Lake management in a warming climate
By Shahram Missaghi, UMN Extension Water Team
Lakes are changing and how we protect and manage them needs to change as well. Freshwater lakes are a tiny fraction (<0.5%) of the total water on earth, and host a web of complex ecosystems, and influence the lives of the many people around them. Lakes are part of the still or standing water (lentic) of inland waters. But, there is a full range of water motion (flow) within lakes that makes each lake a unique dynamic system and constantly changing. Yet, lakes with similar shapes and forms (morphometry) of the same area (climate zones) tend to respond similarly to the changes inside them and within their watersheds.
Lake maps are one of the fundamental tools in studying lakes (limnology). Lake outlines (shape and size/surface area) and bathymetry (contour depth and volume) are recorded on maps (Fig. 1), allowing a host of additional information be derived and calculated. For example, lake mean depth (volume/area) is an important metric for predicting a lake’s potential water quality and ecological processes or classification. Bathymetry can be used to determine the littoral zone (where light can reach to the lake sediment and support aquatic plant growth; around 15 feet deep). The ratio of the littoral zone to the entire lake surface area is then used to classify lakes into two very important types of shallow (littoral zone > 80%) or deep lakes. Shallow lakes tend to have an abundant aquatic plant growth with a vibrant ecosystem whereas deep lakes also offer variable fish habitats at different water depth (different water temperature and oxygen level).
Fig. 1. An example of a lake map; Round Lake, Aitkin County, MN. Minnesota Department of Natural Resources, Lake Finder.
All lakes are susceptible to the land use changes within their watersheds, where an increase in the excessive nutrients in the runoff can degrade lake water quality or lead to excessive plant growth. Consequently and rightfully, lake managers have traditionally focused on managing the amount of the excessive nutrients (loading) that is coming from watershed (external) into the lakes. The treatment and management of external loading into our lakes is considered a major problem. However, the ever-increasing changes of land use and the accelerated changes in the climate have exacerbated this problem, as is evident and supported by many local, regional, national, and global studies. For example, in one of our recent local studies, using computer modeling to predict the future lake water responses to climate change, we were able to show that coolwater fish habitat was squeezed and separated by lethal fish habitat by as much as three weeks and leaving the fish with no potential refuge to go to (note expanded red area in warmer future scenario in Fig. 2).
Fig. 2. Contour map of the response of coolwater fish habitat to two future climate scenarios as compared with current “Today” conditions. The depth of the lake (zero = top of the water column) is on the Y-axis with time on the x-axis. Blue area is the desirable good fish habitat, green represents the stressed fish habitat, and red is the non-habitable or lethal area.
Therefore, lake management needs to expand beyond the traditional focus on external loading for protecting and managing lakes. New lake management schemes, mindful of impacts of climate change, are needed so we can continue their protection and management. To address this lake management need, the UMN Extension in partnership with industry professionals, agency staff, and researchers has been offering a series of workshop on the Applied Lake Management and Stormwater Series, since 2016. These workshops focus on the connection between rain, stormwater, streams, wetlands, and our lakes and on how to adopt strategies to preserve and improve clean water. Workshops are designed for natural resource practitioners and professionals, homeowner associations, lake associations, and particularly for early career professionals.
The next workshop: Fundamentals of Lake Processes—Nutrient (Phosphorus) Impairment, is scheduled for Feb. 22, 2018, in Farmington. The workshop will help participants
- Understand the fundamentals of lake processes
- Learn why and how lakes are impaired by nutrient
- Learn how we can improve the water quality of impaired lakes (de-listing them)
- Learn about lake management schemes & techniques that lead to de-listing a lake
- Learn how to protect lakes from getting impaired.
This workshop is designed to engage all learner through presentations, case studies, and practices. So, save the date and consider registering for the workshop.