Particulate Soil Phosphorus and Eutrophication in Lakes and Streams

Transcription

1 Particulate Soil Phosphorus and Eutrophication in Lakes and Streams Paul R. Bloom Soil, Water, & Climate Department University of Minnesota With contributions by John Moncrief, Carl Rosen and David Mulla

2 Outline Eutrophication Phosphorus Chemistry in Soil Transport of P from Soil to Surface Water Soil P: a P Source for Algae in Surface Waters

3 Eutrophication Creation of high nutrient status of a lake or stream. Results in: Excess algal growth Lower productivity of game fish If severe - fish kills. Generally P is the limiting nutrient.

4 Algal Growth Temperature is a factor in all biological production Excess algae generally most apparent in late summer.

5 Total P and Growth of Algae < 0.02 ppm (20 ppb ) Little algal growth Clear water > 0.02 ppm Accelerated algal growth Lower water clarity

6 Log total phosphorus (ppb) vs. log chlorophyll-a (ppb). (Eco-region reference lakes in MN, summer-mean measurements.) 0.02 ppm 0.02 ppm

7 Total Phosphorus (ppb) vs. Secchi depth (m).

8 Eutrophication P stimulates algal productivity. Light penetration limited at depth. Less algae and plant growth at depth. Decay of surface algae further depletes oxygen. Dead algae fall through the water. Epilimnion Aquatic plants Hypolimnion O 2 depletion

9 Role of Suspended Sediment Other sources of suspended sediment make the problem worse. Soil particles from erosion.

10 Severe Conditions Lead to Blue-Green Algae Excess production of algae can lead N depletion. Blue-green algae are N fixers. Produce their own N Stink and produce toxins

11 Lake Pepin, drought of 1988

12 Phosphorous Chemistry in Soil

13 Soil Phosphorus Forms Solid Non Labile P Labile P inorganic organic slow inorganic organic Soluble P (<1%)

14 Soluble P Inorganic + Some organic P This is the form taken up by plants, > 0.2 ppm in highly fertile soils Compare to 0.02 ppm in a clear water lake Mobile form Small fraction of total P (< 1 lb/a)

15 Inorganic Soluble P Sometimes called ortho-p Reacts rapidly with molybdate reagent: Molybdate reactive P (MRP) Dissolved reactive P (DRP) Soluble reactive P (SRP) Dissolved molybdate reactive P (DMRP) :O: H-O-P-O-H : : : :O: H : :

16 Labile P The most reactive P in soil solids. Mostly inorganic. Estimate with P soil test Varies with soil test used. A bioreactive form of P. Bound to Al-P, Fe-P, Ca-P. Some adsorbed on surfaces. < 10 lb/a to > 300 lb/a

17 Labile P Buffers P in soil solution Plant uptake lowers soluble concentration. Replaced from labile P.

18 Non labile Relatively insoluble and unreactive Organic and inorganic compounds Organic can be % of the P in surface soils In Minnesota typically 50% Slow equilibrium with labile and soluble P 300 lb/a to 3000 lb/a

19 Fate of P Added to Soil P in fertilizer and manure initially soluble With time Fast Slow Dissolved P Labile P Non labile P Most soils have a high capacity to retain P in labile and non labile forms

20 Soil P Transport to Surface Waters

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22 Soil Phosphorus Transport to Surface Waters Surface Runoff Dissolved-P Sediment-P (erosion) Leaching into subsurface drain tiles Dissolved-P (leaching) Minor in most cases.

23 P in Surface Runoff Particulate P (sediment P) Typically 75-90% of runoff P for row crops Organic and inorganic P Typically 50 % organic in fertile Minnesota soils Analysis after hot acid digestion. Soluble P Passes 0.4 micron or 0.2 micron filter. Mostly inorganic P Determined by molybdate reaction (MRP)

24 Example 1 P Lost from Fall Rainfall Simulation Experiment Following Corn No-till Moldboard Following bean Chisel Moldboard D. Ginting, J.F. Moncrief, S.C. Gupta, M.R. Zumwinkle, M. A. Dittrich, and M.J. Hanks

25 Fall runoff - Rainfall simulation- 4 in 1.5 hr P lost, g/ha PHOSPHURUS LOSS FROM 100 mm SIMULATED RAIN PHOSPHORUS LOSS (g ha -1 ) DMRP Particulate P 25% 7% 13% 4% CORN RESIDUE SOYBEAN RESIDUE RESIDUE COVER & TYPE

26 Example 2 Runoff via Surface Tile Inlets Le Sueur Co. Surface Inlet 6 Storm Event July 4th 1998

27 TS Con. (g L -1 ) COD con. (mg L -1 ) TP Con. (mg L -1 ) DMRP Con. (mg L -1 ) TS COD TP DMRP July 24 July Day of Year

28 Deposition of Particulate P Before Delivery to Surface Waters Sedimentation: Sedimentation ponds In ponds that form at tile inlets (80% loss) During transport in ditches. Trapped by: Grassed edge of field buffers strips Riparian buffers

29 Minnesota P Index Assesses Relative Risk of Delivery of P to Surface Waters Transport Mechanism Erosion (PP) Phosphorus Source c Soil P c Management Effects BMPs Structures Delivery = RISK Rainfall Runoff (DP) c Soil P Applied P c Practice Factors = RISK Snowmelt Runoff (DP) c Biomass Applied P c Practice Factors = RISK Overall Risk

30 Soil P: a P Source for Algae in Surface Waters

31 Labile P Provides an Easily Accessible Source of P for Algae Labile P tries to buffer at soluble P at ppm soluble P Algae can draw soluble P down to < 0.01 ppm

32 P Mobilized in 2 Weeks by Algal Growth: 0.6 ppm soil P added to algal culture (Ohio soil) Dorich et al., 1984, JEQ pp

33 Bioavailable P Mobilized by algae Estimated by 0.1 M NaOH extraction Extraction with Fe(OH) 3 impregnated filter paper strips

34 Half of the Labile P Dissolves without the Algae Bioavailable P was twice the DMRP in the no algae control after 2 weeks DMRP about 0.2 ppm

35 Response of Algae to Soil P in Minnesota Soils 10 8 Chl-a response y = 0.078x R 2 = 0.68 p < Fe-oxide paper P (ppm)

36 Soil Particles Can Also Supply P Over Longer Time Periods Slow dissolution of non labile inorganic P Enzymatic hydrolysis of organic P Organic P Soluble P Algae release alkaline phosphatase Reactions in bottom sediment Hydrolysis of organic P Low redox Iron P Soluble P

37 Fate of P in particulate organic matter (POM) Water Column Flux of POM Fluxes of O 2, H2S, NH4, NO3, PO4, Si Active Sediment Aerobic Layer Anaerobic Layer Diagenesis of POM: Production of H2S, NH4, PO4, Si

38 Modeling of P Transformations in Water Internal loading Source: HydroQual, Inc.

39 Total P: Is it the Best Predictor of Negative Impacts of Sediment P? Most experts agree it is the best single parameter. Most other measures like soluble P (DRP) and bioavailable P underestimate the effects of sediment P.

40 Conclusions Particulate P in runoff from row crops contributes to eutrophication in lakes and streams. Labile P (bioreactive P) is can have a rapid impact on growth of algae. Non labile P can contribute to eutrophication over the long term. Total P is a reasonable parameter to estimate impact of P in runoff. Preventing erosion and transport to surface waters is very important in reducing impact.

41 Thank You for Your Attention Questions?