Table 1 Laboratory mean percent error relative to known standards and mean relative percent difference for field duplicates are reported for each parameter.

Parameter	Units	Mean Percent Error	Mean Relative Percent Difference
Temperature	°C	0.02	−0.06
Salinity	psu	−0.29	−0.05
DO	mg/L	0.22	0.57
pH	N/A	−0.26	0.02
Secchi Depth	m	n.d.	1.75
Dissolved Inorganic Carbon	µmol/kg	−0.44	−0.04
Total Alkalinity	µmol/kg	−0.18	−0.04
Biological Oxygen Demand	mg/L	−26.5	6.29
Settleable Solids	mL/L	n.d.	0
Total Suspended Solids	mg/L	−2.13	−1.54
Turbidity	NTU	n.d.	3.97
Chlorophyll-a	µg/L	4.35	6.34
ortho-Phosphate	mg/L	−2.07	3.82
Nitrate + Nitrite	mg/L	−4.99	5.22
Total Kjeldahl Nitrogen	mg/L	−3.7	5.42
Enterococcus spp.	ind/100 mL	n.d.	32.23

No data (n.d.) exists for the mean percent error calculations for Secchi Depth, Enterococcus spp., and Settleable Solids owing to the absence of certified reference materials. While Turbidity was evaluated to within 10% of certified reference values daily, only one daily calibration check with a mean accuracy of 0.8% was recorded in Quarter 1 so the mean percent error was reported as n.d. for this parameter owing to the lack of consistent checks across all samples.

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