Erosion rates evaluated by the <Superscript>137</Superscript>Cs technique in the high altitude area of the Qinghai–Tibet plateau of China     

Yibo Wang  Genxu Wang  Hongchang Hu  Huiyan Cheng 《Environmental Geology》2008,53(8):1743-1749

Studying spatial and temporal variation of soil loss is of great importance because of global environmental concerns. Understanding the spatial distribution of soil erosion and deposition in the high-cold steppe is important for designing soil and water conservation measures. Measured ¹³⁷Cs losses (Bq m⁻²) from long-term high altitude (4,000 m above sea level) watershed plots on the Qinghai–Tibet plateau and derived soil erosion estimates (Mg ha⁻¹ year⁻¹) were significantly correlated to directly measured soil losses from the same plots, over the same period (1963–2005). The local reference inventory was estimated to be 2,468 Bq m⁻². The result of analyzing ¹³⁷Cs distribution and its intensity in the soil profiles in this area shows similarities to ¹³⁷Cs distribution in other areas. ¹³⁷Cs is basically distributed in the topsoil layer of 0–0.3 m. Soil erosions vary greatly in the entire sampled area, ranging from 5.5 to 23 Mg ha⁻¹ year⁻¹, with an average of 16.5 Mg ha⁻¹ year⁻¹ which is a moderate rate of erosion.  相似文献   

Net aboveground primary production and soil properties of floating and attached freshwater tidal marshes in the Río de la Plata estuary,Argentina     

Paula Pratolongo  Patricia Kandus  Mark M. Brinson 《Estuaries and Coasts》2007,30(4):618-626

In the lower delta of the Paraná River, at the head of the Río de la Plata estuary (Argentina), we compared net aboveground primary production (NAPP) and soil properties of the dominant macrophyteScirpus giganteus (Kunth) in a floating and an attached marsh community. Both marshes are tidally influenced but in different ways. The floating marsh site is relatively isolated from tidal influences because its ability to float makes it resistant to overland flow and to sediment inputs from the estuary. The attached marsh lacks the capacity to float and receives sediment supplies from the estuary through overland flow. These hydrologic differences are reflected in lower mineral content in sediments of the floating marsh. Using a leaf tagging technique, estimated NAPP was 1,109 ± 206 g m⁻² yr⁻¹ for the floating marsh and 1,866 ±258 g m⁻² yr⁻¹ for the attached marsh. We attribute the lower NAPP of the floating marsh to isolation from sediment input from overland flow.  相似文献   

Water quality analysis of a freshwater diversion at Caernarvon, Louisiana     

Robert R. Lane  John W. Day  Burnell Thibodeaux 《Estuaries and Coasts》1999,22(2):327-336

Since 1991, Mississippi River water has been diverted at Caernarvon, Louisiana, into Breton Sound estuary. Breton Sound estuary encompasses 1100 km² of fresh and brackish, rapidly subsiding wetlands. Nitrite + nitrate, total Kjeldahl nitrogen, ammonium, total phosphorus, total suspended sediments, and salinity concentrations were monitored at seven locations in Breton Sound from 1988 to 1994. Statistical analysis of the data indicated decreased total Kjeldahl nitrogen with associated decrease in total nitrogen, and decreased salinity concentrations in the estuary due to the diversion. Spring and summer water quality transects indicated rapid reduction of nitrite + nitrate and total suspended sediment concentration as diverted Mississippi River water entered the estuary, suggesting near complete assimilation of these constituents by the ecosystem. Loading rates of nitrite + nitrate (5.6–13.4 g m⁻² yr⁻¹), total nitrogen (8.9–23.4 g m⁻² yr⁻¹), and total phosphorus (0.9–2.0 g m⁻² yr⁻¹) were calculated along with removal efficiencies for these constituents (nitrite + nitrate 88–97%; total nitrogen 32–57%; total phosphorus 0–46%). The low impact of the diversion on water quality in the Breton Sound estuary, along with assimilation of TSS over a very short distance, suggests that more water may be introduced into the estuary without detrimental affects. This would be necessary if freshwater diversions are to be used to distribute nitrients and sediments into the lower reaches of the estuary, in an effort to compensate for relative sea-level rise, and reverse the current trend of rapid loss of wetlands in coastal Louisiana.  相似文献   

Setting load limits for nutrients and suspended solids based upon seagrass depth-limit targets     

Joel S. Steward  Whitney C. Green 《Estuaries and Coasts》2007,30(4):657-670

Total nitrogen (TN), total phosphorus (TP), and total suspended solids (TSS) loadings [log (kg ha⁻¹ yr⁻¹)] were regressed against seagrass depth limits (percent of depth-limit targets) to back-predict the load limits or allocations (kg ha⁻¹ yr⁻¹ or kg yr⁻¹) necessary to meet targeted seagrass depth limits in the Indian River and Banana River (IRBR) lagoons, Florida. Because the load allocations can be applied as total maximum daily loads (TMDL) for the IRBR (U.S. Environmental Protection Agency mandate), the method and results are developed and presented toward that end. The regression analyses indicate that the range of surface-discharge load limits (nonpoint + point source), per watershed area, required to achieve the desired depth limits for seagrass in the IRBR are approximately 2.4–3.2 kg ha⁻¹ yr⁻¹ TN, 0.41–0.64 kg ha⁻¹ yr⁻¹ TP, and 48–64 kg ha⁻¹ yr⁻¹ TSS. This simple regression method may have application to other shallow estuarine lagoons or bays where seagrass growth is limited by light and water transparency, water transparency is strongly affected by watershed pollutant loadings, water residence times are sufficiently long to allow seagrass coverage to respond to and covary with total load inputs, and multiyear monitoring has yielded sufficient variability in both pollutant loadings and seagrass coverages to develop a statistically meaningful relationship.  相似文献   

Benthic metabolism and nutrient cycling along an estuarine salinity gradient     

Charles S. Hopkinson  Anne E. Giblin  Jane Tucker  Robert H. Garritt 《Estuaries and Coasts》1999,22(4):863-881

Benthic metabolism and nutrient exchange across the sediment-water interface were examined over an annual cycle at four sites along a freshwater to marine transect in the Parker River-Plum Island Sound estuary in northeastern Massachusetts, U.S. Sediment organic carbon content was highest at the freshwater site (10.3%) and decreased along the salinity gradient to 0.2% in the sandy sediments at the marine end of the estuary. C:N ratios were highest in the mid estuary (23:1) and lowest near the sea (11:1). Chlorophyll a in the surface sediments was high along the entire length of the estuary (39–57 mg chlorophyll a m⁻²) but especially so in the sandy marine sediments (172 mg chlorophyll a m⁻²). Chlorophyll a to phaeophytin ratios suggested most chlorophyll is detrital, except at the sandy marine site. Porewater sulfide values varied seasonally and between sites, reflecting both changes in sulfate availability as overlying water salinity changed and sediment metabolism. Patterns of sediment redox potential followed those of sulfide. Porewater profiles of inorganic N and P reflected strong seasonal patterns in remineralization, accumulation, and release. Highest porewater NH₄ ⁺ values were found in upper and mid estuarine sediments, occasionally exceeding 1 mM N. Porewater nitrate was frequently absent, except in the sandy marine sediments where concentrations of 8 μM were often observed. Annual average respiration was lowest at the marine site (13 mmol O₂ m⁻² d⁻¹ and 21 mmol TCO₂ m⁻² d⁻¹) and highest in the mid estuary (130 mmol O₂ m⁻² d⁻¹ and 170 mmol TCO₂ m⁻² d⁻¹) where clam densities were also high. N₂O and CH₄ fluxes were low at all stations throughout the year: Over the course, of a year, sediments varied from being sources to sinks of dissolved organic C and N, with the overall spatial pattern related closely to sediment organic content. There was little correlation between PO₄ ³⁻ flux and metabolism, which we attribute to geochemical processes. At the two sites having the lowest salinities, PO₄ ³⁻ flux was directed into the sediments. On average, between 22% and 32% of total system metabolism was attributable to the benthos. The mid estuary site was an exception, as benthic metabolism accounted for 95% of the total, which is attributable to high densities of filter-feeding clams. Benthic remineralization supplied from less than 1% to over 190% of the N requirements and 0% to 21% of the P requirements of primary producers in this system. Estimates of denitrification calculated from stoichiometry of C and N fluxes ranged from 0% for the upper and mid estuary site to 35% for the freshwater site to 100% of sediment organic N remineralization at the marine site. We hypothesize that low values in the upper and mid estuary are attributable to enhanced NH₄ ⁺ fluxes during summer due to desorption of exchangeable ammonium from rising porewater salinity. NH₄ ⁺ desorption during summer may be a mechanism that maintains high rates of pelagic primary production at a time of low inorganic N inputs from the watershed.  相似文献   

Comparison of soil erosion and deposition rates using radiocesium, RUSLE, and buried soils in dolines in East Tennessee   总被引：4，自引：0，他引：4  

K. M. Turnage  S. Y. Lee  J. E. Foss  K. H. Kim  I. L. Larsen 《Environmental Geology》1997,29(1-2):1-10

 Three dolines (sinkholes), each representing different land uses (crop, grass, and forest) in a karst area in East Tennesse, were selected to determine soil erosional and depositional rates. Three methods were used to estimate the rates: fallout radiocesium (¹³⁷Cs) redistribution, buried surface soil horizons (Ab horizon), and the revised universal soil loss equation (RUSLE). When ¹³⁷Cs redistribution was examined, the average soil erosion rates were calculated to be 27 t ha^–1 yr^–1 at the cropland, 3 t ha^–1 yr^–1 at the grassland, and 2 t ha^–1 yr^–1 at the forest. By comparison, cropland erosion rate of 2.6 t ha^–1 yr^–1, a grassland rate of 0.6 t ha^–1 yr^–1, and a forest rate of 0.2 t ha^–1 yr^–1 were estimated by RUSLE. The ¹³⁷Cs method expressed higher rates than RUSLE because RUSLE tends to overestimate low erosion rates and does not account for deposition. The buried surface horizons method resulted in deposition rates that were 8 t ha^–1 yr^–1 (during 480 yr) at the cropland, 12 t ha^–1 yr^–1 (during 980 yr) at the grassland, and 4 t ha^–1 yr^–1 (during 101 yr) at the forest site. By examining ¹³⁷Cs redistribution, soil deposition rates were found to be 23 t ha^–1 yr^–1 at the cropland, 20 t ha^–1 yr^–1 at the grassland, and 16 t ha^–1 yr^–1 at the forest site. The variability in deposition rates was accounted for by temporal differences;¹³⁷Cs expressed deposition during the last 38 yr, whereas Ab horizons represented deposition during hundreds of years. In most cases, land use affected both erosion and deposition rates – the highest rates of soil redistribution usually representing the cropland and the lowest, the forest. When this was not true, differences in the rates were attributed to differences in the size, shape, and closure of the dolines. Received: 10 October 1995 · Accepted: 13 October 1995  相似文献   

Sediment and Nutrient Deposition Associated with Hurricane Wilma in Mangroves of the Florida Coastal Everglades     

Edward Castañeda-Moya  Robert R. Twilley  Victor H. Rivera-Monroy  Keqi Zhang  Stephen E. DavisIII  Michael Ross 《Estuaries and Coasts》2010,33(1):45-58

The distribution of mangrove biomass and forest structure along Shark River estuary in the Florida Coastal Everglades (FCE) has been correlated with elevated total phosphorus concentration in soils thought to be associated with storm events. The passage of Hurricane Wilma across Shark River estuary in 2005 allowed us to quantify sediment deposition and nutrient inputs in FCE mangrove forests associated with this storm event and to evaluate whether these pulsing events are sufficient to regulate nutrient biogeochemistry in mangrove forests of south Florida. We sampled the spatial pattern of sediment deposits and their chemical properties in mangrove forests along FCE sites in December 2005 and October 2006. The thickness (0.5 to 4.5 cm) of hurricane sediment deposits decreased with distance inland at each site. Bulk density, organic matter content, total nitrogen (N) and phosphorus (P) concentrations, and inorganic and organic P pools of hurricane sediment deposits differed from surface (0–10 cm) mangrove soils at each site. Vertical accretion resulting from this hurricane event was eight to 17 times greater than the annual accretion rate (0.30 ± 0.03 cm year⁻¹) averaged over the last 50 years. Total P inputs from storm-derived sediments were equivalent to twice the average surface soil nutrient P density (0.19 mg cm⁻³). In contrast, total N inputs contributed 0.8 times the average soil nutrient N density (2.8 mg cm⁻³). Allochthonous mineral inputs from Hurricane Wilma represent a significant source of sediment to soil vertical accretion rates and nutrient resources in mangroves of southwestern Everglades. The gradient in total P deposition to mangrove soils from west to east direction across the FCE associated with this storm event is particularly significant to forest development due to the P-limited condition of this carbonate ecosystem. This source of P may be an important adaptation of mangrove forests in the Caribbean region to projected impacts of sea-level rise.  相似文献   

Primary production and decomposition ofSarcocornia fruticosa (L.) scott andPhragmites australis Trin. Ex Steudel in the Po Delta, Italy     

Francesco Scarton  John W. Day  Andrea Rismondo 《Estuaries and Coasts》2002,25(3):325-336

From September 1994 through October 1995 aboveground and belowground production ofSarcocornia fruticosa andPhragmites australis was studied at two sites in the Po Delta. In 1995, aboveground production forS. fruticosa in an intertidal site was 678 g dw m⁻² yr⁻¹ with a peak live biomass of 1,008 g m⁻²; belowground production was 1,260 g m⁻² with a peak live biomass of 3,735 g m⁻². A litter bag decomposition study showed that after 69 wk there were 3.7%, 64.3%, and 66.6% of the original mass of leafy stems, woody stems, and roots, respectively. In a reed bed, which experiences brackish conditions,P. australis aboveground production was 876 g m⁻² with a peak live biomass of 780 g m⁻²; belowground production was 2,263 g m⁻² with a peak live biomass of 4,087 g m⁻². After 65 wk, there was 45.4%, 50.4%, and 29.3%, respectively, of leaves, stems, and rhizomes remaining of the initial biomass. At both sites, regular submersion by salt water probably leads to lower aboveground biomass and higher belowground biomass than reported for other Mediterranean coastal sites. The high belowground biomass can contribute to accretion to offset rising sea level.  相似文献   

Tidally-induced shear stress variability above intertidal mudflats in the macrotidal seine estuary     

R. Verney  J.-C. Brun-Cottan  R. Lafite  J. Deloffre  J. A. Taylor 《Estuaries and Coasts》2006,29(4):653-664

Tidal currents and the spatial variability of tidally-induced shear stress were studied during a tidal cycle on four intertidal mudflats from the fluvial to the marine part of the Seine estuary. Measurements were carried out during low water discharge (<400 m³ s⁻¹) in neap and spring tide conditions. Turbulent kinetic energy, covariance, and logarithmic profile methods were used and compared for the determination of shear stress. The c_TKE coefficient value of 0.19 cited in the literature was confirmed. Shear stress values were shown to decrease above mudflats from the mouth to the fluvial part of the estuary due to dissipation of the tidal energy, from 1 to 0.2 N m⁻² for spring tides and 0.8 to 0.05 N m⁻² for neap tides. Flood currents dominate tidally-induced shear stress in the marine and lower fluvial estuary during neap and spring tides and in the upper fluvial part during spring tides. Ebb currents control tidally-induced shear stress in the upper fluvial part of the estuary during neap tides. These results revealed a linear relationship between friction velocities and current velocities. Bed roughness length values were calculated from the empirical relationship given by Mitchener and Torfs (1996) for each site; these values are in agreement with the modes of the sediment particle-size distribution. The influence of tidal currents on the mudflat dynamics of the Seine estuary was examined by comparing the tidally-induced bed shear stress and the critical erosion shear stress estimated from bed sediment properties. Bed sediment resuspension induced by tidal currents was shown to occur only in the lower part of the estuary.  相似文献   

Growth and production of the mummichog (<Emphasis Type="Italic">Fundulus heteroclitus</Emphasis>) in a restored salt marsh     

S.?L.?H.?Teo  K.?W.?AbleEmail author 《Estuaries and Coasts》2003,26(1):51-63

The mummichog,Fundulus heteroclitus, is one of the most important macrofaunal components of salt marsh surfaces and an important link to subtidal areas of the adjacent estuary along the east coast of the U.S. We estimated growth, population size, and production of the mummichog in a restored marsh in order to improve our understanding of the role of this resident fish and to evaluate the success of the restoration. The restored marsh, covering 234 ha, was a former salt hay farm located in the mesohaline portion of Delaware Bay that was restored to tidal influence in August 1996. We separated the mummichog population into two components based on life history stage and summer habitat use patterns. One component, consisting of adults and large young-of-the-year (YOY), exhibited tidal movements to and from the marsh surface and the subtidal creeks. These were examined with an intensive mark and recapture program using coded wire tags. Another component, consisting of small YOY, remained on the marsh surface throughout the tidal cycle. Throw traps were used to sample these small YOY. The mean annual population density of adults and large YOY for the entire marsh was approximately 1.2 fish m⁻² and mean monthly density peaked at 2.9 fish m⁻². The mean annual density of small YOY on the marsh surface was 15.1 fish m⁻² and mean monthly density peaked at 41.4 fish m⁻². Size and season influenced the growth rate of individual fish and instantaneous growth rates ranged from 0.03 to 2.26 mo⁻¹. Total annual mummichog production was estimated to be 8.37 g dw m⁻² yr⁻¹, with adults and large YOY contributing 28.4% (2.38 g dw m⁻² yr⁻¹) and small YOY on the marsh surface contributing 71.6% (5.99 g dw m⁻² yr⁻¹). The seasonal use and population densities were comparable to previous studies in natural marshes while growth and production of mummichog in this restored marsh appeared to be higher. Coupled with the results of other studies on the feeding, movement, and habitat use of this species in this restored marsh, the species has responded well to the restoration.  相似文献   

Denitrification and the stoichiometry of nutrient regeneration in Waquoit Bay, Massachusetts     

Michael G. LaMontagne  Valeria Astorga  Anne E. Giblin  Ivan Valiela 《Estuaries and Coasts》2002,25(2):272-281

To determine the removal of regenerated nitrogen by estuarine sediments, we compared sediment N₂ fluxes to the stoichiometry of nutrient and O₂ fluxes in cores collected in the Childs River, Cape Cod, Massachusetts. The difference between the annual PO₄ ³⁻ (0.2 mol P m⁻² yr⁻¹) and NH₄ ⁺ (1.6 mol N m⁻² yr⁻¹) flux and the Redfield N∶P ratio of 16 suggested an annual deficit of 1.5 mol N m⁻² yr⁻¹. Denitrification predicted from O₂∶NH₄ ⁺ flux ratios and measured as N₂ flux suggested a nitrogen sink of roughly the same magnitude (1.4 mol N m⁻² yr⁻¹). Denitrification accounted for low N∶P ratios of benthic flux and removed 32–37% of nitrogen inputs entering the relatively highly nutrient loaded Childs River, despite a relatively brief residence time for freshwater in this system. Uptake of bottom water nitrate could only supply a fraction of the observed N₂ flux. Removal of regenerated nitrogen by denitrification in this system appears to vary seasonally. Denitrification efficiency was inversely correlated with oxygen and ammonium flux and was lowest in summer. We investigated the effect of organic matter on denitrification by simulating phytoplankton deposition to cores incubated in the lab and by deploying chambers on bare and macroaglae covered sediments in the field. Organic matter addition to sediments increased N₂ flux and did not alter denitrification efficiency. Increased N₂ flux co-varied with O₂ and NH₄ ⁺ fluxes. N₂ flux (261±60 μmol m⁻² h⁻¹) was lower in chambers deployed on macroalgal beds than deployed on bare sediments (458±70 μmol m⁻² h⁻¹), and O₂ uptake rate was higher in chambers deployed on macroalgal beds (14.6±2.2 mmol m⁻² h⁻¹) than on bare sediments (9.6±1.5 mmol m⁻² h⁻¹). Macroalgal cover, which can retain nitrogen in the system, is a link between nutrient loading and denitrification. Decreased denitrification due to increasing macroalgal cover could create a positive feedback because decreasing denitrification would increase nitrogen availability and could increase macroalgae cover.  相似文献   

Soil erosion determinations by using 137Cs technique in the agricultural regions of Gediz Basin, Western Turkey     

M. M. Saç  E. Yumurtaci  G. Yener  B. Camgöz  A. Uğur  B. Özden 《Environmental Geology》2008,55(3):477-483

Gediz Basin is one of the regions where intense agricultural activities take place in Western Turkey. Erosion and soil degradation have long been causing serious problems to cultivated fields in the basin. This work describes the application of two different ¹³⁷Cs models for estimating soil erosion rates in cultivated sites of the region. Soil samples were collected from five distinct cultivated regions subject to soil erosion. The variations of ¹³⁷Cs concentrations with depth in soil profiles were investigated. Soil loss rates were calculated from ¹³⁷Cs inventories of the samples using both proportional model (PM) and simplified mass balance model (SMBM). When PM was used, erosion and deposition rates varied from −15 to −28 t ha⁻¹ year⁻¹ and from +5 to +41 t ha⁻¹ year⁻¹, respectively; they varied from −16 to −33 t ha⁻¹ year⁻¹ and from +5 to +55 t ha⁻¹ year⁻¹ with SMBM. A good agreement was observed between the results of two models up to 30 t ha⁻¹ year⁻¹ soil loss and gain in the study area. Ulukent, a small representative agricultural field, was selected to compare the present data of ¹³⁷Cs techniques with the results obtained by universal soil loss equation (USLE) applied in the area before.  相似文献   

Seasonal variations in sediment sulfur cycling in the Ballastplaat mudflat, Belgium   总被引：2，自引：0，他引：2  

Suwanna Panutrakul  Frank Monteny  Willy Baeyens 《Estuaries and Coasts》2001,24(2):257-265

Sulfate reduction rate (SRR) and pools of reduced inorganic sulfur, acid volatile sulfide (AVS), chromium reducible sulfur (CRS), and elemental sulfur (S^o), were studied from June 1990 till March 1992 at two locations on the Ballastplaat mudflat in the Scheldt estuary. The sediment composition at station A was mainly sand with low organic content whereas sediments at station B were dominated by silt and clay with high organic content. SRR was positively related to temperature; more pronounced at station B (Ea=190 kJ mol⁻¹) than at station A (Ea=110 kJ mol⁻¹). The maximum SRR values observed equalled 14 μmol cm⁻³ d⁻¹ at station B and 1 μmol cm⁻³ d⁻¹ at station A. AVS was the dominant radiolabelled end product of the sulfate reduction reaction, except in surface sediments where pyrite and S^o were more dominant. However, CRS was the predominant reduced inorganic sulfur pool in the sediments. Both AVS and CRS pools showed temporal variations out of phase with SRR. SRR peaked in summer, while the concentrations of AVS and CRS were highest in fall. The accumulation of AVS and CRS started late summer after depletion of oxidants, which had accumulated during winter and spring. The estimated annual SRR and thus sulfide production in the upper 15 cm of station B was of the order of 100 mol m⁻² yr⁻¹, and at station A of the order of 12 mol m⁻² yr⁻¹. The sulfur mass balance shows that only a very small fraction, if any, of the produced sulfide is retained as reduced inorganic sulfur in the sediment.  相似文献   

Assessment of present and future nitrogen loads, water quality, and seagrass (Thalassia testudinum) depth distribution in Lemon Bay, Florida     

David A. Tomasko  Denise L. Bristol  Judith A. Ott 《Estuaries and Coasts》2001,24(6):926-938

Nitrogen loads into Lemon Bay, Florida were modeled to have increased ca. 59% between pre-development (i.e., 1850) estimates (5.3 kg TN ha⁻¹ yr⁻¹. and estimates for the year 1995 (8.4 kg TN ha⁻¹ yr⁻¹). By the year 2010, nitrogen loads are predicted to increase an additional 45% or 58%, depending upon progress being made toward replacing older septic tank systems with centralized sewerage (nitrogen loads of 12.2 and 13.3 kg TN ha⁻¹ yr⁻¹, respectively). Using 1995 estimates, nonpoint sources (stormwater runoff) are throught to be responsible for ca. 76% of the annual nitrogen load, followed by septic tank systems (14%), rainfall (10%), and an insignificant load from baseflow. Based on an empirically-derived nitrogen load:chlorophylla relationship developed for a portion of nearby Tampa Bay, a 45% increase in nitrogen loads into Lemon Bay could result in a 29% increase in annual average chlorophylla concentrations. Using the estimate of a 29% increase in future chlorophylla concentrations, an empirically-derived optical model for Lemon Bay suggests that light attenuation coefficients in the bay would increase ca. 9%, and the average depth limit ofThalassia testudinum in Lemon Bay would decrease by ca. 24%.  相似文献   

Macrofaunal Spatial Patterns in Relationship to Environmental Variables in the Richibucto Estuary,New Brunswick,Canada   总被引：1，自引：0，他引：1  

Lin Lu  Jon Grant  Jeffrey Barrell 《Estuaries and Coasts》2008,31(5):994-1005

Estuarine macrobenthos respond to a variety of environmental gradients such as sediment type and salinity, and organic enrichment. A relatively new influence, organic loading from suspended bivalve culture, has the potential to alter this response. A study on soft-bottom macrobenthic communities was carried out in the Richibucto estuary (46°40′N, 64°50′W), New Brunswick, Canada, with samples collected from 18 stations in late September and early October 2006. The site consisted of a large tidal channel originating upstream in a small river. The channel was punctuated by bag culture of oysters along its length. A total of 88 species were recorded. The mean values of abundance, species richness, and diversity (H′) of macrofauna were 11,199 ind. m⁻² (ranged from 4,371 to 19,930 ind. m⁻²), 23.4 species grab⁻¹ and 3.29 grab⁻¹, respectively. In general species richness and H′ increased from the upper estuary to the estuarine mouth. Multivariate analyses clearly exhibited the spatial distribution in community structure, which coincided with the locations along the estuary (the upper, the lower and the mouth), as well as inside and outside the channel. Species richness and diversity H′ showed strong positive correlations with salinity (21.2–25.2 ppt), and abundance was positively correlated with water depth (1.0–4.5 m). Abundance and species richness were negatively correlated with both of silt–clay fraction (3.3–24.8%) and sorting (σ_I). Species richness was also negatively correlated with organic content (1.9–12.7%). The BIO-ENV analyses identified silt–clay fraction, σ_I and salinity as the major environmental variable combination influencing the macrofaunal patterns, and silt–clay fraction as the single best-correlated variable.  相似文献   

Planktonic and whole system metabolism in a nutrient-rich estuary (the Scheldt estuary)     

Frédéric Gazeau  Jean-Pierre Gattuso  Jack J. Middelburg  Natacha Brion  Laure-Sophie Schiettecatte  Michel Frankignoulle  Alberto Vieira Borges 《Estuaries and Coasts》2005,28(6):868-883

Planktonic gross primary production (GPP), community respiration (CR), and nitrification (NIT) were measured monthly in the Scheldt estuary by the oxygen incubation method in 2003. No significant evolution of planktonic GPP was observed since the 1990s with high rates in the freshwater area (salinity 0; 97±65 mmol C m⁻² d⁻¹) decreasing seaward (22–37 mmol C m⁻² d⁻¹). A significant decrease of NIT was observed with regard to previous investigations although this process still represents up to 20% of total organic matter production in the inner estuary. Planktonic CR was highest in the inner estuary and seemed to be mainly controlled by external organic matter inputs. Planktonic net community production was negative most of the time in the estuary with values ranging from −300 to 165 mmol C m⁻² d⁻¹. Whole estuary net ecosystem production (NEP) was investigated on an annual scale using the results mentioned above and published benthic metabolic rates. A NEP of −39±8 mmol C m⁻² d⁻¹ was estimated, which confirms the strong heterotrophic status of this highly nutrified estuary. NEP rates were computed from June to December 2003 to compare with results derived from the Land-Ocean Interaction in the Coastal Zone budgeting procedure applied to dissolved inorganic phosphorus and carbon (DIP and DIC). DIP budgets failed to provide realistic estimates in the inner estuary where abiotic processes account for more than 50% of the nonconservative DIP flux. DIC budgets predicted a much lower NEP than in situ incubations (−109±31 versus −42±9 mmol C m⁻² d⁻¹) although, as each approach is associated with several critical assumptions, the source of this discrepancy remains unclear.  相似文献   

Lower Seine River and estuary (France) carbon and oxygen budgets during low flow   总被引：1，自引：0，他引：1  

Josette Garnier  Pierre Servais  Gilles Billen  Maïa Akopian  Natacha Brion 《Estuaries and Coasts》2001,24(6):964-976

Ecological processes driving the oxygen budget were investigated in the downstream part of the Seine River and its estuary. Phytoplankton and bacterioplankton production were measured along longitudinal profiles (11 to 17 stations) in a range of low discharges from 300 m³ s⁻¹ in 1993 and 1995 to 140 m³ s⁻¹ in 1996. Values representative of the water column were based on investigations carried out during two tidal cycles. Net primary production was invariably greatest in the freshwater estuary, from Poses to Rouen (from 500 to 1,000 μg C l⁻¹ d⁻¹ between PK 202 and 240) and decreased sharply downstream (from 10 to 25 μg c l⁻¹ d⁻¹ between PK 250 and 310). This decrease was mainly due to the deterioration of the light conditions with the increase in depth and suspended matter concentrations. Heterotrophic activity was maximum in the reach where primary production declined. Judging by the production:respiration ratio (P:R), the system appeared clearly heterotrophic in the Seine River immediately downstream of the Paris region due to high allochthonous organic pollution by the incompletely treated Parisian effluents and in the part of the estuary characterized by intense degradation of autochthonous material. Because the effluents are not treated by a nitrification step, the oxygen consumption due to nitrification was much higher than expected from the P:R ratio. Oxidation of ammonium represented an oxygen consumption of between 1 and 14 g O₂ m⁻² d⁻¹, almost equalling the sum of heterotrophic respirations that were barely balanced by photosynthesis. The reaeration flux at the water-atmosphere interface was deduced from the calculations and a reaeration coefficient was estimated.  相似文献   

Sources of nitrogen to estuaries in the United States     

Mark?S.?CastroEmail author  Charles?T.?Driscoll  Thomas?E.?Jordan  William?G.?Reay  Walter?R.?Boynton 《Estuaries and Coasts》2003,26(3):803-814

The purpose of this study was to quantify the nitrogen (N) inputs to 34 estuaries on the Atlantic and Gulf Coasts of the United States. Total nitrogen (TN) inputs ranged from 1 kg N ha⁻¹ yr⁻¹ for Upper Laguna Madre, Texas, to 49 kg N ha⁻¹ yr⁻¹ for Massachusetts Bay, Massachusetts. TN inputs to 11 of the 34 estuaries were dominated by urban N sources (point sources and septic systems) and nonpoint source N runoff (5% of total); point sources accounted for 36–86% of the TN inputs to these 11 urban-dominated estuaries. TN inputs to 20 of the 34 estuaries were dominated by agricultural N sources; N fertilization was the dominant source (46% of the total), followed by manure (32% of the total) and N fixation by crops (16% of the total). Atmospheric deposition (runoff from watershed plus direct deposition to the surface of the estuary) was the dominant N source for three estuaries (Barnegat Bay, New Jersey: 64%; St. Catherines-Sapelo, Georgia: 72%; and Barataria Bay, Louisiana: 53%). Six estuaries had atmospheric contributions ≥30% of the TN inputs (Casco Bay, Maine: 43%; Buzzards Bay, Massachusetts: 30%; Great Bay, New Jersey: 40%; Chesapeake Bay: 30%; Terrebonne-Timbalier Bay, Louisiana: 59%; and Upper Laguna Madre: 41%). Results from our study suggest that reductions in N loadings to estuaries should be accomplished by implementing watershed specific programs that target the dominant N sources.  相似文献   

Variation and uncertainty in evaporation from a subtropical estuary: Florida Bay     

René M. Price  William K. Nuttle  Bernard J. Cosby  Peter K. Swart 《Estuaries and Coasts》2007,30(3):497-506

Variation and uncertainty in estimated evaporation was determined over time and between two locations in Florida Bay, a subtropical estuary. Meteorological data were collected from September 2001 to August 2002 at Rabbit Key and Butternut Key within the Bay. Evaporation was estimated using both vapor flux and energy budget methods. The results were placed into a long-term context using 33 years of temperature and rainfall data collected in south Florida. Evaporation also was estimated from this long-term data using an empirical formula relating evaporation to clear sky solar radiation and air temperature. Evaporation estimates for the 12-mo period ranged from 144 to 175 cm yr⁻¹, depending on location and method, with an average of 163 cm yr⁻¹ (±9%). Monthly values ranged from 9.2 to 18.5 cm, with the highest value observed in May, corresponding with the maximum in measured net radiation. Uncertainty estimates derived from measurement errors in the data were as much as 10%, and were large enough to obscure differences in evaporation between the two sites. Differences among all estimates for any month indicate the overall uncertainty in monthly evaporation, and ranged from 9% to 26%. Over a 33-yr period (1970–2002), estimated annual evaporation from Florida Bay ranged from 148 to 181 cm yr⁻¹, with an average of 166 cm yr⁻¹. Rainfall was consistently lower in Florida Bay than evaporation, with a long-term average of 106 cm yr⁻¹. Rainfall considered alone was uncorrelated with evaporation at both monthly and annual time scales; when the seasonal variation in clear sky radiation was also taken into account both net radiation and evaporation were significantly suppressed in months with high rainfall.  相似文献   

Quantitative assessment of benthic food resources for juvenile Gulf sturgeon,Acipenser oxyrinchus desotoi in the Suwannee River estuary, Florida, USA     

R. Allen Brooks  Kenneth J. Sulak 《Estuaries and Coasts》2005,28(5):767-775

Gulf sturgeon,Acipenser oxyrinchus desotoi, forage extensively in the Suwannee River estuary following emigration out of the Suwannee River, Florida. While in the estuary, juvenile Gulf sturgeon primarily feed on benthic infauna. In June–July 2002 and February–April 2003, random sites within the estuary were sampled for benthic macrofauna (2002 n = 156; 2003 n = 103). A mean abundance of 2,562 ind m⁻² (SE ± 204) was found in the summer, with significantly reduced macrofaunal abundance in the winter (mean density of 1,044 ind m⁻², SE ± 117). Benthic biomass was significantly higher in the summer with an average summer sample dry weight of 5.92 g m⁻² (SE ± 0.82) compared to 3.91 g m⁻² (SE ± 0.67) in the winter. Amphipods and polychaetes were the dominant taxa collected during both sampling periods. Three different estimates of food availability were examined taking into account principal food item information and biomass estimates. All three estimates provided a slightly different view of potential resources but were consistent in indicating that food resource values for juvenile Gulf sturgeon are spatially heterogeneous within the Suwannee River estuary.  相似文献