How clean are our lakes?

Huntly College is on the western side of the Waikato River. Our recent hydrology investigation was a part of the CREST project for Gifted and Talented students.

The aim of this project was to:

• Cater for Gifted and Talented students
• Offer an opportunity in a scientific topic of regional importance
• Try be selected for the Waikato Science and Technology Fair
• Aim towards the Bronze CREST Award
• Have a water quality focus

Student Selection

Students were offered the opportunity on the basis of their 2005 and 2006 academic results:

• Emma Bagley
• Tara Fisher
• Rachael Foy
• Brandon Hennessy
• Jessica Horrox
• Annamarie Jerry-Hopwood
• William Nicholson
• Toni-Lee Pugh
• Kaylar Paetai
• Lee Smith

Introduction to the CREST programme

Students were introduced to what the CREST Programme is about and time was given for them to choose an investigation which had water quality focus.

Aim of investigation: To find out which lake is the cleanest. Three lakes were chosen: Hakanoa; Waahi; and Kimihia. These three lakes represent our school house teams. After consulting with the local Environmental Coordinator we were able to have Lyn Rodgers from school of support, the following methodologies were undertaken. Materials were borrowed from Environment Waikato.

We planned to:

• Water clarity tests, pH tests, nitrate and phosphate levels, water temperature, sediment content, type of micro-invertebrates found, and general surroundings of the lakes
• Collect and analyse data
• Draw conclusions
• Report to the community

Carrying out our investigation

Data for each lake studied:

TESTS				Waahi				Hakanoa				Kimihia
Trials							Average				Average				Average
Clarity (Cm)				15	15	16	15.3	16	16		16	10			Muddy sediment stirred up.
pH				7	7	7	7	7	7	7	7	7	7	7	7
Temperature Of water(oC)				14	14	14	14	16	16	16	16	14	15		14.5
Nitrate (NO3) mg/L				5	5	5	5	5	5	5	5	0	0	0	0
(PO4) -3 mg/L				0.1	0.25	0.1	0.1	0	0	0	0	0	0	0	0
Temp (Air) (oC)				18	18	18	18	18	18	18	18	18	18	18	18
Sediment				Sand crystals and clear water.				Sand crystals organic bits in water and algae.				Muddy lots of organic bits and protozoa and algae.
Organisms				Fish, mayfly, shrimp.				Dead fish, fish.				Fish, protozoa and mosquito.
Observations				Birds, rubbish, bugs, looked clean.				Ducks water, rubbish, smelly.				Sediment easy to disturb, ducks.

Analysis of data

From the data above we couldn’t find anything wrong with the lakes.
All the levels fell into acceptable ranges however we noticed these differences:

1. Hakanoa was warmer because it is shallower, it gets more sun, and it has lots of organisms. This causes more bacterial growth and faster decomposition
2. Kimihia had no Nitrates could be because the land around it was used differently
3. Waahi had some Phosphate could be because of erosion around the lake
4. Kimihia’s sediment had more mud, protozoa and algae because Kimihia Lake wasn’t naturally made; it is a very shallow flooded paddock
5. Kimihia’s water clarity was poorer due to the muddy sediment

There were signs up on Waahi and Hakanoa Lake saying it is not safe to swim in there. Why was this?

A letter was written to Dean King:

Huntly College,
Bridge St,
Huntly.
12th June, 2006.

Dear Mr King,

We are the CREST group at Huntly College. We have been doing testing for three lakes in Huntly to find out which is the cleanest. We tested Waahi, Kimihia and Hakanoa. We used the tests out of the stream sense kit. However we feel we didn’t succeed because although our results showed that the lakes were ok there are signs saying that we can’t swim in it. What else could we test to explain the signs? Do you know of someone that specialises in lakes that could help us? We have thought about:

1. Micro-organisms
2. Algae
3. Toxins

We didn’t find enough macro-invertebrates in each lake to compare them.

Yours sincerely,

Huntly College CREST Students

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The reason given to us for the signs was the presence of blue-green algae. Blue-green algae releases toxins which harmful and can be deadly to living creatures. The higher temperature in Hakanoa could have explained high levels of blue-green algae. Signs were up in Waahi and Hakanoa warning about not swimming. After some research it was found that Waahi has increasing nutrient levels and nutrients increase blue-green algae. These types of algae bloom are often triggered by fine, warm and settled weather. They feed on nutrients- if they don’t have nutrients they won’t grow. More testing on nitrates and phosphates needs to be done. This is because if there is blue- green then there should be higher counts of nitrate and phosphate.

Cause and effect of blue-green algae:
Blue-green algae, technically known as cyanobacteria, are microscopic organisms that are naturally present in lakes and streams. Just because these bacteria make its own food by photosynthesis it’s given the name blue-green algae.

Consuming water with high levels of blue green algae can affect liver and nervous system in livestock and people. Livestock and pet deaths have occurred when animals consumed very large amounts of accumulated algal scum from along shorelines.

'Bloom' is a common term used to describe an increase in the number of algal cells to a point where they can discolour the water, form scums, produce unpleasant tastes and odours, affect shellfish and fish populations or otherwise create a nuisance and seriously reduce the water quality.

Species of blue-green algae may dominate and increase excessively in water when the:

• nutrient levels, particularly phosphorus and nitrogen are sufficient to support the population growth
• water is still and turbulence is low (lack of mixing)
• weather patterns are stable for a long time
• weather is warm (although blooms can occur in cooler weather too).

Blue-green algal blooms often persist for several weeks, sometimes months, depending mainly on the weather or flow conditions. Cooler, windy weather or increased flow may reduce or prevent blooms from occurring.

Some toxins may persist for more than three months even after the ‘bloom’ dies, before sunlight and the natural population of bacteria in the water degrades them.

How do we prevent these?

It is extremely unlikely that blue-green algal blooms can ever be prevented from occurring in aquatic systems in New Zealand. They are a widely occurring group of organisms that are opportunistic and will develop high populations rapidly under favourable conditions. To exclude only the blue-green algae without eliminating a wide range of other organisms is almost impossible.

The objectives of control and treatment are therefore to:

• minimize nutrient concentrations in streams and storages encourage water conservation measures
• develop or improve techniques to treat and detoxify contaminated water
• phosphorus has been identified as the key nutrient source for many of the blooms. Develop ways to prevent these entering our aquatic systems

What is currently happening out side New Zealand to control this?

• Integrated Catchment Management (ICM) aimed at reducing and managing nutrient flows into waterways from natural and artificial sources
• promoting natural algal grazers through selective fish stocking, aquatic plant restoration, and reduction in the contamination of waterways with pesticides
• supporting the maintenance and restoration of riparian vegetation (i.e. the plants near or at the edges of waterbodies)
• community involvement in tackling catchment management issues
• research programs focused on toxin identification, rapid testing procedures for field use, toxin stability and degradation under different environmental conditions

Prevention of blooms is the primary aim but as they form part of the natural ecosystem, this may not always be possible. It is important, therefore, to be aware of the potential dangers associated with blooms.