Forms of Nitrogen

Nitrogen comes in multiple forms but, much like phosphorus, not all are available to all algae and plants. Total nitrogen is akin to total phosphorus, providing a maximum estimate of nitrogen that might be utilized for plant and algae growth, but different species make better use of some forms than others, and the range of nitrogen forms is wider than for phosphorus, so relationships are more complicated.

Nitrogen gas makes up about 78% of the earth’s atmosphere and reaches equilibrium with the aquatic environment, but only some specialized organisms can use nitrogen gas directly. Included are certain cyanobacteria, or blue-green algae, which is why a low ratio of non-gaseous nitrogen to phosphorus favors cyanobacteria; they have access to a nitrogen source that other algae can’t use.

One key set of nitrogen compounds is the sequence from ammonium to nitrite to nitrate, with conversion of ammonium to nitrite and nitrite to nitrate in the presence of oxygen and specific bacteria. The conversion is fairly fast, especially for nitrite, so nitrate should be the most abundant of these three nitrogen forms when oxygen is abundant. When oxygen is used up, as can occur in the deep zone of lakes over the summer during stratification when decomposition uses up oxygen and atmospheric replenishment is minimal, ammonium accumulates. Ammonium and nitrate are differentially preferred by different species of algae and higher plants, and so can affect aquatic biology. Ammonia, which has one less hydrogen molecule than ammonium and is toxic to aquatic animal life, is present as a fraction of ammonium depending on temperature, pH and other water quality factors, upping the stakes for which forms of nitrogen are present at what concentration.

Total Kjeldahl nitrogen (TKN) is determined by a digestion that turns organic nitrogen into ammonium, so this test measures all but nitrate and nitrite nitrogen. Addition of nitrate/nitrite to TKN is functionally equivalent to total nitrogen. The organic fraction (TKN minus ammonium) is not directly available to support plant growth, but decay processes will make some of that organic fraction available over time.

When assessing nitrogen in lakes and tributaries, the minimum testing to gain reasonable understanding of nitrogen influence includes TKN and nitrate/nitrite, although it is useful to have ammonium as well to separate the organic fraction from TKN.

http://lrrpublic.cli.det.nsw.edu.au/lrrSecure/Sites/Web/hsc_agriculture/lo/6945/applets/Nitrogen/Nitrogen_02.htm

Forms of Phosphorus

Just about everyone working with lakes knows that phosphorus is a key factor in many undesirable features of lakes, most notably algae blooms and. by extension, oxygen and pH fluctuations that impair habitat. But not all phosphorus is created equal. Soluble reactive phosphorus, usually orthophosphate, is the most available form, but is usually only a small fraction of the total phosphorus in any sample. In fact, soluble reactive phosphorus can cycle so fast that its actual measured quantity is not all that important in the interpretation of water quality; low concentrations are normal even in eutrophic lakes.

Total phosphorus is useful as a measure of maximum available phosphorus, but some portion of that total will be refractory, unavailable for uptake by algae. Yet nearly all the empirically determined relationships between phosphorus and other limnological features (e.g., chlorophyll, water clarity) are based on total phosphorus, so measuring total phosphorus is generally an essential part of any lake or tributary monitoring program.

The utility of everything in between soluble reactive and total phosphorus is a matter of some speculation. Empirical work over two decades ago found that total dissolved phosphorus, which is assessed the same way as total phosphorus except that the sample is filtered first, correlates best with algal growth potential. Total dissolved phosphorus is therefore a very useful back-up measurement to go with total phosphorus.

There are other forms of phosphorus that can be measured, and more than one way to measure many of the forms of phosphorus, so there are decisions to be made in any monitoring program that affect results, utility and cost. It is not a simple matter of measuring soluble reactive phosphorus, which is easiest and cheapest to assess. Care should be taken in the choice of phosphorus forms to be measured, the methods for measurement, and the use of resulting data.

Autoanalyzer used for phosphorus measurement

Forming and Running a Lake Association

Creating and managing a lake association is hard work, if you do it right. There are many types of lake organizations, including homeowners associations, watershed alliances, and lake management districts. They differ in the details of formation and their power over members, including taxation, rulemaking, and enforcement. Communication is a central and critical role of each, and can take many forms. Overall, there is a lot to know before starting a lake association and still more to know to run one successfully. NALMS produced a very useful pamphlet on this topic back in the 1980s, which is out of print and out of date, although it still has some great insights and advice. Producing a new, updated version would be another great service for NALMS or NECNALMS to offer. Just sayin’…

Lake Science for Real Estate Agents

If you have a background in lake science and have ever hunted for a lakefront home, you may have been frustrated with real estate agents who don’t know much about the lake itself and use words like pristine for any lake that doesn’t look like a putting green. NALMS developed a program to educate real estate agents about lake features and processes that are important to most lakefront property owners over two decades ago, before the internet was the force it is today. It seems that a rework is in order, one that could link state databases with real estate listings to give searchers useful background information on things like the presence of invasive species, water quality, or management practices that affect lake use, such as drawdown. At the same time, it would be nice to provide basic training for real estate agents so that they would know how to properly describe a lake in terms that a range of buyers could understand. This won’t keep unscrupulous sellers from making inappropriate claims, but it could allow buyer representatives (an increasingly common role for real estate agents) to be better informed and provide what the sellers are really looking for in a lakefront property. Is NALMS listening? Might NECNALMS take this on as a project in New England? Anyone up to the challenge?

 

NALMS 2017 International Symposium Registration Open – Still Time to Register!

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 https://www.nalms.org/.

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!