Estuaries atmospheric deposition

To assess the relative importance of the volatilisation removal process of APs from estuarine water, Van Ry et al. constructed a box model to estimate the input and removal fluxes for the Hudson estuary. Inputs of NPs to the bay are advection by the Hudson river and air-water exchange (atmospheric deposition, absorption). Removal processes are advection out, volatilisation, sedimentation and biodegradation. Most of these processes could be estimated only the biodegradation rate was obtained indirectly by closing the mass balance. The calculations reveal that volatilisation is the most important removal process from the estuary, accounting for 37% of the removal. Degradation and advection out of the estuary account for 24 and 29% of the total removal. However, the actual importance of degradation is quite uncertain, as no real environmental data were used to quantify this process. The residence time of NP in the Hudson estuary, as calculated from the box model, is 9 days, while the residence time of the water in the estuary is 35 days [16]. 

Figure 7.19b Susquehanna River discharge (a), 7Be atmospheric deposition (b), and 7Be inventories in Chesapeake Bay (USA) (c-h), showing lower inventories at the SUSQ station relative to the higher inventories at the BALT and CALV stations due to inputs of 7Be-rich sediments from the head of the Bay followed by redeposition farther down in the estuary. (Modified from Dibb and Rice, 1989.)...

Watershed-estuary system Watershed type Agriculture runoff Non-point source Urban forest runoff Upland human sewage Atmospheric deposition Total... 

Allochthonous DON sources from terrestrial runoff, plant detritus leaching, soil leaching, sediments, and atmospheric deposition may also represent important inputs to estuaries (Berman and Bronk, 2003). DON typically represents about 60 to 69% of the TDN in rivers and estuaries (Berman and Bronk, 2003). The major components of DON include urea, dissolved combined amino acids (DCAA), DFAA, proteins, nucleic acids, amino sugars, and humic substances (Berman and Bronk, 2003). However, less than 20% of DON is chemically characterized. 

Paerl, H.W., Dennis, R.L., and Whitall, D.R. (2002) Atmospheric deposition of nitrogen implications for nutrient over-enrichment of coastal waters. Estuaries 25, 677-693. 

In some estuaries and coastal embayments, atmospheric deposition direcdy to the water surface can account for a substantial fraction of N input (as much as 40% of the N inputs from river plus atmospheric inputs Table 9.6). Flowever, the relative importance of atmospheric deposition as an N source varies considerably among coastal systems and depends on a number of factors, including the nature of watershed N sources and the relative sizes of the contributing watershed and receiving estuary (Vahgura et ai, 2001). 

Table 9.6 Proportion (as a percent) of N inputs to estuaries, bays and continental shelves from atmospheric deposition directly to the water surface compared to river plus atmospheric inputs...

Castro, M. S., DriscoU, C. T., Jordan, T. E., Reay, W. G., Boynton, W. R., Seitzinger, S. P., Styles, R. V., and Cable,. E. (2001). Contribution of atmospheric deposition to the total nitrogen loads to thirty-four estuaries on the Aflantic and Gulf Coasts of the United States. In Nitrogen Loading in Coastal Water Bodies An Atmospheric Perspective, Coastal and Estuarine Studies. AGU. pp. 77-106. 

Figure 11.14 Relative contributions of atmospheric deposition, human sewage, forests, urban non-point sources and agriculture to new N loading in a set of representative US Atlantic (East Coast) and Gulf of Mexico estuaries. Figure adapted from Castro e(af (2003).

Paerl, H. W., MaUin, M. A., Donahue, C. A., Go, M., and Peierls, B. L. (1995). Nitrogen loading sources and eutrophication of the Neuse River estuary, NC Direct and indirect roles of atmospheric deposition. UNC Water Resources Research Institute Report No. 291. 119p. NC. State Univ., Raleigh, NC. 

The continental shelves receive N from the open ocean (820 x 10 molyear ), from estuaries (250 x 10 mol year ), from major rivers (350 x 10 mol year ) and from atmospheric deposition (130 x 10 mol year ). Some is lost to the sediments (120 x 10 mol year ) and fish catch (32 x 10 mol year ), but the majority is removed from the system via sedimentary denitrification (1400 x 10 mol year ). Nitrogen introduced to the shelves from the open ocean appears to contribute the most to shelf denitrification (Seitzinger and Gibhn, 1996). 

Paerl, H. W., and Fogel, M. L. (1994). Isotopic characterization of atmospheric nitrogen inputs as sources of enhanced primary production in coastal Atlantic Ocean waters. Mar. Biol. 119, 635—645. Paerl, H. W., Dennis, R. L., and Whitah, D. R. (2002). Atmospheric deposition of nitrogen Implications for nutrient over-enrichment of coastal waters. Estuaries 25, 677—693. 

Inputs, outputs and exchanges of N with systems adjacent to salt marshes are generally much smaller in magnitude than internal fluxes (Table 22.7). The source and relative importance of various external inputs of N to salt marshes varies from system to system. While the input of N from rivers is potentially large, most of this N is probably not taken up by salt marshes but is processed in aquatic portions of estuaries or routed to the open ocean. On average, the largest input is from N fixation (2-15 g N m year ), followed by atmospheric deposition (0.5-2.2 g N year ). Groundwater inputs are a major source of N in some smaller salt marshes with developed uplands such as found in the northeastern United States. 

WhitaH, D., Hendrickson, B., and Paerl, H. (2003). Importance of atmospherically deposited nitrogen to the annual nitrogen budget of the Neuse River estuary. North Carolina. Environ. Int. 29, 393-399. 

Nitrogen fluxes (in Tg N year ) are reported for contemporary conditions, with estimates under pristine conditions indicated in parentheses. Flux of nitrogen delivered from rivers and estuaries is the direct input of rivers that discharge onto the continental shelf plus the riverine input into estuaries, minus nitrogen consumed in estuaries. Atmospheric nitrogen deposition estimates in this table are those directly onto the waters of the continental shelf and do not include deposition onto the landscape (which is part of the flux from rivers and estuaries). The flux from the deep ocean represents the advection of nitrate-rich deep Atlantic water onto the continental shelf Data in this table are from Howarth (1998). 

All the factors mentioned in the previous sections play a role in the movement of metals through their overall biogeochemical cycle injection into the atmosphere, deposition onto land or water surfaces, transport via rivers and estuaries to the oceans, and sedimentation and ultimate burial in the sediments. The physical/chemical form in which each metal is transported in the aquatic phases of the cycle will depend on the specific metal and its interactions with other dissolved and suspended constituents in accord with the principles discussed above. However, it is important to keep in mind that the physical processes of fluid flow and sediment transport must be combined with the chemical reactions to gain insight into the functioning of the complete system. This point has been well-stated by Turekian (1977) in a discussion of metal concentrations in the ocean ... 

Results from studies investigating nitrogen input to some other estuarine and coastal regions are summarized in Table 3. In this table atmospheric sources for nitrogen are compared with all other sources, where possible. The atmospheric input ranges from 10% to almost 70% of the total. Note that some estimates compare only direct atmospheric deposition with all other sources and some include as part of the atmospheric input the portion of the deposition to the watershed that reaches the estuary or coast. 

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