CHRP Narragansett Bay project: Box Modeling progress M. Brush Aug 2008 (1.) Physical box model (after Officer 1980 and Swanson & Jayko (1988) … (exchanges computed from freshwater inputs and salinity distributions)

RI Sound No horizontal exchange here – a potential weakness and can revisit – but right now I can’t see how to adjust the box model eqns to let this happen. Exchange from 3 to 4 & 5 is based on the relative volume of freshwater in 4 & 5.

Schematic of exchanges: Q = advective (grav. circ.) E = non-advective (tidal) Subscript v denotes vertical exch. Care is taken to divide bottom area into both the surface and bottom layers based on hypsographic analysis

General equations. Note freshwater inputs are divided between surface and bottom layer. I do that by computing the volume of freshwater in each layer and using the ratio to divide incoming river flow. The Hansen-Rattray parameter ( ) divides exchanges between advective and tidal components. I will compute this later using the Officer & Kester method but now have it set at 0.5 All freshwater inputs are time-averaged as it is the longer time scale that drives estuarine circulation. Currently the averaging window is 10 days. I need to test this.

Currently only rivers and precip. Need to add evaporation and WWTFs – does anyone have these time series? USGS daily flows compiled for the only gauged rivers in the watershed: Blackstone Pawtuxet Moshassuck Woonasquatucket Taunton Ten Mile Hunt Time period: 2001 – 2006 (time when most buoys operational) (saving for independent model validation) Precip data from TF Green (can modify if we want but this was the quickest route for now) Freshwater Inputs

Watersheds were delineated in GIS for each NarrBay box. Flow at each of the 7 USGS gauges (red circles) was increased to account for the ungauged portion on an areal basis. Flow in the completely ungauged watersheds was computed from watershed area and flow/area for the Hunt watershed, which is a small, typical (as far as I recall) RI watershed so considered reflective of the others.

Salinity Distributions For now, simple cosine functions for annual salinity fluctuations were developed from Insomniacs data supplemented with data from the buoys, GSO dock, and GSO Fox Is. Station. Insomniacs data at each site on each date from were averaged from 0-3m and 3m-bottom. Values were plotted by day of year (not relative to a specific year) and cosine fcns fit by eye. An example is to the right  See file “salinity functions.pdf” for all boxes. Points: Averaged Insomniac data Thin lines: Bullocks Reach buoy data Thick lines: cosine functions S = surface layer B = bottom layer

Sample Box Model Output (units are m3/d, 1/1/01 – 12/31/06) Q’sE’s Qv’sEv’s

Computed Residence Times Providence River (Box 1-3) – Similar values to what I recall Greenwich Bay (Box 6-7) – seems a little high Entire Narragansett Bay – matches Pilson’s estimates and variability fairly well. 1/1/01 12/31/06 RT, DAYS

Computed Residence Times all y-axes are 0 – 40 days all x-axes are 1/1/ /31/06 Providence River boxes Greenwich Bay (6-7) & Mt Hope (10) Bay Upper Bay boxes

West Passage boxes East Passage boxes Computed Residence Times all y-axes are 0 – 40 days all x-axes are 1/1/ /31/06

Box Model Summary: (1)Running and producing reasonable exchanges and residence times. (2)Conserving volume (3)Need to refine and add WWTFs & Evaporation (4)Further down the road: (a) use daily buoy/PORTS salinities so more event- scale processes can be captured, and (b) try to formulate salinity functions and pycnocline depths as functions of freshwater flow (and other relevant factors) so forecasts are not tied to present conditions (5) Has been coupled to novel ecosystem model – see following pages …

(2.) Ecological model PAR compiled from Eppley Lab (thanks to Dan and Lora Harris). We have through Jun 06. Pell is sending me the rest and my shop will digitize. (E/m2/d) Nutrient Loading: We can work on this (e.g. using Don’s timeseries or Scott’s new estimates), but for now I have used a quick and easy solution. Also need to add in WWTFs. Atmospheric loads are based on historical data (eg Fraher thesis). Here is my approach for watershed loads analogous to what I did for the original Greenwich Bay model: Nixon et al (1995) mass balance paper: Reports annual DIN, DIP load for 5 major rivers I used total annual flow to estimate the average DIN & DIP concentration in the rivers: I used the average of the Taunton, Moshassuck, and Woonasquatucket (no WWTFs) for the ungauged watersheds.

There is still lots to work on, but the model is up and running. See file “Output_Aug08.pdf” for results with no biological tuning... The results are very encouraging! The model produces fairly typical annual cycles of chl, din, dip, & DO, with typical down-estuary gradients. The shape of the cycles needs a bit of work, and there is something going on betweeen the 1 st and remaining years. Also a weird box every now and then (e.g. Box 6 – Greenwich Bay DO). But look at the broad-scale comparison of predicted vs Insomniacs DO … (and I didn’t tune any biological/chemical parameters). Wicked cool!