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Roberts Bay Condition Report for 2011

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Pass

3 out of 3 indicators were rated as PASS.

All three indicators must pass
for the bay to be rated as PASS.

Learn more about how this report is created

Summary:

The overall health of Roberts Bay has improved since 2010 with all water quality parameters below the threshold levels, the caution alert for chlorophyll a has been removed. However, levels of seagrass still remain below the target level. 

Water quality: All three water quality indicators (chlorophyll a, nitrogen, and phosphorus) were rated as pass (below the threshold). The mean for chlorophyll a was calculated as an arithmetic mean and the means for nitrogen and phosphorus were calculated as geometric means (Numeric Nutrient Criteria Recommendations).The mean chlorophyll a level in Roberts Bay has improved since 2010 (0.0098 mg/l) and was scored as good (scored as caution in 2010), below the threshold (0.011 mg/l). The nitrogen level has increased, although the mean nitrogen level was below the threshold (0.540 mg/l), it exceeds the target level (0.450 mg/l) and was scored as good. The phosphorus level has slightly increased, however the mean level (0.0923 mg/l) was still below the target level (0.190 mg/l) and was scored as excellent.

Biotic Indicator:  The total acreage of seagrass has remained relatively constant since 1988 but in 2010 the average level of seagrass (283 acres) was still below the target of 348 acres.

Water Chemistry Ratings

Total nitrogen, total phosphorus, and chlorophyll a levels are monitored carefully by water resource managers and used by regulatory authorities to determine whether a bay meets the water quality standards mandated by the Clean Water Act. The trend graphs for these indicators are shown below, along with their target and threshold values. A target value is a desirable goal to be attained, while a threshold is an undesirable level which is to be avoided. Learn More about these ratings and how they are calculated »

The Five-year Trend Graphs below illustrate the general trend of water quality parameters. They show a six-month running average, which moderates high and low values in the data.

Good

Chlorophyll a

Units: mg/l Year
2011
Historical
period of record
High 0.0246 0.0484
Mean 0.0089 0.0078 0.00773879 0.0082000000
Low 0.0007 0.0003
No. of Samples 60 885

Five-year Trend Graph

     
1/1/20071.7050.0017000mg/l
2/1/20070.5450.0011200mg/l
3/1/20071.1550.0011300mg/l
4/1/20074.8050.0020500mg/l
5/1/20072.9550.0022300mg/l
6/1/20072.4850.0022700mg/l
7/1/20075.4560.0029000mg/l
8/1/20075.9160.0037900mg/l
9/1/20074.3060.0043200mg/l
10/1/20078.3860.0049100mg/l
11/1/20072.4060.0048200mg/l
12/1/20072.9460.0049000mg/l
1/1/20083.8860.0046400mg/l
2/1/20083.0860.0041600mg/l
3/1/20082.6560.0038900mg/l
4/1/20086.2060.0035300mg/l
5/1/20088.1960.0044900mg/l
6/1/20085.6960.0049500mg/l
7/1/20086.9260.0054600mg/l
8/1/200813.9460.0072700mg/l
9/1/200816.6650.0096000mg/l
10/1/200814.6460.0110100mg/l
11/1/20084.4460.0103800mg/l
12/1/20081.6060.0097000mg/l
1/1/20095.9450.0095400mg/l
2/1/20091.4850.0074600mg/l
3/1/20091.9550.0050100mg/l
4/1/20093.9150.0032200mg/l
5/1/200911.9250.0044700mg/l
6/1/20096.3950.0052700mg/l
7/1/200910.0150.0059400mg/l
8/1/20099.1650.0072200mg/l
9/1/200912.8350.0090400mg/l
10/1/200926.1350.0127400mg/l
11/1/20098.7250.0122100mg/l
12/1/20097.2450.0123500mg/l
1/1/20101.2950.0109000mg/l
2/1/20103.0250.0098700mg/l
3/1/20101.1860.0079300mg/l
4/1/20108.3250.0049600mg/l
5/1/201012.4950.0055900mg/l
6/1/201016.7660.0071800mg/l
7/1/201015.3560.0095200mg/l
8/1/201030.6650.0141300mg/l
9/1/201033.6650.0195400mg/l
10/1/201013.9550.0204800mg/l
11/1/201010.4550.0201400mg/l
12/1/20103.1650.0178700mg/l
1/1/20111.7350.0156000mg/l
2/1/20112.3850.0108900mg/l
3/1/20116.8650.0064200mg/l
4/1/20118.5650.0055200mg/l
5/1/20117.4950.0050300mg/l
6/1/201111.7850.0064700mg/l
7/1/201113.7050.0084600mg/l
8/1/201118.1950.0111000mg/l
9/1/201115.0750.0124700mg/l
10/1/201111.8550.0130100mg/l
11/1/20116.6950.0128800mg/l
12/1/20112.0150.0112500mg/l
Loading Chart...
Target
0.0082 mg/l
Threshold
0.011 mg/l
Good

Nitrogen, Total

Units: mg/l Year
2011
Historical
period of record
High 0.791 1.376
Mean 0.4874 0.17399 0.4500000000
Low 0.245 0.065
No. of Samples 60 876

Five-year Trend Graph

     
1/1/2007435.0050.4350000mg/l
2/1/2007208.6050.3218000mg/l
3/1/2007325.0050.3228700mg/l
4/1/2007207.0050.2939000mg/l
5/1/2007347.0050.3045200mg/l
6/1/2007330.2050.3088000mg/l
7/1/2007436.6760.3090800mg/l
8/1/2007358.3360.3340300mg/l
9/1/2007450.3360.3549200mg/l
10/1/2007461.6760.3973700mg/l
11/1/2007427.6760.4108100mg/l
12/1/2007412.8360.4245800mg/l
1/1/2008382.6760.4155800mg/l
2/1/2008334.6760.4116400mg/l
3/1/2008313.1760.3887800mg/l
4/1/2008414.6050.3809400mg/l
5/1/2008398.3360.3760500mg/l
6/1/2008418.6760.3770200mg/l
7/1/2008503.3360.3971300mg/l
8/1/2008581.5060.4382700mg/l
9/1/2008568.3360.4807900mg/l
10/1/2008473.0050.4905300mg/l
11/1/2008426.1760.4951700mg/l
12/1/2008521.1760.5122500mg/l
1/1/2009418.8050.4981600mg/l
2/1/2009319.0050.4544100mg/l
3/1/2009371.0050.4215200mg/l
4/1/2009361.0050.4028600mg/l
5/1/2009521.0050.4186600mg/l
6/1/2009445.0050.4059700mg/l
7/1/2009411.0050.4046700mg/l
8/1/2009329.0050.4063300mg/l
9/1/2009449.6050.4194300mg/l
10/1/2009505.0050.4434300mg/l
11/1/2009413.6050.4255300mg/l
12/1/2009506.0050.4357000mg/l
1/1/2010275.0050.4130300mg/l
2/1/2010399.6050.4248000mg/l
3/1/2010240.0060.3898700mg/l
4/1/2010627.8050.4103300mg/l
5/1/2010499.0050.4245700mg/l
6/1/2010547.0060.4314000mg/l
7/1/2010426.8360.4567100mg/l
8/1/2010517.0050.4762700mg/l
9/1/2010643.2050.5434700mg/l
10/1/2010409.0050.5070100mg/l
11/1/2010751.6050.5491100mg/l
12/1/2010386.4050.5223400mg/l
1/1/2011357.4050.5107700mg/l
2/1/2011296.4050.4740000mg/l
3/1/2011567.0050.4613000mg/l
4/1/2011601.2050.4933300mg/l
5/1/2011533.0050.4569000mg/l
6/1/2011565.0050.4866700mg/l
7/1/2011543.6050.5177000mg/l
8/1/2011696.4050.5843700mg/l
9/1/2011663.0050.6003700mg/l
10/1/2011433.0050.5723300mg/l
11/1/2011425.4050.5544000mg/l
12/1/2011409.4050.5284700mg/l
Loading Chart...
Target
0.45 mg/l
Threshold
0.54 mg/l
Excellent

Phosphorus, Total

Score: Excellent How was this determined?
Units: mg/l Year
2011
Historical
period of record
High 0.26 0.48
Mean 0.0851 0.06715076 0.1900000000
Low 0.05 0.05
No. of Samples 60 866

Five-year Trend Graph

     
1/1/2007144.0050.1440000mg/l
2/1/2007112.0050.1280000mg/l
3/1/2007134.0050.1300000mg/l
4/1/2007100.0050.1225000mg/l
5/1/2007144.0050.1268000mg/l
6/1/2007132.0050.1276700mg/l
7/1/2007152.0050.1290000mg/l
8/1/2007170.0060.1386700mg/l
9/1/2007196.0050.1490000mg/l
10/1/2007150.0050.1573300mg/l
11/1/2007133.3360.1555600mg/l
12/1/2007134.0050.1558900mg/l
1/1/2008166.6760.1583300mg/l
2/1/2008115.0060.1491700mg/l
3/1/2008140.0050.1398300mg/l
4/1/2008168.0050.1428300mg/l
5/1/2008203.3360.1545000mg/l
6/1/2008168.0050.1601700mg/l
7/1/2008153.3360.1579400mg/l
8/1/2008225.0060.1762800mg/l
9/1/2008130.0060.1746100mg/l
10/1/2008100.0060.1632800mg/l
11/1/200875.0060.1418900mg/l
12/1/200891.6760.1291700mg/l
1/1/200998.0050.1199500mg/l
2/1/200966.0050.0934500mg/l
3/1/200968.0050.0831100mg/l
4/1/200982.0050.0801100mg/l
5/1/2009108.0050.0856100mg/l
6/1/200992.0050.0856700mg/l
7/1/2009100.0050.0860000mg/l
8/1/200990.0050.0900000mg/l
9/1/2009108.0050.0966700mg/l
10/1/2009144.0050.1070000mg/l
11/1/200966.0050.1000000mg/l
12/1/200972.0050.0966700mg/l
1/1/201050.0050.0883300mg/l
2/1/201054.0050.0823300mg/l
3/1/201054.0050.0733300mg/l
4/1/201090.0050.0643300mg/l
5/1/2010152.0050.0786700mg/l
6/1/2010135.0060.0891700mg/l
7/1/201052.0050.0895000mg/l
8/1/201074.0050.0928300mg/l
9/1/2010168.0050.1118300mg/l
10/1/2010102.0050.1138300mg/l
11/1/2010164.0050.1158300mg/l
12/1/201064.0050.1040000mg/l
1/1/201158.0050.1050000mg/l
2/1/201150.0050.1010000mg/l
3/1/201192.0050.0883300mg/l
4/1/2011158.0050.0976700mg/l
5/1/2011118.0050.0900000mg/l
6/1/2011106.0050.0970000mg/l
7/1/2011104.0050.1046700mg/l
8/1/2011142.0050.1200000mg/l
9/1/2011112.0050.1233300mg/l
10/1/201172.0050.1090000mg/l
11/1/201152.0050.0980000mg/l
12/1/201156.0050.0896700mg/l
Loading Chart...
Target
0.19 mg/l
Threshold
0.23 mg/l

Dissolved Oxygen

Units: mg/l Year
2011
Historical
period of record
High 9.70 11.40
Mean 6.48 6.47 1.19951
Low 4.50 3.60
No. of Samples 60 1,021

Five-year Trend Graph

     
1/1/20078.0258.0200000mg/l
2/1/20078.4258.2200000mg/l
3/1/20077.8458.0900000mg/l
4/1/20077.5657.9600000mg/l
5/1/20076.2657.6200000mg/l
6/1/20075.5057.2700000mg/l
7/1/20075.2456.8000000mg/l
8/1/20075.4856.3100000mg/l
9/1/20074.8655.8200000mg/l
10/1/20076.5655.6500000mg/l
11/1/20076.6055.7100000mg/l
12/1/20076.5255.8800000mg/l
1/1/20087.1856.2000000mg/l
2/1/20087.3056.5000000mg/l
3/1/20087.0656.8700000mg/l
4/1/20086.2456.8200000mg/l
5/1/20086.3656.7800000mg/l
6/1/20085.2856.5700000mg/l
7/1/20085.9256.3600000mg/l
8/1/20085.5856.0700000mg/l
9/1/20086.5055.9800000mg/l
10/1/20085.6055.8700000mg/l
11/1/20086.8055.9500000mg/l
12/1/20087.1656.2600000mg/l
1/1/20096.2456.3100000mg/l
2/1/20098.0056.7200000mg/l
3/1/20096.8056.7700000mg/l
4/1/20097.3057.0500000mg/l
5/1/20097.5057.1700000mg/l
6/1/20096.3257.0300000mg/l
7/1/20095.8856.9700000mg/l
8/1/20095.9456.6200000mg/l
9/1/20094.6656.2700000mg/l
10/1/20095.6856.0000000mg/l
11/1/20095.8055.7100000mg/l
12/1/20099.0656.1700000mg/l
1/1/20109.5656.7800000mg/l
2/1/20107.7057.0800000mg/l
3/1/20107.7257.5900000mg/l
4/1/20107.4857.8900000mg/l
5/1/20106.5258.0100000mg/l
6/1/20105.6257.4300000mg/l
7/1/20106.1256.8600000mg/l
8/1/20106.9056.7300000mg/l
9/1/20105.5256.3600000mg/l
10/1/20106.4056.1800000mg/l
11/1/20107.6056.3600000mg/l
12/1/20107.2256.6300000mg/l
1/1/20117.6656.8800000mg/l
2/1/20118.3457.1200000mg/l
3/1/20116.6857.3200000mg/l
4/1/20116.6857.3600000mg/l
5/1/20115.9257.0800000mg/l
6/1/20115.8456.8500000mg/l
7/1/20114.8856.3900000mg/l
8/1/20114.9855.8300000mg/l
9/1/20116.9655.8800000mg/l
10/1/20116.3455.8200000mg/l
11/1/20116.6255.9400000mg/l
12/1/20116.8256.1000000mg/l
Loading Chart...
Target
mg/l
Threshold
0.00 mg/l

Light Attenuation

Units: K(1/m) Year
2011
Historical
period of record
High 1.89 3.56
Mean 1.1 1.02 0.44353
Low 0.36 0.19
No. of Samples 60 827

Five-year Trend Graph

     
1/1/20070.9850.9800000K(1/m)
2/1/20070.5650.7700000K(1/m)
3/1/20070.7450.7600000K(1/m)
4/1/20070.9850.8200000K(1/m)
5/1/20070.7150.7900000K(1/m)
6/1/20070.9050.8100000K(1/m)
7/1/20070.7050.7700000K(1/m)
8/1/20070.8850.8200000K(1/m)
9/1/20070.6650.8100000K(1/m)
10/1/20071.1750.8400000K(1/m)
11/1/20071.3350.9400000K(1/m)
12/1/20071.3551.0200000K(1/m)
1/1/20081.2351.1000000K(1/m)
2/1/20080.5451.0500000K(1/m)
3/1/20080.7851.0700000K(1/m)
4/1/20080.8451.0100000K(1/m)
5/1/20080.8250.9300000K(1/m)
6/1/20080.5750.8000000K(1/m)
7/1/20080.9050.7400000K(1/m)
8/1/20081.0650.8300000K(1/m)
9/1/20081.4650.9400000K(1/m)
10/1/20081.2451.0100000K(1/m)
11/1/20080.8551.0100000K(1/m)
12/1/20080.7651.0500000K(1/m)
1/1/20091.0951.0800000K(1/m)
2/1/20090.7451.0200000K(1/m)
3/1/20090.5950.8800000K(1/m)
4/1/20090.8050.8100000K(1/m)
5/1/20091.4250.9000000K(1/m)
6/1/20090.7450.9000000K(1/m)
7/1/20091.1650.9100000K(1/m)
8/1/20090.8650.9300000K(1/m)
9/1/20091.1851.0300000K(1/m)
10/1/20091.5851.1600000K(1/m)
11/1/20091.1851.1200000K(1/m)
12/1/20091.1351.1800000K(1/m)
1/1/20100.6951.1000000K(1/m)
2/1/20100.7351.0800000K(1/m)
3/1/20100.6250.9900000K(1/m)
4/1/20101.2750.9400000K(1/m)
5/1/20101.3450.9600000K(1/m)
6/1/20101.2650.9900000K(1/m)
7/1/20101.1451.0600000K(1/m)
8/1/20101.2751.1500000K(1/m)
9/1/20101.5751.3100000K(1/m)
10/1/20101.5251.3500000K(1/m)
11/1/20101.5251.3800000K(1/m)
12/1/20100.8751.3200000K(1/m)
1/1/20110.6251.2300000K(1/m)
2/1/20110.8651.1600000K(1/m)
3/1/20111.3551.1200000K(1/m)
4/1/20111.3351.0900000K(1/m)
5/1/20110.8250.9800000K(1/m)
6/1/20111.0951.0100000K(1/m)
7/1/20111.1951.1100000K(1/m)
8/1/20111.4151.2000000K(1/m)
9/1/20111.5151.2300000K(1/m)
10/1/20111.2351.2100000K(1/m)
11/1/20110.9051.2200000K(1/m)
12/1/20110.8851.1900000K(1/m)
Loading Chart...
Target
K(1/m)
Threshold
0.00 K(1/m)

Rainfall

Units: inches/yr Year
2011
Historical
period of record
High 39.86 54.47
Mean 36.96 11.4343863503378
Low 14.17
No. of Samples 362 4,835

Five-year Trend Graph

     
1/1/20072.79312.7900000inches
2/1/20071.76281.7600000inches
3/1/20070.31310.3100000inches
4/1/20072.56292.5600000inches
5/1/20070.96310.9600000inches
6/1/20073.18303.1800000inches
7/1/20078.28318.2800000inches
8/1/20074.65314.6500000inches
9/1/20075.15305.1500000inches
10/1/20075.48315.4800000inches
11/1/20070.22300.2200000inches
12/1/20070.89310.8900000inches
1/1/20081.89311.8900000inches
2/1/20082.16292.1600000inches
3/1/20083.02313.0200000inches
4/1/20082.62302.6200000inches
5/1/20081.86311.8600000inches
6/1/20083.91303.9100000inches
7/1/20086.83316.8300000inches
8/1/20086.03316.0300000inches
9/1/20084.26304.2600000inches
10/1/20081.63311.6300000inches
11/1/20080.69300.6900000inches
12/1/20081.43301.4300000inches
1/1/20091.56321.5600000inches
2/1/20090.56280.5600000inches
3/1/20091.22311.2200000inches
4/1/20091.64301.6400000inches
5/1/20094.54314.5400000inches
6/1/20094.21304.2100000inches
7/1/20095.75315.7500000inches
8/1/20094.99314.9900000inches
9/1/20098.83308.8300000inches
10/1/20091.00311.0000000inches
11/1/20091.53301.5300000inches
12/1/20093.03313.0300000inches
1/1/20103.95313.9500000inches
2/1/20102.11282.1100000inches
3/1/20105.09315.0900000inches
4/1/20101.38301.3800000inches
5/1/20100.87310.8700000inches
6/1/20106.31306.3100000inches
7/1/20105.45315.4500000inches
8/1/201012.113112.1100000inches
9/1/20102.24302.2400000inches
10/1/20100.01310.0100000inches
11/1/20102.77302.7700000inches
12/1/20100.86310.8600000inches
1/1/20112.83312.8300000inches
2/1/20110.73280.7300000inches
3/1/20115.81315.8100000inches
4/1/20111.49301.4900000inches
5/1/20112.21312.2100000inches
6/1/20113.24303.2400000inches
7/1/20118.71318.7100000inches
8/1/20117.69317.6900000inches
9/1/20114.01304.0100000inches
10/1/20111.88301.8800000inches
11/1/20111.10301.1000000inches
12/1/20110.16290.1600000inches
Loading Chart...
Target
inches/yr
Threshold
inches/yr

Salinity

Units: PSS Year
2011
Historical
period of record
High 35.40 38.80
Mean 30.77 30.68 5.08972
Low 19.80 1.80
No. of Samples 60 1,023

Five-year Trend Graph

     
1/1/200731.74531.7400000PSS
2/1/200731.82531.7800000PSS
3/1/200733.74532.4300000PSS
4/1/200734.58532.9700000PSS
5/1/200734.60533.3000000PSS
6/1/200736.96533.9100000PSS
7/1/200734.52534.3700000PSS
8/1/200735.00534.9000000PSS
9/1/200736.54535.3700000PSS
10/1/200733.94535.2600000PSS
11/1/200731.62534.7600000PSS
12/1/200733.26534.1500000PSS
1/1/200834.66534.1700000PSS
2/1/200834.52534.0900000PSS
3/1/200834.80533.8000000PSS
4/1/200831.50533.3900000PSS
5/1/200835.92534.1100000PSS
6/1/200835.84534.5400000PSS
7/1/200831.28533.9800000PSS
8/1/200827.00532.7200000PSS
9/1/200828.60531.6900000PSS
10/1/200831.22531.6400000PSS
11/1/200834.68531.4400000PSS
12/1/200832.76530.9200000PSS
1/1/200932.18531.0700000PSS
2/1/200934.76532.3700000PSS
3/1/200934.90533.4200000PSS
4/1/200935.34534.1000000PSS
5/1/200936.18534.3500000PSS
6/1/200934.02534.5600000PSS
7/1/200931.22534.4000000PSS
8/1/200933.40534.1800000PSS
9/1/200930.38533.4200000PSS
10/1/200930.90532.6800000PSS
11/1/200932.94532.1400000PSS
12/1/200927.42531.0400000PSS
1/1/201030.04530.8500000PSS
2/1/201027.16529.8100000PSS
3/1/201031.14529.9300000PSS
4/1/201027.82529.4200000PSS
5/1/201031.38529.1600000PSS
6/1/201033.16530.1200000PSS
7/1/201031.68530.3900000PSS
8/1/201028.92530.6800000PSS
9/1/201026.68529.9400000PSS
10/1/201031.50530.5500000PSS
11/1/201032.84530.8000000PSS
12/1/201033.48530.8500000PSS
1/1/201131.42530.8100000PSS
2/1/201130.24531.0300000PSS
3/1/201133.58532.1800000PSS
4/1/201124.66531.0400000PSS
5/1/201130.28530.6100000PSS
6/1/201134.62530.8000000PSS
7/1/201130.58530.6600000PSS
8/1/201131.28530.8300000PSS
9/1/201125.42529.4700000PSS
10/1/201131.62530.6300000PSS
11/1/201133.52531.1700000PSS
12/1/201132.02530.7400000PSS
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Turbidity

Units: NTU Year
2011
Historical
period of record
High 9.50 24.00
Mean 4.91 4.19 2.16482
Low 0.85 0.85
No. of Samples 60 880

Five-year Trend Graph

     
1/1/20072.0652.0600000NTU
2/1/20071.9251.9900000NTU
3/1/20072.4252.1300000NTU
4/1/20074.2652.6700000NTU
5/1/20072.6452.6600000NTU
6/1/20072.1852.5800000NTU
7/1/20072.7362.6900000NTU
8/1/20073.2362.9100000NTU
9/1/20072.3262.8900000NTU
10/1/20073.9562.8400000NTU
11/1/20072.7262.8600000NTU
12/1/20072.3862.8900000NTU
1/1/20082.3262.8200000NTU
2/1/20081.6362.5500000NTU
3/1/20082.1562.5300000NTU
4/1/20083.1262.3900000NTU
5/1/20083.4262.5000000NTU
6/1/20082.4452.5100000NTU
7/1/20082.9362.6200000NTU
8/1/20084.1053.0300000NTU
9/1/20085.3563.5600000NTU
10/1/20085.8864.0200000NTU
11/1/20083.3864.0100000NTU
12/1/20081.9763.9400000NTU
1/1/20093.2253.9800000NTU
2/1/20093.6653.9100000NTU
3/1/20093.1653.5500000NTU
4/1/20095.4053.4700000NTU
5/1/20096.3253.9600000NTU
6/1/20094.2054.3300000NTU
7/1/20094.3854.5200000NTU
8/1/20094.7454.7000000NTU
9/1/20094.5054.9200000NTU
10/1/20096.4055.0900000NTU
11/1/20095.0854.8800000NTU
12/1/20093.4854.7600000NTU
1/1/20101.1054.2200000NTU
2/1/20102.9453.9200000NTU
3/1/20103.2563.7100000NTU
4/1/20107.0453.8200000NTU
5/1/20106.8854.1200000NTU
6/1/20107.0064.7000000NTU
7/1/20105.4065.4200000NTU
8/1/20107.6056.2000000NTU
9/1/20104.4856.4000000NTU
10/1/20105.4856.1400000NTU
11/1/20107.3856.2200000NTU
12/1/20103.2855.6000000NTU
1/1/20111.2754.9200000NTU
2/1/20113.3654.2100000NTU
3/1/20116.0854.4800000NTU
4/1/20117.0654.7400000NTU
5/1/20114.3054.2300000NTU
6/1/20115.8454.6500000NTU
7/1/20117.2855.6500000NTU
8/1/20114.2655.8000000NTU
9/1/20117.7856.0900000NTU
10/1/20117.1856.1100000NTU
11/1/20112.6855.8400000NTU
12/1/20111.7755.1600000NTU
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Other Measures of Bay Health

In addition to nutrient levels and chlorophyll concentration, dissolved oxygen levels, and water clarity are also objective indicators of bay health. These have complex interactive cycles which are affected by rainfall, temperature, and tidal action, as well as other factors. High nutrient levels (nitrogen and phosphorus) can stimulate excessive growth of marine algae (indicated by chlorophyll a level), resulting in reduced water clarity (and increased light attenuation) and depleted oxygen levels. Both plants and animals in a bay need oxygen to survive, and the seagrasses which provide food and cover for bay creatures need light for photosynthesis.

Bay Contour Maps (2011)

Contour mapping is one of the best ways to visualize spatial differences in coastal water quality. The interactive map shown below presents monthly data for one selected water quality indicator atop an aerial view of the bay. Choose a different water quality parameter from the list at the top to change the map. Learn More about Water Quality Contour Mapping »

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Contour Visibility:

Visit the Water Quality Contour Mapping Tool to view and compare monthly water quality contour maps for ten different water quality indicators. In addition, you can generate your own custom maps.

Contour Legend:

  • Less than 1 mg/l
  • 1.0 - 5.9 mg/l
  • 6.0 - 10.9 mg/l
  • 11.0 - 17.9 mg/l
  • Greater than 18 mg/l

Seagrasses

Among the most important habitats in Florida's estuarine environments, seagrass beds are indispensable for the role they play in cycling nutrients, supplying food for wildlife, stabilizing sediments, and providing habitat for juvenile and adult finfish and shellfish. Use the interactive map below to observe the size, density and location of seagrass beds from year to year. The graph shows how the total amount of seagrass in the bay has changed over time. Learn More about Seagrasses »

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Target
348 acres

Land Use / Land Cover

Land use within a bay's watershed has a major effect on its water quality. In general, less development means better water quality. Land Cover/Land Use classifications categorize land in terms of its observed physical surface characteristics (upland or wetland, e.g.), and also reflect the types of activity that are taking place on it (agriculture, urban/built-up, utilities, etc.). Florida uses as its standard a set of statewide classifications which were developed by the Florida Department of Transportation. Learn More about Land Use and Land Cover »

Roberts Bay is located within the Sarasota Bay Watershed. The chart below shows the land use / land cover characteristics for Sarasota Bay Watershed within the boundary of this Water Atlas. View details about the Sarasota Bay Watershed »

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