The big question now is whether and how these deep bacterial blooms affect the biogeochemical cycles, especially the nitrogen cycle. After all, nitrogen is a fundamental building block of life and tends to be in short supply in Lake Tanganyika. A lack of nitrogen, however, can have drastic consequences for all levels of the ecosystem - from algae to fish. Now, the very area in the water column where the deep blooms grow, drives an active microbial nitrogen cycle, and significant nitrogen loss. Therefore, understanding the effects of the deep blooms and how nitrogen loss changes over time is an important question for the future of Lake Tanganyika.
The researchers were able to show that sulfur bacteria significantly increase nitrogen loss by converting bioavailable nitrogen such as NOx and NH4+ into nitrogen (N2) gas. This process also removes other nutrients from the biosphere. By disentangling the effects of these deep blooms on nitrogen cycling in Lake Tanganyika the study, recently published in Nature Communications, may provide a better understanding of how nitrogen loss is regulated in other similar aquatic ecosystems.
Climate change could intensify nutrient deficiencies
Climate change is now additionally interfering with this ecosystem. "If wind velocities decrease and water temperatures increase as predicted, then we would expect the deep blooms in the north to expand southward to the other side of the lake," say the study's lead authors Cameron Callbeck and Benedikt Ehrenfels of Eawag's Department Surface Waters. "Such an expansion would ultimately accelerate nitrogen loss with potential negative implications for fish catches."