Limnology: the Science Behind Lake Management
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Limnology: The Science Behind Lake Management -·-~-- Ken Wagner imnology is the study of fresh Experimental limnology gained often learn more about what controls waters-basically the freshwater popularity after World War II, with the lake condition, and can fine-tune our L equivalent of oceanography. It is work of G.E. Hutchinson and management methods. When we extend also the basis for colleagues at Yale often cited as leading descriptive and experimental limnology informed lake the way. Many, many other scientists to many lakes and watersheds, we gain management, and is have contributed to this effort, and information that helps us adapt our the foundation upon continue to do so today. management methods for varying which many of our Conscious lake and watershed application. Sound limnology supports management management is largely a post-1960 sound management. techniques have effort, although earlier examples So what are some of the been built. While a certainly exist. Lake management limnological developments that have lot of lake and accelerated greatly in the late 1970s shaped lake management over the last watershed with federal support and annual 30 years? Here I will examine a few management may gatherings of limnologists and lake advances that have made a difference in seem like common sense, many of the managers. NALMS was formed at the the way we manage lakes and principles we assume to be long-held 1980 gathering of these committed watersheds. truths are really rather recent scientists and practitioners, and has developments. Limnology is still a expanded the circle to include industrial Limiting Nutrient Concept young science, but it has already yielded suppliers and lake enthusiasts. As we great advances in water resource move forward, our zeal for lake Leibig's "Law of the Minimum" management. management should be tempered with goes way back, and basically states that Limnology can be divided into two recognition of the limits of our it is the element that is in shortest broad categories of effort: descriptive limnological knowledge and supply relative to the needs of the plant and experimentaL Descriptive appreciation for the efforts that have that will limit growth. Our limnology is what we do in the first part laid the foundation for our successes. understanding of the importance of of a typical diagnostic/feasibility study, When we complement management phosphorus as a limiting nutrient in in which we inventory the physical, with more limnological investigation aquatic systems is only about 50 years chemical, and biological components of (e.g., post-treatment monitoring), we old. Richard Vollenweider publicized a lake and its watershed and assess the role of phosphorus in the late 1960s relationships among these component Birge and Juday sampling in Lake Mendota, and 1970s, and I felt honored to discuss parts of the ecosystem. If we can Wisconsin. (State Historical Society of Wisconsin). his work with him over a cognac at the discern trends and elucidate causes and natal NALMS conference in 1980. He effects, these often provide keys to told me that it was mainly a process of understanding what controls overall elimination, based on the descriptive lake condition. Understanding can work of many researchers and the facilitate protection of desired experimental work of others; not a conditions and manipulations that lead stroke of brilliant thinking, but the to improved conditions. Manipulations summation of a lot of hard work. Dave are experimental limnology, and Schindler, who has spoken on his whole manipJ!lations on a whole lake scale lake fertilization experiments ~ ~eyeral_ constitute lake management.- ---- NALMS symposia, has repeatedly Descriptive limnology developed emphasized the "hard work" side of trem~r1dously between the first and limnologi"Cal_dis~overies._ Other second World Wars, with the pioneering nutrients and factors such as light and work of Edward Birge and Chancey temperature can play a major role in Juday in Wisconsin, a stronghold of lake productivity, but phosphorus has limnological research to this day. 24 SJJtlng21J01 • WltlJNE become the successful focus of use today, and have been supplemented Canadian base have provided us with a management to lower algal biomass. by additional models to cover the range glimpse of the variability of conditions of cases encountered (e.g., nitrogen over time in many lakes and led to the Internal Phosphorus Cycling limitation, anoxia, biotic influences). development of predictive indicators of Development of regional values for water quality based mainly on plankton The failure of seemingly model variables has made models more remains. The major impact of land appropriate watershed management to reliable for local practical application. clearing on lake condition in the 1800s lead to improved lake conditiol)s has Coupled with predictive models of algal has been documented, and recovery of often been traced to high internal growth, water clarity, and oxygen lakes after reforestation has also be loading of phosphorus. Just how deficit, we can now estimate lake observed. Some lakes have been shown phosphorus is cycled and especially the condition in response to potential to have been eutrophic since long before variability in the upward movement of actions in the watershed. NALMS white settlers arrived. Recent work by phosphorus from sediment to surface members such as Dan Canfield and the NALMS member Pete Siver in waters has been the subject of a long late Rob Peters have been instrumental Connecticut has documented the series of investigations. We first learned in this effort. Quantification of correlation between urbanization of that low oxygen promotes the release of uncertainty (how likely are we to be watersheds and declining lake water phosphorus, iron and other substances right or wrong with our predictions, and quality over the last 50 years. from the sediment, and that under by how much?) has facilitated better strongly anoxic ("reducing") conditions technical and economic planning. Trophic Cascade sulfide can be released. Then the importance of iron in controlling Rooted Plant Ecology Our understanding of the phosphorus transport and availability relationship between phosphorus and was ascertained, and later the critical Plants have many strategies for algal biomass has always been role of sulfide in binding iron and surviving in the aquatic environment, complicated and often confounded by allowing available phosphorus transport and understanding their diverse biological interactions that introduce into the upper waters was determined. ecological "tricks" is essential to significant variation into that Recently, the means to evaluate planning a successful plant management relationship. Research that began in the sediment phosphorus release potential program. The knowledge that most late 1970s and progressed through the as a function of fractionation among rooted plants get their nutrition largely 1980s addressed this issue, and I bound forms of phosphorus was from the sediment is only about 20 enjoyed working on this topic as part of developed by a team including former years old, and we continue to study the my Ph.D. research as part of the team at NALMS president and lirnnologist reproductive strategies of many species, the Cornell Biological Field Station. In Gene Welch. We now understand the especially invasive forms. Much of this 1975 Joe Shapiro suggested causal agents for high internal work has been conducted by researchers biomanipulation as a means of phosphorus loading, and are applying it at the Army Corps of Engineers' achieving management goals without to gain better control of algal blooms Waterways Experiment Station and by major physical or chemical alteration of through aluminum additions and NALMS members such as Stan Nichols, lakes, and many researchers took up the aeration systems. Sandy Engel, and John Barko. The challenge. NALMS members Steve development of herbicides that target Carpenter and Jim Kitchell greatly Prediction of Lake Response certain species while preserving others advanced our knowledge in this area is a function of understanding through whole lake experiments in the Once it was determined that physiological differences among upper Midwest. phosphorus loading controlled lake species, and the advancement of Research in a number of locations productivity in many cases, multiple biological methods of plant control like illustrated that if enough large-bodied teams of lirnnologists initiated efforts to the milfoil weevil has been dependent grazing zooplankton are present, algal model the response of lakes to upon both descriptive and experimental biomass may not increase to the extent phosphorus inputs. These efforts were limnology. predicted by simple phosphorus based largely on standard engineering chlorophyll equations. When small fish representations of lakes calibrated with Paleolimnology that eat zooplankton become abundant, large quantities of data for groups of algal biomass may increase beyond the lakes. These "empirical" models were It is a common mistake to assume expected average based on phosphorus generated in the mid- to late 1970s by that lakes follow a unidirectional path at and other chemical features. And if Riehard Velleaweider and-NALMS -~y pace fromlew-to high fertility, large predatory fishcincre~poiflto-~ ~ members like Roger Bachmann, Jack and paleolimnology has aided our where they control the populations of Jones, Peter Dillon, Ken Reckhow, and understanding of historic