DIN Inputs Research Articles

Increasing cascade dams in the upstream area reduce nutrient inputs to the Three Gorges Reservoir in China

The upstream cascade dams play an essential role in the nutrient cycle in the Yangtze. However, there is little quantitative information on the effects of upstream damming on nutrient retention in the Three Gorges Reservoir (TGR) in China. Here, we aim to assess the impact of increasing cascade dams in the upstream area of the Yangtze on Dissolved Inorganic Nitrogen and Phosphorus (DIN and DIP) inputs to the TGR and their retention in the TGR and to draw lessons for other large reservoirs. We implemented the Model to Assess River Inputs of Nutrients to seAs (MARINA-Nutrients China-2.0 model). We ran the model with the baseline scenario in which river damming was at the level of 2009 (low) and alternative scenarios with increased damming. Our scenarios differed in nutrient management. Our results indicated that total water storage capacity increased by 98 % in the Yangtze upstream from 2009 to 2022, with 17 new large river dams (>0.5 km3) constructed upstream of the Yangtze. As a result of these new dams, the total DIN inputs to the TGR decreased by 15 % (from 768 Gg year−1 to 651 Gg year−1) and DIP inputs decreased by 25 % (from 70 Gg year−1 to 53 Gg year−1). Meanwhile, the molar DIN:DIP ratio in inputs to the TGR increased by 13 % between 2009 and 2022. In the future, DIN and DIP inputs to the TGR are projected to decrease further, while the molar DIN:DIP ratio will increase. The Upper Stem contributed 39 %–50 % of DIN inputs and 63 %–84 % of DIP inputs to the TGR in the past and future. Our results deepen our knowledge of nutrient loadings in mainstream dams caused by increasing cascade dams. More research is needed to understand better the impact of increased nutrient ratios due to dam construction.

The seasonal distribution and pollution potential of dissolved heavy metals and nutrients in subterranean estuaries in southern India

In order to better understand the distribution pattern, pollution degree and the submarine groundwater discharge (SGD) of dissolved heavy metals, 15 subterranean estuaries (STEs) along southwest Indian coast were sampled over three contrasting seasons. The average concentration of metals were ranked as, pre-monsoon > monsoon > post-monsoon with 3 to 12-fold higher groundwater metal concentrations than the adjacent seawater. Average SGD derived essential metal fluxes were five times higher than the toxic metal fluxes of which Fe and Zn together contributed >90 %. Using the Single Factor Contamination Index, the majority of sites were minimally contaminated with only two sites indicating moderate ecological risk due to As. Higher fluxes of Fe, Cu and Zn were likely a result of rising anthropogenic activities. The SGD derived nutrient fluxes were an important source of DIP for primary production in coastal waters and represented 30 % and 44 % of the DIN and DIP inputs respectively.

Submarine groundwater discharge enhances primary productivity in the Yellow Sea, China: Insight from the separation of fresh and recirculated components

Submarine groundwater discharge (SGD) is being increasingly recognized as a significant source of nutrient into coastal waters, and generally comprises two components: submarine fresh groundwater discharge (SFGD) and recirculated saline groundwater discharge (RSGD). The separate evaluation of SFGD and RSGD is extremely limited as compared to the conventional estimation of total SGD and associated nutrient fluxes, especially in marginal-scale regions. In this study, new high-resolution radium isotopes data in seawater and coastal groundwater enabled an estimation of SGD flux in a typical marginal sea of the Yellow Sea. By establishing 226Ra and 228Ra mass balance models, we obtained the SGD-derived radium fluxes, and then estimated the SFGD and RSGD fluxes through a two end-member model. The results showed that the total SGD flux into the Yellow Sea was equivalent to approximately 6.6 times the total freshwater discharge of surrounding rivers, and the SFGD flux accounted for only 5.2%–8.8% of the total SGD. Considering the nutrient concentrations in coastal fresh and saline groundwater, we obtained the dissolved inorganic nutrient fluxes (mmol m−2 yr−1) to be 52–353 for nitrogen (DIN), 0.21–1.4 for phosphorus (DIP), 34–226 for silicon (DSi) via SFGD, and 69–262 for DIN, 1.0–3.9 for DIP, 70–368 for DSi via RSGD, with the sum of nutrient fluxes equaling to (1.8–9.3)-fold, (1.3–5.6)-fold and (2.0–9.5)-fold of the riverine inputs. Compared to the conventional estimation of the total SGD flux, the nutrient fluxes derived from the separation of SFGD and RSGD were (1.6–2.1), (1.6–1.8) and (4.0–4.9) times lower for DIN, DIP and DSi, respectively, indicating that the estimates by separating SFGD and RSGD could be conservative and representative results of the Yellow Sea. Furthermore, we suggested that SGD played an important role in nutrient sources among all the traditional nutrient inputs sources, providing 15%–48%, 33%–68% and 14%–43% of the total DIN, DIP and DSi input fluxes into the Yellow Sea, and the high nutrient stoichiometric ratios (i.e., DIN/DIP) in SGD probably contributed to the increasing ratios in the Yellow Sea. In addition delivering large amounts of nutrient into the Yellow Sea, SGD would create primary productivity of 10–49, 1.6–6.8 and 8.8–42 g C m−2 yr−1 based on N, P and Si, which were equivalent to 5.2%–27%, 0.9%–3.7% and 4.7%–23% of the total primary productivity, respectively. In particular, the SFGD-derived DIN flux can be converted to primary productivity of 4.2–28 g C m−2 yr−1 thus demonstrating the disproportionately large role of SFGD in ecological environment of the Yellow Sea relative to its flux. Therefore, we conclude that SGD, particularly SFGD, plays an important role as a nutrient source for the Yellow Sea, and not only affects nutrient budgets and structures but also enhances the primary productivity.

DSPIR Framework as Planning and Management Tools for the La Boquita Coastal System, Manzanillo, Mexico

Coastal ecosystems are attractive sites for tourism. In the central Pacific coast of Mexico in the La Boquita coastal system (LBCS), consisting of a beach and a coastal lagoon, the Driver-Pressure-State-Impact-Response (DPSIR) model was implemented for the spatial and temporal analysis of socio environmental indicators, aiming to gather information for decision-making and implementation of management strategies. The spatial occupation (umbrellas and tables) of the beach showed a 50–200% increase during the Easter season relative to the low season, while the area containing restaurants (called “ramadas”) increased by 396% in 15 years, representing pressure on land use for tourism purposes. The density of beach users ranged from moderate to high (<10 m2/user) during the holiday seasons in the tourism area. The Trophic index (TRIX), used as an indicator of trophic status, revealed mesotrophic-to-eutrophic conditions in lagoon water due to the limited water exchange with the adjacent ocean and to DIN and DIP inputs from adjacent tourist areas. The analysis of the environmental legislation showed that law enforcement in the LBCS is poor or nil, with most environmental regulations either ignored or having inadequate enforcement monitoring. This has led to the current state of socio environmental disruption.

High Resolution Measurements of Nitrous Oxide (N2O) in the Elbe Estuary

Nitrous oxide (N2O) is one of the most important greenhouse gases and a major sink for stratospheric ozone. Estuaries are sites of intense biological production and N2O emissions. We aimed to identify hot-spots of N2O production and potential pathways contributing to N2O concentrations in the surface water of the tidal Elbe estuary. During two research cruises in April and June 2015, surface water N2O concentrations were measured along the salinity gradient of the Elbe estuary by using a laser-based on-line analyzer coupled to an equilibrator. Based on these high-resolution N2O profiles, N2O saturations and fluxes across surface water/atmosphere interface were calculated. Additional measurements of DIN concentrations, oxygen concentration, and salinity were performed. Highest N2O concentrations were determined in the Hamburg port region reaching maximum values of 32.3 nM in April 2015 and 52.2 nM in June 2015. These results identify the Hamburg port region as a significant hot spot of N2O production, where linear correlations of AOU-N2Oxs indicate nitrification as an important contributor to N2O production in the freshwater part. However, in the region with lowest oxygen saturation, sediment denitrification obviously affected water column N2O saturation. The average N2O saturation over the entire estuary was 201% (SD: ± 94%), with an average estuarine N2O flux density of 48 µmol m-2 d-1 and an overall emission of 0.18 Gg N2O y-1. In comparison to previous studies, our data indicate that N2O production pathways over the whole estuary freshwater part have changed from predominant denitrification in the 1980s towards significant production from nitrification in the present estuary. Despite a significant reduction in N2O saturation compared to the 1980s, N2O concentrations nowadays remain on a high level, comparable to the mid 90s, although a steady decrease of DIN inputs occurred over the last decades. Hence, the Elbe estuary still remains an important source of N2O to the atmosphere.

Increasing dissolved nitrogen and phosphorus export by the Pearl River (Zhujiang): a modeling approach at the sub-basin scale to assess effective nutrient management

The Pearl River (Zhujiang in Chinese) has been exporting excess of nitrogen (N) and phosphorus (P), causing eutrophication in the coastal waters of southern China for decades. However, sources of these nutrients and their locations are not well studied for the Pearl River basin. As a consequence, it is difficult to formulate effective management options to reduce these nutrients in the river and to prevent further eutrophication. We developed a sub-basin model based onto the Global NEWS-2 (Nutrient Export from WaterSheds) model for the period of 1970–2050 to analyze trends in dissolved inorganic N and P (DIN and DIP) and to identify the main sources of these nutrients and their locations. We validated our model by comparing modeled nutrient fluxes with observed. Future analyses are based on Millennium Ecosystem Assessment scenario that assumes a globalized world with a reactive environmental management. DIN and DIP inputs to the coastal waters are calculated to increase by a factor of 2–2.5 between 1970 and 2050. Over two-thirds of the DIN and DIP inputs to the coastal waters stem from two down-stream basins (Zhujiang delta and Dongjiang), where agriculture and sewage are important drivers of this increase. Agriculture accounts for over 40 % of DIN inputs to coastal waters. Sewage and agriculture account for over 90 % of DIP inputs. Thus nutrient management in agriculture and sewage in down-stream areas is more effective in reducing coastal eutrophication than nutrient management in up- and middle-stream areas of the Pearl River basin.

Design and Assembly of High Temperature Distributed Aero-engine Control System Demonstrator

This paper covers the development of a distributed high temperature electronics demonstrator for integration with sensor elements to provide digital outputs that can be used by the FADEC (Full Authority Digital Electronic Control) system or the EHMS (Engine Health Monitoring System) on an aircraft engine. This distributed electronics demonstrator eliminates the need for the FADEC or EHMS to process the sensor signal, which will assist in making the overall system more accurate and efficient in processing only digital signals. This will offer weight savings in cables, harnesses and connector pin reduction. The design concept was to take the output from several on-engine sensors, carry out the signal conditioning, multiplexing, analogue to digital conversion and data transmission through a serial data bus. The unit has to meet the environmental requirements of DO-160 with the need to operate at 200°C, with short term operation at temperatures up to 250°C. The work undertaken has been to design an ASIC based on 1.0μm Silicon on Insulator (SOI) device technology incorporating sensor signal conditioning electronics for sensors including resistance temperature probes, strain gauges, thermocouples, torque and frequency inputs. The ASIC contains analogue multiplexers, temperature stable voltage band-gap reference and bias circuits, ADC, BIST, core logic, DIN inputs and two parallel ARINC 429 serial databuses. The ASIC was tested and showed to be functional up to a maximum temperature of 275°C. The ASIC has been integrated with other high temperature components including voltage regulators, a crystal oscillator, precision resistors, silicon capacitors within a hermetic hybrid package. The hybrid circuit has been assembled within a stainless steel enclosure with high temperature connectors. The high temperature electronics demonstrator has been shown to operate from −40°C to +250°C. This work has been carried out under the EU Clean Sky HIGHTECS project with the Project being led by Turbomeca (Fr) and carried out by GE Aviation Systems (UK), GE Research – Munich (D) and Oxford University (UK).

Trends in Automotive Packaging

The long-term trend in automobiles has been increasing electronics content over time. This trend is expected to continue and drives diverse functional, form factor, and reliability requirements. These requirements, in turn, are leading to changes in the package types selected and the performance specifications of the packages used for automotive electronics. Several examples will be given. This abstract covers the development of a distributed high temperature electronics demonstrator for integration with sensor elements to provide digital outputs that can be used by the FADEC (Full Authority Digital Electronic Control) system or the EHMS (Engine Health Monitoring System) on an aircraft engine. This distributed electronics demonstrator eliminates the need for the FADEC or EHMS to process the sensor signal, which will assist in making the overall system more accurate and efficient in processing only digital signals. This will offer weight savings in cables, harnesses and connector pin reduction. The design concept was to take the output from several on-engine sensors, carry out the signal conditioning, multiplexing, analogue to digital conversion and data transmission through a serial data bus. The unit has to meet the environmental requirements of DO-160 with the need to operate at 200°C, with short term operation at temperatures up to 250°C. The work undertaken has been to design an ASIC based on 1.0 μm Silicon on Insulator (SOI) device technology incorporating sensor signal conditioning electronics for sensors including resistance temperature probes, strain gauges, thermocouples, torque and frequency inputs. The ASIC contains analogue multiplexers, temperature stable voltage band-gap reference and bias circuits, ADC, BIST, core logic, DIN inputs and two parallel ARINC 429 serial databuses. The ASIC was tested and showed to be functional up to a maximum temperature of 275°C. The ASIC has been integrated with other high temperature components including voltage regulators, a crystal oscillator, precision resistors, silicon capacitors within a hermetic hybrid package. The hybrid circuit has been assembled within a stainless steel enclosure with high temperature connectors. The high temperature electronics demonstrator has been demonstrated operating from −40°C to +250°C. This work has been carried out under the EU Clean Sky HIGHTECS project with the Project being led by Turbomeca (Fr) and carried out by GE Aviation Systems (UK), GE Research – Munich (D) and Oxford University (UK).

Seasonal variations of water column nutrients in the inner area of Ariake Bay, Japan: the role of muddy sediments

To investigate seasonal variations of nutrient distribution in the mudflat-shallow water system, we conducted field surveys once a month from August 2007 to July 2008 in the inner area of Ariake Bay (IAB), Japan. The NH4 (+)-N concentration of the water column increased in autumn because of the high NH4 (+) release from the sediments, ranging from 850 to 3,001μmol m(-2) day(-1). The NO3 (-)-N concentration was maximal in January, which was thought to be caused by NO3 (-) release from the oxic sediments and by NO3 (-) regeneration due to water column nitrification. The PO4 (3-)-P concentration of the water column was high in summer-autumn due to the high PO4 (3-) release from the reduced sediments, ranging from 22 to 164μmol m(-2) day(-1). We estimated the total amounts of DIN and PO4 (3-)-P release (R DIN and [Formula: see text], respectively) from the muddy sediment area of the IAB. In summer-autumn, R DIN and [Formula: see text] corresponded to about 47.7% of DIN input and about 116.6% of PO4 (3-)-P input from the river, respectively. Thus, we concluded that the muddy sediments were an important source of nutrients for the water column of the IAB during summer-autumn. In addition, we found that phosphorus necessary for the growth of Porphyra (Porphyra yezoensis, Rhodophyceae) would be insufficient in the water column when phosphorus during the Porphyra aquaculture period is supplied only from the river. Therefore, the phosphorus release from the muddy sediments was thought to play an important role in the sustainable production of Porphyra in Ariake Bay.

Direct measurement of dissolved N2 and denitrification along a subtropical river-estuary gradient, China

The spatial pattern and seasonal variation of denitrification were investigated during 2010–2011 in the Jiulong River Estuary (JRE) in southeast China. Dissolved N2 was directly measured by changes in the N2:Ar ratio. The results showed that excess dissolved N2 ranged from −9.9 to 76.4μmolL−1. Tidal mixing leads to a seaward decline of dissolved gaseous concentrations and water–air fluxes along the river-estuary gradient. Denitrification at freshwater sites varied between seasons, associated with changes in N input and water temperature. The denitrification process was controlled by the nitrate level at freshwater sites, and the excess dissolved N2 observed at the tidal zone largely originated from upstream water transport. Compared to other estuaries, JRE has a relative low gaseous removal efficiency (Ed=12% of [DIN]; annual N removal=24% of DIN load), a fact ascribed to strong tidal mixing, coarse-textured sediment with shallow depth before bedrock and high riverine DIN input.

Erratum to: Ammonium Nitrogen Deposition as a Dominant Source of Nitrogen in a Forested Watershed Experiencing Acid Rain in Central Japan

To clarify nitrogen (N) sources, the overall N budget in a forested watershed in Kanagawa Prefecture, Central Japan was estimated by measuring dissolved inorganic N (DIN; NH4 + + NO3 – + NO2 –) from Nov 2004 through Oct 2005. The estimated N budget (–1.43 kg N ha–1 year–1) showed that the N output rate (stream water N) was higher than the N input rate (bulk deposition N) in the watershed. The annual NO2 – and NO3 – input rates were 0.02 and 1.99 kg N ha–1 year–1, respectively. NH4 + was the predominant source in this forested watershed, accounting for 71% (4.99 kg N ha–1 year–1) of DIN input rate. In addition, this study estimated rainfall pH, air temperature, and wind direction, which were considered as controlling factors related to the atmospheric deposition rate of NH4 +. This study showed that the rainfall NH4 + was inversely proportional to the initial pH of the rainfall, which was calculated by adding the amount of H+ consumed by the dissociation process of NH3(aq) to the measured rainfall pH. This result implies that acid rain can elevate the solubility of NH3(g) and the dissociation capacity of NH4 + throughout the process of precipitation. Also, this study provides strong evidence that the high NH4 + deposition rate is mainly derived from NH3(g) emitted from livestock wastes under the NH3 transport condition of warm summer and favorable wind direction.

Ammonium Nitrogen Deposition as a Dominant Source of Nitrogen in a Forested Watershed Experiencing Acid Rain in Central Japan

To clarify nitrogen (N) sources, the overall N budget in a forested watershed in Kanagawa Prefecture, Central Japan was estimated by measuring dissolved inorganic N (DIN; NH4 + + NO3 – + NO2 –) from Nov 2004 through Oct 2005. The estimated N budget (–1.43 kg N ha–1 year–1) showed that the N output rate (stream water N) was higher than the N input rate (bulk deposition N) in the watershed. The annual NO2 – and NO3 – input rates were 0.02 and 1.99 kg N ha–1 year–1, respectively. NH4 + was the predominant source in this forested watershed, accounting for 71% (4.99 kg N ha–1 year–1) of DIN input rate. In addition, this study estimated rainfall pH, air temperature, and wind direction, which were considered as controlling factors related to the atmospheric deposition rate of NH4 +. This study showed that the rainfall NH4 + was inversely proportional to the initial pH of the rainfall, which was calculated by adding the amount of H+ consumed by the dissociation process of NH3(aq) to the measured rainfall pH. This result implies that acid rain can elevate the solubility of NH3(g) and the dissociation capacity of NH4 + throughout the process of precipitation. Also, this study provides strong evidence that the high NH4 + deposition rate is mainly derived from NH3(g) emitted from livestock wastes under the NH3 transport condition of warm summer and favorable wind direction.

Ecologically based indicators for Phaeocystis disturbance in eutrophied Belgian coastal waters (Southern North Sea) based on field observations and ecological modelling

Recent field observations of Phaeocystis globosa colonies (number, size and cell content) and historical ecosystem model simulations have been used to define and diagnose undesirable eutrophication in the Belgian coastal zone (BCZ) as recommended by the EU Water Framework Directive and OSPAR. The proposed methodology included an initial definition of a reference abundance of Phaeocystis cells from which the disturbance could be scaled. This number was based on the Phaeocystis attribute that creates ecosystem disturbance: the ability of Phaeocystis colonies to grow and reach sizes unmanageable for the current copepods. The threshold was set at 4 × 10 6 cells L − 1 and corresponded to the maximum Phaeocystis cells contained in the grazable colonies (< 400 µm) recorded in the BCZ between 1988 and 2000. Interestingly, this cell number was similar to the maximum number of Phaeocystis colony cells simulated for pristine time by the coupled RIVERSTRAHLER-MIRO (R-MIRO) model, suggesting that natural Phaeocystis ecosystems are well balanced and efficiently transfer their production to higher trophic levels. However, both the field observations obtained during the 1988–2000 period and the 1950–2000 historical reconstruction of eutrophication in the BCZ simulated by the R-MIRO model showed Phaeocystis colony cell maxima well above the threshold value. Considering that a return to the pristine reference value is not achievable, another methodology was then proposed based on historical R-MIRO simulations of annual primary (PP) and copepod (CP) productions where the CP:PP ratio can be considered an indicator of trophic efficiency. The analysis of changing CP:PP ratios in relationship with simulated winter concentrations and annual inputs of nutrients showed that the decrease in trophic efficiency was related to the imbalanced DIN and DIP inputs (N:P > 25) explained here by the reduction in DIP loads after 1985 while DIN remained elevated. On this basis, a critical DIN load estimated at 60 kT y − 1 was proposed to re-equilibrate the N:P balance in the BCZ and to favour diatoms over Phaeocystis colonies. More generally we conclude that N:P ratios in nutrient loads (or winter stocks in the coastal area) in excess of 25 in Phaeocystis ecosystems are indicative of Phaeocystis colony dominance and weak trophic efficiency.

Mechanisms for nutrient delivery to the inner shelf: Observations from the Santa Barbara Channel

Oceanic sources of nutrients to the kelp forests of the Santa Barbara Channel were diagnosed using time series from three moorings in 12‐ to 17‐m water depth. An in situ nitrate autoanalyzer on the moorings provided the first high‐resolution time series of nitrate + nitrite (dissolved inorganic nitrogen, DIN) concentrations for this environment. Measurements between February 2001 and May 2003 show that the major mechanisms that supply DIN to the inner shelf of the Santa Barbara Channel are upwelling, diurnal internal motions, and storm runoff. These supply mechanisms vary in importance seasonally. Upwelling dominates increases of inner‐shelf DIN concentration between March and May and accounts for more than half of the annual advective DIN transport to shelf reefs. In summer, baroclinic motions akin to internal waves are an important source of DIN because they occur when surface nutrient concentrations are depleted and other supply mechanisms are inactive. Brief episodes of upwelling become important in late autumn and early winter. DIN inputs from storm runoff, detected as salinity dilution at the moorings and estimated from measurements of stream discharge and nutrient concentration, are significant during winter runoff events.

Export of Dissolved Inorganic Nitrogen in a Partially Cultivated Subtropical Mountainous Watershed in Taiwan

A spatial and temporal investigation of dissolved inorganic nitrogen (DIN; NO3, NO2 and NH4) was conducted under various water discharge conditions in Lanyang-Hsi, a subtropical mountainous stream, which drains through distinct degrees of agriculture-influenced sub-watersheds. In both the cultivated and non-cultivated sub-watersheds, NO3 was the most abundant species accounting for >80% of total DIN, while NH4 and NO2 accounted for <15% and 5% of DIN, respectively. Agricultural activities along the riverbank led to significantly higher NO3 concentrations (13–246 μM) and DIN yields (1300–3800 kg N km−2 yr−1) in main channel when compared to those of non-cultivated tributaries (9–38 μM for NO3 and 550–740 kg N km−2 yr−1 for yield). The much lower and less variable DIN yields observed in tributary stations (mean = 660 ± 120 kg N km−2 yr−1) are considered as the present day background of DIN yield, which is significantly higher than those of most natural watersheds in other regions. Elevated atmospheric DIN deposition is likely the cause for the high background DIN yield. Human activity within the watershed results in additional DIN yield, which accounted for 49% of total N export. However, the reported atmospheric DIN input in northern Taiwan (∼1800 kg N km−2 yr−1) is much higher than the background DIN yield implying that a major fraction (70%) of atmospheric inputs are retained or processed within the watershed. A dilution pattern occurred in the main channel where high NO3 concentrations from the upstream sources decreased significantly in downstream direction due to inputs of NO3-diluted water from non-cultivated areas. We adopted a two-source mixing model to predict the NO3 dilution pattern. This model revealed a third yet not recognized N source in the lower part of watershed. Model results also indicated the importance of water discharge rate in regulating the relative contribution to total DIN export among these sources.

Carbon and nutrient dynamics in a hypertrophic lagoon in southwestern Taiwan

Dissolved and particulate phases of carbon (DIC, DOC, POC) and nutrients (DIN, DIP, DSi, DON, DOP, PN) were investigated bimonthly from August 1999 to August 2000 to study biogeochemical dynamics of carbon and nutrients in Tapong Bay, a small semi-enclosed and hypertrophic lagoon in southwestern Taiwan. The lagoon has only a tidal inlet for exchanging water between Tapong Bay and Taiwan Strait, which may result in low water exchange rates and various oxygen-deficient conditions in bottom water of the inner bay during warm seasons. The water exchange time of Tapong Bay ranges from 7 days (summer) to 13 days (winter) with a mean of 10 days. Nutrient dynamics were largely ascribed to allochthonous inputs, biological and exported removals in the lagoon. Diffusion fluxes from sediments to overlying water accounted for only about 7.6% of annual DIN inputs and 1.0% of annual DIP inputs. High primary productivity (89 mol C m −2 year −1) supported by abundant nutrients primarily drove the lagoon into a hypertrophic condition as particulate organic matter was derived mainly from biological production. Excess of DIP appeared to occur throughout the study period in the lagoon. Temperature, solar radiation and turbidity, rather than nutrients, perhaps controlled seasonal variations of primary productivity. The net ecosystem production (NEP) derived from daily changes of DOC and POC inventories was about 6.3 mmol C m −2 day −1 that was close to 6.7 mmol C m −2 day −1 simulated from the biogeochemical modeling. Therefore, the net ecosystem production (NEP) rate of organic carbon estimated from the biogeochemical model was reliable, and the NEP was temporally variable with an annual mean of 5.8 mol C m −2 year −1, implying that Tapong Bay was an autotrophic system. Although calcification proceeded pronouncedly in warm seasons, an invasion of CO 2 was significant in this system. In terms of nitrogen budget, the annual nitrogen fixation exceeded the annual denitrification with a magnitude of 1.30 mol N m −2 year −1, which may be supported by the abundance of nitrogen fixation microplanktons in the lagoon.

Nitrogen budget of Apalachicola Bay, a bar-built estuary in the northeastern Gulf of Mexico

Apalachicola Bay, a bar-built, sub-tropical estuary in the northeastern Gulf of Mexico (GOM), USA, receives freshwater from the Apalachicola River and exchanges water with the GOM at 4 sltes. The output from a 3-dimensional circulation model and nitrogen measurements in the river and the estuary over a 2 yr period were used to determine nitrogen input to the estuary and exchange with the GOM. The Apalachicola River was the major nitrogen source to the estuary and accounted for 92 and 73% of the total dissolved Inorganic and organic mtrogen (DIN and DON) input, respectively Nitrogen input from the GOM provided the remainder. DIN compnsed 61 % of total dissolved nitrogen (TDN) input to the estuary from the river and 26% of TDN input from the GOM. Maxima in TDN input to the estuary occurred during the high river-flow period (October to February). In contrast, TDN input minima occurred dur~ng the summer (May to September), when river flow was low. Benthic ammonium flux to the water column was maxinlum durlng the summer. However, it was not large enough to satisfy phytoplankton nitrogen demand during that period. The fractlon of DIN input that was exported to the GOM increased linearly as estuarine water residence time decreased from 2 wk during summer to less than 3 d during winter. Seasonal nitrogen budgets indicated that DIN export to the GOM was maximum during winter (87 + 5.4 mg N m-' d-') and minimum during summer (9 + 1 .4 mg N d-'). In contrast to the large decrease in DIN export to the GOM between these 2 periods, DON export to the GOM decreased from 81 * 5.8 mg N m-2 d-' during winter to only 45 i 3.2 mg N m-2 d-' during summer. Estimated denitrification rates indicated that 9% of the annual total nitrogen input to the estuary was removed by that mechanism. The f ratio in Apalachlcola Bay varied from 0.1 1 during the summer to 0.74 during the winter and averaged 0.19 for a 2 yr period. On an annual basis, DON ~ n p u t o the estuary and export to the GOM were in balance, while 66% of DIN input to the estuary was exported to the GOM. The nitrogen budget for Apalachicola Bay was balanced to within 6 % of total nitrogen input.

Synthesis of Nitrogen Pools and Fluxes from European Forest Ecosystems

To investigate which ecosystem parameters determine the risk and magnitude of nitrate leaching we compiled data from published and unpublished sources on dissolved inorganic nitrogen (DIN: NO3 − + NH4 +) in throughfall, DIN leaching loss in runoff or seepage water, and other ecosystem characteristics from 139 European forests. Not all data were available for all sites: 126 sites had at least one year’s data on DIN inputs and DIN leaching loss; 40–50 sites had some data on soil chemistry and/or vegetation pools of N. DIN inputs in throughfall range between < 1 and about 70 kg N ha−1 yr−1 and the losses with seepage or runoff range between < 1 and 50 kg N ha−1 yr−1. Retention of N within the ecosystem increases with increasing DIN deposition and increasing proportion of NH 4 + in deposition. The amount of N in needles and litterfall shows a significant linear relationship with throughfall deposition of DIN, whereas the C:N ratio of the organic (OH) horizon is uncorrelated to the level of throughfall-DIN flux. About 50% of the variability in DIN leaching loss can be explained by the flux of DIN in throughfall. Alternatively, about 60% ofthe variability in DIN leaching loss can be explained in a two-variable multiple regression combining the C:N ratio of the organic soil and the pH of the mineral soil. The survey data suggest that leaching of DIN from forest ecosystems in Europe is related in part to current DIN deposition and in part to the longer-term internal ecosystem N status as reflected in the chemistry of the humus and acidification status of the soil.

Variation in the natural abundance of 15N in the halophyte, Salicornia virginica, associated with groundwater subsidies of nitrogen in a southern California salt-marsh.

To provide insight into the importance of the salt-marsh ecotone as a sink for inorganic nitrogen in perched groundwater, measurements were made of the natural abundance of 15N in dissolved NO3-N and NH4-N and in the salt-marsh halophyte, Salicornia virginica, along an environmental gradient from agricultural land into a salt-marsh. The increase in the natural abundance of 15N (expressed by convention as δ15N) of NO3-N, accompanied by the decrease in NO3-N (and total dissolved inorganic N, DIN) concentration along the gradient, suggested that the salt-marsh ecotone is a site of transformation, most likely through denitrification, of inorganic nitrogen in groundwater. 15N enrichment in S. virginica (and the parasitic herb, Cuscuta salina), along the tidal marsh boundary, relative to high and middle marsh locations, indicated the retention of groundwater nitrogen as vegetative biomass. The correlation between δ15N Salicornia and δ15NNH4 suggested a preference for NH4-N over NO3-N during uptake by this plant. Groundwater inputs enhanced the standing crop, above-ground productivity, and nitrogen content of S. virginica but the ralative effects of pore water salinity and DIN concentration on these parameters were not determined. 15N enrichment of marsh plants by groundwater DIN inputs could prove useful in tracing the fate of these inputs in the marsh food web.

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.