Lake monitoring and research Active

WHY STUDY LAKES?

Limnology (the study of lakes and other freshwater systems) is the science that can provide improved understanding of lake ecosystem dynamics and information that can lead to sound management policies. As more studies are conducted on a variety of lake systems, the accumulated information leads to the development of general concepts about how lakes function and respond to environmental changes.

The condition of a lake at a given time is the result of the interaction of many factors—its watershed, climate, geology, human influence, and characteristics of the lake itself. With constantly expanding databases and increased knowledge, limnologists and hydrologists are able to better understand problems that develop in particular lakes, and further develop comprehensive models that can be used to predict how lakes might change in the future.

While the development of a limnological database and knowledge is important, no amount of generalization can provide a full understanding or predict conditions of any particular lake. Each lake system is unique, and its dynamics can be understood only to a limited degree based on information from other lakes. Just as a physician would not diagnose an individual’s medical condition or prescribe treatment without a personal medical examination, a limnologist or hydrologist cannot accurately assess a lake system or suggest a management strategy without data and analysis from that particular lake and its environment. Lakes are a significant and valuable resource and are experiencing increased pressure from development and use. Many lakes do not have adequate information available for management of the lake, and their water quality needs to be assessed and documented.

The USGS has expertise in hydrologic data-collection in lake settings, water and nutrient budget development, source-loading analysis, and lake water-quality modeling. Our studies typically involve one or more of the following goals:

• describe current and historical characteristics and trophic condition of lakes
• identify and understand lake water-quality problems
• provide an understanding of in-lake processes and watershed inputs
• determine the effective management actions to protect or restore lakes

Monitoring
The USGS monitors lakes to define their current water quality and trophic status. Lake stage and tributary inflows are monitored to assist in developing water and nutrient budgets. Inflowing streams are monitored by traditional techniques or with acoustic Doppler velocity meters in backwater situations commonly encountered at the mouths of tributaries to lakes. Water-quality sampling in streams is often conducted with automated water samplers. Water-quality problems identified in monitoring projects may provide the basis for proceeding with lake-rehabilitation efforts or a diagnostic study.

Groundwater interactions
Groundwater can be an important component of lake budgets and must be quantified in order to compile water and nutrient budgets. We employ groundwater monitoring and modeling where needed to better understand the hydrologic system and a lake’s interaction with groundwater.

Water and nutrient budgets
Accurate water and nutrient budgets are needed to identify nutrient sources or causes of water-quality problems in lakes and are necessary for modeling the response in lake water quality to potential changes in nutrient loading. The USGS is experienced in computing detailed water and nutrient budgets, which account for all major and most minor components of the budgets. Better knowledge of nutrient sources allows planners to focus remediation efforts on those sources where loading reduction will most benefit lake water quality.

Modeling
Many lakes experience multiple water-quality problems and are in need of rehabilitation measures, or the evaluation of measures already implemented. Lake models are useful in understanding specific processes and estimating how a lake will respond to management actions without the costs of implementing the actions. The USGS is experienced in employing eutrophication models such as those contained in the Wisconsin Lake Modeling Suite (WiLMS) and BATHTUB to assess changes in water quality in response to changes in nutrient loading. We are also experienced in applying process-driven watershed, hydrodynamic, and water-quality models to provide a better understanding of the physical and water-quality dynamics, oxygen distribution, productivity in lakes, and mixing associated with lake aeration.