Success Spotlight: Strawbridge Lake

The Princeton Hydro team recently completed a spadderdock removal project at Strawbridge Lake, a 33-acre lake considered to be one of the most valuable open space assets in Moorestown, New Jersey.

Spadderdock is an invasive aquatic plant found in lakes and ponds throughout the Eastern US. It can grow quickly and reach large populations totally covering the water surface and shading the bottom so that nothing else can grow. Spadderdock can eliminate important, native plant species and clog waterways.

Princeton Hydro utilized its Truxor DM 5045, an eco-friendly amphibious machine, to dig up the plants at their roots and remove them from the lake. Check out the below before and after photos to see the dramatic transformation. Special kudos to our Senior Scientist J.P. Bell for a job well done! Read more about pesticide-free #lakemanagement solutions!

Client Spotlight: Roaring Brook Lake, Putnam Valley, NY

A Comprehensive Lake Management Plan Designed by Princeton Hydro

roaring-brook-lake Since 1998, Princeton Hydro has been working with the Town of Putnam Valley, often referred to as the Town of Lakes, to restore and maintain its waterbodies. The most recent area of focus is Roaring Brook Lake, a 115-acre man-made lake surrounded by a wooded landscape community that includes 260+ homes. The lake provides a variety of recreational opportunities for boaters, anglers, swimmers and outdoor lovers and is the center point of the Roaring Brook Lake District.

The Town of Putnam Valley and the Roaring Brook Lake District hired Princeton Hydro to conduct a thorough analysis of the lake’s ecological health, identify problems affecting the quality of the lake, and develop a detailed plan to improve and protect the lake. Specifically, Princeton Hydro will implement a detailed assessment of the lake that involves water quality monitoring, bathymetric mapping (measurement of lake depth and sediment thickness), aquatic plant surveys, and quantification of the lake’s hydrologic and pollutant budgets. These data will be utilized collectively to produce a comprehensive management plan for Roaring Brook Lake and its watershed.

Water Quality Monitoring

Water quality data are used to interpret the existing chemistry of the lake, identify water quality trends, pinpoint problems and assess nutrient levels.

At Roaring Brook Lake, Princeton Hydro will specifically collect in-situ data from the surface to the bottom of the water column. The resulting temperature, dissolved oxygen, pH and conductivity data will be used in combination with laboratory generated data to assess the lake’s thermal stability and investigate the potential for internal phosphorus loading. In addition, samples will be collected to identify phytoplankton and zooplankton in the lake; some of the plankton is considered a nuisance while others are considered valuable relative to the lake’s food web.

Bathymetric Assessment

The bathymetric assessment will generate accurate lake water depth, and provide sediment thickness and distribution data for the entire body of water. These data are then used to evaluate the need for dredging, asses how and where aquatic plants become colonized and other management options that can affect long-term decisions regarding the restoration and protection of Roaring Brook Lake. The bathymetric data are also used in the various trophic models that help predict the lake’s response to incoming nutrients.

Specifically, Princeton Hydro will utilize hydrographic surveying methods to conduct the bathymetric assessment of Roaring Brook Lake. A specialized dual frequency fathometer will be used to measure water depth and the thickness of the unconsolidated sediment present throughout the lake. The fathometer is directly tied into GPS, so data are consistently collected at the exact position of the survey transects. The GPS data and accompanying water depth data will be placed into a GIS format for the generation of morphometric data and bathymetric maps of the lake.

Aquatic Plant Mapping

Aquatic plants hold sediments in place, reduce erosion and provide habitat for fish and other important wildlife and insects. Although native aquatic plants are imperative to a lake’s health, an overabundance of these plants and the presence of invasive plants can have very negative impacts.

Princeton Hydro will be conducting a complete mapping of the aquatic plant community within Roaring Brook Lake to identify the plant species present in the lake, their relative abundance and location, and provide a basis for future evaluation of changes in the plant community. This data will greatly inform lake management activities moving forward. Additionally, with this data, Princeton Hydro will be able to assess the effectiveness of the resident grass carp – currently stocked in the lake – in keeping the submerged vegetation under control.

 

Hydrologic and Pollutant Budget

The hydrologic budget represents the water balance of a lake, accounting on an annual scale for all of the inputs and losses of water. The hydrologic data is used extensively in conducting trophic state analyses and is important in determining the feasibility and utility of many in-lake restoration techniques. At Roaring Brook Lake, Princeton Hydro will investigate and quantify four key components of the hydrologic budget, including direct precipitation, overland runoff (stormwater, snowmelt, etc.), tributary inflow and groundwater seepage.

Once the hydrologic budget is complete and land-use has been categorized and quantified, a pollutant budget can then be developed. The development of a detailed pollutant budget is a critical component of any lake management plan. For the purpose of the Roaring Brook Lake study, the term pollutant refers to the nutrients nitrogen and phosphorus as well as total suspended solids. The pollutant budget represents a quantification of the input of pollutants from various sources to the lake. Because the amount of nitrogen and phosphorus present in the lake stimulates eutrophication and results in water quality impacts, proper quantification of the nutrient load is critical for the development of a site-specific and cost effective management plan.

Data Analysis

The data analysis for Roaring Brook Lake will focus on identifying an acceptable in-lake condition (i.e. specific level of algal biomass in the lake) and correlate this to the lake’s annual phosphorus load through a robust water quality model.

The data analysis will involve the review of both historical and current data and will be used to identify correlations and relationships between existing pollutant concentrations/loads and unacceptable water quality conditions (i.e. algal blooms, high rates of turbidity, nuisance densities of aquatic plants, etc.). Water quality thresholds and goals will be established for assessing the long-term progress of the lake management plan.

Lake Management Plan

roaring-brook-lake-1Properly managing your lakes and ponds starts with developing a customized management plan and involves a holistic approach to ensure continued success.

A good management plan is informed by substantial data collection and analysis (as described above); includes any necessary permit requirements and a proposed timetable for implementation; provides recommendations for priority ranking of particular activities and restoration measures; and discusses predicted benefits of the plan’s implementation and how each activity is linked to the established water quality goals. A well-crafted and thorough lake management plan will also include a review of the various Federal, State, County and local grants, programs and initiatives that may provide funding for the identified in-lake and watershed projects.

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Princeton Hydro’s work with Roaring Brook Lake marks the 16th project they’ve conducted for the Town of Putnam Valley. Princeton Hydro’s proven success in watershed management stems from the cumulative training and experience of its staff, and its ability to develop watershed management solutions that are both practical and effective, which has led to the firm’s very high success rate in improving water quality.

If you’re interested in developing a customized, comprehensive management plan for your lake or pond, please contact us!

 

 

 

 

Natural VS. Artificial Lakes

In addition to deep versus shallow, waterbodies can also be compared and contrasted as naturally occurring or as the result of an artificial impoundment or reservoir. While there are a wide variety of natural lakes -from the glacial lakes of northern regions, to oxbow lakes adjacent to rivers, to coastal lakes that can be connected to the ocean – most of these natural systems have a number of common characteristics. Some of these include variable nutrient and sediment loading (from low to high, depending on the nature of the watershed) and low to moderate watershed-to-lake area ratios. In addition, natural waterbodies tend to have distinct and sometimes extensive littoral zone fringe habitat along the shoreline. Littoral habitat is the interface between the land and the open waters of a lake. Typically, rooted aquatic macrophytes (plants and mat algae) are found in the littoral zone, along with a number of aquatic organisms that use this habitat for food and/or cover. Thus, the littoral zone of lake is frequently the most productive areas of this ecosystem.

Graphic adapted from www.cues.cfans_umin.edu

Graphic adapted from www.cues.cfans_umin.edu

In contrast, large artificial impoundments, frequently called reservoirs, are waterbodies typically created by placing a dam across a stream or river (see below). This often results in the triangular shape of a reservoir; the deepest portion is located just behind the dam. Unlike many natural lakes that have a number of small inlet or inflow streams, a reservoir typically has one main inflow, which is essentially the river or stream that was originally dammed. Traveling upgradient from the dam towards the main inlet, water depth will decline. Additionally, many reservoirs are a type of hybrid of natural lakes and rivers. The upgradient/inflow part of the reservoir functions more like a riverine system, while the main body of the reservoir near the dam functions more like a lake (see below).

Graphic adapted from Reservoir Limnology: Ecological Perspectives, edited by K.W. Thornton, B.L. Kimmel and F.E. Payne, 1990

Graphic adapted from Reservoir Limnology: Ecological Perspectives, edited by K.W. Thornton, B.L. Kimmel and F.E. Payne, 1990

Since reservoirs are essentially dammed rivers, they tend to have very large watershed-to -lake area ratios, which means they tend to experience substantially higher nutrient and sediment loads compared to natural lakes. Thus, the level of productivity (algae growth) in the open waters of a reservoir is substantially higher than those of a natural lake. This means reservoirs have the tendency to experience larger and more frequent algal blooms. High rates of sediment loads also means rates of sedimentation will be higher in reservoirs compared to natural lakes. Finally, since the water level of reservoirs are highly dependent on inflow from the main riverine source, as well as water withdrawals in the case in drinking water supplies, the establishment of a littoral zone in reservoirs tends to be very limited.

In summary, a reservoir of comparable size to a natural lake will typically have a higher level of algal productivity, higher rates of sedimentation, and a smaller amount of biological diversity (with the general absence of a littoral zone). Thus, water quality problems can be larger and more frequent in reservoirs when compared to many natural lakes. Since many reservoirs are vital sources of potable water for millions of people throughout the United States, the general management activities for a reservoir tends to be higher relative to many natural lakes.

Join us next time, when we will discuss lake and pond productivity, the role the watershed plays in productivity, and how this impacts their recreational, potable and ecological value.