- Long term monitoring of water quality in the Lamprey River
- Nutrient budget for the Lamprey River watershed and its sub-basins
- Changes in riparian nitrogen dynamics over time
LONG-TERM MONITORING OF WATER QUALITY IN THE LAMPREY RIVER
We are addressing long-term changes in water quality associated with changes in land use, human population growth and changes in other ecosystem properties over time in the entire Lamprey River basin. To accomplish this, samples have been collected weekly and during major storm events since October 1999 from the Lamprey River at the USGS gauging station in Durham, NH. Samples are analyzed for total dissolved nitrogen (TDN), nitrate (NO3-N), ammonium (NH4-N), orthophosphate (PO4-P), dissolved organic nitrogen (DON) and dissolved organic carbon (DOC). Additionally, samples collected since October 2002 are also analyzed for silica, major anions (Cl, SO4-S), major cations (Na, Mg, K, Ca), dissolved inorganic carbon (DIC), total suspended sediment, particulate carbon and particulate nitrogen. Parameters monitored in the field include pH, conductivity, dissolved oxygen (DO) and temperature. In January 2004, we initiated long-term monitoring of dissolved nutrients and organic matter in the North River and in a small tributary to the Lamprey in Lee (Wednesday Hill Brook) that has only 52% of its watershed covered by forests. Total phosphorus was added to our suite of parameters for long-term monitoring in October 2005. Results to date show that nitrate concentrations have significantly increased over time in the main stem of the Lamprey, but DOC concentrations have not changed significantly.
NUTRIENT BUDGET FOR THE LAMPREY RIVER WATERSHED AND ITS SUB-BASINS
To develop a detailed hydrologic budget for the Lamprey River watershed, we have monitored precipitation inputs and stream water outputs at several locations in the watershed. Precipitation and stream samples were collected on a storm event to weekly basis during 2004 and on an event to monthly basis since January 2005. During 2004, we monitored 11 precipitation stations with the help of volunteers throughout the basin. Precipitation volume was monitored at all stations and at six stations, precipitation samples were analyzed for nitrate, ammonium, phosphate, DON, DOC, major anions, major cations and silica. Results from the 2004 precipitation analysis showed that chemical concentrations did not vary significantly throughout the basin, but the amount of rainfall did vary with more precipitation occurring at areas of higher elevation (i.e. Pawtuckaway State Park). Stream samples were collected from twelve sub-basins of the Lamprey watershed and also from the main stem at the USGS gauging station in Durham, NH (referred to as “Lamprey”). Stream samples were analyzed for nitrate, ammonium, phosphate, DON, DOC, major anions, major cations, silica and field parameters. Analysis of sub-basin stream samples demonstrated that average annual concentrations could be represented by a monthly sampling regime and since January 2005, several sub-basins are sampled monthly. Weekly and storm event sampling was continued at the Lamprey, North River and a small tributary in Lee (Wednesday Hill Brook) to accurately document seasonal and storm event trends. We developed a nitrogen budget for the Lamprey based on measured and estimated inputs and measured N outputs in stream water. Inputs included in the budget were measured N in wet deposition (i.e. precipitation and snowfall), estimates of nitrogen input from food and feed (based on Census population data and a nitrogen consumption rate of 5 kg N/person/yr) and estimates of fertilizer application (based on agricultural land use data and recommended rates of nitrogen application for each crop type). Annual nitrogen retention rates for the Lamprey Watershed ranged from 78% to 93% (see image). These results suggest that small changes in long-term nitrogen retention could lead to large changes in nitrogen export to downstream sensitive ecosystems such as Great Bay.
CHANGES IN RIPARIAN NITROGEN DYNAMICS OVER TIME
Most nitrogen applied to the Lamprey River watershed is retained or transformed somewhere along the flow path. Only 10-30% of that which is applied to the landscape actually enters surface waters, but the exact mechanisms of retention or transformation are unknown. One area where a significant amount of nitrogen can be retained or transformed is in the riparian zone. To document nitrogen transformations along flow paths in the Lamprey watershed, we have installed riparian well fields in two first order streams which drain several suburban developments. Groundwater samples from the well fields were collected monthly from 2004-2007 and seasonally until present. Samples are are analyzed for nitrate, ammonium, phosphate, DON, DOC, major anions, major cations and SiO2. Prior to sampling, water table elevation is recorded to develop a flow net for each well field to link groundwater biogeochemistry with groundwater hydrology. Results to date show little long-term variation in chemical constituents, but constituent concentrations vary spatially from upslope to the stream edge. At this time, we are unable to determine how much of this variation is due to N processing mechanisms and how much is due to dilution from stream water.
For more information contact: Michelle Daley