Allochthonous dissolved organic matter controls bacterial carbon production in old-growth and clearfelled headwater streams

Forests are vital to maintaining headwater stream integrity in forested biomes, which ensures the delivery of aquatic ecosystem services downstream. Forest harvesting, however, can alter land–water linkages and compromise stream integrity. Historically, the main effects of forestry on streams have been documented by studies that used relatively few (mainly abiotic) indicators and which focused on single harvesting events. However, forest management is expected to intensify in the future to meet increasing global wood demand and it is likely that our present understanding does not adequately capture the cumulative effects that streams will be subjected to under intensive forest management. To address this, we assessed the effects of varying forest management intensities on the integrity of 15 forest headwater streams in northwestern New Brunswick, Canada. We used a comprehensive approach to link multiple biotic and abiotic indicators of stream ecosystem integrity to reach‐ and catchment‐level characteristics including forest management (e.g., cumulative harvesting over time, road density, forest condition). Most indicators detected the gradient in forest management intensity with abiotic indicators responding most strongly. Streams in catchments with highest management intensity (especially road density) tended to have higher fine inorganic sediment deposition and entrainment, water cations and carbon, dissolved organic matter humification, and water temperature. These abiotic differences were associated with higher biofilm biomass and shredder densities, but lower leaf decomposition. Evidence from our multi‐indicator approach elucidated a potential effects pathway of higher inorganic sediment content in biofilms of organic matter potentially limiting or altering its use by microbial and benthic macroinvertebrate (BMI) communities and resulting in reduced leaf decomposition rates. Overall, this study shows that current best management practices in an intensively managed watershed (and legacy effects from past management such as older road systems) do not fully protect against an increased delivery of terrestrial materials to streams with resulting habitat and biotic changes, but that they are mostly effective at preventing the impairment of BMI communities.

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“…Regardless, neither were related to harvesting, and this agrees with other studies (Burrows et al. , Cawley et al. , De Wit et al.…”

Section: Discussionsupporting

confidence: 92%

“…The hypothetical DOC‐related increase in biofilm at intensively managed sites would have occurred despite its more humic nature and may be because microbial communities in forested headwater streams are adapted to the inputs of terrestrial—and more humic—DOC (Kreutzweiser and Capell , Burrows et al. , Emilson et al. ).…”

Section: Discussionmentioning

confidence: 99%

Linking stream ecosystem integrity to catchment and reach conditions in an intensively managed forest landscape

et al. 2018

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“…FI values from ambient water samples usually are positively correlated with bioavailability (Johnson et al 2011), but we observed a significant negative correlation across the narrower range of variation generated by leaf-litter leachate. A similar negative correlation has been observed in samples from headwater streams adjacent to old-growth forests (Burrows et al 2013). However, Burrows et al (2013) also reported a possible reversal in the relationship of FI and bioavailability around FI values >1.4.…”

Section: Discussionsupporting

confidence: 77%

Leaf-litter leachate is distinct in optical properties and bioavailability to stream heterotrophs

et al. 2015

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Dissolved organic C (DOC) leached from leaf litter contributes to the C pool of stream ecosystems and affects C cycling in streams. We studied how differences in leaf-litter chemistry affect the optical properties and decomposition of DOC. We used 2 species of cottonwoods (Populus) and their naturally occurring hybrids that differ in leaf-litter phytochemistry and decomposition rate. We measured DOC and nutrient concentration in leaf leachates and determined the effect of DOC quality on heterotrophic respiration in 24-h incubations with stream sediments. Differences in DOC composition and quality were characterized with fluorescence spectroscopy. Rapidly decomposing leaves with lower tannin and lignin concentrations leached ∼40 to 50% more DOC and total dissolved N than did slowly decomposing leaves. Rates of heterotrophic respiration were 25 to 50% higher on leachate from rapidly decomposing leaf types. Rates of heterotrophic respiration were related to metrics of aromaticity. Specifically, rates of respiration were correlated negatively with the Fluorescence Index and positively with Specific Ultraviolet Absorbance (SUVA 254) and T280 tryptophan-like fluorescence peak. These results reveal that leaf-litter DOC is distinctly different from ambient streamwater DOC. The relationships between optical characteristics of leaf leachate and bioavailability are opposite those found in streamwater DOC. Differences in phytochemistry among leaf types can influence stream ecosystems with respect to DOC quantity, composition, and rates of stream respiration. These patterns suggest that the relationship between the chemical structure of DOC and its biogeochemistry is more complex than previously recognized. These unique properties of leaflitter DOC will be important when assessing the effects of terrestrial C on aquatic ecosystems, especially during leaf fall.

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“…A study by Ghosh and Leff (2013) revealed a strong influence of carbon availability on bacterial utilization of dissolved organic nitrogen and dissolved inorganic nitrogen. Burrows et al (2013) found that an increasing contribution of terrestrial dissolved organic matter was the strongest variable driving benthic bacterial carbon production in forested, Tasmanian headwater streams.…”

Section: Bio-products and Pharmaceuticalmentioning

confidence: 96%

Substratum‐Associated Microbiota

Furey

Liess

2014

Water Environment Research

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A review of literature on substratrumassociated microbiotia from 2013 covers topics on benthic algae, bacteria and viruses from a range of aquatic environments, but focuses on freshwater ecosystems. Advances in laboratory, field, and assessment methods are highlighted as are updates in taxonomy and systematics. Aspects of water quality, waste‐water treatment, biofuels, nutrient cycling, food‐web interactions, land use changes, and environmental challenges such as climate change, pollutants, and impacts of medical substances are presented. our understanding of the ecology, taxonomy and assessment of substratum‐associated microbiota. In response to increased pressures from anthropogenic stressors and climate change on aquatic environments, researchers are re‐evaluating current knowledge and approaches to research, biomonitoring and assessment. In this review of the 2013 literature, advances in laboratory, field, and assessment methods are highlighted as are updates in taxonomy and systematics. A literature review of similar topics was completed in 2013 (Furey and Liess, 2013).

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Allochthonous dissolved organic matter controls bacterial carbon production in old-growth and clearfelled headwater streams

Cited by 22 publications

References 68 publications

Linking stream ecosystem integrity to catchment and reach conditions in an intensively managed forest landscape

Linking stream ecosystem integrity to catchment and reach conditions in an intensively managed forest landscape

Leaf-litter leachate is distinct in optical properties and bioavailability to stream heterotrophs

Substratum‐Associated Microbiota

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