Forest defoliator outbreaks alter nutrient cycling in northern waters

Insect defoliators alter biogeochemical cycles from land into receiving waters by consuming terrestrial biomass and releasing biolabile frass. Here, we related insect outbreaks to water chemistry across 12 boreal lake catchments over 32-years. We report, on average, 27% lower dissolved organic carbon (DOC) and 112% higher dissolved inorganic nitrogen (DIN) concentrations in lake waters when defoliators covered entire catchments and reduced leaf area. DOC reductions reached 32% when deciduous stands dominated. Within-year changes in DOC from insect outbreaks exceeded 86% of between-year trends across a larger dataset of 266 boreal and north temperate lakes from 1990 to 2016. Similarly, within-year increases in DIN from insect outbreaks exceeded local, between-year changes in DIN by 12-times, on average. As insect defoliator outbreaks occur at least every 5 years across a wider 439,661 km2 boreal ecozone of Ontario, we suggest they are an underappreciated driver of biogeochemical cycles in forest catchments of this region.

Diversity and distribution of sediment bacteria across an ecological and trophic gradient

Can we cluster bacterial sediment communities based on lake size, depth, and trophic status? Or, are bacterial microbial communities an emergent property of their geography, integrating regional physical and climatic conditions? Lakes in Minnesota are uniquely situated to address these questions because of their wide geographic range and variability in size and basin land-use. In this study, we selected twenty lakes with varying morphological and chemical properties across four ecological regions of Minnesota. Our objectives were to (i)) evaluate the diversity and spatial variation of the bacterial community at the sediment-water interface and (ii) determine how lake location and watershed land-use impact aqueous chemistry and influence community structure. Our data indicate that sediment communities from similar depth intervals are more likely to cluster by ecological region rather than any individual lake properties (e.g., trophic status, TP concentration, lake depth). However, composition is tied to a given lake, wherein samples from the same core were more alike than samples at similar depths across lakes. Our results illustrate the diversity within lake sediment microbial communities and provide insight into relationships between taxonomy, physicochemical, and geographic properties of north temperate lakes.