Controls on Suspended Particle Properties and Water Clarity along a Partially-Mixed Estuary, York River Estuary, Virginia Kelsey A. Fall 1, Carl T. Friedrichs 1, Grace M. Cartwright 1, and David G. Bowers 2 1 Virginia Institute of Marine Science 2 School of Ocean Sciences, Bangor University

Motivation: Water clarity a major water quality issue in the Chesapeake Bay. Despite decreases in sediment input water clarity has continued to deteriorate (especially in the Lower (i.e., Southern) Chesapeake Bay). 1/12 good poor good poor Percent of Secchi Depths which passed USA Environmental Protection Agency (EPA )water clarity thresholds (Williams et al., 2010)

1/12 good poor good poor Annual means of the dimensionless product of Secchi Depth times the diffuse light attenuation coefficient (Z SD K d ) for upper, middle and lower Bay (Gallegos et al.,2011). Gallegos et al. (2011) suggested that the most likely explanation for the change in the product of Z SD times K d is an increase in the concentration of continually suspended, small particles of non-algal organic matter. Percent of Secchi Depths which passed USA Environmental Protection Agency (EPA )water clarity thresholds (Williams et al., 2010) Motivation: Water clarity a major water quality issue in the Chesapeake Bay. Despite decreases in sediment input water clarity has continued to deteriorate (especially in the Lower (i.e., Southern) Chesapeake Bay).

Objective: Investigate the influence of suspended particle properties (size, concentration, composition) on inherent and apparent optical properties in a partially-mixed estuary. YORK RIVER CHESEAPEAKE BAY VIMS Latitude Longitude Study Site: York River Estuary, VA, U.S.A Partially mixed, microtidal estuary located adjacent to the lower Chesapeake Bay. Although the York is microtidal, tidal currents dominate suspension and peak spring surface currents can reach ~1 m/s. Depths along axis of the main channel decrease from about 20 m near the mouth to about 6 m near West Point. The channel bed is mostly mud, and Total Suspended Solids (TSS) increases up estuary to the primary ETM located near West Point. This study: Utilized observations from water column profiling cruises at different stations along the York ( June 2013, Sept. 2014, October 2014, August 2015). Average Total Suspended Solids (TSS)Average Salinity Distance from the Mouth (km) West Point ETM 2/12 Surface Bottom TSS mgL -1 Salinity (ppt) Surface Bottom

Coastal Hydrodynamics and Sediment Dynamics (CHSD) Water Column Profiler Deployed off vessel at various depths for along channel surveys. CHSD Profiler ADVs PICs LISST CTD (Smith and Friedrichs, 2014, 2010; Cartwright et al., 2013; 2009; Fugate and Friedrichs, 2002). Pump Sampler Pump sampler Water samples analyzed for total suspended solids (TSS) and organic content LISST-100X: Particle size distribution (~ μm) Beam attenuation from optical transmission Apparent density (ρ a ) :ρ a =SPM/VC Area Concentration (A T ) Particle imaging camera system (PICS) particle sizes, density, and settling velocities (~30 μm μm) Acoustic Doppler Velocimeter (ADV) provide estimates of: mass concentration of suspended particle matter Bottom: turbulence/bed stress, bulk settling velocity CTD with a turbidity sensor water clarity proxy Radiometer or LI-COR light sensor Vertical profile of diffuse light attenuation (K d ) 3/12

4/12 (Neukermans et al., 2014; Smith and Friedrichs, 2010) Example from surface water September 2014: Characterization of Particle Size with the LISST ( μm) and PICS ( μm) A i cm 2 /L Particle Size μm LISST PICS Note: Area peaks at ~3 at lowest size class. Figure adjusted to see larger grain sizes better. Area Concentration Distributions [A i ] Combine PICS and LISST to create new volume and area distributions from μm where: Particle area concentration (per Liter) for size class (i):

Combine PICS and LISST to create new volume and area distributions from μm where: μm: LISST μm: Linearly weighted average of LISST and PICS μm: PICS 4/12 (Neukermans et al., 2014; Smith and Friedrichs, 2010) LISSTAVGPICS LISST PICS Example from September 2014: Note: Area peaks at ~3 at lowest size class. Figure adjusted to see larger grain sizes better. A i cm 2 /L Area Concentration Distributions [A i ] Particle Size μm Characterization of Particle Size (AREA) with the LISST ( μm) and PICS ( μm)

Combine PICS and LISST to create new volume and area distributions from μm where: μm: LISST μm: Linearly weighted average of LISST and PICS μm: PICS 4/12 (Neukermans et al., 2014; Smith and Friedrichs, 2010) LISSTAVGPICS LISST range dominates particle area. A i cm 2 /L Area Concentration Distributions [A i ] Particle Size μm Example from surface water September 2014: Characterization of Particle Size (AREA) with the LISST ( μm) and PICS ( μm)

Combine PICS and LISST to create new volume and area distributions from μm where: μm: LISST μm: Linearly weighted average of LISST and PICS μm: PICS 4/12 (Neukermans et al., 2014; Smith and Friedrichs, 2010) LISSTAVGPICS LISST range dominates particle area. But PICS range contributes to volume concentration V μL/L Volume Concentration Distribution [V i ] Small organics(?) flocs Particle Size μm A i cm 2 /L Area Concentration Distributions [A i ] Particle Size μm Example from surface water September 2014: Volume ≈ Area x Size Characterization of Particle Size (AREA) with the LISST ( μm) and PICS ( μm)

Particle surface area not volume is important in examining water clarity, because it is the area that is effective in blocking light. Note difference between D 50A and D 50v 4/12 (Neukermans et al., 2014; Smith and Friedrichs, 2010) D 50A =6.2 microns A T =11.38 cm 2 /L D 50v =24.4 microns V μL/L Volume Concentration Distribution [V i ] Particle Size μm A i cm 2 /L Area Concentration Distributions [A i ] Particle Size μm Example from surface water September 2014: Volume ≈ Area x Size Characterization of Particle Size (AREA) with the LISST ( μm) and PICS ( μm)

Trends in Particle Size (in terms of D 50A ) along the York D 50A (microns) TSS (mg/L) A. TSS versus D 50A MouthETM 5/12

Trends in Particle Size (in terms of D 50A ) along the York D 50A (microns) TSS (mg/L) A. TSS versus D 50A MouthETM Organic Fraction D 50A (microns) B. Organic Fraction versus D 50A MouthETM 5/12

Trends in Particle Size (in terms of D 50A ) along the York D 50A (microns) ρ a (kg/m 2 ) TSS (mg/L) C. Apparent Density versus D 50A A. TSS versus D 50A MouthETM MouthETM Organic Fraction D 50A (microns) B. Organic Fraction versus D 50A MouthETM Observations show small, organic particles suggested by Gallegos et al., /12

In water light is either absorbed or scattered, Absorption removes light while scattering influences the vertical penetration of light and increases the probability that it will be absorbed. Typically scattering>>absorption (especially in estuarine systems). attenuation = describe the amount of light lost through either absorption or scattering. Inherent and Apparent Optical Properties of Surface Water LICOR 6/12 Kirk et al., 2007

In water light is either absorbed or scattered, Absorption removes light while scattering influences the vertical penetration of light and increases the probability that it will be absorbed. attenuation = describe the amount of light lost through either absorption or scattering. Measurements of Attenuation: Inherent and Apparent Optical Properties of Surface Water LICOR 1. Beam Attenuation Coefficient ( beam c) Inherent: Depends only on medium, not ambient light field (laser source, 670 nm) Measured by LISST beam transmission (T): where x is beam path length. LISST x=0.05 m. 6/12

In water light is either absorbed or scattered, Absorption removes light while scattering influences the vertical penetration of light and increases the probability that it will be absorbed. attenuation = describe the amount of light lost through either absorption or scattering. Measurements of Attenuation: Inherent and Apparent Optical Properties of Surface Water LICOR 1. Beam Attenuation Coefficient ( beam c) Inherent: Depends only on medium, not ambient light field (laser source, 670 nm) Measured by LISST beam transmission (T): where x is beam path length. LISST x=0.05 m. = 5 cm LISST Laser Transmitted light absorbed light scattered light transmitted light * beam c proportional to scattering 6/12 Assumed loss

In water light is either absorbed or scattered, Absorption removes light while scattering influences the vertical penetration of light and increases the probability that it will be absorbed. attenuation= describe the amount of light lost through either absorption or scattering. Measurements of Attenuation: Inherent and Apparent Optical Properties of Surface Water LICOR 2. Diffuse Attenuation, K d (apparent): Apparent: Depends on medium and ambient light field Measurement of change of downward irradiance (E d ) with depth (z) by either Radiometer or LICOR Measures PAR ( nm) TRIOS 6/12

In water light is either absorbed or scattered, Absorption removes light while scattering influences the vertical penetration of light and increases the probability that it will be absorbed. attenuation= describe the amount of light lost through either absorption or scattering. Measurements of Attenuation: Inherent and Apparent Optical Properties of Surface Water LICOR 2. Diffuse Attenuation, K d (apparent): Apparent: Depends on medium and ambient light field Measurement of change of downward irradiance (E d ) with depth (z) by either Radiometer or LICOR Measures PAR ( nm) TRIOS depth z Sunlight Light Sensor 1.Light absorbed 2.Light Scattered out of path length 3.Light Scatter out of path length is scattered back in 4. Light Scattered in from outside of path length 6/12 Net Loss Net Gain

In water light is either absorbed or scattered, Absorption removes light while scattering influences the vertical penetration of light and increases the probability that it will be absorbed. attenuation= describe the amount of light lost through either absorption or scattering. Measurements of Attenuation: Inherent and Apparent Optical Properties of Surface Water LICOR 2. Diffuse Attenuation, K d : Apparent: Depends on medium and ambient light field Measurement of change of downward irradiance (E d ) with depth (z) by either Radiometer or LICOR Measures PAR ( nm) TRIOS depth z Sunlight Light Sensor 2 1.Light absorbed 2.Light Scattered out of path length 3.Light Scatter out of path length is scattered back in 4. Light Scattered in from outside of path length 6/12

In water light is either absorbed or scattered, Absorption removes light while scattering influences the vertical penetration of light and increases the probability that it will be absorbed. attenuation= describe the amount of light lost through either absorption or scattering. Measurements of Attenuation: Inherent and Apparent Optical Properties of Surface Water LICOR 2. Diffuse Attenuation, K d (apparent): Apparent: Depends on medium and ambient light field Measurement of change of downward irradiance (E d ) with depth (z) by either Radiometer or LICOR Measures PAR ( nm) TRIOS depth z Sunlight Light Sensor 1.Light absorbed 2.Light Scattered out of path length 3.Light Scatter out of path length is scattered back in 4. Light Scattered in from outside of path length 6/12 3 3

In water light is either absorbed or scattered, Absorption removes light while scattering influences the vertical penetration of light and increases the probability that it will be absorbed. attenuation= describe the amount of light lost through either absorption or scattering. Measurements of Attenuation: Inherent and Apparent Optical Properties of Surface Water LICOR 2. Diffuse Attenuation, K d (apparent): Apparent: Depends on medium and ambient light field Measurement of change of downward irradiance (E d ) with depth (z) by either Radiometer or LICOR Measures PAR ( nm) TRIOS depth z Sunlight Light Sensor 1.Light absorbed 2.Light Scattered out of path length 3.Light Scatter out of path length is scattered back in 4. Light Scattered in from outside of path length 4 6/12

In water light is either absorbed or scattered, Absorption removes light while scattering influences the vertical penetration of light and increases the probability that it will be absorbed. attenuation= describe the amount of light lost through either absorption or scattering. Measurements of Attenuation: Inherent and Apparent Optical Properties of Surface Water LICOR 2. Diffuse Attenuation, K d (apparent): Apparent: Depends on medium and ambient light field Measurement of change of downward irradiance (E d ) with depth (z) by either Radiometer or LICOR Measures PAR ( nm) *K d proportional to absorption depth z Sunlight Light Sensor 2 1.Light absorbed 2.Light Scattered out of path length 3.Light Scatter out of path length is scattered back in 4. Light Scattered in from outside of path length /12

1. Beam Attenuation Coefficient ( beam c) Inherent: Depends only on medium, not ambient light field Measured by LISST beam transmission (T): where z is beam path length. LISST z=0.05 m. Measures C at 670 nm (+/- 0.1 nm) proxy for scattering 2. Vertical Diffuse Light Attenuation Coefficient (K d ) Apparent: Depends on medium and ambient light field Measurement of change of downward irradiance (E d ) with depth (z) by either Radiometer or LICOR Sensitive to absorption 7/12 (Boss, 2003; Kirk, 1994; Lund-Hansen et al., 2010; LISST-100 User’s Guide; Neukermans et al., 2014) LISST Beam Attenuation Coefficient beam c m -1 Aug Sept June 2013 K d m -1 Vertical Diffuse Light Attenuation Coefficient Distance from the Mouth (km) Aug Sept June 2013 Inherent and Apparent Optical Properties of Surface Water in the York LICOR

Preliminary Look at Controls on Optical Attenuation (beam c and K d ): Total Suspended Solids (TSS) determined by pump samples K d m -1 K d versus TSS TSS (mgL -1 ) beam c m -1 beam c versus TSS TSS (mgL -1 ) 8/12 Both K d (absorption and scattering) and beam c (scattering) increase with increasing TSS But I care about the particles- need to account for attenuation due to dissolved matter and water

Preliminary Look at Controls on Particulate Optical Attenuation (K dp and beam c p ): Total Suspended Solids (TSS) determined by pump samples K d m -1 K d versus TSS TSS (mgL -1 ) c m -1 beam c versus TSS TSS (mgL -1 ) Use intercept from to estimate attenuation due to non particles (water, CDOM,etc.) in in K d to calculate attenuation due particles. beam c≈ c p. K dDISS ~0.26 m -1 8/12

K dp m -1 K d versus TSS beam c p m -1 beam c p versus TSS TSS (mgL -1 ) r 2 =0.65 r 2 =0.71 9/12 Both K dp (absorption and scattering) and beam c p (scattering) increase with increasing TSS Preliminary Look at Controls on Particulate Optical Attenuation (K dp and beam c p ): Total Suspended Solids (TSS) determined by pump samples

K dp m -1 A (cm 2 /L) beam c p m -1 A (cm 2 /L) K d versus A T beam c p versus A T r 2 =0.83 r 2 =0.97 Attenuation (both beam and diffuse) are explained better by A T than TSS. Both are absorption and scattering are sensitive to Area. Also, C p less noisy than K dp. Preliminary Look at Controls on Particulate Optical Attenuation (Beam c p and K dp ): Total Area Concentration (cm 2 /L) from the LISST 10/12 Bowers et al., 2011

If we remove the effect of area (normalize K DP and beam c p by A T ) can we determine what other properties influence attenuation? i.e What causes the scatter/spread in our data? K dp m -1 A (cm 2 /L) beam c p m -1 A (cm 2 /L) K d versus A beam c p versus A r 2 =0.83 r 2 =0.97 Preliminary Look at Controls on Particulate Optical Attenuation (Beam c p and K dp ): Total Area Concentration (cm 2 /L) Attenuation (both beam and diffuse) are explained better by A T than TSS. Both are absorption and scattering are sensitive to Area. Also, C p less noisy than K dp. 10/12

Preliminary Look at Controls on Attenuation per Area (beam c P /A T and K dp /A T ): Apparent Density (ρ a ) :ρ a =SPM/VC Apparent Density, (kg/m 3 ) K dP normalized by A T versus apparent density r 2 =0.40 p-value = 1e-08 r 2 =0.10 p-value = 9e-03 Beam attenuation efficiency, c p /A T Apparent Density, ρ a (kg/m 3 ) beam c P normalized by A T versus apparent density 11/12 Diffuse Attenuation Efficiency :, K dp /A T

Preliminary Look at Controls on Attenuation per Area (beam c P /A T and K dp /A T ): Apparent Density (ρ a ): ρ a =SPM/VC K dP normalized by A T versus apparent density r 2 =0.40 p-value = 1e-08 r 2 =0.10 p-value = 9e-03 Beam attenuation efficiency, c p /A T Apparent Density, ρ a (kg/m 3 ) beam c P normalized by A T versus apparent density Diffuse Attenuation Efficiency :, K dp /A T Theory suggests: More opaque particles (denser particles) will absorb more light. We see evidence that absorption is proportional to both area and density and scattering is controlled mainly by particle area. Apparent Density, (kg/m 3 ) K d increases with density more strongly than beam c p. 11/12

Conclusions: Observations found small, organic particles suggested by Gallegos et al., Preliminary results from the York indicate importance of these small, more organic particles on optical properties. Particle Beam Attenuation Coefficient (C p ) and Particle Diffuse Attenuation Coefficient (K dP ) are better explained by total particle area concentration (A T ) than total suspended solids (TSS). Field observations support optical theory: Particle Diffuse Attenuation Coefficient (K dP ) increases more strongly with density than beam attenuation (beam c p ). Absorption which is proportional to area and density (Bowers et al., 2011). Beam c p was not sensitive to density, but was influenced by of particle area. Scattering is proportional to particle area. (Bowers et al., 2011) Future work will include (i) many more sampling cruises and (ii) deployment of a LISST that can detect smaller particle sizes. 12/12

Acknowledgements Marjy Friedrichs Tim Gass Wayne Reisner Ken Moore Jarrell Smith Steve SynderFunding: Erin Shields Questions? 11/11