Methane Bellows Hypothesis and its Link to Biogeochemical Cycling Processes at the Mesotidal Freshwater - Seawater Interface of the Columbia River Estuary (A Discussion) Part I. Source of River’s Methane Super-Saturation: Groundwater Input Part II. Significant Methane Contribution to Estuary: Intertidal Bellows Phenomenon Part III. Other Estuary Impacts on Water Quality: Neap / Spring Nutrient Records 1

Part I: Willamette Corvallis Willamette always supersaturated in methane (range: x, average: 56x) At a given time, degree of super-saturation can differ significantly over a short distance (CD-WP: ~100nM) Evidence for groundwater source: most enhanced in low flow summer period, but also other low flow periods 2

CD-WP difference correlates inversely with river flow amount added in ~2 km river stretch can double the WP concentration Groundwater source of Si and N (but not P) also evident in same river stretch NOTABLY: nutrient addition evident during high not low river flow periods! 3

Conclude Nutrients introduced by seepage from rain saturated soils (seasonally driven process) Methane ascribed to discharge from Willamette aquifer discharge (a more persistent year round process) Question: Why is there a strong correlation between  Si and  N but not  P? 4

Part II: Cathlamet Bay Tidal Outwash (RM17 Site) – Conservative vs Non-conservative Mixing T – S (left, bottom) display conservative, two-endmember mixing under both spring and neap tidal forcing and low flow, summer conditions Si – S (right, bottom) trends similar, indicating minimal biogeochemical modification (i.e., loss due to diatom production) at this land-to-sea margin 5

Methane Tidal Bellows Effect No Yes sulfate Salinity NoneWeak Strong Methane Bellows Effect? BAT-to-estuary transect during an ebb tide on Fall 2008 cruise provided evidence for prospect Monitoring sites over ebb cycle on May 2009 cruise confirmed phenomenon and showed it is confined to river & upper portion of the estuary 6

RM17 Monitoring evaluates tidal outwash from Cathlamet Bay Methane Bellows Effect evident in high flow late spring (top) and low flow late summer (bottom) periods sampled during 2009 CMOP campaigns ‘excess’ CH 4 (observed – predicted) persistent in intermediate salinity bottom water during low flow late summer period Question: If methane source restricted to freshwater, how is latter observation explained? 7

RM17 Monitoring May 2010 – high flow period springneap methane bellows effect apparent during neap (right) BUT NOT spring (left) tidal outwash expressed both in fresh surface & intermediate salinity deep waters (similar to observation from May 2009 – 10,600 m 3 /s) 8

RM17 Monitoring August 2010 – low flow period methane bellows effect apparent during neap (left) AND spring (left) tidal outwash ‘excess’ CH 4 (observed – predicted) persistent in intermediate salinity bottom waters during both neap and spring tidal forcing (similar to September 2009 – 2970 m 3 /s) Questions: How is methane introduced to the outwash water? Is hydrostatically driven groundwater discharge an important consideration? 9

Non-conservative mixing evident for ammonium under neap and spring tidal forcing: apparent excess indicates a significant estuarine source Conservative mixing for nitrate and phosphate evident under spring BUT NOT neap tidal forcing. Both of these nutrients show depletion, NOT an excess Question: What is the biogeochemical explanation for the apparent depletion of each? Part III – Nutrients RM17 Monitoring August 2010 – low flow period 10

‘excess’ type analysis applied to nutrient data RM17 Monitoring August 2010 – low flow period Denitrification would account for nitrate depletion but depletion does not appear associated with tidal outwash Question: where else might denitrification occur? within estuarine bottom waters, ETM? Metal oxide dynamics might account for phosphate depletion Questions: What is the process? …redox cycling? …flocculation during estuarine mixing? neapspring 11

Overall Summary Groundwater source evident for methane, nitrate, silicate but not phosphate in Willamette River. Methane source ascribed to discharge of Willamette aquifer, most highly expressed in low flow, summer period. N and Si source is seasonal rainfall-driven seepage from soil. Finer details of hydrology remain to be studied. Methane tidal bellow confirmed phenomenon in upper Columbia River Estuary. Buildup of ‘excess’ methane from tidal bellow apparent in stratified bottom waters of the CRE during low river flow and neap tidal forcing conditions. Physics of this process remain unclear. Groundwater discharge driven by tidally controlled hydrostatic forces now suspected. Silicate behaves conservatively in estuarine mixing during spring and neap tidal forcing, even under low river flow conditions. Significant estuarine source of ammonium with concentration buildup in saline bottom waters that appears independent of spring / neap tidal forcing. Nitrate and phosphate display conservative mixing behavior under spring but not neap tidal forcing. Both nutrients lost during neap tidal conditions: suspected causes are denitrification (N) and metal oxide redox cycling / flocculation (P). Both biogeochemical processes may be linked to ETM dynamics. 12

13 an extra compare with Methane Record - Slide 9