Nutrient Dynamics in Streams

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Nutrient Dynamics in Streams
Lakes Stratified, low oxygen N changing
form P precipitation Streams Usually well
mixed Usually well oxygenated (exception --
hyporheic zone) Closely tied to terrestrial
ecosystem Downstream transport
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Dissolved Load Major ions -- Ca, Na, K, N and
P missing (low concentrations) Where do these
nutrients come from?
Sources 1. Rain Na, Cl, SO4,
NO3 Concentrations depend on the source of the
storm Salt spray SO4 from coal NO3 from
auto emissions
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Sources (cont.) 2. Erosion -- chemical
weathering of rock examples granite --
SiO2 limestone -- Ca, CO3, NO3 dolomite --
Mg, CO3 3. Atmosphere -- gases CO2, O2,
N2 4. Biological -- N fixation 5. Pollution
point sources (pipes) non-point (agriculture
runoff)
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Four studies of nutrient dynamics in
streams Primarily concerning inputs Vitousec
(1977) White Mnts. of New Hampshire 57
streams 500 - 1700 m elevation High Alpine
tundra (timberline at about 1400
m) Krumholtz High-elevation
fir Spruce-fir Low Northern hardwoods
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Vitousek (cont.) Chloride not much in
rocks source rainwater not biologically
active (conservative) concentrations lower at
higher elevations High elevation little ET
(little vegetation, cooler) stream
rainwater Low elevation higher ET (more
vegetation, warmer) Cl gets concentrated (ET
removes water)
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Vitousek (cont.) Sulfate rainwater
source biologically active, anthropogenic
overload looks like chloride
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Vitousek (cont.) Sodium conservative from
rock weathering and rain very different from
Cl 1. Soil contact time shallow
high-elevation soils 2. Weathering rate faster
at lower elevations where temperature is
higher and more vegetation
Precipitation low Na
Stream higher Na
Weathering
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Vitousek (cont.) Calcium and magnesium Biologi
cally important, not conservative From
weathering Similar to Na Available in amounts
well above biological demand Potassium From
weathering Biologically important No
explicable pattern Nitrate From precipitation
and weathering (N-fix not important
here) Biologically very important, often
limiting No relationship with
altitude Related to successional stage of
vegetation
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Bond (1979) Wasatch Mountains of Utah (ski
resorts, Sundance, Alta) Annual hydrograph
dominated by spring runoff Made graphs of
concentration versus of discharge
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12
2
10
4
10
12
Depth (m)
10
14
6
8
8
8
6
4
2
10
6
0
4
12
2
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Dissolved oxygen (mg/L) in Lawrence Lake,
Michigan. 1968. From Wetzel 2001, Figure 9-7.
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Hysteresis loops
Concentration higher on rising limb
Concentration lower on rising limb
Concentration increases with discharge
Concentration decreases with discharge

Q
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Bond (cont.) Magnesium Concentrations lower
at higher flows Counter-clockwise
hysteresis Sulfate Concentrations lower at
higher flows Clockwise hysteresis Calcium
Concentrations lower at higher flows Clockwise
hysteresis Note high concentrations Phosphoru
s Little variation with flow Very high
concentrations How do we explain these
patterns?
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Bond (cont.) 1. Time water in contact with
soil
Surface runoff -- short Sub-surface runoff
(interflow) -- intermediate Groundwater -- long
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This explains magnesium
Rising limb -- flow includes GW, sub-surface
flow, and surface runoff Falling limb -- mostly
GW more water has spent more time in the soil.
Therefore, weathering-derived chemicals should be
higher Generally higher flows have less GW and
therefore less
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2. Terrestrial plant uptake Very little during
early spring Important in summer Reduces
falling limb concentrations of important plant
nutrients such as SO4 3. Instream chemical
processes Calcium Ca concentrations very
high. This is a travertine stream. Ca held in
solution by CO2 solubility CaCO3 CO2 H2O ?
Ca(HCO3)2 ? Ca2 2HCO3-1 High summer
temperatures reduce the solubility of CO2 Ca
precipitates as marl? 4. High concentrations of
P are very strange.
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Gibbs (1970) Looked at chemical concentrations
in rivers throughout the world Plotted total
cations versus Na/NaCa
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Gibbs (cont.) tropics -- relatively low
dominated by Na high precipitation soils
thoroughly leached, little weathering chemistry
rainwater temperate -- moderate dominated
by Ca and other rock-derived
chemicals arid-land rivers -- high
dominated by Na water evaporates Ca becomes
saturated, precipitates relatively more
Na Same story for anions
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Turner and Rabalais (1991) Nutrients in
Mississippi River -- long-term Nitrate
little change until about 1950 increased,
recent decrease? Silicate decreased, recent
increase? Total P no older data increasing?

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Turner and Rabalais (cont.) Nutrients in
Mississippi River -- long-term Fertilizer use
increased from 1940 to about 1980 and then has
gone down some. 44 of N and 28 of P applied
as fertilizer has ended up in the Gulf of
Mexico. Nitrate correlated with N fertilizer
applied Silicate negatively correlated with P
fertilizer
Explain this!
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Summary of these four studies Sources Atmospher
e marine vs continental air masses (Cl, Na,
SO4) anthropogenic inputs (SO4, NO3) Soil
weathering type of rock contact time, depth
of soil temperature, soil acids Pollution
point sources non-point agricultural runoff
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Summary of these four studies (cont.) Processes
Terrestrial vegetation transpiration upta
ke Instream processes evaporation chemical
precipitation autotrophic uptake (Si) Next we
will look more at what happens in streams.
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Nutrient Dynamics in Streams (2)
Lakes Stratified, low oxygen N changing
form P precipitation Cycles Streams Usually
well mixed Usually well oxygenated (exception
-- hyporheic zone) Closely tied to terrestrial
ecosystem Downstream transport -- Spirals
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Diffusion
Diffusion
N
N
Runoff
Runoff
2
2
Denitrification
Denitrification
N
-
fixation
N
-
fixation
Nit
Nit
NO
NH
NO
NH
3
4
3
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Nitrogen cycle in a lake (complex)
I
I
I
I
I
I
Plant N
Plant N
Excreation (A)
I
Excretion (A)
I
Death
Death
A
A
Animal
Animal
N
N
PON DON
PON DON
Death
Death
Detritus
Detritus
A
Mineralization
Sedimentation
Sedimentation
Sediments
Sediments
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Nitrogen cycle in a lake (simplified)
-
-
PON
Fish
Zooplankton
Algae
Immobilization
Detritus
DIN
Mineralization
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Nitrogen cycle in a lake ( very simplified)
-
-
PON
Immobilization
DIN
Mineralization
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Nitrogen cycle (?) in a stream (complicated)
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Nitrogen cycle (?) in a stream (simplified)
DIN
PON
Immobilization
Invertebrates
Fish
Algae
DIN
Detritus
Mineralization
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Nutrient spiralling -- the coupling of nutrient
cycling with downstream transport
Dissolved Inorganic
Dissolved Inorganic
Dissolved Inorganic
Particulate Organic
Dissolved Inorganic
Particulate Organic
Particulate Organic
Particulate Organic
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Spiralling length -- the average distance a
nutrient atom travels while it completes a cycle
from dissolved to particulate organic
(immobilization) and back to dissolved
(mineralization)
Spiralling length -- uptake length plus turnover
length
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Uptake length -- Distance traveled in dissolved
form Turnover length -- Distance traveled as
organic particle
Dissolved Inorganic
Dissolved Inorganic
Particulate Organic
Uptake length
Turnover length
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Spiralling length -- How is it measured? 1. Add
nutrient and measure uptake 2. Radioisotopes 3.
Stable isotopes
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Spiralling length -- How is it measured? 1. Add
nutrient and measure uptake 2. Radioisotopes 3.
Stable isotopes
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Spiralling length -- How is it measured? 1. Add
nutrient and measure uptake Problem -- Nutrients
added at levels above natural levels. But still
useful.
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Spiralling length -- How is it measured? 1. Add
nutrient and measure uptake 2. Radioisotopes 3.
Stable isotopes
32P and 33P used by Elwood, Newbold, and
Mulholland at Oak Ridge National Laboratory.
Problems No useable radioisotope of nitrogen.
Difficult to get permission to add
radioactive material to streams.
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Spiralling length -- How is it measured? 1. Add
nutrient and measure uptake 2. Radioisotopes 3.
Stable isotopes -- 13C, 15N
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LINXLotic Intersite Nitrogen eXperiment

• The Experiment
• Physical, chemical, and ecological
  characterization of stream
• 6-week 15NH4 addition to stream water
• Determine NH4 uptake length and rates, N
  turnover rates, and food web transfer of N

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LINX
10
OH
2
Ammonium Uptake Length (m)
MN
NM
NC
PR
NH
OR
MI
KS
AZ
TN
AK
0
0
5
10
15
20
25
30
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NH4 Concentration (µg/L)
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LINX
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Spiralling length -- How is it measured? 1. Add
nutrient and measure uptake 2. Radioisotopes 3.
Stable isotopes -- 13C, 15N Problems No usable
stable isotope of phosphorus. Expensive (isotope
and analysis).
Summary -- Excellent progress is being made on
our understanding of nutrient dynamics in streams.
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