The central theme of this project is to attempt to quantify the effect of riparian cover on stream water temperature at small spatial scales, with a view to alleviating potential future temperature extremes within low lying salmonid nursery streams.

Quantifying The Effect of Semi-Natural Riparian Cover on Stream Temperatures: Implications for

Salmonid Habitat Management

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Diarmuid Ryan

Dept of Environmental and Biological Sciences.University College Dublin.

Study site criteria . Small Open

(5 sites)Small Covered (5 sites)

Large Open (4 sites)

Large Covered (4 sites)

Altitude(m) 80-160Mean=114

85-160Mean=101

50-140Mean=82.5

50-150Mean=95

%Slope 6-14Mean=9.8

8.7-13.2Mean=10.7

8-10.1Mean=9.2

9.4-16.6Mean=11.5

30%ile flow (m3/s)

0.36-0.9Mean=0.51

0.32-0.64Mean=0.43

1.3-3.4Mean=2.1

2.2-2.7Mean=2.5

Wetted Width(m)

3-4Mean=3.75

3-5Mean=4

9-11Mean=9.75

10-13Mean=11

Pool Depth (m) 0.4-0.7Mean=0.52

0.4-0.7Mean=0.46

0.8-1.4Mean=1.2

0.7-1.3Mean=1.1

U/S Catchment (km2)

12.2-37.6Mean 18.34

11.9-36.8Mean=18.62

51.7-143.5Mean=77.6

47.7-103.8Mean=79

% Light Penetration

100 10-18Mean=14.6

100 11-23Mean=16

Channel aspect Mixed Mixed Mixed Mixed

Previous studies have focused on daily maximum temperatures achieved within either wholly forested or open catchments.

This study focuses on discrete stream sections with contrasting cover.

Sites were chosen according to a number of factors.

All flow through or adjacent to agricultural land.

Of those with riparian buffer: • Largely semi-natural riparian

vegetation.• for the most part 1-2 trees wide.

(Minimal loss of agricultural land)

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Site photographs: examples

Large Open Site (LO1 Derry) Small Closed Site (LT2 Dereen)

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Small Closed Site (ST3 Shillelagh) Small open Site (SO5 Donard)

Site photographs: examples

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Method:• Sites 300m in length. • Temperature loggers

secured at either end of site .

• Loggers set to record stream temperature every 30mins

Hydrometric data obtained from the EPA. Sunshine and air temperature data collected from meteorological stations to the North East and to the South of sites.

LT4

SO1

SO4

LT2

LO1

ST5

SO2

ST1

LO3

SO3 LT1

ST2

ST3

LO2

ST4

LT3

LO4

SO5

Hyd.St

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Logger positioning

Daily minimum water temperatures

• Measurements taken from the downstream end of study sites.

• No measureable temperature difference due to cover

• Larger streams do not cool as much as small ones during the night.

• The minimum temperature correlates with local air temperature regardless of site type

• deviation from the mean suggests that this may not be significant.

• There is no measureable difference due to cover. 7

Daily maximum water temperatures

• Small open sites (nursery streams) reach higher temperatures on average during summer months than closed equivalents regardless of other environmental factors.

• No differences between level of cover measured within larger streams.

• Correlation between air temperature and daily maximum stream temperature.

• Difference in temperature reached between small open and closed streams increased due to the warmth of the day.

• This trend was not noted in larger streams.

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4

6

8

10

12

14

16

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Max Air Temp 16-18⁰C Max Air Temp 18-20⁰C Max Air Temp 20-22⁰C

Tem

pera

ture◦C

Mean Summertime Daily Maximum Water Temperature

Small Open Sites

Small Covered Sites

Large Open Sites

Large Covered Sites

There is evidence of a strong relationship between air and water temperatures within small sites regardless of riparian

cover. • Correlation visible between air temperature and stream temperature obvious within time series.

• Covered stream temperatures do not increase towards air temperatures as rapidly as their open counterparts.

• within open sites a slightly steeper slope was recorded. This becomes more evident during warmer days when risks to fisheries are greatest.

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Temperature effects due to environmental variables during warmer days.

• The higher the air temperature, the greater the difference in maximum water temperature reached between open and closed sites.

• Relationship recognised between sunshine and water temperature within small open sites.

• No visible effect noted within closed sites.

• Effect of changing flows was also examined.10

Daily maximum water temperature increase within sites (300m)

• Large difference in temperature increase through sites due to riparian cover.

• Effect less apparent within large sites

• Strong correlation between magnitude of water temperature increase and air temperature within open sites.

• This effect is not apparent within closed sites.

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Fine Temporal scales: Daily Temperature Profiles

• Rate of daily heating during

the day is not greatly affected by air temperature.

• Rate of heating is similar across all temperature ranges.

• Start of day temperatures the same as closed counterparts.

• Rate of increase greater than in closed sites.

• Rate increases with increasing air temp

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Daily Profile Comparison of Stream TypesFrom a biological perspective when: • Air temp 20-220C Open

streams spend 4.5hrs over 15.90C/day

• Air temp >220C Open streams spend 8.5hrs over 15.90C/day

This result illustrates the potential detrimental effects to salmonid populations resident in open nursery streams within the Slaney catchment.

According to the observations small semi-natural riparian buffer strips have the potential to significantly mitigate against this.

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Actual cooling effect of Riparian cover within study sites.

• Increasing rate of heating measured between u/s and d/s ends throughout the day within small open sites.

• No measurable difference in temperature detected between u/s and d/s ends (300metres) of small open sites

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Within Site Temperature Increases

• The rate of increase is quite similar, however maximum temperature reached is greater as the number of daily sunshine hours increases.

• Warrants further investigation.

• The average rate of heating through small open sites during the day is dependent on air temperature.

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To ConcludeThe overall aim of this project is to develop management options to alleviate the potential effects of climate change on nursery streams while ensuring the habitat remains preferable for salmonids.

Biological surveys were also carried out within the chosen study sites. • Salmonid density/health/diet• Benthic Macroinvertebrate density• Macroinvertebrate drift density

At this stage no obvious signs that riparian cover depresses the overall availability of food items for salmonids within the study sites.

Further work

•Complete biological sampling•Examine if heating/cooling effects continue over greater spatial scales downstream of the study sites

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Thanks for your time...

I would like to acknowledge the contribution of Inland Fisheries Ireland in providing financial and logistical support towards the completion of this project.