Turbidity (TURB)

Status and Trends

Turbidity is a measure of water clarity and is often due to suspended solids in the water as well as color and dissolved organic matter. A rough measure of turbidity can be made with a Secchi Disk, but more accurate measurements need to be taken with a turbidimeter. Turbidity is measured in NTUs, the abbreviation for nephelometric turbidity unit.

A normal range for turbidity in river water has not been established, but in finished drinking water turbidity should be less than one NTU. Highly turbid waters will appear to be murky or muddy. Turbidity in excess of five NTUs can be easily detected. Turbidity at that level may not affect your health, but water treatment may be desirable. Excessive turbidity may interfere with disinfection processes and is measured by municipalities to monitor the efficiency of public water supply filtration systems used to remove parasites and viruses in water.

Median turbidity ranged from 1.9 NTUs on Town Creek to 10.7 NTUs on Conococheague Creek at MD 68. Median turbidity was below 5.53 NTUs at 52% of all stations. High turbidity (TURB > 9.29 NTU) occurred at seven stations (13%) and intermediate median values occurred at 35% of the stations. Intermediate values predominated in agricultural or urbanizing areas of the state.

Trends of decreasing concentration occurred at 48% of all stations and trends were increasing at one station located near the mouth of Braddock Run and on Cherry Creek.

Turbidity was positively correlated with TSS, a closely related parameter, at 65% of all stations. Turbidity, in addition to the strong correlation with TSS, was positively correlated with CHLA at 62% of all 37 stations where chlorophyll is sampled. Both TURB and CHLA exhibited declining trends in over half of all the stations where the two parameters were significantly correlated suggesting that phytoplankton may be a dominant contributor to TURB at these stations.

Turbidity (TURB) data for sampled locations are summarized in these plots.

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This page was updated on 12/5/2005