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A Short Primer on Oxygenation for Lake Management

Circulation is one way to oxygenate a lake, but here we consider methods that do not destratify the lake. These are often called hypolimnetic oxygenation, referring to the bottom layer of a stratified lake as the target of the action. In some cases it is important to maintain stratification, either to support a coldwater fishery or to keep separate water layers for some supply function. There are four basic ways to add oxygen to deeper waters without causing mixing and a lot of information to gather and consider when designing an appropriate oxygenation system. The Practical Guide to Lake Management in Massachusetts, available online from the DCR within the Mass.gov website, has a useful review of this technique, and a 2015 publication available from the Water Research Foundation has considerable additional detail.

Hypolimnetic oxygenation is a technique for increasing deep water oxygen and managing algae through control of nutrient levels. The central process is the introduction of more oxygen, intended to limit internal recycling of phosphorus, thereby controlling algae. The extra oxygen also reduces the accumulation of other undesirable substances, such as iron, manganese, ammonia and hydrogen sulfide, which makes this process attractive for water supplies. The four general approaches include hypolimnetic aeration chambers, speece cones, diffused oxygen, and sidestream supersaturation.

Hypolimnetic aeration chambers use an air compressor as with whole lake circulation, but in this case the upward plume is contained in a chamber to avoid mixing with the surface waters; water is pulled in, oxygenated by air contact, and returned to near where it came from initially.  Use of air can be effective but is not efficient; transfer is slow and the vertical distance of contact rarely allows more than 30% of the oxygen in air (which is only 21% oxygen to begin with) to be transferred. A lot of water has to be moved through the chamber to reach common oxygen goals, and the cost of power to do that can be substantial.

Speece cones are chambers where deep water is pumped in along with pure oxygen, and the rate of input of each is supposed to balance, such that all the oxygen is dissolved in the water. The oxygenated water is then put back in the deeper part of the lake. Any excess oxygen rises to the surface or is trapped in the chamber; at best this is a waste, and at worst it could cause unintended mixing. Installation of Speece cones in a lake can be challenging, and maintenance can be tedious. This approach can be effective and efficient, but tends to be hard to operate well.

Diffused oxygen is a simple process of releasing small bubbles of pure oxygen into the water column at a deep enough depth to allow complete absorption before the bubbles can rise enough to cause destratification. This generally requires about 20 feet of bubble travel distance, so this approach may not be applicable to lakes with only a thin layer of bottom water. In earlier years, the delivery mechanism had not been perfected, but these days adding diffused oxygen is fairly straightforward and reliable. Liquid oxygen is allowed to convert to gas and moves through delivery lines under the pressure of the gas, resulting in very low power use that offsets the cost of the pure oxygen.

Sidestream supersaturation involves removing water from the targeted deeper water layer, oxygenating it in chambers on land, and putting it back in the deep zone. Speece cones are sometimes used, but rather than placing them in the lake, they are on land and used to supersaturate withdrawn water. As long as the temperature of the withdrawn water has not been increased (which can be a risk when supersaturating), the oxygenated water moves mostly laterally in the target area. This allows thinner layers of bottom water to be oxygenated than would be possible with diffused oxygen. This approach is still being improved, but shows great promise.

Proper application requires the following information:

  • An accurate nutrient budget with a detailed analysis of internal sources of phosphorus
  • The oxygen demand that must be met by the system; calculations and related interpretation for design purposes are best performed by experienced professionals
  • Lake morphometry and stratification data to facilitate choice of system and features for maximum effectiveness
  • Location and details of any land based facilties and the power source

Factors favoring the use of this technique include:

  • A substantial portion of the P load is associated with anoxic sediment sources within the lake
  • Studies have demonstrated the impact of internal loading on the lake.
  • External P load has been controlled to the maximum practical extent or is documented to be small; historic loading may have been much greater than current loading
  • Hypolimnetic or sediment oxygen demand is high (>500 mg/m2/day)
  • In addition to phosphorus management, control of other reduced compounds such as hydrogen sulfide, ammonia, manganese and iron, is desired
  • Adequate phosphorus inactivators are present for reaction upon addition of oxygen
  • Shoreline space for a compressor, pump and/or oxygen storage is available where access is sufficient, power is available, and noise impacts will be small
  • The lake is bowl shaped, or at least not highly irregular in bathymetry (few separate basins and isolated coves)
  • Long-term application of the technique is accepted
  • Coldwater fishery habitat is abundant or an important goal

Hypolimnetic oxygenation is fairly common in drinking water reservoirs but less often found in recreational lakes, as ongoing management and related costs can be substantial. Permits are required, and potential applicants should consult with their local and state environmental agencies.

Four methods of hypolimnetic oxygenation

A Short Primer on Circulation for Lake Management

Forcing water in a lake to circulate can oxygenate deeper waters and can also exert some direct control over algae growth, but there are risks and limits. The Practical Guide to Lake Management in Massachusetts, available online from the DCR within the Mass.gov website, has a useful review of this technique, and a 2015 publication available from the Water Research Foundation has considerable additional detail.

Whole lake circulation is a technique for management of algae that tends to affect nutrient levels. The central process is the introduction of more oxygen, intended to limit internal recycling of phosphorus, thereby controlling algae.  Other important processes may apply as well, however. Circulation strategies increase turbulence and minimize stratification. Whole lake artificial circulation is also referred to as destratification or whole lake aeration. Thermal stratification and features of lake morphometry such as coves create stagnant zones that may be subject to loss of oxygen, accumulation of sediment, or algal blooms.  Artificial circulation minimizes stagnation and can eliminate thermal stratification or prevent its formation.  Movement of air or water is normally used to create the desired circulation pattern, and this has been accomplished with surface aerators, bottom diffusers, and water pumps. Algae may simply be mixed more evenly in the available volume of water in many cases, but turbulence, changing light regime and altered water chemistry can cause shifts in algal types and reduce biomass.

The use of air as the mixing force also provides some oxygenation of the water, but the efficiency and magnitude of this transfer are generally low.  In some instances, wind or solar driven pumps have been used to move water.  For air mixed systems, the general rule is that an air flow rate of 1.3 cubic feet per minute per acre of lake (9.2 m3/min/km2) will be needed to maintain a mixed system. However, there are many factors that could require different site specific air flow rates, and undersizing of systems is the greatest contributor to failure for this technique. The objective is to move at least 20% of the target water volume per day, and in cases where oxygen demand is very high, it may be necessary to move all the water every day.

Algal blooms are sometimes controlled by destratification through one or more of the following processes:

  • Introduction of dissolved oxygen to the lake bottom may inhibit phosphorus release from sediments, curtailing this internal nutrient source.
  • In light-limited algal communities, mixing to the lake’s bottom will increase the time a cell spends in darkness, leading to reduced photosynthesis and productivity.
  • Rapid circulation and contact of water with the atmosphere, as well as the introduction of carbon dioxide-rich bottom water during the initial period of mixing, can increase the carbon dioxide content of water and lower pH, leading to a shift from blue-green algae to less noxious green algae.
  • Turbulence can neutralize the advantageous buoyancy mechanisms of blue-green algae and cause a shift in algal composition to less objectionable forms such as diatoms.
  • When zooplankton that consume algae are mixed throughout the water column, they are less vulnerable to visually feeding fish. If more zooplankters survive, their consumption of algal cells may also increase.

The main drawbacks relate to the difficulty of maintaining mixed conditions in a lake.  It is very hard to mix a lake from top to bottom, and mixing near the bottom may entrain sediment and increase turbidity by resuspended particles. And it gets harder to mix a lake during prolonged hot, dry periods as the lake heats up. The energy necessary to overcome a thermal gradient increases as the water warms; the energy required to mix layers with temperatures of 20 an 25 C is much higher than for layers with temperatures of 10 and 15 C, even though both have 5 C differences.

Further, not all of any lake is deep enough to impose a light limitation, and mixing may actually make nutrients more available to algae. This situation can be greatly aggravated if the mixing system is not run continuously or is undersized, as nutrients may build up in deep water then be moved upward by the mixing system. Providing enough power to mix the entire target area and distributing that power so that it is effective are critical aspects of any circulation system.

Proper application requires the following information:

  • An accurate nutrient budget with a detailed analysis of internal P sources
  • Data related to each of the five possible control mechanisms (oxygenation/P inactivation, light limitation, pH/carbon source adjustment, buoyancy disruption, and enhanced grazing) should be analyzed and evaluated in terms of potential algal control. Specifically:
    • Is there anaerobic release of phosphorus that can be mitigated by oxygenation of deep waters?
    • Is the mixing zone deep enough to promote light limitation of algae?
    • Is there a large amount of carbon dioxide in the bottom waters that could be mixed to the surface to favor the growth of non-blue-green algae?
    • Is mixing predicted to counteract the buoyancy advantage of blue-greens over other algae?
    • Will a dark, oxygenated refuge be created for zooplankton?  
  • Reliable estimate of the oxygen demand that must be met by the system
  • Reliable estimate of the amount of air necessary to mix/destratify the lake
  • Lake morphometry data that facilitates choice of aerator type and placement of aerators for maximum effectiveness
  • Location and details of compressor and power source
  • Monitoring to track oxygen and nutrient levels after implementation
  • Monitoring to track water clarity and algal types and quantity   

Factors favoring the use of this technique include:

  • A substantial portion of the P load is associated with anoxic sediment sources within the lake
  • Studies have demonstrated the impact of internal loading on the lake
  • External P load has been controlled to the maximum practical extent or is documented to be small; historic loading may have been much greater than current loading
  • Hypolimnetic or sediment oxygen demand is high (>500 mg/m2/day)
  • In addition to phosphorus management, control of other reduced compounds such as hydrogen sulfide, ammonia, manganese and iron, is desired
  • Adequate phosphorus inactivators are present for reaction upon addition of oxygen
  • Shoreline space for a compressor or pump is available where access is sufficient, power is available, and noise impacts will be small
  • The lake is bowl shaped, or at least not highly irregular in bathymetry (few separate basins and isolated coves)
  • Long-term application of the technique is accepted
  • Coldwater fishery habitat is limited or not a concern

There are many possible circulation systems available. Air-driven systems are most common, and deliver compressed air to diffusers placed appropriately to maintain mixed conditions. Pumps that move water up or down are also popular. Pumps that move the water upward run the risk of worsening surface water quality if undersized. Pumping oxygenated water with algae from the surface to greater depth is theoretically more sound.

Permits are required, and potential applicants should consult with their local and state environmental agencies.

Whole lake circulation with diffused air

A Short Primer on Dilution and Flushing for Lake Management

Adding low nutrient water and keeping water moving through a lake can help prevent algae blooms, but there are caveats and limits. The Practical Guide to Lake Management in Massachusetts, available online from the DCR within the Mass.gov website, has a useful review of this technique. Lake waters that have low concentrations of an essential nutrient are unlikely to exhibit algal blooms. While it is preferable to reduce nutrient loads to the lake, it is possible to lower (dilute) the concentration of nutrients within the lake by adding sufficient quantities of nutrient-poor water from some additional source.  High amounts of additional water, whether low in nutrients or not, can also be used to flush algae out of smaller, linear impoundments faster than they can reproduce.  

When water low in phosphorus is added to the inflow, the actual phosphorus load will increase, but the mean phosphorus concentration should decrease. Dilution or flushing washes out algal cells, but since the reproductive rate for algae is high (blooms form within days to a few weeks), only extremely high flushing rates will be effective without a significant dilution effect. A flushing rate of 10 to 15% of the lake volume per day is appropriate to minimize algal biomass build-up. That means that the entire volume of the lake has to be exchanged in about a week, which will be a tall order in anything but a smaller pond with a substantial source of additional water.

Outlet structures and downstream channels must be capable of handling the added discharge for this approach to be feasible.  Qualitative downstream impacts must also be considered.  Water used for dilution or flushing should be carefully monitored prior to use in the lake.  Application of this technique is most often limited by the lack of an adequate supply of water.

The classic example of successful flushing is Moses Lake in Washington, which is not a small pond, but had a lot of river water available to flush it. Gene Welch and other studied this project over many years and concluded that flushing worked well for both water quality management and biological improvements. Examples in New England are much harder to come by. The lake in Look Park in Northampton MA has been successfully flushed by diverting a nearby river through it when necessary, but that is the only example that comes to mind.

Dilution is even harder to implement, as it requires very clean water. With phosphates often used to meet the anti-corrosion rule under the Safe Drinking Water Act, use of a public water supply may not result in lower phosphorus concentrations. The MWRA has refilled at least one emergency supply reservoir after winter drawdown with water that might otherwise have gone to consumers, and it has improved the phosphorus concentration. Few such cases are known, however. And even where clean dilution water is available, this may not prevent cyanobacteria from growing at the sediment-water interface using nutrients available there, then rising in the water column to form a bloom when available phosphorus near the surface is minimal.

If dilution or flushing seems like a viable alternative for a lake, the following information is needed to evaluate potential success:

  • Accurate hydrologic and nutrient budgets to allow evaluation of potential benefits
  • Assessment of probable in-lake effects and an evaluation of downstream impacts
  • Reliability of source water
  • Routing information for new water source
  • Monitoring program to track changes in detention time, nutrient levels and water clarity

Factors favoring the use of this technique include:

  • Actual reduction in nutrient inputs from identifiable sources is not practical, either for technical or jurisdictional reasons
  • Water level fluctuation will not differ greatly from pre-treatment conditions
  • Adequate water of a suitable quality is available for dilution or flushing
  • Downstream problems with water quantity or quality will not be caused

Permits for such use of water are typically required, and potential applicants should consult with their local and state environmental agencies.

Warning: Public water may contain high P!

Moses Lake in Washington, successful flushing.

The Value of Natural Shoreline

Beyond the buffer zone lies the actual lake shore, which can vary tremendously among lakes without any human intervention. Yet with “management” of the shoreline by people, we get an extremely wide range of conditions and features. Dense vegetation, lawns, natural rocks, riprap, or any combination thereof is possible. And the adjacent shallow water area is just as important, with conditions ranging from a jumble of rocks and woody debris to open sand under natural conditions and often a sterile open water habitat when people decide to “clean up” the nearshore zone.  

Findings from work in Vermont more locally and the National Lakes Assessment more nationally have documented how important the condition of the shoreline and nearshore zone is to overall lake function and species diversity. More fish, more birds, more reptiles and more amphibians can all be expected when the shoreline is in a natural condition, documented in multiple papers in Lake and Reservoir Management, including a 3-paper series by Kaufman et al. in 2014, based on data generated in the National Lake Assessment.

A useful environmental guideline is that if we don’t clearly understand all the linkages in a habitat, leave it as natural as possible for best results. The reasoning behind this is that the condition of the habitat is a complex function of many factors and has evolved into what it is over time as a function of those factors, and disturbing those conditions is not likely to have a desirable result unless we have a clear understanding of all the factors and how they interrelate. Much as with buffer zones, however, there is a human tendency to want to organize the shoreline and nearshore zone, to give it order and aesthetic appeal based on some innate sense of what it should look like. Beauty may be in the eye of the beholder, but functionality can be objectively assessed and rarely corresponds to what most people think is pretty.

New Hampshire and Vermont have shoreland protection laws that encourage natural shorelines, but the protection of the nearshore zone seems less clear (or enforceable). The Wetlands Protection Act in Massachusetts (and similar statutes in most New England states) provides some protection of both shorelines and the nearshore zone, although that protection is subject to interpretation by locally empowered commissions. There is generally solid recognition of the value of lake edges in New England, but actual management of this zone is not as well developed as we might like.

Pretty but not very functional as habitat

Much better habitat, not the best access

Buffer Zones for Lake Protection

Buffer zones are intended to provide a vegetative filter for runoff approaching a waterway, acting to trap particulates and absorb flows to minimize the entry of contaminants into streams and lakes. Buffer strips provide additional habitat benefits, and may be the best way to prevent problems by acting on a watershed-wide basis. The desirability is undeniable, but effectiveness is a complex function of buffer zone width, slope, soils and vegetative features. Engineered buffer zones can be very effective, but may not be overly natural or attractive. Natural buffers have been found to require substantial width (>100 feet, with removal still increasing at widths >500 feet), and few landowners are willing to concede enough land to buffers to maximize effectiveness. Any buffer is a good thing, but if buffers are to be a major factor in water quality management, they need to be wide enough and well-structured to hold and process runoff.

Perhaps the biggest impediment to use of buffers is a societal tendency to favor open lawn areas and avoid high and dense vegetation. Sociologists have suggested that this is a primal response related to personal safety, as though tigers might be hiding in the high grass by the lake! Landscape architects have suggested that it is an aesthetic issue, with disorganized, natural growths suggesting sloppiness and lack of care by the owner. Robert Kirschner of the Chicago Botanical Garden gave a great talk called “What will the neighbors think?” a few years ago at the NECNALMS conference, in which he described the steps lakefront (or streamfront) property owners could take to make effective buffer strips look organized and acceptable within the neighborhood. In Maine, the LakeSmart program recognizes shorefront owners who maintain landscapes that minimize runoff impacts on lakes. We need both a cultural shift in what is “acceptable” and application of clever guidance that facilitates effective buffers without losing aesthetics.

A landscaping compromise to add buffer functionality without sacrificing aesthetics.

Alewife in Lakes

This is a hot button topic in several New England states, eliciting citations of contradictory research and a lot of emotion, depending on one’s priorities for lake management. The fundamental issue is that alewife (usually Alosa pseudoharengus, but other related herring species are sometimes involved) feed by straining water through gill rakers for plankton, much like baleen whales filter out krill and larger plankton in the ocean, leaving very low biomasses of zooplankton for other fish to eat. Where adult alewife enter lakes from the ocean  as anadromous fish, spawn, and leave, the juveniles remain during summer and decimate the zooplankton, but those lakes tend to evolve ecologically, with zooplankton reaching winter maxima and managing to support the food web. But where a landlocked alewife population is established, zooplankton density may be depressed all year long, severely limiting food for small fish that feed visually on large zooplankton. Alewife may provide a valuable food base for some gamefish, but do so at the expense of the rest of the fish community.

Restoring a historic alewife run is therefore a very different policy decision than stocking alewife into a lake where they will be landlocked. For fishing enthusiasts, the potential for trophy gamefish is attractive when a landlocked alewife population is established. But for those interested in clear water, the alewife will promote the greatest amount of algae possible for whatever level of fertility is present. In a lake with enough phosphorus to support algae blooms, the presence of alewife all year is almost a guarantee of blooms, whereas a different fish assemblage might minimize bloom potential by favoring zooplankton control of algae.

If stocking of alewife was accompanied by a nutrient control program to limit the potential for algae blooms, it might be more palatable, but fishery agencies that are the normal advocates for such stocking have never been in the business of overall lake management, and are not known to be advocates for nutrient control. This lack of a more holistic approach to lake management has led some to refer to fishery agencies as government of the fish, by the fish, and for the fish. At the same time, those focused on water clarity have been called Secchi disk worshipers and such a narrow focus is also not holistic. Those promoting anadromous alewife runs are on pretty sound ground, but the debate goes well inland from coastal areas.

Alewife, Alosa pseudoharengus

The Concept of Limiting Factor for Algae

The concept of a limiting factor is very old, summarized in Leibig’s Law of the Minimum, which used a bucket with staves of different lengths to show that the shortest stave controlled the depth water could attain in the bucket. The theory is simple, perhaps too simple to capture the variation induced by having multiple species present with varying optimal nutrient ratios, light requirements, and maximum growth rates. In reality, multiple factors control the growth of algae, with some species more impacted by one factor than others. There is therefore constant competition going on, with each species increasing in abundance to the extent possible before some species-specific limit is reached based on the relation of the individual species’ needs and available resources.

There are very few generalizations that apply to all algae with regard to limiting factors. Light is very important to photosynthesis, but some algae survive under very low light and some are “facultatively heterotrophic”, consuming organic compounds, bacteria, other algae, and even zooplankton to gain energy rather than depending on photosynthesis. Nitrogen is a key nutrient, but cyanobacteria with specialized cells called heterocytes can convert dissolved nitrogen gas into ammonium. Since our atmosphere is 78% nitrogen, it is virtually impossible to prevent these algae from acquiring some nitrogen. Phosphorus is the closest thing to a sure limiting factor, being relatively rare in the earth’s crust but critical to energy transfer. There is no substitute for phosphorus, and it can be controlled by multiple means in active management practices, so it is the logical target of choice in algae control programs that seek to prevent algae growth to bloom proportions.

Approaching algae management with multiple limiting factors is a good idea. In many cases, best management practices that control phosphorus also limit nitrogen and other nutrients. Increased flushing can reduce detention time such that growth rates are insufficient to generate blooms. Adjusting the fish community to encourage more and larger herbivorous zooplankton can increase algae consumption rates and funnel energy into desirable fish while limiting algae biomass. Yet control over planktonic algae will lead to deeper light penetration, which may provide benthic algae enough light to grow using nutrients available at the sediment-water interface during decomposition or other release mechanisms. Dredging can remove algae resting stages and nutrient reserves, limiting benthic production, but the cost is usually extreme.  

Using the concept of limiting factor(s) for algae is appropriate but more than a little complicated. The situation is far more complex that the simple bucket analogy suggests, and the more we can learn about the lake we want to manage the more successful we are likely to be in achieving our goals.

NECNALMS Leaders Meet

Representatives of all six New England states met in Concord in early December to review programs and get updates on lake issues in each state. The spread of invasive plants and increased frequency of cyanobacteria blooms continue to be the primary biological threats. Retirements and reduced staffing in state agencies represent the primary administrative issue. Funding cutbacks, especially for federal “pass-through” monies, constitute the greatest economic disincentive for lake management. Yet the demand for lake management remains high, and many lake associations and towns have been addressing issues on their own. NECNALMS continues to seek ways to support efforts by New England states to foster effective and sound lake management.

Lake leaders discussed past and future conferences. New Hampshire is due to host NECNALMS in 2018, but with the normal organizers very involved in national efforts by NALMS and changes in policies at the typical conference venues, it is not certain that there will be a 2018 NECNALMS conference. It is possible that NALMS will come to New England in 2019, in which case the NECNALMS leadership will be very involved in planning that conference starting in mid-2018. A decision will be made soon.

The 2017 NALMS symposium was held in early November just outside Denver, CO, and was both well-attended and well-run. The program was diverse and opportunities for interactions were plentiful. The Colorado Lake and Reservoir Management Association was the local host, and did a fine job on the arrangements. NALMS has been experiencing some financial stress relating to federal freezes on programs and funds, but is managing carefully to avoid shortfalls. The 2018 conference will be held in Cincinnati, OH and a decision on the 2019 location should be made this coming spring.

NECNALMS leaders are also very active on the national and international levels through NALMS. Perry Thomas of VT serves as the Region I director, while Amy Smagula of NH is the NALMS Secretary. Jeff Schloss of NH is the conference planner, while Ken Wagner of MA returns to duty at the start of 2018 as Editor-in-Chief of the NALMS peer-reviewed scientific journal, Lake and Reservoir 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