Recoupling terrestrial, benthic and pelagic habitats by constructing littoral zones diversifies carbon flows to aquatic macroinvertebrates

Abstract

Shoreline restoration measures are increasingly implemented to stimulate biodiversity recovery in degraded lake ecosystems. However, the underlying mechanisms of observed recovery processes often remain disclosed. Here, we mechanistically studied how the creation of littoral shorelines in a degraded pelagic-driven lake affected fluxes of organic material across shoreline gradients, which are known to be essential for the functioning of aquatic food webs. We assessed how new connections among habitat types (dry shorelines, littoral zones and the limnetic water column) affected carbon fluxes in the food web of the 70.000 ha large shallow turbid lake Markermeer (the Netherlands), to which 16% of soft sediment littoral shoreline was added by constructing 1300 ha of wetland islands in 2016. Development of islands and littoral habitats with water less than 1.5 m deep improved underwater light conditions compared to the surrounding turbid limnetic habitats of ∼4 m deep, and therefore stimulated benthic primary producers. Field monitoring and stable isotope analyses revealed increases of benthic primary production and of organic material fluxes from the shoreline into the pelagic zone, which both stimulated the macroinvertebrate diversity. During the early phase of the restoration project (<8 years) benthic primary production transferred best to higher trophic levels compared to carbon-rich terrestrial material, likely due to the relatively higher quality of benthic food for macroinvertebrates. We conclude that the creation of sheltered shallow habitats in limnetic-dominated lakes can diversify carbon fluxes among habitats which stimulates the base of the aquatic food web. This makes lake restoration via re-coupling of terrestrial, pelagic and benthic habitats an effective forward-looking restoration measure for degraded monotonous lake ecosystems.