Search

Lowman, H.E.; Hirsch, M.E.; Brzezinski, M.A., and Melack, J.M., 2023. Examining the potential of sandy marine sediments surrounding giant kelp forests to provide recycled nutrients for growth. Journal of Coastal Research, 39(3), 442–454. Charlotte (North Carolina), ISSN 0749-0208. Permeable marine sediments are biogeochemically active and may contribute dissolved nutrients to support primary production in coastal regions. This study examined the potential of permeable marine sediments near giant kelp forests in the Santa Barbara Channel, California as a source of ammonium (NH4+) to the overlying water column to support the observed growth of kelp during summer months when nitrate availability is low. Several nearshore sites located in coastal California in <20 m water depth were sampled for porewater nutrient concentrations, flushing rates, and nutrient fluxes in addition to diel fluctuations in nutrient concentrations of the overlying water column. Time-series analyses of porewater temperatures indicate that porewater flushed to a depth of 15 cm approximately every two hours, and mean NH4+ concentrations of porewater at these depths was 40 µM. The results of flow-through bioreactor incubations indicate that the top 2 cm of sediment are a net source of dissolved nitrogen to the overlying water column and are capable of supplying from 0.05 to 0.90 mmol NH4+ m–2 day–1. Diel water sampling demonstrates that kelp forests may be exposed to NH4+ concentrations greater than 1 µM for multiple hours (four–eight) over a day. These measured reservoirs and exchange rates of NH4+ suggest sandy marine sediments provide a significant source of nitrogen to the water column and may help meet the nitrogen demand by giant kelp during summer in the Santa Barbara Channel. [ABSTRACT FROM AUTHOR]

Fishes and other consumers excrete metabolic waste products, including dissolved nutrients rich in nitrogen, which is an essential nutrient for primary production. Relatively little is known about the magnitude and variability of nutrients excreted by fishes in kelp forest ecosystems and whether consumer-derived nutrients are important for supporting kelp productivity. In this study, the supply of ammonium (NH 4 +) excreted by the dominant fishes (30 species representing ∼85% of total fish biomass) was investigated on nearshore rocky reefs in California. Using rapid field incubations, the amount of excreted dissolved ammonium was measured as a function of body size (n = 460 individuals) and predictive models were developed relating mass to excretion rates at the family-level. Mass-specific excretion rates ranged from 0.08 to 3.45 μmol·g−1·hr−1, and per capita ammonium excretion rates ranged from 5.9 to 2765 μmol·individual·hr−1. Ammonium excretion scaled with fish body mass to the ¾ power, as predicted by the metabolic theory of ecology; mass-specific excretion rates were higher in smaller fishes, but larger fishes contributed more ammonium per individual. When controlling for body size, ammonium excretion rates were greatest among surfperch (Embiotocidae), damselfish (Pomacentridae), and wrasses (Labridae), and the general trophic groups of planktivores and micro-carnivores. When body size differences were considered, the greatest mean excretion rates per individual were observed in larger-bodied species, such as California Sheephead (Semicossyphus pulcher) and Lingcod (Ophiodon elongatus). Empirical estimates of nutrient excretion by fishes, among the first measured in temperate kelp forests, were consistent with those in other aquatic systems. Ultimately, empirically derived excretion rates are the first step to quantifying the relative importance of consumers to nutrient cycling in kelp forest ecosystems. • Excretion of ammonium increases with body size in 30 species of kelp forest fishes. • Rates of ammonium excretion depend on taxonomy and trophic guild. • Empirical excretion estimates help quantify consumer-derived nutrient cycling. [ABSTRACT FROM AUTHOR]

Benthic grazing by estuarine bivalves can be an important top-down process impacting pelagic food webs. In the low-salinity zone of the San Francisco Estuary mass balance calculations and models have reported that clams (especially the invasive Potamocorbula amurensis ) suppress phytoplankton blooms. However, spring blooms frequently occur. We aimed to understand this clam paradox using a biogeochemical modelling approach to evaluate the effects of clam grazing and excretion on phytoplankton production and nutrient uptake. The conceptual framework combines both the reduction of phytoplankton biomass by grazing and the role of ammonium (from clam excretion, wastewater plant discharge and sediment efflux) in minimizing chlorophyll accumulation, since phytoplankton cannot access nitrate (the major form of available nitrogen) for growth, due to ammonium suppression of nitrate uptake. We constructed the CLAMFLOW model by adding a clam module (with pathways of nitrogen for clam grazing, clam excretion and sediment efflux) to an existing phytoplankton-nitrogen-flow model. Whatever the parameter that was varied in the model (clam abundance, grazing, excretion, sediment efflux or flow) it decreased the peak nitrate uptake by the phytoplankton and shifted the time to reach peak uptake so delaying the likelihood of bloom initiation. Outcomes of the CLAMFLOW model were to demonstrate how clams can indirectly impact phytoplankton growth through excretion of ammonium, and to illustrate how most published laboratory filtration rates are likely too high for application in the field. There are management implications from using too high a clam grazing rate in models that may overestimate their impact on trophic estuarine and wetland productivity. We suggest that improved prediction of bloom occurrences requires the use of lower filtration rates combined with observed clam abundances, and a suitable combination of flow and ammonium source concentrations. This simple modular model (CLAMFLOW) offers portability to other ecosystems and is designed to connect with estuary scale three-dimensional circulation or numerical biogeochemical models. Our model and results are applicable to other situations, including aquaculture development and bivalve restoration efforts, where the biogeochemical effects of bivalves on phytoplankton productivity need to be quantitatively understood. [ABSTRACT FROM AUTHOR]

• Greater than 55% of input nitrogen remained in the substrate at end of production. • Five percent of input nitrogen was utilized by plant shoots. • Infiltration into soil below growing beds was less than 2.5% of input nitrogen. • Runoff nitrogen accounted for 6.5% of input nitrogen. • Unaccounted nitrogen was 27.7% of input nitrogen and is attributed to denitrification. To reduce nitrate contamination of groundwater in intensive agricultural production areas, crop producers should identify nitrogen (N) inputs and outputs to calculate potential N available for leaching into groundwater. However, poor understanding of N fate in container plant production may result in inaccurate estimation of potentially leachable N. To improve understanding of container-applied N fate, an experiment was conducted to measure N inputs and outputs from a woody ornamental plant (Lagerstroemia indica 'Whitt II') production system fertilized with controlled-release and surface-applied fertilizer. Two experimental bed types, polyethylene-lined and unlined, were installed at a production nursery in California. Measured N inputs included: the substrate, with fertilizer and roots, and irrigation water N. Outputs included: N remaining in the substrate and plant shoots at the end of the production cycle, nitrous oxide-N gas lost from the substrate and bed soil, and aqueous N lost in runoff during the production cycle. There was a significant difference in runoff N losses from the lined and unlined beds. The difference in runoff N lost between bed types was the amount of N infiltrating into the soil below the growing bed surface. The majority of input N either remained in the growing substrate (57%) at end of production cycle or was taken up by the plant shoots (5%). Nitrous oxide-N lost from the growing substrate and the bed soil was 1.5% and 0.01% of input N, respectively. Runoff and soil infiltration N accounted for 6.5% and 2.4% of input N, respectively. Unaccounted N was 27.7% of input N and is attributed to complete denitrification. Future work should address the amount of aqueous N lost from the growing substrate to reduce surface and groundwater contamination. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: A free vehicle benthic chamber has been used to define benthic nutrient fluxes on the Southern Oregon and Northern California shelf (90–200m). We measured fluxes on two occasions, in the spring and fall of 2007, to assess variability in fluxes and bioirrigation rates. Chambers were also employed to assess the impact of changing oxygen content on benthic fluxes. Oxygen uptake rates are similar to within 30% between sites in Oregon, Northern California and Central California, suggesting that a large portion of the Western US continental shelf experiences the same oxygen demand. Oxygen uptake (−2 to −10mmolm−2 d−1) at S. Oregon/N. California sites is likely responsible for <50% of the organic carbon (Corg) oxidized in these sediments as denitrification and other electron transport processes generate much of the observed TCO2 flux (4 to 31mmolCm−2 d−1). Much like other coastal regions, these sediments are generally a net sink of water column fixed N as nitrate uptake rates (−0.6 to −2.2mmolNm−2 d−1) typically exceed ammonium effluxes (0 to 1.9mmolNm−2 d−1). As chamber oxygen concentrations decline during incubation, the concentration vs. time trends in phosphate, nitrate, and silicate remain linear. We interpret this to signify that there is no short-term change in the flux of these species as a response to changing oxygen concentration. However, there is a non-linear response for ammonium, with some ammonium fluxes increasing non-linearly by as much as a factor of 14. This occurs after an incubation period of 5–15h when oxygen levels are 50%–20% of their ambient values. This change in flux may be related to rather small changes in chamber oxygen concentration, suggesting that under hypoxic conditions, there could be an enhanced efflux of ammonia to the water column. This would provide a positive feedback leading to enhanced primary productivity and increasing hypoxia. [Copyright &y& Elsevier]

Abstract: The Study of Organic Aerosols in Riverside, CA (SOAR) field campaign, conducted in the summer and fall of 2005, focused on developing a stronger understanding of seasonal influences on the sources and processes contributing to some of the highest levels of particulate matter in the United States. On-line single-particle mass spectrometry measurements showed that carbonaceous particles generally dominated the submicron size range (>75% by number), compared to primarily aged sea salt and dust in the supermicron size range. During periods with high PM2.5 (particulate matter <2.5 μm) mass and number concentrations, hygroscopic water-containing carbonaceous particles internally mixed with sulfate and nitrate extended up into the supermicron size mode. The mixing state of carbonaceous particles changed with season. In the summer, carbonaceous particles were primarily mixed with secondary (oxidized) organic carbon and sulfate; whereas in the fall, they were mixed mostly with ammonium nitrate. During each season, different processes contributed to the highest pollution levels. In the summer, photochemical production of highly aged secondary organic carbon resulted in daily peaks in both number and mass particle concentrations, followed by removal in the afternoon by the arrival of the clean marine air masses from the coast. In contrast, cooler, more stagnant meteorological conditions in the fall season resulted in the buildup over several days of submicron carbonaceous particles mixed with semivolatile ammonium, nitrate, and amines. In addition, Santa Ana wind events in the fall led to dust and biomass burning particles dominating both the submicron and supermicron size ranges. [Copyright &y& Elsevier]

Abstract: We describe the results of a series of 96-h enclosure experiments conducted using water from stations in the northern San Francisco Estuary (SFE) along a gradient in ammonium (NH4) and nitrate (NO3) concentrations. Using dual-labeled 13C/15N tracers, we followed the timing and sequence of primary (carbon, C) production and phytoplankton nitrogen (N) use during experimental phytoplankton blooms. Our results show that diatoms consistently drive the phytoplankton blooms in the enclosures. By tracing both C and N uptake we provide clear evidence that high rates of C uptake are linked to phytoplankton NO3, and not NH4, use. Results from kinetics experiments demonstrated higher specific uptake rates (VMAx) for NO3 compared to NH4 in the SFE. Finally, dissolved inorganic carbon and nutrient drawdown ratios in the enclosures from the chronically high NH4 regions of the SFE were substantially lower than predicted from the Redfield ratio, suggesting suppressed C uptake, in relation to other elemental uptake. Our conceptual model of the DIN interactions that lead to higher primary production and phytoplankton blooms in the SFE suggests that higher rates of primary production that accompany phytoplankton NO3 uptake are sufficient to outpace phytoplankton losses, leading to blooms, compared to the lower rates associated with NH4 uptake (only 20% of that based upon NO3). Historical changes in wastewater practices have increased the proportion of NH4 to the DIN pool in the SFE leading to reduced access to NO3 by phytoplankton. This may help to explain some of the reduced primary production and phytoplankton biomass observed there since the 1970s. [Copyright &y& Elsevier]

Abstract: This paper presents an analysis of the aerosol chemical composition, optical properties and size distributions for a range of conditions encountered during a field measurement campaign conducted between July 7–29, 2005 at Point Reyes National Seashore, north of San Francisco, CA. The fractional mass loading derived from hourly measurements of an Aerodyne Mass Spectrometer (AMS) during this period are compared with filter-pack measurements from the Pt. Reyes IMPROVE station with good agreement found between the two if it assumed that chloride is primarily from large sea-salt particles (not measured by the AMS). During the first half of the campaign (July 7–17), conditions at the site were largely maritime while flow during the second half of the campaigns (July 18–29) was influenced by a thermal trough that added a cyclonic twist to the incoming marine air, bringing it from the south with a more extensive over-land trajectory. Neither flow regime was associated with air coming from the San Francisco Bay area to the south. The AMS measurements are partitioned into clear and foggy conditions which are then used to calculate the equivalent molar ratio of ammonium to the sum of sulfate, nitrate and chloride. Ratios calculated from measurements made before the onset of the thermal trough on July 18th were associated with acidic or near-neutral particles. Measurements made after July 18th yield ratios that appear to have excess ammonium. Model calculations of the equilibrium gas-phase mixing ratio of NH3 suggest very high values which we attribute to agricultural practices within the park. Reported as an incidental finding is evidence for the cloud droplet activation of large particles (DP > 0.2 μm) with a corresponding reduction in the single scattering albedo of the non-activated particles, followed by a return in the particle size spectrum to the pre-fog conditions immediately afterwards. [Copyright &y& Elsevier]

Re-examination of data distributions from several forested sites in the eastern Sierra Nevada Mountains shows consistent, positive outliers and skew for NH, NO, and mineral N in resin lysimeters and resin capsules, indicating that most values were low but hotspots of high N flux were present in most cases. Exact causes of these N flux hotspots is not known, but could include water flux hotspots (e.g., preferential flowpaths), microbial hotspots, and possibly the entry of N-enriched O horizon interflow. Soil and resin stake (PRS probe) data from one site (North Lake Tahoe) also showed consistent, positive outliers and skew for NH, NO, and mineral N, suggesting the presence of microbially produced hotspots. Bicarbonate-P data from soils and ortho-P data from PRS probes also showed highly positive skew and extreme outliers, but Bray (HCl/NHF-extractable) P in soils did not. Other measured nutrients (extractable Mg, K, SO, and Ca) also showed positive skew and outliers, but less so than NH, NO, and mineral N. Calcium stood out among measured nutrients as the most abundant nutrient with the least outliers and the lowest (sometimes negative) skew. The differences in distributions of NH, NO, and mineral N and those of Ca may reflect relative abundance: the most abundant ion, Ca, shows little evidence of hotspots whereas the much less abundant ions, NH, NO consistently show evidence of hotspots. We hypothesize that the differing distributions of N and Ca reflect the relative biological competition for these nutrients and that positively-skewed distributions and hotspots will be characteristic of any other nutrient when it is in limited supply relative to biological demand. [ABSTRACT FROM AUTHOR]

Nutrient enrichment is an important stressor in coastal ecosystems. This analysis tests the hypothesis that changes in nutrient loads, imbalances in nitrogen:phosphorus, and changes in nitrogen form, especially shifts to increasing loads of chemically reduced, rather than oxidized nitrogen, can have major impacts on food webs, from primary producers through secondary producers to fish. The application of cumulative sums of variability, the running total of deviations from normalized values over time, is a sensitive method for comparing rates of change between and among all parameters, including organisms of all trophic levels. This approach was applied to the San Francisco Estuary, California, demonstrating that abrupt changes in nutrient loads and nutrient form over the past several decades were correlated with food web changes, including pelagic fish collapse. Remediation of pelagic fish populations should be centered on reduction of nitrogen loads and reestablishment of balanced nutrient ratios delivered from point source discharges. [ABSTRACT FROM AUTHOR]

Following an invasion of exotic annual grasses into California oak woodlands, grass species dominance shifted from native perennials to exotic annuals. In combination with other ecosystem and species characteristics, species-specific N preferences may influence species coexistence and dominance. If species N preferences follow dominance patterns in California oak woodlands, then the more dominant exotic grasses should prefer the most abundant inorganic soil N form (NH4 +), while the subordinate native grasses should prefer the less available inorganic (NO3 −) or organic (glycine) soil N forms. To investigate this prediction, we applied 15N-labeled NH4 +, NO3 −, and glycine to soil and measured % 15N recovery by two dominant annual grasses (Bromus diandrus and Bromus hordeaceus) and two subordinate perennial grasses (Elymus glaucus and Nassella pulchra). As expected, shoots of B. diandrus recovered more 15N-NH4 + (74%) than either 15N-NO3 − (51%) or 15N-glycine (39%). B. diandrus also captured at least 3.2 times more 15N-NH4 + than subordinate grasses. Dominant B. hordeaceus, however, demonstrated no N form preferences. As hypothesized, shoots of subordinate E. glaucus and N. pulchra recovered 2.1–2.3 times more 15N-NO3 − than 15N-NH4 + and increased %N by 4.8–5.7% in response to the application of 15N-NO3 −. Both subordinate grasses did not prefer 15N-glycine over 15N-NH4 +, suggesting that the importance of this N form in structuring species coexistence in California oak woodlands is minimal. These results support our theory that species N preferences follow dominance patterns in California oak woodlands. To further understand the role of these species-specific N preferences in structuring dominance, the importance of N form versus such characteristics as rooting distribution and species phenologies needs to be explored in the presence of interspecific competition. [Copyright &y& Elsevier]

Abstract: The nitrogen uptake capabilities of the toxigenic diatom Pseudo-nitzschia australis (Frenguelli), freshly isolated from Monterey Bay California, were examined in unialgal laboratory cultures at saturating photosynthetic photon flux densities (100μmolphotonsm−2 s−1) and 15°C. The kinetics of nitrogen (nitrate, ammonium, urea and glutamine) uptake as a function of substrate concentration were estimated from short (20.5min) incubations using the 15N-tracer technique. Based on the estimated maximum specific uptake rates and measures of N affinity (the initial slope of the uptake versus nutrient concentration curve), nitrate is the preferred nitrogen substrate, followed by glutamine and ammonium, which are equivalent. Rates of urea uptake by P. australis did not saturate at concentrations as high as 36μg-atNL−1, and urea uptake as a function of concentration could not be described by Michaelis–Menten kinetics over the concentration gradient tested. Although there is a clear preference for nitrate at equivalent concentrations (compared to ammonium, urea, and glutamine), these laboratory results demonstrate the capability of this pennate diatom to utilize both inorganic and organic forms of nitrogen, supporting field observations that P. australis blooms during both upwelling and non-upwelling conditions off the west coast of North America. Substantial differences in the nitrogenous nutrition of P. australis can be expected in these environments, and anthropogenic inputs of N substrates such as ammonium and urea can support its growth, and may contribute significantly to both harmful diatom blooms and the maintenance of seed populations at non-bloom abundances, particularly during periods of reduced or absent upwelling. [Copyright &y& Elsevier]

Abstract: Cultural eutrophication is frequently invoked as one factor in the global increase in harmful algal blooms, but is difficult to definitively prove due to the myriad of factors influencing coastal phytoplankton bloom development. To assess whether eutrophication could be a factor in the development of harmful algal blooms in California (USA), we review the ecophysiological potential for urea uptake by Pseudo-nitzschia australis (Bacillariophyceae), Heterosigma akashiwo (Raphidophyceae), and Lingulodinium polyedrum (Dinophyceae), all of which have been found at bloom concentrations and/or exhibited noxious effects in recent years in California coastal waters. We include new measurements from a large (Chlorophyll a >500mgm−3) red tide event dominated by Akashiwo sanguinea (Dinophyceae) in Monterey Bay, CA during September 2006. All of these phytoplankton are capable of using nitrate, ammonium, and urea, although their preference for these nitrogenous substrates varies. Using published data and recent coastal time series measurements conducted in Monterey Bay and San Francisco Bay, CA, we show that urea, presumably from coastal eutrophication, was present in California waters at measurable concentrations during past harmful algal bloom events. Based on these observations, we suggest that urea uptake could potentially sustain these harmful algae, and that urea, which is seldom measured as part of coastal monitoring programs, may be associated with these harmful algal events in California. [Copyright &y& Elsevier]

In recent years, the extreme eutrophication of the Salton Sea has been associated with massive fish kills and associated bird kills. Analysis of the magnitude and direction of high wind events indicates that major fish kills are preceded by strong and persistent wind events, with a 24-h accumulated wind magnitude above a critical threshold of approximately 90 m/s. Twelve of the 14 cases of reported fish kills analyzed were found to be preceded by such wind conditions. The winds could potentially produce upwellings of hypolimnetic water at the upwind end of the Sea, resulting in the entire water column being low in dissolved oxygen and high in concentrations of hydrogen sulfide and ammonium. Remotely sensed thermal infrared data from the MODIS instrument on the Terra satellite was available for 5 of the 14 fish kills analyzed. Evaluation of satellite-derived surface temperature maps for these 5 fish kills shows that upwellings did take place after the wind events, affecting a large fraction of the Sea’s area. The location of the upwelling and the fish kills coincided in all cases, confirming the relationship among wind patterns, upwellings, and fish kills in the Salton Sea. The importance of physically mediated processes, such as upwellings, need to be considered in evaluating future remediation strategies for the Salton Sea. [ABSTRACT FROM AUTHOR]

Abstract: The red tide forming dinoflagellate genus Cochlodinium appears to be expanding globally, as well as blooming and/or causing more economic losses within its previously reported geographic distribution. Despite the widespread occurrence of this organism in the Pacific, Atlantic, and Indian oceans, relatively few studies of its ecophysiology have been conducted. Here we summarize the ecophysiological characteristics through both a literature review and by assessing recent bloom events in Monterey Bay, CA, USA. Using this comparative approach, we identify the basic characteristics of this organism: Cochlodinium is found in both warm and cool (11–30°C) waters in the western and eastern Pacific, respectively, at moderate salinities (30–34). The production of pelagic vegetative seed banks or benthic seed beds by this organism and ability to survive ballast water transport likely facilitate its ability to colonize and establish itself in new habitats. It is a strong vertical migrator capable of utilizing both inorganic and organic nitrogen sources as well as mixotrophy and may be associated with moderate nutrient loading. These characteristics provide Cochlodinium with an adaptive capability conducive to rapid colonization of newly opened ecological niches, which may partially explain the apparent global expansion of its geographic range and bloom frequency. [Copyright &y& Elsevier]

Nitrite (NO2--N) toxicity symptoms have been observed on lettuce (Lactuca sativa) at various locations in California. The objective was to evaluate the symptoms of ammonium (NH4+-N) and nitrite (NO2--N) toxicity on Sundevil iceberg lettuce and Paragon romaine lettuce and to determine lettuce growth and biomass production under different levels of NO2--N. Hydroponic studies under greenhouse conditions were conducted using nutrient solutions containing nitrate (NO3--N) and two other forms of nitrogen (NO2--N and NH4+-N) applied at a constant concentration (50 mg NL-1) or using different NO2--N levels (0, 5, 10, 20, 30, and 40 mg N L-1) and a constant NO3--N level (30 mg N L-1). Crown discoloration (brownish color) was observed for lettuce grown in both NO2--N and NH4+-N solutions approximately 3 weeks after transplanting into the hydroponic systems. Lettuce grown in NO3--N solution produced larger biomass and greater number of leaves per plant than lettuce grown in NO2--N or NH4+-N solutions. Increasing the concentration of NO2--N suppressed plant height, fresh and dry biomass yield, and number of leaves and increased the root vascular discoloration. Lettuce growth was reduced more than 50% at NO2--N concentrations greater than 30 mg N L-1. Even at 5 mg NO2--N L-1, growth was reduced 14 and 24% for romaine and iceberg lettuce, respectively, relative to that obtained in nitrate solution. Although concentrations between 5 and 40 mg NO2--N L -1 reduced dry biomass similarly for both lettuce types, toxicity symptoms were more severe in iceberg lettuce than in romaine. [ABSTRACT FROM AUTHOR]

Abstract: The substantial inventory of nitrate (NO3) in San Francisco Bay (SFB) is unavailable to the resident phytoplankton most of the year due to the presence of ammonium (NH4) at inhibitory concentrations that prevents NO3 uptake. Low annual primary productivity in this turbid estuary is generally attributed to the poor irradiance conditions. However, this may not be the only cause; spring phytoplankton blooms occur irregularly in north SFB only when NH4 concentrations are low, <4μmolL−1 and NO3 uptake by phytoplankton occurs. Field measurements and enclosure experiments confirm the NH4 inhibition process to be the cause of low NO3 utilization most of the year. Detailed analysis of spring blooms in three embayments of SFB over 3 years shows a consistent sequence of events that result in bursts of chlorophyll. The first requirement is improved irradiance conditions through stabilization of the water column by stratification or reduced tidal activity. Second, NH4 concentrations must be reduced to a critical range, 1 to 4μmolL−1 through dilution by precipitation and by phytoplankton uptake. This enables rapid uptake of NO3 and subsequent increase in chlorophyll. The resulting bloom is due to both the initial uptake of NH4 and the subsequent uptake of NO3. The NO3 uptake step is crucial since it is the larger nitrogen source and uptake occurs at higher rates than that for NH4 at the concentrations that occur in SFB. Existing models of light-limited, non-nutrient limited productivity in SFB require modification to include the NH4 inhibition effect. From measured NH4 uptake rates and initial concentrations, calculations can be made to predict the length of time that favorable irradiance conditions are required for the phytoplankton population to reduce ambient NH4 concentrations to non-inhibiting concentrations and allow bloom formation to begin. For Suisun Bay, the time required is so long that blooms are unlikely in any season. For San Pablo and Central Bays, these times are too long in summer but sufficiently short in spring to allow bloom development, depending on the ambient NH4 concentration prior to the productivity season. NH4 sources to SFB are primarily anthropogenic, from agricultural drainage and sewage treatment plants, and if not sufficiently diluted by runoff and precipitation can prevent development of the spring phytoplankton bloom. Attention should be paid to the form of N making up dissolved inorganic nitrogen (DIN) in nutrient-rich estuaries. [Copyright &y& Elsevier]

Revegetation on disturbed, low organic matter content, decomposed granite (DG) substrates are limited by low plant-available moisture and nitrogen. Data from a single DG site in northern California, USA, showed that a significant fraction of the ammonium from fertilizers or organic matter mineralization was fixed into silicate interlayer positions. To evaluate the broader relevance of NH fixation, the NH fixation capacities of 11 other drastically disturbed DG substrates throughout California were evaluated. The fixation capacities of the substrates were quite varied and increased as added NH application levels increased (124–1,670 kg NH ha−1). When amended with 124 kg NH ha−1, 7 of the 11 substrates fixed between 14 and 78% of the added NH. Analysis of particle size fractions of a typical material indicated that the very fine sand fraction had the highest fixation capacity and the clays and very coarse sands had the lowest, on a gravimetric basis. The overall fixation capacities showed no significant relation to potential predictive characteristics, including extractable K+, NH, or total N levels. Three methods of cation exchange capacity (CEC) measurement were tested for their ability to predict NH fixation. The Ba method which utilizes an indicator cation that is not subject to interlayer fixation was not a reliable indicator of NH fixation. The NH method had the strongest relation to NH fixation in the DG materials. The difference between the measured CEC of the NH method and the Ba method was found to be most predictive of NH fixation. [ABSTRACT FROM AUTHOR]

Granitic materials represent a common erosive substrate in California and much of the western United States. When granitic rocks weather, they disintegrate into coarse textured, non-cohesive substrates, known generally as decomposed granite (DG). Because of low moisture and N availability, revegetation of these substrates for erosion control is difficult. If nitrate based fertilizers are used, they can be rapidly leached, while NH fertilizers may be sequestered mineralogically by interlayer fixation. In this study, we focus on the occurrence of NH fixation on a decomposed granitic substrate and show that the fixation capacities of these sandy saprolites are significant despite analyses indicating that the samples are predominantly quartz, have low clay contents and have low cation exchange capacities (CEC). At field loading rates equivalent to less than 300 kg N ha−1, 36–42% of added NH may become unavailable to plants due to interlayer collapse and fixation for an unknown period of time. Ammonium fixation did not vary significantly in relation to substrate weathering class in these samples. Oriented X-ray diffraction analysis revealed the presence of vermiculite in particle size fractions from clay to very coarse sands. While other studies have identified silt as the most active fraction, the relative fixation capacity of these granite saprolites was greatest in the fine and very fine sand fractions when considered on a gram for gram basis of each individual particle size. We found that the extractant cation also influenced the measured levels of NH fixation in these granite saprolites. At loading rates of 0–150 kg NH ha−1, extraction with KCl resulted in apparent NH fixation capacities that were twice as great as those found with NaCl extractions when tested at low NH concentrations and close to 35% greater at higher NH amendment loading. Estimation of available ammonium in the decomposed granite using conventional KCl extraction methods appears to cause fixation, rather than extraction of at least part of the substrate’s NH content. [ABSTRACT FROM AUTHOR]

Examines the ubiquitous distribution of ammonium fine particles observed during fall stagnation conditions in the South Coast Air Basin, California using remote sensing. Role of the primary atmospheric base in the determination of the acid-neutralizing capacity of tropospheric air masses; Risk factors for cardiopulmonary disease and mortality; Implications of vehicular ammonium emissions on regional air quality.

1 Smoke-stimulated germination in the post-fire flora of California chaparral does not appear to be triggered by nitrate. Application of freshly prepared unbuffered KNO3 solutions (pH c. 6.2) failed to enhance germination of five populations of Emmenanthe penduliflora or one Phacelia grandiflora population, regardless of light or stratification conditions. 2 KNO3 buffered at acidic pH (or unbuffered solutions equilibrated with atmospheric CO2) did induce germination, but KNO3 solutions at pH 7 failed to induce germination. Induction of germination is therefore not due to the nitrate ion per se, but rather to high [H+], although buffered controls gave weak germination at low pH, suggesting a role for H+ plus nitrate. However, other anions such as sulphate were equally as effective as nitrate at breaking dormancy. 3 The germination response to KNO3 was affected by the type of filter paper used and this may be linked to differences in pH. 4 NO2, at concentrations present in biomass smoke, was highly effective at inducing germination, and other oxidizing agents also induced germination. 5 Several growth regulators, including nitrite and gibberellin, were stimulatory only at acidic pH, but KCN was stimulatory across a broad pH range. 6 Germination decreased at smoke exposures longer than a few minutes. Also, smoked water samples effective at breaking dormancy were acidic and were less effective when buffered to pH >7. 7 Physical scarification of the seed coat induced germination but the effect was not due to penetration of a water barrier, or to enhanced oxygen uptake or to wound responses such as CO2 or ethylene production. 8 Different effects of the gibberellin inhibitor CCC (chlorocholine chloride) suggested that the mechanisms of scarification-induced and smoke-induced germination may differ. 9 We conclude that either oxidizing gases in smoke and/or acids generated on burnt sites play a role in germination of post-fire annuals in chaparral. [ABSTRACT FROM AUTHOR]