Detection of ecological impact of fine sediment inputs

Overview of studies & key findings

Elizabeth Conroy & Mary Kelly-Quinn

SILTFLUX Biological Studies

(Focus largely on deposited sediment) Experimental work

Observational field

Study 1 Detection and quantification of a pollutant

Study 3: Linking localised sediment inputs with ecological conditions

Study 2: Relationship between macroinvertebrate metrics and sediment metrics

Study 4: Linking land use (catchment scale) with ecology

Study 5 : Mechanistic study

Study 1: Detection and quantification of a pollutant

A key consideration was how well various methods of measuring deposited sediment represented the quantities present

Methods evaluated: Visual estimation of % sediment surface cover

Measurement of suspended sediment concentration

Resuspension of sediment and measurement of turbidity Point suction method using Turner-Hills deposited sediment sampler (DSS)

Added known amounts of sediment

% sediment surface cover gives good estimate of the level of deposited sediment Turbidity and re-suspendable sediment methods warranted further investigation

under field conditions Further carried these three methods through field studies

See: International Journal of Sediment Research An Evaluation of Visual and Measurement-Based Methods for Estimating Deposited

Fine Sediment

Conroy, E.a, Turner, J.N.b, Rymszewicz, A.c, Bruen, M.c, O’Sullivan, J.c, Kelly-Quinn, M.a

a School of Biology and Environmental Science, University College Dublin b School of Geography, Planning and Environmental Policy, University College Dublin c UCD Dooge Centre for Water Resources Research, School of Civil, Structural and Environmental Engineering, UCD Earth Institute,

University College Dublin

Study 1: Detection and quantification of a pollutant - Key Findings

Multiple pressures may be present in river systems including the SILTFLUX sites

Need to firstly understand the response to sediment (then consider combined effects of sediment and other stressors)

Experimental work - Controlled conditions

Opportunity to test a range of biological metrics

Further evaluated in field study

Detecting macroinvertebrate response to sediment

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Study 2: Response to sediment & relationship

between macroinvertebrate metrics and sediment metrics

Experimental study

Indoor channels

Gravel substrate, water and seeded with macroinvertebrates

Fine sediment added to channels

Eight treatment levels (0, 5, 10, 30 50, 70, 90, 100% sediment surface cover)

Four replicates

Seven days

Measured drift (response) & taxa remaining in

channels 6

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Study 2: Drift response to sediment

Study 2: Metrics Tested: Correlations %EPT and % E abundance with %

sediment surface cover

Experimental study

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Study 2: Relationship between macroinvertebrate metrics and sediment metrics

Field study % EPT abundance and % EPT richness metrics were most strongly correlated with

sediment surface cover % sediment surface cover was better correlated with the biological metrics than

either turbidity or resuspended sediment methods

Study 3: Linking localised sediment inputs with ecological conditions

Cattle access drinking points

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Eight sites • four high/good water quality status • four moderate water quality status

Two habitats sampled

• mid-channel and • margins

Study 3: Cattle Access – Key findings Some evidence of site specific impacts downstream of cattle access points

Impacts were generally more evident in autumn samples, particularly in

high/good status rivers – due to higher use of access points during summer

Community structure was altered downstream of cattle access points in 3 out of the 4 good status rivers and downstream changes in univariate metrics were observed for all four high/good status rivers

Two of the four moderate status streams showed downstream changes in community structure, abundance and richness metrics

These two moderate status rivers had high or prolonged livestock activity

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Study 4: Linking land use with ecological conditions

Instrumented and intermediate sites

Quantitative and semi-quantitative macroinvertebrate sampling

Hydrochemistry and environmental data

Pasture: Clodiagh and Slaney catchments

• low % pasture < 30% and high % pasture > 30%

Tillage: Urrin and Glyde catchments

• Low % tillage < 15% and high % tillage > 15%

U/S Control Site: Reference conditions

Q-value ≥ 4

D/S Site: Defined by land-use gradient

Intermediate sites

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Study 4: Land use effects –Key findings

Pasture land use (Clodiagh and Slaney catchments)

Spring reach-scale samples indicated no significant differences in community

structure between sites with low percentage pasture and those with a high percentage of pasture in either catchment

Autumn patch and reach-scale differences in community structure were

reported in both catchments mainly due to increases in tolerant taxa Low % pasture sites had very lower abundances of tolerant taxa

The high % pasture sites pasture had greater abundances of tolerant taxa e.g.

Chironomidae

Study 4: Land use effects –Key findings

Tillage land use (Glyde and Urrin catchments)

Only River Urrin showed significant changes in macroinvertebrate communities between high and low percentage tillage sites

Autumn patch and reach-scale indicated increases in tolerant taxa e.g. Glossosoma

spp., Chironomidae and Oligochaeta in the high % tillage sites in the Urrin

Spring reach-scale samples indicated downstream increase in a number of EPT taxa together with substantial reductions in abundances of Chironomidae

This spring increase in EPT was partially due to higher abundances of Seretella ignita, which is considered to be a pollution-tolerant taxon in the Irish Q-value metric (Mc Garrigle, 2002)

The limited or complete lack of differences between sites in the Glyde may be related to hydromorphological conditions

Glyde channelised and has low slope

Mechanisms involved

Schematic showing the direct and indirect effects of suspended, saltating, and deposited fine sediment on stream properties (green boxes), their in-stream physical effects (purple boxes) and aquatic biota impacted (orange boxes)

Study 5: Macroinvertebrate responses to burial by sediment

• Three Ephemeroptera Baetis rhodani, Ecdyonurus insignis Rhithrogena semicolorata

• Two Trichoptera Hydropsyche siltalai, Rhyacophila dorsalis

• Amphipoda Gammarus duebeni

• Five different sediment particle sizes • Two burial depths • Upland and lowland species • Body size

MEASURED EMERGENCE TIMES FOR HEAD & WHOLE BODY

Video clips

Study 5: Macroinvertebrate responses to burial by sediment burial

Responses were variable across the species tested burial depth > sediment particle class > taxa source No detectable effect linked to body size

Variable responses of taxa from upland and lowland locations. Some upland taxa taking longer or failing to emerge from burial e.g. Ecdyonurus insignis

Upland taxa may be more sensitive to sediment effects than lowland taxa (Matthaei et al., 2006; Connolly and Pearson, 2007; Larsen et al., 2009)

This may have implications for the development and applicability of proposed

sediment-sensitive biological metrics across large geographical areas

Further analysis of the SILTFLUX data will test the relationship between

the macroinvertebrate metrics and sediment fluxes

Further mechanistic studies, based on EPT taxa at family and species level, are required to enhance our understanding of how, and at what level, pressures such as sediment impact taxa – essential for identification of indicators and metrics of sediment impact

Sediment impact remain to be disentangled from other stressor impacts

At present, EPT metrics fulfil a useful role as general indicators of

ecological degradation in agricultural catchments It would also be useful to test the new metric developed by Murphy et al.

(2015) in an Irish context. This will require the collection of data on the amount of organic sediment in erosional zones (oFSIsp) and the total fines in depositional zones (ToFSIsp)

Conclusions

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Thank you