Post on 16-Jan-2016
2014 Dissolved Oxygen Assessment
CHRP MeetingDecember 17, 2014
Heather Stoffel
5/215/2
65/3
16/5
6/106/1
56/2
06/2
56/3
07/5
7/107/1
57/2
07/2
57/3
08/4 8/9
8/148/1
98/2
48/2
99/3 9/8
9/139/1
89/2
39/2
80.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
BR CP NP MV QP
Dis
solv
ed O
xyge
n (m
g/L)
Daily Bottom Oxygen Levels for Upper Bay and West Passage
This is the over all range of exceedences for each station for all years of data in a down bay gradient. The ranges considers inter-annual variability due to weather. An exceedence is greater than 1 day. The Seekonk (PD) to Mt View (MV) and Poppasquash Pt (PP) are consistently in exceedence every year. That is why this area is listed as impaired for dissolved oxygen. Areas of concern are areas like Quonset Pt (QP). The Seekonk, Providence River, and Greenwich Bay have the worst exceedence with average exceedences of a month or more a year.
Seasonal Cumulative River Flow from the Blackstone River and Seasonal Mean Surface Temperature from North Prudence Station
2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 20140
20,000
40,000
60,000
80,000
100,000
120,000
18
19
20
21
22
23
24
Sept Aug July June Temperature (C, NP-S)
Flo
w
(cu
.ft.
/se
c) T
em
pe
ratu
re ( C
)
mph
°
Seasonal wind directions tend to be from the SSW.
Dry seasons (7.83 mph) tend to have slightly higher average wind speed compared to wet seasons (7.35 mph).
2012 had lowest wind speed for dry season (7.02 mpH)
2009 had SSE wind direction
Dry Years
Wet Years
(2002, 2005, 2007, 2010, 2014)
(2001, 2003, 2004, 2006, 2008, 2009, 2011, 2013)
PD BR CP NP GB SR MV QP PP MH0
10
20
30
40
50
60
70
Exceedences During Dry Years
200220052007201020122014
RID
OCS
Day
s
PD BR CP NP GB SR MV QP GD PP MH TW0
20
40
60
80
100
120
Exceedences During Wet Years
20012003200420062008200920112013RI
DO
CS D
ays
Dissolved Oxygen Exceedences Over Time
North Prudence is showing a downward trend towards compliance. An exceedence is 1 day. The Providence River is in exceedence consistently over all years.
(Grouped data in 5 year intervals with the exceptions of 2011-2014 * indicates not complete dataset.)
PD (2004-2005)*
BR (2001-2005)
CP (2003, 2005)*
NP (2001-2005)
PD (2006-2010)
BR (2006-2010)
CP (2006-2010)
NP (2006-2010)
PD (2011-2013)*
BR (2011-2014)
CP (2011-2014)
NP (2011-2014)
0
20
40
60
80
100
120
Dissolved Oxygen Exceedence Ranges for Upper Bay from 2001-2014
5 year intervals for Upper Bay Stations
RI D
OCS
(Day
s)
0 5 10 15 20 25 30 350
1
2
3
4
5
6
7
BR CP NP GB SR MV QP PP MH
Surface Chlorophyll (ug/L)
Bo
tto
m D
iss
olv
ed
Ox
yg
en
(m
g/L
)Comparison of Seasonal Average Surface Chlorophyll Levels to
Bottom Dissolved Oxygen in Upper Narragansett Bay
R²= -0.597p< 0.00005
Chlorophyll as an Indicator
• Many New England and Mid-Atlantic estuaries use 20 ug/L as a threshold during the growing season (i.e., EPA-National Coastal Condition Reports (NCCR) threshold)
• The figure showing the relationship between low bottom oxygen and surface chlorophyll also shows that on average seasonally Bullock Reach and Greenwich Bay are consistently over the 20 ug/L threshold (which under the EPA-NCCR definition would be “poor” water quality for chlorophyll)
• Many of Upper Narragansett Bay stations have events with peaks above the 20 ug/L threshold
From the Seekonk River to North Prudence on average is considered eutrophic based on EPA definitions. Mt View and Quonset have episodic events at eutrophic levels. (Data (2001-2012) June 1-Sept 30)
PD BR CP NP MV QP GD0
20406080
100120140160180200220240 Summer Chlorophyll Ranges in Narragansett
Bay
Stations - North to South
Chlo
roph
yll R
ange
(ug/
L)
Comparison of Chlorophyll Seasonal Ranges for Upper Bay and West Passage Stations
BR (01-05) BR (06-10) BR (11-14) NP (01-05)* NP (06-10)* NP (11-14) MV (04-05)*
MV (06-10) MV (11-14)0
102030405060708090
100110120130140150
Stations - North to South
Chlo
roph
yll R
ange
(ug/
L)
* Indicates data gaps greater than 15 days
Bullock Reach remains eutrophic throughout all years. North Prudence chlorophyll levels have dropped since 2006. Mt. View ranges vary, but remain below 20 ug/L.Data is grouped over 5 years to account for inter-annual variability and several years are examined during assessments.
Conclusions
• 2014 was a “good year” (drier and cooler than average).
• NP appears to be showing a downward trend in oxygen exceedences and chlorophyll levels.
• MV may also be showing a downward trend in oxygen, but further analysis is needed.
• MH needs further examination. It is possible hypoxia is increasing in this area.