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 https://www.nalms.org/.

Your Lake and You Publication Available

For many years NALMS has had this newspaper-style publication available, one that has a lot of basic info on lakes and can be customized for any particular lake, association, or state. Your Lake and You has recently been updated and is provided as an electronic file that may be very useful to your lake group. As explained on the NALMS website, the 2017 online edition of the Your Lake & You! booklet is an updated version of the 8-page newspaper and helps explain to homeowners the steps they can take to protect the lakes they live on and love. This wonderful resource is loaded with basic lake information, strategies for taking better care of lakes, and descriptions of resource publications. Find it online at https://www.nalms.org/nalms-publications/.

Lakes Appreciation Month Wraps Up

In case you missed it, July was officially “Appreciate Your Lake” month. For members of NALMS, July represents a time to reflect on how we value lakes, usually with a focus on individual favorites. A number of people were interviewed on National Public Radio’s program Here and Now, segments of which can be found online hereOf course, you can appreciate your lake any time, and some of us like our lakes even better at other times of year besides summer. But summer is the key season to most, and July marks the annual kick off of the Secchi Dip In, an annual collaborative data collection effort that has resulted in a magnificent data base that allows us to know what the distribution of water clarity is for all regions of the USA. If you measured Secchi transparency in July 2017, please submit your data to this valuable data base. Check out the NALMS website for more on Lakes Appreciation Month and what you can do for your lake!

 

Algae Mats

Two groups of algae form almost all the mats: green and blue-green algae. These mats mostly form on the bottom, utilizing nutrients at the sediment-water interface, then move upward as they trap their own photosynthetic gases or accumulate gas released from the sediment under thick tangles of filaments. These mats may continue to grow for a time at or near the surface as a function of stored nutrients from their time on the bottom or from additional nutrients in the water column. Yet ultimately they tend to wind up on the surface, often blown to the edges by wind, in large decaying masses that turn various colors from yellow to blue and may be quite malodorous. In great quantities, they can really detract from the lake experience.

One partial exception includes the “cotton candy” or “cloud” growths of certain filamentous greens, mostly in the Spirogyra group. These algae do get their start at the bottom, but grow upward in a loose, slimy affiliation that looks like a mass of light green cotton candy or a cloud in the water. When you try to grab it, there is not much to grab, but your hand feels slimy. These algae produce a lot of mucilage, hence the slimy feel, and have enough structural strength to expand into these underwater, microscopic, “tinker-toy” conglomerations.

Sometimes a green mat will remain anchored to the sediment while part of it floats upward, creating a pillar in the water. Blue-green mats of Plectonema are brown to black and don’t rise in New England lakes until late summer, if at all, but from about Maryland south they can be a major impediment to lake use from early summer on. In New England, blue-green surface mats are most often chunks of Oscillatoria that break free of the bottom; these are very dark blue to black, often with brown sediment on the underside (still attached from the bottom) and they often have a distinct and unpleasant odor.

Algae mats are a clear indication that nutrients have accumulated in the sediment in water shallow enough for light to penetrate to the bottom. Once formed, algae mats are very hard to kill, as the outer filaments protect the inner filaments to a large degree. Removing the sediment is the most effective approach, but is very expensive and involves an often tedious permitting process. Treating the sediment with a phosphorus inactivator or algaecide before dense mats form is often effective, but results are not permanent.

Green algal mats   

Blue-green algal mats

Spring Fish Kills

A lot of fish agency staff would like to have that proverbial nickel for every phone call they get about dead fish in the spring. Consultants get this too, and one can pretty much count on a couple of calls a week about dead fish in late May and June, but sometimes right after ice out. There are lots of things that can kill fish, including disease, angling mortality, toxic substances, low oxygen, and high temperatures, but the vast majority of fish-kills boil down to two main influences: low oxygen under the ice and spawning stress in late spring.

First, consider what defines a fish-kill. Two dead fish washing up on shore doesn’t really qualify; most agencies apply some number like 50 to a species or 100 to multiple species. It would be very wasteful to investigate every dead fish that shows up. If 50 fish (or whatever reasonable threshold is applied) of a species can be found at once, that is considered to represent some kind of event. Likewise, if 100 fish of multiple species are found in a short time span, that suggests something more than typical die off. So please don’t get on the phone to your fish agency or consultant when 5 dead sunnies float to shore. By all means, take a lap around the lake and see if this is a widespread phenomenon, in which case a call may be in order, but don’t panic over a few dead fish.

So if we do find enough dead fish to raise an alarm, what might this mean? The first conclusion that many jump to is that there is something undesirable in the water and fish are dying from it. Well, that may be true, but even if so, that doesn’t mean people will die from it if they go in the water, but that is a leap that many people make. If dead fish are plentiful after the ice goes out, it probably means that oxygen got too low and less healthy fish died. This could be one species that lives in the affected area (catfish on the bottom come to mind), or it could be multiple species that coincide in an isolated area (a shallow bay where thick ice met the bottom off shore and prevented them from leaving). These winter fish-kills may not be detected until the ice goes out, but the fish did not likely die after ice-out.

The other, and far more common cause of spring fish-kills is spawning mortality. Many species, most notably perch and sunfish, spawn in shallow areas in the spring. Perch tend to be earlier spawners, and the water is colder and better oxygenated, so they are less likely than sunfish to experience stress while spawning. Sunfish, on the other hand, start spawning in May in much of New England and may continue to do so well into summer. They make nests in shallow water subject to fluctuations in oxygen and temperature within and among days. They don’t eat but they do defend the nests against other fish. The energy balance just doesn’t work out in some cases, and some fish die. If we have extremely variable weather, the stress is often greater.

If a June fish-kill is one species, all of similar size, most commonly 5-6 inch sunfish, you can pretty much count on it being spawning mortality. If the kill involves multiple species or a wide range of sizes, then there might be something worth reporting. It should be noted that the timing of fish-kills in late spring often coincides with a period of herbicide application, leading to another leap to a conclusion that is rarely justified. Over 20 years of fish-kill investigation in Massachusetts, covering hundreds of investigated events, only a handful were linked to herbicides and these were almost always a function of low oxygen created by dying vegetation; toxicity to fish from properly applied herbicides is very, very rare.

Spring fish-kill

Two Main Plant Types

Plant taxonomy aside, there are really two main plant types when we are considering management: annuals and perennials. At this point all those whose eyes glaze over when the Latin genus names start rolling out should be paying attention, and gardeners and home landscapers probably already get it. Much of the decision about what to do rests on whether a plant reappears annually from seeds or other resting stages (propagules) or comes back from root stalks or stems (or never really dies back in winter). Perennial plants are easier to deal with (just like in your garden or lawn); if you kill the plant, it won’t return from its vegetative parts. For annuals, however, killing the plant just buys time; seeds, winter buds, turions, and other structures germinate and form new plants, usually in the following spring. Management strategies therefore have to consider whether the target plants are annuals or perennials, when they produce propagules, and when growth begins.

If one is applying drawdown, it can be effective on perennial plants like the milfoils, but will have little impact on annuals like naiad or most pondweeds. In fact, drawdown often stimulates propagule germination, so a shift from perennials to annuals can be expected over a period of years with continued annual drawdown.

If one is using herbicides, killing the plant before it can drop seeds is essential to eventually gaining control over an annual, but the seed bank may be large enough to allow recovery for years to come. If a contact herbicide is used, the root system of a perennial is usually unharmed and will allow plant regeneration. Systemic herbicides, which move throughout the plant and are intended to kill it all, can provide more lasting results with perennials, but are more expensive than contact herbicides and may be a waste of money for annual plant control.

Benthic barriers kill nearly all plants over which they are placed, but if the barrier is removed, propagules from annual plants are likely to sprout. Hand harvesting practitioners know that it is essential to get the whole plant out, roots included, if a perennial species is to be controlled by that means. Dredging may be the only all-purpose tool for rooted plants, removing the plant and the seed bank, but at a very high cost with a lot of permitting, so we don’t see this approach used much.

Some plants apply a mix of perennial and annual strategies, making them harder to manage. Bigleaf pondweed produces seeds but does not die back completely in most winters and survives many drawdowns and herbicide treatments. This is a native species in New England and is not a major nuisance plant in most cases, but it has created problems for swimming in some lakes. Many perennials do produce seeds, but viability tends to be low; they don’t depend on these for annual persistence, but it does mean that removing a stand of a perennial plant may not be a one-time job.

So be sure to know which plants apply which strategies when considering control; success may depend upon it.

Curlyleaf pondweed, an annual  

Eurasian water milfoil, a perennial

Invasive Species Statistics

Invasive species cost the USA over $120 billion annually, considering both management expenses and losses due to lack of management. The USA has experienced invasions by over 4000 plant species and 2300 animal species. About half of all pest species in the USA are exotic species, with nurseries, mail order, and the aquarium trade leading the way in new introductions. Just recently a shipment of an invasive snail not yet known in the USA was intercepted on its way to Hartford, CT. These are not trivial numbers.

We know about the impacts to agriculture and lake recreation, but often we get resistance to management from regulatory or private groups concerned over non-target impacts. This may be a valid concern in some cases, but doing nothing also has impacts on non-target species. About 30% of endangered species in the USA got on that list, at least in part, due to invasive species impacts. About 27 of 40 fish that have become extinct over the last century were eliminated by invasive species. After development, invasive species is the largest cause of loss of biodiversity. Doing anything represents risk to some component of an aquatic ecosystem, but so does doing nothing, and this needs to be recognized to get balanced decisions when considering possible management options.

Invasive species experts encourage managers to treat invasions like we do communicable diseases in medicine. Key steps include quarantine, assessment of damage, consideration of treatment options, and implementation of rapid response, rehabilitation, or maintenance. Prevention is important to avoid invasion in the first place or prevent re-infestation, but won’t reverse an invasion in progress.

Variable water milfoil

Zebra mussels

Celebrate Lakes Appreciation Month by telling us about your favorite

Whether it’s memories of idyllic summers spent in a cabin by the lake, learning how to swim or water ski, or morning coffee on the dock in your backyard we all have experiences we savor about our favorite lake. We’d love to hear about your favorite and what makes it so special.  Not only are those reflections fun to read about, but by sharing those experiences with decision makers, groups like NEC-NALMS and our national organization NALMS, can help make the importance of protecting those critical resources more apparent.

So why not leave us a comment to tell us about your favorite and what makes it so special?!

 

Where Drinking Water Comes From

Drinking water comes from the same places as all other water, it just tends to get treated differently to become potable supply. Treatment is required if specific source water conditions are not met. The risks from even natural sources of contamination (e.g., birds, wildlife, erosion) are substantial enough to necessitate treatment in most cases. Yet there is general recognition that drinking water sources need protection, even if that protection is not always provided. A study by the Nature Conservancy revealed that on average about 37% of the land in drinking water supply watersheds is protected from human–derived contamination sources. The other 63% is mostly in private ownership with varying degrees of development (8% on average) and agriculture (15% on average). There is geographic variation, with water supplies for west coast cities having a greater proportion of protected land than for eastern cities, and with northern New England having less developed lands but more agriculture than southern New England. Each case is to some extent unique, leading to differences in the level of treatment necessary.

About 85% of the population of the USA gets its water from public supplies, a percentage that has increased over decades from around 70%. About two thirds of that water is surface supply, a value that has been declining for years from a high of about three quarters. The remainder of the potable supply comes from wells, which have increased in use over the years. This is interesting in that public water supplies are fairly tightly controlled by law and regulation, and many wells are part of public supplies, but private well supplies experience minimal regulatory control. This suggests that an increasing portion of the population is less protected against water quality threats, although it is also true that water from wells is usually of acceptable quality.

About a decade ago 77% of surveyed people did not know where their drinking water came from. That is a scary statistic that suggests a low level of interest in this critical resource. Such lack of knowledge, and presumably concern, is very disappointing but is also consistent with the limited public support for water resource management. Education may not turn everyone into cooperating supporters of better land and water management, but it is a safe assumption that we won’t get more enlightened policy or greater support without such education.