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!

 

 

 

 

Deep vs. Shallow Lakes

While natural lakes tend to be categorized based their geomorphology (e.g. glacial lakes vs. riverine-created oxbow lakes), here we compare deep versus shallow waterbodies.

The depth of a lake has a profound effect on its ecology. If a lake is deep enough, typically a mean depth of 8 to 10 feet or greater, it can thermally stratify, which means the surface waters are a lot warmer than the deep waters. If the bottom waters are “sealed off” from the atmosphere, they can’t mix with the surface waters due to temperature differences in the summer (called stratification). In turn, the bottom waters can become depleted of dissolved oxygen. This can have a potentially negative impact on deep water fishery habitat and the lake’s nutrient (generally nitrogen and phosphorus) loads. Many of our clients utilize sub-surface aeration systems to keep the bottom waters in deeper lakes oxygenated over the summer month to enhance the fishery habitat and minimize the phosphorus that “leaks” from the sediments in the absence of dissolved oxygen.

Lake Stratification

Graphic adapted from Nebraska DEQ slide found on slideshare.net

In sharp contrast to deep lakes, shallow lakes (typically mean depths less than 8 feet) can remain well-mixed and oxygenated from surface to bottom over the summer months. Thus, the depletion of dissolved oxygen is typically not a problem in many shallow lakes. However, shallower water depths result in a larger portion of the lake bottom receiving a sufficient amount of sunlight to stimulate aquatic macrophyte (aquatic plants and mat algae that initiate growth along the sediments) growth. Thus, shallow lakes, or shallow areas of deeper lakes, can experience nuisance densities of aquatic macrophytes that can negatively impact their ecological value and recreational use. Such conditions tend to be fairly common in the Northeast region of the United States since there are far more shallow lakes than deep ones.

In addition to sunlight reaching the bottom, shallow lakes – as well as deeper lakes – can also experience planktonic (freely floating in the water column) algal blooms. Essentially, the more nutrients, such as nitrogen and, in particular, phosphorus, in the water column, the more algae that can grow in the open waters. Some algae, such as blue-green algae (also called cyanobacteria) can produce nasty and unpleasant surface scums when nutrient concentrations are high. Thus, in shallow lakes there is interplay between rooted aquatic vegetation and mat algae (the macrophytes) vs. the free floating planktonic algae. The more nutrients in the water column, the more planktonic algae present; the lower the nutrient concentrations, the clearer the water and the more aquatic macrophytes. Of the two shallow lake conditions, most lake management programs lean toward the clear water condition with more macrophytes since it is easier to manage for recreational use. However, whether you have a shallow or deep lake, the foundation of any effective, long-term lake management program is to minimize its nutrient load.

Nutrient Loading in Shallow Lakes

Graphic adapted from www.ecologyandsociety.org

Check back for our coming discussion of the difference between natural lakes and artificial impoundments. For more information, please feel free to contact me at flubnow@princetonhydro.com.