Pressures and their mechanisms governing loading of P fractions to surface waters

Transcription

1 Pressures and their mechanisms governing loading of P fractions to surface waters NFR, Miljø2015 -Tvers Project Rolf D. Vogt R. Vogt m.fl.. Røyseth m.fl. D. Barton G. rderud E. Romstad H. Gunnarsdottir

2 atchment studies Stream water studies Studies Winter lake water studies hristian W. Mohr Kaja pland Sediment studies Yemane Gebrelasse Neha Parekh Lluís Gómez Gener Ruikai Xie Katarzyna Lukawska

3 atchment studies Soil and soil-water plots along topographic gradient Forested site - Dalen Agricultural site - Huggenes

4 Deep marine deposits with layers of clay Forested watershed Dalen Poorly buffered acid sensitive site Barren rock outcrop with pockets of sand 50 cm sand and loam

5 Mohr, 2011 P pools in forest soils mg/kg P Ridge E B Slope Soil Horizon AE B1 B2 Extremely high organic P content in the forest floor Due to nutrient cycling Valley Bottom A B1 B2 High content of apatite in the clay in the valley bottom Sol-P Al-P Fe-P a-p ccluded-p ther inorganic-p rganic-p

6 Mohr, 2011 hemistry of forest soil water Governed by DNM, giving a low ph and significant Al species Extremely high P content in throughfall Throughfall + soil water + stream E B 1 2 AE B1 B2 A B1 B2 D mg /L E B 1 2 AE B1 B2 A B1 B2 ph 3,50 5,50 7,50 E B 1 2 AE B1 B2 A B1 B2 µg Al/L Al-organic bound Al-inorganic bound E B 1 2 AE B1 B2 A B1 B2 DP SRP µg P/L Stream Stream Stream Stream

7 Agricultural site - Huggenes Soil samples from middel of the field and close to streambank Increasing content of marine clays towards the bottom of the pit Ap Bg Ap Bg Bg ambisol Stagnosol 7

8 pland, 2011 P pools in agricultural soils High P content in Ap layer due to fertilizing Higher P content in Ap layer close to stream verland flow? Increase down through B- Apatite in the marine clays Uptake by roots in B SEM images of apatite found in Huggenes sediment Gebreslasse, 2012

9 Drainage water Drainage pipes were found to be an important pathway for P release into the stream P from Ap through macropores Erosion of marine clays in the horizon in which the pipes are buried

10 Stream water studies Streams draining into western Vansjø apturing a gradient in land-use from agriculture to forest Agriculture Forest 100 % Land -use distribution 75 % 50 % 25 % Forest ther Agriculture 0 % STØ 1 HUG VAS ÅRV SPE AUG GUT DALEN

11 Parekh, 2012 Stream water chemistry Acid forest streams are efficiently neutralized upon mixing with agricultural runoff DNM content also lost Sorbed to particles Shift from soft and dilute seasalt (Nal) to hard (a 3 ) water

12 P Fractionation lear distribution depending on discharge and land-use 100 % Agriculture E E E E E Forest E E E E High conc. of Particulate P esp. during discharge Episodes (E) 75 % 50 % Particulate-P dominate in runoff from Agricultural land DNM-P dominate in discharge from forested catchments ug P/L 25 % 0 % STØ1 ØRE HUG VAS ÅRV SPE AUG GUT DALEN 430 Particle P P4 Dissolved rganic P STØ1 ØRE HUG VAS ÅRV SPE AUG GUT DALEN Parekh, 2012

13 Suspended particle bound P lear co-variation between total-p and amount of suspended solids The particle bound P is mainly inorganic in streams draining agricultural and organic in forest streams SPM 100 % 90 % 80 % 70 % 60 % 50 % 40 % 30 % 20 % 10 % 0 % Vas Støa1 Støa2 Hug Hobk Spe Aug Gut Dalen Sample sites Gebreslasse, 2012 SPM- SPM-I Parekh, 2012

14 40 What happens with particle bound P? Agriculture 430 Totalfosfor (µg/l) juni-september Forest Partikulært P P4 Løst organisk P Tot-P in the lake varies between μg P/L april-oktober År ug P/L STØ1 ØRE HUG VAS ÅRV SPE AUG GUT DALEN Lake There is low total-p concentrations in the lake compared to what comes with the streams.. Is it possible that Particle bound P does not contribute so much to the total-p in the lake as it is just sedimented?

15 40 What happens with particle bound P? ug P/L ug P/L Agriculture 70 Totalfosfor (µg/l) juni-september Forest Partikulært P4P P4 Løst organisk Løst organisk P P Tot-P in the lake varies between μg P/L april-oktober År 85% STØ1 ØRE HUG VAS ÅRV SPE AUG GUT DALEN Lake So if this is the case.. Then the background flux of humic bound P from forests will play a major role

16 Gebreslasse, 2012 The role of particles P in the stream-sediments is much higher than in the soils Silt has large adsorption capacity R-rg-Fe/Al-P 4 It is possible that eroded silt and clay scanvenges P 4 in the stream P in the lake sediments are much lower than in the stream sediments This may imply that P that is bound to organic material or Fe is remobilized from the sediments g P / kg Natural soils Agricultural soils Suspended Sediments. Stream Sediments Lake Sediments

17 Gómez Gener, 2010 Data from: Skarbøvik et al., 2011 Lake studies Focus on winter as this was lacking in previous studies Practically no: Bioassimilation of P 4 Photobelaching of DNM Influx of particle matter P fractionation very different from summer: Tot-P only 15 µg /L Dominating P fraction was P 4 (45%) followed by organic-p (30%) and particle bound P (25%) Vanemfjorden Grepperødfjorden Storefjorden Summer 2010: Avg. tot-p 26 µg/l rga nic P 15 % P4 26 % Partic le-p 59 % rga nic P 19 % P4 19 % Partic le-p 62 % P4 36 % rga nic P 3 % Partic le-p 61 %

18 Xie et al., 2012 Sediment studies Total P content in lake sediments decreases with decreasing organic matter and clay content

19 Main conclusions so far.. atchment High P in top soil and in marine clays in both forest and agricultural fields Streamwater Drainage pipes are important flowpath for P P fractions many governed by land-use and flow intensity Lake P fractionation in winter lake water very different from summer Free P 4 dominate Sediment Highest P pools found in river delta Particle bound P from forest more available

20 Thank you for your attention