The influence of in-stream processes on stream nutrient chemistry: insights from low- and high-resolution data

Susana Bernal1 Anna Lupon2

Juan Lluís Riera2

Francesc Sabater2

Eugènia Martí1

Photo: A. Lupon 1Centre for Advanced Studies (CEAB-CSIC)

2University of Barcelona (UB) All in Catalonia, Spain

FONT DEL REGÀS IN AUTUMN

WORKSHOP ON HIGH RESOLUTION TIME SERIES HELMHOLTZ UFZ

MAGDEBURG JULY 2014

Based on Frissell et al. 1986

Hierarchical organization of stream ecosystems

The “kidney” The “nephron”

catchment

section

reach

subreach

microhabitat

Forest & Landscape Ecology

Stream Ecology

Characterization of stream nutrient dynamics

9/98 3/99 9/99 3/00 9/00 3/01 9/01 3/02

mg

NO

3-N

L-1

0.0

0.5

1.0

1.5

2.0

SOURCES HYDROLOGIC TRANSPORT

IN-STREAM CYCLING BIOTIC PROCESSING

Stream nutrient dynamics result from the combination of sources and in-

stream nutrient transformations.

The relevant time-scales for understanding biogeochemical transformation at each hierarchical level differ.

Conceptual model of in-stream nutrient cycling

von Schiller D., Bernal S., Sabater F., Marti E. 2014. Freshwater science (in press)

I O = I - UnetUnet = Ugross - R

water column

Ugross

assimilationsorption

co-precipitationnitrification

active streambed

R

mineralizationdesorptiondissolution

Unet < 0 Unet > 0Unet ~ 0

~100 m

Mass balance

In-stream net areal uptake rate (Unet, in mg/m2/s). Empirical approaches

von Schiller, D., Bernal, S. Martí, E. 2011. Biogeosciences

𝑈𝑈𝑈𝑈 =𝑄𝑇𝑇𝑇 ∙ 𝐶𝑇𝑇𝑇 + 𝑄𝐺𝐺 ∙ 𝐶𝐺𝐺 − 𝑄𝐵𝑇𝑇 ∙ 𝐶𝐵𝑇𝑇

𝑤𝑤 ∙ 𝑥

Q discharge (L/s) C concentration (mg/l) ww wet width (m) x lenght (m)

~100 m

~15 m

Spiraling method

Downstream distance (m)

Conc

entr

atio

n

Cl- (dilution)

Nutrients (dilution + bgc)

𝑈𝑈𝑈𝑈 =𝑄 ∙ 𝐶

1 𝑘⁄ ∙ 𝑤𝑤

Q discharge (L/s) C concentration (mg/l) ww wet width (m) k slope (1/m)

A decade+ of stream ecology at La Tordera catchment (NE Spain)

①

③

The Fuirosos stream (since 1999) ① 14.3 km2 m a.s.l. = 115 P = 470 mm PET = 1390 mm RC = 7% Temporary Semiarid Med ②

② The Santa Fe stream (since 2002)

2.5 km2 m a.s.l. = 1140 P = 992 mm PET = 989 mm RC = 17% Perennial Subhumid Med

③ The Font del Regàs stream (since 2009) 13 km2

m a.s.l. = 470 P = 857 PET = 1064 mm RC = 28 % Perennial Subhumid Med

Temporal variation of in-stream net areal uptake rate (Unet)

Unet > 0 Uptake > Release Unet < 0 Uptake < Release Unet ≈ 0 Uptake ≈ Release

Unet can be highly variable over time within the same stream. The stream can alternatively act as a net source, net sink, or be at bgc steady-state.

Sta Fe Fui

-150

-100

-50

0

50

100

150

NO3

Sta Fe Fui-15

-10

-5

0

5

10

15

Sta Fe Fui-15

-10

-5

0

5

10

15U

net (

µg/m

2 /m

in)

2.4 15.9

NH4 1.8 8.1

PO4 10.9 4.6 IQR/|med|

2004-2006. 2 YEARS OF MONTHLY SAMPLING at Sta. Fe and Fuirosos

Uptake

Release

Bernal, S., von Schiller, D., Sabater, F., Martí, E. 2012. J. Geophysical Res. von Schiller, D., Bernal,S., Sabater, F., Martí, E. 2014. Freshwater Science (in press)

Unet > 0 Uptake > Release Unet < 0 Uptake < Release Unet ≈ 0 Uptake ≈ Release

The temporal variation of Unet is not random, but can follow a seasonal pattern that differs among nutrients. Nutrient processing by stream biota responds to the seasonality of environmental variables.

AU WT SP SM0

20

40

60

80

100

AU WT SP SM0

20

40

60

80

100

AU WT SP SM0

20

40

60

80

100NO3 NH4 PO4

Freq

uenc

y (%

) Temporal variation of in-stream net areal uptake rate (Unet)

Adapted from Bernal, S., von Schiller, D., Sabater, F., Martí, E. 2012. J. Geophysical Res.

Spatio-temporal variation of stream nutrient concentration 2010-2011. 2 years of bimonthly sampling at Font del Regàs

SW Rip GW

1.5 m Piezometer

(a) Longitudinal pattern of stream nutrient concentrations

(b) Riparian groundwater nutrient chemistry along the reach

Chl

orid

e(m

g l-1

)

0

10

20

Nitr

ate

( g

N l-1

)

0

200

400

600

Am

mon

ium

( g

N l-1

)

0

15

30

45

8/10

10/10

12/10

2/1

1 4/1

1 6/1

1 8/1

1

10/11

12/11

Ph

ospa

te(

g P

l-1)

0

15

30

45

Bernal, S., Lupon, A., Ribot, M., Sabater, F., Martí, E. 2014. Biogeosciences (in review)

Spatio-temporal variation of in-stream net uptake rate (Unet)

Streamwater

Stream Biota

IN OUT

Groundwater

Unet 𝑈𝑈𝑈𝑈 =

𝑄𝑇𝑇𝑇 ∙ 𝐶𝑇𝑇𝑇 + 𝑄𝑇𝑅𝑅𝐵 ∙ 𝐶𝑇𝑅𝑅𝐵 + 𝑄𝐺𝐺 ∙ 𝐶𝐺𝐺 − 𝑄𝐵𝑇𝑇 ∙ 𝐶𝐵𝑇𝑇𝑠𝑈𝑠𝑠𝑈𝑈𝑈 𝑙𝑈𝑈𝑠𝑙𝑈

NO3 334.0 59.9 224.0 40.1

NH4 4.8 51.6 4.5 48.4

PO4 12.1 52.2 11.1 47.8

σ2 Among sites

% σ2 Within sites

%

-4

-2

0

2

4

230440

6401400

16401840

20502255

24652680

3000-10

-5

0

5

10

-40

-20

0

20

40 NO3

NH4

PO4 Une

t (µg

N o

r P /m

/s)

The longitudinal variation of Unet within a single date can be as high as within the same stream segment over time.

Distance from headwaters (m)

Adapted from Bernal, S., Lupon, A., Ribot, M., Sabater, F., Martí, E. 2014. Biogeosciences (in review)

Spatio-temporal variation of in-stream net uptake rate (Unet)

Unet > 0 Uptake > Release Unet < 0 Uptake < Release Unet ≈ 0 Uptake ≈ Release

# eve

nts

020406080

100

# eve

nts

020406080

100

Distance from headwaters (m)

230

440

640

400

640

840

2050

2255

2465

2680

3000

3200

3430

3690

# eve

nts0

20406080

100

NO

3 N

H4

PO4

In-stream bgc transformations can either follow a spatial pattern (NO3), or be consistent along the reach (NH4). Nutrient processing by stream biota responds to the spatial pattern of environmental variables.

Bernal, S., Lupon, A., Ribot, M., Sabater, F., Martí, E. 2014. Biogeosciences (in review)

Streamwater

Stream Biota

IN OUT

Groundwater

Unet 𝑈𝑈𝑈𝑈 =

𝑄𝑇𝑇𝑇 ∙ 𝐶𝑇𝑇𝑇 + 𝑄𝑇𝑅𝑅𝐵 ∙ 𝐶𝑇𝑅𝑅𝐵 + 𝑄𝐺𝐺 ∙ 𝐶𝐺𝐺 − 𝑄𝐵𝑇𝑇 ∙ 𝐶𝐵𝑇𝑇𝑠𝑈𝑠𝑠𝑈𝑈𝑈 𝑙𝑈𝑈𝑠𝑙𝑈

Frequency of events (%)

High resolution spatio-temporal variation of stream nutrient concentration

2010-2011. 1 year of sampling at 12-h intervals

Chlo

ride

(mg/

l)

0

5

10

15

NItr

ate

(mg/

l)

0.0

0.3

0.6

0.9

9/10 11/10 1/11 3/11 5/11 7/11 9/11 Am

mon

ium

(g/

l)

0

20

40

60

9/10 11/10 1/11 3/11 5/11 7/11 9/11

Phos

phat

e (

g/l)

0

20

40

Can high resolution data provide some mechanistic explanation on the spatio-temporal variation of in-stream nutrient processing?

∆Am

mon

ium

(µg/

l)

-20

0

20

9/10 11/10 1/11 3/11 5/11 7/11 9/11

Pho

spha

te (

g/l)

-20

0

20

2010-2011. 1 year of sampling at 12-h intervals

Nitr

ate

(g/

l)

-200

-100

0

100

200

d.l. ~ 5 ppb (87% of the cases)

d.l. ~ 4 ppb (92% of the cases)

Analytical resolution can still be a limiting factor.

High resolution spatio-temporal variation of stream nutrient concentration

Spatio-temporal pattern of diel cycles of stream nitrate concentration

Nitrate Chloride

∆𝐶 =𝐶𝑛𝑛𝑛𝑛𝑛 − 𝐶𝑑𝑑𝑑

𝐶𝑛𝑛𝑛𝑛𝑛× 100

ΔNO3 during base flow conditions was conspicous at the MID and DOWN sites in spring.

Upstream

Midstream

Downstream

Lupon, A., Marti E., Sabater, F., Bernal, S. 2014. Ecology (in review)

2010-2011. 1 year of sampling at 12-h intervals

C

(%)

-10

0

10

20

30

Time (day/month)19/03 02/04 16/04 30/04 14/05 28/05 11/06 25/06

∆ C

(%)

-10

0

10

20

30

ΔNO3 resulted from in-stream bgc processes.

Lupon, A., Marti E., Sabater, F., Bernal, S. 2014. Ecology (in review)

Stream

Riparian grounwater Nitrate Chloride

Spatio-temporal pattern of diel cycles of stream nitrate concentration

Rip groundwater Stream water

∆𝐶 =𝐶𝑛𝑛𝑛𝑛𝑛 − 𝐶𝑑𝑑𝑑

𝐶𝑛𝑛𝑛𝑛𝑛× 100

2012. Spring (4 months) of sampling at 6-h interval + GPP

∆ C

(%)

-10

0

10

20

30

Dai

ly P

AR

(mol

/m2 /d

ay)

0

5

10

15

20

25

GPP (g O

2 /m2/day)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

[DO] = GPP– R ± E GPP gross primary productivity R respiration E reaeration

Oximeter

single-station diel DO change method (Bott 2006) 30 min-interval

∆NO3 vs GPP: R2 = 0.74

Time (day/month)19/03 02/04 16/04 30/04 14/05 28/05 11/06 25/06

∆ C

(%)

-10

0

10

20

30

Temporal variation of ΔNO3 explained by the influence of light inputs on the assimilation of NO3 by stream photoautotrophs.

Lupon, A., Marti E., Sabater, F., Bernal, S. 2014. Ecology (in review)

Stream

Riparian grounwater Nitrate Chloride

Spatio-temporal pattern of diel cycles of stream nitrate concentration

Rip groundwater Stream water

GPP vs PAR: R2 = 0.74

2012. Spring (4 months) of sampling at 6-h interval + GPP

Spatio-temporal pattern of diel cycles of stream nitrate concentration

Lupon, A., Marti E., Sabater, F., Bernal, S. 2014. Ecology (in review)

Spatial variation of ΔNO3 explained by changes in light and temperature regimes along the stream.

UP 57 66

MID 99 73 83 25

DOWN 103 80 104 57

T (º

C)

5

10

15

20

Time (day/month) 12/03 26/03 09/04 23/04 07/05 21/05 04/06 18/06 02/07

PA

R (m

ol m

-2d-1

)

0

8

16

24

>10ºC

>4 mol/m2/d

days T>10ºC

% days ΣPAR>4 mol/m2/d

%

2012. Spring (4 months) of sampling at 6-h interval + GPP

Past, Present, Future

Long term monitoring vs. hypothesis-driven studies. Analytical resolution issues (PO4, NH4).

Powerful tool for exploring major drivers of in stream solute concentrations within and between catchments at different spatio-temporal scales.

Advances Understand environmental drivers of in-stream nutrient processing. Better assessment of the contribution of in-stream processes to stream nutrient dynamics. Perspective

Hands on work

High resolution temporal data Provide some mechanistic explanation on the spatio-temporal variability of in-stream nutrient processing shown by low resolution data.

I O = I - UnetUnet = Ugross - R

water column

Ugross

assimilationsorption

co-precipitationnitrification

active streambed

R

mineralizationdesorptiondissolution

Thanks to Daniel von Schiller, Miquel Ribot, Silvia Poblador, Eduardo Martín, Clara Romero, Roser Ventosa.

Financial Support MONTES (Consolider-Ingenio, Spanish, MICINN) MED_FORESTREAM (Spanish MEC) REFRESH and EUROLIMPACS (EU) Juan de la Cierva contracts (Spanish MEC) JAE_DOC postdoctoral contract (CSIC).

SUSANA BERNAL postdoc associate at CEAB-CSIC sbernal@ceab.csic.es

Acknowledgements