Dam construction in lakes may have significant negative effects on aquatic ecosystems, and it is therefore considered as a major threat to aquatic biodiversity. Many studies have been conducted to investigate how fish are affected by dam removal. Dams can impact the flora and fauna of lakes by influencing the structure of food webs and nutrient dynamics. In this study, I investigated whether or not dam removal in lake outlets affect the proportion of piscivorous perch, including a separate analysis of perch with lengths between 120-180 mm (the length interval at which the diet changes from insects to fish). I used data from 27 lakes located in Värmland, Dalarna and Västmanland. The proportion of piscivorous perch was 43% higher where the dam had been removed. The results showed a (non-statistically significant) trend on the effect of dam removal on the mean proportion of piscivorous perch. Dam removal had no effect on the mean proportion in the length interval 120>180 mm. Dams alter the composition, structure, and function of the surrounding environment; therefore, the outcomes of dam removals can be unpredictable. There are few published studies on how lentic fish communities respond to dam removals in lake outlets; therefore, such knowledge would be valuable and can provide relevant information to water managers, hydropower companies and decision-makers. / Dammkonstruktion i sjöar har betydande negativa effekter på akvatiska ekosystem, och anses därför som ett stort hot mot akvatisk biodiversitet. Det har gjorts många studier på hur fisk påverkas av dammar, och utrivning av dessa, eftersom de kan ha effekter på sjöars flora och fauna, genom att påverka näringsvävens struktur och näringsämnesdynamik. I denna studie undersökte jag om dammutrivningar i sjöutlopp påverkar proportionen av fiskätande abborrar, samt om medel-proportionen av fiskätande abborrar mellan 120–180 mm påverkas av utrivning (det längdintervall när dieten ändras från insekter till fisk). Jag använde data från 27 sjöar som var lokaliserade i Värmland, Dalarna och Västmanland. Resultaten visade att proportionen av fiskätande abborrar var 43% större där dammen hade rivits ut. Dammutrivning visade en (icke statistisk signifikant) trend på att det fanns en effekt av dammutrivning på medelproportionen av fiskätande abborrar. Dammutrivning hade ingen signifikant effekt alls på medelproportionen av fiskätande abborre i längdintervallet 120>180 mm. Dammar förändrar sammansättningen, strukturen och funktionen i den omgivande miljön, därför kan dammutrivningars resultat vara oförutsägbart. Det finns få publicerade studier av hur fiskesamhällen reagerar på dammutrivningar i sjöutlopp, därför skulle sådan kunskap vara värdefullt och kan ge relevant information till förvaltare av vatten, såsom myndigheter, kraftbolag och beslutsfattare.

Dammar har använts till många saker genom århundrandena, bland annat energiutvinning, reglering av vattennivå och transport av timmer. När dammar inte längre är i bruk och inte är ekonomiskt gynnsamma är dammutrivning en vanlig restaureringsmetod för att återställa ekosystemen. Dammar påverkar generellt ekosystemen negativt då det blir en begränsad konnektivitet inom och mellan vattendragen och sjöarna. Fiskars migration av och spridning av fröer från växter hindras av dammarna. Genom att riva ut dammar öppnas vägar för organismer att förflytta sig. Med utrivning av dammarna sker även en vattennivåsänkning som leder till att undervattensväxter kan bli mer utsatta. Undervattensväxter (makrofyter) som lever i det grunda vattnet bidrar med skydd och habitat för både fisk och bentisk fauna, samt zooplankton. Syftet med min undersökning är att undersöka om täckningsgraden av makrofyter förändras av dammutrivning. Även koncentrationen av fosfor i vattnet samt ljustillgången (mätt som siktdjup) förväntades ha en påverkan på täckningsgraden av makrofyter i sjöarna. Resultaten visade att det inte fanns ett signifikant samband mellan täckningsgraden och dammutrivning. Ett samband mellan täckningsgrad och siktdjup kunde inte heller bevisas. Däremot fanns ett positivt samband mellan täckningsgrad och koncentration fosfor i vattnet. Den här studien visar att makrofyter inte påverkas negativt av dammutrivning vilket är positivt då makrofyter har en viktig roll i ekosystemen. / Dams have been used for many things throughout history, such as an energy source, for regulation of water levels and timber transport. When dams are no longer economically viable, dam removal is a common method of restoring the ecosystem. Dams generally effect the ecosystems negatively, as they limit the connectivity in and between rivers, streams, and lakes. For example, fish migration and the spread of seeds are typically disrupted by the dams. When dams are removed, the water levels are normally reduced, which can lead to aquatic plants becoming more vulnerable. Aquatic plants (macrophytes) that grow in shallow parts of a lake provide habitat for fish, bentic invertebrate fauna and zooplankton and they thus form an important part of the limnic ecosystems. The purpose of my study was to investigate if the coverage of macrophytes changes after dam removal in lakes. Also, the concentration of phosphorus in the water and the light availability (measured with Secchi depth) were predicted to influence the coverage of macrophytes. The results showed that there was not a significant effect of dam removal or Secchi depth on the coverage of macrophytes. The concentration of phosphors had a positive significant effect of on macrophyte coverage. My study indicates that dam removal does not affect macrophytes negatively, which may be important due to macrophytes’ important role in the ecosystem.

Master of Arts / Department of Geography / Lisa M.B. Harrington / While environmental concerns have played a secondary role in dam removal rationales thus far, the Condit and Elwha removal projects could signal a change in governmental and public priorities in dam management in the United States (Born et al. 1998; Bednarek 2002). For this research, I compared two dam removal projects designed to restore native salmon runs in two rivers in Washington State: the Condit Dam on the White Salmon River and the Elwha and Glines Canyon Dams on the Elwha River. This thesis asks: given choices of preserving dams that produce clean electricity and the well-established lake-based habitats created by their reservoirs or re-establishing a free-flowing river to reestablish fish and wildlife populations, how are decisions made, and what does the process and outcome mean to local communities? Research interview data was used in combination with policy documents to answer three research questions: 1) What factors affect decision-makers’ and other stakeholders’ support for (or rejection of) dam removal? 2) How did stakeholders’ perceptions and opinions play a role in the decision-making process? and 3) What can we learn from problems and successes evident from the dam removal decision processes? The main factors influencing both the Condit Project and the Elwha Project were environmental (salmon restoration), political (meeting legislative requirements for fish passage), and economic (finding the least cost fish passage alternative). The primary motivation for both projects was salmon restoration via the provision of federally mandated fish passage. The possibility of regaining a valuable resource spurred Tribal, federal, and state agencies to advocate for the removal alternative. Dam owners in both cases desired the least cost option, resulting either in their consent to removal (Condit Project) or selling the dams and relinquishing responsibility to the federal government (Elwha Project). Both took over two decades to complete and were removed in 2011. Perceptions of the relative importance of removal/retention options and dissatisfaction with the decision-making process led to polarization of the communities affected by the dam removals and contributed to the 20+ year project timelines. In order to promote good will and understanding between decision makers and stakeholders, two lessons can be learned from the Condit and Elwha Projects: 1) actively seek to include both proponents and opponents in decision-making and 2) establish robust communication among stakeholders and decision makers. Additionally, preliminary evidence indicates that dam removal does result in movement of salmonids to river reaches that had been blocked by dams, and dam removal may also lead to unintended consequences related to local environmental quality and resource access, such as short term air quality concerns and longer term effects on groundwater availability.

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Throughout the years, dams have had important function for humans. However, many dams have today lost their function, which raises the question of dam removal. The outcomes of dam removal and their effects on fish communities are not fully investigated, which emphasizes the importance of continuing to study the effect of removal. In this study, I investigated whether or not dam removal in small lake outlets affected fish diversity. I also investigated the effects of the lake area and concentration of nutrients. The data collection was carried out in parts of Värmland, Dalarna and Västmanland counties, where 27 lakes, both with and without removed dams, were sampled. To sample fish, four to eight multimesh gill nets (depending on the area of the lake) were placed at varying depths. Water samples to measure nutrient concentrations were collected in places where the lakes were the deepest. A total of 3 223 individuals and 11 species were caught, with the most common species being perch. The effective species number varied between 1 and 3.44. There was a positive relationship between lake area and fish diversity. Dam removal, concentration of total phosphorus and total nitrogen had no effect on fish diversity. Dam removals can be considered as disturbances in complex systems and their effects may vary. Fish diversity is affected by colonization period and interactions between species, which likely takes long, which may explain why area but not dam removal affected fish diversity in my study. The lakes in the study were relatively homogeneous with respect to nutrient availability, which likely explains why nutrient concentration did not affect fish diversity. It is important to continue investigating the consequences of dam removal in other habitats than rivers, so that management of different water habitats can be carried out in the best way. / Dammar har genom tiderna fyllt en viktig funktion för människan. Många dammar har dock idag tappat sin funktion, vilket lyfter frågan om dammutrivning. Utfallen av dammutrivningar och dess effekter på fisksamhället är inte helt utredda, vilket trycker på vikten att fortsätta att studera effekten av utrivningar. I den här studien undersökte jag om dammutrivningar i mindre sjöutlopp påverkade fiskdiversiteten. Jag undersökte även effekterna av sjöarnas area och koncentration av näringsämnen. Datainsamlingen genomfördes i delar av Värmlands, Dalarnas och Västmanlands län, där 27 sjöar, både med och utan utriven damm, provtogs. För att provta fisk användes fyra till åtta provfiskenät (beroende på sjöns area) som placerades i varierande djup. Vattenproverna samlades in på platser där sjöarna var som allra djupast. Totalt fångades 3223 individer och 11 arter där den vanligaste arten var abborre. Det effektiva artantalet varierade mellan 1 och 3,44. Det fanns ett positivt samband mellan sjöarea och fiskdiversitet. Dammutrivning eller koncentration av total-fosfor eller total-kväve visade sig inte ha någon effekt på fiskdiversiteten. Dammutrivningar kan ses som störningar i komplexa system och att effekterna av dem varierar. Fiskdiversitet påverkas av koloniseringsperiod och interaktioner mellan arter, vilket sannolikt tar lång tid, något som kan förklara varför area men inte dammutrivningar inte påverkade fiskarnas diversitet i min studie. Sjöarna i studien var relativt homogena med avseende på näringstillgång, vilket sannolikt förklarar varför näringsämneskoncentrationen inte påverkade fiskdiversiteten. Det är viktigt att fortsätta arbeta med konsekvenserna av dammutrivningar i andra miljöer utöver älvar så att förvaltning av olika vattenmiljöer kan göras på bästa sätt.

Sammanfattning Dammutrivningar blir alltmer vanligt på grund av att många är föråldrade och kostar mer att driva och underhålla än vinsten de ger i energi. Effekten av utrivningar på halten miljögifter i fiskar är relativt okänd, men det finns observationer som indikerar att det dammutrivningar kan minska kvicksilverhalten i fiskar. Syftet med min studie var att undersöka skillnaderna i kvicksilverhalten hos gädda (Esox lucius), mellan sjöar som har fått dammen i sjöutloppet utriven respektive dammen intakt. Jag undersökte 66 provtagningar från 18 oligotrofa svenska skogssjöar. I sjöar där dammutrivning skett innehöll en medelstor gädda 500 ng/g kvicksilver, medan motsvarande värde i sjöar med dammen intakt var 740 ng/g kvicksilver. Det fanns ingen signifikant effekt av vare sig antal år efter utrivning eller provtagningsår. Kvicksilverhalten var nära förknippad med gäddans längd och varierade mellan sjöar, och i fyra av sjöarna, översteg mätningarna 1000n ng/g (gränsvärdet för konsumtion inom EU) medan gäddor från de andra sjöarna hade värden som mestadels under detta gränsvärde. / Abstract Dam removals are becoming increasingly common because many are outdated and cost more to operate and maintain than the value of that they provide in energy. The effect of dam removal on the level of environmental toxins in fish is relatively unknown, but there are observations that indicate that dam removal can reduce mercury concentrations in fish. The aim of my study was to investigate differences in the mercury concentration of pike (Esox lucius) between lakes that have had their outlet dams removed and those that have their dams intact. I examined 66 samples from 18 oligotrophic Swedish forest lakes.n lakes where the dam had been removed, a pike of average length contained 500 ng/g mercury, whereas the corresponding value for lakes with the dam intact was 740 ng/g of mercury. There was no significant effect of the number of years after removal or sampling year. The mercury concentration was closely associated to pike length and varied between the lakes, and in four of the lakes, all measurements exceeded 1000 ng/g (the limit value for consumption in EU), whereas most pike from the other lakes had values below this limit value.

This thesis explores the background of the Klamath Basin Restoration Agreement, a 250 page water use agreement among irrigators, Indian tribes, fishermen, environmental groups, federal and state agencies in the Klamath Basin. The agreement is contextualized in terms of water rights law, Indian law and the Endangered Species Act. The specific details of the agreement are explored. Finally, this thesis evaluates the agreement's merits and suggests a path forward for the agreement to become law.

Graduation date: 2006 / Dam removal is increasingly viewed as a river restoration tool because dams affect so many aspects of river hydrology, geomorphology, and ecology; but removal also has impacts. When a dam is removed, sediment accumulated over a dam’s lifetime may be transported downstream; and the timing, fate and consequences of this sediment remain some of the greatest unknowns associated with dam removal. In this thesis, I develop a conceptual model for erosion and deposition following removal of sediment-filled dams in mountain streams, and use field studies to document actual change. The data show that reservoir erosion in mountain rivers is likely to occur by knickpoint migration, with 85% of stored sediment being released during a single storm event in two field studies, at shear stresses less than that required for mobilization of the median surface particle size. Coarse sediment is predicted to deposit close to the dam with channel aggradation decreasing exponentially with increasing distance downstream, although some channel features are shown to have a greater propensity for aggradation than others. Field studies show that turbidity associated with dam removal and reservoir erosion may decrease hyporheic exchange, but gravel deposition (e.g., 470 m3 of gravel from Dinner Creek Dam) has the potential to more than offset that decrease, and increased hyporheic exchange is shown to reduce diurnal temperature change. Macroinvertebrate density and taxa richness did not respond to dam removal itself, but rather with time-lagged reservoir erosion. Following reservoir erosion, macroinvertebrate density recovered quickly, although longterm taxa community composition appears to be altered. On the Sandy River, field measurements of shear stress and patterns of sediment deposition following cold lahars were used as an analog to predict the fate of fine sediment, which is likely to deposit far from the dam. Results show that the Sandy River has little capacity for fine sediment storage in pools above RK 6.4 (~ 42 kilometers below Marmot Dam) at discharges associated with reservoir sediment releases. Taken as a whole, this paper illustrates a complex suite of process that may accompany removal of sediment-filled dams in mountain rivers.