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The Sheepscot River Turbidity Pilot Study, - page 2 / 12





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In January of 2006, Maine Department of Environmental Protection (DEP) published a summary of available water quality information for the Sheepscot River (Whiting 2006).  This report identified nutrient enrichment (nitrate and total phosphorus (TP)) and moderate turbidity as on-going problems in this river.  In 2005, DEP put out a draft TMDL (Total Maximum Daily Load) water quality assessment for the West Branch of the Sheepscot (Meidel and DEP 2005).  The TMDL report called for reductions in nutrients and turbidity.

In consultation with the Sheepscot Valley Conservation Association (SVCA), the DEP Salmon River program planned a field season for 2006 that would include some follow-up from these assessments.  Specifically, we wanted to: (1.) get a better spatial resolution on turbidity sources by sampling from around the watershed at many sites on the same day, (2.) look at nutrients and turbidity relative to stream stage by sampling before a storm, sampling again on the rising river stage, and then sampling on the falling stage, and (3.) measure total nitrogen (TN) along with TP (because TN is commonly used by EPA and state agencies for establishing water quality criteria for nutrients under the Clean Water Act).  SVCA provided volunteers for turbidity/total suspended solids (TSS) sampling on two dates, one in May and another in October.  DEP sampled nutrients and turbidity/TSS on sequential dates in June at different river stages.  This report is the product of that collaboration.  This report is a “pilot study” in the sense that it is an exploration of the potential for volunteers to perform monitoring on an on-call basis as is required by storm event sampling.  If successful, additional studies are proposed.


SVCA volunteers were asked to collect bottles of water on the rising river stage or near the peak flow (which we operationally defined as within 4-12 hours after major storm events).  The storms were to have at least 1.0 inches of rain in a 24 hour period, which is an intensity that is sufficient to generate strong runoff and turbidity events.  One spring and one fall storm were selected.  Volunteers sampled at ten sample sites on May 15 and eight sample sites on October 12-13.  These samples were processed at Maine’s Health and Environmental Testing Laboratory (HELT) in Augusta for turbidity and TSS.  

Maine DEP sampled three sites on July 7 just before significant rain was expected.  Eleven sites were sampled on July 9 after significant rain fell on July 7 and 8.  A third set of samples were collected at three sites on July 14 on the falling river stage.  All SVCA and DEP sample sites for 2006 are illustrated in Figure 1.  Turbidity, TSS, TN and TP were processed at the Sawyer Environmental Center and Research Lab (SECRL) at the University of Maine in Orono.  Water clarity was measured in the field using a 120 cm turbidity tube.  A turbidity tube is a 3-inch diameter clear plastic cylinder that is graduated in centimeters and has a small secchi disk on the bottom plug.  The observer records the water depth in cm at which the secchi target first becomes invisible.  If the target is visible when the cylinder is full, the observer records the maximum reading as

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