Presentation on theme: "A Balancing Act What Do We Need To Know To Maintain Water Quality In The Spokane/Coeur d’Alene Basin? Mark Solomon, UI-Idaho Water Resources Research Institute."— Presentation transcript:
A Balancing Act What Do We Need To Know To Maintain Water Quality In The Spokane/Coeur d’Alene Basin? Mark Solomon, UI-Idaho Water Resources Research Institute Dan Strawn, UI-Environmental Soil Chemistry
Balance: Geochemistry (Vance, 1995) Species are either immobilized or released depending on water and sediment chemistry interaction. Aquifer level fluctuation can change that interaction. Recharge water chemistry can also change that interaction.
Current Research Objectives Efficacy and cost of shoreline non-disturbance buffers in reducing nutrient runoff to CdA Lake. Presence, fate and transport of mineral species and contaminants in the SVRPA. SVRPA geochemical interaction with different possible recharge sources. Identifying/quantifying sources of nutrients to CdA Lake. Zero-sum watershed nutrient cycling. Social, political and economic responses to management and regulatory change.
CdA shoreline non-disturbance buffers Need: maintain or reduce nutrient loading to lake from shoreline development as required by Lake Management Plan. Data gap: shoreline buffer width nutrient removal efficiency not localized for soils and substrate specific to lake. Multidisciplinary research proposal: Biophysical: Instrument, monitor and analyze representative paired developed/undeveloped field sites. Social: Survey lakeshore property owners regarding socio-political beliefs and attitudes that may affect implementation of nutrient control regulation if deemed necessary by responsible authorities. Economic: Analyze opportunity costs to aggregate property owners of different shoreline buffer widths. Analyze opportunity costs to region if LMP is replaced by CERCLA remedy. Education: develop and implement live and virtual extension outreach campaign based on project research to improve stakeholder acceptance of necessary effective nutrient management.
Within a watershed P biogeochemical cycling controls fate of P Erosion/runoff Surface water Mineral P Organic P Sorbed P Municipal Agriculture Plants Natural watershed Domestic Inputs Seepage mineralization uptake precipitation dissolution adsorption desorption
Speciation of P in water Dissolved Inorganic Orthophosphate Dissolved reactive phosphorus Bioavailable Organic phosphate compounds Pythic acid (2-50% in plant P), phospholipids, nucleic acids Must be degraded to be bioavailable Suspended colloids Phosphate attached to small mineral particles Mobile May pass through filter membrane P needs to desorb or dissolve to become bioavailable Soil and sediment P P associated with minerals
Operationally defined P categories in surface water Phosphorus category DefinitionSpeciation Dissolved P (DP) Soluble P (SP) Total P <0.45 μm filter or extraction P available for plant growth Dissolved reactive P (DRP), soluble reactive P (SRP), or molybdate- reactive P (DMRP) are used interchangeably Orthophosphate Colloidal P (<0.45μm) Easily desorbed P Dissolved organic P Particulate P (PP)Suspended P that does not pass through 0.45μm filter P adsorbed on mineral and organic particles Ca, Al, Fe-P minerals May convert to DP Total P (TP)DP+PPAll suspended and dissolved P species Bioavailable P (BAP) DP + PP determined to biologically available via extraction correlation such using an assay or simulation Dissolved orthophosphate Readily desorbed or mineralized P
Important points: Phosphorus available for bio-uptake is only dissolved orthophosphate. Concentration of dissolved orthophosphate depends on geochemistry of the system. Within the watershed, understanding solid phase P is key to predicting P mobility to surface water.
Types of solid phase P in soils, sediments, vadose zones (fixed P) Adsorbed Attachment to the surface of a mineral particle Must desorb to become bioavailable Precipitated Mineral bound phosphorus Example: apatite (Ca-P), vivianite (Fe-P), variscite (Al-P) Must dissolve to become bioavailable Desirable phase for water quality Undesirable phase for agronomy
Site-specific geochemical factors that affect P speciation pH Salinity Total P concentration Cation and anion concentration Temperature Redox Mineral surfaces for adsorption Mineral P Organic P Sorbed P mineralization uptake precipitation dissolution adsorption desorption
Example: Minerals have different adsorption potential Nidhi Khare Dean Hesterberg, et al.
pH effect on P fixation http://www.sesl.com.au/fertileminds/200909/Understanding_P_fertilisers.php
Redox effects on P cycle Phosphorus exist as P 5+ in natural environments, and will not get reduced However, phosphate strongly associates with Fe oxides Colloids Soil and sediment Coatings on rocks and sand grains Iron oxides undergo reductive dissolution when reducing conditions exist Microbes use Fe as a secondary electron acceptors in low oxygen environments Dissolution of iron oxides releases sorbed or precipitated phosphate Patrick et al., 1973
Buffer Width Analysis: Geochemistry Considerations What is the ability of soil or vadose zone to sequester P? Sequestration is adsorption or precipitation Typically 20% to >90% Need to know: Soil properties pH, mineralogy, porosity, particle size, redox potential, organic matter content, microbial activity Solution properties Ion constituents, pH, redox potential, temperature, residence time
Arsenic Geochemistry Throughout the world, there are many instances of As poisoning occurring from humans drinking groundwater Sources of arsenic can be natural or anthropogenic Granitic, carbonaceous, or pyritic minerals may be naturally elevated in As Management of surface and groundwater environments impacts arsenic solubility
Key points for understanding As geochemistry Arsenic has two common oxidation states As(III), and As(V) Organic matter and dissolved oxygen cause redox changes Dissolved arsenic is an oxyanion Arsenate- H 2 AsO 4 - Arsenite- H 3 AsO 3 There are many forms of organic arsenic Iron oxides are important minerals that adsorb As Phosphate will competitively exchange on mineral surfaces with As
Arsenic Geochemistry Hua ZhangHua Zhang, H.M. SelimH.M. Selim
Arsenic in the Coeur d’Alene and Spokane ground and surface Waters CDA River, CDA Lake and Spokane River have elevated As in sediments An oxic cap keeps the As from fluxing into surface water Must maintain redox status (DO) of system to prevent fluxes of As to surface water Well monitoring of SVRPA indicates elevated As Predominantly below drinking water standard of 10 ppb Source unknown Need to measure effects of different management on As geochemistry in SVRPA
SVRPA Hydro-Geochemistry Modeling The project will develop site-specific knowledge of: Influence of oxidation state on arsenic mobility and the effect of pumping condition on availability of dissolved arsenic and phosphorus for transport Sources and sinks for arsenic and phosphorus within the aquifer and on the aquifer boundaries Factors influencing arsenic and phosphorus transport (e.g., sorption/desorption mechanisms); and cross-correlation and interactions of arsenic, phosphorus, dissolved oxygen, dissolved organic carbon, and other chemicals of concern (e.g., heavy metals).
SVRPA Hydro-Geochemistry Modeling (cont.) Questions to be addressed Can specific geological factors be identified that are important for determining the distribution of arsenic, phosphorus, and other species of interest? What are the necessary water chemistry considerations for augmented aquifer recharge source waters? Are there optimal locations for siting of potential aquifer recharge projects? Can knowledge of underlying geology guide water well placement to areas of acceptable water quality? To what extent are phosphorus levels in aquifer discharge sensitive to changes in aquifer management? Does water chemistry indicate whether wells within a definable geographic area receive recharge predominantly from one source or another.
SVRPA Hydro-Geochemistry Modeling (cont.) Project Partners: Idaho Department of Water Resources Washington Department of Ecology Kootenai Aquifer Protection District Spokane County Water Resources Idaho Department of Environmental Quality Panhandle Health District
Lakes as Data Depositories Sediment core obtained from Lake Coeur d’Alene showing estimated dates of deposition and yellow lines indicating points of sectioning. (Carter, 2012) Loading and concentration of phosphorus over the depth of two cores. The dashed line at 11.5 cm indicates the location of the ash layer (1980) and the dashed line at 18 cm indicates the location of the Cs-137 peak (1963) within the cores.
Development Of Hindcasting And Predictive Tools To Assess Nutrient Control Technologies Correlate historical landscape scale changes in nutrient control BMP application with their signature in lakebed sediment cores. Model terrestrial and stream processes delivering P from the Lake Creek, Idaho watershed to the lacustrine environment of Coeur d’Alene Lake. Assess the ability of a model (WEPP) to simulate long- term changes in sediment and P loading in response to major changes in land use and BMP implementation.
Protecting the balance in the face of climate change: Zero-sum watershed- based nutrient cycling Climate change induced shifts in hydrographs Higher energy rain-on-snow precipitation events as transition zone moves upward Increased energy for pollutant transport Accelerated export of nutrients from the forest to the lacustrine environment Reduced availability of nutrients for forest plant communities More susceptible to insects and disease More vulnerable to wildfire Accelerate destabilizing shifts in area river hydrographs Remobilize bank-deposited contaminants
Protecting the balance in the face of climate change: Zero-sum watershed- based nutrient cycling (cont.) Reduced summer baseflow (7Q10) 25% reduction already found in Idaho headwater streams. A 25% reduction in 7Q10 translates to a 66% reduction in allowable loading for certain parameters such as nutrients, TSS, TDS, and temperature. It is proposed that Zn currently limits production in CdA Lake Remediation will reduce Zn input
Protecting the Balance: Research Questions Can forest ecosystems be made more resilient to climate change by reducing the level of exported nutrients from the forest ecosystem? Where, in what form, and in what magnitude do currently exported nutrients originate in a forest ecosystem? How can forest ecosystem nutrient export be minimized? What will be the effect of reduced Zn input on lake productivity? Will reduced Zn input change lakebed contaminated sediment mobility? How will climate change affect natural zinc weathering? In the built environment, can nutrients now exported as waste products from WWTP and on-site disposal be retained and repurposed as a resource? How will dischargers respond to significantly lower permit limits induced by reduced 7Q10 design minimum flows? Can repurposing of discharge waste as an asset reduce economic, social and political cost of compliance? Can repurposed nutrients be used to augment resilience of critical watershed ecosystems?