Nitrogen in the Hyporheic zone

DEGREE OF MASTER OF SCIENCE IN ENGINEERING, SECOND CYCLE, 30 CREDITS

STOCKHOLM, SWEDEN 2019

Stream Restoration and Mitigation of

Nitrogen in the Hyporheic zone

Interpretation of tracer tests from Tullstorps brook

Sunna Mjöll Sverrisdóttir

KTH ROYAL INSTITUTE OF TECHNOLOGY

Abstract

Streams and rivers have been modified in the past centuries for agricultural purposes. The Baltic Sea suffers from problems regarding eutrophication.

Regulations of point-sources have decreased nutrient levels, but for a scattered source of nutrient pollution, streams are important. One way of mitigating nitrogen is with coupled denitrification and nitrification processes when stream water is transported through flow paths in the hyporheic zone, an area in the stream sediments where groundwater and stream water mix. Tullstorps brook is an agricultural stream that flows into the Baltic Sea. It has had problems with high nutrient loads and poor water quality and has therefore been restored.

The fieldwork in this project was conducted in Tullstorps brook in May 2019,

where Rhodamine WT (RWT) tracer test and Hydraulic Conductivity (HC)

measurements were done in 3 reaches, and compared to similar fieldwork since

before restorations, during the summer of 2015. Two reaches in an agricultural

setting that have been restored, Reach 4 and Reach 6, were measured, as well as

a control reach, Reach 5, which is in a natural setting. The tracer tests indicated a

significant decrease in the velocity in remediated reaches. The results of exchange

velocity between the stream flow and the hyporheic zone suggest an increase

after remediation of the reaches and the residence time seems to be decreasing

simultaneously. When comparing the hydraulic characteristics, different stream

flow during measurements was considered in a qualitative manner. The results

of HC measurements show a decrease from 2015 to 2019 in the remediated

reaches. In Reach 4 it decreased from 1.20E-03 m/s to 5.0E-4 m/s and in Reach

6, HC decreased from 7.70E-04 m/s before remediations to 5.6E-04 m/s after

remediation actions. All the measurements have uncertainties, especially since

homogeneity is assumed to some extent and the natural environment will always

be heterogeneous.

Keywords

Hyporheic Zone, Stream Restorations, Nitrate Mitigation, Tracer test, Solute

Transport, Eutrophication, Nitrogen.

Acknowledgements

Firstly, I would like to thank my advisors at KTH, Joakim Riml and Ida Morén for your guidance and input. I want to thank my examiner, Anders Wörman, for his important feedback and for giving me the opportunity to work on this project and Sam Ekstrand, for his very helpful reflections and input. Special thanks go to Katrine Sörensen and the many people that have made the Tullstorps brook project happen. Without your help and input, this project would not have been possible.

Secondly, for all the help with solving the problem when our measuring equipment broke down a week before the field trip, I want to thank Peter B. Andersen at Kem- En-Tec. Also, special thanks to Håkan Danielsson at Länsstyrelsen in Dalarna who let us borrow their equipment and made the measurements possible.

Thirdly, an enormous thank you to my boyfriend Huldar Bjarmi Halldórsson for all the support with programming, proofreading and cooking. Also, I would like to thank my friends at KTH who dragged me to fika when I needed a break and made these past 2 years the best ones yet.

Lastly, I would thank my wonderful parents for always being there and for helping

me pursue this degree.

Author

Sunna Mjöll Sverrisdóttir <sunnasv@kth.se>

Environmental Engineering and Sustainable Infrastructure KTH Royal Institute of Technology

Place for Project

Stockholm, Sweden

KTH Royal Institute of Technology

Examiner

Anders Wörman

KTH Royal Institute of Technology

Supervisor

Joakim Riml

KTH Royal Institute of Technology

Table of Contents

List of Figures viii

List of Tables x

Nomenclature xi

List of Abbreviations xii

1 Introduction 1

1.1 Problem formulation . . . . 3

1.2 Aim and Research Questions . . . . 4

1.3 Methodology . . . . 4

1.4 System Boarders and Delimitations . . . . 5

1.5 Report Outline . . . . 5

2 Theoretical Framework 6 2.1 Eutrophication . . . . 6

2.1.1 The Baltic Sea . . . . 7

2.1.2 International Cooperation and Policies . . . . 8

2.2 Stream Restorations . . . . 9

2.2.1 Hyporheic Exchange . . . 10

2.2.2 Restoration methods . . . . 11

2.2.3 ASP-Model for analysis of measured data . . . 12

2.2.4 Benefits and Costs of Stream Restorations . . . . 15

3 Methods 17 3.1 Site Specific Field Measurements . . . . 17

3.1.1 Study Area . . . . 17

3.1.2 Comparison data . . . 18

3.1.3 Tracer tests with RWT . . . 18

3.1.4 Risk Analysis . . . 20

3.1.5 HC measurements . . . 21

3.2 Additional Stream Characteristics . . . 22

3.3 Physical Model . . . 22

3.4 Literature review . . . 23

3.5 Interviews . . . 24

3.5.1 Interview guide . . . 24

3.5.2 Data analysis of interviews . . . 26

4 Field Measurements in Tullstorps Brook 27 4.1 Tullstorps Brook . . . 27

4.2 Remediation Actions in Tullstorps Brook . . . 29

4.3 Comparison data . . . 32

4.4 Tracer tests with RWT . . . 35

4.5 Calibration Curves . . . 36

4.6 HC Measurements with a Piezometer . . . 37

5 Results 39 5.1 Summary of previous research in Tullstorps brook . . . 39

5.1.1 HC and Other Stream Characteristics Before Remediation . 39 5.1.2 BTC’s from 2015 RWT Tracer Tests . . . 40

5.2 Analysis of 2019 Measurements at Tullstorps Brook . . . 42

5.2.1 HC and other Characteristics after Remediation . . . 42

5.2.2 Optimised Hydraulic Parameters after Remediation Actions 44 5.3 Comparison of Hydraulic Parameters . . . 49

5.4 Relative Nitrogen Removal . . . 55

5.5 Cost-benefit of stream restoration projects . . . 56

5.5.1 Funding of Stream Restoration Projects . . . 60

6 Discussions 61 6.1 Fieldwork at Tullstorps brook . . . 61

6.1.1 HC Measurements . . . 61

6.1.2 RWT Tracer Tests . . . 62

6.2 Optimising Hydraulic Parameters with the ASP-model . . . 63

6.3 Nitrate retention . . . 63

6.4 The economic context . . . 64

6.5 Future Work . . . 65

7 Conclusions 66

8 List of Interviews 68

References 69

List of Figures

2.1 Hyporheic exchange, displayed in both plan and lateral view.

Riffles and pools are example of measures that can induce hyporheic exchange. Developed from Hester and Gooseff (2010) and Morén et al. (2017b) . . . 12 3.1 Flow chart illustrating which methods were used to reach the

objectives. . . . 17 3.2 The equipment used for tracer test injections and a RWT injection

in Tullstorps brook. . . 19 3.3 RWT concentration at the upstream logging site at Reach 4. . . 21 4.1 Location of Tullstorps brook and its catchment in Skåne. . . 28 4.2 A two-stage ditch and a traditional ditch. Developed from

(Tullstorpsåprojektet, 2015). . . . 31 4.3 Examples of remediation actions in Tullstorps Brook. . . 32 4.4 Location of Reaches 4, 5 and 6 in Tullstorps brook. . . 33 4.5 Discharge in Tullstorps brook that was predicted from the HYPE

model by SMHI. Source: (SMHI, 2018). . . 35 4.6 Injection points and inspection sites during RWT tracer tests in 2019 36 4.7 Calibration Curves for the measurement sites at all reaches in

Tullstorps brook . . . 37 5.1 Observed and normalised modelled Breakthrough Curve (BTC)

from RWT tracer tests in Tullstorps brook in 2015. Source: (Morén et al., 2017b). . . 41 5.2 HC Measurements at 3 cm and 7 cm Sediment Depth . . . 43 5.3 Comparison of K

values in 2015 and 2019 in Tullstorps brook. . . . 43 5.4 Observed and normalised modelled BTC from RWT tracer tests in

Tullstorps brook at May 7 2019 in Reach 4. . . 45 5.5 Observed and normalised modelled BTC from RWT tracer tests in

Tullstorps brook at May 6 2019 in Reach 5. . . 46 5.6 Observed and normalised modelled BTC from RWT tracer tests in

Tullstorps brook at May 6 2019 in Reach 6. . . 48

5.7 Comparison of stream flow during each RWT tracer test. . . 50

5.8 Comparison of optimised stream velocity, u, for all reaches in 2015 and 2019. *High error in optimisation for Reach 6 2019. . . . . 51 5.9 Comparison of optimised flow-weighted exchange velocity, W, for

all reaches in 2015 and 2019. *High error in optimisation for Reach 6 2019. . . . 52 5.10 Comparison of optimised flow-weighted residence time of water

flowing through a stream tube, T, for all reaches in 2015 and 2019.

*High error in optimisation for Reach 6 2019. Value for 2019 results too high to include. . . 53 5.11 Comparison of optimised Longitudinal dispersion coefficient, E, for

all reaches in 2015 and 2019. *High error in optimisation for Reach 6 2019. . . . 54 5.12 Comparison of optimised depth of the hyporheic zone, ϵ, for all

reaches in 2015 and 2019. *High error in optimisation for Reach

6 2019. Value for 2019 results too high to include. . . 55

5.13 The modelled values from 2015 and 2019 with and without reaction 56

List of Tables

4.1 Overview of measurements that are analysed compared in this project. . . 34 5.1 Characteristics of Reaches 4, 5 and 6 during measurements in 2015.

Source: (Morén et al., 2017b; SMHI, 2018) . . . 40 5.2 Optimised parameters from RWT tracer tests in Tullstorps brook in

2015. Source: (Morén et al., 2017b). . . 42 5.3 Characteristics of Reaches 4, 5 and 6 during measurements in 2019. 44 5.4 Optimised hydraulic parameters for all reaches from tracer tests in

2019 . . . 49

Nomenclature

ϵ Depth of the hyporheic zone [m]

η Porosity in sediments [ −]

τ Minimum travel time after which reactions commence [s]

A Cross-section of the stream [m

]

c Depth decaying factor of hydraulic conductivity [[1/m]]

C

Total concentration of solute in the stream [kg/m

] E Main stream dispersion coefficient [m

/s]

G

Total solute mass per volume pore water in the storage zone[kg/m

] J

Exchange rate of solute mass per unit cross-section area of stream [kg/m

s]

K

Hydraulic conductivity at the surface, y=0 [[m/s]]

K

Hyporheic zone equilibrium partitioning constant [ −]

K

Main channel equilibrium partitioning constant [ −]

P Wetted perimeter of the main channel [m]

q

Darcy velocity of water travelling along the curve-linear coordinate s [m/s]

r

First-order reaction rate in the pore water of the hyporheic zone [1/s]

r

First-order reaction rate in the main channel [1/s]

T Average total residence time from inlet to exit of hyporheic flow path[s]

t Time [s]

U Flow velocity in the main stream [m/s]

W Average hyporheic exchange velocity [m/s]

x Location along the reach [m]

List of Abbreviations

ASP Advective-Storage-Path BSAP Baltic Sea Action Plan BTC Breakthrough Curve

EC European Commission

EU European Union

GHG Greenhouse gas HELCOM Helsinki Commission HC Hydraulic Conductivity

N Nitrogen

P Phosphorus

RWT Rhodamine WT

SMHI Swedish Meteorological and Hydrological Institute VISS Vatteninformationssystem Sverige

WFD Water Framework Directive

WTP Willingness To Pay

1 Introduction

Streams and rivers have long served as the lifeline of societies, due to the need for water resources and transport ways. They serve as important habitats for flora and fauna as well as for recreational value. Over the past centuries, streams have been altered to serve transport requirements, manage flood risk and to lower groundwater level for agricultural purposes (Boano et al., 2014). This is a result of increased agriculture and accelerated land use, as well as urbanization (Boano et al., 2014; Magliozzi et al., 2017). The changes have occurred in both urban and agricultural setting and include measures such as channeling and straightening of streams, modified soil compaction, that affects HC, and changes in stream velocity (Magliozzi et al., 2017).

Furthermore, an increase in agriculture and more intensive use of nutrients in agriculture in the past century has resulted in high nutrient concentrations in agricultural streams (HELCOM, 2009), and subsequently their receptors. In fact, agriculture is one of the major culprit when it comes to threats to surface waters, because runoff from agricultural fields is a diffused source (i.e. non-point source), which causes excess nutrient loads in waterways (EEA, 2018). Additionally, nutrient loads are expected to intensify with climate change, urbanization and aggravated agriculture (Kaushal et al., 2014). Nutrient pollution can cause severe water quality problems in waterways. The main problems that arise due to abundance of Nitrogen (N), in particular, is contamination of drinking water resources and eutrophication, which is due to the enhanced growth of phytoplankton. The growth subsequently reduces light in the water and depletes oxygen as the phytoplankton degrades (Newcomer Johnson et al., 2016).

Water quality problems from excess nutrient load is a worldwide problem. In the

United States, for example, almost two-thirds of coastal estuaries and rivers are

affected by it (Newcomer Johnson et al., 2016). In Denmark, it is estimated that

coastal waterbodies are contaminated by 30% more nitrogen than the European

Union (EU) Water Framework Directive (WFD) standards approves (Andersen

et al., 2019). In Sweden, and its neighbouring countries, the focus has been

on the Baltic sea, where eutrophication is a severe problem which threatens

its ecosystems and biodiversity (HELCOM, 2009). Of the nutrient load in the Baltic sea, approximately half of the N and Phosphorus (P) nutrient pollution is transported there via streams and rivers (Fölster et al., 2012; Naturvårdsverket, 2006). A good deal of research has been done and countermeasures have been undertaken in the past years to reduce the concentration of nutrients in streams and the Baltic Sea, and thus safeguarding water quality (Morén et al., 2017b, 2018). Action plans, as restrictions on nutrient usage and higher restrictions on wastewater treatment, have been implemented within the EU and are an example of how the problem is being treated at its source (EEA, 2018).

For a diffused source of pollution, however, as from excess nutrients in agriculture, streams play a vital role in mitigation efforts (Newcomer Johnson et al., 2016). There are ways of restoring streams and rivers with actions that can improve water quality and protect ecosystems (Boano et al., 2014). One example of a nutrient retention process is that nitrate can be permanently removed from streams with coupled denitrification and nitrification processes if water is transported through an anoxic zone in the river corridor. This zone can be found in stream sediments and is called the hyporheic zone (Newcomer Johnson et al., 2016).

The word hyporheic comes from the Greek words ’hypo’, which means below, and ’rheos’, which means flow (Boano et al., 2014). ’Hyporheic’ therefore means

’under the flow’ and this term was first introduced by Orghidan (1959). The common understanding is that streams collect water from the catchment via groundwater and surface runoff and simply convey it downstream. However the transport processes are much more complex, as the exchange between the surface flow and the shallow groundwater flow is a continuous process (Bencala et al., 2011). This means that streams are not simple channelized transport systems, or as (Bencala et al., 2011, p. 1) phrased it: “The stream is not a pipe”.

The flow of water through the hyporheic zone, mixing with the aquifer and getting

back to the surface water is called hyporheic flow exchange and is important

for a number of ecological processes, including nutrient transport and retention

(Boano et al., 2014). Anthropological changes of streams over the past century

have affected the retention of nutrients in streams negatively (Newcomer Johnson

et al., 2016), as they affect the processes that induce hyporheic exchange by reducing geomorphic variability (Boano et al., 2014; Gooseff et al., 2007). A channelized stream, for example, eventually can start to behave like the pipe Bencala et al. (2011) claimed it was not. These kind of altered streams can be restored back to a more natural stage with stream restoration measures. They are conducted for various purposes, such as to improve the ecology and increase water quality (Degerman, 2008). Even though hyporheic exchange is seldomly included quantitatively in the planning of these stream restorations, it can be impacted by modification of factors such as the streambed surface, hydraulic head variations and HC (Hester and Gooseff, 2011).

1.1 Problem formulation

The hyporheic zone in streams has been researched for more than half a century.

Nonetheless, it was not until the turn of this century that researchers shifted focus towards modelling of the complicated processes that occur in the hyporheic zone. Nowadays, there is great interest in the research of what mechanisms in the hyporheic zone can prove essential for the restoration of waterways and how they can affect various processes, e.g. reduction of eutrophication of surface waters and subsequently their receptors (Boano et al., 2014). It is therefore of the utmost importance to continue exploring the nutrient mitigation potential of the hyporheic zone in streams with specific site testing that can quantify the reduction.

Moreover, even though research on stream restoration and the hyporheic zone

has developed, some practical aspects of conducting the restorations are not

always considered. One important aspect is cost estimation of this kind of stream

restorations. It is vital to recognize them because solutions cannot be seen as

practical if stakeholders are not introduced to the benefits of carrying out the

restorations. While the EU recognizes the importance of monetary benefits when

it comes to water management, there is no framework available for cost estimates

when it comes to reducing nutrient loads and other chemicals for the purpose of

increasing water quality (Andersen et al., 2019).

1.2 Aim and Research Questions

The aim of this project is to investigate the nitrate mitigation potential of stream restoration methods in small agricultural streams with specific site testing at Tullstorps brook. It also aims to analyse the changes in hydraulic parameters of a stream from before and after remediation actions. These parameters control the hyporheic exchange and are of great importance for the relative nitrogen removal and they are the average stream velocity in the main channel, u, the flow-weighted exchange velocity, ⟨W ⟩, the residence time of water flowing through a stream tube, ⟨T ⟩, and the longitudinal dispersion coefficient, E. Finally, this project aims to investigate the financial aspects of stream restoration projects by analysing if stream restorations can be financially beneficial or if they are a financial burden.

From these aims, three research questions arose:

(i) What are the main changes in hydraulic parameters of reaches in Tullstorps brook before and after stream remediation actions?

(ii) Are there indications of increased nitrogen mitigation of reaches in Tullstorps brook after stream remedation actions?

(iii) Can stream restoration projects be financially beneficial for stakeholders?

1.3 Methodology

To answer the research questions of the project, both quantitative and qualitative methods were used. The quantitative method included field measurements in Tullstorps brook, an agricultural stream in Sweden, and modelling of the results.

The tools used for this part of the methods include Matlab as well as field instruments, which are described further in chapter 4.

Another method in the study was of qualitative perspective, but with an

acceptance of quantitative data. This was done by interviewing stakeholders and

experts on the subject. The tools used for data collection included interview

schedules and an interview guide and a recorder. The interviews both served

as primary data collection, but also to triangulate accuracy of information that

was acquired from further reading on the subject. The methods are explained in further detail in chapter 3.5.

1.4 System Boarders and Delimitations

The scope of the study is limited to small agricultural streams and their environment. Small streams are considered to have a stream flow <1 m

. The area of focus is Sweden, but other geographical areas was considered for comparison reasons. The site specific measurements will be conducted at Tullstorps brook in Skåne. For the purpose of narrowing down the topic of the report, the nutrient mitigation is mostly focused on N and will only loosely touch upon P.

1.5 Report Outline

This report is divided into 7 main chapters. Firstly, the theoretical framework

of the study will be introduced along with the current guidelines and directives

that apply to the topic. Secondly, the methods that were used for the purpose of

this study will be presented. Thirdly, the evidence that this project produced will

be presented as results and lastly, the results of this paper will be discussed and

concluded.

2 Theoretical Framework

This study is based on a theoretical framework that will be briefed in chapters 2.1 - 2.2.4. where the he main concepts used in this study are introduced.

2.1 Eutrophication

Eutrophication is a severe environmental threat that reduces water quality and negatively impacts biodiversity in surface waters, lakes and seas (Morén et al., 2018). Eutrophication can indicate an undesirable amount of nutrients, N and P, as well as sometimes organic matter (HELCOM, 2009). The nutrients enhance changes in the ecology that are not wanted. The unwanted effect of eutrophication is because of anthropological actions that have increased the amount of nutrients in surface waterways, lakes and seas (HELCOM, 2009). The problem has been growing rapidly since around the middle of last century, in fact the amount of waters that suffer from hypoxia has doubled since the 1960s (van Beusekom, 2018).

The first cases that were reported had to do with untreated effluent from farming or wastewater from municipalities (van Beusekom, 2018). The consequences of eutrophication are usually site specific and quite complex. The main effects include increase in phytoplankton growth, which hinders the pathway for light into waters. This can be measured as water clarity, by using the Secchi-meter to estimate the depth that the light can reach (van Beusekom, 2018; HELCOM, 2009). Eutrophication can also cause increased harmful algae blooms, reduction of seagrass and escalated amount of green macroalgae blooms (van Beusekom, 2018). Another effect is oxygen depletion, which can negatively affect the fauna of the sea (HELCOM, 2009).

The problem of eutrophication is a global one, but the severity of the effects

differ. Water systems can handle some extent of nutrient enrichment without it

having drastic consequences, but if the concentrations get too high it will become

a cause for concern. One of the water systems that is facing great problems

due to eutrophication is the Baltic Sea. For the past years, the countries, that

surround the Baltic Sea, have expressed great concerns about its environmental status (HELCOM, 2009). Eutrophication in the Baltic sea is one of the reasons for why the hyporheic zone, in its ascending streams, has been of interest for remediation actions and thus one of the reasons for conducting this project.

2.1.1 The Baltic Sea

The Baltic Sea is a 21.700 km

body of brackish water in Northern Europe. It has a mean depth of 52 m and it is the only inland sea in Europe. The countries that surround the Baltic Sea are Sweden, Finland, Denmark, Estonia, Latvia, Lithunia, Poland, Germany and Russia (HELCOM, 2009). Discharges from advanced agriculture and populated areas in the Baltic states have caused nutrient enrichment of N and P, that has resulted in eutrophication problems (HELCOM, 2009).

The Baltic Sea used to be a clear-water sea. However, in only one century it has altered to a highly eutrophic habitat HELCOM (2007). The Baltic sea is especially vulnerable to eutrophication because of limited water exchange with other seas and subsequently the high residence time. Furthermore, the water mass in the Baltic Sea is sometimes stratified due to different values of salinity, which reduces vertical mixing of waters and can cause oxygen depletion in certain layers (HELCOM, 2009).

There is consensus in the scientific community regarding the source, mechanism and impact of eutrophication in the Baltic Sea (HELCOM, 2009). The consequences of eutrophication include increased algal and plant growth. When this biomass decomposes, it results in an increased oxygen consumption which can cause decreased oxygen levels. This can eventually lead to the death of animals, which subsequently requires additional oxygen consumption. Hypoxia is therefore a severe problem in the Baltic sea and has negatively affected fish species, for example the cod, as well as benthic animals (Murray et al., 2019;

Morén et al., 2018). The areas in the Baltic sea that have the highest nutrient

concentration are in the Southwestern part. Those areas are about a 100 times

more densely populated than the Northern parts and have more agricultural

activities (HELCOM, 2009). There is therefore a direct link between population density, agriculture and nutrient loads.

Even though eutrophication is still causing problems in surface waters, coastal waters and open seas, average nitrogen loads have been decreasing within the majority of rivers within the EU. In Sweden, the average concentration of nitrate in rivers has reduced from 0.7 mg NO3-N/L in 1992 to 0.5 mg NO3-N/L in 2012.

In Denmark, nitrate loads reduced from 7.8 mg NO3-N/L in 1992 to 3.2 mg NO3- N/L in 2012 (EEA, 2015). This reduction can be traced back to the EU WFD, implemented in the year 2000, which is introduced further in chapter 2.1.2.

2.1.2 International Cooperation and Policies

The EU WFD establishes objectives for environmental quality. Article 4 states that, within the EU, waterbodies should have ’good ecological status’ and massively modified waterbodies should have ’good ecological potential’. As of 2018, about 40 % of surface waters can be considered to have ’good ecological status’ or ’good ecological potential’ and 38 % have ’good chemical status’ within the EU. The Baltic Sea states have been challenging the threat of eutrophication for decades. Their cooperation has mainly been under the Baltic Marine Environment Protection Commission, otherwise known as Helsinki Commission (HELCOM). HELCOM initiated a target-based plan in 2007 to reduce nutrients, known as the Baltic Sea Action Plan (BSAP) (HELCOM, 2009).

In 2007, Baltic states pledged to “achieve a Baltic Sea in good environmental status by 2021” (HELCOM, 2007, p. 5). The states aim for a Baltic Sea that is not affected by eutrophication. That includes clear water, nutrients at natural value, natural levels of algae blooms, oxygen at natural level and natural occurence and distribution of plants and animals (HELCOM, 2007, 2009). This is an important addition to support the EU WFD, as Russia is not a part of the EU but participates in HELCOM (Backer et al., 2010). According to Murray et al.

(2019), the goals of the BSAP are unrealistic, especially when the long retention

time of both water and nutrients is considered. Meaning that the effect of the

measures that are being implemented now will not be immediate. This has been

recognized by the HELCOM states, for example when the plan was revisited in 2013 and the countries implemented an ecosystem approach to management of human activities (Murray et al., 2019).

2.2 Stream Restorations

Stream restoration projects are as diverse as they are many. The projects vary in size and they depend on the ecological setting, what should be restored and the source of the problem (Degerman, 2008). Even though stream restoration projects can be different, they have some important properties in common. Multidisciplinary cooperation, good communication, long-term thinking and timely planning is necessary. Also, persistence is essential because the projects often span decades and the spatial scope can be enormous (Degerman, 2008).

Stream restorations are often conducted to improve the ecology of the river, where the fauna and flora are highlighted and certain species are for example used to determine the success (Rubin et al., 2017). In fact, according to a report from the Swedish Environmental Protection Agency and the Swedish National Board of Fisheries, fishing organization are often the ones pointing out the need for stream restoration, even though municipalities and authorities usually initiate this kind of projects (Degerman, 2008).

Streams are often restored to remove pollutants and thus improve water quality.

In order to control the effect of pollutants, nutrients and other reactive solutes in streams, the importance of the hyporheic exchange must be understood (Wörman et al., 2002). Streams and rivers transport pollutants, and thereof excess nutrients, from fields to receptors like seas and lakes (Riml et al., 2016).

As mentioned in chapter 1, about 50% of the nutrient pollution in the Baltic Sea can be traced to rivers and streams (Fölster et al., 2012; Naturvårdsverket, 2006).

Therefore, the retention of nutrients in these waterways is of great interest (Riml

et al., 2016).

2.2.1 Hyporheic Exchange

The transport of reactive solutes, such as nutrients and contaminants, can be managed by the exchange between the stream and the hyporheic zone. Substances can be stored temporarily by flow-induced uptake in the hyporheic zone and is primarily controlled by advection between surface waters and the hyporheic zone (Wörman et al., 2002; Gooseff et al., 2007). The hyporheic flow exchange occurs in the hyporheic zone, which is an interface area that connects the surface water flow and the aquifer groundwater flow (Boano et al., 2006; Gooseff et al., 2007).

It can be defined as the intersection where interchange of water and solute fluxes between shallow groundwater and surface water occur (Boano et al., 2006; Lautz et al., 2010). In the hyporheic zone, cycling of chemicals such as metals, carbons and nutrients occurs. This happens because the water and solutes mix within the hyporheic zone. The hyporheic zone is rich with biotically and chemically active sediment and with the mixing, the stream water meets the microbes in the hyporheic zone (Kiel and Cardenas, 2014). For biochemical reactions, as coupled nitrification and denitrification to occur, a low oxygen environment is needed.

In the hyporheic zone, oxygen is removed from the oxygen-rich stream water by microbially mediated heterotrophic respiration, creating this redox gradient (Morén et al., 2017b).

Hyporheic exchange is important for both lateral and vertical exchange between streams, groundwater and the floodplains (Boano et al., 2006; Kiel and Cardenas, 2014). However, for nitrogen mitigation in the hyporheic zone, the reduction potential is significantly higher for vertical exchange than for lateral exchange (Kiel and Cardenas, 2014). The exchange between groundwater and surface water can be controlled by stream morphology and topography (Wörman et al., 2006).

The exchange can also be driven by transient flow conditions, as stream-stage variations causes spatially and temporally distributed pressure in the stream bed (Maier and Howard, 2011).

Hyporheic exchange is as well induced by obstacles in the river, like meanders, riffles and steps (Gooseff et al., 2007). Generally, hyporheic exchange is caused by a variable pressure distribution on the streambed (Wörman et al., 2002, 2006).

This creates flow paths, as it forces water and solutes to infiltrate the hyporheic

zone at these increased pressure zones and leave the zone in a decreased pressure zone downstream (Wörman et al., 2002).

2.2.2 Restoration methods

When nutrients are being transported via streams and rivers, they can be retained under the right circumstances. By strategically planning the geomorphologic structure of the stream, nutrients can be withheld by filtering and chemical processes that occur in the stream bed, more accurately in the hyporheic zone of the stream (Riml et al., 2016). Hyporheic exchange can be induced by managing the outline of the stream and various different conditions can trigger the exchange of surface water and solutes with the hyporheic zone (Wörman et al., 2002).

In meandering rivers, hyporheic exchange can take place (Wroblicky et al., 1998;

Boano et al., 2014). In fact, direct connection has been shown between sinuosity and lateral hyporheic exchange in the bends of a meandering river and in the parafluvial zone (Wroblicky et al., 1998; Boano et al., 2006; Kiel and Cardenas, 2014). With meanders, hyporheic flow is induced and it affects the residence time in a stream by generating difference in elevation head at the bends (Boano et al., 2006; Stonedahl et al., 2013).

Hyporheic exchange can also occur when streamflow is interrupted by spatially

varied slopes or by an interference in the stream bed which induces mixing in the

hyporheic zone due to increased pressure upstream (Wörman et al., 2002). The

latter can be due to natural reasons, when so-called bedforms develop naturally

in the stream bed. That can be because of flow over loose sediments, due to

biotic processes or because of timber and stones in the stream (Wörman et al.,

2002). These interruptions can also be anthropogenic, when riffles and pools are

constructed or when a boulder or a log is placed in the river for this purpose.

(a) Vertical hyporheic exchange. (b) Lateral hyporheic exchange.

Figure 2.1: Hyporheic exchange, displayed in both plan and lateral view.

Riffles and pools are example of measures that can induce hyporheic exchange.

Developed from Hester and Gooseff (2010) and Morén et al. (2017b)

When streams are restored in order to induce hyporheic exchange, different restoration methods are applied depending on each situation, sometimes more than one. This is the case of Tullstorps brook, the site specific study that is used in this project and the measures are briefed in chapter 4. By retaining the nutrients, it subsequently results in reduced effects of eutrophication.

2.2.3 ASP-Model for analysis of measured data

Hyporheic exchange can be modelled by recreating observed BTC’s, which display the relationship between solute concentration and time, along a stream. The Advective-Storage-Path (ASP)-model is one model that describes solute transport and also takes into account the hyporheic exchange. In fact, it was brought forth by Wörman et al. (2002) to provide a better representation of the hyporheic exchange. Previous models, like the first-order exchange and the diffusive model, included simplification of the physical processes that occur in the exchange of surface water to the hyporheic zone (Wörman et al., 2002). This chapter explains the theory behind the model to the extent that is needed to be able to cross- reference certain parameters and equations when presenting and discussing the results of the project. The theory is thoroughly explained and derived in the papers from Wörman et al. (2002) and (Morén et al., 2017b).

The model includes several assumptions; it assumes steady state conditions,

complete mixing of the RWT and stream water and a geomorphologically stable

stream sediment bottom. A no-flow boundary is in the hyporheic zone at y = -ϵ

Morén et al. (2017b). The model is a combination of the equation for mass balance for solute in a stream and the equation for the net solute mass flux. From velocity in the stream and the residence time of a solute in the hyporheic zone, the ASP- model can estimate the distribution of solute mass (Wörman et al., 2002).

As explained by Morén et al. (2017b), there is a direct connection between the residence time in the hyporheic zone, T, the exchange velocity, W and the depth of the hyporheic zone, ϵ. The depth of the hyporheic zone is directly proportional to the residence time and inversely proportional to the velocity:

⟨T (x)⟩ = 2ϵ

⟨W (x)⟩ (1)

where ⟨T ⟩ is the average total residence time from inlet to exit of hyporheic flow path [s], ⟨W ⟩ is the average hyporheic exchange velocity [m/s] and ϵ is the depth of the hyporheic zone [m].

Along a stream, temporal solute transport, which includes the hyporheic exchange, can be described as:

∂C

(x, t)

∂t + U ∂C

(x, t)

∂x − E ∂

C

(x, t)

∂

x

= P

A J

(x, t) − r

C

(x, t) (2)

where C

[kg/m

] is the total concentration of solute in the stream, A [m

] is the cross-section of the stream, U [m/s] is the flow velocity in main channel, J

[kg/(sm

)]is the mass flux across the streambed interface, E is the longitudinal dispersion coefficient, P [m] is the wetted perimeter of the main channel, x [m] is the location along the reach, t [s] is time and r

[1/s] is the first-order reaction rate in the main channel. C

includes both the dissolved phase concentration, C

, and the adsorbed phase concentration, C

(Morén et al., 2017b).

Along a stream, continuity off mass in the hyporheic zone can be described

as:

∂G

η

∂t + ∂G

∂s = r

G

η (3)

where η [-] is the porosity in the sediments, r

[1/s] is the first-order reaction rate in the pore water of the hyporheic zone, G

= G

+ G

[kg/m

] is the total solute mass per volume pore water in the storage zone and G

stands for the dissolved phase and G

for the adsorbed phase.

According to Morén et al. (2017b), it is vital to be able to show the nitrate decay and the fact that the denitrification process in the hyporheic zone can only occur when the oxygen level is low enough in the hyporheic zone: “The first-order reaction rate in the pore water of the hyporheic zone r

(1/s) applies to both the dissolved and adsorbed phase, but takes the value 0 for 0 < τ < τ

and a finite positive value for τ

≤ τ ≤ T , where τ =

(s) is the time since an infinitely small solute parcel entered the hyporheic zone, T (s) is the total residence time along the specific streamline and τ

(s) is a minimum travel time after which reactions commence.”

(Morén et al., 2017b, p.8880) Finally, q

[m/s] is the constant Darcy velocity of water travelling along the curve-linear coordinate s [m]. Thus, the denitrification occurs during conditions when oxygen levels are low enough during the time of τ

< τ < T . Finally, the net solute mass flux between the stream water and the hyporheic zone in the sediments, which is the ASP-model, can be described as:

J

= 1

2 ⟨W (x)⟩

(

− C

(t) +

∫

0

G

(t, τ = T )f (T )dT )

(4)

With f(T), 4 allows to choose different residence time distributions. In this report,

exponential residence time distribution is used, as was done in the report from

Morén et al. (2017b), because “exponential distributions can be associated with

hyporheic exchange, specifically if the hyporheic zone is constrained by underflow

induced by the hydraulic head gradient.” (Morén et al., 2017b, p. 8881) The form

of residence time distribution is:

f (T ) = 1

⟨T ⟩ exp ( −T

⟨T ⟩ )

(5)

The solution of the model is developed from equations 2, 3 and 4. It is solved for a pulse injection of a solute that is injected at t=0 and x=0. By assuming that no reaction in the hyporheic zone, r

= 0, when 0 < τ < τ

and that no concentration of RWT is present in the stream at the time of injection, the solution of the model in the Laplace domain can be written as:

C

= M Q exp

[(

U 2E − (

( U

2E )

+ p

E + r

E − 1

2E P A

⟨W ⟩⟨T ⟩ (1 + K

(p + r

(1 + K

exp( −

(1 + (p + r

(1 + K

) ⟨T ⟩)

) x

] (6)

where Q [m

/s] is the flow in the main channel, M [kg] is the mass of the RWT solute, K

[-] is the main channel equilibrium partitioning constant equal to C

/C

, K

is the hyporheic zone equilbrium partitioning constant equal to G

/G

and p the Laplace parameter (Morén et al., 2017b).

2.2.4 Benefits and Costs of Stream Restorations

In general, projects aiming for restoration of ecosystems are seen as net-cost by

both the private and the public sector (Groot et al., 2013). However, it is often

due to the fact that cost-benefit analyses are limited or imprecise (Groot et al.,

2013). Another problem is the limited knowledge about the value of ecosystem

services and the consequences of loosing them (Pretty et al., 2003). The study by

Groot et al. (2013) concluded that the bulk of ecosystem restoration projects are

profitable when they looked at 225 case studies for various ecosystems projects

that included oceans, coral reefs, coastal systems, coastal and inland wetlands

and rivers and streams as examples. The monetary value of retaining nitrogen

loads in streams and receptors can be measured (Gren, 2008). The economic

benefits of nitrogen load abatement can be significant in terms of real estate value, seaside recreational activitites, Greenhouse gas (GHG) emissions, drinking water contaminations and ammonia induced air pollution (Andersen et al., 2019).

According to Pretty et al. (2003) the best method to evaluate the environmental cost of eutrophication is the Willingness To Pay (WTP) to avert damage and the WTA (Willingness to Accept) reimbursements for accepting the situation.

They investigated the damage cost of eutrophication in freshwaters in the UK and the main cause of costs were, for example, decrease in value of waterfront properties, costs of treating nitrogen for drinking water purposes and decrease in recreational and tourist opportunities (Pretty et al., 2003). The WTP for reduced eutrophication in the Baltic Sea has been investigated for all 9 countries that have coastline to it. It showed that the WTP was highest amongst the Swedish population and lowest in Latvia, they estimated it was partially due to the fact that Sweden has a long coastline connected to the Baltic Sea (Ahtiainen et al., 2014).

One of the biggest obstacles for nutrient reduction in streams is that the projects are often long-term and spread over a large geographic area (Degerman, 2008).

It can therefore be difficult to see immediate benefits because the result is often neither regional nor immediate. Nevertheless, economic benefits from reducing N loads have been researched in terms of seaside estates and coastal recreation. A new study in Danish coastal areas used Secchi-depth, i.e. water clarity, to connect with nutrient loads. The more nitrogen content, the lower the Secchi-depth gets.

(Andersen et al., 2019). The study came to the conclusion that it is important to tailor nutrient reduction to each scenario in order to ensure economic benefits.

Each specific coastal area has different needs in terms of ecological, human and

physical circumstances (Andersen et al., 2019).

3 Methods

This chapter describes the methods that were used to answer the research questions described in chapter 1.2 and explains why these methods were chosen.

Figure 3.1 explains how the methodological approach is linked to each research question.

Figure 3.1: Flow chart illustrating which methods were used to reach the objectives.

3.1 Site Specific Field Measurements

Site specific field measurements were conducted in a small agricultural stream in the south of Sweden. The purpose of the measurements was to answer research question 1 and 2. The surface water modelling, with the ASP model (Wörman et al., 2002), were then necessary to analyze the measurements and model the results.

3.1.1 Study Area

Tullstorps brook, a small agricultural stream in southern Sweden was chosen for doing fieldwork in this project. The reasons for choosing this stream are threefold.

First, it is well suited for estimating the retention of nutrients in streams and the effect of restoration because when focusing on water quality in remediation projects, small agricultural streams are usually targeted (Morén et al., 2018).

Second, Tullstorps brook does not contain any lakes on its way to the Baltic Sea

and it has been measured with high level of nutrient pollution (Riml et al., 2016).

Third, it was chosen because previous hydraulic field measurements have been conducted in the area, thus making it suitable for comparison studies (Morén et al., 2017a).

3.1.2 Comparison data

Measurements were done in 2015 in the goal reach and nonremediated parts of the stream (Morén et al., 2017b), that now have been restored (Sörensen, 2019).

Therefore, there is a need for quantifying the effect of the restoration on water quality.

3.1.3 Tracer tests with RWT

To evaluate the solute transport in the stream, RWT tracer tests were conducted.

The equipment that was used was a Cyclops-7 submersible sensor conncected to a

DataBank handheld datalogger (Turner Designs, Inc.). The equipment and RWT

injection is displayed in figures 3.2a-3.2c.

(a) Cyclops-7 submersible sensor during calibrations (Turner Designs, Inc.).

(b) Injection point in Reach 4, shortly after injection of RWT.

(c) Databank handheld logger (Turner Designs, Inc.).

Figure 3.2: The equipment used for tracer test injections and a RWT injection in Tullstorps brook.

The tracer tests were performed in a manner so that specific characteristics of Reach 4 and Reach 6 could be estimated. Tracer test bring forth integrated results for all the transport pathways in the stream, thus giving a holistic idea of the solute transport in the stream (Morén et al., 2017a). From the samples, BTC were detected, where concentration is plotted against time (Riml et al., 2016). RWT is a fluorescent dye tracer that is is widely used in hydrological investigations. It is well suited for conducting tracer test in streams because it can be dissolved in water, it is easily observed as it is immensely fluoroscent (Wilson et al., 1986).

The dye is a conservative tracer and should therefore not degrade significantly

on its path. This can be confirmed by integrating the original BTC, and the value of concentration under the curve multiplied with the discharge during the measurement should give the mass of concentration that was injected. RWT can, however, degrade faster when exposed to sunlight (Bechtold et al., 2012).

That is why it is good to do the tracer test in the evening. That can also prevent unnecessary concern from residents that see a strange color in the stream. RWT releases light on a spectrum that is not commonly found in normal waters and is thus not affected by other fluorescents in the environment. Furthermore, when released in small dosages, RWT does not cause harm to the environment as is further described in chapter 3.1.4 (Wilson et al., 1986).

3.1.4 Risk Analysis

When injecting chemicals into a natural environment, in order to investigate, it is important to consider the ecotoxicity potential (Field et al., 1995). That is, that the researcher does not cause harm or induce irreversible changes to the environment under examination. The threshold of concentration of RWT harmfulness in drinking water has been researched. Field et al. (1995) came to the conclusion that the concentration of RWT would not be harmful to humans if it is lower than 2 mg/L. For smaller creatures that inhabit streams and rivers, dosages down to 0.01 mg/L showed some response but did not have negative affect as the creatures adapted quickly to the new environment (Rowiński and Chrzanowski, 2011).

The maximum concentration that was obtained during the tracer test was 0.423 mg/L for the injection in Reach 4 and 0.238 mg/L for the injection in Reach 5 and Reach 6. The exposure time of high concentrations is short, i.e. short time of the peak. For the upstream logging site in Reach 4, RWT concentration was

>0.1 mg/L for the duration of 11 minutes and >0.01 mg/L for the duration of 24

minutes. This can be observed in figure 3.3. It should be noted that because the

stream that was studied in this project is neither used for recreational activities

nor for drinking water purposes, thus the risk to human health is even smaller

(Riml et al., 2016).

Figure 3.3: RWT concentration at the upstream logging site at Reach 4.

3.1.5 HC measurements

HC is one of the hydraulic functions that can affect hyporheic exchange (Hester and Gooseff, 2011). It goes without saying that if the stream sediments have low permeability, the water cannot penetrate through the flow-paths of the hyporheic exchange as easily as if it is high, and that is why it is important to investigate it.

HC studies have been conducted in the stream recently, for example by Riml et al.

(2016). Nevertheless, the stream reaches have been restored since then. Thus,

there is a need for new measurements to see if any changes in the parameter can

be observed. Some restoration measures can include replacing soil, changing the

alignment of the cross-sections of the river or other factors that could affect the

HC. Furthermore, the restoration measures might have caused deceleration of

the river flow, which intensifies sedimentation and subsequently affects the HC

(Riml et al., 2016). Therefore, it is useful to compare the new measurements to

the existing ones to see if any significant changes can be observed.

3.2 Additional Stream Characteristics

Along with the RWT tracer tests and the HC measurements, other characteristics of the stream were observed. The depth, d, and width, w, of the stream were measured in 4 cross-sections in Reach 4 and in 5 cross-sections in Reach 6. For Reach 5, the depth was measured every 0.5 m because additional topographical measurements were done in that reach every 0.5 m. Those measurements are not considered in this project due to time constraints. The estimated flow in the stream, Q, during the measurements was obtained from the HYPE model from Swedish Meteorological and Hydrological Institute (SMHI). The length of the stream, x, was measured from with the help of GPS points and ArcGIS and is determined from the length from cyclope at Site 1 to the cyclope at Site 2 in each Reach. The slope of the stream, S

was evaluated from maps from the Swedish Geological Survey, SGU, for the 2015 measurements. The slope for the 2019 measurements was not estimated because there are should not be any changes when the whole reach is considered,

3.3 Physical Model

When predicting the effect of stream restoration measures, a mathematical formulation of the solute processes is needed. A physical model can enhance the comprehension of the physical processes that occur in hyporheic exchange. The software that was used in this projects was Matlab and ArcGIS. The purpose of using ArcGIS was solely to create maps of the study area. That is, the program was not used for any analysis purposes. Matlab, however was used for optimisation to analyse and generate results by using inputs from the field measurements. The model that the analysis is based on is called the ASP-model and the theory behind it has been described in chapter 2.2.3.

The model was optimised with calibration where the parameters in the model

where altered to revise the model fit against the measured values. By minimizing

the difference between the measured and modelled values, the model parameters

can be optimized as equation 7 displays.

θ = ˆ arg min

θ

( 1 N

( ∑

i⊂NA

(C

(θ) − C

)

(max(C

) − min(C

))

+

∑

i⊂NB

(log(C

(θ)) − log(C

))

(max(log((C

)) − min(log(C

)))

))

(7)

where, ˆ θ is the least square estimates of the model parameter θ. C

is the modelled concentration and C

is the measured concentration in Tullstorps brook. N = N

+N

is the number of observed values, N

is the observed values in group A and N

is the number of observations in group B (Riml et al., 2013).

In this project, focus is set on the hyporheic exchange when optimising the parameters in the BTC’s. According to Wörman and Wachniew (2007), the hyporheic exchange parameters are the ones who have the biggest impact on the tail of the BTC. As the peak in the BTC can reach a high value compared to the values in the tail, the root mean square error was expressed on a logarithmic scale to a certain extent. This was done by having all concentration values that were lower than 20% of the peak concentration on a logarithmic scale (observations in group B) and the rest on a linear scale (observations in group A). Thus, the details in the tail are included in the optimisation.

Matlab script files from Morén et al. (2017b) and Wörman et al. (2002) were used to analyse the collected fieldwork data. A Matlab script file, developed by Hollenbeck (1998), was used for the numerical transform inversion of Laplace, based on the de Hoog algorithm.

3.4 Literature review

A literature review was conducted to attempt to answer the research question 3,

Can stream restoration projects be financially beneficial for stakeholders?. The

aim of this review was to get a rough estimate of whether stream restoration can be

financially beneficial for municipalities, the government and other stakeholders or

if they are seen as a financial burden. A large part of the references that were used

are published and reviewed articles. However, when presenting results from the

Tullstorps brook project, reports such as construction plans, estimation of value of ecosystem services and descriptions of the area were used. It should be considered that those report are not published and have not been reviewed and they are therefore analysed with that in mind. To put the projects in context, directives and goals from international cooperation through the EU and the countries that have shorelines along the Baltic sea, called HELCOM, were analyzed.

3.5 Interviews

Interviews were conducted to provide evidence for research questions 1 and 3.

To be able to answer research question 1, it was necessary to interview the project coordinator for the Tullstorps brook project. That interview allowed triangulation of the accuracy of available information on the project. It also made sure that all information was up to date in this ongoing project.

The other interview served as triangulation of data for research question 3 and to get reflections on matters of the subject in general. The focus in that interview was on the general aspects of stream restoration and eutrophication, as well as the cost-benefit, monitoring and other practical aspects of stream restoration projects. When respondents for the interviews were gathered, the emphasis was not on having multiple respondents, but rather to have in-depth interviews that could produce evidence and reflections of high quality (Dalen, 2011).

The interview length ranged from being 45-65 minutes long and were conducted face-to-face. In total, 2 interviews were conducted. Even though Rowley (2012) suggests about 6-8 interviews of this length, she still states that this is dependant on each and every thesis. In this thesis, the interviews are not the main methods and serve as reflections and data gathering, and not to identify any pattern, which require a large number of interviews.

3.5.1 Interview guide

The interviews that were conducted were semi-structured. This is the most

common way of conducting interviews for research (Rowley, 2012). For an

inexperienced researcher, Rowley (2012) states that a semi-structured interview should consist of 6-12 questions that have a certain order. Those questions can then include some sub-questions. According to Bryman (2016), it is good to prepare themes in a semi-structured interview. Themes allow for more discussions within each theme, without loosing the thread of the interview (Bryman, 2016). It is vital to prepare particular themes beforehand to make sure that the interview is directly connected to the objectives (Dalen, 2011). Therefore, an interview guide with different themes was prepared, with individual questions for each theme.

As stated earlier, two separate interview guides were prepared. For the interview regarding the Tullstorps brook project, the project coordinator was interviewed.

There was need to prepare a separate interview guide just for that interview, as it served a different purpose, to get more detailed information about the study area.

For the Tullstorps brook interview the themes that were used were:

• Background questions

• Tullstorps brook project - The beginning

• Tullstorps brook project - What has been done?

• Tullstorps brook project - Next steps

• Tullstorps brook project - Future of the project

• Tullstorps brook project - General

• Cost-benefit of stream restoration projects

For the other interview, the guide was much more general and broad. The themes allowed for reflections on the topic of eutrophication and stream restorations, without much restrictions. To be able to find evidence that related to research question 3, the interview was narrowed down to cost-benefit and monitoring. The themes that were used for that interview were:

• Background questions

• Eutrophication - Baltic Sea

• Stream restoration - in general

• Monitoring of stream restoration in Sweden

• Cost-benefit of stream restoration projects

• Guidelines for stream restoration in Sweden

Even though both interviews were semi-structured, the interviews varied from one interview to the other. This was because each interviewee had different competences and background and the interviews were adjusted to each situation.

Different interview guides were used for the case study and for the more general interview. The interview guides can be found in Appendices A and B. However, it should be noted that as it was a semi-structured interview, some questions were added later to reflect on discussions that arose during the interview.

3.5.2 Data analysis of interviews

All interviews were recorded and then transcribed. According to Rowley (2012), it is good practice to send the transcript to the interviewee for them to review it.

This was done, with the purpose of allowing the interviewee to add or retract any information. There are a few key components that are necessary when it comes to data analysis of interviews. They are: “organizing the data set; getting acquainted with the data; classifying, coding, and interpreting the data; and, presenting and writing up the data” (Rowley, 2012, p.268).

First of all, the data set was organized by transcribing each interview in a separate

document. Next, when getting acquainted with the data, the transcripts were

read thoroughly and connected to the themes that were described in Chapter

3.5.1. When classifying, coding and interpreting the data, the themes were each

given a different colour to be able to draw together answers that were related in

the interview. Whilst this was done, text that was evaluated as irrelevant to the

thesis project was removed. The interview interpreting is tricky, as it can easily

become biased. Therefore, the data from the interviews was treated as “insights,

perspectives, and questions for further research” (Rowley, 2012, p.269), rather

than as findings.

4 Field Measurements in Tullstorps Brook

Site specific field measurements were conducted in three reaches in Tullstorps brook, a small agricultural stream in the south of Sweden. The new field measurements were compared to previous measurements, done by Morén et al.

(2017a) in 2015, before the targeted reaches in Tullstorps brook were restored.

The methods used for the field measurements and the analysis of the results are also based on the work done by Morén et al. (2017a) and will be further briefed in Chapters 4.1-4.6.

4.1 Tullstorps Brook

Tullstorps brook is situated in Southern Sweden, more specifically in Trelleborg

municipality in the county of Skåne. The brook is about 25 km long (Sörensen,

2019) and its catchment area covers 6300 ha. It has its origin in Alstad and flows

into the Baltic Sea to the South at Skateholm (Tullstorpsån, 2019). The location

of the brook is displayed in figure 4.1

¯

Catchment Area Tullstorps Brook

0 0.751.5 3 4.5 6Kilometers

Figure 4.1: Location of Tullstorps brook and its catchment in Skåne.

The catchment of Tullstorps brook is located in an area that has a great deal of agricultural activities. In fact, about 85 % of the area can be considered arable land. It has been modified to a large extent in the past, where the brook was straightened and lowered and ditches were built around the fields to have quick runoff from fields to the brook. The stream has had problems with high nutrient loads and the brook is estimated to discharge about 250t of nitrogen and 4t of phosphorus to the Baltic Sea and it is considered to have poor ecological status (Tullstorpsån, 2019). The brook has had problems with erosion due to steep banks in its modified reaches. The modified reaches in the river channel lack variations of deep and shallow areas, that could serve as habitats for animals and plants (Tullstorpsån, 2019). Due to these problems, it has been the target of significant remediation measures, starting already in 2009 (Olofsson, 2017).

In 2009, an organisation was formed around the remediation actions, called

Tullstorpsåprojektet. According to Katrine Sörensen (2019), the project manager

of Tullstorpsåprojektet, the project had an interesting start, as it was initated by

the local landowners:

It started out when some of the farmers in the catchment were interested in doing wetlands and then there was a guy working at the municipality who was helping them out, and then he saw that there were a lot of people interested, so why not do a project that could involve all of us. Then he met Otto, the chairman who is a politician. He is really into environmental issues and he thought that we should have one big project with a holistic approach instead of having many small ones. He was the main driver in making this project what it is today; a big project where all the landowners stand together.

(Sörensen, 2019)

The people behind the project were also convinced that it was a good time to kickstart an environmental project like this one, since funding was available and no legislation had been implemented yet:

He [Otto] also understood the idea of the whip and the carrot, whereas right now there is a big carrot when doing environmental measures.

They were a bit afraid that if they did not do it now, then later on the farmers would be having more regulations regarding how they produce on the field etc. (Sörensen, 2019)

The aim of the projects is to improve the ecological status and the water quality of Tullstorps brook, as well as to avert flooding and erosion (Morén et al., 2017a).

The main purpose of the project was to increase the status of the stream in order to get ‘good status’, according to the WFD (Sörensen, 2019).

4.2 Remediation Actions in Tullstorps Brook

According to the project manager, Sörensen (2019), about 11 km of the brook have

been remediated and about 148 ha of wetlands have been created. An additional

5.5 km of the upper part of the stream is planned for restoration in the coming

years and the goal is to create a total of 220 ha of wetlands. The restoration of the

next part of the stream should start already next year (Sörensen, 2019). According

to weekly water samples that have been taken in the river throughout the project,

the total nitrogen concentration has gotten lower during the summer months by