1. Controls on Suspended Particle Properties and Water Clarity along a Partially-Mixed Estuary, York River Estuary, Virginia, USA 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

2. 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). 1/10 good poor good poor Percent of Secchi Depths which passed USA Environmental Protection Agency (EPA )water clarity thresholds (Williams et al., 2010)

3. 1/10 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).

4. 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 of 7 water column profiling cruises at different stations along the York (3 in June 2013 and 4 in Sept. 2014). TSS mgL -1 Average Total Suspended Solids (TSS) Salinity (ppt) Average Salinity Distance from the Mouth (km) West Point Surface Bottom Surface Bottom 2/10

5. 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 CTD with a turbidity sensor water clarity proxy Laser In-Situ Scattering and Transmissometry (LISST-100X) Suspended particle size distribution (~2.5-500 μm) Optical Transmission Particle imaging camera system (PICS) –Added 2012 particle sizes, density, and settling velocities (~30 μm- 1000 μm) Acoustic Doppler Velocimeter (ADV) provide estimates of: mass concentration of suspended particle matter Bottom: turbulence/bed stress, bulk settling velocity Radiometer (Summer 2013) or LI-COR light sensor (new 2014) Vertical profile of diffuse light attenuation (K d ) 3/10

6. Particle area concentration (per Liter) for size class (i): Characterization of Particle Area with the LISST (2.5-500 μm) and PICS (30-1000μm) Particle surface area important property to consider, because it is the area that is effective in blocking light. Used LISST and PICs to determine particle area concentration per size class (i) [A i ]: Example from surface water September 2014: LISST PICS 4/10 (Neukermans et al., 2014; Smith and Friedrichs, 2010) Note: Area peaks at ~3 at lowest size class. Figure adjusted to see larger grain sizes better. A i cm 2 /L Particle Size μm Area Concentration Distributions [A i ]

7. Characterization of Particle Area with the LISST (2.5-500 μm) and PICS (30-1000μm) Combine PICS and LISST to create new volume and area distributions from 2.5-1000 μm where: 2.5-60 μm: LISST 60-200 μm: Linearly weighted average of LISST and PICS 200-1000 μm: PICS 4/10 (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

8. Characterization of Particle Area with the LISST (2.5-500 μm) and PICS (30-1000μm) Combine PICS and LISST to create new volume and area distributions from 2.5-1000 μm where: 2.5-60 μm: LISST 60-200 μm: Linearly weighted average of LISST and PICS 200-1000 μm: PICS 4/10 (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:

9. Characterization of Particle Area with the LISST (2.5-500 μm) and PICS (30-1000μm) Combine PICS and LISST to create new volume and area distributions from 2.5-1000 μm where: 2.5-60 μm: LISST 60-200 μm: Linearly weighted average of LISST and PICS 200-1000 μm: PICS 4/10 (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(?) Microflocs Macroflocs 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

10. Characterization of Particle Area with the LISST (2.5-500 μm) and PICS (30-1000μm) Define particle size characteristics with new distributions ( D 50A, A T, D 50V ): D 50A : Median grain size based on area distribution. A T : Total area per liter (A T =Σa i ) D 50V : Median grain size based on volume distribution. 4/10 (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

11. Inherent and Apparent Optical Properties of Surface Water LISST Beam Attenuation Coefficient C m -1 Distance from the Mouth (km) Sept. 2014 June 2013 1. Beam Attenuation Coefficient (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) 5/10 (Boss, 2003; Kirk, 1994; Lund-Hansen et al., 2010; LISST-100 User’s Guide; Neukermans et al., 2014)

12. K d m -1 Vertical Diffuse Light Attenuation Coefficient Distance from the Mouth (km) Sept. 2014 June 2013 Sept. 2014 June 2013 5/10 1. Beam Attenuation Coefficient (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) 2. Vertical Diffuse Light Attenuation Coefficient (K d ) Apparent: Depends on medium and ambient light field Measured by either Radiometer or LICOR downward irradiance (E d ) at two depths (z 1,z 2 ): Measures PAR (400-700 nm) (Boss, 2003; Kirk, 1994; Lund-Hansen et al., 2010; LISST-100 User’s Guide; Neukermans et al., 2014) Inherent and Apparent Optical Properties of Surface Water LISST Beam Attenuation Coefficient C m -1 Distance from the Mouth (km)

13. Similar Temporal and Spatial Variability: Sept. 2014 June 2013 5/10 (Boss, 2003; Kirk, 1994; Lund-Hansen et al., 2010; LISST-100 User’s Guide; Neukermans et al., 2014) Sept. 2014 June 2013 1. Beam Attenuation Coefficient (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) 2. Vertical Diffuse Light Attenuation Coefficient (K d ) Apparent: Depends on medium and ambient light field Measured by either Radiometer or LICOR downward irradiance (E d ) at two depths (z 1,z 2 ): Measures PAR (400-700 nm) Inherent and Apparent Optical Properties of Surface Water K d m -1 Distance from the Mouth (km) C m -1 Distance from the Mouth (km) Vertical Diffuse Light Attenuation Coefficient LISST Beam Attenuation Coefficient

14. r 2 =0.88 K d m -1 C m -1 Strong linear regression between C and K d : Beam Attenuation versus Light Attenuation 5/10 (Boss, 2003; Kirk, 1994; Lund-Hansen et al., 2010; LISST-100 User’s Guide; Neukermans et al., 2014) Inherent and Apparent Optical Properties of Surface Water 1. Beam Attenuation Coefficient (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) 2. Vertical Diffuse Light Attenuation Coefficient (K d ) Apparent: Depends on medium and ambient light field Measured by either Radiometer or LICOR downward irradiance (E d ) at two depths (z 1,z 2 ): Measures PAR (400-700 nm)

15. Preliminary Look at Controls on Optical Attenuation (C and K d ): Total Suspended Solids (TSS) K d m -1 K d versus TSS C m -1 C versus TSS TSS (mgL -1 ) 6/10 (Lund-Hansen et al., 2010)

16. K d m -1 K d versus TSS C m -1 C versus TSS TSS (mgL -1 ) Preliminary Look at Controls on Optical Attenuation (C and K d ): Total Suspended Solids (TSS) K dDISS C DISS K dDISS ~0.22 m -1 C DISS ~2.8 m -1 Use intercept from linear fit for TSS < 40 mg/L to estimate attenuation due to water and dissolved constituents (K dDISS and C DISS ). 6/10 (Lund-Hansen et al., 2010)

17. K d m -1 K d versus TSS C m -1 C versus TSS TSS (mgL -1 ) Preliminary Look at Controls on Optical Attenuation (C and K d ): Total Suspended Solids (TSS) K dDISS C DISS K dDISS ~0.22 m -1 C DISS ~2.8 m -1 6/10 (Lund-Hansen et al., 2010) Calculate light (K dP ) and beam (C p ) attenuation due to particles: 1. K dP = K d - K dDISS 2. C p = C - C DISS

18. Preliminary Look at Controls on Optical Attenuation (C and K d ): Total Suspended Solids (TSS) K dP m -1 TSS mgL -1 K dP versus TSS Remove K dDISS ~0.22 m -1 Remove C DISS ~2.8 m -1 C P m -1 C P versus TSS TSS mgL -1 6/10 (Lund-Hansen et al., 2010) K d m -1 K d versus TSS C m -1 C versus TSS K dDISS C DISS K dDISS ~0.22 m -1 C DISS ~2.8 m -1

19. Preliminary Look at Controls on Optical Properties (C P and K dP ): Area vs TSS r 2 =0.87 r 2 =0.67 r 2 =0.97 r 2 =0.78 K dP versus A T C P versus A T K dP versus TSS C P versus TSS A T cm 2/ L TSS mgL -1 K dP m -1 C P m -1 K dP m -1 C P m -1 A T cm 2/ L 7/10

20. Preliminary Look at Controls on Optical Properties (C P and K dP ): Area vs TSS r 2 =0.87 r 2 =0.67 r 2 =0.97 r 2 =0.78 K dP versus A T C P versus A T K dP versus TSS C P versus TSS A T cm 2/ L TSS mgL -1 K dP m -1 C P m -1 K dP m -1 C P m -1 A T cm 2/ L Attenuation explained better by A T than TSS. (Also C p less noisy than K dp ) 7/10

21. Preliminary Look at Controls on Optical Properties (C P and K dP ): Relationship to Area Attenuation explained better by A T than TSS. Others (e.g., Neukermans et al., 2014) suggest that attenuation due to particles (both diffuse light and beam) become nearly constant when normalized by A T : ≈ constant, ≈ constant r 2 =0.87 r 2 =0.97 K dP versus A T C P versus A T A T cm 2/ L K dP m -1 C P m -1 A T cm 2/ L 8/10

22. Preliminary Look at Controls on Optical Properties (C P and K dP ): Relationship to Area Attenuation explained better by A T than TSS. Others (e.g., Neukermans et al., 2014) suggest that attenuation due to particles (both diffuse light and beam) become nearly constant when normalized by A T : ≈ constant, ≈ constant r 2 =0.87 r 2 =0.97 K dP versus A T C P versus A T A T cm 2/ L K dP m -1 C P m -1 A T cm 2/ L 8/10 Does this hold for York estuary? What are causes of any observed variations? (note that above plots are log-log, not linear) Next step: Normalize K dp and C p by A T to see if it is independent of particle composition.

23. Preliminary Look at Controls on Optical Properties (C P and K dP ): Relationship to Area Others (e.g., Neukermans et al., 2014) suggest that attenuation due to particles (both light and beam) become nearly constant when normalized by A T : ≈ constant, ≈ constant 8/10 Does this hold for York estuary? What are causes of any observed variations? (now the above plots are linear) K dP normalized by A T versus organic matter content C P normalized by A T versus organic matter content K dP /A T C P /A T Fraction Organic Content No, our measurements (erroneously?) do not show area-normalized attenuation to be constant.

24. Preliminary Look at Controls on Optical Properties (C P and K dP ): Relationship to Area Others (e.g., Neukermans et al., 2014) suggest that attenuation due to particles (both light and beam) become nearly constant when normalized by A T : ≈ constant, ≈ constant 8/10 K dP normalized by A T versus organic matter content C P normalized by A T versus organic matter content K dP /A T C P /A T Fraction Organic Content We need to consider instrument limitations, smallest particle measured by the LISST is 2.5 μm, while filters used to measure organic content capture grains down to 0.7 μm. Our LISST is NOT able to adequately include the smallest particles which could contribute a significant portion of A T.

25. Simple Solution: Use iterative approach to estimate the particle area not captured by the LISST (A Tsp for sizes 0.7-2.5 microns) needed to make both K dp /(A T +A Tsp ) and C p /(A T +A Tsp ) nearly constant. Iterations suggest A Tsp ≈ 20 cm 2 /L Δ With A tsp ☐ Without A Tsp K dP /A T and K dP /(A T +A Tsp ) C P /A T and C P /(A T +A tsp ) Preliminary Look at Controls on Optical Properties(C P and K dP ): Relationship to Area The addition of the A tsp shows area-normalized attenuation to be nearly constant. Fraction Organic Content K dP normalized by A T versus organic matter content C P normalized by A T versus organic matter content 8/10

26. Simple Solution: Use iterative approach to estimate the particle area not captured by the LISST (A Tsp for sizes 0.7-2.5 microns) needed to make both K dp /(A T +A Tsp ) and C p /(A T +A Tsp ) nearly constant. Iterations suggest A Tsp ≈ 20 cm 2 /L Δ With A tsp ☐ Without A Tsp Preliminary Look at Controls on Optical Properties(C P and K dP ): Relationship to Area The addition of the A tsp shows area-normalized attenuation to be nearly constant. Now adjust D 50A calculation to account for additional A Tsp. by evenly distributing A Tsp among new additional sizes classes (0.7-2.5 microns). Fraction Organic Content K dP normalized by A T versus organic matter content C P normalized by A T versus organic matter content 8/10 K dP /A T and K dP /(A T +A Tsp ) C P /A T and C P /(A T +A tsp )

27. Preliminary Look at the Relationship Between Particle Size and Composition (Organic Content): 102025 Fraction Organic Content D 50A in Log Space r 2 =0.0023 p=0.80 r 2 =0.16 p=0.01 r 2 =0.23 p=0.005 D 50A has a stronger, more significant negative correlation to organic matter content (i.e. smaller particles are more organic). D 50V does not show this trend. 9/10 Δ Adjusted D 50A Unadjusted D 50A ☐ D 50V Δ Adjusted D 50A Unadjusted D 50A D 50 in Log Space

28. Preliminary Look at the Relationship Between Particle Size and Composition (Organic Content): 102025 Fraction Organic Content D 50 in Log Space r 2 =0.0023 p=0.80 r 2 =0.16 p=0.01 r 2 =0.23 p=0.005 9/10 Δ Adjusted D 50A Unadjusted D 50A ☐ D 50V The most relevant D 50 for attenuation light (i.e. medium size by area) is much smaller than the “classic” D 50 by volume. D 50A for surface waters is 10 to 20 times smaller than D 50v. Δ Adjusted D 50A Unadjusted D 50A D 50 in Log Space

29. Conclusions: Strong linear regression between Beam Attenuation Coefficient (C) and Vertical Diffuse Attenuation Coefficient (K d ), which allows (C) to be a proxy of K d (surface water clarity for photosynthesis) when K d values are not available. After removing effects of water and dissolved materials, both Particle Beam Attenuation Coefficient (C p ) and Particles Diffuse Attenuation Coefficient (K dP ) are better explained by total particle area concentration (A T ) than total suspended solids (TSS). There is a contribution of area of smaller particles that cannot be detected by the current LISST (A Tsp ~0.7 - 2.5 microns ) that needs to be accounted for when looking at total total particle area concentration (A T + A Tsp ) as well as D 50A. Preliminary results from the York indicate importance of these small, more organic particles on optical properties. The medium particle size for attenuating light in surface waters is 10 to 20 times smaller than the classic D 50 by volume. Future work will include (i) many more sampling cruises and (hopefully) (ii) deployment of a LISST that can detect smaller particle sizes. 10/10

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