Category Archives: Watershed Management

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

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.

Size Matters

The relative size of a watershed vs. the area of the lake it drains into has a large influence on water quality, independent of land use in the watershed. Lakes which are small relative to the area of their watersheds are subject to higher loading of nutrients per unit area and shorter detention times (more rapid flushing). As the watershed gets larger or the lake gets smaller, lake water quality becomes more and more a function of incoming stream water quality. Internal processes may not matter much when the watershed is delivering large amounts of water and associated contaminants such as sediment, bacteria, nitrogen and phosphorus.

On the other hand, a larger lake with a smaller watershed may be minimally affected by its watershed on a day to day or week to week basis, with seasonal influences or even annual influences being the shortest time frame for change identifiable by monitoring. For lakes with detention times of close to a year or more, internal processes may dominate water quality, such as loss of oxygen in deep water and release of phosphorus from affected sediment. The inputs from the watershed matter in the long run, but do not greatly affect daily to monthly conditions when the incoming water is such a small percentage of the lake volume.

There is not an official cutoff for small and large watershed to lake area ratios, but a generally accepted scale has ratios of 50:1 having very high watershed influence on a short term basis. In all cases land use matters, but in the range of ratios of 20-30:1 that influence becomes very important. A watershed that is 20 times the size of the lake it drains into may have limited negative impacts if all forested, while the same ratio for a largely urbanized watershed may greatly impact water quality in the lake after storms.

It is therefore recommended that lake studies include a careful analysis of watershed to lake area ratio and land use within that watershed. Simple but fairly reliable models can be used to predict water quality based on these and a few other easily obtained watershed features, and represent an economical head start to understanding your lake and its management needs. Watershed and land use data can be readily obtained online for most areas, with a host of GIS-based programs available for use by those with minimal cartography skills. Try these out! It is actually fun as well as very educational. Do you know what flows to your lake?

Watershed size and land use mapping is now pretty easy from the comfort of your home.

Low Impact Development

Development and property management techniques that minimize water pollution impacts off-site are called Low Impact Development, or LID. There is some very clever engineering involved in some cases, but for the most part this is not rocket science. Sources on the property should be minimized, but recognizing limits on residential properties, the vehicle for off-site transport, runoff, is restricted. The idea is to limit impervious surfaces and collect as much runoff as possible for infiltration or detention on the property. The focus is on actions at the individual property level, rather than some larger downstream facility to hold greater quantities of runoff long enough to allow it to be purified by natural or engineered means.

Typical techniques include bioretention (rain gardens), porous pavement, grass swales, and green roofs. These techniques can work in almost any climate; having a cold winter is not really a deterrent. Sizing is important, but the most critical limitation tends to be soil type. Turning runoff into ground water provides excellent treatment and has not resulted in extensive ground water contamination, although each case must be considered individually. However, not all soils are conducive to receiving as much runoff as can be derived from roofs, driveways and packed lawn areas. Engineering in such cases is most critical and may be challenging. Where runoff cannot be percolated, it may be detained and purified by various means before being released to a stream or lake.

There is a fair amount of literature out there that explains the techniques and reviews results, but one does have to do a lot of reading to get up to speed. One accessible reference that is helpful and has an extensive reference list is Ahiablame, L.M., Engel, B.A. & Chaubey, I. Water Air Soil Pollut (2012) 223: 4253. doi:10.1007/s11270-012-1189-2. Another publication, free from the USEPA, is Reducing Stormwater Costs Through Low Impact Development Strategies and Practices. The key limitation to wider application has been insufficient documentation of results, which is a difficult problem. One can demonstrate success at the individual property level, but showing positive impacts on an entire lake ecosystem is challenging, since the extent of application has to be very high. Another troublesome aspect is that removal of phosphorus, probably the most important nutrient entering our lakes, is not especially high; one cannot completely counter the impact of development on a lake with LID. The good news is that there is very little downside; anything homeowners can do to limit contaminated runoff from leaving the home site will benefit the lake, and application of LID techniques is less expensive than alternative measures.

Reducing Stormwater Costs through Low Impact Development

Being Lake Smart

The best watershed management is applied at the source, but this means getting property owners to actively participate. Watershed management is a challenge, but there are programs to help. One such program is LakeSmart, a program of the Maine Lakes Society (MLS). LakeSmart educates, assists, and recognizes property owners who maintain their home sites in ways that manage storm water and waste water to minimize impacts on lakes. The program was created in 2004 by the Maine Department of Environmental Protection (DEP), expanded in 2009 by a partnership between the Society and DEP, and is now fully privatized under the Maine Lakes Society. The MLS presents its distinctive blue and white signs to homeowners who meet program criteria, and is approaching its 5-year goal of 60 lake association participants by 2018.

LakeSmart awards were presented to over 80 homeowners during the summer of 2015.   Posted at the lakeside and driveway entrances of a property, the distinctive blue and white sign identifies the owner as a person who cares enough to take action to protect the lake. Properties that display the sign show others what lake-friendly living looks like, arouse interest, and motivate similar behavior by other community members. The MLS model for running LakeSmart is cost-effective, leveraging the power, interest and commitment of lake association members to speed the program’s spread.

Many homeowners grew up with suburban landscaping and are accustomed to its tidy lawns and open space. But suburban lawns, with big driveways and wide paths, are deadly for our lakes. LakeSmart landscaping provides a healthy alternative that mimics nature’s rich mosaic of plants, shrubs, winding paths, and shady trees. It looks great, enhances privacy, and works hard to protect property values, wildlife habitat, water quality, recreational opportunities and the vitality of local economies. It looks even better when you understand how important it is to minimize nutrient inputs to lakes. It may be hard to believe that one person’s expansive lawn or eroding camp road could be a threat to something as large and enduring as a lake, but when added to a shoreline full of similar sites, it can have a very real impact, especially over multiple years. All storm water that gets into a lake carries nutrients. Over time, the cumulative impact can be thousands of pounds of pollutants. The result, “death by a thousand cuts,” leads to algae blooms, fish kills, and the loss of water clarity and spawning habitat. One tiny rivulet from one rainstorm may not seem like much, but when multiplied across a lake watershed and added up over decades, eroded soil can turn a lake into a smelly, pea green mess.

This is a program that can be applied anywhere. It is certainly easier to build a lake-friendly property from the start, but retrofitting and minimizing impacts is not really that hard in most cases. Check out the MLS LakeSmart program at http://mainelakessociety.org/lakesmart-2/ and contact Maggie Shannon at the Maine Lakes Society at msshannon@mainelakessociety.org  for more information.

Limits to Best Management Practices

A recent post discussed the role of watershed management in protection vs. restoration of lakes. The reason why watershed management cannot be a mainstay of lake restoration is not obvious to everyone, and here we explore the limits to best management practices in the watershed from the perspective of lake impacts.

Best management practices (BMPs) are procedural or structural techniques used to limit the delivery of contaminants from land to water and eventually the lake. BMPs may restrict what land uses or activities can occur, preventing generation of contaminant loads, or BMPs may focus on trapping contaminants on the way to the lake. “Best” does not necessarily mean adequate or effective, but it is often assumed that if all appropriate practices are applied, the lake will be protected. This is rarely true.

A well designed detention facility.

The USEPA has accumulated a huge database on the actual results from various management methods, with a focus on storm water BMPs, as non-point source inputs from developed or agricultural land are by far the biggest input sources these days. The overall average phosphorus reduction that is achieved by individual BMPs is about 50%. This is not the average of all possible projects, but those where the technique was properly applied and monitored; inadequate design, sizing or construction could provide less benefit. A few techniques approach the 90% mark for phosphorus removal, most notably infiltration into appropriate soils and inactivation and filtration, but these are rarely applicable on a watershed-wide basis.

Leaching basin.

Development and agriculture increase phosphorus loading by an order of magnitude or more in the absence of BMPs, which then reduce those loads by some percentage, averaging 50% on average where properly applied and less in many cases where implementation is incomplete or absent. But if we assume that all developed or agricultural uses are addressed by BMPs that yield a 50% reduction in phosphorus from the tenfold or greater increase expected without BMPs, we have a five-fold increase in loading. Even if we could achieve a 90% reduction, that still represents a doubling of loading from pre-development, pre-agricultural conditions. Human use of land is a losing equation for lakes.

This doesn’t mean that any development or agriculture will doom your lake. Where the human activity occurs and how it is managed matters a lot, and the overall percentage of the watershed in human uses is very important. Most practitioners agree that serious problems can be avoided up to about 25% of the watershed in developed or agricultural uses with judicious BMP application. However, it is simply not reasonable to assume that incoming water quality will be acceptable in urban areas (typically >75% developed) or farm country. The size of the watershed relative to the lake and the depth of the lake will matter too, so simple thresholds will not likely be reliable in all cases. Yet it is clear that where human activities dominate the landscape, application of BMPs will not be able to keep up with the generated loads.

Protection vs. Restoration

There has been a lot of discussion at the annual NALMS symposium over the last 5 years about the value of watershed management. Much of this discussion was a reaction to federal and state directives to focus on watershed management to solve lake problems, as we know from many years of experience that some problems cannot be solved with watershed management (e.g., internal phosphorus loading, excessive plant density) and watershed management has proven very difficult over large areas under multiple jurisdictions. In articles in LakeLine and presentations at NALMS meetings a few people have made statements that have been interpreted as opposing watershed management, but these statement are being misinterpreted in the context of protection vs. restoration.

First of all, there is very little lake restoration going on. We often rehabilitate lakes, altering them to meet use goals, but that is not the same thing as restoration. For lakes created by erecting a dam, true restoration would mean removing the dam and eliminating the lake; this is not usually what lake managers have in mind when they use the word “restoration”. But whether we call it restoration or rehabilitation, reducing nutrient levels, algae blooms and nuisance vascular plant growths is rarely achieved by watershed management once the lake gets to the point of supporting such growths. Once in a while we find the “smoking gun” and can implement a focused watershed management plan, but usually it is a slow, incremental process that very rarely moves the lake adequately in the right direction. Consequently, in-lake efforts are often needed to meet use goals, including phosphorus inactivation, dredging, herbicides, harvesting and other commonly applied methods.

Protection, however, is another matter. If a lake is in a desirable state, it is wrong to assume it will always be that way. Watershed influences can be gradual or catastrophic, but their presence is undeniable. If the watershed is large enough (>10:1 ratio with lake area is a commonly cited threshold), inputs over many years will eventually change the character of the lake, and water quality issues become more probable when the watershed is >50 times the area of the lake, even with no human activities in the lake. However, human activities greatly accelerate loading of sediment, nutrients and a variety of other contaminants. Thresholds as low as 6% development in the watershed have been cited as resulting in measurable changes in water quality, and at development levels on the order of 25-30% it is rare not to see deterioration of water quality. Watershed management is therefore essential to protecting lakes, but the potential to adequately protect the lake declines as the percentage of development or agriculture increases.

Developed vs. Forested Land.

Watershed management is a logical component of any lake management plan. It is wrong to hold an invasive plant control project hostage until the applicant produces a watershed management plan, but it is entirely reasonable to expect holistic lake management programs to incorporate watershed management. If protection of desirable features is the goal, watershed management is a must. If rehabilitation of degraded conditions is needed, watershed management is not likely to be the whole answer. Keep protection and restoration elements of any plan separate when discussing lake management to avoid controversy over the role of watershed management.

Agriculture by a Lake.

Climate change impacts quantitatively assessed

Some impacts of climate change have known for years, but others are still surfacing. About a decade ago a representative of the USGS in Maine presented data at the NECNALMS conference for the date that ice cover broke up for multiple lakes in Maine. While there was variability typical of systems influenced by climate change, it was very clear that the date the ice was going out was getting earlier over decades. In about a 60 year period the average ice out date for the 2000s was about 2-3 weeks earlier than it had been in the 1950s. This should have been impressive enough in its own right, but apparently few other than ice fisherman really took notice.

Now we have another interesting measure that might be scarier. Oxygen consumption is an important feature in lakes, causing oxygen to become depleted (called anoxia) in many lakes deep enough to stratify, at which point oxygen can’t rapidly move downward from upper waters and decomposition gradually removes  oxygen from the bottom up to the boundary point, called the thermocline. Fish like trout that need cold water (<21 oC) but high oxygen (>5 mg/L) can get “squeezed”, faced with water too warm above and water with too little oxygen below. There may be no “trout water” during late summer, causing mortality. Further, loss of oxygen in deep water can allow phosphorus bound to iron to be released into the water column where it can support algae blooms, most often cyanobacteria that are favored by this type of release. In shallow water, high oxygen demand is indicative of elevated decomposition, and while complete loss of oxygen in water <15 ft deep is rare, that decomposition releases phosphorus that can fuel algae blooms. So oxygen consumption matters a lot to lake condition.

Data from Long Pond in Brewster and Harwich on Cape Cod, collected by the Natural Resources Department as part of a very useful water quality monitoring program, were plotted in an effort to understand the variation in oxygen consumption observed over time. What was found was that a relatively small difference in temperature, brought on by warmer spring air temperatures, resulted in a major increases in the rate of oxygen consumption, or oxygen demand (see figure). Oxygen demand below about 550 mg/m2/day is considered unlikely to cause severe anoxia, while values higher than 1000 mg/m2/day usually cause most of the bottom water layer to become anoxic in August and values greater than 2000 mg/m2/day will typically cause anoxia in July. Long Pond has an oxygen depletion problem, and it worsens appreciably with increasing temperatures in the deepest water.

Using a statistical technique called regression, the portion of the variability attributable to any tested factor can be evaluated. For Long Pond, and probably many other lakes, change in temperature explains much of the variation in oxygen demand (62% for Long Pond, a high percentage for a single factor). And this doesn’t require a large change either; the range of oxygen demand in Long Pond more than doubles for a temperature increase of only 3 Co (5.4 Fo)! The influence of the current direction of climate change is pushing our lakes toward a higher metabolism, almost like they have a fever, and the implications for all users, human or otherwise, are not good.

Oxygen demand as a function of temperature in Long Pond, MA.