All posts by NE

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.

Where to Get Help

Found an odd plant in your lake? Is the water green when it used to be clear? Not catching as many fish as you used to? Just want to understand what is going on in your lake? These and many more common questions do not necessarily have easy answers. In all likelihood, there is someone around who can in fact answer any lake-related question you can come up with, but finding them can be a chore. Here are a few ideas of where to get help.

In Maine, the Department of Environmental Protection (ME DEP) is home to two groups of lake experts in the Lake Assessment Section and the Invasive Plant Section. The Volunteer Lake Monitoring Program (VLMP) works closely with ME DEP, maintains the Lake of Maine website, and certifies volunteers to collect water quality data and conduct shallow water plant surveys.  Their program website contains a wealth of information, and their staff are very helpful.  Maine also has an umbrella organization that provides assistance to lake associations and individuals across the state, the Maine Lakes Society (MLS). This network of professionals and interested laypeople has their finger on the pulse of proposed legislation pertinent to lakes and keeps members informed; anyone interested in Maine lakes should be a member of this group.

New Hampshire Department of Environmental Services has a solid lakes staff, and the University of New Hampshire also has very talented people who can answer lake questions. Both run volunteer monitoring programs. The New Hampshire Lakes Association is well organized and is celebrating 25 years of service to the lakes community this year; New Hampshire lakes enthusiasts would be well advised to get involved with this group.

Vermont’s Agency of Natural Resources, Department of Environmental Conservation, has an active lakes unit and runs a volunteer monitoring program. The Federation of Vermont Lakes and Ponds is the state lake association and those interested in Vermont lakes should be members. There is also a newly formed statewide organization, the Coalition of Vermont Lakes, which focuses largely on lake restoration.

Massachusetts has a highly fragmented approach to lake assessment and management, so it is difficult to recommend one agency to contact. The Department of Environmental Protection handles permitting on a regional basis, but the Department of Conservation and Recreation has a Lakes and Ponds Program that does more outreach and actual lake management than the DEP. The Department of Fish and Game houses the fishery expertise in Massachusetts, as well as the Natural Heritage and Endangered Species Program, which handles endangered species issues. The Massachusetts Congress of Lake and Pond Associations is the state level organization for lake enthusiasts, and just held a very successful annual conference. If you live in the western part of the commonwealth, the Lake and Pond Association- West is a subset of MA COLAP that you should join.

Connecticut has suffered the greatest losses of lake-related personnel in recent years; there is no identifiable lakes assistance program, but there are knowledgeable people in the Department of Energy and Environmental Protection (DEEP) who can help. Lake water quality monitoring is conducting by the Water Monitoring and Assessment Program at DEEP. The Inland Fisheries Division conducts fish surveys in lakes and large rivers under the Warmwater Fish Monitoring Program. The Agriculture Experiment Station conducts aquatic plant surveys under the Invasive Aquatic Plant Survey Program. There is also a Connecticut Federation of Lakes that offers membership and educational programs to anyone interested in lakes in Connecticut.

Rhode Island has a Department of Environmental Management (RIDEM) that does have personnel who work with lakes, but not a defined lakes program. Save The Lakes (STL), RI’s association of lakes groups, is actively campaigning for a new hire at the department whose focus would be freshwater systems. But until then RIDEM provides STL a list of state contacts for Lakes, ponds and rivers which is available on the STL website. In addition, the University of Rhode Island Watershed Watch, celebrating 30 years of service in 2017 and hosting the NECNALMS conference at URI in early June, has a wealth of knowledge and monitoring data on RI’s lakes. Their website is a central clearinghouse of information for the state and region.

And do not forget about the various consulting firms in New England. While these are for-profit entities, they are for the most part very dedicated to the profession and the welfare of our lakes, and are almost always willing to talk with lake stakeholders about problems and options. Be mindful of how much time you take up, but do not hesitate to contact local firms for advice.

Finally, NECNALMS itself and the international North American Lake Management Society are educational resources with websites and members who can help. These are groups you should strongly consider joining, both for the programs offered and the networking opportunities they present. No one has all the answers, but collectively we can usually figure things out, and both NECNALMS and NALMS represent some of the best minds in the business and the most dedicated lake professionals out there.

Invasive Species Primer

So what exactly is an invasive species? There is no textbook answer, or at least not one that everyone agrees on. The most common professional definition is a species not indigenous to the area that does ecological and/or economic damage when it becomes established. It is not merely any species that cause a nuisance, as many native species (such as water lilies or coontail) can do reach nuisance densities and are quite native to New England. It is not a species that invades but maintains a low density or even goes unnoticed, not impairing any use of the lake. And there are such species to be sure. When professionals talk about aquatic invasive species, they are usually referring to plants or animals that arrive at a lake and become a dominant component of the aquatic community, negatively impacting other species or uses of the lake. Several non-indigenous species of Myriophyllum, the watermilfoil genus, qualify, but there are native milfoils as well, some of which are even on various state endangered species lists! The zebra mussel is a great example, not well established in many New England lakes, but causing both economic and ecological harm when it invades. The list of invasive species for each state varies a bit, but there are a few dozen species that just about everyone agrees we would be better off without.

What is it about invasive species that make them objectionable? For the most part, species termed invasive displace other species by some competitive advantage or lack of predators, and become abundant enough to influence lake features that affect lake uses. Dense plant growths can include native species, but among the worst conditions are associated with Eurasian or variable leaf watermifoil, fanwort, and hydrilla, all species that came to New England in the last century and have not been well integrated into aquatic communities. It is possible that at some point balance will be achieved, and some people or even agencies make the argument that we don’t need to act; if we wait them out, the invaders will become part of functioning aquatic systems. This might be true in some cases, but given the track record, it does not seem responsible to wait that long to test the theory.

Invasive animal species, like the zebra mussel or spiny water flea, alter the flow of energy in a lake and affect the aquatic food web. Aggressive snakehead fish similarly impact the food web, but from the top down via predation. Just how much damage is done can vary greatly depending on the condition of the infested lake. Lakes with very healthy native plant communities that cover the bottom in the zone where light is adequate tend to resist colonization by invasive plants, although it is reasonable to expect eventual dominance by the invader. Lakes with no hard substrate or very little calcium in the water column are not likely to support dense populations of zebra mussels, but one can expect that all native freshwater clam shells will be colonized and those species are likely to be eliminated. There can even be some upside, as with clearer water from the filtering effect of zebra mussels, but this tends to favor buoyant cyanobacteria, so ultimately zebra mussels may promote objectionable algae blooms.

Invasive species are analogous to infectious diseases. Not every disease will kill you, but none are considered pleasant or desirable. Living with a disease is highly personal experience, but acting as a vector for that disease is irresponsible. Having an invasive species in a lake and deciding not to act to control it may be a valid position in some circumstances, but the potential impacts on other lakes in the area should be considered in making management decisions. This is a complicated area of judicial, regulatory and scientific interaction, and blanket statements that universally apply are hard to come by.

The cost of impacts vs. the cost of control is also a difficult topic. Actually putting dollar figures on impacts is not always easy, and even accurate estimation of control costs can be challenging. Ideally, eradication is the goal, but that may not be feasible in all cases. There is a whole school of thought on invasion ecology that considers the potential for control along a timeline of species establishment and impact. Often invasive species are not noticed or managed until they have reached the point on the curve where eradication is very expensive. Clearly prevention is the most cost-effective approach to invasive species management, and rapid response is the clear second choice for action, but both of these are given way less attention than they deserve in our monitoring and regulatory systems at the state level. Maintenance and restoration are the more expensive alternatives that apply once an invader has become established, and the cost can indeed by staggering. Millions of dollars are spent annually in New England alone to manage invasive species, rarely with eradication as a result or even a goal.

There is a very real need to enable citizens with an interest in lakes to recognize invasive species and to empower groups to take early action. In Massachusetts, the process and timeline for getting a permit for a rapid response program are the same as for addressing a longstanding infestation or addressing nuisance native species. We have no mandate to control invasive species, but we have laws and regulations that protect many species; if the control of an invasive species conflicts even a little with protection of an endangered species, the chances of getting a permit to control the invader are very slim. A more holistic approach is needed, but until we reach that stage of enlightenment, it is important for lake monitors to recognize invasive species and bring them to the attention of appropriate state agencies.

Source: http://senecacountycce.org/natural-resources/invasive-nuisance-species/invasion-curve

 

Ice Out and Its Meaning for Lakes

The annual date of ice out for some lakes is fodder for prognostication and even wagers, but for aquatic plants and animals, that date has deeper ecological significance. Light and temperature are key cues in the aquatic environment, and ice cover keeps lakes cold and dark in late winter. As the air temperature warms, the ice melts, usually leaving open water around the edge and then falling apart over deeper water over a short time period. If that date is earlier, algae and rooted plants can get a head start on spring growth. If that date is later, growth is delayed. Temperature also affects when hibernating aquatic animals, like turtles and frogs, become active. Fish are active even under the ice, as any ice fisherman will tell you, but are more aggressive after ice-out and turn to spawning activities based on temperature cues.

While lakes may not actively manage time, it is a lot like it is for people; if you get up early, you can get a lot more done in a day, and you may not be able to finish your to-do list if you sleep in. As the water warms and light penetrates further without ice, lots of biological processes increase in lakes. Bacteria decompose organic bottom sediments, using oxygen and releasing various substances into the water column. Algae take up nutrients and use sunlight to photosynthesize and make more biomass. Zooplankton eat algae and reproduce more frequently, but small fish also eat zooplankton and limit that trophic level by early summer in most lakes. Fish spawn and make small fish that eat those zooplankton.  In the meantime, rooted plants are growing, either from seeds, various winter buds, or root stocks, anywhere that light penetrates to a hospitable bottom substrate. Benthic invertebrates, often dependent on those plants, grow, reproduce and are eaten by fish or each other. A lake waking up from what seems like a winter sleep is indeed a busy place!

With variation in ice out date from year to year, and weather variation once the ice does go out, the sequence and intensity of cues will vary considerably from year to year, making every year unique to some extent. General patterns of plant growth, algae succession, fish spawning and other biological processes are known, but small changes can make quite a difference. A cold snap or windy period in May can retard stratification or cause a downturn in fish spawning that is not recoverable in that year. A very mild winter like we had going into 2016 can let perennial plants like invasive species of watermilfoil get a very early start (some plants may not even have died back to roots and stems) that outcompetes native species and makes it hard for harvesting programs to keep up. Weather plays a big role, and is influenced by climate change.

Climate change is a popular topic and the subject of spirited debates, but the data clearly show that lakes have been experiencing earlier ice-out dates over the last century (see graph). We seem to be losing a day of ice about every decade, such that based on the period of record going back about 150 years ice-out is now occurring two weeks earlier on average. Just keep in mind that aquatic organisms do not live in the “average”, and lakes have experienced both very late and very early ice out dates in just the last few years.

Ice out dates for various lakes. 

Source: https://www.epa.gov/climate-indicators/climate-change-indicators-lake-ice

 

 

 

 

Zooplankton: The Missing Link

Most people know what algae are, and most have seen both blooms in lakes and pictures taken with a microscope that reveal the fine details of algae cells. Even more people are familiar with fish, even if it is just through the menu at their favorite restaurant. But there are not many fish that eat algae directly; we need an intermediate link to complete the open water food web. That link is the zooplankton, which are small animals, rarely bigger than the head of a pin, that eat mostly algae and are in turn eaten by small fish.

Zooplankton includes small aquatic animals in the water column, mostly crustaceans. The main zooplankters are cladocerans, copepods, and rotifers (see photos), although there are tinier forms (like protozoans) and bigger types (like water mites). They can be filter feeders or selective grazers, picking out what they want from the aquatic soup in which they live. Filter feeders exert the most control over algae, with the filtering capacity proportional to the cube of body length. Consequently, large (>2 mm) bodied cladocerans like Daphnia are preferred for biological control of algae. However, those larger forms also represent the biggest energy “packet” for small fish, and once spring spawning produces the young of the year for each fish species, predation on those larger zooplankton can be intense. Peak zooplankton abundance tends to be in late May or early June, when the quality of algae as food resources is highest, warmer water increases growth rates, and predation by small fish is not yet maximal. This often leads to a clear water phase in even the most nutrient enriched lakes, but it doesn’t last. Types of algae shift toward less edible forms (like many cyanobacteria) and hungry small fish depress the populations of large zooplankton species.


In lakes used by sea-run alewife for spawning, the seasonal pattern tends to be shifted. Spawning alewife don’t eat a lot of zooplankton, but the young of the year live for the summer in those lakes, filtering out zooplankton with their gill rakers and decimating late spring/summer zooplankton. The zooplankton peak in those lakes is usually in winter by evolutionary adjustment. Stocking landlocked alewife in lakes is sometimes encouraged to support trophy gamefish production, but without that long evolutionary adjustment period, this tends to prevent large-bodied, algae-grazing zooplankton from becoming abundant and makes the open water food web much less efficient. It may indeed produce some large gamefish, but at the expense of many other species, possibly the gamefish themselves, as their young need zooplankton for at least a short period in early life.

Common zooplankton of freshwater lakes.

 

Zebra Mussels in Laurel Lake, Massachusetts

Laurel Lake, just off Rt 7 in Lee and Lenox, MA, is the only lake in MA infested with zebra mussels…so far! Zebra mussels got into the lake sometime around 2008 and were discovered in 2009. There has been a lot of discussion over the last decade, but only a small drawdown and boat washing station have been established in response to this problem. Zebra mussel larvae, called veligers, have been able to flow out of the lake and into the Housatonic River each summer, and now at least two reservoirs in Connecticut have become infested. The Laurel Lake Preservation Association (LLPA) has been working with the Towns of Lee and Lenox to fund studies of the lake and possible solutions; a detailed summary of work done from 2010 through 2016 by Water Resource Services Inc. was recently released. Now the LLPA is seeking help at the state and federal level, working to get all agencies with responsibility for or interest in the lake to cooperate on a solution before other lakes in the area become infected. Stay tuned for developments.

Zebra mussels growing on freshwater mussel (Pyganodon).

 

NECNALMS 2017 Conference Program Information

Our New England Waters: Real World Watershed
Monitoring and Management Options
Annual New England Lakes and Watershed Conference
June 9th & 10th, 2017
Kingston, Rhode Island

Hosted by:
• URI  Watershed Watch
• New England Chapter of the North American Lake Management Society, and
• Save The Lakes – Rhode Island’s Association for Lakes

Friday, June 9, 2017: Workshops
1-2:45 PM and 3:15-5 PM
• Invasive organism ID (plants and animals, G. Knoecklein , NEAR)
• Harmful Algae Blooms – Understanding their ecology and control (K. Wagner, WRS)
• Shoreland management (R. Hartzel, Geosyntec)
• GIS and web based tools for watershed assessments (G. Bonynge, URI)
Attendees can participate in any 2 workshops.

NECNALMS business meeting – 5:15-6 PM
Dinner at 6:30 PM
Paint Your Lake session (paint and sip) – 7:30-9:30 PM

Saturday, June 10, 2017: General Sessions (9 AM – 4 PM)

Group Session: 9 – 9:30 AM – Welcomes and updates:

Concurrent sessions: 9:30 – 10:30 PM

Citizen Science – what can volunteers do to help our waters?
Assessment tools – what works, what doesn’t, what is really useful? (K. Wagner)
Volunteer monitoring – 30 years of RI Watershed Watch (L. Green)

Changing Climate, How might it affect my lake?
Projections of coupled terrestrial and aquatic ecosystem change relevant to ecosystem service valuation at regional scales? (N . Samal, UNH)
OASIS reservoir operation model application to optimize water availability in the Scituate Reservoir (S. Paul, URI)

Break: 10:30 – 11 AM, Vendor Fair, Raffle open, refreshments

Group Extended Session 11 AM – Noon – Discussion with different perspectives, and audience questions focused on Herbicides – as a panel with users, regulators, and managers – alternatives, and when are they the right choice?

Lunch: Noon -1 PM – Buffet lunch
Optional gatherings for interest groups to network as desired:
Volunteer monitoring – L. Green
Simple lake assessment tools – G. Knoecklein?
HABs – H. Snook?

Concurrent sessions: 1:00 – 2:00 PM

In-lake algae control
Morses Pond (T. Stewart tentatively)
Proactive management of HABs using in-lake phosphorus inactivation technology (D. Meringolo, Solitude)

Fisheries
Fisheries – How do we make sure The Big Ones will there for our kids? (M. Lenker, ESS)
Case study in fish management (C. Nielsen, ESS)

Restoring Lakes
“Septic socials” – how to talk about waste disposal issues (G. Bradley, VT DEC)
The Dynamics of Dredging (J Davis, ACE)

Break: 2:00 – 2:30 PM – raffle drawings, networking

Group Extended Session 2:30 – 4 PM: Cyanobacteria: toxic issues, basic ecology and offering tours of the EPA Mobile lab – Hilary Snook

For more information contact eherron@uri.edu

Use of Aluminum to Treat Lakes

Aluminum compounds are coagulants used in water and wastewater treatment to settle solids and pull dissolved solids out of solution. In water treatment these compounds convert impurities into particles that can be settled or filtered. In wastewater treatment aluminum does the same thing, but is also noted for its ability to find phosphorus and lower the fertility of effluents. Over 40 years ago it was hypothesized that aluminum could do in lakes what it did in treatment facilities and might be especially useful for inactivating phosphorus in sediment that was being recycled to create what we now call an “internal load”. While a lot has been learned in the intervening years that makes such treatments more effective, even the earliest treatments provided enough benefits to make continued use worthwhile. Although aluminum treatments will clear the water of most algae, it is not an algaecide, defined simply by the root words as something that kills algae.

Aluminum application to a lake.

While the majority of regulatory agencies in New England appear to understand why and how aluminum is used in lake management, there seems to be some confusion in a few places about aluminum use. The State of New York created a regulatory definition of algaecide that expands coverage to any additive that prevents algae from growing. This would include aluminum, which limits phosphorus availability, and is not on the federal list of registered algaecides, since the EPA does not consider it to be one. Consequently, aluminum treatment cannot be permitted in New York. Of course, by this logic algaecides would also include oxygen if added to keep phosphorus bound to iron and unavailable to algae, and to air used to circulate water, thereby disrupting the growth of many buoyant cyanobacteria. It would also include water used to dilute phosphorus concentrations or even flush a small lake. Arguments about other additives being “natural” simply do not hold water. New England states have generally not bought into this faulty logic, but apparently the Connecticut Department of Health has applied the New York definition of an algaecide in some cases and has not approved aluminum treatments in drinking water supplies, despite approval by CT DEEP for such treatments in recreational lakes.

There is no doubt that control of phosphorus before it enters a lake is preferable where feasible, but there are very real limits on our ability to do that, and where phosphorus has accumulated in a lake, it has to be inactivated to rehabilitate the lake. It is much like fixing a boat that has sprung a leak; the leak needs to be patched, but that won’t get rid of the water that has leaked in. Aluminum treatments offer control of internal loading, and can also be used to treat inflows where watershed management is not yet up to the task or to reduce phosphorus availability in the water column after significant loading events. We have learned over the years how to prevent toxicity, making it a relatively safe technique. Creating regulatory restrictions based on faulty logic or incomplete understanding of the technique hinders lake management in a time when we need every viable technique we can get.

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.