Näringsretention i återskapad våtmark på betesmark : studier av en mad vid Bornsjön
It is important to construct or recreate different types of wetlands and study their retention of nutrients, since knowledge of their effectiveness in this matter is poor. In 2003 a wetland was constructed on an old meadow on the western shore of Lake Bornsjön in central Sweden. The main purpose of...
| Autor principal: | |
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| Formato: | L3 |
| Lenguaje: | sueco Inglés |
| Publicado: |
SLU/Dept. of Soil Sciences
2005
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| Materias: |
| _version_ | 1855571916719390720 |
|---|---|
| author | Ångman, Elin |
| author_browse | Ångman, Elin |
| author_facet | Ångman, Elin |
| author_sort | Ångman, Elin |
| collection | Epsilon Archive for Student Projects |
| description | It is important to construct or recreate different types of wetlands and study their retention of nutrients, since knowledge of their effectiveness in this matter is poor. In 2003 a wetland was constructed on an old meadow on the western shore of Lake Bornsjön in central Sweden. The main purpose of the wetland was to reduce the amount of phosphorus entering the lake, which is the back-up water supply for Stockholm when the city cannot obtain water from Lake Mälaren. Large areas around Lake Bornsjön consist of agricultural land and the nutrient concentrations in the inflows to the lake are usually relatively high (approx. 1 mg/l total nitrogen and 0.05-0.1 mg/l total phosphorus). The inflow to the wetland is also affected by sewage water from private houses.
The purpose of this study was to investigate how this fairly newly constructed wetland
functioned during spring high flood and whether the uptake or outflow of nutrients changed
when the growing season started. The study was performed between 29 March and 24 May
2005. The flow was measured continuously at two points and water samples were collected at
least once and at most four times a week. The wetland received the highest nutrient load
during the early part of April. This was also the period when some nutrient retention was
estimated to occur. The retention of phosphorus in the wetland over the period was calculated to be 10 % (0.16 kg P/ha) of that reaching it in inflow and the retention of nitrogen 8 % (1.34 kg N/ha). On 3 May, it was raining heavily and the nutrient concentration in the inflow was about 10 times higher than normal. When these extreme values were included in the calculations, the retention was 45 % of phosphorus and 50 % of nitrogen. In the subsequent part of the study period the wetland became a source of nutrients, even after the growing season had started. Decreasing oxygen concentration and increased concentration of total organic carbon in the outflow suggested that decomposition of organic matter was taking place in the wetland. Since the area has not been harvested since the 1980s, organic material has probably accumulated in the wetlands. When the soil thaws in spring, old organic material starts decomposing and this process most likely negates the effects of nitrogen and phosphorus uptake by plants.
No studies have been done on this type of wetland during the conditions of middle Sweden.
Wetlands and ponds of southern Sweden with a high nutrient load have been found to reduce
560 kg N/ha/yr and 37 kg P/ha/yr in average. Another study on wetlands with overland flow
and high nutrient load showed net retention of nitrogen (0-13 %) and sometimes of phosphorus (-48-+20 %). These numbers seems comparable to the results for the present
wetland.
Wetlands are complicated and dynamic systems that are difficult to control and investigate, and they can frequently become a source of nutrients as well as a sink. The biological diversity and the recreation value of an area often increase when a wetland is created. The wetland in this study seemed to be very much appreciated by people using the area for recreation since the number of birds had increased. It was concluded that wetlands might be regarded as more valuable if other aspects in addition to nutrient retention were considered. |
| format | L3 |
| id | RepoSLU11674 |
| institution | Swedish University of Agricultural Sciences |
| language | swe Inglés |
| publishDate | 2005 |
| publishDateSort | 2005 |
| publisher | SLU/Dept. of Soil Sciences |
| publisherStr | SLU/Dept. of Soil Sciences |
| record_format | eprints |
| spelling | RepoSLU116742017-11-24T09:42:44Z Näringsretention i återskapad våtmark på betesmark : studier av en mad vid Bornsjön Ångman, Elin näringsretention konstruerad våtmark betesmark mad Bornsjön It is important to construct or recreate different types of wetlands and study their retention of nutrients, since knowledge of their effectiveness in this matter is poor. In 2003 a wetland was constructed on an old meadow on the western shore of Lake Bornsjön in central Sweden. The main purpose of the wetland was to reduce the amount of phosphorus entering the lake, which is the back-up water supply for Stockholm when the city cannot obtain water from Lake Mälaren. Large areas around Lake Bornsjön consist of agricultural land and the nutrient concentrations in the inflows to the lake are usually relatively high (approx. 1 mg/l total nitrogen and 0.05-0.1 mg/l total phosphorus). The inflow to the wetland is also affected by sewage water from private houses. The purpose of this study was to investigate how this fairly newly constructed wetland functioned during spring high flood and whether the uptake or outflow of nutrients changed when the growing season started. The study was performed between 29 March and 24 May 2005. The flow was measured continuously at two points and water samples were collected at least once and at most four times a week. The wetland received the highest nutrient load during the early part of April. This was also the period when some nutrient retention was estimated to occur. The retention of phosphorus in the wetland over the period was calculated to be 10 % (0.16 kg P/ha) of that reaching it in inflow and the retention of nitrogen 8 % (1.34 kg N/ha). On 3 May, it was raining heavily and the nutrient concentration in the inflow was about 10 times higher than normal. When these extreme values were included in the calculations, the retention was 45 % of phosphorus and 50 % of nitrogen. In the subsequent part of the study period the wetland became a source of nutrients, even after the growing season had started. Decreasing oxygen concentration and increased concentration of total organic carbon in the outflow suggested that decomposition of organic matter was taking place in the wetland. Since the area has not been harvested since the 1980s, organic material has probably accumulated in the wetlands. When the soil thaws in spring, old organic material starts decomposing and this process most likely negates the effects of nitrogen and phosphorus uptake by plants. No studies have been done on this type of wetland during the conditions of middle Sweden. Wetlands and ponds of southern Sweden with a high nutrient load have been found to reduce 560 kg N/ha/yr and 37 kg P/ha/yr in average. Another study on wetlands with overland flow and high nutrient load showed net retention of nitrogen (0-13 %) and sometimes of phosphorus (-48-+20 %). These numbers seems comparable to the results for the present wetland. Wetlands are complicated and dynamic systems that are difficult to control and investigate, and they can frequently become a source of nutrients as well as a sink. The biological diversity and the recreation value of an area often increase when a wetland is created. The wetland in this study seemed to be very much appreciated by people using the area for recreation since the number of birds had increased. It was concluded that wetlands might be regarded as more valuable if other aspects in addition to nutrient retention were considered. Att anlägga eller återskapa olika typer av våtmarker och studera näringsretentionen i dessa är angeläget eftersom man idag har dålig kunskap hur våtmarker kan minska närsaltsbelastningen på vattnen. År 2003 anlades vid sydvästra delen av Bornsjön en våtmark (mad) med främsta syfte att öka retentionen av fosfor till sjön. Bornsjön är Stockholm stads vattenreserv ifall uttaget av Mälarens vatten måste stoppas. Området kring sjön består till stor del av jordbruksmark och näringshalterna i sjöns tillflöden är ofta relativt höga (1 mg/l totalkväve and 0.05-0.1 mg/l totalfosfor). Tillflödet till våtmarken påverkades dessutom av enskilda avlopp. Syftet med examensarbetet var att se hur denna relativt nyanlagda våtmark fungerade under vårens högflödesperiod och om det eventuella upptaget eller utsläppet av närsalter förändrades när växtsäsongen kommit igång. Studien utfördes mellan den 29 mars och 24 maj år 2005. Flödesmätningar gjordes kontinuerligt vid två punkter och vattenprover insamlades minst en gång och som mest fyra gånger per vecka. Den största andelen näringsämnen belastade våtmarken under den första delen av april. Det var också under den perioden som det skedde en fastläggning av näringsämnen. Därefter utgjorde våtmarken en källa för näringsämnen, även då växtsäsongen kom igång. Syrehalten, pH-värdena och ökningen av totalt organiskt kol i utflödet tydde på att nedbrytning pågick i våtmarken. Eftersom marken inte skördats sedan 80-talet har antagligen stora mängder organiskt material ansamlats. När marken tinar börjar gammalt organiskt material brytas ner och denna process överskuggar förmodligen effekten av att växterna i våtmarken tar upp kväve och fosfor. Retentionen av totalfosfor i den nyanlagda våtmarken beräknades till 10 % och av totalkväve 8 %. Det motsvarar en ganska blygsam avskiljning på 0,16 respektive 1,34 kg/ha under perioden. Den 3/5 regnade det häftigt och närsaltskoncentrationerna i det tillrinnande vattnet var ca 10 ggr högre än de normala. Inkluderas dessa extremhalter i beräkningen motsvarar retentionen av totalfosfor istället 45 % och av totalkväve 50 %. Inga studier har gjorts på den här typen av våtmark under mellansvenska förhållanden. Skånska våtmarker och dammar med hög närsaltsbelastning har i en studie beräknats reducera närsalter med i genomsnitt 560 kg N/ha/år och 37 kg P/ha/år men då är också belastningen på dessa mycket högre än i denna studie. En studie på översilningsytor gav en retention på 0-13 % av kväve och -48-+20 % för fosfor. Dessa siffror verkar vara mest jämförbara med de för Maden 2. Översilningsytorna belastades också med kväve och fosfor i samma storleksordning som våtmarkerna i denna studie. Våtmarker är komplicerade och dynamiska system som är svåra att kontrollerna och undersöka; de kan ofta bli en källa till näringsämnen såväl som en fälla. Ofta ökar dock den biologiska mångfalden och rekreationsvärdet i området när en våtmark skapas och därför blir våtmarker mer värdefulla om man ser till fler aspekter än näringsretention. Den här undersökta våtmarken verkade vara mycket uppskattad av människor som använder området för rekreation eftersom antalet fågelarter har ökat. SLU/Dept. of Soil Sciences 2005 L3 swe eng https://stud.epsilon.slu.se/11674/ |
| spellingShingle | näringsretention konstruerad våtmark betesmark mad Bornsjön Ångman, Elin Näringsretention i återskapad våtmark på betesmark : studier av en mad vid Bornsjön |
| title | Näringsretention i återskapad våtmark på betesmark : studier av en mad vid Bornsjön |
| title_full | Näringsretention i återskapad våtmark på betesmark : studier av en mad vid Bornsjön |
| title_fullStr | Näringsretention i återskapad våtmark på betesmark : studier av en mad vid Bornsjön |
| title_full_unstemmed | Näringsretention i återskapad våtmark på betesmark : studier av en mad vid Bornsjön |
| title_short | Näringsretention i återskapad våtmark på betesmark : studier av en mad vid Bornsjön |
| title_sort | näringsretention i återskapad våtmark på betesmark : studier av en mad vid bornsjön |
| topic | näringsretention konstruerad våtmark betesmark mad Bornsjön |