NETLAKE Citizen Science

Within NETLAKE Working Group 3, a large scale citizen science monitoring program is being launched in 2016 across NETLAKE sites. In this monitoring programme, two topics will be addressed, namely decomposition/temperature and plastics.

1) Decomposition of allochthonous litter in lakes across Europe

Europe has several climatic zones, ranging from (sub)artic in the North to mediterranean in the south. These different climates with their different temperature regimes across the year, result in different lake types. Mediterranean lakes have a longer warm period compared to subarctic lakes, and thus a more active decomposing community.

Decomposition entails the breakdown of (dead) material such as dead animals, tree leaves (mostly in autumn) and water plants, and is a vital process in the circle of life. Decomposition provides essential nutrients for plants and algae to grow on. Microbes (fungi and bacteria) play a big part in this decomposition process.

To be able to compare the rate of decomposition across lakes in Europe, the same litter will be placed in the various lakes over the same time period in the form of Lipton tea bags. These pyramid tea bags will be buried in - and placed upon - the sediment for 90 days. After this time period, they are reweighed and the extent to which the tea leaves have been decomposed by microbes can be determined.

• How does the decomposition of foreign (allochthonous) material differ between lakes in Europe?
  To be able to explain differences in decomposition process across Europe, lakes will need to be classified according to their climate (temperature i.e. iButton) and trophic status. Trophic status scales a lake according to its biological productivity. Low visibility (low Secchi depth), green color (Forel-Ule scale) and wide reed-leaves indicate a high trophic status, because they indicate a high nutrient content in the lake for algae and plants to grow on.
• How does decomposition differ between the pelagic and littoral zone in European lakes?
  Because decomposition not only occurs in or on top of the sediment but also in the water column, tea bags can also be placed in the open water (pelagic). We expect decomposition to take place much slower in the open water compared to the shore line (littoral).

2) Microplastics in European lakes

Global plastic consumption is increasing rapidly, resulting directly in a growing accumulation of end-of-life plastics. Improperly discarded plastic ends up in both terrestrial and aquatic ecosystems. Because of the plastic's longevity, this is an emerging environmental problem.

Plastic waste is usually divided according to its size:

• Recognizable plastic pieces belong to the macro-plastics. Its sources are not only discarded bottles on lake shores but also agriculture (plastic wrappings) and fishing (broken fishing lines).
• Microplastics are plastic pieces smaller than 5 mm which originate mostly from cosmetic sources or synthetic clothing. Think of peelings and toothpaste that use plastic abrasives, or small particles of fleece clothing that en up in the draining water during washing. Microplastics can also come from macro-plastics that disintegrate.

Because plastic particles of all sizes take hundreds of years to biodegrade,  they accumulate in the food web. Plastic particles (of all sizes) are often seen as food particles and eaten. Birds are regularly found emaciated and with their stomachs full of plastic. In addition, they can get entangeld in plastic waste and pieces of plastic may block their intestinal tract.

The same goes for microplastics. These are also seen as food particles by zooplankton (water fleas) and ingested. And because zooplankton is eaten by fish, which end up on our plates, microplastics accumulate throughout the food web. In addition to the presence of the plastic itself, problems are caused by chemical additives that cause particle toxicity and hormonal disruption in the organisms that ingest it.

Although the EU is working on legislation to tackle the problem, wastewater treatment plants currently don't remove most of these microplastics. Consequently, 15.6 kg/day of microplastic input is estimated to end up in the river Rhine in the Netherlands alone. So far, hardly any data has been collected regarding microplastics in European lakes.

3) Sedimentation

Sediment accumulates at the bottom of a lake over time and can add up to several meters of accumulated material in a decade. The material that sediments to the bottom includes sand, silt and clay brought in by any inflowing rivers, but also dead organic matter from the lake water column. This can include particles from algal blooms and the dead bodies of zooplankton, fish and indeed any creatures that feed in the lake.  As it contains organic matter, this sediment will contain a large percentage of carbon. Some of this carbon may quickly be released as methane or carbon dioxide as bacteria break down the organic material near the surface sediments. However, the accumulated buried sediment represents a store of carbon that may never be released. Lakes have different rates of sedimentation, and knowing these can be used to estimate the carbon stored in the lake beds. 

Climate change is caused by the input of extra carbon dioxide by humans. The amount of carbon that is buried in lake beds is not precisely known but is an important parameter in understanding, predicting and possibly counteracting the effects of climate change on lake ecosystems.