Effect of forested wetlands on nitrate concentrations in ground water and surface water on the Delmarva Peninsula

Abstract

Abstract:The Delmarva Peninsula is an extensively farmed region in which nitrate from commercial fertilizers and poultry has entered the ground water and streams. The peninsula contains forested wetlands in a variety of settings, and their size and location are a result of the surrounding hydrologic and soil conditions. Three regions, here referred to as hydrogeomorphic regions, were selected for study. Each region has characteristic geologic and geomorphic features, soils, drainage patterns, and distribution of farmland, forests, and forested wetlands. In all three regions, forested wetlands generally occupy poorly drained areas whereas farmlands generally occupy well-drained areas. The three hydrogeomorphic regions studied are the welldrained uplands, the poorly drained uplands, and the surficial-confined region. The well-drained uplands have the largest amount of farmland and the smallest amount of forested wetlands of the three regions; here the forested wetlands are generally restricted to narrow riparian zones, The poorly drained uplands contain forested wetlands in headwater depressions and riparian zones that are interspersed among well-drained farmlands. The surficial-confined region has the smatlest amount of farmland and largest amount of forested wetlands of the three regions studied. Wetlands in this region occupy the same topographic settings as in the poorly drained uplands. Much of the farmland in the surficial-confined region was previously wetland. Nitrate concentrations in ground water and surface water on the peninsula range widely, and their distribution reflects (1) the interspersion of forests among farmland, (2) hydrogeologie conditions, (3) types of soils, and (4) the ground-water hydrology of forested wetlands. The well-drained uplands had higher median nitrate concentrations in ground water than the poorly drained uplands or the surficial-confined region. The highest nitrate concentrations were in oxic parts of the aquifer, which are beneath well-drained soils that are farmed, and the lowest were in anoxic parts of the aquifer, which are beneath poorly drained soils overlain by forested wetlands. The effect of forested wetlands on water quality depends on the hydrogeologic conditions, extent of farming, and type of soils. The three regions contain differing combinations of these factors and thus are useful for isolating the effects of forested wetlands on water quality.

Metolachlor metabolite (MESA) reveals agricultural nitrate-N fate and transport in Choptank River watershed

“…Nitrate-N concentrations were positively correlated with percent cropland area, whereas MESA concentrations were surprisingly unrelated to percent cropland area (Hively et al, 2011), which suggests that additional factors, such as differences in drainage and geomorphology, may be influencing the delivery of agricultural waters to the sampling sites. Multivariate analyses of these data (Hively et al, 2011) along with prior regional studies Böhlke and Denver, 1995;Denver et al, 2010;Phillips et al, 1993) have suggested that multiple factors influence nitrate-N concentrations in the stream waters. Agricultural drainage, percentages of agricultural, forested, developed and conservation reserve lands, and percentages of hydric soils and forested wetlands were examined, but in these previous analyses, no definitive causal relationships were discernible among these factors.…”

“…In the cropland areas, the surficial aquifer is under heavy influence from agrochemical application to fields (Graphical Abstract, Table 1) Denver et al, 2010, in press;Phillips and Bachman, 1996;Phillips et al, 1993). Cropland areas with well drained soils contribute more to deeper regional groundwater resources than cropland areas on poorly drained soils, and thus the proportion of surficial groundwater contribution from cropland will be less in well drained areas than in poorly drained areas (Table 2).…”

“…The Choptank River watershed is located on Mid-Atlantic Coastal Plain soils (Ator et al, 2005) with parent materials defined by the superposition of Quaternary age upper-delta-plain sands and gravel deposited on Miocene and Pliocene age marine-inner-shelf sands and surficial unconfined aquifers ranging in depth from 8 to more than 30 m. The nature of these soils strongly influences the hydrology and chemistry of the Choptank River and its headwater streams Phillips and Bachman, 1996;Phillips et al, 1993). The two major land uses in the watershed are cropland and forest.…”

“…In contrast to nitrate-N, once MESA enters ground water, it is very stable (Phillips Table 1 Conceptual model of landscape characteristics that influence transport, processing, and delivery of nitrate-N and MESA to headwater streams of the Choptank River (Ator et al, 2005;Bachman and Phillips, 1996;Denver et al, 2010, in press;Phillips and Bachman, 1996;Phillips et al, 1993 Steele et al, 2008); MESA persists over decadal time scales (Denver et al, 2010). In surface water, the modeled half-life for all MESA processing (phototransformation, transport, etc.)…”

Improved methods for quantifying potential nutrient interception by riparian buffers

“…A number of riparian transect studies have documented substantial nutrient filtering along hydrologic flow paths (Peterjohn and Correll 1984;Lowrance et al 1985;Jacobs and Gilliam 1985;Cooper 1990;Jordan et al 1993), yet other studies have described more variable results (Osborne and Kovacic 1993;Phillips et al 1993;Altman and Parizek 1995;Hill 1996;Correll et al 1997;Vidon and Hill 2004). In whole watershed analyses, evaluations of riparian effects have been mixed, showing strong (Weller et al 1996;Baker et al 2001;Johnson et al 1997;Norton and Fisher 2000;Jones et al 2001) or weak (Omernik et al 1981;Osborne and Wiley 1988) riparian effects.…”