P in Groundwater and Groundwater dependent ecosystems

Transcription

1 P in Groundwater and Groundwater dependent ecosystems Geological Survey of Denmark and Greenland Ministry of Energy, Utilities and Climate Lærke Thorling, Catharina Madsen and Bertel Nilsson

2 Take home messages Natural eutrophic lakes may exist due to groundwater P input. Knowledge of the surrounding geology can help selecting the potential natural eutrophic lakes Naatural dissolved P in groundwater is not alone inorganic P The distribution and speciation of P in groundwater is highly dependent on the geology and redox-conditions

3 Typical textbook example of the P cycle. No groundwater!

4 Antropogen and natural P Anthropogenic P fluxes are enhanced in surface water system by fertiliser and sewage Leaching to groundwater usually insignificant. Transport of P in surface water may happen both as particulate P and in dissolution Ground water P sources are suggested to be: degrading of organic matter reductive dissolution of adsorbed P.

5 Sample Ground and Surface water What P do we measure? What can be compared? Overall P After filtration Dissolved P Particulate P Analytical result P tot P Ortho P PO 4 P P tot particulate Calculation of organic bound Dissolved: P tot -PO 4 -P = P org

6 Typical concentrations in the Danish environment

7 Sources to P in surface water DK P source to streams Mean P tot mg/l Waste Water Agriculture Nature

8 P in Danish Groundwater All kinds of data

9 P in groundwater DK- Monitoring data

10 Speciation of P in Groundwater Monitoring network DK

11 P and redox cond. in Groundwater DK monitoring data In oxic groundwater P = PO 4. In reduced Groundwater organic P plays a role Oxic groundwater : O 2 1 mg/l Reduced groundwater: O 2 <1 mg/l, NO 3 <1 mg/l, Fe >0,01 mg/l, SO 4 >20 mg/l

12 P and redox cond. in Groundwater DK monitoring data P tot highly Redox dependent PO 4 the same in all GW except very reduced GW Organic P is a signature of reduced GW This gives indications of geochemical processes A: oxic B: anoxic nitrate C: reduced SO4 > 20 D reduced SO4 20

13 P tot : Geographical distribution in DK Water works wells 2014

14 P tot : Dependence on Geology Chalk early Tertiary marine silty Quaternary meltwater sand and clay Quaternary till sand and clay Quaternary marine interglacial Limestone late Tertiary sand Quaternary meltwater sand Quaternary till sand Solid rock Bornholm

15 Redox and geology HUSK OVERSÆT TIL ENGELSK

16 Redox and geology

17 Hydrogeology meets Ecology-Who is responsible? Where goundwater meets surfacewater different scientific and administrative systems meet to. So many brilliant people with different skills work together in this projekt, thanks to all.

18 Center for Lake Restoration Funded by the Villum Foundation

19 Oxidation of exposed brown-coal layers in gravel pits? 2. Leaching from agriculture? 3. Release from old lake/river bed sediments? 4. Pure Natural reasons?

20 TP in shallow groundwater near lake shore

21 GEOLOGICAL SURVEY OF DENMARK AND GREENLAND Recent flow model and hydrogeological conditions (Kazmierczak et al., 2016) seepage lake (groundwater input 70% of lake water balance) steady state flow conditions part of groundwater passing beneath the lake and discharging at the eastern lake shore

22 GEOLOGICAL SURVEY OF DENMARK AND GREENLAND Conclusions so far..(relevant today) Lake water budget did not differ significantly throughout Holocene, amount of the lake water discharging into aquifer is negligible due to the location of the lake low in the landscape, close to the main river. P driven lake eutrophication started when accumulation of gyttja at the lake bottom generated high discharge zones with focused groundwater inflow?

23 Next step: Seeking answers in the muddy lake sediments Ole Bennike, GEUS 2017

24 Data from Nørresø Geological Survey of Denmark and Greenland Ministry of Energy, Utilities and Climate

25 Inlets & springs (measured) underwater seeping and springs (unknown) Outlet Spring

26 Fluxes of water and Phosphorous Measured or DK- known background -Seepage and underwater springs not accounted for -P-precip = dry and wet deposition considered constant over the year Catharina Madsen

27 LUWQ in the very LONG run Lake sediments hold information on land use and water quality over thousands of years. The correlation between cultural, landscape and 1000 s of years of agriculture in Denmark around Nørresø. Time- B.P Aia Aistrup 2017

28 Conclusions and future research P in groundwater is mainly geogenic P concentrations are highly dependent on local geology and redox-conditions. Such a thing as natural eutrophic lakes are found. The dynamics of phosphorous release in aquifers organic/in-organic is poorly understood? Does organic P have different transport and environmental fate than inorganic P Is it organic P at all? What happens at the goundwater surfacewater interface? (Se other speakers)

29 THANK YOU FOR YOUR ATTENTION Lærke Thorling