An Overview of Nutrient Chemistry in Subtropical Ecosystems

Transcription

1 An Overview of Nutrient Chemistry in Subtropical Ecosystems Jehangir H. Bhadha, Ph.D University of Florida Everglades Research and Education Center. August 23 rd, 2012.

2 Acknowledgements UF - Faculty: Dr. Samira Daroub (EREC- Soil and Water Science) Dr. Timothy Lang (EREC- Soil and Water Science) Dr. Manohardeep Josan (EREC- Soil and Water Science) Dr. James Jawitz (Soil and Water Science) Dr. Ramesh Reddy (Soil and Water Science) Dr. Mark Clark (Soil and Water Science) Dr. Willie Harris (Soil and Water Science) Dr. Mark Brenner (Geological Sciences) Dr. John Jaeger (Geological Sciences)

3 Outline Nutrient Cycle: problems, eutrophication Carbon Cycle: soil subsidence Nitrogen Cycling: fixation, mineralization, nitrification, denitrification Phosphorus Cycling: water quality parameters, forms of P, internal loading of P Florida Everglades Isolated Wetlands

4 Nutrient pollution Carbon (C), Nitrogen (N), and Phosphorus (P) Eutrophication Harmful algal blooms and associated algal toxins; Dissolved oxygen impairments; Fish kills; Taste and odor issues Impacts Public Health Drinking water Recreational use Shellfish contamination Socioeconomic Water cuts/outages Ecosystem Imbalances and shifts in trophic conditions

5 The Nutrient Cycle

6 The Problem Nutrient pollution is a MAJOR challenge to sustainable water resources Lake in China Huntsville, Alabama Fishkill due to algal growth

7 Aquatic Life Impacts Low dissolved oxygen levels (hypoxia) Algae, fed by N&P, use DO as they respire When DO levels in the water get low enough, aquatic life, particularly immobile species like oysters and mussels become stressed or die, resulting in significant impacts on marine food webs and the economy Fish kills Have been noted on all U.S. coasts and in many inland waters Frequency and magnitude have increased as nutrient pollution has worsened both hypoxia and harmful algal blooms (HABs) Dead zones Often used in reference to the absence of life (other than bacteria) when habitats have no oxygen Most dramatic U.S. example is off the coast of Louisiana & Texas Second largest eutrophication-related hypoxic zone in the world Associated with the nutrient pollutant load discharged by the Mississippi and Atchafalaya Rivers

8 National Scope of Nutrient Problem Rivers and streams (from national surveys) Over 47% of streams have medium to high levels of phosphorus Over 53% of streams have medium to high levels of nitrogen Lakes and reservoirs 5 million acres identified as impaired Coastal and estuarine 300 hypoxic zones in U.S. waters and not just on the coast 78% of assessed continental U.S. coastal areas exhibit eutrophication symptoms

9 C cycling Carbon Cycle is a complex series of processes through which all of the carbon atoms in existence rotate.

10 Carbon storage in shallow aquatic system Reddy & DeLaune, 2008

11 Soil Subsidence in the EAA

12 Environmental & Ecological significance of Soil Organic Matter Major component of global Carbon budget Source of CO 2 and Methane Provide plant nutrient support micro life Down stream carbon source Source of cation exchange capacity

13 N cycling Nitrogen cycle is the process by which N is converted between its various chemical forms. This transformation can be carried out via both biological and non-biological processes.

14 Important processes in the N cycle include: Fixation Mineralization Nitrification Denitrification.

15 Nitrogen fixation generally refers to the natural process, by which nitrogen (N 2 ) in the atmosphere is converted into ammonia Mineralization is the process through which organic N substance gets converted to an inorganic form of N Nitrification is the biological oxidation of ammonia with oxygen into nitrite followed by the oxidation of these nitrites into nitrates Denitrification is a microbially facilitated process of nitrate reduction that may ultimately produces nitrogen (N 2 ) through a series of intermediate gaseous nitrogen oxide products

16 N-Cycle

17 Nitrogen Cycle in shallow aquatic systems Reddy & DeLaune, 2008

18 N uptake by plants Ammonium (NH 4+ ) cation Nitrate (NO 3- ) anion Both ions are commonly present in soil solutions and are readily taken up by the roots Constitute about 1% of N in the soil Due to rapid nitrification in soils, plants absorb predominately NO 3-.

19 Influence of N on plant growth N deficiency in corn N deficiency in wheat N deficiency in ornamentals

20 Let s think for a while! What will happen to the atmospheric nitrogen gas if organisms responsible for denitrification are removed from the biosphere?

21 Phosphorus Cycle in shallow aquatic systems Reddy & DeLaune, 2008

22 Forms of Phosphorus Inorganic Phosphate (soluble) Ca/Mg-bound Fe/Al-bound Residual (nonreactive) Organic Cell membrane lipids Nucleic acids (DNA, RNA) ATP (metabolism)

23 Water Quality Parameters Dissolved Reactive P (DRP) Water samples filtered through 0.45 um filter and analyzed for phosphate. Also called Soluble Reactive P (SRP) Total Dissolved P (TDP) Water samples filtered through 0.45 um membrane filter and analyzed for total P Particulate P: Organic (POP), Inorganic (PIP)

24 DRP TP TP DOP POP/ PIP mm filter DRP + DOP TDP

25 P cycling in wetlands 1. Florida Everglades 2. Isolated wetlands, north of Lake Okeechobee

26 Everglades: The River of Grass Largest sub-tropical wetland (1.5 million ha) Evolved as Oligotrophic system Organic matter accumulation over limestone Historic Nutrient Sources to the glades Everglades Environments Nutrient Cycles of Everglades Carbon, Nitrogen, Phosphorus, Sulfur

27 Historical Perspective Historic Map Current Map Connected system Predominance of sheet flow Sawgrass Plains Ridge & Slough Rainfall driven From: SFWMD, FL

28 Water Flow in the Everglades Historic Flow Current Flow The plan (CERP) flow From U.S. Army Corps of Engineers, Jacksonville District, Florida

29 Everglades Wetland Transition Nutrient-limited system (Oligotrophic) High C:N:P ratios Low organic matter accumulation Slow turnover rates Longer residence time Fast Slow Nutrient-enriched system (Eutrophic) Low C:N:P ratios High organic matter accumulation High turnover rates Shorter residence time

30 Phosphorus accumulation in Wetlands Vegetation, periphyton and planktons, plant litter, soil physiochemical properties, water flow velocity, water depth, hydraulic rettention time, length to width ratio of wetland, P loading, and hydrologic fluctuations

31 Total P concentration in WCA-2A soil (0-10 cm) DeBusk et al., 2001

32 WCA-2A Cattail Sawgrass & Slough Soil P gradient effects on vegetation due to long term P loading in the Everglades Scale in Kilometers

33 Isolated Wetlands Within the Lake Okeechobee Drainage Basin: Source and Sink of P Background and Motivation Intensive agricultural practices maintained surplus of P leading to eutrophication of Lake Okeechobee P loading to the Lake continues to be ~100 Mg yr -1 over the legally mandated target of 140 Mg yr -1 (LO Protection Act, 2000) In response: Ag. Industry is mandated to achieve P load reductions, beef and dairy cattle ranches are being targeted One of the strategies is to restore isolated wetlands on pasturelands (809 km 2 ) Our interest was to investigate the role of internal loading of P associated with these isolated wetlands

34 What is Internal Loading of Nutrients? Loading associated with processes from within an aquatic system responsible for nutrient release. e.g., from soil/sediment and pore water Transport Mechanisms Diffusion Wind Bioturbation Gaseous Exchange Attached Algae Rooted Aquatic Plants DISSOLVED PHOSPHORUS Physico-Chemical Mobilization Desorption Dissolution Ligand Exchange Enzymatic Hydrolysis PARTICULATE PHOSPHORUS Microbial Mobilization

35 Why is Internal Loading Important? Wetlands on agricultural lands can solubilize high concentrations of P, subsequently releasing it back into the water column Water table fluctuations can transport P from ground to the water column P loads associated to internal loading are significant compared to external loads

36 Regional Morphology Over the past 50 years the hydroscape of LO drainage basin altered by ditches and canals to accommodate farming/pastures Isolated wetlands cover nearly 7% of the approximately 5160 km 2 LO drainage basin area Nearly 800 historically drained isolated wetlands have been connected to LO by Kissimmee River and Taylor Creek Km

37 Relating soil characteristics with P concentrations Under flooded conditions biogeochemical cycling of P is dominant within a few centimeters at the soil-water interface. However, due to the transient hydrologic conditions soil-water interface can exist below the surface, hence there is a need to investigate even the deeper horizons. Objectives 1. determine differences in soil characteristics as a function of depth between wetland and the surrounding upland 2. determine the P status within deeper horizons that may be affected by water-table fluctuations

38 Depth (cm) Ap Muck 17 cm 5 cm C1 10 cm E Sandy, 2.5Y 6/2; splotches of OM C1 Mixed and stratified C2 Stratified C1 Mixed and stratified Bt High chroma; Feoxide C2 Stratified Red-edge effect C2 Stratified C3 Sandy loam Core 4 Btg1 Sandy loam, 10R 5/1; masses associated with Fe redox Btg2 Sandy clay Core 1 C3 Loamy sand C4 Sandy loam Core 2 C4 Loamy sand C5 Sandy clay; gleyed 5/5B Core 3 C3 Loamy sand C4 Sandy loam UPLAND WETLAND Bhadha and Jawitz, 2010

39 Soil Texture Wetland Upland

40 Qtz decreases. Ka, Sm increases. Sequence of X-ray diffraction patterns for clay fraction at four different depth intervals.

41 WETLAND UPLAND

42 P fluxes and Mass Balance Calculations Internal loading of P can occur via diffusive and advective processes. Due to the transient hydrology advection could be a significant component. Objectives 1. calculate diffusive and advective fluxes across soil-water interface of SRP based on measured in-situ pore water concentrations 2. develop a P-budget that will help us evaluate the importance of diffusion and advection from wetlands affected by flooding and drying cycles

43 Wetland water fluctuation (cm) Measured wetland stage (cm) Evaluating Long-term Wetland Hydroperiod R 2 = 0.59 n = U.S.G.S. stage data for Cypress slough (ft) (39%) (69%) (17%) (29%) (32%) Hydroperiod Bhadha et al., 2011

44 Hydrologic Budget P = precipitation O D = direct overland flow O I = indirect overland flow D IN = ditch inflow GW IN = groundwater inflow ET = evapotranspiration D OUT = ditch outflow GW OUT = groundwater outflow

45 Pore Water Concentrations High P at 10 cm depth: MS1: 3.9 (± 2.1) mg L -1 MS2: 3.4 (± 1.4) mg L -1 MS3: 2.2 (± 0.4) mg L -1 Below 10 cm concentrations drop <0.02 mg L -1, (except for MS1)

46 Advective Flux of SRP Into the wetland Mean Flux: 8.0 (±10.1) mg m -2 d -1 Total Load: 0.9 kg Out of the wetland Mean Flux: 13.3 (±15.1) mg m -2 d -1 Total Load: 10.6 kg

47 Mass Balance Estimates Runoff at 1 mg L -1 Runoff at 0.6 mg L -1 Load into Wetland Water Column (kg) Load out of Wetland Water Column (kg) Atmosphere: 0.15 (1%) Runoff: 3.8 (38%) Diffusion: 5.2 (52%) Advection: 0.9 (9%) Internal Loading Ditch Flow: 2.5 (19%) Inflitration: 10.6 (81%)

48 Conclusions Calculated advective fluxes are greater than diffusive fluxes increase in frequency of high intensity rain events could increase P load Based on MBC, internal loading of P via diffusion and advection accounts for 61% of total P entering the wetland currently BMPs address reducing P via external sources; need to target internal sources Wetlands show low hydroperiods with multiple drawdown and subsequent flooding events negative effect on P loading due to alternating redox conditions

49 Soil P Release and Storage Capacity Objectives 1. determine the EPC 0 values from the experiment, and compare to measured pore water concentrations 2. determine soil P storage capacity (SPSC) based on oxalate-extractable Fe, Al, and P concentrations Experimental Design EPC and SPSC experiments were conducted on samples collected from all four cores Samples from surface (0-2 cm) followed by every 10 cm depth increments (10-12 cm, cm.)

50 What is Equilibrium P Concentration (EPC)? It is the aqueous concentration (mg L -1 ) at which the soils/sediments neither adsorb nor desorb any P Good indicator of whether the soil behaves as a source or sink of P For e.g., if the EPC was higher than the incoming water, then soils would behave as a source of P, and vice versa What is Soil P Storage Capacity (SPSC)? It is calculation of how much additional P (mg kg -1 ) can be added before reaching the P saturation ratio (PSR) threshold SPSC = (Changepoint PSR) ox(fe + Al) 31

51 Desorption Sorption (mg kg -1 ) Adsorption Surface horizon EPC 0 values core 1 core 2 core 3 core 4 R 2 = R 2 = Initial concentration (mg L -1 ) R 2 = R 2 = Wetland surface = 1.8 (±1.3) mg L -1 Upland surface = 8.9 mg L -1

52 Depth (cm) Soil phosphorus storage capacity, SPSC (mg kg -1 ) Core 1 without Fe with Fe Core 2 without Fe with Fe Core 3 without Fe with Fe Core 4 without Fe with Fe High Fe (Red-edge effect)

53 Practical Implication and Recommendation Wetland restoration Upland Wetland Ditch Dam structure

54 Thank You