Group 1 : Aquatic vegetation survey and determination of the water surface height by levelling

 The date was 3.10, and our tasks were an aquatic vegetation survey and determining the water surface height by levelling. The weather was partly cloudy, with an atmospheric temperature of +5 °C. There was no rain. We were participated Chloé, Kerkko, Juliette, and Thomas.

Task 7 : Aquatic Vegetation Survey

The task involved identifying water plants on the lake shore and in the water and determining the vegetation cover. The plants and their prevalence should also be mapped for comparing areas. These can be used to infer the ecological state of the lake regarding eutrophication and overgrowth. They also affect what species of fish and waterfowl live in the area. The time of year was not optimal for the survey since most plants were withering during autumn. 

Water plants in limnology are grouped by their ecological niche :

• Aerial vegetation (helophytes) : Plants that grow above the water.
• Submerged vegetation (elodeids) : Plants that are completely underwater.
• Surface vegetation (lemnids) : Plants that float on the water surface.
• Bottom vegetation (isoetids) : Plants rooted at the lake bottom.
• Free floaters : Plants that float freely in the water.
• Suspended vegetation : Plants that hang in the water.
• Water mosses (bryids) : Mosses that grow in or around water.

We looked at three spots on the lake: around the beach in the northeast, near the outlet in the east, and along the south shore. The eastern shoreline had solid ground with a gentle slope, while the southwestern shore was wet, soft, and mossy, with a steeper slope into the lake.

Locations of the survey

On the Beach :

• Bur-reed (Sparganium emersum)

• Floating pondweed (Potamogeton natans)

• Watermilfoil (Myriophyllum alterniflorum)

• Yellow waterlily (Nuphar lutea)

Near the Outlet :

• Marsh calla (Calla palustris)

• Yellow iris (Iris pseudacorus)

On the South Shore :

• Common reed (Phragmites australis)

• Marsh Labrador tea (Rhododendron tomentosum)

Kerkko used his former knowledge, I naturalist and Wikipedia to name the plants so the accuracy of the identifications is questionable. He also didn’t include plants that he could not guess a name for. There was a lack of bottom vegetation and water mosses in the survey since we didn’t have tools to collect them.

Observations and analysis :

The survey showed mostly mixed vegetation with fewer floating plants. The limited number of surface-floating plants indicates possible eutrophication, as excessive nutrient input can lead to overgrowth of certain species, reducing biodiversity. The water appeared to have low nutrients, as seen by the presence of species that thrive in cleaner waters. This balance suggests that while the lake is not in perfect condition, it is not severely degraded either.

The hill next to the lake contributes soil and debris when it rains. This process can lead to an accumulation of particles on the lake's surface, which can negatively affect water clarity and quality. Increased rainfall can wash more sediment into the lake, potentially altering habitats and nutrient levels, which can impact the growth of aquatic plants and the health of the overall ecosystem.

Conclusion :

The aquatic vegetation survey of Pieni-Valkeinen Lake provided valuable insights into the current ecological state of the water body. The variety of plants identified indicates the lake's nutrient levels and overall health. While some species suggest that the lake is in relatively good condition, ongoing monitoring is essential to prevent eutrophication caused by runoff and sediment deposition.

Future surveys should aim to include more plant types and consider seasonal changes to gain a fuller understanding of the ecosystem. Effective management of runoff and sediment from the hill is crucial to maintain water quality and support a diverse aquatic environment.

Task 6 :  Determining the water surface height by levelling

The goal of this task is to measure the water level in 2 different points, one for Pieni-Valkeinen Lake and the other one for Iso-Valkeinen Lake. Those measurements can be done thanks to a levelling machine, this one is pretty accurate and could measure a height to nearest millimeter. The levelling machine offer the possibility of measuring the difference of height between two points, which allow us to obtain the water level. It is essential to precise that the levelling machine has to be straight, a bubble on one side help us to find if we put it in the right way. The difficulty was to balance the bubble in the middle and to have the best placement to do the measures. 

Optical level instrument

Firstly, we have to determinate the water level of Pieni-Valkeinen.

That’s why after balancing and adjusting the measurement tools described before, we took 2 measurements of height. The first measure was made at the manhole cover, knowing that the altitude of the first measurement point compared to the sea level is equal to H0 = +99,064 m. 

Reference location of Pieni-Valkeinen

Pieni-Valkeinen's map

H1 = 149,2 cm = 1,492 m

The second measure was made at the lake edge in order to calculate the difference levelling machine and lake surface.

H2 = 339,1 cm = 3,391 m

Thanks to these values, we can now calculate the water level of this lake by following these steps :

The height of the levelling machine is H0 + H1 = 100,6 m

Finally, the water level is equal to : H0 + H1 – H2 = 97,17 m

We wanted to compare the final value to the reference value that we can see in the map, the water level of the Piene-Valkeinen lake must be equal to 96,3 meters. By calculating the relative gap between these experiment and theoretical values : RG = 1% ;

we can conclude that the value of the water level of this lake that we found by experimentation is extremely close to the theoretical one. So that, the measurement uncertainties are not so important in this case. 

Secondly, we have to determinate the water level of Iso-Valkeinen lake.

We also took 2 measurements of height. The first measure was made in the middle of a stump near the lake, knowing that the altitude of this point compared to the sea level is equal to H0 = +91,781 m. 

Reference location of Iso-Valkeinen

Iso-Valkeinen's map

H1 = 275 cm =  2,75 m

The second measure was made at the lake edge in order to calculate the difference levelling machine and lake surface.

H2 = 254,8 cm = 2,548 m

Thanks to these values, we can now calculate the water level of this lake by following these steps :

The height of the levelling machine is H0 + H1 =  94,53 m.

Finally, the water level is equal to : H0 + H1 – H2 = 91,98 m

We wanted to compare the final value to the reference value that we can see in the map, the water level of the Iso-Valkeinen lake must be equal to 89,1 meters. By calculating the relative gap between these experiment and theoretical values : RG=3%

For the water level of this lake the result is less accurate but the relative gap is under 5% so the measure is totally consistent.

Conclusion :

To conclude on this experience, we can say that the measurement is globally consistent. Nevertheless we can notice little difference with the theorical values. Those difference could come from several things. The first one is about the way that we balance the bubble in the middle of the circle to put the machine straight. We have tried to do our best to put it out the center but of course it was not perfectly in the center. Secondly, some mistakes could have be made during the lecture of the measurement. Finally, maybe we were not exactly at the good position when we took the measure, just one or two millimeters could influence the final results.