After more than two decades of multi-state programs aimed at improvement of Chesapeake Bay water quality, multiple pollution issues still exist for the Bay region. Foremost, the Bay continues to suffer from eutrophication, including hypoxia of deep water and seasonal algal blooms that result from excess loading of nutrients from Bay watershed tributaries. Nitrate concentrations in Chesapeake Bay appear to decline in drought periods, as illustrated during the dry years of 1999 through 2002. Reductions in nitrate loads during dry times occur presumably because fewer precipitation events and amounts result in less runoff carrying pollution into headwaters of rivers feeding into the Chesapeake Bay. This study examines the role of precipitation events and land use in water quality variations for select first-order streams of Lancaster County. The region is an intensive agricultural area within the drainage basin of the Susquehanna River, which is a major source of nutrients delivered to the bay. Stream water quality (nitrate nitrogen, total dissolved solids, conductivity) was collected as part of a 3-year (2007-2009) student summer REU research project. Additional data were collected for summer 2011. Two urban, two agricultural, and two forested first-order streams near Millersville, Pennsylvania were assessed using Lamotte water quality test kits.

Non-parametric analysis of variance revealed statistically significant differences across land use for nitrate-nitrogen, with the highest average stream concentrations for agricultural land uses. Days with precipitation showed significantly higher nitrate concentrations for agricultural and forested land uses, but not for urban land uses. For conductivity, statistically significant differences were also found across land use, with highest stream levels for urban land uses. For all land use categories, conductivity was significantly lower on days with precipitation. The contrasting results across pollutant type likely occur as a result of the differing nature of pollutant sources for nitrate and total dissolved solids, as well as means of delivery to the stream.

Analyses of pollutant loads across multi-day rain events showed a strong drop off in conductivity only for urban streams during first few days of event. Nitrate rose strongly with day into rain event up to 4 days for agricultural sites, but not for other land uses. No clear tends in either nitrate or conductivity appeared with increasing period without rain for up to 4 days. Heavy rain events significantly increased nitrate concentrations in agricultural streams, while no trend was observed for other locations.

Continuing studies will help establish the link between a variety of other hydroclimatic factors, stream order and water quality in river headwaters that feed into the Chesapeake Bay. Considering that the vast majority of stream miles of major rivers exist within the headwater region, the health of the Susquehanna's low order tributaries are likely to be strongly tied to the overall health of the Chesapeake Bay.