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Lake Sediment

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Submitted By bluelantern9
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Lake Sediments

Introduction

Three lakes in the University of Waikato act as stormwater detention systems. Stormwater from various sources in the campus is directed into the Knighton Lake, Oranga Lake and Chapel Lake. As part of the detention system, the lakes are expected to allow some contaminants to be deposited into the sediments.

For each of the three lakes, sediment samples are taken from ten different locations within each of the lakes. The sediment samples are examined for five particular metals. These are Nickel (Ni), Copper (Cu), Zinc (Zn), Arsenic (As) and Lead (Pb).

The purpose of this report is to find out what the level of each metal contaminant in each of the lakes and compare the level against Australian and New Zealand Guidelines for Fresh and Marine Water Quality 2000 Volume 1 (ANZECC, 2000). Also to find the possible source of each metal tested.

Results

Table 1. Metals concentration in sediments from Knighton Lake,
University of Waikato, 2000 | Ni | Cu | Zn | As | Pb | minimum (ppm) | 8 | 39 | 416 | 15 | 40 | Maximum (ppm) | 13 | 79 | 1515 | 25 | 170 | Mean (ppm) | 11 | 62 | 892 | 21. | 88 | standard Deviation | 1.65 | 12.32 | 317.93 | 3.27 | 44.23 | | | | | | |

The Knighton Lake results when compared against the guidelines showed that the concentration of nickel and copper are below the trigger value and therefore are at an acceptable level. The results for the arsenic and lead are just above the trigger level. The zinc level however is at a very high level, its 484.8 ppm higher than the ISQH-High value in the ANZECC, 2000.

Table 2. Metals concentration in sediments from Oranga Lake,
University of Waikato, 2000 | Ni | Cu | Zn | As | Pb | minimum (ppm) | 10 | 68 | 1097 | 14 | 17 | Maximum (ppm) | 17 | 134 | 1895 | 29 | 89 | Mean (ppm) | 14 | 105 | 1502 | 22 | 40 | standard Deviation | 2.27 | 25.35 | 249.13 | 4.21 | 24.67 | | | | | | |

The Oranga Lake results when compared against the guidelines showed that nickel and lead levels are below the trigger value and the arsenic, copper and zinc are above the trigger value. Zinc level is found to be at extremely high levels, it is 1,092 ppm higher on average in comparison to the ISQG-High value.

Table 3. Metals concentration in sediments from Chapel Lake,
University of Waikato, 2000 | Ni | Cu | Zn | As | Pb | minimum (ppm) | 5 | 15 | 52 | 5 | 78 | Maximum (ppm) | 8 | 26 | 247 | 9 | 177 | Mean (ppm) | 6 | 20 | 106 | 7 | 137 | standard Deviation | 0.92 | 4.17 | 60.06 | 1.37 | 35.11 | | | | | | |

The Chapel Lake results when compared against the guidelines showed that nickel, copper, zinc and arsenic are below the ISQG-Low value. The level of lead in the sediment is found to be at a high level, below the ISQG-High value but is above the trigger value of 50 ppm.

Analysis

In each of the three lakes, nickel is the only metal contaminant in the sediments that is below the levels recommended in the ANZECC, 2000 guidelines. Meaning that little or no further nickel metals are entering the lakes, we could conclude that nickel found in the lake is naturally forming. Zinc levels for both the Knighton and Oranga Lakes are very high. From the stormwater map the lakes that have high levels of zinc and arsenic has a lot of stormwater directed to it and has minimal amount of vegetation.

The zinc level in the two lakes is at a high level and I consider it to be a problem. One major effect of increased zinc level in the lakes is that the acidity level will increase. Another is that some fish can accumulate zinc in their bodies. A possible source for the amount of zinc in the lakes is the use of zinc as coating on steel to avoid corrosion. Many building in the campus have a corrugated roof coated with zinc to avoid rusting.

The Chapel Lake showed the least amount of contamination in all five metals tested, the only metal above the trigger level is the lead concentration (Table 3). Based on this, we can assume that the Chapel Lake is healthier than the other two lakes. This could be due to the smaller size and more vegetation compare to the other two lakes.

Arsenic level for the Knighton Lake and Oranga Lake are found to be high. This is a problem because when arsenic enters an environment it cannot be destroyed. So the amount that enters the lake accumulates over time. Plants absorbs arsenic fairly easily this could be the reason why the Chapel Lake has a lower level of arsenic. Arsenic is used in treating timber. Around the Knighton and Oranga Lake, there are a number of decks and footpaths made out of treated wood. This could be a possible source of the arsenic entering the lakes.

Copper is used as piping. This could be the source of the copper in the lakes other than the naturally forming copper within the lakes. I do not see the levels of copper in the lakes as a problem.

Lead is used as sheets and is utilized in the construction industry for weathering, roofing and cladding, to prevent water penetration; lead metals entering the lakes could be from building surrounding the lakes. Lead can also enter the environment through gas emission from vehicles. The concentration of lead is high in the section of the lakes where the stormwater pipes are connected to the car parks; perhaps the increase in lead levels in these parts are from vehicle emissions.

Conclusion

Overall the health of the three lakes is in different levels of concerns. Chapel Lake is the healthiest of the three lakes, then Knighton and then Oranga Lake. Arsenic and zinc level in the lake are at a level where it is considered a problem. Further accumulation of arsenic and zinc will results to effects in the health of the lake biology and the pH level in Knighton and Oranga Lake. The high levels of contaminants in the sediments are human caused. There is a high concentration of metals found where the stormwater pipes leads into the lakes.

Other parameter I would like to measure is the depth level of the lakes and the size of the lakes. This will show how much water is in the lakes under normal condition (i.e. during fine days) and the volume of water and sediments that are entering through the lakes.

I would like to measure the levels of other metals such as chlorine, especially for the Oranga Lake where the stormwater pipes from the swimming pool exit to this lake.

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