Sheffield Floods

A first look at aquatic invertebrate data collected before and after the

June 2007 floods

Anna Ritchie and Lina Ilia

Setting

• In June of 2007 more rain fell in two days than would usually fall within two months.

Research questions

• How are stream invertebrates impacted by flooding?– Impact on abundance and diversity?

• Are both benthic and hyporheic communities affected in similar ways?

Stream invertebrate communities

• Benthic macroinvertebrates:– Live on the upper layer of riverbed substrates– Commonly used for biological assessment

• Hyporheic invertebrates:– Live beneath and adjacent to the riverbed– Both surface and groundwater influences– Comparatively little is known and understood

about their ecology

Sampling in the Don Catchment

Sheffield

Barnsley

Rotherham

Chesterfield

• 20 sites on 12 rivers were sampled (hyporheic and benthic) at the end of may

• Sites were re-sampled at the beginning of July, after the June floods

• Sampling included some sites directly downstream of reservoirs

Benthic vs Hyporheic hypotheses

• Benthic abundance and diversity were expected to decrease

• Hyporheic abundance and diversity were expected to increase

Are there differences between pre- and post-flood samples?

– Does abundance change?– Does diversity change?– Are there different taxa present before and

after the floods?– Do individual taxa respond differently?– Do dams have an influence on the flood

effect?

Pre- and Post-Flood invertebrate abundance

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

hyporheic benthic

Ch

ang

e in

Lo

g10

Ab

un

dan

ce

Paired t-test, p=0.59N=20

Paired t-test, p<0.001N=11

hyporheic benthic

-14

-12

-10

-8

-6

-4

-2

0

2

hyporheic benthic

chan

ge

in #

tax

a

p<0.001N=11

p=0.41N=20

hyporheic benthic

Change in diversity

Are the same taxa present before and after the floods?

• Benthic– Taxa present only after floods

• Helodidae*, Corixidae*

– Taxa present only before floods• Ceratopogonidae, Empididae

• Hyporheic:– Taxa present only after floods:

• Bosminidae, Sididae, Calanoida,

– Taxa present only before floods:• none

Do different taxa respond differently to the flood event?

Benthic taxa

00.5

11.5

22.5

33.5

Lo

g10

ab

un

dan

ce

Pre-flood

Post-flood

Hyporheic taxa

00.5

11.5

22.5

33.5

Lo

g1

0 a

bu

nd

an

ce Pre-flood

Post-flood

*

*

**

***

What about the dams?

Sheffield

Barnsley

Rotherham

Chesterfield

Hyporheic

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

1 2C

ha

ng

e i

n l

og

10

a

bu

nd

an

ce

Benthic

-1.6

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

01 2

Ch

ang

e in

lo

g10

ab

un

dan

ce

no dam with damno damwith dam

p<0.001N=6

p=0.001N=5

p=0.047N=6

p=0.052N=14

Change in mean invertebrate abundance between sites with and

without dams

Benthic vs Hyporheic hypotheses

• Benthic abundance and diversity were expected to decrease – Supported by the results

• Hyporheic abundance and diversity were expected to increase– Not supported by the results

Conclusions

• The two communities show different patterns before and after floods as well as between sites with and without dams

However these patterns may be a result of various other factors (such as insect emergence or water chemistry)

Next steps. . .

– More thorough description of hyporheic invertebrate community

– Investigate the importance of other measured variables (ex: substrate, discharge, water chemistry)

– Resample in 2008 to look for seasonal effects, compare trends between years, and investigate the recovery of the communities

Acknowledgements

Marie Curie Early Stage Research Training Fellowship, Environment Agency, University of Sheffield Catchment Science Centre, Lorraine Maltby and Phil Warren, Everyone who helped out in the field during our mad dash to catch the immediate flood effects, and everyone who listened and offered advice…