Stream Biogeochemical Cycles Flashcards
Nancy Grimm and Stuart Fisher, 1984
Exchange between interstitial and surface water: implications fro stream metabolism and nutrient cycling
Higher ER in surface sediments than deep seds
using the chamber method/looking at streams as 2 layer may underestimate ER
Deep sediments show substantial O2 and NO3 uptake
Surface sediments are active in NO3 removal
Metabolism rates in surface community shows high productivity and autrotophy, but show high productivity and heterotrophic when include hyporheic zone
Despite high rates of GPP, desert streams may still be heterotrophic during the summer
There is significant flux of water into and out of deep sediments
Stream autotrophy needs to be balanced by heterotrophy of they would fill with OM
Emily Bernhardt, et al., 2005
Can’t see the forest for the stream? In-stream processing and terrestrial Nitrogen export
Showed high rates of stream NO3- processing
Changes in NO3- removal from stream processes may have reduced NO3- export
2 changes that may have increased denitrification:
- increase in heterotrophic assimilation of N w/ new organic debris dams (trees)
- increase in autotrophic assimilation of N leads to more algae
2 processes likely responsible for NO3- removal in streams:
- assimilative uptake by microbes, subsequent storage of export as PON or DON
- denitrification, which may be a large sink,
Changes in N processing in streams has occurred, and could explain ~30% of decline in WS NO3- export
These changes are distinct stream changes, from WS changes
WS studies can’t ignore in-stream processes
Scott Ensign and Martin Doyle, 2006
Nutrient spiraling in streams and river networks
Streams w/ gradual increase in channel length has less nut recycling than rapidly increasing channel length
Recycling of N increases with increasing channel size
N recycled more intensely in higher order streams and mid order
P uptake relatively constant as you move downstream
High order streams equally as important as headwaters for PO4 uptake
Larger, higher order rivers equally or more significant for nut uptake than headwaters
Much attention has been given to headwaters
Critical to address ecological connectivity of headwaters with lower end members (rivers, lakes, estuaries)
Spiraling length (S) (Ensign and Doyle 2006)
the distance required for a nutrient atom to complete 1 cycle from the dissolved inorganic form in H2O column (Sw) through particulate phase (Sp) and finally consumer phase (Sc)
Limitations on nutrient addition experiments (addressed in Ensign and Doyle, 2006)
- Only Sw portion of total S is measured –> no uptake or transfer
- results only representative of particular time and Q
- few examine channel corridor or network –> representative of watershed
Brian Roberts, 2007
In-stream biotic control on nutrient biogeochemistry in a forested stream, West Fork of Walker Branch
[DIN] and [SRP] highest in summer, lowest in spring and autumn
ER highest in spring and autumn and low in summer
GPP high during spring, declined during summer, slight increase in Fall
High day-to-day variability in GPP/ER
A strong relationship with NO3- and DIN uptake + metabolism rates
Importance of in-stream biotic activity on regulating N retention and export
Autotrophy important of regulating DIN –> temporal variability in DIN retention and export
Stream metabolism may be used to estimate in-stream nutrient uptake and retention rates
Poole, et al., 2008
Hydrologic spiraling: the role of multiple interactive flow paths in stream ecosystems
Flow path length, hydraulic gradients, conductivity control residence times
Short flow paths buffer channel temp, while long flow paths have the potentail to alter local temp
long flow paths/residence times may drive DOM mineralization and lower O2 conc.
habitats, H2O quality, and biota influenced by discharge and recharge location and path lengths
variation in channel morphology creates multiple scales of hierarchically organized HZ flow paths
Concept of hydrologic spiraling provides useful framework for visualizing patterns of HZ exchange
highlights potential for downstream movement outside channel and clarifies roles of flow path lengths on creating simultaneous discharge and recharge w/ in reach
Kathleen Lohse, et al. 2008
Interactions between biogeochemistry and hydrologic streams
Atm deposition important source of N, maybe C
Throughfall and stemflow intercept water, influence deposition of solutes (DOC, DON, DIN)
land-atm coupling among fast and slow processes control biosphere material and exchange
Soil H2O content regulates microbe-mediated transformation and gases losses - couples H20, C, N cycles and influences res times
Soil decomp is a fundamental source of nutrients for plants and mircrobes
Recharge rates, depth, flow path length, and reactant supply control C, N couplig in gw
stream hydraulics, spiraling, HZ exchange and connectivity drive hydrologic and bgc coupling in streams
- fundamental interactions of water, C, N occur at landscape, soils, gw and streams
Hydrologic transitions result in disproportionately high rates of C, N cycling
Kathy Welch, et al. 2010
Spatial variation in the geochemistry of glacial meltwater streams in Taylor Valley, Antarctica
Bonney streams enriched in NO3, depleted in SRP (P deficient)
Fryxell streams N deficient, enriched in P
S Fryxell streams -> highest HiSO4 conc from enhanced chemical weathering in larger HZ
S and E Fryxell streams have high HZ weathering and increased TDS
stream chemistry stoichiometry influences lakes
Higher solute concentration in longer streams (S LF)
Sea salt ions higher closer to ocean and Taylor Glacier
Nutrient availability varies with landscape age and distance to coast/inland
Higher N/P further inland
Anthony Aufdenkampe, et al, 2011
Riverine coupling of biogeochemical cycles between land, ocean, and atmosphere
most freshwaters supersaturated w/ CO2, large net freshwater to atm flux
Most systems flux of OC intro rivers is greater than the ability to stabilize and bury it, so OC is metabolized or photolyzed and returned to am as CO2
estimates of CO2 outgassing = 0.75 - 1.4 Pg C/yr
globally substantial but rarely considered in C budget
transport of OC poor minerals from deep soils into enviros w/ fresh C could augment estimates of global C sequestration from erosion
benefits for C budget to consider the coupling of Earth’s system by rivers and inland waters
rivers receive, transport, and process the equivalent of terrestrial NEP in watersheds -> not just export as pipes
Mike Gooseff, et al., 2011
Hydrological Connectivity of the Landscape of the MDV, Antarctica
Hydrologic reservoirs in MDV: atm, glaciers, soils/permafrost, streams, hyporheic zones, lakes
Streams are critical link between glaciers and lakes, deliver H2O to soils
Connections are spatially consistent and temporally short
Function of climate conditions
Streams connected to soils through HZ
extend <10 m of stream edge
Observed as damp band of sediment
Longer streams = more HZ storage
Algal mats = source of nutrients and POM to lakes
Lake water vol. balance between streamflow and evap/sublimation
MDV ecosystem has evolved as function of dynamic hydrologic connection
Mike Gooseff, Jeb Barrett, Joe Levy, 2013
Shallow groundwater systems in a polar desert, MDV Antarctica
Gw confined to shallow depths and often in unsaturated conditions
4 significant groundwater features:
local soil-moisture patches from snowmelt, water tracks, wetted margins, HZ
snowpatches support microbe and invert populations
20-64% from aeolian
greater VWC, less EC
Water tracks are bands of soil moisture that route water downslope
5-10x more solutes, 3x more C rich , Move salts 6x faster
areas of microbe metabolism and maybe PP
Wetted margins accumulate salts
HZ thaw depths ~65 cm, max thaw in January
seasonal filling of streambed sediment must occur before surface flow
exchange of H2O enhances res time
Zones of enhanced nutrient cycling
GW systems facilitate and buffer fluxes of energy and matter -> control patterns of biota
MDV landscape is discretely hydrologically connected
W/ warming, increase in gw role, may become accelerant of ecosystem and landscape processes
Peter Raymond, et al., 2013
Global carbon dioxide emissions from inland waters
95% of streams sampled were supersaturated with CO2
Found decreasing K with increasing stream order,
stream river est. CO2 flux ~1.8 Pg C/yr
lakes/reservoirs= ~0.3 Pg C/yr
large fluxes from streams/rivers based on their surface area
Hot spots for CO2 exchange
~70% of CO2 evasion is from streams located on 20% of earh
~50% of lake emissions are from the world’s largest lakes
Tropical lakes contribute disproportionately
ignoring inland water CO2 evasion could lead to significant errors in C budges
Adam Wlostowksi, et al., 2016
Patterns of hydrologic connectivity in the MDV, Antarctica: a synthesis of 20 years of hydrologic data
EC data supports idea that hydrologic connections between streams and HZ mediate solute loads in MDV streams
median EC increases with increasing stream length
longer streams are more annually intermittent than shorter streams
glacial source at higher elev, greater vol. of HZ storage
Longer streams have higher median surface temps, EC,
Longer streams behave isostatically w/ EC, shorter streams characterized by dilution
streams have annual and inter-annual chemostatic behavior
variability in EC relatively small
Increase in Q complimented by increase in HZ storage
Flood events increase HZ flux rates
Freeze-thaw can crack HZ and export more material for weathering
expansion of wetted width can pull more salts/solutes
High inter-annual variability in Q - contingent on climatic conditions
Singley, et al., 2017
Characterizing hyporheic exchange processes using high-frequency EC-Q relationships on sub-hourly to interannual timescales
Hydrologic and hydraulic processes govern response of EC (proxy for HZ solutes) to diel and seasonal Q variability
Patterns identified:
1. high flow periods increase turnover of HZ storage
2. effect of seasonally variable Q + HZ exchange on EC-Q differs between short and long streams
Shorter streams more prone to turnover over HZ H2O b/c smaller storage
Longer streams buffer against freshening b/c more storage
3. interannual period of freshening that coincides with shifts in C-Q dynamics and total annual Q
Effects of unsteady flow on HZ exchange
Carbon storage on land is a balance between
Primary production and decomposition
Biogeochemistry Chapter 5: Terrestrial C cycle main points
NPP captures <1 % of available sunlight
rest evaporates H2O and heats air
NPP is determined by length of growing season and temperature first, nutrients second
Humans have altered NPP and decomposition on land
Transfer of OC to atmosphere, reduced NPP
CO2 dissolved in water partitioned between these DIC compounds
dCO2 < 4.3 pH < HCO3- < 8.3 pH < CO3-
Most freshwater is 5-8 pH, so HCO3- dominates
What is the paradox with DOM delivered to rivers and how is it explained?
50-75% of DOM are fulvic and humic acids. It is assumed that this DOC is recalcitrant, yet it is rapidly assimilated.
Explanations:
- DOM is unavailable to microbes in anoxic conditions, and becomes more available when it enters oxic conditions
- Exposing DOM to sunlight increases is lability and makes it more readily available
- DOM can reduce depth of light, which limits GPP, which drives the system towards heterotrophy
Rivers are different from lakes because…
flow maintains constant nutrient supply, turbulance mixes water column, scouring limits burial capacity in sediments
DOC compounds include:
carbohydrates and amino acids from decomposed plants
humic and fulvic acids from soil organic matter
Human impacts on inland waters
Reduce soil res time, incrase res time in impoundments
Increased nutrient and sediment loadas to rivers
Reservoirs = C sources, replace C sinks (from flooded terrestrial land)
Dams reduce annual river flow
Eutrophication of inland/coastal waters increases N, P
Altered loads of dissolved and supsended materials
State factors that define ecosystem characteristics
Climate Parent material topography potential biota time
Bowen ratio
Ratio of sensible heat flux (energy to air as heat) : latent heat flux (energy to air as evapotranspiration)
Wet ecosystems have bowen ratio <0.5 , latent heat flux dominates
Dry ecosystem bowen ratio >0.5, sensible heat flux dominates
Controls on photosynthesis at the cellular/leaf level
availability of light and CO2
temperature (governs reaction rates)
availability of N (required to produce enzymes)
2 major groups of photosynthesis reactions
light harvesting - transform light into forms of chemical energy
C fixation - use products of light harvesting to convert CO2 to sugars
Photorespiration
breaking down sugras to CO2
Very inefficient, respires away 20-40% of C fixed by photosynthesis
BUT without it, continued light harvesting destroys photosynthetic pigments
Pelagic photosynthesis drivers
light availability and phytoplankton biomass
Stream primary producers
macrophytes
benthic algae
epiphytic algae (attached to plants)
planktonic algae
Terrestrial ecosystem GPP driven by
length of phtosynthetic season primarily, secondarily soil nutrients and water availability
Reed, et al., 2021
Aquatic-Terrestrial Linkages Control Metabolism and Carbon Dynamics in Mid-Sized, Urban Stream influenced by snowmelt
Mean CO2 flux ~3x higher during snowmelt
Net source of CO2 to atm
Wide range in daily GPP and ER variation
Steady hydrology allows for year round primary production
NEP negative = net heterotrophy
NEP more negative during snowmelt –> ER enhanced during snowmelt
Greater mobilization of OC into channel or activation of other terrestrial floodways
decoupling of GPP and ER with high productivity –> allochthonous OC fueling metabolism
CO2 flux supported by mix of heterotrophic CO2 and CO2 inputs from watershed
GPP varies, slightly higher during snowmelt –> less scour or long enough for new PP establishment
Increasing light and higher nutrients in spring
Varying degrees of Aquatic-terrestrial linkages that can occur with seasonal flow regimes
