Impact of warming on stream ecology in Hengill area, Iceland«lle Keraval.pdf · FOURTH YEAR...

Impact of warming on stream ecology in Hengill area, Iceland

Maëlle Keraval

Faculty of Life and environmental

Sciences

University of Iceland

20XX


Maëlle Keraval

30 ECTS

Baccalaureus Scientiarum degree in Biology

Supervisor Gísli Már Gíslason

Faculty of Life and Environmental Sciences

School of Engeneering and Natural Sciences University of Iceland

Reykjavík, August 2014


30 eininga ritgerð sem er hluti af Baccalaureus Scientiarum gráðu í líffræði

Höfundarréttur © 2014 Maëlle Keraval

Öll réttindi áskilin

Líf- og umhverfisvísindadeild

Verkfræði- og náttúruvísindasvið

Háskóli Íslands

Askja, Sturlugötu 7

101 Reykjavík

Sími: 525 4000

Skráningarupplýsingar:

Maëlle Keraval, 2014, Impact of warming on stream ecology in Hengill area, Iceland, BS

ritgerð, Líf- og umhverfisvísindadeild, Háskóli Íslands, 40 bls.

Prentun: Háskólaprent

Reykjavík, ágúst 2014

Útdráttur

Upptakakvíslir Hengladalsár í Hengladölum austan Reykjavíkur hafa verið notaðir sem náttúruleg

rannsóknarstofa í rannsóknum á loftslagshýnun. Lækirnir eru frá 6°C til 45°C heitir og eru sviðaðir að

fletu leyti hvað varðar eðlis og efnafræðilega þætti, nema hvað varðar hita. Hiti þeirra er mjög stöður

allt árið.

Búsist er við að loftslagshlýnun verði mjög mikil á norðurheimskautsvæðum og er áætlað að hiti

hækki um 4°C á næstu 100 árum. Á Íslandi eru margvíslegar gerðir af ám og lækjum, heitir lækir og

kaldar jökulár og allt á milli, og eru kaldir og heitir lækir í namunda við hvern annan.

Þetta skapar tækifæri til að rannsaka áhrif hita á vistfræði straumvatna, og í Hengladölum hefur einn

lækur (meðalhiti 7°C) verið hitaður með varmaskipti um 3°C. Þessi lækur og hlýr við hliðina á

honum, 24°C heitu að meðaltali voru notaðir til að rannsaka klak og rek, í kalda og hlýrri hluta

upphitaða lækjarins og í heita læknum. Niðurstöður sýna að að þéttleiki hryggleysingja hækkaði við

upphitunina, en hélst sá sami í óupphitaða hlutanum. Einnig breyttist hlutdeild þeirra tegunda sem

voru ríkjandi í upphitaða hlutanum.

Lykilorð: macroinvertebrates, stream ecology, climate change, geothermal activity

Abstract

Global warming is predicted to be more dramatic in the Arctic area where an increase of 4ºC is

expected over the next century. In Iceland, hot and glacial streams exist with variable temperatures

and are found with a short distance of each others.

This offers opportunities to study the impact of temperature on stream ecology, particularly in the

Hengill area were a warming-up system has been set up on a cold stream in order to study a sudden

increase of temperature. The downstream section of the colder stream has been warmed whereas

upstream section remains at its natural temperature. Results from this study show that an increase of

temperature has an impact on stream ecology with a higher macroinvertebrates density and dominance

and diversity changes.

Keywords: macroinvertebrates, stream ecology, climate change, geothermal activity

2

Maëlle Keraval

University of Iceland Supervisor : Mr.Gísli Már Gíslason Polytech Clermont Ferrand Tutor : Ms.Gwendoline Christophe

FOURTH YEAR ENGINEERING INTERNSHIP REPORT May-July 2014

Impact of warming on stream ecology in

Hengill area, Iceland.

STREAM ECOLOGY IN THE HENGILL

AREA, ICELAND

Campus des Cézeaux

24 Avenue des Landais

BP 206

63174 Aubière Cedex

France

Institute of Life and

Environmental Sciences,

University of Iceland

Askja - Natural Science Building

IS-101 Reykjavik Iceland

Iceland

3

Acknowledgements

First I would like to thank Gísli Már Gíslason for his supervision throughout the laboratory work and

his support in discovering Iceland. I would also like to thank Aron Dalin Jóasson for patiently helping

me with macroinvertebrate identification. I would like to thank Jón S. Ólafsson for showing me the

Hengill area and his Phd student Dan, and Kera, for involving me in field work there.

Finally I would like to thank Gwendoline Christophe, my supervisor from Polytech Clermont-Ferrand,

for help and encouragement during this project. I would not forget to remember Mrs. Véronique

Quanquin professor of communication at Polytech Clermont-Ferrand who gave me the necessary

advices to write this report.

4

Glossary

Density : number of individuals per m3 of water

Evenness : Diversity

Geothermal : Something pertaining to the internal heat of the earth.

Filter feeders : One of the four feeding groups of macroinvertebrates, feed on particles or small

organisms strained out of water.

Hatching samples : Samples composed of emerged flies

Scrapers : One of the four feeding groups of macroinvertebrates, feed on diatoms and algae ( for

example snails and Chironomids).

Shredders : One of the four feeding groups of macroinvertebrates, feed on coarse plants

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Table of contents

Acknowledgements ................................................................................................................................ 3

Glossary .................................................................................................................................................. 4

Table of abbreviations ........................................................................................................................... 7

Introduction ........................................................................................................................................... 8

1.The project in the Institute of Life and Environmental Sciences ................................................... 9

1.1 Introducing the Institute of Life and Environmental Sciences .................................................. 9

1.2. Introducing the project ............................................................................................................. 9

2. Background-(Bibliographic study) ................................................................................................ 10

2.1 Icelandic geothermal streams .................................................................................................. 10

2.2The impact of geothermal activity on streams and their ecosystems ....................................... 10

2.3 Global warming ....................................................................................................................... 11

3. Methods ............................................................................................................................................ 13

3.1 Study area ................................................................................................................................ 13

3.2 Experimental design methodology .......................................................................................... 14

3.3 Temperature and flow ............................................................................................................. 14

3.4 Drift and Hatching Samples .................................................................................................... 14

3.5 Identification of macroinvertebrates ....................................................................................... 15

4. Results .............................................................................................................................................. 16

4.1 Temperature variation ............................................................................................................. 17

4.2 Flow ........................................................................................................................................ 19

4.3 Density, Dominance, Emergence and Diversity of macroinvertebrates ................................. 20

5. Discussion ......................................................................................................................................... 24

5.1 Temperature and flow ............................................................................................................. 24

5.2 Density and dominance ........................................................................................................... 24

5.3 Emergence and diversity ......................................................................................................... 25

Conclusion ............................................................................................................................................ 26

References ............................................................................................................................................ 27

Appendix .............................................................................................................................................. 28

Appendix A -Trophic level definition ........................................................................................... 28

Appendix B- Drift and Hatching samples ..................................................................................... 29

Appendix C- Data collection list of drift samples from stream 8, stream 7 oupph (not heated)

and stream 7upph (heated) ............................................................................................................ 30

6

Table of figures

Figure 1 Stream 8 (on the right) and stream 7 (on the left) flowing downstream ................................ 12

Figure 2 Sontek FlowTracer measuring velocity .................................................................................. 13

Figure 3 Drift net placed at the end of a selected section and Hatching net placed over the water

surface ................................................................................................................................. 14

Figure 4 Table relating the different sampling week day and the n° used in the following graphs ..... 15

Figure 5 Evolution of temperature over time ....................................................................................... 16

Figure 6 Relation between temperature difference between stream 7 two sections (upstream and

downstream sections) and stream 8 temperature ............................................................... 17

Figure 7- Comparison of evolution of temperature over time summer 2012/2013 ............................... 18

Figure 8 Evolution of stream flow over time. ........................................................................................ 18

Figure 9 Evolution of the number of individuals caught per hour for each stream in summer 2013 .. 19

Figure 10 Evolution of the number of individuals flowing downstream for each stream, in

individuals/m3 in summer 2012 ........................................................................................... 19

Figure 11 Evolution of the number of individuals flowing downstream for each stream, in


Figure 12 Evolution of the number of Simuliidae larvae flowing downstream for each stream, in

individuals/m3 ..................................................................................................................... 21

Figure 13 Evolution of the number of Radix Peregra flowing downstream for each stream, in


Figure 14 Evolution of the number of Chironomidae larvae flowing downstream for each stream,

in individuals/m3 in summer 2013 ....................................................................................... 21

Figure 15 Evolution of Hatching cycle fly diversity over time(2013). .................................................. 22

Figure 16 Percentage of some taxas in the total animal number of stream 7 oupph and stream 7

upph samples.(2013) ........................................................................................................... 23

Figure 17 Example of a food « web » system ....................................................................................... 28

Note : All graphs and tables are personal creations.

7

Table of abbreviations

K+ : Potassium ion

P : Phosphorus

N : Nitrogen

Oupph : not heated-up

St : Stream

Upph : heated-up

8

Introduction

Global surface temperatures have risen by 0.74ºC in the last century and are projected to increase

between 0.6 to 4.0º over the next century. The global warming is expected to have more serious

consequences in Artic.

The global warming has been expected to affect biota distribution. Changes in biota related to climate

change have been observed in the Artic and in Iceland where there have been significant changes in

vegetation, bird populations, fish populations and invertebrates.

In this scenario, one of the challenges in biological research is predicting prediction how that would

affect ecosystems. Changes in taxonomic and functional structure of ecosystems have been expected

by the end of the century. Many studies have evaluated how temperature can affect them.

Unfortunately, many studies on the effects of warming are restricted to a small laboratory scale.

Although the advantage of being able to replicate environmental conditions in a controlled manner is

interesting, those experiments miss variability and are restricted to simple assemblages. In contrast to

laboratory experimentation, there are some studies on the effects of warming on natural systems. One

of the main problems with this research is confusion of latitudinal (or altitudinal) gradients, making it

difficult to disentangle the effects of biogeography, physical parameters and temperature.

The streams at Hengill in Iceland create a good model system to investigate the effects of warming, as

they provide a relevant temperature gradient which cannot be confused by environmental variables or

biogeography effects. In this current study, two streams were chosen, a cold one and a warm one,

which present similar chemical features and are only separated by approximately two meters in their

stream outlet. The downstream section of the cold stream was heating up through collecting water

from upstream and conducting by a pipe into the warm stream and then returning the heated up water

to downstream.

The challenge of this study is to understand how the identification and counting of macroinvertebrates

in drift samples is going to respond to that increase of temperature. First, a comparison of stream

temperature evolution over time and density (individuals/m3) in summer 2012 and 2013 will permit to

see evolution in a larger time interval. According to other studies on the same subject, animal

abundance is expected to be higher and the biodiversity lower in the heated up stream. At the same

time, this stream section is thought to present some dominant communities closer to those of a warm

stream so the communities in this stream could be more similar to the warm one than to the cold one.

9

1.The project in the Institute of Life and

Environmental Sciences

1.1 Introducing the Institute of Life and

Environmental Sciences

Academic staff and specialists at the faculty conduct research within a few main subject areas:

molecular biology, microbiology, fish and marine biology, ecology and evolutionary biology,

biogeography, human geography, tourism studies and environmental science.

Each group conducts research that usually falls within one or more subject areas. The groups also

engage in varied collaborative efforts, with both international and domestic partners.

Organisms develop in an ecological context, at times very quickly, but most often over a long period

of time. Research groups within the faculty deal with questions covering the whole of this spectrum.

Some research focuses on the properties of ecosystems, for example the great fluctuations in the biota

of Lake Mývatn ( Iceland) and the territorial behaviour of foxes in Hornstrandir. Examples of research

on evolutionary biology are, for example, the hunt for genes that relate to the adaptability of cod at

depth, classification of crabs that survived the Ice Age under glaciers, the hybridisation of birch and

dwarf birch, and the research and development of promoter sequences.

In summary, the Institute of Life and Environmental Sciences deals with a great diversity of projects

and different subjects.

1.2. Introducing the project

For several years, stream ecology has been studied by some laboratories in Iceland (Institute of Life

and Environmental Sciences, Institute of Freshwater Fisheries Iceland...).

The water temperature, velocities, physico chemical parameters, flora and insect evolution have been

analysed for several summers in streams located in a particular area named Hengill in Iceland. The aim

of the studies is to investigate the output of the streams over a temperature gradient, this output being

mineral and organic, living and dead material but moreover flows through the river and leaves the

water ecosystem -in the case of fly hatching. The increase in water temperature within the same stream

would have a perceptible effect on the quantity of material and compounds leaving the ecosystem as

well as other factors such as dominance and diversity.

The study takes part in this project, focusing on summer 2013 datas analysis. First, every summer

2013 week, samples of three streams were collected in Hengill area. The temperature, the velocity and

the depth of each collection area were also obtained. Then, during summer 2014, the insects of those

samples were identified and counted in the laboratory. Moreover, the field work was pursued to

maintain the ecology stream surveillance so other samples were collected in several streams to take

part in different studies. That is why one of the internship roles was to participate in a sampling

expedition in the Hengill area at the beginning of July. Moreover, the same kind of measurement and

analysis were done for summer 2012 samples so a comparison with the summer 2013 results would be

possible.

Later, the water chemistry and the flora weight of each stream will be analysed for the 2013 samples.

10

2. Background-(Bibliographic study)

2.1 Icelandic geothermal streams

Located in the middle of the Northern Atlantic Ocean, Iceland is a volcanic island. There are rich

basaltic soils and intense geothermal activity providing energy production and building heating.

On an ecological point of view, freshwater ecosystems are directly affected by these particular

conditions of soil composition, geothermal activity, isolated location... Icelandic streams in general are

species-poor due to the island biogeography. Iceland is relatively young and isolated in the North

Atlantic Ocean (Ólafsson et al. 2002, Gíslason, 2005, as cited in Friberg et al., 2009).

An area is classified as “geothermal” when hot water or steam comes out of the surface. This source

of power and energy is broad and appears to be inexhaustible, thus has its exploitation been conducted

without taking to account any conservation or protection measures. It is only thirty years ago that Jón

Jónsson (1980) and Jón Steinar Guðmundsson (1980) raised the need to preserve and restore

geothermal areas that are being altered by human utilization (Ólafsson et al. 2010). They are the first

scientists criticising the state of abandoned sites where installations and pipelines remain in the

landscape, impacting both sightseeing and ecosystems. It is nowadays clear that geothermal areas have

to be used with care and preserved as any other sensitive ecosystem. Their specific characteristics and

rareness make them particularly subject to human threats. Moreover in Iceland the waste water from

half of the population is not treated at all and the other half only receive primary treatment (Urban

waste water treatment (CSI 024) - Assessment published Jan 2009).

Several studies are proceeding on naturally heated geothermal Icelandic streams in order to observe

the impact of an increase in temperature on nutrient and species poor northern hemisphere rivers.

These naturally heated streams present a broad range of temperature and allow results and discussions

in relation to global warming.

2.2The impact of geothermal activity on streams

and their ecosystems

In 2009, Friberg et al. published a paper concerning the relationship between structure and function in

streams contrasting in temperature (Friberg et al., 2009). The study was executed on Icelandic

naturally heated geothermal streams, providing information about ecosystem structure and functional

attributes of geothermal streams. In those nutrient poor streams, there seems to be no significant

correlation between chemicals and temperature -even for N and P- except for oxygen and K+. Oxygen

as well as potassium concentrations are lower in warmer streams (Friberg et al., 2009).

Macroinvertebrate communities show differences in composition and structure along a temperature

gradient. While density increased with temperature, it appears that evenness follow an opposite trend.

Warm streams present a higher density of macroinvertebrates but with the domination of one or some

species. Indeed, the snail Radix peregra was found in streams above 14°C, dominating the warmest

streams with up to 63% of the total number of individuals. On the other hand Chironomidae were

particularly abundant in the colder streams although the evenness was then higher than warmer

streams. A species of black flies (Simulium vittatum) was recorded in cold and warm streams with

higher densities in the warmer.. According to Friberg et al. (2009), the number of filter-feeders

11

increases exponentially with temperature, although scrapers are the dominant feeding group with no

significant response to temperature in number but with a swift of species dominancy. Chironomids

were the main scrapers in colder streams whereas the snail Radix peregra was completely dominant in

the warmest. Given the difference of biomass between snails and chironomids, they concluded that

scrapers biomass is more important in warm streams along with a probable increase of algae and

biofilm biomass (Friberg et al., 2009).

Geothermal activity does not only imply changes in temperature but also has influence on other

parameters such as pH and carbon content. Elmasdóttir et al. suggest that the barren soils surrounding

some study sites are affected by strong acidity, which affects nutrient uptake and aluminium toxicity

on plants (Andersson, 1988 as cited in Elmasdóttir et al., 2003).

Similar trends can be drawn from observation of invertebrate communities. As explained by Ólafsson

(2000, as cited in Elmasdóttir et al., 2003) many species found at high soil temperatures do not live in

colder soils, and the contrary too (Elmasdóttir et al., 2003). For example the community structure of

primary producers can be influenced by temperature and higher biological community. Temperature

and Macroinvertebrate community don’t influence the balance of the primary producer groups of

green algae and cyanobacteria. However warming allows an increase of the Bryophyte cover

compared to epilithic algae. Indeed in warmer streams, snails are abundant and eat the epilithic algae.

They suppress the competition for the dominance between these two primary producers. Thus warm

streams have got a high bryophyte cover and a high population of snails, while cold streams are

dominated by epilithic algae and Chironomidae (Appendix A and Gudmundsdottir et al.2011).

2.3 Global warming

Surface temperatures are projected to increase by 3–5 °C globally, and up to 7.5 °C in high latitudes,

within the next century (Woodward et al. 2010).

When communities or ecosystems are subjected to environmental stress they can behave in ways that

cannot be predicted from studying a single species in isolation, due to the complex array of species

interactions within the ecological network (Raffaelli, 2004;Woodward, 2009). Indeed, each organism

has got a trophic level in a food « web » (Appendix A). But there is more than one food chain for most

organisms, since they eat more than one kind of food or are eaten by more than one type of predator.

By quantifying the percentage cover of macrophytes, invertebrates and fish biomass along a

temperature gradient in seven streams in the Hengill area, it was found that all these trophic levels

were influenced by warming. In warmer streams, Macrophyte cover increased and invertevrates grew

faster and provided a greater secondary production which entailed a boost of the top predator biomass

in warmer environments (Hannesdóttir et al.2012 and Appendix A). Therefore warming didn’t

necessarily influence just the small organisms in aquatic ecosystems.

12

Figure 1 Stream 8 (on the right) and stream 7 (on the left) flowing downstream

Across multiple levels of organization, warming influences the structure and functioning of

ecosystems. A natural experiment took place in the Hengill area where biogeography, water chemistry

and other gradients ( i.e., pH, nutrient, ..) don’t entail so much shift in ecosystem composition.

Despite the food-web complexity and the simplicity of experimentation, species richness decreases

with warming because of the isolation of Iceland and the lack of warm-adapted species. So with global

warming, dramatic changes would be expected to be seen in these sensitive ecosystems. For example,

abundance from the cold to the warm streams, chironomids decline from 96% to 0% of

macroinvertebrate abundance. The top predator, the Brown trout, is able to live between 6°C to 25°C

and feed on chironomids or Radix Peragra and Simulidae flies. Both, chironomids and Radix Peragra,

are algal grazers but are separated by the thermal gradient. Brown trout are expected to be bigger in

warmer streams because Radix peregra individual body mass is orders of magnitude greater than that

of the chironomids preyed upon in the colder streams (Gudmundsdottir et al.2011).

So the Hengill streams provide a valuable model system for assessing the likely impacts of future

warming in response to climate change in fresh waters which are likely to be profound.

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3. Methods

3.1 Study area

The Hengill area is one of the most active geothermal areas of Iceland and is also the second largest

(100km²) (Torfason, 1998 as cited in Ólafsson et al, 2010). The geothermal area is linked to the

volcanic activity that originated in the Hengill Mountain.

It has been chosen as a study site due to the broad range of temperature characterising the different

streams, varying roughly between 6°C to 25°C (Friberg et al., 2009). Another important condition that

makes the site interesting for researchers to run experiments, is the absence of human pressure on the

area.

Two streams only separated by approximately two meters flow toward the same outlet but present

completely different temperatures (figure1). The coldest ranges between 5,8°C and 10,2°C, while the

warmest varies from 22,0°C to 23,9°C during the summer, on average (Friberg et al., 2009). Part of

the cold stream water is pumped into a pipe, circulated into the warmer stream, and is then released

into the initially cold stream (appendix B). Experiments are thus carried out upstream and downstream

from the releasewater (differentiated by “stream 7 upph” for “heated up” and “stream 7 oupph” for

“not heated up”) as well as on the warm stream used for the heating system (called “stream 8”).

Figure 2 Sontek FlowTracer measuring velocity

14

Figure 3 Drift net placed at the end of a selected section and Hatching net placed over the water surface

3.2 Experimental design methodology

The experiment was carried out the heated downstream section of stream 7. Two dams had been built

upstream of stream 7 and 8. Dam stream 7’s water is conduct by a pipe into stream 8 dam in order to

heat it. Then the pipe returns the heated water to downstream of stream 7. The three experimental

sections were defined as: stream 8, stream 7 heated up (called “stream 7 upph”) and stream 7 not

heated up (called “stream 7 oupph”) (Appendix B).

3.3 Temperature and flow

The temperature (°C) and the velocity (m/s) were measured once a week, on each of the three sections

previously defined, just upstream of the drift nets. It was measured during all sampling weeks.

Temperature was measured three times with an Ama-digit ad 12th Precision thermometer. The velocity

and the deep were measured in three sites of the net entrance, on both extremes and the middle of the

net entrance. It was run using a Doppler Sontek FlowTracer (figure 2) and a Handheld ADV flow

meter.

3.4 Drift and Hatching Samples

The drift samples were taken with net placed in the outlet of each selected section for a certain time

depending the flow and the amount of material collected. Drifts samples were collected forabout 1,5

hour at “stream 7 upph” and “stream 7 oupph” section’s outlet, whereas only 45 minutes were

collected at “stream 8” section’s outlet, once a week. The drift nets were 45cm abroad and 30cm high,

with a 500nm mesh.

The samples were stored in 70% ethanol and brought to the laboratory for a posterior identification

and weight.

In order to better know the hatching ratio of the streams, three pyramidal nets were places over the

surface of the water at each stream section. The nets had been randomly placed at the first week in the

experimentation and were collected once a week. The nets had been constructed especially for this

study using a 250μm mesh and with a 15×15cm net entrance. The hatching samples were stored in

70% ethanol and brought to the laboratory for identification and counting (figure 3 and Appendix B).

15

Sampling dates

(2012 and 2013)05 June 11 June 18 June 24 June 01 July 08 July 15 July 22 July 29 July 06 August 12 August19 August 23 August

Sampling

number1 2 3 4 5 6 7 8 9 10 11 12 13

Figure 4 Table relating the different sampling week day and the n° used in the following graphs

3.5 Identification of macroinvertebrates

Identification of macroinvertebrates was run using LEICA MZ12 microscopy, focusing from 8 to 100

augments. First, fauna was isolated from flora in each sample. Then the population of the fauna was

furtheridentified which was possible thanks to some identification key. The size, thenumber of

segments of the antennae, the wing venation and many other characteristics helped to identify them.

According to the biology taxonomy, macroinvertebrates were identified from order to family, genus or

species when possible. The main orders found were: Diptera, Gastropoda, Hemiptera, Hymenoptera,

and Coleoptera.

After this identification, each member of different taxas was counted and registered in an excel file in

order to compare the evolution in time and between the different steams (Appendix C). .Books were

used for identification, for example: A field guide to the Insects of Britain and Nothern Europe

Michael Chinery, An introduction to the aquatic Insects of North America , R.W Merrit and K.W

Cummins.

16

4. Results

This results section will show temperature, flow, density, dominance, emergence and diversity results

with a comparison with summer 2012 results when possible.

In order to understand the following graphs and results, it is important to have precise dates

corresponding to the different sampling numbers (figure 4).

In most graphs, the first weeks results are absent because of the lack of results or of technical issues in

the field (e.g., streams weren’t deep enough, measurement materials didn’t work).

Figure 5 Evolution of temperature over time

17

Figure 6 Relation between temperature difference between stream 7 two sections (upstream and downstream

sections) and stream 8 temperature

4.1 Temperature variation

The upstream part of stream 7, which is not heated (oupph), has a temperature ranging from 5.8 to

9.3°C while the downstream section is heated up (upph) from 8.8 to 14.5°C. The stream 8 temperature

varies from 20,0 to 20.7°C and is very constant throughout the time whereas stream 7 shows important

variations in both upstream (Δ=3.5°C) and downstream (Δ=5.7°C) sections (figure 5). The variation is

highest on the 12th of August (date sampling 11) for both parts of stream 7. Those two sections follow

the same trend of temperature variation throughout the time.

The temperature difference between the upstream and downstream section of stream 7 (« Stream 7

temperature variation » curve) appears to be constant throughout the time, except from the 29th of July

(sampling date 9) to the 19th of August (sampling date 12). Indeed the heated-up section had a higher

temperature than “usual” compared to the upper not heated section because stream 8 had got its higher

temperatures during this time (figure 5). So, the difference of temperature between the two sections of

Stream 7 seems related with stream 8 temperatures by an affine linear relationship (figure 6). This

temperature increase entailed a stronger heating of stream 7.

18

Figure 7- Comparison of evolution of temperature over time summer 2012/2013

Figure 8 Evolution of stream flow over time.

Compared to summer 2012 temperatures, the streams seem to be colder in 2013(figure 7). In 2012 the

stream 8 temperature was constant and had a difference of only 1°C with compared to stream 8

temperature in 2013 at the same period. Compared to 2012 temperatures, between the sampling dates 5

and 8, the stream 7 oupph temperature is lower by 4.2°C on average in 2013, while the stream 7 upph

temperature is lower by 7.6°C on average in 2013.

19

4.2 Flow

The streams observed in this study are little but very turbulent. This phenomenon is due to the fact the

fact that the stream bed is made of stones and pebbles that can be several centimetres large. This

explains the broad scale of velocity measured at the outlet of each of the 3 sections. The flow is

calculated by the multiplying of the velocity measurement by the depth of each stream for each

sampling week. The stream flows are different due to the high variation of flow between stream 8

(ranging from 0.005 to 0,035 m3/s) and stream 7 (ranging from 5.10-5 to 0,005 m3/s) (figure 8).

The stream flow of the upper section of stream 7(not heated) is lower than that of the downstream

section (heated) due to the input of the heating system (figure 8).

The stream flow results will be used as a comparative scale for the amount and density of material and

animals collected in the drift nets.

Figure 9 Evolution of the number of individuals caught per hour for each stream in summer 2013

Figure 10 Evolution of the number of individuals flowing downstream for each stream, in individuals/m3 in

summer 2012

20

Figure 11 Evolution of the number of individuals flowing downstream for each stream, in individuals/m3 in

summer 2013

4.3 Density, Dominance, Emergence and

Diversity of macroinvertebrates

Density

Density in the drift samples is the number of individuals per m3 of stream water. It is obtained by

multiplying of the total number of individuals with the flow and then with the sampling time.

Hot temperarures are thought to increase macroinvertebrate number. The number of animals caught in

the drift nets is much higher in stream 8 (from 98 to 2370 individuals/hour) than in stream 7, despite

two results of higher numbers of animals for stream 7 (heated-up) during the first and 6th weeks of the

sampling fieldwork (figure 11). Except for the second sampling date (June 11th), the number of

individuals caught is always higher in the heated-up section than in the not heated-up section in

summer 2013(figure 9). However, this number of individuals per hour has to be correlated with the

stream flow in order to allow comparison between streams and sections (figure 11). The stream flow is

higher in stream 8 (figure 8) so the density of individuals/m3 is higher for both sections of stream

7(figures 10 and 11).

In 2012 and 2013, this downstream flow density shows similar patterns to stream 7 in the upstream

and downstream sections except for week 5 to week 7. In 2012, stream 7 upph had its highest

temperature, approximately 15°C, in weeks 5 to 7(figure 7). Moreover, during this period, the stream 7

upph density had its highest density (200 individuals/m3) in 2012. But the stream 7 oupph had the

most important density in 2013 during week 6 while its temperature was just 6.23°C. In 2013 the

downstream section of stream 7 had a temperature maximum of 15°C and its density was higher than

that of the stream 7 oupph but there was less than 50 individuals/m3 (figure11).

On average, stream 7 (heated-up) had the higuest density throughout the time in 2012 and 2013.

21

Figure 12 Evolution of the number of Simuliidae larvae flowing downstream for each stream, in

individuals/m3

Figure 13 Evolution of the number of Radix Peregra flowing downstream for each stream, in individuals/m3

in summer 2013

Figure 14 Evolution of the number of Chironomidae larvae flowing downstream for each stream, in

individuals/m3 in summer 2013

22

Dominance

Many species have been found in the drift samples, but only three of them show interesting variation

between streams.

The number of Simuliidae larvae is very low for the upstream section of stream 7 whereas it is higher

in the downstream section. Moreover this stream 7 upph Simulidae larvae density follows the

variation of stream 8 Simulidae larvae density (figure 12).

The freshwater snail Radix peregra is very common in Iceland and especially in the Hengill area. It

was completely absent from the upper section of stream 7 but some individuals were collected at the

outlet of the downstream section. It is actually the dominant invertebrate collected from the stream 8

drift samples, with almost 68% of the total community when greatest (figure13).

In the same way, the Chironomidae larvae represents 70.4% of the stream 7 oupph total community.

However these individuals were generally found in both sections of stream 7 in the same densities

(figure 14).

Figure 15 Evolution of Hatching cycle fly diversity over time(2013).

23

St7 oupph St7 upph

Chironomidae larvae 70,40% 4,50%

Chironomidae pupas 4,80% 10,60%

Chironomidae flies 18,40% 26,48%

Simuliidae larvae 0,09% 2,40%

Simuliidae pupas 0,00% 0,16%Simuliidae flies 0,15% 1,68%Clinocera larvae 0,07% 0,10%

Clinocera pupas 0,00% 0,01%Clinocera flies 0,02% 0,23%Limoniidae larvae 0,02% 0,15%

Limoniidae flies 0,01% 0%

Limnophora larvae 0,56% 0,15%Limnophora flies 0,05% 0,70%

Tipulidae larvae 0,01% 0,70%

Tipulidae flies 0,01% 0,03%

Figure 16 Percentage of some taxas in the total animal number of stream 7 oupph and stream 7 upph

samples.(2013)

Emergence and diversity

In order to study the effect of temperature on freshwater living larvae’s hatching rates, it is important

to take into account only the flies emerging from larvae and pupa which is part of the living cycle

which takes place in streams (Chironomidae, Simulidae, Limnophora, Limoniidae, Tipulidae,

Clinocera flies). Flies and other animals that were caught in the nets but had no development cycle

steps linked to stream ecosystems are not counted.

Fly cycle diversity observed for the heated-up section of stream 7 is higher than for the downstream

section, and for stream 8. Moreover, changes in diversity over time seem to follow similar trends

between the upstream and downstream sections of stream 7 (figure 15).

Focusing on figure 16 results, the emergence of flies from larvaes before pupas seems to be greater in

stream 7(heated) for all fly cycles and especially for Chironomidae. Indeed, the flies percentages are

bigger in stream 7 upph than in stream 7 oupph. Moreover the number of Simulidae flies is twice

more important compared to larvae one in stream 7 heated.

24

5. Discussion

In order to discuss the results, it is important to understand that only part of the data are available at

this time. Further experiments will be conducted at a later point, such as the vegetation weighing,

invertebrate weighing, and water chemistry analysis.

It should also be taken into account that summer 2012 was particularly dry and warm in comparison to

Icelandic averages, especially July. Water levels in the different streams were low and this may have

an influence on the results and their interpretation for 2012 and 2013. August, however, had more rain

and so was closer to standard conditions.

5.1 Temperature and flow

As a result of temperature measurement, the efficiency of the heating design methodology (stream 7

heated with stream 8 water thanks to a pipe) is confirmed. Indeed, the temperature difference between

summer 2012 and summer 2013 in stream 7 that is heated by the stream 8 is higher than stream 7 not

heated (figure 7). So this is evidence that stream 8 thoroughly heated this section of stream 7 because

between summer 2012 and 2013 the stream 8 temperature also increased. Although the R² coefficient

is not equivalent to 0.99 but just close to, there is a pattern shown through the graph relating the stream

8 temperature with the temperature difference between steam 7 upph and stream7 oupph (figure 6). An

affine linear relation is shown and confirms that stream 8 temperature variation entails greater stream 7

upph temperature variation than without any heating. In the heating experimentation context, the

stream 7 oupph can be used as a control case. The stream 7 heated-up results will help to understand

what could be the consequences of global warming on stream ecology.

According to figure 7, stream 8 presents a constant temperature over time despite the changes in flow

and climate conditions. However, the temperatures of stream 7, both the heated-up and not heated-up

sections, vary over time, with a maximum variation of 5.6°C. It appears that the water temperature of

stream 8 is completely independent of climatic conditions and that its temperature is related to

groundwater heated up in contact with warm soils or steam from the geothermal activity. Stream 7 is

dependent on climatic conditions and precipitation. This is shown by the daily temperature variations

that are more significant for stream 7 than stream 8 which is mostly constant over time. Although the

rivers flow very close to each other (the minimal distance is only approximately two meters) they have

different origins and are not affected in the same way by the local geothermal activity.

However, it is important to mention that the aim of the heating-up system was to maintain a roughly

constant difference of temperature between the upstream and downstream parts of stream 7, which

appears to be successful despite how climatic conditions affected the streams (figure 5). Indeed, the

temperature and flow variations of stream 7 are directly dependent on rain and water runoff.

5.2 Density and dominance

According to figures 10 and 11, it appears that the increase in temperature between the upstream and

downstream sections of stream 7 has a small but not very clear impact on the density (individuals/m3).

It seems that the density in the heated-up section of stream 7 is higher than in stream 8, and quite

similar concerning Simuidae larvae density (figures 11 and 12), although the water temperature is not

as high (figure 5). This pattern shows that the increase in temperature within the same stream amplifies

the potential of the stream even with a “slight” change of temperature compared to stream 8 mean

temperature.

25

Changes in temperature within the same stream induce changes in communities. For instance, it seems

that the Simuliidae larvae develop more in warmer water, as well as the Radix peregra snail. The

Chironomidae, dominant in the cold water of stream 7 oupph, is no longer dominant in stream 8, but

replaced by the Radix peregra which dominates without any contest up to 68% of the total samples.

This increase in Radix peregra is not seen as clearly in the stream 7 heated-up section despite the

increase of temperature, which is explained by the total absence of snails in the upper section. But the

Simulidae larvae density follows the same trend in stream 8 and stream 7 heated-up. Warming of the

water increases the stream potential which effects the available pool of life.

Due to Simulidae, the filter feeders community number follows the temperature increase while the

scrapers community is not totally dominated by snails (Radix Peregra) in stream 7 heated-up (figures

12, 13 and14). It could be because the stream 7 upph temperature is not as high as that of stream 8.

However, the snails increase in stream 7 upph could be encourage by epilithic algae dominance, that

they can eat, in a cold stream like stream 7.

5.3 Emergence and diversity

Warming is thought to increase growth velocity and that is shown with the positive link between fly

cycle emergence and hot temperature (figure 16).

Temperature increase is thought to decrease the diversity of a stream. The results obtained show that

the diversity is the lowest in the colder stream (figure 15). However, the stream 8 diversity is

sometimes lower than that of stream 7 oupph. Therefore, if the experimentation was runned more

longer in time, stream 7 oupph diversity might be higher on average than warmer stream diversty.

Moreover, the stream 7 upph diversity is the highest on average throughout summer 2013. However,

heating would make stream 7 becoming a disturb system. If stream 7 was acting like a disturb

ecosystem, a not balanced thing allowed it to has more biodiversity.

26

Conclusion

As a result of this study, some results and hypothesis of ancient studies on this subjet have (not) been

confirmed. Moreover, the efficiency of the Hengill area experiment is successful even if, not yet a

perfect system.

Comparing theanimal density, stream 7 was more productive in the downstream section than the

upstream. The heated up section is more productive than stream 8. The increased temperature may

allow a higher number of macroinvertebrates to live there. The dominance into invertebrates is

influenced by temperature increase with the great arrival of Simulidae and snails in stream 7 heated-

up. The link between the emergence of flies and their diversity and temperature increase is not obvious

yet because of the delicate balance of the heating system of stream 7.

Although it is important to highlight how climate change will affect ecosystems, global warming is

just a small part of climate change. The climate is already knownto be changing. Precipitation patterns

are expected to change, as well as the ocean currents. Climate change is a complex phenomenon with

interlinked biological, meteorological, chemical and physical responses. For this reason, studies on

natural systems are crucial because they provide checks on the effects of global warming and the

current climate changes.

27

References

Christensen, B. Hewitson , A. Busuioc , A. Chen , X. Gao ,I. Held , R. Jones , R.K.Kolli , W-T Kwon, R. Laprise , V. R. Magaña , L. Mearns , CG. Menéndez, J. Räisänen, A. Rinke, A. Sarr, Whetton (2007) Regional Climate Projections. In: Solomon S, Qin D, Manning M, Chen Z, Marquis M, Averyt KB, Tignor M and Miller HL (eds). Climate Change 2007

Elmarsdóttir, Ingimarsdóttir María, Hansen Iris, Ólafsson Jón S., and Ólafsson Erling, (2003) Vegetation and invertebrates in three geothermal areas in Iceland. International Geothermal Conference, Reykjavík, Sept. 2003, Reykjavík: S12 Paper086, pp49-55.

Eoin, J O Gorman, Doris E Pichler, Georgina Adams, Jonathan P Benstead, Haley Cohen, Nicola Craig, Wyatt F Cross, Benoît O L Demars, Nikolai Friberg, Gísli Már Gíslason, Rakel Gudmundsdóttir, Adrianna Hawczak, James M Hood, Lawrence N Hudson, Liselotte Johansson, Magnus P Johansson, James R Junker, Anssi Laurila, J Russell Manson, Efpraxia Mavromati, Daniel Nelson, Jón S Ólafsson, Daniel M Perkins, Owen L Petchey, Marco Plebani, Daniel C Reuman, Björn C Rall, Rebecca Stewart, Murray S A Thompson, Guy Woodward, Guy In, Ute Woodward, Eoin J O ' Jacob, Gorman(2012) Impacts of Warming on the Structure and Functioning of Aquatic Communities : Individual-to Ecosystem-Level Responses

European Environment Agency Urban waste water treatment (CSI 024) - Assessment published Jan 2009

Friberg, J. B. Dybkjaer , J. S. Olafsson‡, G.M Gislason ,S. E. Larsen and T. L. Lauridsen (2009) Relationships between structure and function in streams contrasting in temperature

Gudmundsdottir, G.M Gislason, S. Palsson, J. S. Olafsson, A. Schomacker, N.Friberg, G.Woodward, Elizabeth R. Hannesdottir, Brian Moss (2011) Effects of temperature regime on primary producers in Icelandic geothermal Streams

Hannesdóttir, G. M. Gíslason, J. S. Ólafsson, P. Ólafur, Ólafsson, Eoin J O ' Gorman (2014) Increased Stream Productivity with Warming Supports Higher Trophic Levels

Woodward*, J. B. Dybkjaer, J. S. Olafsson, G. M. Gislason, E. R. § and N. Friberg(2010) Sentinel systems on the razor’s edge: effects of warming on Arctic geothermal stream ecosystems

28

Appendix

Appendix A -Trophic level definition

The trophic level of an organism is the position it occupies in a food chain. A food chain represents a

succession of organisms that each eat another organism (excepting primary producers) and are, in turn,

eaten themselves (excepting the apex predators). The number of steps an organism is from the start of

the chain is a measure of its trophic level. The path along the chain forms a food "web". The three

basic ways in which organisms are identified as producers, consumers and decomposers (figure 17).

Producers (autotrophs) are typically plants or algae. Plants and algae use nutrients from the soil or the

ocean and manufacture their own food using photosynthesis. For this reason, they are called primary

producers. In this way, it is energy from the sun that usually powers the base of the food chain.

Consumers (heterotrophs) are species that cannot manufacture their own food and need to consume

other organisms. Decomposers (detritivores) break down dead plant and animal material and wastes

and release it again as energy and nutrients into the ecosystem for recycling. Decomposers, such as

bacteria and fungi (mushrooms), feed on waste and dead matter, converting it into inorganic chemicals

that can be recycled as mineral nutrients for plants to use again.

Figure 17 Example of a food « web » system

Trophic levels can be represented by numbers, starting at level 1 with plants. Further trophic levels are

sequentially numbered according to how far the organism is along the food chain.

Level 1: Plants and algae make their own food and are called primary producers.

Level 2: Herbivores eat plants and are called primary consumers.

Level 3: Carnivores that eat herbivores are called secondary consumers.

Level 4: Carnivores that eat other carnivores are called tertiary consumers.

Level 5: Apex predators that have no predators are at the top of the food chain.

29

Appendix B- Drift and Hatching samples

30

Appendix C- Data collection list of drift samples

from stream 8, stream 7 oupph (not heated) and

stream 7upph (heated) Stream 8

Date (2013) June 5 June 11. June 18 June 24 July 01. July 08. July 15. July 22. July 29. Aug 6. Aug 12. Aug 19. Aug 23.

Collecting Time

(min) 45 45 45 45 45 45 45 45 45 45 45 45 45Chironomidae

larvae 30 18 31 51 17 13 8 11 7 36 8 7 3

Chironomidae

pupas 2 6 5 2 4 0 0 1 1 6 1 0 0

Chironomidae

flies 9 18 19 18 3 6 6 6 8 15 0 2 7

Simuliidae larvae 12 3 10 14 25 37 36 33 30 66 60 42 14

Simuliidae pupas 0 1 1 0 0 0 1 1 2 2 0 2 0

Simuliidae flies 1 0 0 0 0 3 3 2 2 1 4 2 4

Clinocera larvae 0 0 0 0 0 0 0 0 0 0 0 0 0

Clinocera pupas 0 0 0 0 0 0 0 0 0 0 0 0 0

Clinocera flies 0 1 0 0 0 0 0 0 0 0 0 0 0

Limoniidae larvae 0 0 0 0 0 0 0 0 0 0 0 0 0

Limoniidae flies 0 0 0 0 0 0 0 1 0 0 0 1 0

Limnophora

larvae (Muscidae) 2 2 7 13 26 25 21 26 36 111 35 35 21

Limnophora flies 1 0 4 3 1 1 1 0 1 0 4 3 0

Tipulidae larvae 0 0 0 0 0 0 1 1 0 0 0 0 1

Tipulidae flies 1 0 1 0 0 0 0 0 0 1 0 0 0

Ephydridae 0 0 0 0 0 1 0 1 0 1 2 1 2

Lonchopteridae 0 0 0 0 0 0 0 0 0 0 0 0 0

Lecidomyiidae 0 0 0 0 0 0 0 0 0 0 0 0 0

Dolichopodidae 0 0 0 0 0 0 0 1 0 1 1 0 1

Empididae 0 0 0 0 0 0 0 0 0 0 0 2 0

Syrphidae 0 0 0 0 0 1 0 1 0 0 0 0 0

Scathophagidae 0 0 0 0 0 0 0 1 0 0 0 0 0

Driomyzidae 0 0 0 0 0 0 0 0 0 0 0 0 0

Bibionidae 1 0 0 0 0 0 0 0 0 0 0 0 0

Scimyzidae 0 0 0 0 0 0 0 0 0 0 0 0 0

Heleomyzidae 0 3 0 0 0 0 0 0 1 0 0 0 0

Canaceidae 0 0 0 0 0 0 0 0 0 0 0 0 0

Coleoptera larvae 0 0 0 0 0 0 0 0 0 0 0 0 0

Staphilinidae

immature 0 0 0 0 0 0 0 0 0 0 0 0 0

Staphinilidae flies 0 0 0 0 0 0 0 0 0 0 0 0 0

Carabidae 0 0 0 0 0 0 0 0 0 0 0 0 0

Carabidae flies 0 0 0 0 0 0 0 0 0 0 0 0 0

Braconidae 0 0 0 0 0 0 0 0 0 0 0 0 1

Aphyte immature 0 0 0 0 0 0 0 0 0 11 0 0 0

Aphyte mature 0 2 0 0 0 1 0 0 0 0 0 0 0

Ichneumonidae 0 0 0 0 0 0 1 0 1 1 0 3 0

Platygastridae 0 0 0 0 0 0 0 0 0 1 4 0 0

Scelionidae 0 0 0 0 0 0 0 0 0 6 0 0 0

Ceraphronidae 0 0 0 0 0 0 0 0 4 0 5 0 0

Hemiptera 0 0 0 0 0 0 0 0 0 0 0 0 0

Hemiptera flies 1 0 0 0 0 0 0 0 0 0 0 0 0

Delphacidae 0 0 0 1 0 2 3 0 0 0 0 0 0

Delphacidae

immature 0 0 0 0 0 0 0 0 0 0 0 0 0

Coccoidae 0 0 0 0 0 0 0 0 0 0 0 0 0

Shield bugs 0 0 0 0 1 0 0 0 0 0 0 0 0

Aphididae 1 0 0 0 2 0 5 2 1 4 2 2 7

Aphidoidae

immature 0 1 0 3 0 0 0 0 2 0 0 0 0

Collembola

Proisotoma 4 1 3 1 2 2 1 0 2 1 1 12 1

Collembola

Hypogastruridae 0 0 1 1 0 0 0 0 0 1 1 0 0

Collembola

Isotomidae 0 0 0 0 0 0 0 0 0 0 1 0 0

Collembola

Sminthurides 0 1 0 2 0 0 0 0 0 0 0 0 0

Citellata Oligochaeta 3 41 39 11 13 10 1 0 0 64 0 0 3

Ostracod 0 0 0 0 0 0 0 0 0 0 0 0 0

Radix peregra 522 611 1030 406 678 737 467 643 328 1228 269 328 299

Galba Truncatula 0 0 0 0 0 0 0 0 0 1 0 0 0

Eggs 481 185 187 168 90 49 68 21 6 80 185 137 26

Acarina 10 38 39 46 7 28 0 3 1 116 0 0 0

Spiders 0 0 0 0 0 1 1 1 0 1 2 0 0

Butterfly larvae 0 0 0 0 0 0 0 0 0 0 0 0 0

Moth 0 0 0 0 0 0 0 0 0 0 0 0 0

Diptera

Coleoptera

Hemiptera

Hexapoda

Gastropoda

Arachnida

Lepidoptera

Hymenoptera

31

Stream 7 oupph


Collecting Time

(min) 135 135 135 135 135 135 135 135 135 135 135 135 135

Chironomidae

larvae 2248 1406 125 125 111 304 115 163 77 0 0 53 223Chironomidae

pupas 113 47 22 22 26 22 11 12 3 0 0 34 30Chironomidae

flies 320 202 66 66 92 27 29 34 7 0 0 160 294

Simuliidae larvae3 0 0 0 0 0 0 2 0 0 0 1 0

Simuliidae pupas0 0 0 0 0 0 0 0 0 0 0 0 0

Simuliidae flies6 1 0 0 1 0 0 1 0 0 0 0 2

Clinocera larvae1 1 0 0 0 0 0 0 0 0 0 0 0

Clinocera pupas 0 0 0 0 0 0 0 1 0 0 0 0 0

Clinocera flies 0 0 0 0 2 0 0 0 0 0 0 1 2


Limoniidae flies0 0 0 0 0 1 0 0 0 0 0 1 0

Limnophora

larvae

(Muscidae)0 0 0 0 0 0 1 0 0 0 0 0 0


Tipulidae larvae 0 1 0 0 0 0 0 0 0 0 0 0 3

Heleomyzidae 0 0 0 0 0 0 0 0 0 0 0 0 1

Sciaridae flies 0 0 0 0 0 1 0 0 0 0 0 0 0

Ephydridae 8 0 0 0 0 0 0 1 0 0 0 0 0Ceratopogonidae

larvae 0 0 0 0 1 2 1 3 0 0 0 12 0

Ceratopogonidae

pupas 0 0 0 0 0 0 0 0 0 0 0 2 0Ceratopogonidae

flies 0 1 0 0 0 0 0 0 0 0 0 1 2Empididae

larvae0 0 0 0 0 0 1 0 0 0 0 0 0

Empididae 2 0 0 0 0 0 0 1 3 0 0 0 1

Lonchopteridae 0 0 0 0 0 0 0 0 0 0 0 0 0

Tipulidae flies 0 0 0 0 0 0 0 0 0 0 0 0 1

Dolichopodidae 1 0 0 0 0 0 0 0 1 0 0 1 1

Driomyzidae 1 0 0 0 0 0 0 0 0 0 0 0 0

Plecoptera Coleoptera larvae 13 5 0 0 0 0 1 0 0 0 0 0 0Hydroporus

negrita 0 0 0 0 0 0 0 0 0 0 0 0 0

Giant acarina 0 0 0 0 0 0 0 2 0 0 0 0 0

Staphilinidae

immature 0 0 0 0 0 0 0 1 0 0 0 0 0Staphinilidae

flies0 0 0 0 0 0 0 0 0 0 0 0 0

Braconidae 2 0 0 0 0 0 0 0 0 0 0 0 0

Platygastridae 0 0 0 0 1 0 1 0 0 0 0 0 0

Ichneumonidae 0 0 0 0 0 0 0 0 0 0 0 1 1

Ceraphronidae 0 0 0 0 0 0 1 0 0 0 0 0 3

Scelionidae 0 0 0 0 0 0 0 1 0 0 0 1 0

Hemiptera flies0 0 0 0 0 0 0 0 0 0 0 0 0

Aphididae 4 0 0 0 0 0 0 0 0 0 0 0 0

Delphacidae0 0 0 0 0 0 0 0 0 0 0 0 1

Coccoidae 0 0 0 0 0 1 0 0 0 0 0 0 0

Collembola

proisotoma 0 0 0 0 0 0 0 0 0 0 0 0 0

Collembola

Sminthurides 38 3 13 13 4 2 1 4 3 0 0 14 23

Collembola

Hypogasfruridae 0 0 2 2 0 0 0 0 0 0 0 3 4

Harpacoidea

Copepoda 0 0 0 0 0 0 0 0 0 0 0 0 0


Radix peregra 4 0 3 3 4 4 4 4 1 0 0 16 13

Eggs 0 0 0 0 0 0 0 0 0 0 0 0 5

Acarina 23 4 3 3 6 2 0 1 0 0 0 5 1

Spiders 1 0 0 0 0 0 0 0 0 0 0 0 1

Butterfly larvae0 0 0 0 0 0 0 0 0 0 0 0 0

Moth 0 1 0 0 0 0 0 0 0 0 0 0 0Lepidoptera

Arachnida

Gastropoda

Diptera

Coleoptera

Hymenoptera

Hemiptera

Hexapoda

32

Stream 7 upph


Collecting Time

(min) 140 180 120 135 45 45 135 135 135 135 135 135 135

Chironomidae

larvae 3725 952 344 131 171 643 214 230 132 125 65 132 292Chironomidae

pupas 254 104 111 38 26 39 23 22 8 8 7 26 23

Chironomidae flies 641 214 191 79 110 142 72 59 45 31 19 71 42

Simuliidae larvae 10 0 1 2 6 7 7 9 11 11 20 53 19

Simuliidae pupas 4 1 3 0 0 1 0 0 0 1 0 1 0

Simuliidae flies 65 4 16 1 2 3 0 3 0 0 7 7 1

Clinocera larvae 3 1 1 2 0 0 0 0 0 0 0 0 0Clinocera pupas 0 0 0 0 0 0 1 0 0 0 0 0 0

Clinocera flies 1 1 0 0 3 2 1 2 0 2 0 0 3


Limoniidae flies 0 0 0 0 0 0 0 0 0 0 0 0 0Limnophora larvae

(Muscidae) 1 0 0 0 1 1 0 0 0 0 0 3 4


Tipulidae larvae 9 2 2 0 1 4 1 5 0 0 0 3 22Tipulidae pupas 2 0 1 0 0 0 0 0 0 0 0 0 0

Tipulidae flies 0 0 0 0 0 0 1 0 0 0 0 1 0

Ephydridae 32 7 2 2 1 0 0 4 1 0 0 4 8

Lonchopteridae 0 2 0 0 0 0 0 0 0 0 0 0 0Anthomyiidae 0 0 0 0 0 0 0 0 0 0 0 1 0

Dolichopodidae 0 0 0 0 0 0 0 0 0 0 0 2 3

Syrphidae 0 0 0 0 0 1 1 1 0 0 0 1 0

Ceratopogonidae

larvae 0 0 0 0 2 1 0 6 0 0 0 0 10Ceratopogonidae

pupas 0 0 0 0 1 0 0 2 0 0 0 0 0

Ceratopogonidae

flies 0 0 0 0 0 1 0 0 0 1 3 1 0

Bibionidae 0 0 0 0 0 0 0 0 0 0 2 0 0

Sepsidae 0 0 0 0 0 0 0 0 1 0 0 0 0Cecidomyiidae 0 0 0 0 0 2 0 0 1 0 0 0 0

Sciaridae 0 0 0 0 0 1 0 0 0 0 0 0 0

Phoridae 0 0 0 0 0 1 0 0 0 0 1 0 0Heleomyzidae 1 9 0 0 0 0 0 2 0 0 0 0 0Scathophagidae 0 2 0 0 0 0 0 1 0 0 0 0 0

Anthomyzidae 0 1 0 0 0 0 0 0 0 0 0 0 0

Piophilidae 0 1 0 0 0 0 0 0 0 0 0 0 0

Sphaeroceridae 0 2 0 0 0 0 0 0 0 0 0 0 0

Empididae larvae 0 0 0 0 0 2 0 2 0 0 1 1 4

Empididae 3 1 1 0 0 0 2 1 2 0 1 11 2

Canaceidae 0 0 0 0 0 0 0 0 0 0 0 0 0

Plecoptera 15 3 1 0 0 0 0 0 0 0 0 0 0

Adults 0 1 0 0 0 2 1 0 1 0 0 0 0

Coleoptera larvae 0 1 0 0 0 0 0 0 0 0 0 0 0

Hydroporus negrita 0 0 0 0 0 0 0 0 0 0 0 0 0

Carabidae flies 0 0 0 0 0 2 0 0 0 0 0 0 0

Unidentified flies 1 0 0 0 0 0 0 0 0 0 0 0 0

Aphyte immature 0 2 0 0 0 0 0 0 0 0 0 0 0

Aphyte mature 0 0 0 0 0 0 0 0 0 4 0 0 16

Ichneumonidae 5 0 0 0 0 1 0 1 1 0 0 1 2

Scelionidae 0 0 0 0 0 0 0 0 0 0 0 0 0

Braconidae 0 0 0 0 0 2 1 0 0 0 0 1 2

Ceraphronidae 0 0 0 0 0 0 0 0 0 2 5 1 2

Platygastridae 0 0 0 0 0 0 0 0 0 5 4 5 1

Scelionidae 1 1 0 1 0 0 0 0 2 2 1 1 0

Hemiptera

immature 0 0 0 0 0 0 0 0 0 0 0 0 0

Hemiptera flies 8 0 0 0 0 0 0 0 0 0 0 0 0

Coccoidae 3 0 0 0 0 0 0 0 0 0 0 0 0

Aphididae 2 1 0 2 2 4 2 0 2 0 10 25 9

Aphids 0 0 0 0 0 2 0 0 0 0 0 0 0

Delphacidae 0 1 0 0 2 7 3 1 0 0 0 0 0

Shield bugs 0 1 0 0 0 0 0 0 0 0 0 0 0

Collembola

Proisotoma 99 16 4 7 8 3 12 4 5 3 2 28 12

Collembola

Hypogasfruridae 0 0 0 0 0 0 0 1 0 0 0 0 1Collembola

Sminthurides 0 0 0 3 4 0 0 2 0 1 0 0 0


Ostracod 24 3 6 9 0 1 0 2 1 2 0 1 3

Radix peregra 68 10 4 7 11 23 3 12 9 6 15 36 148

Galba truncatula 9 7 3 0 1 1 0 3 0 1 1 7 6

Eggs 473 262 147 103 86 307 139 219 110 18 82 213 231

Acarina 28 12 6 7 10 7 4 3 4 4 1 9 6

Spiders 4 1 1 0 1 1 0 1 0 0 0 0 0

Nematode 2 0 0 0 0 0 0 0 0 0 0 0 0

Diptera

Gastropoda

Arachnida

Hexapoda

Hemiptera

Coleoptera

Hymenoptera

33

Summary

Global warming is predicted to be more dramatic in the Arctic area where an increase of 4ºC is

expected over the next century. In Iceland, hot and glacial streams exist with variable temperatures and

are found with a short distance of each others.

This offers opportunities to study the impact of temperature on stream ecology, particularly in the

Hengill area were a warming-up system has been set up on a cold stream in order to study a sudden

increase of temperature. The downstream section of the colder stream has been warmed whereas

upstream section remains at its natural temperature. Results from this study show that an increase of

temperature has an impact on stream ecology with a higher macroinvertebrates density and dominance

and diversity changes.

Keywords: macroinvertebrates, stream ecology, climate change, geothermal activity

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