DOM cycling Flashcards
Odum, 1956
Primary Production in Flowing Waters
Main conclusions/results
Streams are among the most productive biological environments
Observed curves of Oxygen in streams can be used to calculate GPP, ER, and diffusion
Ratio of GPP:ER can be used to classify comunitites as predominantly heterotrophic or autotrophic
Light is likely the main cause of GPP patterns
Current (Q) can stimulate metabolism as it renews depletions and removes by-products
Downs, Howard-Williams, and Vincent, 1986
Sources of Organic nitrogen, phosphorus and carbon in antarctic streams
Main conclusions/results
Five sources of OM identified: bird life, autochthonous agal production, streambed soils, lacustrine and marine sediments, glacial ice (wind and snow deposits)
in-situ photosynthesis not considered dominant source of organic compounds
1st melt had highest OM content - winter deposition of snow and sediment on glaciers could be important
DOM content compares to temperate streams, but higher POM (low % CPOM)
Unexpectedly high conc. of POM
DOP
Aiken, Mcknight, Harnish, and Wershaw, 1996
Geochemistry of Aquatic Humic Substances in Lake Fryxell Basin, Antarctica
DOC conc of streams highest in early flows, decreased steadily throughout season
Lake Fryxell DOC > streams
Increases w/ depth, max ~32 mg/L at bottom
Low stream DOC conc compared to temperate and arctic, similar to semi-arid environments
Stream fulvic acids may have undergone less humification than lakes (lakes higher FA % of DOC)
3 sources of DOC in the lakes:
- active leaching of biomass in stream channels
- degradation of OM in sediments and bottom waters of LF –> results in generation of OM that diffuses into water column
- relict OM in the evaporated ancestral lake area diffusing into freshwater as the lake grows
McKnight, et al. 2001
Spectroflourometric characterization of DOM for indication of precursor OM and aromaticity
Ratio of emission intensity can serve as simple index to identify sources of FAs
Microbial sources ratio ~1.9
Terrestrial sources ratio ~1.4
Microbe derived FAs have emission max at lower wavelengths than terrestrial sources
Difference in at least 0.1 in index may indicated difference in sources
Measurement of FA source could provide important data for C budgets
Mullholland et al., 2001
Inter-biome comparison of factors controlling stream metabolims
Less daily variation in rates of ER than GPP
PAR is dominant control on GPP - Daily GPP rate significantly correlated with PAR
Nutrient conc. secondary control on GPP
P conc. and stream channel hydraulics (size of transient storage zone) control rate of R
R dominates NEP in all but 1 site (Sycamore creek - desert stream).
Streams are generally net sinks of OM rather than sources
Allochthonous C important fo fuelling heterotrophic metab
Energy dissipation method underestimates reaeration, and underrestimate declines with increasing H2O depth
Cole, et al. 2007
Plumbing the Global Carbon Cycle: Integrating Inland Waters into the Terrestrial Carbon Budget
Freshwater ecosystems are active components of global C cycle (not just passive pipes)
C burial and degassing > C exports from inland waters
2x as much C enters inland water systems from land as is exported to the sea (some of the remaining is stored and most is degassed)
~ 40% transferred to atm as CO2, 12% stored in sed, 48% to oceans
Inland waters oxidize a substantial fraction of OM they receive from the land
Small lakes may be disproportionately important in sed C storage
Lakes store 30-60% of OC as oceans per year, with much smaller area
Battin et al., 2009
Biophysical controls on organic carbon fluxes in fluvial networks
high-gradient streams -> rough, permeable streambeds create opportunities for subsurface retention an storage w/ low flow, frequent exchange w/ surface water
low gradient streams -> depositional environments, fine seds accumulate, reduce potential for surface-subsurface fluxes and retention/storage
microbe communities acclimate to changing resources in fluvial networks and increase metabolic capacity
R declines and NEP increases from headwaters downstream
In fluvial network, headwaters receive most of terrestrial DOC
DOC in downstream ecosystems is legacy of previous metabolic activity
Metabolism of DOC downstream is promoted by photolysis (produces CO2 from DOC), co-metabolism (algal exudates of labile OM can enhance transformation of recalcitrant DOC), shifts in microbe community (enhances metab capacity for transfer of recalcitrant DOC), and sedimentation of DO aggregation (increases res time and contact of OC with reactive zones)
James Cullis, Stanish, McKnight, 2014
Diel flow pulses drive particulate OM transport from microbial mats in glacial meltwater stream in the MDV
POM transport in MDV is supply limited
Mats are resistant to disturbance under normal diel flood pulses
Critical flow threshold of >100 l/s where additional sources of POM contribute (Nostoc or deeper orange mats?)
Time since resetting flood event and regrowth of mobile benthic biomass were primary drivers of POM transport variations btwn flood pulses
Importance in supply limitation and flow variability in controlling OM flux
Irena Creed, et al., 2015
The river as a chemostat: fresh perspectives on DOM flowing down the river continuum
As rivers move downstream, hysteresis dampens and chemostasis emerges
Catchment processes dominate low order streams (Q, res time, DOM production high and decay low) - conc. changes with flow
High order streams chemostatic b/c catchment processes overwhelmed by instream processes
* downstream shift from hydro drivers to instream bgc processes
More aromatic DOM in low-order streams, less complex, aliphatic DOM in high order
high spatial heterogeneity and temporal variability in DOM in headwaters
Convergence of median DOC conc. ( reduction in high and low extreme conc) downstream
Dampening occurs @ stream orders where dominance shifts from hydro integration to bgc processes - usually 3-4th order
Irena Creed, et al. 2017
Global change-driven effects on DOM composition: implications for food webs of norther lakes
Increased DOM delivery from terrestrial systems leads to browning of freshwaters
Changes in allochthonous DOM lead to changes in base of food web -> impact productivity and community comp
Foodweb becomes more reliant on terr DOM subsidies, which constrains the transfer of energy
browning - shifts from auto to heterotrophs. DOM may increase PP from nuts, but then overriden by light attenuation limits
Light avail constrains biomass and phyto PP
Shift from auto to hetero, reduction in production and transfer of high quality EFAs - changes quality of food for higher trophic levels.
Aquatic autotroph EFAs are needed by consumers (absent in terr autotrophs and OM)
Shifts from biolabile DOm to refractory DOM will shift phyto community comp by favoring cyanobacteria
Methylation and methyl-hg uptake increases
Shift to terrestrially derived DOM -> more biorefractory, aromatic, larger and heavier
Effects physiochemical properties of lakes, productivity and nutritional quality
Changes in DOM sources initiate cascade of biological outcomes
Travis Drake, Raymond and Spencer, 2018
Terrestrial Carbon inputs to inland waters: a current synthesis of estimates and uncertainty
Terrestrial landscapes transfer ~5.1 Pg C/yr to aquatic
0.95 Pg C/yr as river export
0.6 Pg C/yr as storage
3.9 Pg C/yr outgassed
-0.3 Pg C/yr non-terrestrial C fixation from waters
Most from CO2 from soil respiration and mineralization of terrestrial OC
Primary OC inputs from terrestrial landscapes:
from photosynthesis of atm CO2, enters directly as plant + litter detritus or leached material
Primary IC inputs from terrestrial landscapes:
CO2 + CH4 as products of soil respiration, chemical weathering - HCO3- and CO3 2- , Mechanical weathering and erosion of carbonate rocks
Emily Bernhardt, et al. 2017
The metabolic regimes of flowing waters
light availability and flooding are dominant drivers of river productivity
Contrast to lakes, limited evidence that nutrient availability controls metabolism rates, but variation in stream metab rates can affect nut dynamics
When light and disturbance not limiting, nut supply may limit metab
ER has higher temp sensitivity than GPP
Rivers with flood events have lower productivity, even under high light regimes
Enormous variability in metab across rivers, and little success in explaining variance
For effective management and conservation, need to devote as much to metab regimes as flow regimes
Canadell, et al., 2021
Regimes of primary production and their drivers in Alpine streams
Avg GPP highest in nival then glacial then krenal streams
Glacial max GPP values before snowmelt
Krenal stream similar before and after, nival rapidly higher after
PAR availability at streambed is dominant control on GPP –> determined by hydrology, turbidity, day length, solar angle
Existence of stability threshold where physical disturbance dominates over PAR on regulating GPP
Differing photosynthetic efficiencies (bryophytes vs. algae) could be responsible for different levels of GPP
Early stages of snowmelt and end of glacial melt = ‘windows of opportunity’ for benthic algal growth
Plasticity of primary producers to take advantage of this short window in alpine streams
timing and magnitude of GPP might shift with climate change
Kohler, et al., 2022
Glacier shrinkage will accelerate downstream decomposition of organic matter and alters microbiome structure
Upstream reaches have significantly lower decomp rates than downstream reaches
Avg decomp rate decreased with % glacier coverage and glacial index
Translates to the acceleration of OM decomp as glaciers recede
Fungi primarily using algae OM vs. allochthonous –> role of fungi as decmop may be downplayed in glacier streams
glacier shrinkage induces shift in microbiome from “gray” foodweb sustained by chemolithoautotrophs to “green” foodweb sustained by photoautotrophy
