used to deepen the pond edges and prevent future plant and algae growth (see Dredging section later in this publication). Nutrient Control Strategies As was previously discussed, aquatic plants and algae grow to nuisance levels in response to excess levels of phosphorus and nitrogen in the pond water. Thus, strategies that reduce nutrient entry into the pond will have the benefit of preventing future plant and algae growth. Nutrient control strategies are rarely employed by pond owners because they are often perceived as too difficult and expensive, and they also do not provide an immediate reduction in plant growth. Rather, nutrient reductions will lead to a gradual and long-term reduction in plant and algae growth. In an era of quick fixes for all problems, pond owners are unfortunately more likely to choose other approaches, such as herbicides, to control plants and algae. Buffer Strips Perhaps the easiest method to control nutrients entering a pond is to establish a buffer strip of vegetation. Maintaining a strip of vegetation around the pond and also around streams and springs that feed the pond is very beneficial for capturing nutrients before they enter the water. Buffer strips act to slow water down and encourage infiltration of the water into the soil where the plant roots can capture and utilize nitrogen and phosphorus. Buffers also act to remove sediment from the water by slowing water velocity. The composition of a buffer does not need to be fancy. A simple, 30-foot wide strip of taller grass will often suffice on gentle slopes around the pond. A wider buffer with more diverse vegetation is better, especially on steeper slopes that provide runoff to the pond. Buffer strips planted with native vegetation and wildflowers can also attract wildlife to the pond area. A buffer area that includes larger vegetation capable of shading some of the pond water will also help reduce plant growth by limiting direct sun and cooling the water temperature. 12

15 Erosion and Sediment Control Most phosphorus enters a pond attached to soil particles that are suspended in water entering the pond. Practices that reduce erosion near the pond and sediment delivery to the pond through the water supply can be effective in reducing aquatic plant and algae growth. Reducing sediment delivery also prevents the pond from becoming shallower and thus reduces aquatic plant growth. Erosion control around the pond involves the creation and maintenance of the vegetated buffer strip as described above. Reducing sediment delivery to the pond through surface runoff or surface streams is more difficult. The processes that cause sediment delivery to streams and springs are often large-scale land-use activities that are out of the pond owner s control (e.g., stormwater runoff from housing developments and shopping centers upstream). Assuming that sediment cannot be reduced in the incoming runoff water, the pond owner can reduce the impact of sediment on the pond by creating a small sediment pond or shallow pool at the inlet of the main pond. Water passing through this sediment pond or pool on its way to the pond will have an opportunity to drop its sediment load in the pool. This pool should be of such dimensions that it can be easily cleaned with a backhoe. A sedimentation pool helps the pond in the same way that sediment is removed by buffer strips. Limit Fertilizer and Manure Applications Fertilizers and manures applied to lawns, golf courses, and farm fields may run off into adjacent ponds and lakes. Some of the nutrients contained in these products may run off from the land where they are applied because plants are never able to utilize 100 percent of the nutrients. Heavy rain immediately after application of fertilizers and manures is especially likely to cause runoff of nutrients into nearby ponds and lakes. Just as these fertilizers are intended to stimulate growth of grass and crops, they also act to stimulate growth of aquatic plants and algae in receiving waters. Reducing fertilizer and manure application rates on lands near ponds and prohibiting use of these products within the buffer area around the pond will reduce nutrients entering the pond. Limit Other Nutrient Sources Other sources of nutrients to ponds can often be controlled or diverted. Barnyards, feedlots, and pastures may contain high amounts of animal wastes rich in nutrients. Fencing ponds and streams to limit animal access will help reduce nutrient runoff and soil erosion into ponds and the streams that feed them. Just as domestic animals may contribute nutrients to ponds, excessive amounts of wildlife can also be problematic. The most likely cause for concern is large flocks of Canada geese. A recent study in the northeastern United States found that Canada geese can be a large contributor to phosphorus additions to ponds. A flock of 200 geese were found to produce about 100 grams of phosphorus each day, enough to stimulate large quantities of algae. Approaches to limit the numbers of geese and the length of time that they visit the pond will reduce the nutrient load to the pond. Finally, human wastes can be a significant source of nutrients to some ponds and lakes. Care should be taken to locate septic systems as far from the pond or lake shore as possible. Homeowners with septic systems need to properly maintain the system to ensure that malfunctions don t occur that could cause nutrient pollution into nearby ponds. In the absence of strategies to control nutrients entering ponds, many pond owners are limited to reacting to excessive growth after it has started. It is important to realize that acting to reduce plant and algae growth without addressing the underlying cause may simply create alternate problems. For example, reducing submerged and floating aquatic plants may lead to increased algae growth by releasing nutrients formerly bound up in living plant material. A truly integrated approach is usually necessary that incorporates water quality measurements, pond construction features, and physical, biological, and chemical controls to create a balanced aquatic plant management plan. Sediment and nutrient levels in farm ponds can be greatly reduced by fencing the pond and piping drinking water to troughs. Canada geese can increase aquatic plant and algae growth through their wastes. 13

16 Raking and other physical removal of plants can be advantageous because they also remove nutrients from the pond. Physical Control Strategies Physical control strategies are akin to pulling weeds from your flower beds. Many of these processes are time consuming and labor intensive, but they often have longerterm benefits than chemical control. That s because removal of plants and algae from the pond also removes the nutrients associated with the plants, which makes fewer nutrients available for future plant growth. Harvesting Physical harvesting of aquatic plants and algae can be very effective, especially for small quantities of plants near the shorelines. Also, unlike many other aquatic plant control strategies, hand or mechanized removal of aquatic plants and algae does not require a state permit. Many pond owners have developed innovative tools and techniques to accomplish aquatic plant harvesting. All these methods involve some type of cutting, mowing, raking, digging, skimming, or pulling. Harvesting techniques must often be repeated several times each growing season to eliminate new growth as it appears. Many submerged aquatic plants can reproduce through fragmentation. As a result, attempts to cut and harvest these plants can result in increased growth due to sprouting from fragments left behind. Before attempting to harvest submerged plants, make sure you properly identify the plant and determine if it can spread through fragmentation. If the problem plant is known to reproduce from fragments, avoid attempting to harvest the plant and focus on other physical, biological, or chemical control techniques. Plants and algae that are harvested from the pond should be removed from the vicinity of the pond edge. This will prevent the nutrients released from the decay of the plants from being washed back into the pond water. In larger ponds and lakes, mechanized harvesters may be used to remove aquatic plants and algae. These mechanized harvesters can be expensive because of high maintenance costs. The most widely used type of mechanized equipment is called a plant harvester (weed cutter). Plant harvesters are used mainly on large lakes and cut off the underwater rooted vegetation 4 to 5 feet below the water surface. As with hand removal of plants, mechanized removal offers the advantages of removing much of the nutrients associated with the aquatic vegetation, thus reducing future plant growth. Mechanized weed cutters that do not harvest or collect the weeds for transport to shore are not recommended because plant fragments can live for long periods of time, develop root systems, and grow in areas that previously were unaffected with a weed problem. On larger lakes, consultants can be hired to mechanically remove large amounts of aquatic plant growth with plant harvesters. Aeration Aeration can be beneficial to the overall health of some ponds and lakes, but it should be viewed as part of an integrated management plan to reduce plant and algae growth rather than a solution to the problem. The most efficient type of aeration involves introducing air bubbles at the bottom of the lake or pond through diffusers or hoses with small holes. This type of aeration, called diffuse aeration, requires electric power and some installation by a profes- 14

17 sional. The air bubbles rising from the diffusers on the bottom of the pond oxygenate the water and push the oxygen-poor water to the surface where it is reaerated through an exchange with atmospheric oxygen. In addition, some oxygen is directly transferred from the air bubbles to the surrounding water. The resulting aeration of the bottom pond water activates a number of complex processes that can help control algae by precipitating phosphorus out of solution and keeping phosphorus bound to the bottom sediments. Aeration of the bottom water layers can also be beneficial to reduce the depth of the organic muck layer that forms on the bottom of the pond. Aerobic (oxygen-loving) bacteria work much faster than anaerobic bacteria in breaking down organic material on the bottom of the pond. The other type of pond aeration involves surface aeration through fountains. Fountains generally only aerate a shallow layer of water near the pond surface, so they have little or no benefit to reduce phosphorus levels and control algae. The mechanical agitation of the pond surface by the fountain will reduce the growth of some floating plants, such as water lily and duckweed, that prefer to grow in stagnant water. Drawdown Most aquatic plants and algae begin growing in shallow water near the pond edge. Partially draining the pond to expose these shallow areas called drawdown is another physical method to reduce the growth of aquatic plants. Drawdown is usually done during the fall to expose pond sediments to freezing temperatures during the winter. The degree of plant control from a drawdown depends on the plant species present and the minimum winter temperatures. A drawdown accompanied by below-freezing temperatures provides the greatest aquatic plant control. Drawdown is often difficult for pond owners to accomplish because they cannot easily draw the water level down and keep it lower for an extended time over the winter. More often, drawdown is done on larger lakes and reservoirs that can easily control the water level. A permit for drawing down an impoundment is required for ponds larger than one acre or for any pond drawdown to conduct an activity that requires another state permit, such as a Pennsylvania Department of Environmental Protection Waterways Obstruction and Encroachment Permit. Additional information is available through your local office of the Pennsylvania Fish and Boat Commission and the Pennsylvania Department of Environmental Protection. Dredging As sediment and organic debris enter the pond, they will settle to the bottom and reduce the water depth. This sedimentation process occurs quickly in ponds that receive erosion and stormwater from disturbed areas and slowly in ponds that are spring fed in undisturbed areas. Shallower water from sedimentation allows sunlight to reach more of the pond bottom, resulting in increased plant and algae growth. Dredging sediment from the pond can be a remedy to reduce plant growth, albeit a time-consuming and expensive one. The first steps in any dredging project should be to locate where the sediment originates and then determine how the sediment delivery may be controlled. Restoration of a pond to its original configuration usually provides significant benefits, but they can be short lived if the sedimentation is allowed to continue. Dredging is a regulated activity that may require a drawdown permit and a dredging permit before proceeding. Pond owners should consult the local office of the Department of Environmental Protection before beginning any dredging project. Biological Control Strategies Many pond owners desire biological or natural techniques to control unwanted aquatic plants. These methods are less physically demanding than mechanical control strategies described above and are usually less damaging to the pond ecosystem when compared to the chemical control strategies described in the next section. Diffuse aeration Fountain aeration Drawdown of lakes and ponds will reduce plant growth by freezing bottom sediments during winter. 15