Diatoms are microscopic, photosynthetic, single-celled organisms that are useful in studies of water qualities (eg pH, nutrients, salinity). By analyzing changes in the species composition of diatoms back in time, gives an opportunity to interpret the marine environment affected by various factors (Andren et al, 1999). The aim of the study was to study changes in diatom abundance and composition in Hallsfjärden, a bay in the Baltic Sea located north of Himmerfjärden in Södertälje. The site was chosen because it is a bay that is assumed to have a large environmental impact due to external factors such as increased population growth, water treatment plants, industrial areas, dredging and a link to Lake Mälaren. The purpose of the study therefore to investigate whether there was an environmental impact in Hallsfjärden, in order to draw conclusions about what happened in the area and what has affected the water the last 100 years.      The survey is conducted by sampling sediment cores, studied by biostratigraphy of fossil diatoms to reconstruct past environmental conditions. The results of the analysis showed that oxygen deficiency was a particular problem, which is related to the eutrophication that are threatening some diatoms and thereby changes the species composition of ecosystems in Hallsfjärden. A plausible interpretation of the analyze results is that Hallsfjärden was adversely affected by the Södertalje area's population growth and Himmerfjärdsverkets startup by high emissions of nutrients. It has on the other hand appeared a positive impact for Himmerfjärdsverkets gradually improved purification with clearer water conditions. Hallsfjärden have proved to be a particularly sensitive ecosystem in this study, with low salinity and strong thermocline, which means that it is more affected by eutrophication and pollution in its drainage area. This causes a problem of eutrophication in Hallsfjärden due to the bay showing the influence of the surrounding areas and its emissions, which later exports further to the Baltic Sea via Himmerfjärden with the southbound flow. / Kiselalger är mikroskopiska, fotosyntetiserande, encelliga organismer som är användbara vid studier om vattenkvalitéer (till exempel pH, näringsämnen, salthalt). Genom att analysera förändringar i artsammansättningen av kiselalger bakåt i tiden kan tolkningar göras om hur havsmiljön påverkats av olika faktorer (Andrén m.fl., 1999). Målet med studien var att studera förändringar i kiselalgernas förekomst i Hallsfjärden, en havsvik i Östersjön belägen norr om Himmerfjärden i Södertälje. Platsen valdes för att det är en havsvik som antas ha stor miljöpåverkan på grund av yttre faktorer såsom en ökad befolkningstillväxt, reningsverk, industriområden, muddring och en kontakt med sjön Mälaren. Syftet med studien var därmed att undersöka om en miljöpåverkan fanns i fjärden, detta för att kunna dra slutsatser om vad som hänt samt vad som påverkat vattenområdet de senaste 100 åren.      Undersökningen är utförd genom provtagning av sedimentkärnor som undersökts avseende biostratigrafin av fossila kiselalger för att rekonstruera tidigare miljöförhållanden. Analysresultatet visade att syrebrist var ett utmärkande problem, vilket i samband med eutrofiering hotar vissa kiselalgsarter och förändrar därmed artsammansättningen i ekosystemen i Hallsfjärden. En sannolik tolkning av analysresultatet är att Hallsfjärden påverkats negativt av Södertäljeområdets befolkningstillväxt och Himmerfjärdsverkets uppstart genom höga utsläpp av näringsämnen. Det har å andra sidan synts en positiv inverkan efter Himmerfjärdsverkets successivt förbättrade rening med klarare vattenförhållanden. Hallsfjärden har i studien visat sig vara ett särskilt känsligt ekosystem med låg salthalt och starka språngskikt, vilket gör att det påverkas mer av eutrofiering och föroreningarna i området. Detta medför en övergödningsproblematik i Hallsfjärden, då fjärden visar en påverkan av omkringliggande områden och dess utsläpp av föroreningar, vilka även sedan exporteras ut i Östersjön via Himmerfjärden med den sydgående strömmen.

A sediment core from Himmerfjärden estuary, south of Stockholm, was examined to detect records of eutrophication on the site since the opening of the sewage treatment plant Himmerfjärdsverket in 1974. The core was analysed with respect to the diatom record and lithology. Four macrofossil that were found in the sediment were dated using 14C-dating.    This study aims to detect changes in the environment of Himmerfjärden by using the diatom stratigraphy record. The results have been interpreted and discussed regarding natural environmental and climate change and/or anthropogenic impact, and detected changes will be associated with the history of the sampling site. The results show that the lowermost zone started to deposit around 1300-1490 cal yr BP and the homogeneous sediment indicates that the area was not suffering from hypoxia at that time. There is a successive transition towards more distinct lamination further up in the core which show that the environment in Himmerfjärden have changed and become hypoxic. This may have to do with factors such as the opening of heavily trafficked Södertälje Canal, and also the increased nutrient input from Himmerfjärdsverket.    This study could be a part of the process of working towards a “good environmental status” in the Baltic Sea. However, continued and improved work is needed for further and more accurate interpretations.

<p>Naturvårdsverket rankar övergödningen som det allvarligaste hotet mot Östersjön. Strategin för att bekämpa övergödningen i Östersjön har varit att reducera antropogena utsläpp av fosfor och kväve från punktkällor och diffusa källor. Många forskare anser att primärproduktionen i egentliga Östersjön huvudsakligen är begränsad av kväve varför Sverige har infört ett ambitiöst och kostsamt program för avancerad kväverening på reningsverk. Andra experter hävdar istället att reducerade kväveutsläpp är meningslösa eller rent av skadliga.</p><p>I ljuset av dessa fundamentalt olika åsikter och de helt motsatta strategier de innebär syftar denna studie till att försöka klargöra vilka åtgärder som borde vidtas för att minska övergödningen genom att undersöka området Himmerfjärden som ofta används som ett exempel på lyckad kväverening. Området har också studerats intensivt sedan 1970-talet.</p><p>Detta arbete har använt en processbaserad dynamisk massbalansmodell för salt för att beräkna vattenutbytestider i Himmerfjärden. Flöden av vatten och näringsämnen till och från fjärden har beräknats och det har visats att bidraget av kväve och fosfor till Himmerfjärden från reningsverket är mycket marginellt jämfört med bidraget från Östersjön.</p><p>Denna studie har också genom att granska litteratur och mätdata från Himmerfjärden visat att det finns goda skäl att ifrågasätta hypotesen om att primärproduktionen i Himmerfjärden skulle vara långsiktigt begränsad av kväve. Resultaten av denna studie kommer att användas i framtida massbalansmodelleringar av fosfor, kväve och cyanobakterier i Himmerfjärden.</p> / <p>The Swedish Environmental Protection Agency has ranked eutrophication as the most severe threat to the Baltic Sea. The strategy to combat the eutrophication in the Baltic has been to reduce antrophogenous emissions of phosphorus and nitrogen from point and diffuse sources. Many scientists argue that the primary production in the Baltic proper is primarily limited by nitrogen which is why Sweden and other countries have implemented an ambitious and expensive program of advanced nitrogen removal in sewage treatment plants. Other experts argue that reduced nitrogen load to the Baltic Sea is either pointless or even harmful.</p><p>In the light of these fundamentally different views and the very opposite management strategies they imply, this study aims to more bring clarity to which measures should be taken to reduce eutrophiction by investigating the area of Himmerfjärden. Himmerfjärden is often used as an example of successful removal of nitrogen and the area has been intensively monitored since the 1970’s.</p><p>This work used a process-based dynamic mass balance model for salt to calculate water retention times in Himmerfjärden. Water and nutrient flows to and from the bay have been calculated. It was shown that the contribution of nutrients to Himmerfjärden from the treatment plant is small compared to the contribution from the Baltic Sea.</p><p>This study showed by reviewing literature on Himmerfjärden that there are good reasons to question the hypothesis of Himmerfjärden being nitrogen limited in the long-run. The findings of this study will be used in future mass balance modelling of phosphorus, nitrogen and cyanobacteria in Himmerfjärden.</p>

Naturvårdsverket rankar övergödningen som det allvarligaste hotet mot Östersjön. Strategin för att bekämpa övergödningen i Östersjön har varit att reducera antropogena utsläpp av fosfor och kväve från punktkällor och diffusa källor. Många forskare anser att primärproduktionen i egentliga Östersjön huvudsakligen är begränsad av kväve varför Sverige har infört ett ambitiöst och kostsamt program för avancerad kväverening på reningsverk. Andra experter hävdar istället att reducerade kväveutsläpp är meningslösa eller rent av skadliga. I ljuset av dessa fundamentalt olika åsikter och de helt motsatta strategier de innebär syftar denna studie till att försöka klargöra vilka åtgärder som borde vidtas för att minska övergödningen genom att undersöka området Himmerfjärden som ofta används som ett exempel på lyckad kväverening. Området har också studerats intensivt sedan 1970-talet. Detta arbete har använt en processbaserad dynamisk massbalansmodell för salt för att beräkna vattenutbytestider i Himmerfjärden. Flöden av vatten och näringsämnen till och från fjärden har beräknats och det har visats att bidraget av kväve och fosfor till Himmerfjärden från reningsverket är mycket marginellt jämfört med bidraget från Östersjön. Denna studie har också genom att granska litteratur och mätdata från Himmerfjärden visat att det finns goda skäl att ifrågasätta hypotesen om att primärproduktionen i Himmerfjärden skulle vara långsiktigt begränsad av kväve. Resultaten av denna studie kommer att användas i framtida massbalansmodelleringar av fosfor, kväve och cyanobakterier i Himmerfjärden. / The Swedish Environmental Protection Agency has ranked eutrophication as the most severe threat to the Baltic Sea. The strategy to combat the eutrophication in the Baltic has been to reduce antrophogenous emissions of phosphorus and nitrogen from point and diffuse sources. Many scientists argue that the primary production in the Baltic proper is primarily limited by nitrogen which is why Sweden and other countries have implemented an ambitious and expensive program of advanced nitrogen removal in sewage treatment plants. Other experts argue that reduced nitrogen load to the Baltic Sea is either pointless or even harmful. In the light of these fundamentally different views and the very opposite management strategies they imply, this study aims to more bring clarity to which measures should be taken to reduce eutrophiction by investigating the area of Himmerfjärden. Himmerfjärden is often used as an example of successful removal of nitrogen and the area has been intensively monitored since the 1970’s. This work used a process-based dynamic mass balance model for salt to calculate water retention times in Himmerfjärden. Water and nutrient flows to and from the bay have been calculated. It was shown that the contribution of nutrients to Himmerfjärden from the treatment plant is small compared to the contribution from the Baltic Sea. This study showed by reviewing literature on Himmerfjärden that there are good reasons to question the hypothesis of Himmerfjärden being nitrogen limited in the long-run. The findings of this study will be used in future mass balance modelling of phosphorus, nitrogen and cyanobacteria in Himmerfjärden.

In the Himmerfjärden Bay a large excess of nitrogen over phosphorus in the discharge from a large sewage treatment plant (STP) has suppressed growth of diazotrophic cyanobacteria in its inner parts. Implementation of nitrogen removal in the STP in 1997 drastically reduced nitrogen load and triggered growth of diazotrophs, mainly Aphanizomenon sp. This study is part of a long-term series of experiments with the overall aim to test how algal biomass and production in a receiving area can be reduced, without stimulating nitrogen fixation and biomass growth by diazotrophic cyanobacteria. Nitrogen removal was discontinued in the STP during two years (2007-8) and resumed in 2009, and the discharge shifted from 25 to 10 m depth, above the seasonal pycnocline. Cellular 15N showed that N2 was the most important N source for diazotrophic cyanobacteria, and that uptake of combined nitrogen was insignificant. As biomass was declining and at the end of the productive season, we could detect a small, but significant, increase in cellular δ15N at the inner bay stations (H3 and H4). However, this coincided with an increased proportion of Anabaena spp. of the total diazotrophic biomass. This may indicate that Anabaena spp. has a higher uptake of combined nitrogen compared with Aphanizomenon sp. or that declining populations of Aphanizomenon sp. take up combined nitrogen. We also found no evidence of uptake of combined nitrogen during the winter months when nitrogen supply is ample and Aphanizomenon sp. is devoid of heterocysts. During the first half of summer (week 21-27) heterocyst frequencies were higher at the outer stations B1 and H2, compared to the inner bay stations (H4 and H5). The lower frequencies at the inner bay stations are likely due to the reduced growth rate suffered by the Aphanizomenon sp. due to stronger competition for phosphorus by non-diazotrophs at these stations and hence lower need for heterocysts. Towards the end of summer conditions even out along the bay, as the surplus phosphorus from the spring bloom is used up at the outer stations and no heterocyst gradient is present. Heterocyst frequency varied significantly over the summer, with minimum values in the beginning of July, coinciding with the highest water temperatures, and higher frequencies in early and late summer. We suggest this is primarily due to a more efficiently functioning nitrogenase enzyme at high temperatures with a reduced need for “expensive” heterocysts. Spring heterocyst differentiation occurred around 4-6 weeks after depletion of dissolved inorganic nitrogen (DIN) and only when water temperature was 5-9 oC and a pycnocline established. It seems that temperature and light in concert will initiate growth, leading to an internal nitrogen deficiency which starts heterocyst differentiation. / Himmerfjärden eutrophication study

Folketshus är en plats där olika idéer och intressen möts. Genom att placera en multifunktionell byggnad på landsbygden vid en industri, skaps möjligheter för möten där folket kan uppleva sammankomsten mellan naturen och industrin. Urbaniseringen kräver massiva industrier för att samhället skall kunna fungera. Men hur det påverkar  det landsbygden?      Himmerfjärdsverket är ett avloppsreningsverk vid ett kustområde med sommarstugor på landsbygden, och ligger ca en timme från Stockholms innerstad. Med sina unika förutsättningar ligger den stora industrin isolerat mitt i ett vackert naturområde. För att uppmärksamma industriers effekt på miljön vägleds folket i området genom en stig som leder från vägen till reningsverket och vidare ner till kusten där den landskapsformade betongbyggnaden står. Landskapet förlängs och integreras i byggnaden genom ett lutande tak och öppningar i bjälklaget som synliggör våtmarken under. Samspelet mellan utomhus inomhus präglar konceptet genom fristående rum under det stora betongtaket. Byggnaden ger möjligheter för utbildning, forskning och övernattning med ett vandrarhem som tillgängliggör landsbygden för alla. / The community house is where different ideas and interests meet. By placing a multifunctional building in the rural by an industry, meeting opportunities are created for people to see the encounter between the nature and the industry. Urbanism requires massive industries for the society to function. But how does this affect the rural? Himmerfjärdsverket is a sewage treatment plant by a coastal area with summer cottages in the countryside, located one hour from Stockholm city. With its unique conditions, the industry is isolated in a beautiful nature site. To raise awareness on the industrial impact on the environment, people are lead through the site by a path that leads from the road till the treatment plant and down to the coast where the landscape shaped building is located. The landscape is extended and integrated in the building, with a leaning roof and openings in the slab that is connecting the inside, to the wetland under. The interaction between the outside and inside have influenced concept. The building opens opportunities for education, research and a hostel which makes the rural available for everybody.

This PhD study focusses on the use of MEdium Resolution Imaging Spectrometer (MERIS) data for reliable and quantitative water-quality assessment of optically-complex waters (lake, brackish and coastal waters). The thesis is divided into two parts: A. intercalibration of reflectance measurements in different optically-complex water bodies (Paper I), and validation of various satellite processing algorithms for the coastal zone (Paper II). B. Applications: the use of MERIS data in integrated coastal zone management mostly using Himmerfjärden bay as an example. Himmerfjärden bay is one of the most frequently monitored coastal areas in the world and it is also the recipient of a large urban sewage treatment plant, where a number of full-scale nutrient management experiments have been conducted to evaluate the ecological changes due to changes in nutrient schemes in the sewage plant. Paper I describes the development and assessment of a new hyperspectral handheld radiometer for in situ sampling and validation of remote sensing reflectance.  The instrument is assessed in comparison with readily available radiometers that are commonly used in validation. Paper II has a focus on the validation of level 2 reflectance and water products derived from MERIS data. It highlights the importance of calibration and validation activities, and the current accuracy and limitations of satellite products in the coastal zone.  Bio-optical in situ data is highlighted as one of the key components for assessing the reliability of current and future satellite missions. Besides suspended particulate matter (SPM), the standard MERIS products have shown to be insufficient to assure data quality retrieval for Baltic Sea waters. Alternative processors and methods such as those assessed and developed in this thesis therefore will have to be put in place in order to secure the success of future operational missions, such as Sentinel-3. The two presented manuscripts in the applied part B of the thesis (paper III and IV), showed examples on the combined use of in situ measurements with optical remote sensing to support water quality monitoring programs by using turbidity and suspended particulate matter as coastal indicators (manuscript III). The article also provides  a new turbidity algorithm for the Baltic Sea and a robust and cost-efficient method for research and management.  A novel approach to improve the quality of the satellite-derived products in the coastal zone was demonstrated in manuscript IV. The analysis included, the correction for adjacency effects from land and an improved pixel quality screening.  The thesis provides the first detailed spatio-temporal description of the evolution of phytoplankton blooms in Himmerfjärden bay  using quality-assured MERIS data, thus forwarding our understanding of ecological processes in in Swedish coastal waters. It must be noted that monitoring from space is not a trivial matter in these optically-complex waters dominated by the absorption of coloured dissolved organic matter (CDOM). These types of coastal waters are especially challenging for quantitative assessment from space due to their low reflectance.  Papers III and IV thus also provide tools for a more versatile use in other coastal waters that are not as optically-complex as the highly absorbing Baltic Sea waters. The benefits of the increased spatial-temporal data coverage by optical remote sensing were presented, and also compared to in situ sampling methods (using chlorophyll-a as indicator). / <p>Research funders:</p><p>European Space Agency (ESA, contract no.21524/08/I-OL)</p><p>NordForsk funding: Nord AquaRemS Ref. no. 80106</p><p>NordForsk funding:  NordBaltRemS Ref.no. 42041</p><p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>