Nitrogen is a key element controlling the species composition, diversity, dynamics, and functioning of many terrestrial, freshwater, and marine ecosystems. Many of the original plant species living in these ecosystems are adapted to, and function optimally in, soils and solutions with low levels of available nitrogen. The growth and dynamics of herbivore populations, and ultimately those of their predators, also are affected by N. Agriculture, combustion of fossil fuels, and other human activities have altered the global cycle of N substantially, generally increasing both the availability and the mobility of N over large regions of Earth. The mobility of N means that while most deliberate applications of N occur locally, their influence spreads regionally and even globally. Moreover, many of the mobile forms of N themselves have environmental consequences. Although most nitrogen inputs serve human needs such as agricultural production, their environmental conse- quences are serious and long term. Based on our review of available scientific evidence, we are certain that human alterations of the nitrogen cycle have: 1) approximately doubled the rate of nitrogen input into the terrestrial nitrogen cycle, with these rates still increasing; 2) increased concentrations of the potent greenhouse gas N 2O globally, and increased concentrations of other oxides of nitrogen that drive the formation of photochemical smog over large regions of Earth; 3) caused losses of soil nutrients, such as calcium and potassium, that are essential for the long-term maintenance of soil fertility; 4) contributed substantially to the acidification of soils, streams, and lakes in several regions; and 5) greatly increased the transfer of nitrogen through rivers to estuaries and coastal oceans. In addition, based on our review of available scientific evidence we are confident that human alterations of the nitrogen cycle have: 6) increased the quantity of organic carbon stored within terrestrial ecosystems; 7) accelerated losses of biological diversity, especially losses of plants adapted to efficient use of nitrogen, and losses of the animals and microorganisms that depend on them; and 8) caused changes in the composition and functioning of estuarine and nearshore ecosystems, and contributed to long-term declines in coastal marine fisheries.

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Human alteration of the global nitrogen cycle: sources and consequences

Impatti, adattamento e vulnerabilita Le cause e le responsabilita dei cambiamenti climatici sono state trattate sul numero di ottobre della rivista Cda. Approfondiamo l’argomento presentando il documento: “Cambiamenti climatici 2007: impatti, adattamento e vulnerabilita” votato ad aprile 2007 dal secondo gruppo di lavoro del Comitato Intergovernativo sui Cambiamenti Climatici (Intergovernmental Panel on Climate Change). Si tratta del secondo di tre documenti che compongono il quarto rapporto sui cambiamenti climatici.

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Climate Change 2007: Impacts, Adaptation and Vulnerability.

The widespread occurrence of nitrogen limitation to net primary production in terrestrial and marine ecosystems is something of a puzzle; it would seem that nitrogen fixers should have a substantial competitive advantage wherever nitrogen is limiting, and that their activity in turn should reverse limitation. Nevertheless, there is substantial evidence that nitrogen limits net primary production much of the time in most terrestrial biomes and many marine ecosystems. We examine both how the biogeochemistry of the nitrogen cycle could cause limitation to develop, and how nitrogen limitation could persist as a consequence of processes that prevent or reduce nitrogen fixation. Biogeochemical mechansism that favor nitrogen limitation include: A number of mechanisms could keep nitrogen fixation from reversing nitrogen limitation. These include: The possible importance of these and other processes is discussed for a wide range of terrestrial, freshwater, and marine ecosystems.

Nitrogen limitation on land and in the sea: How can it occur?

A primary focus of coastal science during the past 3 decades has been the question: How does anthropogenic nutrient enrichment cause change in the structure or function of nearshore coastal ecosystems? This theme of environmental science is recent, so our conceptual model of the coastal eutrophication problem continues to change rapidly In this review, I suggest that the early (Phase I) con- ceptual model was strongly influenced by limnologists, who began intense study of lake eutrophication by the 1960s The Phase I model emphasized changing nutrient input as a signal, and responses to that signal as increased phytoplankton biomass and primary production, decomposition of phytoplankton- derived organic matter, and enhanced depletion of oxygen from bottom waters Coastal research in recent decades has identified key differences in the responses of lakes and coastal-estuarine ecosystems to nutrient enrichment The contemporary (Phase II) conceptual model reflects those differences and includes explicit recognition of (1) system-specific attributes that act as a filter to modulate the responses to enrichment (leading to large differences among estuarine-coastal systems in their sensitivity to nu- trient enrichment); and (2) a complex suite of direct and indirect responses including linked changes in: water transparency, distribution of vascular plants and biomass of macroalgae, sediment biogeochem- istry and nutrient cycling, nutrient ratios and their regulation of phytoplankton community composition, frequency of toxic/harmful algal blooms, habitat quality for metazoans, reproduction/growth/survival of pelagic and benthic invertebrates, and subtle changes such as shifts in the seasonality of ecosystem functions Each aspect of the Phase II model is illustrated here with examples from coastal ecosystems around the world In the last section of this review I present one vision of the next (Phase III) stage in the evolution of our conceptual model, organized around 5 questions that will guide coastal science in the early 21st century: (1) How do system-specific attributes constrain or amplify the responses of coastal ecosystems to nutrient enrichment? (2) How does nutrient enrichment interact with other stressors (toxic contaminants, fishing harvest, aquaculture, nonindigenous species, habitat loss, climate change, hydro- logic manipulations) to change coastal ecosystems? (3) How are responses to multiple stressors linked? (4) How does human-induced change in the coastal zone impact the Earth system as habitat for humanity and other species? (5) How can a deeper scientific understanding of the coastal eutrophication problem be applied to develop tools for building strategies at ecosystem restoration or rehabilitation?

https://www.int-res.com/articles/meps/210/m210p223.pdf

Our evolving conceptual model of the coastal eutrophication problem

Framework Convention on Climate Change

Determination of total nitrogen in aqueous samples after potassium persulfate digestion compared favorably in both precision and nitrogen recovery with determinations obtained using Kjeldahl digestion.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1977.22.4.0760

Determination of total nitrogen in aqueous samples using persulfate digestion1

The response of phytoplanktonic growth to experimental nutrient addition in a tributary of the Chesapeake Bay estuary varied with season and nutrient availability. In bioassay experiments employing...

Nutrient Enrichment Studies in a Coastal Plain Estuary: Phytoplankton Growth in Large-Scale, Continuous Cultures

Similar NH4+ and NO3−.uptake kinetic patterns were observed in Neoagardhiella baileyi (Harvey ex Kiitzing) Wyinne & Taylor and Gracilaria foliifera (Forssk?l) Borgesen. NO3− was taken up in a rate-sturating fashion described by the Michaelis-Menten equation. NH4+ uptake was multicomponent: a saturable component was accompanied by a diffusive or a high K component showing no evidence of saturation (at ≤50 μM [NH4+]). Nitrogen starved plantsi(C/N atom ratios > ca. 10) showed higher transient rates of NH4+ uptake at a given concentration than plants not N-Iimited. Only plants with high N content exhibited diel changes inNH4+ uptake rates, and showed transient rates of NH4+ accumulation which did not greatly exceed the capacity to incorporate N in steady-state growth. NH4+ was preferred over NO3−even in plants preconditioned on NO3−as the sole N. source, NO3− uptake was suppressed at 5μM [NH4+], but simultaneous uptake occurred at unsurpressed rates at lower concentrations. Potential for N accumulation was greater via NH4+uptake than via NO3−uptake. Changing capacity for NH4+ uptake with N content appears to be a mechanism whereby excessive accumulation of N was avoided by N-.satiated plants but a large accumulation was possible for N-depleted plants.

Nutritional studies of two red algae. ii. kinetics of ammonium and nitrate uptake1, 2

The mutualistic relationship between corals and their dinoflagellate endosymbionts is a key factor in the evolutionary success of hermatypic (reef building) corals. The endosymbiotic algae benefit corals in numerous ways that have contributed to the long term persistence of coral reefs over geologic time. In this chapter we review ecological and physiological aspects of the interactions between corals and their symbiotic algae in light of recent advances in our knowledge of the diversity of these symbionts. While the role of symbiont diversity in promoting coral survival during environmental bleaching events has been a major focus of recent research, its importance in other physiological and ecological contexts such as inorganic nutrient dynamics and photosynthetic carbon fluxes has received much less attention. We suggest that cost-benefit analysis is a useful approach to examine these symbioses in the context of environmental change and human impacts upon corals and coral reefs. Weighing the costs versus the benefits of the symbiotic association under specific environmental perturbations has potential for use as an indicator of the health of not only corals but indeed the whole coral reef ecosystem. Drastic changes in the stability of the symbiosis, evidenced by changes in the ratio of zooxanthellae to animal biomass in corals, may turn out to be a useful diagnostic indicator of stresses to coral reefs. By using new tools developed to assess the stability of the symbiosis, we may be better able to understand and predict the effects of future stressors and perturbations that threaten these beautiful reef ecosystems.

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Interactions Between Corals and Their Symbiotic Algae

Of several genera tested, only those Pacific reef corals symbiotic with zooxanthellae take up and retain ammonium. Uptake and retention are enhanced by light, and the normal daylight period is sufficient to sustain ammonium retention during the night. Ammonium uptake kinetics for several species indicate that a two-process mechanism may be involved. If a correction is made for diffusion, uptake kinetics can be characterized by the Michaelis-Menten equation.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1978.23.4.0725

Christopher F. D'Elia

Papers

Determination of total nitrogen in aqueous samples using persulfate digestion1

Nutrient Enrichment Studies in a Coastal Plain Estuary: Phytoplankton Growth in Large-Scale, Continuous Cultures

Nutritional studies of two red algae. ii. kinetics of ammonium and nitrate uptake1, 2

Interactions Between Corals and Their Symbiotic Algae

The uptake, retention, and release of ammonium by reef corals 1