Dead zones in the coastal oceans have spread exponentially since the 1960s and have serious consequences for ecosystem functioning. The formation of dead zones has been exacerbated by the increase in primary production and consequent worldwide coastal eutrophication fueled by riverine runoff of fertilizers and the burning of fossil fuels. Enhanced primary production results in an accumulation of particulate organic matter, which encourages microbial activity and the consumption of dissolved oxygen in bottom waters. Dead zones have now been reported from more than 400 systems, affecting a total area of more than 245,000 square kilometers, and are probably a key stressor on marine ecosystems.

Supporting Online Material for Spreading Dead Zones and Consequences for Marine Ecosystems

. Water masses can become undersaturated with oxygen when natural processes alone or in combination with anthropogenic processes produce enough organic carbon that is aerobically decomposed faster than the rate of oxygen re-aeration. The dominant natural processes usually involved are photosynthetic carbon production and microbial respiration. The re-supply rate is indirectly related to its isolation from the surface layer. Hypoxic water masses ( Hypoxia development and continuation in many areas of the world's coastal ocean is accelerated by human activities, especially where nutrient loading increased in the Anthropocene. This higher loading set in motion a cascading set of events related to eutrophication. The formation of hypoxic areas has been exacerbated by any combination of interactions that increase primary production and accumulation of organic carbon leading to increased respiratory demand for oxygen below a seasonal or permanent pycnocline. Nutrient loading is likely to increase further as population growth and resource intensification rises, especially with increased dependency on crops using fertilizers, burning of fossil fuels, urbanization, and waste water generation. It is likely that the occurrence and persistence of hypoxia will be even more widespread and have more impacts than presently observed. Global climate change will further complicate the causative factors in both natural and human-caused hypoxia. The likelihood of strengthened stratification alone, from increased surface water temperature as the global climate warms, is sufficient to worsen hypoxia where it currently exists and facilitate its formation in additional waters. Increased precipitation that increases freshwater discharge and flux of nutrients will result in increased primary production in the receiving waters up to a point. The interplay of increased nutrients and stratification where they occur will aggravate and accelerate hypoxia. Changes in wind fields may expand oxygen minimum zones onto more continental shelf areas. On the other hand, not all regions will experience increased precipitation, some oceanic water temperatures may decrease as currents shift, and frequency and severity of tropical storms may increase and temporarily disrupt hypoxia more often. The consequences of global warming and climate change are effectively uncontrollable at least in the near term. On the other hand, the consequences of eutrophication-induced hypoxia can be reversed if long-term, broad-scale, and persistent efforts to reduce substantial nutrient loads are developed and implemented. In the face of globally expanding hypoxia, there is a need for water and resource managers to act now to reduce nutrient loads to maintain, at least, the current status.

/pdf/dynamics-and-distribution-of-natural-and-human-caused-21e6uqwqxc.pdf

Dynamics and distribution of natural and human-caused hypoxia

Prefaces. 1. Introduction: Recent Trends in Science. 2. Do We Need a New, Holistic Ecology? 3. Models in Ecology. 4. Energy and Ecology. 5. Entropy and Ecology. 6. Exergy and Ecology. 7. Network and Hierarchical Concepts of Ecosystems. 8. Utility Theory, Indirect Effect and Ascendency. 9. Catasrophe Theory and Ecology. 10. Chaos, Fractals and Ecology. 11. Ecosystem Health. 12. Development of Ecosystems. 13. Dynamic of Ecosystems. 14. Goal Functions. 15. A Tentative Pattern of Ecosystem Theories. 16. Epilogue. 17. Appendix 1: Definitions of Concepts. 18. References. 19. Index.

Integration of Ecosystem Theories: A Pattern

A critical review of reductionist approaches for assessing the progress towards sustainability

The need for predictive process-oriented planktonic ecosystem models is widely recognized by the aquatic science community. We conducted a meta-analysis of recent mechanistic aquatic biogeochemical models (153 studies published from 1990 to 2002), to assess their ability to predict spatial and temporal patterns in the physical, chemical and biological dynamics of planktonic systems. The selected modeling studies covered a wide range of model complexity, ecosystem-types, spatio-temporal scales and purposes for model development. Despite the heterogeneous nature of this data set, we were able to identify model behavior trends and illuminate aspects of current modeling practice that need to be reevaluated. Temperature and dissolved oxygen had the highest coefficients of determination (respective median r(2) values were 0.93 and 0.70) and the lowest relative error (median RE < 10%), nutrients and phytoplankton had intermediate predictability (median r(2) values ranging from 0.40 to 0.60 and median RE similar to 40 %), whereas bacteria (median r(2) = 0.06) and zoo-plankton (median RE = 70 %) dynamics were poorly predicted. Longer simulation periods (i.e. months to decades) reduced model predictability, and increased model complexity did not improve fit. Aquatic biogeochemical modelers need to be more consistent in how they apply conventional methodological steps during model development (i.e. sensitivity analysis, validation), and the aquatic modeling community should adopt generally accepted standards of model performance. Recent advancements in data assimilation techniques, the combination of the present family of models with goal functions (derived from non-equilibrium thermodynamics) and the development of models with a stronger physiological basis are promising frameworks for obtaining more accurate simulations of planktonic processes.

https://faculty.washington.edu/mtbrett/2004_Arhonditsis_MEPS.pdf

G. Bendoricchio

Papers

Description of the three shallow estuaries: Mondego River (Portugal), Roskilde Fjord (Denmark) and the Lagoon of Venice (Italy)

Exergy as goal function of ecosystems dynamic

Modelling nutrient emissions from river systems and loads to the coastal zone: Po River case study, Italy

Defining and modelling the coastal zone affected by the Po river (Italy)

A trophic model for Ulva rigida in the Lagoon of Venice