排序方式： 共有16条查询结果，搜索用时 15 毫秒
1.
Data for uranium concentrations in 29 rivers and eight estuaries are presented. The river data expands the existing database on riverine uranium transport to include more smaller watersheds which collectively account for a large portion of material transport from the continent to the oceans. Riverine concentrations for these smaller watershed range from less than 50 to 660 pM. The results for these systems, when combined with previously published data on mostly larger rivers, do not change significantly the calculated global riverine flux and thus earlier estimates by Palmer and Edmond [Palmer, M.R., Edmond, J.M., 1993. Uranium in river water. Geochim. Cosmochim. Acta, 57, pp. 4947–4955] are substantiated. Uranium transport through eight diverse estuaries was studied to assess the importance of estuarine removal in the global marine uranium budget. Results indicate that uranium is conservatively transported in most systems studied. Results reported here for the Savannah estuary, however, indicate significant uranium removal. Our results suggest that uranium is removed in salt marsh estuaries at a rate of ca. 70 μmol/m2. This compares to a rate of 15 μmol/m2 for Delaware salt marshes [Church, T.M., Sarin, M.M., Fleisher, M.Q., Ferchlman, T.G., 1996. Salt marshes: an important sink for dissolved uranium. Geochim. Cosmochim. Acta, 60, pp. 3879–3887]. We suggest that uranium removal to salt marsh sediments is due to anaerobic microbially mediated processes. We use these results to estimate the global significance of the salt marsh sink in the oceanic budget of uranium. We estimate that 2.7×107 mol of uranium are removed to salt marshes annually as compared to an annual global riverine input of 3–6×107 mol estimated by Palmer and Edmond [Palmer, M.R., Edmond, J.M., 1993. Uranium in river water. Geochim. Cosmochim. Acta, 57, pp. 4947–4955]. 相似文献
2.
3.
4.
Isaac R. Santos Felipe Niencheski William Burnett Richard Peterson Jeffrey Chanton Carlos F.F. Andrade Idel B. Milani Axel Schmidt Kay Knoeller 《Journal of Hydrology》2008,353(3-4):275-293
We investigated the distribution of naturally occurring geochemical tracers (222Rn, 223Ra, 224Ra, 226Ra, CH4, δ18O, and δ2H) in the water column and adjacent groundwater of Mangueira Lagoon as proxies of groundwater discharge. Mangueira Lagoon is a large (90 km long), shallow (4–5 m deep), fresh, and non-tidal coastal lagoon in southern Brazil surrounded by extensively irrigated rice plantations and numerous irrigation canals. We hypothesized that the annual, intense irrigation for rice agriculture creates extreme conditions that seasonally change groundwater discharge patterns in the adjacent lagoon. We further supposed that dredging of irrigation canals alters groundwater fluxes.
While the activities of 222Rn in shallow groundwater were 2–3 orders of magnitude higher than in surface water, CH4 and radium isotopes were only 1 order of magnitude higher. Therefore, 222Rn appears to be the preferred groundwater tracer in this system. Radon concentrations and conductivities were dramatically higher near the pump house of rice irrigation canals, consistent with a groundwater source. Modeling of radon inventories accounting for total inputs (groundwater advection, diffusion from sediments, and decay of 226Ra) and losses (atmospheric evasion, horizontal mixing and decay) indicated that groundwater advection rates in the irrigation canals (25 cm/d) are over 2 orders of magnitude higher than along the shoreline (0.1 cm/d). Nearly 75% of the total area of the canals is found in the southern half of the lagoon, where groundwater inputs seem to be higher as also indicated by methane and stable isotope trends. In spite of the relatively small area of the canals, we estimate that they contribute nearly 70% of the total (57,000 m3/d) groundwater input into the entire Mangueira Lagoon. We suggest that the dredging of these canals cut through aquitards which previously restricted upward advection from the underlying permeable strata. The irrigation channels may therefore represent an important but previously overlooked source of nutrients and other dissolved chemicals derived from agricultural practices into the lagoon. 相似文献
5.
L. Felipe H. Niencheski Herbert L. Windom Willard S. Moore Richard A. Jahnke 《Marine Chemistry》2007,106(3-4):546-561
The Patos–Mirim Lagoon system along the southern coast of Brazil is linked to the coastal ocean by a narrow mouth and by groundwater transport through a Holocene barrier. Although other groundwater systems are apparently active in this region, the hydraulic head of the lagoon, the largest in South America, drives groundwater transport to the coast. Water levels in wells placed in the barrier respond to changing water level in the lagoon. The wells also provide a measure of the nutrient concentrations of groundwater flowing toward the ocean. Additionally, temporary well points were used to obtain nutrient samples in groundwater on the beach face of the barrier. These samples revealed a subterranean freshwater–seawater mixing zone over a ca. 240 km shoreline. Previously published results of radium isotopic analyses of groundwater and of surface water from cross-shelf transects were used to estimate a water flux of submarine groundwater discharge (SGD) to nearshore surface waters of 8.5 × 107 m3/day. Using this SGD and the nutrient concentrations in different compartments, nutrient fluxes between groundwater and surface water were estimated. Fluxes were computed using both average and median reservoir (i.e. groundwater and surface water) nutrient concentrations. The SGD total dissolved inorganic nitrogen, phosphate and silicate fluxes (2.42, 0.52, 5.92 × 106 mol day− 1, respectively) may represent as much as 55% (total N) to 10% (Si) of the nutrient fluxes to the adjacent shelf environment. Assuming nitrogen limitation, SGD may be capable of supporting a production rate of ca. 3000 g C m2 year− 1in the nearshore surf zone in this region. 相似文献
6.
Nutrient flux and budget in the Ebro estuary 总被引：1，自引：0，他引：1
S. Falco L.F. Niencheski M. Rodilla I. Romero J. González del Río J.P. Sierra C. Mösso 《Estuarine, Coastal and Shelf Science》2010
The Ebro river flows to the Mediterranean coast of Spain. During its final stretch, the Ebro behaves in a similar way to a highly stratified estuary. This paper describes the transport of nutrients to the Ebro estuary, evaluates the general movement of nutrients in the estuarine region, using a mass balance approach, and estimates the amounts of nutrients discharged to the coastal environment. Given the strong saline stratification, this study only includes the surface layer that contains the continental freshwater. The annual nutrient budget for the Ebro estuary shows a net excess for nitrogen and phosphorus, while silicate almost attains equilibrium between addition and removal. There are several reasons for gains in nitrogen and phosphorous: a contribution of dissolved and particulate compounds in the freshwater (some of which are mineralized); a lower uptake of phytoplankton indicated by chlorophyll reduction in the estuary; an entrainment of the nutrient-rich upper part of the salt wedge; and, to a lesser extent, the impact of wastewater and agricultural water use. The biggest load discharged into the Mediterranean Sea by the Ebro is nitrogen, followed by silicate with over 10 000 tons of each deposited annually. Phosphorus is discharged at relatively low concentrations and with an annual load of about 200 t yr−1. 相似文献
7.
Previous studies in the Amazon Basin and the Upper Pantanal show widespread mercury contamination of fish and water as a result
of gold mining, and subsequent volatilization of mercury during the recovery process. A study was initiated to assess whether
atmospheric transport of mercury to the south has resulted in elevated levels in water and fish in the Lower Pantanal. Water
samples were collected from streams and rivers from the Pantanal (Mato Grosso do Sul) down into the southernmost state of
Brazil (Rio Grande do Sul) for total Hg concentration and oxygen isotopic analyses. Based on oxygen isotopes and conductivity,
surface water samples can be considered as mixtures of three endmembers: groundwater, rain and “aged” surface water. Lowest
concentrations (<2 ng/L) of total Hg were observed in the northernmost samples, especially those associated with the groundwater
sources. Further south, Hg concentrations tended to increase, but higher concentrations (>2 ng/L) likely reflect direct input
from more localized watershed sources. Fish collected from streams in the Pantanal had extremely low concentrations of total
Hg regardless of their size or feeding habit, although one large carnivorous fish (>2 kg) had concentrations approaching 400 ng/g
wet wt. All concentrations, however, were considerably lower than those observed in similar species from the region of the
Amazon Basin affected by gold mining. 相似文献
8.
The southern portion of the Brazilian coast is dominated by coastal lagoons formed by sandy barrier spits with small inlets. This coastal configuration is a barrier to the surface flow of freshwater to the sea; thus, we suspect that a significant amount of freshwater flows through the permeable sands, beneath the barrier spits, where it mixes with seawater. We excavated an 18-m-deep well into the barrier spit which separates the Patos Lagoon from the South Atlantic. Using this well, we were able to sample interstitial waters from discrete layers, at 1-m intervals, which were analyzed for salinity, temperature, pH, nutrients (ammonium, nitrate, phosphate, and silicate), uranium, molybdenum, and barium. Similar analyses were made on surface water samples from the Patos Lagoon estuarine mixing zone.Results of well samples show a continuous increase in salinity with depth reaching 18 at the bottom. Ammonium and silicate are high, generally around 100 and 100–150 μM, respectively, throughout the subterranean profile. Phosphate shows a distinct maximum at about 6 m (ca. 25 μM), and nitrate is generally low in all well samples. Uranium and molybdenum exhibit a minimum in the well profile at about the same location where barium exhibits a maximum (greater than 2 μM). When results are compared to the surface lagoon–seawater mixing data, ammonium, phosphate, silicate, and barium in well samples of similar salinity show considerable enrichment, while a comparison of uranium and molybdenum data indicates significant depletion of these metals in most well samples.Based on these and other data, we deduce that the following processes are active: products of remineralization of organic detritus accumulated in lagoon sediments are advected through permeable sediments to the oceans; dissolution of biogenic solids and/or solid silicates mobilizes silicate; phosphate, uranium, and molybdenum are mobilized from phosphate-rich sediment layers; sulfate reducers remove uranium and perhaps molybdenum from solution throughout most of the well profile; barium is desorbed from solids in the subterranean mixing zone. These results demonstrate that freshwater discharged to the ocean through permeable sediments may have a significantly different composition than that discharged at the surface. 相似文献
9.
Embryo production was reduced in female grass shrimp exposed to sediments with added coal fly ash and to sediments collected from an estuarine station containing high PAH concentrations due to its proximity to a highway storm drain. Grass shrimp embryos exposed to pore water from the high PAH and high metal sediments showed both reduced hatching and increases in DNA strand breaks (comet assay). Sediments with added coal fly ash had high concentrations of vanadium and selenium which may have contributed to effects similar to those observed with sediments with high PAH. The embryo pore water bioassay (hatching/DNA strand breaks) gave results comparable to those observed for reproduction effects (reduced embryo production/embryo hatching) with female grass shrimp exposed to whole sediment. 相似文献
10.
Américo I. Torres Carlos F. Andrade Willard S. Moore Mauricio Faleschini José L. Esteves Luis F. H. Niencheski Pedro J. Depetris 《Environmental Earth Sciences》2018,77(4):145
Submarine groundwater discharge (SGD) is herein recognized as a significant pathway of material transport from land to the coastal SW Atlantic Ocean and thus, it can be a relevant factor affecting the marine biogeochemical cycles in the region. This paper focuses on the initial measurements of 226Ra, 228Ra and 222Rn made in Patagonia’s coastal zone of Chubut and Santa Cruz provinces (42°S–48°S, Argentina). 226Ra activity ranged from 2.9 to 73.5 dpm 100 L?1, and 228Ra activity ranged from 11.9 to 311.0 dpm 100 L?1 in groundwater wells. The radium activities found in Patagonia’s marine coastal regions and adjacent shelf indicate significant enrichment throughout the coastal waters. Groundwater samples presented the largest 222Rn activity and ranged from 2.66 to 1083 dpm L?1. Conversely, in the coastal marine environment, the 222Rn activity ranged from 1.03 to 6.23 dpm L?1. The Patagonian coastal aquifer showed a larger enrichment in 228Ra than in 226Ra, which is a typical feature for sites where SGD is dominant, probably playing a significant role in the biogeochemistry of these coastal waters. 相似文献