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The Sheepscot River Turbidity Pilot Study, - page 11 / 12





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With respect to nutrients, nitrate was found to be about 65% of the TN value.  Based on our June samples, there is a pulse of turbidity and TP during a storm.  TN changed very little or increased slightly during the flood stage, but was diluted in the recovery period after the storm peak.  The highest turbidities and TP occurred on the ascending flood stage of the hydrograph.  This is a typical “first flush” pattern for NPS pollution and is associated primarily with overland flow.  The rising part of the flood hydrograph can also be influenced by melting snow pack during “rain on snow” events, which is often a major runoff event.  Otherwise, snow melt tends to recharge groundwater and influences river stage indirectly by providing head pressure on groundwater springs and seeps.  This hydrologic head pressure causes groundwater to flow more vigorously.  Groundwater is usually not turbid, but it can carry organic enrichment (TN and TP in dissolved and often organic forms).

The Sheepscot does not appear to be greatly enriched with TN, however TP is well above recommended baseline regional values.  We agree with the TMDL decision to continue to manage NPS pollution sources, improve agricultural practices, and control roadside and stream bank erosion.  The turbidity problem is serious enough to hamper salmon feeding and is serious enough to degrade salmon habitat (Newcomb and Jensen 1996).  

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