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Groundwater-surface water mixing shifts ecological assembly processes and stimulates organic carbon turnover.

Stegen JC, Fredrickson JK, Wilkins MJ, Konopka AE, Nelson WC, Arntzen EV, Chrisler WB, Chu RK, Danczak RE, Fansler SJ, Kennedy DW, Resch CT, Tfaily M - Nat Commun (2016)

Bottom Line: Environmental transitions often result in resource mixtures that overcome limitations to microbial metabolism, resulting in biogeochemical hotspots and moments.Riverine systems, where groundwater mixes with surface water (the hyporheic zone), are spatially complex and temporally dynamic, making development of predictive models challenging.Our results indicate that groundwater-surface water mixing in the hyporheic zone stimulates heterotrophic respiration, alters organic carbon composition, causes ecological processes to shift from stochastic to deterministic and is associated with elevated abundances of microbial taxa that may degrade a broad suite of organic compounds.

View Article: PubMed Central - PubMed

Affiliation: Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, Richland, Washington 99352, USA.

ABSTRACT
Environmental transitions often result in resource mixtures that overcome limitations to microbial metabolism, resulting in biogeochemical hotspots and moments. Riverine systems, where groundwater mixes with surface water (the hyporheic zone), are spatially complex and temporally dynamic, making development of predictive models challenging. Spatial and temporal variations in hyporheic zone microbial communities are a key, but understudied, component of riverine biogeochemical function. Here, to investigate the coupling among groundwater-surface water mixing, microbial communities and biogeochemistry, we apply ecological theory, aqueous biogeochemistry, DNA sequencing and ultra-high-resolution organic carbon profiling to field samples collected across times and locations representing a broad range of mixing conditions. Our results indicate that groundwater-surface water mixing in the hyporheic zone stimulates heterotrophic respiration, alters organic carbon composition, causes ecological processes to shift from stochastic to deterministic and is associated with elevated abundances of microbial taxa that may degrade a broad suite of organic compounds.

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Turnover in microbial community composition.Microbial community turnover in terms of composition (a,b), phylogeny (c,d) and phylogenetic  model deviation (e,f). Turnover metrics are related to either changes in Cl− (a,c,e) or changes in NPOC (b,d,f). Solid red lines indicate a nonlinear spline fit (a,b) or linear models (c–f); dashed blue lines (e,f) indicate  model deviation significance thresholds; values above +2 or below −2 are considered significant. Mantel test statistics are provided.
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f5: Turnover in microbial community composition.Microbial community turnover in terms of composition (a,b), phylogeny (c,d) and phylogenetic model deviation (e,f). Turnover metrics are related to either changes in Cl− (a,c,e) or changes in NPOC (b,d,f). Solid red lines indicate a nonlinear spline fit (a,b) or linear models (c–f); dashed blue lines (e,f) indicate model deviation significance thresholds; values above +2 or below −2 are considered significant. Mantel test statistics are provided.

Mentions: Bray–Curtis was nonlinearly related to changes in Cl− concentration (Fig. 5a), but a weak relationship was observed with respect to changes in NPOC concentration (Fig. 5b). βMNTD was significantly (P=0.001 for both) related to changes in both Cl− and NPOC concentrations (Fig. 5c,d); the relationship with Cl− (r=0.70) was stronger than with NPOC (r=0.52). Although a change in NPOC concentration probably reflects alteration of the resource environment, a change in Cl− concentration arises due to the transport of surface water into (or out of) the subsurface domain. The Bray–Curtis and βMNTD patterns therefore suggest that the transport of surface water may directly influence OTU relative abundances and community phylogenetic structure. One parsimonious interpretation is that the transport of surface water into the subsurface enhances organismal dispersal across system compartments (that is, from surface water to the hyporheic zone to the broader aquifer). Importantly, this indicates that organismal dispersal can influence community composition, but it does not rule out a strong influence of the resource environment. An alternative interpretation is that uranium contamination—which closely tracks groundwater–surface water mixing conditions in the study system38—may influence community composition. Konopka et al.57 showed, however, that microbial activity in the study system is not altered by prevailing uranium concentrations due to formation of carbonate uranyl complexes.


Groundwater-surface water mixing shifts ecological assembly processes and stimulates organic carbon turnover.

Stegen JC, Fredrickson JK, Wilkins MJ, Konopka AE, Nelson WC, Arntzen EV, Chrisler WB, Chu RK, Danczak RE, Fansler SJ, Kennedy DW, Resch CT, Tfaily M - Nat Commun (2016)

Turnover in microbial community composition.Microbial community turnover in terms of composition (a,b), phylogeny (c,d) and phylogenetic  model deviation (e,f). Turnover metrics are related to either changes in Cl− (a,c,e) or changes in NPOC (b,d,f). Solid red lines indicate a nonlinear spline fit (a,b) or linear models (c–f); dashed blue lines (e,f) indicate  model deviation significance thresholds; values above +2 or below −2 are considered significant. Mantel test statistics are provided.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4829693&req=5

f5: Turnover in microbial community composition.Microbial community turnover in terms of composition (a,b), phylogeny (c,d) and phylogenetic model deviation (e,f). Turnover metrics are related to either changes in Cl− (a,c,e) or changes in NPOC (b,d,f). Solid red lines indicate a nonlinear spline fit (a,b) or linear models (c–f); dashed blue lines (e,f) indicate model deviation significance thresholds; values above +2 or below −2 are considered significant. Mantel test statistics are provided.
Mentions: Bray–Curtis was nonlinearly related to changes in Cl− concentration (Fig. 5a), but a weak relationship was observed with respect to changes in NPOC concentration (Fig. 5b). βMNTD was significantly (P=0.001 for both) related to changes in both Cl− and NPOC concentrations (Fig. 5c,d); the relationship with Cl− (r=0.70) was stronger than with NPOC (r=0.52). Although a change in NPOC concentration probably reflects alteration of the resource environment, a change in Cl− concentration arises due to the transport of surface water into (or out of) the subsurface domain. The Bray–Curtis and βMNTD patterns therefore suggest that the transport of surface water may directly influence OTU relative abundances and community phylogenetic structure. One parsimonious interpretation is that the transport of surface water into the subsurface enhances organismal dispersal across system compartments (that is, from surface water to the hyporheic zone to the broader aquifer). Importantly, this indicates that organismal dispersal can influence community composition, but it does not rule out a strong influence of the resource environment. An alternative interpretation is that uranium contamination—which closely tracks groundwater–surface water mixing conditions in the study system38—may influence community composition. Konopka et al.57 showed, however, that microbial activity in the study system is not altered by prevailing uranium concentrations due to formation of carbonate uranyl complexes.

Bottom Line: Environmental transitions often result in resource mixtures that overcome limitations to microbial metabolism, resulting in biogeochemical hotspots and moments.Riverine systems, where groundwater mixes with surface water (the hyporheic zone), are spatially complex and temporally dynamic, making development of predictive models challenging.Our results indicate that groundwater-surface water mixing in the hyporheic zone stimulates heterotrophic respiration, alters organic carbon composition, causes ecological processes to shift from stochastic to deterministic and is associated with elevated abundances of microbial taxa that may degrade a broad suite of organic compounds.

View Article: PubMed Central - PubMed

Affiliation: Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, Richland, Washington 99352, USA.

ABSTRACT
Environmental transitions often result in resource mixtures that overcome limitations to microbial metabolism, resulting in biogeochemical hotspots and moments. Riverine systems, where groundwater mixes with surface water (the hyporheic zone), are spatially complex and temporally dynamic, making development of predictive models challenging. Spatial and temporal variations in hyporheic zone microbial communities are a key, but understudied, component of riverine biogeochemical function. Here, to investigate the coupling among groundwater-surface water mixing, microbial communities and biogeochemistry, we apply ecological theory, aqueous biogeochemistry, DNA sequencing and ultra-high-resolution organic carbon profiling to field samples collected across times and locations representing a broad range of mixing conditions. Our results indicate that groundwater-surface water mixing in the hyporheic zone stimulates heterotrophic respiration, alters organic carbon composition, causes ecological processes to shift from stochastic to deterministic and is associated with elevated abundances of microbial taxa that may degrade a broad suite of organic compounds.

Show MeSH
Related in: MedlinePlus