Understanding nutrients in the Chesapeake Bay watershed and implications for management and restoration: The Eastern Shore

Abstract

), onlineFor more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprodTo order this and other USGS information products, visit http://store.usgs.gov Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. SEE CHAPTER 2The Eastern Shore ( fig. 1) includes only a small part of the Chesapeake Bay watershed, but contributes disproportionately large loads of the excess nitrogen and phosphorus that have contributed to ecological and economic degradation of the bay in recent decades. Chesapeake Bay is the largest estuary in the United States and a vital ecological and economic resource. The bay and its tributaries have been degraded in recent decades by excessive nitrogen and phosphorus in the water column, however, which cause harmful algal blooms and decreased water clarity, submerged aquatic vegetation, and dissolved oxygen. The disproportionately large nitrogen and phosphorus yields from the Eastern Shore to Chesapeake Bay are attributable to human land-use practices as well as natural hydrogeologic and soil conditions. Applications of nitrogen and phosphorus compounds to the Eastern Shore from human activities are intensive. Also, hydrogeologic and soil conditions promote the movement of these compounds from application areas on the landscape to groundwater and (or) surface waters, and the proximity of much of the Eastern Shore to tidal waters limits opportunities for natural removal of these compounds in the landscape. The Eastern Shore only includes 7 percent of the Chesapeake Bay watershed, but receives nearly twice as much nitrogen and phosphorus applications (per area) as the remainder of the watershed and yields greater nitrogen and phosphorus, on average, to the bay ( fig. 2). SOURCE INPUTS TO THE EASTERN SHORE Sources of Nitrogen and Phosphorus on the Eastern Shore SEE CHAPTER 3Agricultural operations contribute the vast majority of nitrogen and phosphorus to the landscape on the Eastern Shore. Land use in the area has been primarily agricultural for several hundred years. Nitrogen and phosphorus applications in support of agriculture increased substantially during the second half of the last century, however, but have since stabilized or decreased ( fig. 3). More than 90 percent of nitrogen and phosphorus reaching the land in the Eastern Shore is applied as part of inorganic fertilizers or manure, or (for nitrogen) fixed directly from the atmosphere in cropland ( fig. 4). Nonagricultural sources such as atmospheric deposition, septic systems, sewage treatment plants, or other urban sources...

Water quality in the surficial aquifer near agricultural areas in the Delaware Coastal Plain, 2014

“…Concentrations of nitrate above natural background levels are likely impacted by anthropogenic activity (Debrewer and others, 2007). Recent studies on the Delmarva Peninsula have shown that nitrate concentrations in groundwater increased about 2 mg/L as N in parts of the surficial aquifer used for domestic supply from 1988 to 2001 in response to increased nitrogen applications in previous decades (Denver and others, 2004;Ator and Denver, 2015). Headwater streams on the Delmarva Peninsula, which derive most of their flow as groundwater discharge from the surficial aquifer, also show nitrate concentrations above natural levels during base flow (Ator andDenver, 2015, Denver andothers, 2004).…”

“…With the exception of phosphorus, these chemicals typically contribute to the major ions in groundwater affected by agricultural activities (Hamilton and others, 1993). In well-drained soils, phosphorus is typically bound to soils and sediments and not dissolved in water (Ator and Denver, 2015).…”

“…Certain conditions increase the likelihood of nitrate moving into shallow groundwater. These conditions include the amounts and timing of nitrogen application to the land; the presence of well-drained, sandy soils that promote oxic soil and aquifer conditions (dissolved oxygen greater than 1 milligram per liter or mg/L); and a relatively high water table (Ator and Denver, 2015;Rudolph, 2015). These conditions are common in many parts of the Delaware Coastal Plain and have resulted in widespread nitrate movement into the surficial aquifer in many areas.…”

“…Nitrate, the major form of nitrogen that is soluble in water, is a common contaminant in groundwater and surface water in the Coastal Plain of Delaware (Ator and Denver, 2015). Nitrate concentrations in the surficial aquifer are commonly far greater than would be expected under natural conditions, and often high enough to affect the suitability of water for human consumption (Debrewer and others, 2007).…”

Nitrogen Fluxes Into, Out Of, and Within a Virginia Permaculture Livestock Farm

“…Nitrogen that is leached into groundwater can advect into riparian zones (Williams et al 2014) and enter streams slowly during base flow (Howden et al 2011). In areas that have been used for agriculture for many years, groundwater can be contaminated with N and account for a significant portion of N flux into streams (Canter 1996, Howden et al 2011, Ator and Denver 2015. Because of the long residence time of groundwater, N from decades ago advects into streams today (Hamilton 2012) and will continue to do so for a long time, even if N application immediately ceased.…”