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Impact of Terrestrial Organic Matter on Boreal Lake Ecosystems
Recent research conducted by a collaborative team from Finland and the Netherlands has shed light on the significant role that terrestrial organic matter (t-OM) plays in boreal lake ecosystems. The study explores how different groups of consumers in these lakes rely on t-OM, using stable hydrogen isotopes to assess this reliance across various ecological contexts.
The research focused on 19 consumer groups, ranging from algae to top-tier predators, across 35 distinct boreal lakes. By employing Bayesian mixing models, the team analyzed stable isotopes of hydrogen to evaluate the extent to which these consumers depend on terrestrial energy sources.
Postdoctoral Researcher Ossi Keva, who contributed to the research while at the University of Jyväskylä, noted, “Our findings reveal significant variations in energy dynamics between dystrophic and eutrophic lakes. Agricultural activities in catchment areas tend to diminish the reliance on terrestrial organic matter among consumers at all levels, primarily due to the rise in algal biomass. Conversely, lakes surrounded by forested areas show a stronger reliance on t-OM.”
Understanding Energy Transfer in Lake Food Webs
Utilizing stable isotopes allows for an in-depth analysis of energy and biomass transfer within lake food webs. In particular, hydrogen isotopes serve as a powerful tool in distinguishing between aquatic and terrestrial biomass. This differentiation arises because terrestrial plants exhibit significant enrichment in the heavier isotope due to water loss through transpiration, a phenomenon not observed in submerged aquatic producers.
The study highlighted that while pelagic zooplankton primarily obtain their energy from algal production, a substantial proportion of the energy for benthic macroinvertebrates is derived from terrestrial sources. According to Keva, “These patterns of energy origin were similarly reflected in the dietary sources of planktivorous and benthivorous fish.”
Influence of Land Use on Organic Matter Sources
The investigation revealed a clear connection between land-use practices within catchment areas and the sources of dissolved and particulate organic matter in lakes. Lakes situated in agricultural catchments are generally more eutrophic, resulting in an organic matter pool primarily comprised of algal material. In contrast, dystrophic lakes nestled in forested regions tend to possess a higher proportion of terrestrial-derived organic matter.
As a result, the reliance of aquatic consumers on terrestrial energy shifts significantly. The research documents a decline in consumer allochthony from dystrophic lakes to eutrophic ones, illustrating how land-use changes can alter the dynamics of lake ecosystems.
Keva emphasizes the broader implications of the study: “Our findings underscore that land-use practices in catchment areas significantly impact the transport of organic matter from terrestrial landscapes to lake ecosystems. This, in turn, affects the origin of lake organic matter, the dynamics of energy within these systems, and the overall function of aquatic food webs.”
This comprehensive study on consumer allochthony provides crucial insights into how environmental gradients shape the interactions between terrestrial and aquatic ecosystems, highlighting the need for careful management of land and water resources.
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