Joseph R. Scudlark

Sources of nitrogen in wet deposition to the Chesapeake Bay region

Nitrogen-containing compounds in wet deposition can provide significant sources of nutrients to phytoplankton and potentially contribute to eutrophication in estuaries and coastal waters. Quantifying both inorganic and organic forms of nitrogen in wet deposition as well as determining their sources is important for understanding how to control eutrophication. Stable nitrogen isotope data can provide information regarding what source processes produced nitrogen in precipitation and air mass trajectories can predict where the air mass which produced the precipitation was geographically located before the event occurred. In this study, the wet deposition concentrations, fluxes, and δ15N values of ammonium, nitrate, and dissolved organic nitrogen were determined for 60 precipitation events collected from May, 1993 to December 1994 at a site near the Chesapeake Bay, an estuary currently experiencing eutrophication. Grouping the concentration data according to season showed a peak in ammonium coupled with depleted δ15N values in the spring which were indicative of agricultural emissions. A peak in nitrate in the spring seemed to indicate greater soil emissions at that time, but concentrations were also high at other times of the year. No trend was observed for the dissolved organic nitrogen with season. Back trajectories were calculated for each precipitation event and grouped into five major transport patterns. Combining the flux and isotopic composition data with the air flow history revealed that dominant sources of ammonium in precipitation to the region are probably fertilizers, soil, and animal excreta emissions which have the highest fluxes in air masses originating from the southwest and west. The dominant source of nitrate to the region is probably fossil-fuel combustion and the highest fluxes originate from the northwest and west. Speculation on the dissolved organic nitrogen sources is probably premature, but its flux pattern is similar to the nitrate pattern, suggesting that their sources may be similar.

Inorganic and organic sulfur cycling in salt-marsh pore waters.

Sulfur species in pore waters of the Great Marsh, Delaware, were analyzed seasonally by polarographic methods. The species determined (and their concentrations in micromoles per liter) included inorganic sulfides (≤3360), polysulfides (≤326), thiosulfate (≤104), tetrathionate (≤302), organic thiols (≤2411), and organic disulfides (≤139). Anticipated were bisulfide increases with depth due to sulfate reduction and subsurface sulfate excesses and pH minima, the result of a seasonal redox cycle. Unanticipated was the pervasive presence of thiols (for example, glutathione), particularly during periods of biological production. Salt marshes appear to be unique among marine systems in producing high concentrations of thiols. Polysulfides, thiosulfate, and tetrathionate also exhibited seasonal subsurface maxima. These results suggest a dynamic seasonal cycling of sulfur in salt marshes involving abiological and biological reactions and dissolved and solid sulfur species. The chemosynthetic turnover of pyrite to organic sulfur is a likely pathway for this sulfur cycling. Thus, material, chemical, and energy cycles in wetlands appear to be optimally synergistic.

The wet deposition of trace metals to the western atlantic ocean at the mid-atlantic coast and on Bermuda

Abstract The concentration of the trace metals Cd, Cu, Fe, Mn, Ni, Pb, V and Zn has been measured in atmospheric precipitation events at the middle Atlantic coast (Lewes, DE) and on the western Atlantic island of Bermuda. The purpose is to assess the sources, transport, and wet deposition of trace metals to the western Atlantic during non-summer months when trace metals are likely to be transported by westerly air mass flow from N America to the open Atlantic. The concentrations, and wet deposition of trace metals are greater at the coast than on Bermuda, and the other at both sites (Fe > Zn > Pb > Cu, Mn, Ni > V > Cd) is similar. The trace metal enrichment factors for all metals but Mn, based on crustal Fe, are significantly greater than unity, and the order (Cd > Pb > Zn > Cu > Ni > V) is also the same at the coast as on Bermuda. This evidence suggests common sources from North America for trace metals in western Atlantic precipitation and important atmospheric transport of trace metals to the Atlantic Ocean. Calculations using enrichment factors from sea salt aerosol (Na based) indicate recycling of trace metals from the sea surface, while generally considered not to be important, could be a potentially significant process contributing to Mn and V enrichments in open western Atlantic precipitation.

A method for the collection, handling, and analysis of trace metals in precipitation.

A method is described for the automated collection, proper handling, and accurate analysis of trace metals (Fe, Zn, Cu, Mn, Pb, Cd, Ni, V) in precipitation. The method has been successfully used in both rural coastal (Lewes, DE) and semiremote (Bermuda) marine environments but should be generally applicable. The collection device is a commercially modified automatic collector with polyethylene bag liners in the collecting buckets. Strict protocols for acid washing, deployment, and blanking are necessary to ensure accurate contamination-free samples. The freshly collected event samples are postacidified below pH 1.6 with ultraclean HCl to ensure desorption and preservation of the sample. Trace metal concentrations are quantitatively analyzed by heated graphite atomization in an atomic absorption spectrophotometer. A comparison of the results obtained by this method with earlier published trace metal results suggest that serious sampling and analytical artifacts may be present in most earlier data bases. 24 references, 5 table.

Atmospheric wet deposition of trace elements to chesapeake bay: CBAD study year 1 results

The atmospheric wet deposition of selected trace elements (AI,As,Cd,Cr,Cu,Fe,Mn,Ni,Pb,Se and Zn) was examined at two Maryland Chesapeake Bay sites from June 1990 to July 1991 as part of the Chesapeake Bay Atmospheric Deposition (CBAD) Study. Weekly integrated samples were collected using a modified wet-only collector and rigorous trace element handling protocols. Wet depositional fluxes were directly calculated as the product of the elemental concentration and the corresponding measured precipitation depth. The monthly integrated atmospheric fluxes exhibited a high degree of spatial and temporal variability. The arithmetically averaged annual wet flux (μg m−2 yr−1) from the two sites were as follows: AI (13,600), As (49), Cd (48), Cr (88), Cu (260), Fe (10,400), Mn (1190), Ni (257), Pb (556), Se (214) and Zn (1335). With the exception of AI, Fe and to a lesser extent Mn and Cr, the elemental fluxes are predominantly derived from anthropogenic sources. The magnitude of the measured wet fluxes are generally comparable to simultaneously estimated dry fluxes. Compared with dissolved fluvial inputs, atmospheric deposition appears to provide significant fluxes of many elements of environmental concern.

Factors Influencing the Atmospheric Depositional Fluxes of Stable Pb, 210Pb, and 7Be into Chesapeake Bay

Atmospheric depositional fluxes of 7Be and210Pb (bulk) and stable Pb (wet) were measuredsimultaneously for one year (from September 1995–August 1996) atStillpond, Maryland on the uppereastern shore of the Chesapeake Bay. The annual total(bulk) depositional fluxes of 210Pb and 7Bewere 0.78 and 13 dpm cm-2, respectively, andagree well with other previously reported results atnearby locations such as Norfolk, VA and Lewes, DE. The wet depositional flux of stable Pb (58 ng cm-2 yr-1)was also similar to thatmeasured at other Chesapeake sites during 1990–1991(55 ng cm-2 yr-1, for both Wye and Elms,Maryland). This suggests that a constant Pb flux hasbeen reached since the mandatory use of unleadedgasoline was instituted. The concentrations of7Be, 210Pb, and to a lesser extent stable Pbwere diluted exponentially by precipitation, based onconcentrations versus precipitation plots. Due tohigher enrichment of 210Pb in the lowertroposphere, the dilution effect was largest on210Pb (i.e., controlled mainly by below-cloudscavenging processes), and thus its depositional fluxincrease is negligible as precipitation amountincreases. A good correlation between the amount ofprecipitation and total depositional flux of 7Beand stable Pb, which are more enriched in the uppertroposphere, suggests that precipitation amount isimportant in controlling their fluxes (i.e.,controlled by both below-cloud scavenging and in-cloudcondensation processes). Based on 7Be versus210Pb plots, it appears that 7Be, relativeto 210Pb, is less efficiently scavenged bysnowfall. Our results suggest that in addition toprecipitation amounts, marine air-mass transport orsnowfall may be important factors in controlling theseasonal variability of the fallout fluxes of tracemetals in coastal areas.

Atmospheric wet deposition of trace elements to Chesapeake and Delaware Bays

Abstract The atmospheric wet depositional fluxes of selected trace elements (Al, Fe, Mn, Pb, Cd, Zn, Cu, Ni and Cr) were examined at two mid-Atlantic sites, which were located on the shore of the Delaware (Lewes) and Chesapeake (Stillpond) Bays from September 1995 to August 1996. Sampling was carried out on a weekly integrated basis, using “clean” techniques developed especially for trace elements. Monthly integrated depositional fluxes showed large variability in space and time for most of the measured elements, with similar ranges of variation for both sites. A good correlation ( r 2 =0.80 , Fe/Al=0.59) between Al and Fe fluxes at both sites suggests their major origin from the earths crust (resuspended regional soils). Based on the enrichment factor calculation, it is suggested that at least half of the Cr and Mn and more than 90% of the Cd, Zn, Pb, Cu, and Ni are from non-crustal (presumably anthropogenic) sources. Seasonal variations of Al, Fe and Mn appear to be mainly controlled by local/regional agricultural activities, whereas Pb and Cd fluxes are largely dictated by precipitation amounts. Factors controlling fluxes of other elements (Zn, Cu, Ni and Cr) are not clearly distinguished due to large episodic inputs of local/regional contamination sources. A comparison of annual trace element fluxes during 1991–1996 reveals a factor of 2–4 higher fluxes of Zn, Cu and Ni during 1995–1996 at both sites, indicating regional (i.e., mid-Atlantic region) increase of the fluxes during the sampling period. The similar annual fluxes and trends at both sites suggest that these data can be employed to estimate atmospheric wet flux of trace elements to mid-Atlantic coastal waters (including Chesapeake/Delaware Bays and mid-Atlantic Bight).

The sedimentary flux of nutrients at a Delaware salt marsh site: A geochemical perspective

AbstractA basic geochemical approach has been used to study the diagenetic cycling and sediment-water exchange rates of essential nutrients at a site in a Delaware salt marsh. The pore water nutrients Si (OH)4, NH4+, PO4−3, and NO3− were analyzed and compared seasonally, and potential diffusive fluxes were calculated from the corresponding pore water concentration gradients. Concurrent direct flux measurements were also made using closed chambers deployed on the salt marsh surface under ambient and controlled conditions. The differences in these two approaches allows for estimation of nutrient production and consumption in the root zone and at the salt marsh surface. Silicate and phosphate appear to be primarily geochemically controlled, while the nitrogen species undergo dynamic seasonal redox fluctuations resulting from microbial mediation (e.g., nitrification and denitrification). Specifically:silicate behaves rather conservatively according to silica solubilityphosphate flux is controlled by the corresponding sequestering or reductive remobilization of surface iron oxides, andammonium has a strong upward flux which appears to undergo quantitative nitrification in spring. None of the measured flux rates would have a major impact on the nutrient budget for the local estuary, Delaware Bay.

Atmospheric input of inorganic nitrogen to Delaware Bay

The coastal waters of the mid-Atlantic region of the United States receive inputs of atmospheric pollutants as a consequence of being located downwind from major industrial and urban emissions. These inputs are potentially the largest received by any marine area of the country. Of current interest is the atmospheric input of dissolved inorganic nitrogen (DIN = NO3−+NH4+). We have conducted a first-order examination of the magnitude of atmospheric DIN deposition relative to other large-scale inputs for Delaware Bay, a partially urbanized mid-Atlantic coastal plain estuary. The following loading terms: direct atmospheric deposition, indirect atmospheric loading, urban point discharges, fluvial input, benthic flux, and salt marsh export were evaluated. On an annual basis, municipal-industrial effluents provide a dominant source (ca. 40%) of the DIN inputs to the estuary. Total (wet plus dry) atmospheric deposition accounts for about 15% of the total annual DIN inputs. However, during summer, which is characterized by low river-flow and seasonally maximum atmospheric loading, this figure increases to around 25%. Although atmospheric input can satisfy only a fraction of the primary production demands, this summer flux may represent an ecologically important source of external DIN, half of which is directly deposited to surface photic zones where it is readily available for biological uptake.

Identification of sources of pollutants in precipitation measured at the mid-Atlantic US coast using potential source contribution function (PSCF)

Abstract Potential source contribution function (PSCF) was employed to study the source receptor relationships for 14 chemical species (Mn, SO42−, Zn, Al, Fe, Cu, Cr, Ni, Cd, NO3, NH4+, K+, Mg2+,and Pb) found in precipitation collected at Lewes, Delaware. This study identified areas of the Eastern United States as possible emission source areas that could have contributed to the 14 element concentrations observed at Lewes. The identified regions in the Eastern United States generally coincide well with known emission source areas. The likely emission sources for these chemical species include oil- and coal-fired power plants, incinerators, motor vehicles, and iron and steel mills.