<p>Eutrophication was recognized in the early 1900's and results in severe algal blooms, increased biomass production and eventually leads to an altered ecosystem. In Mälardalen we find the most eutrophic lakes. Most of the applied phosphorus and nitrogen into seas and oceans comes from agriculture, and the nutrients losses are affected by local weather conditions and soil type. Guidelines for storage and distribution of manure were introduced in the 80s, and the rules were strengthened January 1, 2010. Localities and previous county administrations can whether there are special reasons, grant an exemption for manure application during winter-periods despite the current ban.</p><p>In this essay I have examined how many exemptions of manure application that has been granted at the Sagån river, and what implications it has for the eutrophication of Lake Mälaren. Sagån’s catchment area extends through Enköping, Sala, Heby, Västerås and Uppsala. Since 2000, 23 waivers of manure application have been granted, most of these deviations have occurred on snow-covered ground or when the weather change considerably. This means that much of the nutriment in the manure went down to the nearby water when the snow melted. Computations were made In order to find out how much phosphorus was spread each time. The conclusion is that the pig manure contains significantly more phosphorus, meaning greater phosphorus losses. However, these calculations are only estimates.</p><p>Several farmers were contacted to find out what they think about the regulation of the management and application of manure. They believe that the new legislation does not pose a problem for them. But farmers with small distribution areas in relation to the number of animals could have some problems.</p>

Eutrophication was recognized in the early 1900's and results in severe algal blooms, increased biomass production and eventually leads to an altered ecosystem. In Mälardalen we find the most eutrophic lakes. Most of the applied phosphorus and nitrogen into seas and oceans comes from agriculture, and the nutrients losses are affected by local weather conditions and soil type. Guidelines for storage and distribution of manure were introduced in the 80s, and the rules were strengthened January 1, 2010. Localities and previous county administrations can whether there are special reasons, grant an exemption for manure application during winter-periods despite the current ban. In this essay I have examined how many exemptions of manure application that has been granted at the Sagån river, and what implications it has for the eutrophication of Lake Mälaren. Sagån’s catchment area extends through Enköping, Sala, Heby, Västerås and Uppsala. Since 2000, 23 waivers of manure application have been granted, most of these deviations have occurred on snow-covered ground or when the weather change considerably. This means that much of the nutriment in the manure went down to the nearby water when the snow melted. Computations were made In order to find out how much phosphorus was spread each time. The conclusion is that the pig manure contains significantly more phosphorus, meaning greater phosphorus losses. However, these calculations are only estimates. Several farmers were contacted to find out what they think about the regulation of the management and application of manure. They believe that the new legislation does not pose a problem for them. But farmers with small distribution areas in relation to the number of animals could have some problems.

Hälsosamma ekosystem försörjer oss med livsviktiga resurser och tjänster – ekosystemtjänster så som skydd mot översvämning. I Norra Östersjöns vattendistrikt, som Mälaren tillhör, är statusen på den ekosystemtjänsten dålig. Detta beror till stor del på en omfattande dikning och brist på svämplan i området. Under perioder med skyfall riskerar därför området runt Mälaren och dess tillrinnande vattendrag att drabbas av översvämningar som skadar matproduktion, infrastruktur och miljö. Övergödning är redan ett problem i området och stora tillskott av fosfor till följd av översvämmade jordbruksmarker kan orsaka stora algblomningar och försämrad livsmiljö för vattenlevande organismer. Under augusti och september 2023 föll ovanligt stora mängder regn över mellersta Sverige vilket ökade vattenföringen i vattendragen runt Mälaren och översvämmade vissa av dem. Högfrekventa turbiditetsmätningar från in-situ sensorer installerade i Sagån, Hågaån och Fyrisån, tre vattendrag i Mälarens avrinningsområde, har använts för att undersöka skyfallens effekter på deras vattenföring och beräknad fosfortransport. Resultaten visade en signifikant korrelation mellan ökad vattenföring och ökad fosfortransport, en signifikant ökning under 2023 jämfört med 2018–2022 och signifikanta skillnader mellan vattendragen. Översvämmade Sagån hade extremt höga toppar i beräknad fosfortransport. Resultaten indikerar att övergödningsproblemen i Mälaren kan förvärras i ett framtida klimat med mer intensiva skyfall om inte åtgärder tas för att stärka avrinningsområdets förmåga att hantera stora mängder nederbörd. / Healthy ecosystems provide us with vital resources and services – ecosystem services such as flood protection. In the North Baltic Sea Water District, to which Lake Mälaren belongs, the status of that ecosystem service is poor, largely as a result of extensive draining in the area leading to a lack of floodplains. During periods of torrential rain, the area around Lake Mälaren and its tributaries is therefore at risk to be affected by floods that cause damage to food production, infrastructure and the environment. Eutrophication is already a problem in the area and large additions of phosphorus as a result of flooded agricultural land can cause large algal blooms and degraded habitat for aquatic organisms. During August and September 2023, unusually large amounts of rain fell over central Sweden, which increased the flow of water in Lake Mälarens tributaries and flooded some of them. High frequency turbidity data from in-situ sensors installed in Sagån, Hågaån and Fyrisån, three tributaries to Lake Mälaren, was used to study the effects of the heavy rains on their waterflow and estimated phosphorus transport. The results showed a significant correlation between increased water flow and increased phosphorus transport, a significant increase in 2023 compared to 2018-2022 and significant differences between the tributaries. Flooded Sagån had extremely high peaks in estimated phosphorus transport. The results indicate that the eutrophication problems in Lake Mälaren may worsen in a future climate with more intense downpours unless measures are taken to strengthen the catchment's ability to handle large amounts of rainfall.