Form Of Dissolved Inorganic Nitrogen Research Articles

Composition and distribution of nutrients and environmental capacity in Dapeng Bay, northern South China Sea

Seawater physicochemical parameters and environmental capacity are important ecological indicators and typical features of the marine environment. It has great significance in the marine material cycle and ecological health. In September 2021 (wet season) and March 2022 (dry season), two voyage investigations were conducted at 12 stations (D1-D12) on Dapeng Bay (DPB), northern South China Sea. The distribution of nutrient, water-quality status, environmental capacity, and impact of ecological environment were discussed. Results showed that NH4-N was the main form of dissolved inorganic nitrogen (DIN) during the wet season, with concentrations ranging from 0.008 mg/L to 0.109 mg/L, accounting for ~53 % of DIN. Conversely, NO3-N was the main form of DIN during the dry season, with concentrations ranging from 0.005 mg/L to 0.117 mg/L, accounting for ~50 % of DIN. The DIP concentration ranged from 0.002 mg/L to 0.019 mg/L, accounting for ~51 % and 31 % of the total dissolved phosphorus in the wet and dry seasons, respectively. The distributions of NH4-N, NO3-N, NO2-N, and DIP were relatively similar, decreasing from the inner bay to the outer bay. The eutrophication indices of 12 stations <1, indicating a poor eutrophication state. Single-factor indices including chemical oxygen demand (COD), DIN, and dissolved inorganic phosphorus (DIP) were less than the class I seawater-quality standard. However, except for station D1, the overall water quality was good. Dissolved oxygen with DIP had a significantly negative correlation during the dry season, indicating that DIP was primarily dominated by marine biological activity and organic-matter decomposition. The remaining environmental capacities of COD, DIN, and DIP in DPB were calculated to be 13,742, 1418, and 141 tons, respectively. Based on the functional-zone division of the sea area, the remaining environmental capacities of COD, DIN, and DIP were exceeded 75 % of the total environmental capacity. This study provided a scientific basis for the protection of marine ecological environment and the sustainable development of DPB.

Alteration of soil-surface electrochemical properties by organic fertilization to reduce dissolved inorganic nitrogen leaching in paddy fields

Dissolved inorganic nitrogen (DIN) adsorbed onto soil colloids plays an important role in soil N leaching, but previous studies have not clearly defined the mechanisms of this process in paddy soils under organic fertilization. In this study, we investigated how ongoing fertilization can change soil DIN leaching via affects on soil-surface electrochemical properties and physical properties, and the main influences of soil properties on DIN leaching were characterized. Five fertilization regimes applied during a 5-year field experiment were employed to study this mechanism, i.e., no fertilizer, chemical fertilizer, chemical fertilizer plus hog manure, hog manure, and chemical fertilizer plus oil cake. Increasing levels of applied manure decreased DIN leaching from the soil profile, especially for NH4+, the main form of DIN in the leachate and soil. Compared to chemical fertilizer, organic fertilization changed the surface electrochemical and physical properties more effectively with regards to decreased soil bulk density (9.84–20.49 %, P < 0.05) and specific surface area (26.38–44.88 %, P < 0.05), as well as enhanced water-holding capacity (19.05–42.86 %, P < 0.05) and the number and density of soil-surface charges (7.97.55–98.44 %, P < 0.05). Furthermore, organic fertilization significantly increased the NH4+ adsorbed by soil. Structural equation modeling showed that soil-surface electrochemical properties had the greatest impact (β = –0.88, P < 0.05) on the NH4+ content of the leachate when compared with the soil NH4+ adsorption capacity and physical properties. The increase in the soil-surface charge, surface charge density, surface potential, and surface electric field strength under organic fertilization increased soil NH4+ retention in soil (P < 0.001), and thus, these changes decreased the risk of NH4+ leaching. Our results suggest that continuous substantial organic fertilization may mainly decrease early DIN leaching from cultivated paddy soils in the Dongting Lake area by altering soil-surface electrochemical properties, where soil-surface electrochemical properties can be set as an internal factor to predict soil ion migration in agriculture systems, such as the Dongting Lake area or other similar regions.

Spatial variation and availability of nutrients at an oyster reef in relation to submarine groundwater discharge

Submarine groundwater discharge (SGD) is often an overlooked component of the solute budgets in coastal embayments and is not considered in oyster restoration, conservation, and management plans. A combination of spatial and temporal geochemistry (nutrients, trace metals, alkalinity components, stable isotopes, and major ions) of porewater and surface water combined with SGD-derived solute fluxes and turnover times was used to examine the significance of SGD in delivering nutrients to paleovalley systems in coastal embayments, thus sustaining the health and productivity of oyster reefs. A 1-km2 area encompassing a paleovalley system, in Copano Bay, Texas, exhibited significant differences in the spatial and temporal hydrogeochemical characteristics (major ions, stable isotopes and nutrients) along the reef when compared to the other environments (i.e., paleovalley, estuary-wide). Solute fluxes (i.e., dissolved organic carbon (DOC), dissolved inorganic nitrogen (DIN), total alkalinity, DIC, etc.) are slightly larger at the reef, followed by the margin and shoreline. During dry conditions, SGD from the 1-km2 area was estimated to supply anywhere between two-fold to one order of magnitude more nitrogen (in the form of DIN) than the riverine inputs to Copano Bay. During a wet year SGD equates the river input in the form of DIN. In addition, SGD-based turnover times, averaging <11 days for all nutrients, are significantly shorter than the average estuary flushing time (i.e., 38 days). Results from this study suggest that SGD within a paleovalley system is an important component in the estuarine nutrient budget through significant inputs and cycling processes between the subsurface and water column, particularly during low surface flows. Thus, estuarine environments such as paleovalley margins and interfluves provide favorable conditions to oysters through preferably enhanced SGD solute fluxes and should be considered in oyster restoration efforts.

Nitrogen cycling in a freshwater estuary

Freshwater estuaries may be important control points but have received limited research attention, emblematic of a general under-appreciation of these ecosystems and the services they provide. These ecotone environments exist at the interface of rivers flowing into large lakes, where seiches cause mixing of lotic and lentic waters within flooded river deltas. We assessed the dissolved inorganic nitrogen (DIN) retention and processing controls in the Saint Louis River Estuary (SLRE), which receives inputs from rivers, urban sources, and Lake Superior. Nitrate (NO3–N) was the dominant form of DIN and was consistently highest in the lower estuary due to seiche-delivered Lake Superior water and nitrification of ammonium from urban sources. The estuary transitioned from a net NO3–N source during high flows to a net sink during summer baseflow conditions. NO3–N availability controlled site-specific denitrification rates while sediment organic matter explained the spatial pattern in denitrification potential. As the estuary shifted from a riverine state to one with more lake influence, seiches delivered Lake Superior NO3–N to the lower portion of the estuary, alleviating the final denitrification control and activating the estuary’s ‘denitrification pump’. This amplified removal condition is maintained by critically delivered NO3–N during periods of warm temperatures and long residence times. Often these controls are unsynchronized in streams where NO3–N is typically lowest during summer baseflow. Similar ephemeral biogeochemical processes are likely found within other seiche-prone lakes where organic-rich sediments accumulate at river mouths and are supplied with chemically distinct lake water during low flow periods.

Dissolved inorganic nitrogen concentrations in an estuarine tidal flat

Tay, H.W., Bryan, K.R. and Pilditch, C.A., 2013. Dissolved inorganic concentrations in an estuarine tidal flatWaikareao Estuary is a shallow tidally dominated estuary located in Tauranga Harbour, New Zealand. The primary aim of this study was to determine the seasonal variations in nitrate and ammonium concentration in sediment pore-waters on a tidal flat margin in the Waikareao Estuary. Vertical profiles of sediment pore-water were sampled 5, 10, 25, 50 and 75-cm depths to provide snapshots of nutrient concentration at different times of the year. Pore-water recycling processes were an important source of dissolved inorganic nitrogen (DIN) to the estuary during low tide with greatest concentrations observed in mid-winter and summer. Pore-water profiles showed ammonium as the dominant form of DIN in the wells. Nitrate concentration was higher in surface sediment and ammonium dominated the mid-depth regions (25–50 cm). The vertical stratification of the DIN in the wells suggested oxidation at the surface produced higher nitrate concentrations while at deeper depths, ammonification and dissimilatory nitrate reduction to ammonium produced higher ammonium concentrations. Long-term monitoring by the Regional Council of Kopurereroa Stream which discharges into Waikareao Estuary, showed higher nitrate concentrations than the tidal flat wells and other monitored sites. This further highlights that the primary source of nitrate into estuaries is through freshwater discharge and ammonium is dominated by sediment recycling processes.

Submarine Groundwater Discharge-Derived Nutrient Loads to San Francisco Bay: Implications to Future Ecosystem Changes

Submarine groundwater discharge (SGD) was quantified at select sites in San Francisco Bay (SFB) from radium ( 223 Ra and 224 Ra) and radon ( 222 Rn) activities mea- sured in groundwater and surface water using simple mass balance box models. Based on these models, discharge rates in South and Central Bays were 0.3-7.4 m 3 day −1 m −1 .A l- though SGD fluxes at the two regions (Central and South Bays) of SFB were of the same order of magnitude, the dissolved inorganic nitrogen (DIN) species associated with SGD were different. In the South Bay, ammonium (NH4 + ) concentrations in groundwater were three-fold higher than in open bay waters, and NH4 + was the primary DIN form dis- charged by SGD. At the Central Bay site, the primary DIN form in groundwater and associated discharge was nitrate (NO3 − ). The stable isotope signatures (δ 15 NNO3 and δ 18 ONO3 )o f NO3 − in the South Bay groundwater and surface waters were both consistent with NO3 − derived from NH4 + that was isotopically enriched in 15 Nb y NH4 + volatilization. Based on the calculated SGD fluxes and groundwater nutrient concentrations, nutrient fluxes associated with SGD can ac- count for up to 16 % of DIN and 22 % of DIP in South and Central Bays. The form of DIN contributed to surface waters from SGD may impact the ratio of NO3 − to NH4 + available to phytoplankton with implications to bay productivity, phyto- plankton species distribution, and nutrient uptake rates. This assessment of nutrient delivery via groundwater discharge in SFB may provide vital information for future bay ecological wellbeing and sensitivity to future environmental stressors.

Leaf litter breakdown in Mediterranean streams: effect of dissolved inorganic nutrients

Agricultural runoff and urban activities can increase the inputs of nitrogen (N) and phosphorus (P), into headwater streams, leading to eutrophication and thus substantially affecting the structure and functions of benthic communities. A high P concentration in water stimulates the activity of heterotrophic microorganisms associated with leaf litter and, hence, influences decomposition rates and the availability of detrital resources for macroinvertebrates. Litter breakdown of alder (Alnus glutinosa) leaves enclosed in coarse mesh bags was studied in five low-order Mediterranean streams with different trophic status defined by their soluble reactive phosphorus (SRP) concentrations. Decomposition rates differed significantly between these streams and increased with the eutrophication gradient, but these differences were not always related to the availability of P in water. Leaf mass loss was directly correlated with shredder density, but macroinvertebrate density and diversity were not related to P availability in water, and ammonium concentration had a negative effect on macroinvertebrate diversity and shredder relative abundance. A significantly positive effect of nitrate concentration in water on aquatic hyphomycete sporulation rates was observed, but there also was a negative effect of % ammonium on dissolved inorganic nitrogen (DIN). The predominantly available ionic form of DIN could thus affect the structure of the aquatic hyphomycete community. These results suggest that the response of litter decomposition to eutrophication in forested headwater streams is strongly influenced by local stream characteristics and by the nature of nutrient pollution.

Retrieval of Dissolved Inorganic Nitrogen from Multi-Temporal MODIS Data in Haizhou Bay

It is important to map dissolved inorganic nitrogen (DIN) concentrations in order to accurately predict the outbreak of red tides. This study aims to determine the feasibility of retrieving DIN in Haizhou Bay, East China from multi-temporal MODIS satellite data and to assess the impact of DIN concentration level on its inversion accuracy. DIN was modeled from the reflectance of MODIS bands and their combinations both linearly and nonlinearly. It was found that individual MODIS bands are loosely correlated with DIN concentrations. Of the various combinations of multiple bands, bands 3 and 4 bear a highly positive correlation with DIN concentrations. In particular, (R3 + R4)/(R3 − R4) is a more accurate predictor of DIN than R3 × R4/(R3 − R4). All the regression models involving this exploratory variable have an R2 value over 0.7 and a relative accuracy of around 70%. However, regression residuals are dependent of each other for DIN <70 μg/L. The removal of these observations from the regression analysis led to the establishment of the best model in the form of DIN<70 = 7.403 (R3 + R4)/(R3 − R4) + 37.14 (R2 = 0.87, n = 19). It improved the model accuracy to RMSE = 17.48 μg/L (15.8%) against the validation dataset. MODIS data allow accurate retrieval of DIN concentrations >70 μg/L in murky coastal waters. During the study period of 2004–2006, Haizhou Bay experienced a deteriorating trend in DIN in that low concentration areas decreased while areas of a high DIN concentration level expanded.

Water quality and eutrophication in the Guangzhou Sea Zone of the Pearl River estuary

To gain a better understanding of water quality and eutrophication, we investigated the seasonal and spatial distribution of water quality at 17 stations in the Guangzhou Sea Zone (GZSZ). Nutrients, chlorophyll-a (Chl-a), salinity, chemical oxygen demand, and other physical and chemical parameters were determined in February, May, August and October from 2005 to 2007. The concentrations showed ranges of 93.2–530.4 μmol/L for dissolved inorganic nitrogen (DIN), 0.62–3.16 μmol/L for phosphate (PO4-P) and 50–127 μmol/L for silicate (SiO3-Si). The results indicated that DIN was strongly influenced by domestic sewage coming from Guangzhou City and NO3-N was the main form of DIN in most areas, while concentrations of phosphate and silicate were generally controlled by Pearl River runoff, land-based sources along the land or islands, and algae assimilation. N/P ratios were very high in both dry season and wet season, and varied from 57 to 667, suggesting that P was potentially the most limiting nutrient in the GZSZ. The concentrations of Chl-a were 3–96 μg/L, and were highly correlated with the distribution characteristics of COD. The concentrations of nutrients have increased over the past two decades (1982–2007). This means it is necessary to control the input of nutrients to the GZSZ, especially that of phosphate.

Ammonium and nitrate uptake by leaves of the seagrass Thalassia testudinum: impact of hydrodynamic regime and epiphyte cover on uptake rates

Seagrasses rely on the uptake of dissolved inorganic nitrogen (DIN) from both sediment pore water and the water column for metabolic processes. Rates at which their leaves remove nutrients from the water column may be influenced by physiological factors, such as enzyme kinetics, and physical factors, including water flow and the presence of epiphytes on the leaf surface. While there is some evidence of the individual effects of these factors on uptake rates for individual plants, there is little information on the effects of these factors on seagrasses that are situated in their natural environment. In order to isolate the combined effects of water flow and epiphyte cover on uptake rates for Thalassia testudinum leaves while they were situated in a natural canopy we applied 15N-labeled ammonium and 15N-labeled nitrate in a series of field flume experiments. Hydrodynamic parameters related to thickness of diffusive boundary layers, including bottom shear stress and the rate of turbulent energy dissipation, were estimated from velocity profiles collected with an acoustic Doppler velocimeter. Rates of NH 4 + uptake for leaves with and without epiphyte cover were proportional to bottom shear stress and energy dissipation rate, while rates of NO 3 − uptake were not. For epiphytes, rates of both NH 4 + and NO 3 − uptake were dependent on hydrodynamic parameters. Epiphytes covering the leaf surface reduced rates of NH 4 + uptake for seagrass leaves by an amount proportional to the spatial area covered by the epiphytes (∼90%) and although epiphytes reduced NO 3 − uptake rates, the amount was not proportional to the extent of epiphyte cover. Results suggest that the rate at which seagrass leaves removed ammonium was limited by the rate of delivery to the surface of the leaves and was greatly reduced due to blockage of active uptake sites by epiphytes. Conversely, rates of nitrate uptake for the seagrass leaves were limited by the rate at which the leaves could process nitrate rather than the rate of delivery. Our findings quantitatively demonstrate the potential impact of hydrodynamic regime and epiphyte cover on rates of DIN uptake by T. testudinum leaves and how the importance of these factors in affecting uptake rates can vary depending on the form of DIN being assimilated.

The characteristics of nutrients and eutrophication in the Pearl River estuary, South China

In the spring of 1998, 24-h time series and synchronization of vertical profiles of NO3–N, NO2–N, NH3–N, PO4–P, chlorophyll a, suspended substance, salinity, temperature and other chemical parameters were taken at 10 stations in the Pearl River estuary in order to analyze the status and characteristics of nutrients and eutrophication. The results indicated that dissolved inorganic nitrogen (DIN) mainly came from the four river channels in the main estuary, and NO3–N was the main form of DIN in most area. The concentration of DIN was general above 0.30 mgl−1 in the estuary, and more than 0.50 mgl−1 in most part. Phosphate from four river channels was not the main sources, but land-based sources from the area near Shenzhen Bay or along the estuary were obvious, and other land-based sources outside the estuary brought by coastal current and flood tide current were also the main contributions. The concentration of phosphate was generally about 0.015 mgl−1 except the area near Shenzhen Bay. The ratio of N:P was generally high, and it was higher in the north than in the south. The highest ratio was higher than 300, and the lowest one was over 30. The concentration of chlorophyll a was about 0.8–7.8 mgm−3, and turbidity and phosphate may be the main two limiting factors for algal bloom in the estuary. The concentration of nutrients decreased slightly in the past decade, but still stayed at a high level. The nutrients mainly came from domestic sewage, industrial wastewater, agriculture fertilizer and marine culture in the Pearl River estuary.

Export of nitrogen from catchments within a temperate forest: Evidence for a unifying mechanism regulated by variable source area dynamics

Considerable variation in the export of dissolved inorganic nitrogen (DIN) and dissolved organic nitrogen (DON) was observed among catchments located within an old‐growth sugar maple forest in central Ontario. Although discharge was a strong predictor of N‐export, rates of export were variable for each catchment, ranging from −50% to +50% from the catchment‐average response for DIN and −25% to +25% from the catchment‐average response for DON. Among the catchments, a unifying flushing behavior was apparent for NO3−‐N, the dominant form of DIN in the discharge waters, providing a basis for explaining the variation in the export of DIN. Flushing occurs when a water table rises to the soil surface with subsequent mobilization of nutrients stored near or at the soil surface to surface waters. Catchment‐specific flushing behaviors were captured in “flushing” characteristic time constants, defined as the time interval required for a decline in N concentrations in discharge waters toe−l (37%) of their initial concentration. Variation in flushing behavior was linked to variation in N export; catchments with short flushing times (interpreted as catchments with source areas that are less variable) were observed to export less N than catchments with long flushing times (source areas that are more variable). A hypothesis was formulated in which catchment topography and its influence on variable source area dynamics accounts for variation in flushing behavior, hence variation in the export of NO3−‐N among the catchments. The implication of this hypothesis is that to predict accurately the export of NO3−‐N from catchments within a landscape, we need first to consider the influence of the topographic complexity of the catchments. Our understanding of the mechanisms of processing and export of DON is not sufficient for accurate prediction at this point, highlighting the need for additional research on DON.

Nutrient uptake in the reef-building coral Acropora palmata at natural environmental concentrations

Experiments were carried out over 15 mo to assess the net exchange of dissolved inorganic nitrogen (DIN) by the symbiotic coral Acropora palmata (Lamarck) under near-natural environmental conditions. Specimens were enclosed in situ in transparent acrylic chambers and changes in the ambient seawater concentrations of nitrate, nitrite and ammonium determined over 1 h closed incuba- tion~. There was a consistent depletion of nitrate and a more variable but significant mean depletion of ammonium within the experimental chambers, indicating simultaneous net uptake of both ions by the coral. No exchange of nitrite could be detected. No significant changes in concentration of any form of DIN occurred in ambient seawater control chambers. Contrary to previous predictions from studies of uptake kinetics in isolated zooxanthellae and other coral species, mean net rates of nitrate uptake exceeded that of ammonium uptake by a factor of 2. Nitrate uptake was dependent on substrate concentration, with a linear response over the range of ambient seawater concentrations encountered in the study. Rate of ammonium uptake was apparently independent of substrate concentration and the rate of uptake of each ion was independent of the concentration of the others. A diurnal rhythm was noted in nitrate uptake rates, after changes in concentration had been taken into account, which suggests that although uptake continued over the complete 24 h period, maximal rates of uptake were not maintained throughout the night. These results support previous studies which have demonstrated the capability for dual uptake of both nitrate and ammonium by zooxanthellae, but suggest that under natural conditions nitrate rather than ammonium provides the primary external source of dissolved inorganic nitrogen in this species.

The control of nitrate and ammonium concentrations in a coral reef lagoon

One Tree Reef lagoon is surrounded by an emergent rim which restricts exchange between lagoonal waters and the surrounding ocean. For this reason, the loss rate of dissolved inorganic nitrogen (DIN) through mixing processes is slow in the central lagoon compared to rates of advective input, uptake, regeneration and loss to the atmosphere. We present some hypotheses concerning the importance of these fluxes to the observed patterns of concentration of nitrate+nitrite and ammonium. A scaling analysis of these fluxes indicates that the relative influence of advection across the windward reef crest on lagoonal concentrations changes with season and differs for the two forms of DIN. Advective flux, dominated by DIN derived from production on the algal pavements of the reef crest, is significant in controlling DIN concentration in the peripheral regions of the lagoon. Loss to the atmosphere is a more important flux from the nitrate+nitrite pool in the centre of the lagoon, particularly in summer. Regeneration is a significant input to the ammonium pool of the central lagoon in winter. The relative magnitudes of all fluxes are more similar to each other in the summer than the winter, indicating the potential for shifts in the dominance hierarchy at small time and space scales. One form of DIN in One Tree Reef lagoonal waters (nitrate+nitrite) is controlled by input and another (ammonium) by recycling as well as input. The relative importance of these fluxes changes as a result of temperature pertubations at the physiological level as well as the rate of water turnover at the “system” level. It is proposed that the degree of consistency of the seasonal concentration patterns is a function of the period, rather than the amplitude of the temporal oscillations in the fluxes controlling these concentrations. This has important implications for sampling strategies. This paper provides a conceptual framework for hypothesis testing at a manageable scale, in the context of ecosystem function.