macroinvertebrate resource utilisation in upland streams: riparian management impacts

Macroinvertebrate Resource Utilisation in Upland Streams:

Riparian Management Impacts

Irish Freshwater Biologists Meeting 2012

C. Barry & Y. McElarney

Agri-Environment Branch

Newforge Lane, Belfast

Riparian Management Impacts

RCC – interpretative paradigm for resource utilisation / carbon flow in river food webs

High terrestrial inputsLow nutrient inputsLow PP low P:R

Increasing light and nutrientsgreater PP

P:R increasing

High light & nutrients& C inputs from upstream processing P:R decreasing

But,

● Variation of riparian vegetation at low stream orders

– alters resource availability and quality

● Resource utilisation by functional feeding group

-feeding mechanisms to determine resource

use

-opportunism and generalist feeding

frequent

●To eat is to assimilate?

How to assess macroinvertebrate resource utilisation?

Natural abundance Carbon and Nitrogen Stable Isotope Analysis 13C:12C 15N:14N

Consumer isotopic ratios reflect the isotopic ratios of their diet in a consistent way

► You are what you eat, less what you excrete

Fractionation: stuff happens to lighter isotopes more readily

●Physical: evaporation ●Chemical: respiration

Grass

SeagrassRabbit

Fox

Geese

0

2

4

6

8

10

12

-30 -28 -26 -24 -22 -20 -18 -16

Carbon isotopic signature

(d13C)

Nitr

og

en is

oto

pic

sig

nat

ure

(d15

N)

Ratios unwieldy; reported as signatures-

deviation from standards (δ13C, δ15N)

Measure stable isotope signatures for

● Macroinvertebrates

● Potential dietary sources

Some consumers use several different resources…. Mixing models

SIAR in R … Bayesian mixing model

Methods

No Buffer (n=6)

Natural Upland catchments (n=5)

Unplanted Buffer (n=4)

Broadleaved Buffer (n=4)

Recently Harvested (n=6)

Quantitative estimates of biomass and C & N isotopic analysis for

●macroinvertebrates ●biofilm ●biofilm chl a ●macrophytes ●macroalgae

●benthic organic matter ●riparian vegetation ●seston ●Light penetration

Physico-chemistry sampled seasonally on 3 occasions

25 streams sampled once in summer (50m reach)

Methods: deriving macroinvertebrate dietary reliance

Seratella ignita

Simulium

Baetis rhodani

Ecdyonurus insignis

Elmis aenea

Gammarus duebeni celticus

Leuctra fusca

River conditioned detritus

Scapania undulata

Seston

Biofilm

Ulothrix tenuissima

-3

-2

-1

0

1

2

3

4

-34 -33 -32 -31 -30 -29 -28 -27 -26

δ13C (‰)

δ15N (‰)

Stream with an unplanted riparian buffer

5 potential resources / end members

Resource: River conditioned detritus

1. Baetis 2. Ecdyonurus 3. Elmis 4. Simulium 5. Leuctra 6. Gammarus 7. Seratella

0.0

0.2

0.6

0.8

1.0

0.4

Die

tary

rel

ianc

e (%

)Methods: deriving macroinvertebrate dietary reliance

1. Baetis 2. Ecdyonurus 3. Elmis 4. Simulium 5. Leuctra 6. Gammarus 7. Seratella

0.0

0.2

0.6

0.8

1.0

0.4

Resource: Biofilm

Die

tary

rel

ianc

e (%

)Methods: deriving macroinvertebrate dietary reliance

1. Baetis 2. Ecdyonurus 3. Elmis 4. Simulium 5. Leuctra 6. Gammarus 7. Seratella

0.0

0.2

0.6

0.8

1.0

0.4

Resource: Ulothrix tenuissima(filamentous green alga)

Die

tary

rel

ianc

e (%

)Methods: deriving macroinvertebrate dietary reliance

1. Baetis 2. Ecdyonurus 3. Elmis 4. Simulium 5. Leuctra 6. Gammarus 7. Seratella

0.0

0.2

0.6

0.8

1.0

0.4

Resource: Seston(suspended fine particulate organic matter)

Die

tary

rel

ianc

e (%

)Methods: deriving macroinvertebrate dietary reliance

1. Baetis 2. Ecdyonurus 3. Elmis 4. Simulium 5. Leuctra 6. Gammarus 7. Seratella

0.0

0.2

0.6

0.8

1.0

0.4

Resource: Scapania undulata

(bryophyte)

Die

tary

rel

ianc

e (%

)Methods: deriving macroinvertebrate dietary reliance

Allochthonous

(Terrestrial)%

Autochthonous

(in situ PP) %

Total Invertebrate mass

mg m-2

Allochthonous mass

mg m-2

Autochthonous mass mg m-2

Baetis 15 85 174 26 148

Simulium 61 39 35 21 14

Ecdyonurus 10 90 180 18 162

Elmis 20 80 3 1 2

Gammarus 83 16 342 283 55

Leuctra 89 11 38 34 4

Seratella 47 53 91 43 48

Plectrocnemia 69 31 57 39 18

Total mg m-2465 450

Terrestrial vs. Aquatic

Functional feeding groups

Predator

Shredder

Collector

Grazer/Scraper

C & N stable isotope analysis

Allochthonous

Autochthonous

Methods: Apportioning macroinvertebrate biomass

0

100

200

300

400

500

600

700

800

900

CE

185

CE

0

CE

148

OB

13

CE

133

CM

14

CF

4

CM

15

CE

56

CM

6

CM

1

B20

8

CF

8

CF

2

CF

3

CF

5

B20

9

OB

41

B12

6

CM

2

CE

44

OB

74

CF

6

OB

0

B20

7

Inve

rteb

rate

Bio

mas

s (m

g m

2 Dw

t.)

Autochthonous AllochthonousA

CE = No buffer: Conifers to stream edge OB = Open buffer (unplanted)

CF = Clear felled B = broadleaved buffer CM = Natural upland (control)

Macroinvertebrate Biomass Apportionment by site

Un-skewed distributions

- consumers exploiting a wide variety of resources

- greater niche availability / utilisation

► Clear felled sites, Natural upland sites (control), no buffer sites*

Skewed distributions

-consumers exploiting resources of similar origin

-Suggests high abundance of such resources and/or resources of the same origin present in different forms…. FPOM, CPOM

► Broadleaved buffer & Open buffer sites

Caveat

*Depleted consumer δ13C indicative of methane C

►while terrestrial in origin, the approach regards consumers as utilising an autochthonous resource

100% terrestrial 100% aquatic

Consumer frequency distributions of reliance on terrestrial C

Species Specific Resource utilisation

Sh = shredder Co = Collector Gr = Grazer

0.0

0.2

0.4

0.6

0.8

1.0

Mea

n p

rop

ort

ion

al d

evia

tio

n f

rom

ter

rest

rial

die

t

n = 25 n = 7 n = 2 n = 4n = 4n = 18 n = 20n = 4n = 13n = 13n = 14n = 23n = 23 n = 3 n = 1

Sh Co GrCoGr ShShShSh GrGrCo CoCo Co

Error bars = 1SD

Conclusions

• Light reduction, slope & organic biofilm mass most important variables driving resource utilisation among sites

• Biomass and species richness greater at buffered compared to un-buffered sites

• Invertebrate community structure and resource use at buffered sites show little similarity to unimpacted control sites

• Broadleaved buffer sites show high invertebrate biomass but a community largely specialised for an allochthonous diet

Acknowledgements

AFBI Staff

Lesley Gregg, Rachel Patterson, Alex Higgins

Colm McKenna, Kirsty McConnell,

Louise Davis, Elaine Hamill,

Phil Dinsmore, Brian Stewart

Forest Service, NI

Ian Irwin, Colin Riley

EPA (Strive) for part funding study (project 2007-W-MS-3-S10):

An Effective Framework For assessing aquatic ECosysTem responses to implementation of the Phosphorus Regulations (EFFECT)

Department of Agriculture and Rural Development (DARD) for remainder of project funding.

Results: Isotopic overview

0

10

20

30

40

50

60

-10 -5 0 5 10 15 20

Car

bo

n:N

itro

gen

(m

ola

r)

Coniferous

Deciduous

Grasses

River conditioneddetritusMacro-algae

Bryophyta

Biofilm

Macro-Invertebrates

δ15N (‰)

0

10

20

30

40

50

60

-50 -45 -40 -35 -30 -25

Car

bo

n:N

itro

gen

(m

ola

r)

Coniferous

Deciduous

Bryophyta

Grasses

River conditioned detritus

Macro-algae

Biofilm

Macro-Invertebrates

δ13C (‰)