New Paper by Dick Osgood Addresses Inadequacy of Best Management Practices

Long time NALMS member, consultant, and past speaker at NECNALMS Dick Osgood has published a paper on the inadequacy of normal best management practices (BMPs) to restore eutrophic lakes to compliance with water quality standards. Dick’s paper, in the September issue of Inland Waters, is based on a review of many restoration efforts, documenting an opinion held by a number of long-term practitioners in lake management for some time. In essence, the degradation caused by development and agriculture in many lakes is not sufficiently counteracted by BMPs as applied in actual cases.

In some cases the application has not been at a scale sufficient to reduce loading enough to meet standards, but in many cases even maximum application is not enough to offset the inputs from the watershed. Where the ratio of watershed to lake area is <10:1, the probability of success through watershed BMPs increases, but there are few cases of success where the ratio is larger. Most BMPs reduce loading by no more than 50%, while development and agriculture tend to increase loading by tenfold or more.

While the paper is new, the debate is not, and there has been considerable defensive posturing by watershed management enthusiasts and institutions. But this paper is not saying that watershed management can’t work, only that we have been unsuccessful applying it in a manner that leads to success. Some of this is a result of technical limitations (e.g., heavily urbanized watersheds will never function like natural landscapes), but a lot of it is related to institutional failure (e.g., lack of funding, regulatory restrictions, inadequate jurisdiction). And if what we desire is success, measured as compliance with water quality standards for lakes, we need to do what works, not what is philosophically satisfying, politically popular, or simply affordable. In-lake management does not guarantee success, but has a better track record than watershed management. Some combination of watershed and in-lake methods is likely to be needed in most cases, but it seems clear that in-lake management deserves more attention than it has been given in many years by agencies responsible for environmental management and regulation.

The Impact of Lawns on Lakes

The late Stan Dobson, a famous limnologist with a practical interests, gave a talk in 2007 about the measured impact of lawns on water quality in the Madison, WI area. He found that of all the watershed factors one could correlate with measures of water quality, the one that explained the greatest portion of variation in nutrient levels, algae blooms, and loss of species diversity was the percent of the watershed in lawn. Now not all lawns are created equal, and having a grassy area associated with a home or business is not always the worst thing the owner can do, but the tendency to fertilize lawns and the substantial probability that the associated nutrients will reach a downstream waterbody are what make this correlation so strong. Lawns are a very real problem for lakes. They don’t have to be, but they are because of societal “pressure” to manage them in ways that are not good for lakes.

The nutrient issue is exacerbated by lawn care companies that over-fertilize (the chemicals cost less than the labor to retreat if results are unacceptable) and do not scientifically adjust the ratio of nutrients to fit each treated area (can you imagine a lawn care professional in a white lab coat testing soil content before deciding what mix of fertilizer to apply?). People doing lawn care on their own may not be any more responsible. This has resulted in a big push to get phosphorus out of lawn fertilizers, as most established lawns do not need more, and enough towns and even states have banned the use of high P fertilizer on lawns to get the fertilizer manufacturers to voluntarily reduce P content. Measured changes in downstream waters, including some peer reviewed literature (including 2 papers in Lake and Reservoir Management that are freely available), show a significant decrease in P concentration as a result. We still have issues with applied pesticides and nitrogen, but at least the over-application of P is on the wane.

But there is more to lawns than just chemical additives. Creation of lawn to the water’s edge, either at the lake or on any of its tributaries, eliminates buffers for nutrients, sediment, and anything else on the lawn (naturally, not just from additions) and increases loading to lakes. Loss of shoreline structure has been demonstrated (again, check out papers in Lake and Reservoir Management) to reduce species diversity and hurt fish communities and fishing. Loss of vegetative structure away from the water has known negative impacts on terrestrial ecology as well (hey, we can’t be totally lake-centric!). In short, lawns are not good for the environment. They don’t have to be measurably bad, but there is very little to be said in their favor from an ecological or water management viewpoint.

This does not mean that all responsible owners should do away with all lawn area, but it does mean that we should think twice about how much lawn we create and how we manage it. Bob Kirschner of the Chicago Botanical Garden and some other folks associated with NALMS have given some great presentations on how far you can take ecological landscaping before you are perceived as an “irresponsible” citizen of the community by those who look at lawns and landscaping as the taming of nature and a sign of culture. And it is a lot further than many lakefront property owners have gone. Yet there are some great examples out there of ecologically sensitive landscaping and more seem to be popping up all the time. The Maine program called Lake Smart espouses this approach and is achieving some success. New Hampshire and more recently Vermont have shoreland protection legislation that helps, but there is a major need for an education component to attain success, rather than just enforcement. We need to change the way that society perceives developed landscapes, with a focus on lessening impacts on our water resources.

Incompatibility of Common Lake Management Goals

When we speak of lake management goals, we are usually thinking about objectives like maximizing water quality for drinking water supply or contact recreation, improved conditions to enhance fishing opportunity, physical arrangements to increase boating access or enjoyment, or protection of habitat features that support valued wildlife. But it is very hard for a lake to be all things to all users. Not all goals are completely compatible, especially in smaller waterbodies where spatial separation of uses is difficult to achieve. A lake can serve multiple uses, but usually it is necessary to have a priority order for uses and goals, so that conflicts can be resolved.


The cleanest water may be just what we want for a drinking water supply or swimming area, but that water will not support the most productive fishery.  A lake with ample facilities for launching big powerboats may not be the best for a peaceful circuit by canoe or for observing wildlife. If the lake is large enough, some segregation of uses can be achieved, and in some smaller lakes temporal separation has been applied, as with early hour restrictions on motors. But the fundamental split between lower nutrients for clearer water and higher nutrients for more fish production is tough to overcome in a single lake. Some reservoirs with the classic elongate and dendritic pattern can achieve some semblance of a desirable range of nutrient concentrations for a range of uses, but stability is hard to maintain.

The best fishing experience does not have to be a simple matter of the number or size of fish caught; an aesthetic place to fish can be an important contributor to enjoyment. Drinking water is treated to meet strict standards in most cases, so the effects of elevated nutrients can be counteracted to some degree. But when conditions shift one way or the other, which goal has primacy will have considerable influence on the actions to be taken. Not all lake management goals are compatible, and this needs to be recognized in planning efforts.

What is a Balanced Fish Community?

Fishery management is very challenging. It involves physical, chemical and biological factors, plus the interactions between them. There are multiple life stages for each species, multiple species, and multiple trophic levels. The community is in constant flux, so stability is not a very applicable term. Instead, we tend to think in terms of a balanced fish community, one in which the various components are found in relative proportions that minimize fluctuations in year class strength, overall biomass, and energy flow. There is no one “right” combination, but a balanced fish community will have predator and prey species at a ratio that prevents either from being dominant. A balanced fish community will sometimes have strong temporal variations, such as when young of the year are produced and there are suddenly many small fish present, but predation is expected to foster an annual cycle of increase and decrease that maintains balance.

Range of species and sizes.

Lakes provide a variety of fish habitats and food resources, but not all lakes are created equal and some are better suited for some species than others. A deep lake with a cold bottom layer with adequate oxygen through the summer will support trout much better than a shallow lake with only a warmer upper layer during summer. Species such as pickerel and pike are “sit and wait” predators, doing best in lakes with ample submerged vegetation where they can hide until prey come near, while others such as walleye tend to prowl open water chasing schools of smaller fish. Largemouth and smallmouth bass are intermediate in predator tactics, with slightly different temperature and cover preferences. Prey species have similarly variable preferences, including yellow and white perch, multiple sunfish species, and a suite of minnows. And larger specimens of many prey species become predators of smaller fish. So there are many considerations in managing a fishery, and achieving balance can be elusive, but similarity of the results of successive surveys over 3 to 5 year intervals is a good indication of balance.

Overabundant and stunted sunfish.

In theory, stocking fish can help maintain balance if it compensates for weak year classes of key species, or adds species that occupy habitats and/or consume food resources that are otherwise not fully utilized, but that is not typically how stocking is used in New England states. Rather, gamefish are stocked to support fishing where natural production is inadequate. Prey species are stocked to support gamefish growth, but usually this involves species that overlap with existing species and destabilize the fish community.  Landlocked alewife represent a controversial example; they provide an impressive forage base but out-compete other fish by efficient filtering of all but the smallest zooplankton from the water column. Good fishing is usually the key goal of fish stocking programs, which is not mutually exclusive with community balance, but the two often do not go hand in hand.

Top Down vs. Bottom Up Control of Algae

A lot of research over about two decades led to the conclusion that algal abundance may be strongly influenced by cascading influences from the top of the food web. Certainly low nutrient availability will minimize algae biomass, but just because nutrients are abundant does not always translate into high algae biomass. The reason appears to be that a favorable biological structure can result in rapid consumption of algae as they are produced, preventing the build-up of algal biomass. Having abundant large predatory fish reduces the number of small fish, which in turn reduces predation on zooplankton, allowing greater grazing pressure on algae. Not just any zooplankton will depress algae, however, and the forms that generate the greatest grazing pressure (large bodied herbivores, especially Daphnia) are also the preferred food of many small fish. But a greater biomass of big grazing zooplankton will increase consumption of algae, resulting in the lowest biomass of algae for whatever level of fertility is present.

Small (Chydorus) cladoceran zooplankton

So can the most favorable biological structure possible achieve algae control when nutrients are abundant? The answer appears to be “no”. At phosphorus levels in excess of about 80 ug/L, research in Europe has found that no amount of zooplankton can prevent algae blooms. As blooms are probable at phosphorus levels above about 25 ug/L, there is an intermediate zone where biological structure can make a major difference, but nutrient controls may be necessary to prevent blooms. And since some cyanobacteria grow to large particle sizes at the sediment-water interface before rising in the water column, presenting zooplankton with a difficult challenge for consumption, even low nutrients in the water column and an elevated biomass of large bodied zooplankton may not be able to control cyanobacteria.

Large (Daphnia) cladoceran zooplankton

Creating a favorable biological structure provides benefits and is strongly encouraged. Nutrient control is clearly a critical part of algae management. But there is not much reason for a debate over the relative value of bottom up vs. top down controls; we need every tool we can get to keep our lakes in desirable condition!

Evaluating Risk Associated with Cyanobacteria

Cyanobacteria have taken center stage in many newscasts in the last couple of years, and have gotten more attention from the USEPA and state environmental agencies in the last 3 years or so than in the two decades before that. Cyanobacteria are not new; they are among the oldest organisms on the face of the earth, and are adapted to life under a wide range of conditions. But they do best in warm, freshwater with elevated phosphorus levels and a low ratio of nitrogen to phosphorus. Urbanization and agricultural use of land tends to create conditions that favor cyanobacteria, and the warmer temperatures related to climate change are fostering increases in blooms. All of this has been well documented in scientific literature with minimal bias; all political wrangling aside, we understand why cyanobacteria are becoming a more common problem and recognize the risks associated with these organisms.

But how is that risk assessed? New England states have a range of systems in place, but most fall short of addressing the issue to the extent necessary to allow appropriate response. The World Health Organization came up with thresholds of 20,000 and 100,000 cells/mL for low, moderate, and high risk, but cell counts are approximate and do not directly translate into toxin concentrations, which is where the risk really lies. Most states adopted a compromise concentration of 70,000 cells/mL, but it is certainly not true that 69,999 cells/mL is acceptable while 70,001 cells/mL represents extreme hazard. Thresholds create hard boundaries along a gradient with a lot of important variation. Some states now encourage toxin testing, but the ability to economically and rapidly test for the range of known toxins is very limited. Consequently, lakes get posted with warnings to avoid contact when cyanobacteria levels are elevated without actual confirmation of a hazard. Warnings do not legally prevent lake use, but rational people usually take those warnings seriously.

So what is the actual risk? This is a tough question. There is no doubt that some cyanobacteria produce toxins, including liver, nerve and skin toxins, but many species do not produce toxins. We know which species potentially produce toxins, and have identified the genes that allow toxin production, but because a species can produce toxins does not mean that it will. Many very dense blooms contain no toxins. Major die off of a bloom of toxin-producing cyanobacteria can result in elevated toxins in the water without a high cell concentration, although rarely for more than a few days. Risk is a matter of toxicity and exposure, and we don’t know enough about either to make definitive statements in many cases. Posting a lake for elevated cyanobacteria can help control exposure, but failure to follow up on toxicity leaves open questions and impairs our future ability to predict risk. We still have a lot of work to do to characterize cyanobacterial risk.

Managing in a Regulatory Climate

Many years ago when someone or a group felt that something about a lake was not right, they organized and changed it. Lake level was lowered, sediment was scraped, herbicides were applied, shorelines were bulkheaded, and so on. Many of these actions were appropriate, but many were not and most have impacts to other aspects of lake ecology that were not being considered or mitigated. In some cases the results were disastrous, not curing the targeted problem and making things worse in other ways. The dawn of ecological thinking and the incorporation of such thought into government resulted in many environmental laws, starting in the 1960s and peaking in the 1970s, with follow up ever since. Many environmental agencies were created, some completely new (the federal EPA) and others altered to redirect their mission (the federal USACE). State agencies underwent similar formation or transformation. The basic premise was that we needed to regulate how we treated the environment to avoid catastrophes while “fixing” perceived problems.

It is good that we have such agencies and the laws and regulations that guide them, but like most institutions over time, the mission is sometimes perverted or focus is lost. Incremental adjustments to regulations or changes in definitions create unforeseen consequences for legitimate activities. People use the system as a weapon instead of a tool. Agendas get created, processes become more complicated, and it becomes harder to manage. Lake management is suffering from just such a progression.

The fundamental problem with permitting systems is that they are managed by regulatory agencies with little or no obligation to solve a problem. Permits are not applied for because it is a fun thing to do; we request permits because we want to solve a problem. It is rare to have a regulatory staffer say “Oh, I see your problem. And I understand why you want to do what you have laid out in this application. There are a few issues we have to address, but let me see if I can find a way to make this work…” Instead, the regulator views his/her job as preventing environmental damage, not solving an existing environmental problem. If, after a frustrating process of submission, hearings, delays, and revisions,  you give up trying to solve the problem, that is just as good as the agency issuing a denial. The permit system has been upheld. The potential risks from the proposed action have been averted. It doesn’t matter to the regulator that the problem has not been solved.

If someone is advancing a clearly detrimental request, say asking to fill a cove of a public lake full of endangered species to build a supermarket accessible by boat, all to make a few bucks, it is pretty easy to rule that out. But most requests have merit and raise management issues that need attention. What happens when the request is to control an invasive species known to reduce biodiversity, one that will impact some of the endangered species in that same lake, but the options for control may do some temporary harm to the lake? This is a balancing act, but one in which the actual problem may be given very limited consideration. After all, no state in New England (or anywhere for that matter) has a law saying that if an invasive species is found it must be addressed, but most states do have a law that says you can’t harm a protected species or damage wetlands, of which lakes are usually considered to be a category.

Any action that reduces the invasive species may be rejected under current regulatory systems if it is perceived as being harmful to some interest of an applicable law, such as taking individuals of an endangered species, and the burden of proof is on the applicant. The regulatory agency is under no obligation to properly justify its assumptions at that stage (you would have to go to court for that) and can require all sorts of studies of the applicant before rendering a final decision, which may still be unfavorable. And if the applicant gives up and the invasive species eliminates some endangered species in the lake? Apparently that is acceptable, as opposed to losing some of the endangered population in the process of eliminating and invasive species and saving the endangered species in the long run!

The problem is twofold: 1) Lack of big picture thinking by agency staffers, partly attributable to having limited background in aquatic ecology and lake management, and 2) Vesting authority in a regulatory process without any obligation to solve the problems that result in requests for permits. Both of these are solvable, but appear to require political intervention; scientific logic and economic sense are just not getting the job done these days.

Zebra mussels killed this mollusk

Understanding Detention Time and Flushing Rate

The average length of time which water spends in a lake is quite simply the volume of the lake divided by the inflow of water from all sources. The flushing rate is the inverse of detention time, or the amount of time it takes to replace the volume of a lake. This is best understood as an example.

A 100 acre lake with an average depth of 10 feet holds 1000 acre-feet of water, or 43.56 million cubic feet. If surface water inflows average 10 cubic feet per second, that adds 864,000 cubic feet per day. If direct precipitation is 46 inches per year, that adds another 383 acre-feet of water per year, or about 46,000 cubic feet per day. If groundwater in-seepage contributes another 20,000 cubic feet per day, the grand total of water inputs would be 930,000 cubic feet per day, with the surface inflow being dominant in this case (which is not always the case, so adding in direct precipitation and groundwater is important). The volume of 43,560,000 cubic feet divided by an average inflow of 930,000 cubic feet per day yields a detention time of just under 47 days. The flushing rate would be just under 8 times per year.

In the example above, if the inflow was less, the detention time would increase and the flushing rate would decrease. If more water was somehow put in the lake, the detention time would decrease and the flushing rate would increase. One could use sources of outflow to get detention time and flushing rate, with surface outflow, evaporation, and out-seepage of groundwater as the primary outflows (unless there is a major withdrawal of some kind), but the inflow and outflow have to match over the long run for the lake to remain stable, and it is easier to get values for inflow sources than outflows.

A key point is that it is only the volume of the lake and the total inflow or outflow that matter to detention time and flushing rate. One cannot change these values by altering an outlet structure, dredging a channel, or other physical manipulations within the lake. If no more water is added or subtracted from a lake with the same volume, the detention time and flushing rate do not change. Dredging and other lake manipulations may alter the circulation pattern, and if the lake is subdivided into parts, this may affect detention and flushing of one part, but the overall detention time and flushing rate cannot change without a change in lake volume or inflow quantity.

Detention and flushing rate are important to lake function and many management options. A lake with a detention time of less than about two weeks is unlikely to develop algae blooms, as the water does not stay around long enough to let blooms form. Lakes with very long detention times, more than a year, are less subject to watershed influences on a day to day or even season to season basis; there is simply not enough inflow to alter water quality over a short space of time. And most water quality models that allow us to predict changes with specified management actions depend on detention time or flushing rate as an important term in the mathematical model; being off by even a small amount affects calculations and reliability.

Detention time and flushing rate are not constants, however, and vary over time with changing inflows. For lake with long average detention times, this is not a major influence, but for lakes with average detention times of days to a few months, the variation within a year can be meaningful. A lake with an average detention time of a month could experience much lower summer inflows and have the same water present for 3 months, while spring thaw and related snowmelt and rain reduce the detention time to a matter of days in April.

Detention time and flushing rate can vary over space as well. A “dead end” part of a lake may have a much longer detention time and be flushed much less than some area in the main path of inflows, leading to stagnation and possible water quality problems in that dead end cove or segment of the lake. Rerouting water through the dead end may improve circulation and reduced detention time for that area but unless this is new inflow to the system, it will not change the average detention time for the whole lake.

One other related concept is important to understand when managing lakes. If a lake is long and linear, with most inputs at one end and the outlet at the other end, as with certain human-made reservoirs, the movement of water is called “plug-flow” in engineering terms, and is similar to water moving through a garden hose. Each increment of inflow pushes the next increment forward, and while there will be some mixing, water entering the lake at any time will have more or less similar detention time to water entering at any other time, with variation due mainly to changes in inflow rate. An algae bloom that forms in such a lake will be removed after about one flushing, or replacement of the equivalent of about one lake bottom.

But for the more typical lake configuration of a bowl with various input sources and an outlet somewhere along shore, the engineering model is called a “continuously stirred tank reactor”. In this model, each increment of water added is completely mixed with all other water in the lake, and while average detention time is calculable, the actual detention time for any increment of water can be highly variable. Because of the mixing, it takes much longer to get any undesirable water mass flushed out of the system. Just replacing the water volume of the lake one time (one flushing) will not get rid of all of an algae bloom or a spike of phosphorus or an oil spill; it takes 3 to 5 flushings to clear the lake.

Sources of Plankton Blooms

For many years it was generally thought that planktonic algae blooms involved a few resting stages germinating from the bottom or a few cells hanging on from some previous time in the water column encountering adequate nutrients under sufficient light, resulting in enough growth to discolor the water and be called a “bloom” (Note: there is no technical definition of a bloom; it is in the eye of the beholder, although there is general agreement that there should be reduced clarity and increased color involved). This mode of bloom formation is certainly possible and does occur, but for the harmful algal blooms currently getting so much media attention, there are two other modes of bloom formation that seem to be dominant.

One mode is metalimnetic accumulation, which means that algae accumulate in the boundary layer between upper, well-lit, warmer waters (the epilimnion) and lower, darker, colder waters (the hypolimnion). This can only happen where the lake is deep enough to develop a thermal gradient, usually more than 20 feet in New England, but thermal stratification can develop in shallower lakes under the right circumstances. Algae in this zone get enough light from above and enough nutrients from below to grow into a dense layer which may be disrupted by wind or may synchronously rise in response to lower light availability or changes in temperature that signal breakdown of thermal stratification. These blooms are most often evident in late summer or early fall, but can be moved into upper waters by summer storms. Several types of golden algae that produce taste and odor use this mode of growth, and water supplies with intakes in this boundary layer have to deal with them. Several blue-green algae known for toxicity also utilize this mode of growth and are a threat to both human health and lake ecology.

The other mode involves growth at the sediment-water interface, much like algae mats, with an eventual rise in the water column, again like the mats. But we think of these algae as planktonic forms, and never really considered their origin. It appears that these algae, mostly blue-greens and often potentially toxic forms, gain most nutrients from decay or other releases from sediment, accumulate excess amounts in cells, grow to full “maturity” on the sediment, then produce gas pockets in cells and rise over just a few days to form a ready-made bloom at the surface.

These bottom-formed blooms are particularly problematic in lakes known for being “clean” for many decades. The inputs from the watershed over many years were assimilated into the bottom sediments and at some point the balance tipped, such that the accumulated nutrients, especially phosphorus, became available for uptake at the sediment-water interface. It appears that this is related to oxygen loss in the surficial sediment, largely a function of organic build up. The water column may still have low nutrient levels, but the rising blue-greens already have enough extra nutrients to survive for days to a few weeks, and the resulting blooms seems to come out of nowhere to impair lake use and threaten ecological functions. Worse yet, this appears to bring nutrients into surface waters, allowing follow on blooms when the initial algae die off. This mode of bloom formation is both a harbinger of eutrophication and a vector of it.

Planktothix sp., a metalimnetic bloom former

Dolichospermum lemmermannii, a bottom bloom former

NALMS 2017 International Symposium Registration Open

The 2017 NALMS conference will be held in Westminster, CO, just outside Denver. This annual gathering showcases the best in lake management through presentations, exhibits and networking. This is a gathering of researchers, consultants, governmental representatives and lake enthusiasts. If you work on lakes, you really can’t afford to miss it. But if you just love your lake and want to know more about how to keep it in its best condition, this is a golden opportunity. The best experts in lake management are readily accessible and enjoy interacting at this gathering. It is always a great event, starting with workshops and progressing through 3 days of interactive sessions. This year it all starts on Monday, November 6th and ends on Thursday, November 9th. Check out details at the NALMS website at