5 TERRALAC core projects

Related projects:

Collaborators
Dr. Jörg Tittel (UFZ Magdeburg)
Prof. Roger Jones (University of Jyväskyla, Finland)

Subproject 1: Quantity and quality of surface and subsurface input of particulate and dissolved organic carbon to the experimental lakes

Investigators:

Nils Meyer (PhD student, TU Berlin)

Prof. Dr. Martin Kaupenjohann (TU Berlin)

Prof. Dr. Gunnar Nützmann (IGB Berlin)

Dr. Jörg Lewandowski (IGB Berlin)

Hypotheses:

1. Rising soil temperatures (during and outside the vegetation period) lead to increased degradation of solid soil organic matter (in the top and in the deep soil) and thus to a release of soluble organic compounds. The influx of this dissolved organic C is higher than the aboveground entry of particulate C in the experimental lakes, but it has less importance to the lacustrine food web, because of its higher proportion of refractory C.
   
2. Heavy rain after long dry periods leads to rising shares of particulate, less refractory C in the percolation water draining into the lake. This can be explained by the domination of preferential flow in the hydrological regime.
   

Subproject 2: Primary production

Investigators:

Soren Brothers (PhD student, IGB Berlin)

Dr. Jan Köhler (IGB Berlin)

PD Dr. Sabine Hilt (IGB Berlin)

Hypotheses:

1. At comparable nutrient concentrations clear, macrophyte-dominated and turbid, phtyoplankton-dominated shallow lakes can have a comparable primary production.
2. Shifts between the turbid, phytoplankton-dominated and clear, macrophyte-dominated regimes in previous centuries can be correlated with the share of allochthonous carbon in the food web (allochthony). Allochthony is higher in the clear regime.
   
   

Subproject 3: Microbial C turnover

Investigators:

Katrin Attermeyer (PhD student, IGB Neuglobsow)

PD Dr. Hans-Peter Grossart (IGB Neuglobsow)

Dr. Michael Hupfer (IGB Berlin)

Dr. Peter Casper (IGB Neuglobsow)

Hypotheses:

1. The input of terrigenous organic carbon increases microbial production in biofilms and sediments more than in the pelagic zone. Due to the vast surface of submersed macrophytes this effect is more pronounced in clear lakes than in turbid ones.
2. The microbial C turnover in sediments which is greatly influenced by terrigenous organic matter input affects the mobilization of P as well as the release of greenhouse (CO₂ and CH₄).
   
   

Subproject 4: Secondary production and allochthony

Investigators:

Kristin Scharnweber (PhD student, IGB Berlin)

PD Dr. Thomas Mehner (IGB Berlin)

Dr. Mario Brauns (IGB Berlin)

Prof. Dr. Norbert Walz (IGB Berlin)

Dr. Martin Pusch (IGB Berlin)

Hypotheses:

1. The secondary production in benthic habitats exceeds that of pelagic habitats under macrophyte dominance, whereas pelagic secondary production dominates in the phytoplankton stable state.
   
2. Artificial enhancement of allochthonous POC supply will result in a greater reliance of all consumers on allochthonous nutrients, as indicated by shifts in the stable isotope signatures. The increase of external subsidy will be more pronounced at macrophyte dominance.
   
3. Reciprocal subsidies between lakes and adjacent forests via Aeolian insects create a temporally limited, but short-term important nutrient coupling between land and water.

Subproject 5: Foodweb modelling

Investigators:

Betty Fritz (PhD student, University Potsdam)

Prof. Dr. Ursula Gaedke (University Potsdam)

Objectives:

1. a further development and refinement of the concept of TERRALAC
   
2. a consistency check and synthesis of the measurements conducted by subproject 1-4
   
3. systematic analysis and comparison of the different food webs under different treatments
   
4. generalisation of the results and computation of different scenarios in close cooperation with the subprojects

Related projects:

Dr. Jari Syväranta
Hypothesis:

1. Stable isotopes of hydrogen are a more sensitive tracer of allochthonous subsidy to lakes than carbon isotopes. Mixing models combining H, C and N result in more reliable estimates of the proportion of allochthonous sources to lake metabolism.

Dr. Sarian Kosten, IGB fellow 03/2011-11/2011
Hypotheses:

1. Warming will increase CO2 and – to an even larger extent – CH4 emissions from shallow lakes
2. Lakes with high amounts of in-lake produced carbon relative to terrestrial carbon will produce more CH4.

Prof. Michael Vanni, IGB fellow 06/2011-08/2011
Hypotheses:

1. The importance of subsidies will decline exponentially with distance into the recipient habitat.Specifically, the importance of aquatic insect subsidy into terrestrial ecosystems will decline exponentially with distance from the lakeshore into the terrestrial habitat
2. The importance of insect subsidies from lake to land will differ: between the two TERRALAC lakes, and Between sides of lakes with and without C additions