Mild Winter in Mid-Atlantic Raises Concerns For Lakes

By Dr. Fred Lubnow, Senior Technical Director of Ecological Services

The Winter of 2022 – 2023 is turning out to be a mild one, at least in the Mid-Atlantic region of the United States. Anecdotally, there has been no measurable amount of snowfall in 2023 as of early March. In northeastern Pennsylvania, January and February 2023 mean monthly temperatures were 9.6 and 7.5 degrees warmer relative to their long-term respective average values. In northern New Jersey, January and February 2023 mean monthly temperatures were 11.9 and 5.6 degrees warmer relative to their respective long-term average values (Northeast Regional Climate Center CLIMOD database).

This has had a profound impact on lake ecosystems. For example, in early 2023, both Harveys Lake (Luzerne County, PA) and Lake Hopatcong (Morris and Sussex Counties, NJ) have had no lake-wide ice cover. While measurable amounts of both snowfall and ice cover are still possible in the remaining weeks of March, it highly unlikely that such conditions would persist for weeks. Such ice-free conditions on our lakes, ponds and reservoirs will certainly have a profound impact on these ecosystems as we move into the 2023 growing season.

Algae May Grow Earlier in the Season

Undoubtably, current conditions are at a minimum partially attributed to climate change and will have a direct impact on the upcoming 2023 growing season. In the absence of ice, and more importantly snow-cover over the ice, aquatic plants and algae can begin to grow earlier in the season. Some plants, such as the invasive species curly-leaved pondweed (Potamogeton crispus), prefer cooler temperatures and tend to attain their highest densities in the spring and early summer. However, under such ice-free conditions, we have seen curly-leaved pondweed growing along the bottom of New Jersey lakes as early as February. This can result in more nuisance plant densities earlier in the year.

While most cyanobacteria, the group of algae known to have the potential to produce cyanotoxins, tend to attain their maximum growth and biomass over the hot summer months, there are several genera that are more tolerant of cool temperatures. For example, one filamentous genus, Aphanizomenon, is one of the first cyanobacteria to appear in the plankton in the spring. Indeed, over the last few years Aphanizomenon has been appearing earlier in the year and at higher densities in many of the lakes monitored and managed by Princeton Hydro. Another cyanobacteria known to bloom in cooler waters is Coelosphaerium. Coupled with slightly warmer temperatures over the late winter and early spring, cyanobacteria blooms could become more common and larger in magnitude, earlier in the year. Such blooms are frequently called Harmful Algal Blooms (HABs).

Many cyanobacteria produce resting spores called akinetes during conditions of environmental stress, such as colder temperatures and desiccation. These akinetes settle to the bottom and are re-activated as water temperatures increase. Warmer late winter and early spring temperatures, particular over the sediments, could mean more akinetes actively growing into vegetative cells earlier in the growing season.

Milder Winters Could Lead to New Invasive Species

Last year (2022), was the first time that the cyanobacteria Cylindrospermopsis was identified in Lake Hopatcong. In fact, this genus was the most abundant cyanobacteria in Lake Hopatcong during our July and August sampling events, but was no longer found by the early October sampling event. The Cylindrospermopsis found in Lake Hopatcong may be an invasive species that historically has been found in tropic and subtropic waterbodies. However, over the years, this cyanobacterium has been found in temperate waterbodies. Milder and warmer winters may mean more invasive species such as Cylindrospermopsis appearing in Mid-Atlantic waterbodies.

What Should You Do?

In the absence of ice and snow-cover to put the sediments in the dark and prevent photosynthesis, coupled with warmer temperatures in the late winter and early spring, may lead to more aquatic plant and algal growth earlier in the year. So what should be done about this?

1. Sample Early: March or April

First, we recommend initiating sampling earlier in the year, sometime in March or April; do not wait until May to begin sampling. Second, in addition to sampling the surface waters, sampling should also be conducted in near-shore areas, immediately above sediments and at the sediment-water interface. Samples should be examined under the microscope for the presence of akinetes and/or inactive colonies of cyanobacteria. Third, near-shore areas should also be surveyed for the presence of submerged, aquatic plants, in particular invasive species such as curly-leaved pondweed or hydrilla.

2. Encourage Residents to Reduce Nutrients Entering the Waterway

Finally, while most climate models indicate that HABs will more than likely increase in warmer conditions, the magnitude of this response will be strongly dependent on the availability of nutrients, in particular phosphorus. While phosphorus will drive the growth of cyanobacteria, the availability of external sources of nitrogen can increase the probability of a HAB producing cyanotoxins such as microcystins, which is a nitrogen “heavy” molecule.

Thus, if colonies of cyanobacteria or akinetes are found in the sediments over the spring, the lake community and stakeholders should be informed and efforts should be implemented to reduce the availability of nutrients such as using non-phosphorus fertilizers, picking up pet wastes, goose management, routine pump-outs of septic systems once every three years, where possible stabilize exposed soil by planting native vegetation and consider the use of green infrastructure such as rain gardens. By letting the community know that cyanobacteria may be lurking on the sediments over the spring season, it may mobilize efforts to implement both in-lake and watershed measures to minimize the potential development of HABs.

Princeton Hydro provides pond and lake management and monitoring services to hundreds of waterbodies in the Northeast.  If you would like to learn more about our services for your community, please send us a message through our website.

Dr. Fred Lubnow, Princeton Hydro’s Senior Technical Director, Ecological Services, is an expert in aquatic and watershed management, restoration ecology, community and ecosystem ecology, and the use of benthic macroinvertebrate and fish in-stream bioassessment protocols. Dr. Lubnow has managed hundreds of lake projects and provides technical expertise for a variety of lake and watershed restoration projects.

His experience in lake and reservoir restoration includes the design and implementation of dredging, aeration, chemical control of nuisance species, nutrient inactivation (i.e. alum) and biomanipulation. His experience in watershed restoration includes the design and implementation of structural Best Management Practices (BMPs), the development of Total Maximum Daily Load (TMDL) pollutant budgets, and the design, implementation and analysis of watershed-based monitoring programs.

• Lake and Pond Management
• Lake Restoration
• Natural Resource Management