Chesapeake Bay River Input Monitoring Program

The USGS Chesapeake Bay River Input Monitoring (RIM) Program was established to quantify loads and long-term trends in concentrations of nutrients and suspended material entering the tidal part of the Chesapeake Bay Basin from its nine major tributaries. These nine rivers account for approximately 93% of the stream flow entering Chesapeake Bay from the non-tidal part of its watershed. Results of the RIM program are being used by resource managers, policy makers, and concerned citizens to help evaluate the effectiveness of strategies aimed at reducing nutrients and sediment entering Chesapeake Bay from its tributaries. Water samples are collected upstream of the transition area between the tidal and non-tidal regions of the nine rivers (Figure 1). This transition zone historically has been referred to as the "Fall Line" for the many sets of falls and rapids that are found at this point on the rivers. Below the Fall Line in the tidal areas of these rivers, tides can transport water, nutrients, and suspended material from downstream, making it difficult to determine the cause of any observed changes. Because water-quality samples are collected above the influence of tides, any observed changes in nutrients or suspended material can be attributed to upstream causes. [Summary provided by the USGS.]