William E. Lynch Jr.Aquatic Ecosystem Management SpecialistOhio State University Extension Program

Winter (ice – 39 F)Low biomasses of all

types

Early Spring (40 – 50 F)Diatom bloom

Spring – Early Summer (50 – 72 F)

Green algae bloomP Limited SystemsN Limited Systems

Mid - Late Summer (72 – 80+ F)

Green algae

Mid - Late Summer (72 – 80+ F)

Cyanobacteria bloom

Fall (80+ – 50 F)Green algae or

cyanobacteria earlyDiatom bloom late

Large Lakes and Reservoirs2009

Large Lakes and Reservoirs2009

2010

2010

Those Where Microcystin > 20ppb(WHO Recreational Standard) 2010: Microcystin > 20

ppb

Note: Nearly all were less than 1 ppb; WHO’s drinkingwater standard

Why warnings for waters with low microcystin levels?Some also had low levels of anatoxin and

saxotoxin. WHO has not defined contact and drinking

water standards for those two toxins.Research has indicated they are more

detrimental to human health, and quite likely at low levels.

Agencies across the U.S. often issue warnings when anatoxin and saxotoxin are detectable. “Better safe than sorry” strategy.

Suspected based on provided description

Confirmed based onsite visit or provided sample

Ponds & Small Lakes

Have HAB’s Really Increased? • Yes, to an extent. An increase in ponds and small

lakes.• Calls and emails to OSU Extension’s Aquatic

Ecosystem Specialist have increased noticeably.• However, nearly 40% of contacts reported their

ponds have had these blooms in the past, often 10 years ago.

# of Contac

ts

Note: nearly all occurred in August and Sept.

Are They New to Ohio’s Waters?No, cyanobacteria are have been in Ohio

from the very beginning.Thus, they are not a recent invasive from

a distant global location;Nor are they recent mutations now

capable of causing problems.Simply, they remain at low densities until

ecological conditions are created that allow them to reproduce quickly and create dense blooms.

What Creates Favorable Ecological Conditions for Cyanobacteria?First and foremost, development of a nuisance

algae bloom is indicative of elevated nutrients, particularly an excess of phosphorus.

Nitrogen : phosphorus ratios greater than 20:1 promote filamentous and good planktonic algae while ratios less than 10:1 promote development of HABs.

High water temperatures do not cause HABs directly, but can cause minor blooms in waters with slightly elevated nutrient levels.

Nitrogen – Phosphorus Ratio ImportantN:P ratios > 30:1 results in blooms of

planktonic green algae that are beneficial to aquatic food webs. Ratios > 20:1 acceptable.

N:P ratios between 10:1 and 20:1 can support cyanobacteria blooms, particularly in warm water.

N:P ratios < 10:1 typically result in HAB’s as cyanobacteria flourish in nitrogen limiting systems. Remember many HAB species can fix nitrogen.

0

25

30

20

15

10

5

SummerN:P Ratio

Cyanobacteria Abundance (%) of Algal Community

0 25 50 75 100

oligotrophic

mesotrophic

eutrophic

hypereutrophic

Adapted from:United Nations Environment ProgramDiv. Of Technology, Industry, & Economics

N:P Ratio

4/15

5/10

6/9

acceptable

desirable

No HAB’s

N:P Ratio – Grand Lake St. Mary's ExampleN:P Ratio

4/15

5/10

6/9

acceptable

desirable

7/14

No HAB’s

***

Toxins first detectedin late June

N:P Ratio – Grand Lake St. Mary's ExampleN:P Ratio

4/15

5/10

6/9

acceptable

desirable

7/14

No HAB’s

***

Toxins first detectedin late June

8/19

9/15

10/7

HAB’s Widespread

Grand Lake St. Mary's 2010 P Levels Phosphorus

4/15

5/10

6/9

Target (<34 ppb)

7/14

8/19

9/15

10/7

ppb

Grand Lake St. Mary's 2010 N Levels Nitrogen

4/15

5/10

6/9

Target (<930 ppb)

7/14

8/19

9/15

10/7

ppb

Summer Water Temperatures

Play A Role!

High N:P ratio:• No HAB

• High N:P ratio:• No HAB

• High N:P ratio:• HAB’s rare

< 74oF 74oF - 80oF

>80o

F

Summer Water Temperatures Play A Role!

• High N:P ratio:• No HAB

• Mod. N:P ratio• No HAB

• High N:P ratio:• No HAB

• Mod. N:P ratio• No HAB

• High N:P ratio:• HAB’s rare

• Mod. N:P ratio• HAB’s

uncommon

< 74oF 74oF - 80oF

>80o

F

Summer Water Temperatures Play A Role!

• High N:P ratio:• No HAB

• Mod. N:P ratio• No HAB

• Low N:P ratio• HAB’s rare

• High N:P ratio:• No HAB

• Mod. N:P ratio• No HAB

• Low N:P ratio• HAB’s common

• High N:P ratio:• HAB’s rare

• Mod. N:P ratio• HAB’s

uncommon

• Low N:P ratio• HAB’s common

< 74oF

74oF - 80oF

>80o

F

Sources of Nutrients

External – little P input

Internal – little P input

“All is Fine Scenario”

External – large increase in watershed P loading

Internal – little P input, but slowly increasing

“Beginnings of a Problem”

External – continued large watershed P loading

Internal – large P inputs from bottom sediment build-up

“The Worst of Problems”

External – watershed P loadings reduced

Internal – large P inputs from bottom sediment build-up

“The Long Road to Recovery”

Internal Sources of Excessive Phosphorus50% of particulate organic P

deposited on bottom is biologically regenerated and returned to water above as phosphate.

Internal P cycling from anoxic bottom sediments during summer stratification.

Shallow lakes (e.g. Grand Lake) rarely stratify, but localized oxygen depletions in muck laden bays and creek mouths will allow release of phosphorus.

External Sources of Excessive Phosphorus

Very small watersheds allow “local” sources to have major effects.

Runoff from small scale domesticated animal paddocks (the pet horse)

Lawn fertilizerCanada geeseLeaking septic systemsFeeding fish

Ponds & Small Lakes

External Sources of Excessive PhosphorusLarge Lakes & ReservoirsVery large watersheds allow “widespread” sources to accumulate and have major cumulative effects.

Runoff from manure applied to fields.

Agricultural fertilizer runoff.

Particulate P problem enough but . .

Dissolved reactive P is a major problem (100% bio-available)

Also Play a Role . . .Lake Retention Time – once a molecule of

water enters a lake, how long is retained in the lake before going out the outlet. Calculated as volume / discharge rate.High retention times a major HAB concern if

water is high in phosphorus.Low retention times discourage HAB’s due to

nutrient flushing plus high clay turbidity levels.Aquatic Vegetation Community – the more

abundant the plant and filamentous algae community, the less likely an intense HAB will occur.

Intensity & Timing of Rainfall Events – Wet springs followed by dry summers enhance development of HAB’s.

Keeping a Perspective . . . Waters with high nutrient loadings and low N:P

ratios will experience HAB blooms, even in cool summers.

Many of the HAB blooms in 2010 were “small scale”. In larger waters, they were very localized to bays and headwater areas. Most were caused by Microcystis, a non-nitrogen fixing cyanobacteria.

Very high water temperatures likely caused many of the “small scale” HAB’s. A cooler summer in 2011 may cause HAB numbers to decrease markedly.

Given the lack of definitive, science-based data on anatoxin and saxotoxin toxicity, warnings will continue to be posted on state lakes for the foreseeable future.

Final ThoughtsHAB’s is ponds and small lakes are

correctable with bottom aeration, nearby land use adjustments, algaecides, and even alum treatments. Improvements attained quickly.

Intense HAB’s in large lake and reservoirs are more difficult to correct and will require major changes in watershed management and adoption of agricultural BMP’s. Quick fixes are costly and fleeting given the external sources of nutrients constantly entering the water body. Questions?